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Complete Heavy Metal Removal from Fly Ash by Heat Treatment: Influence of Chlorides on Evaporation Rates
Abstract
Thermal treatment is a promising way for the decontamination and inertization of residues from waste incineration. The evaporation of heavy metal compounds thereby is of great significance. It is the goal of this work to identify, by analyzing evaporation rates, the predominant thermochemical reactions of the heavy metals with other constituents of fly ash, with respect to volatilization. To this end, experiments were performed with fly ash from a municipal solid waste (MSW) incineration plant as well as with synthetic powder mixtures in the temperature range of 670−1000 °C. The rates of Cd, Cu, Pb, and Zn evaporation can be described accurately by a simple first-order rate law and a rate coefficient which itself follows an exponential temperature dependence analogous to the Arrhenius equation. The degrees (completeness) as well as the rates of evaporation of the heavy metals are markedly influenced by chlorides contained in the fly ash, largely as NaCl. Experiments with model substrates indicate that the heavy metals Zn and Cu in fly ash, which are the least volatile among the group investigated, are predominantly present as chlorides. Their evaporation is completed by shifting the oxide/chloride equilibrium if surplus chlorine, e.g., in the form of NaCl, is available. The heavy metal evaporations are probably limited by reactions that form heavy metal silica/alumina compounds.
... The migration of heavy metals is influenced by the composition of fly ash, reaction temperature, and atmosphere [13][14][15]. Chlorides (CaCl 2 , KCl, NaCl) in fly ash, especially CaCl 2 , can promote the volatilization of heavy metals [16,17]. Most of the chlorides can be recovered by washing [18], thus inhibiting the volatilization of heavy metals during heat treatment [10]. ...
... There was an increase in this volatilization as temperature increased and, when the temperature reached 1150 °C, it decreased. As temperature increased, Zn could react with SiO2 and Al2O3 and form stable metallic species, such as Zn2SiO4/ZnAl2O4 [16,34], which can also promote the immobilization of Zn. In addition, the production of liquid slag can also promote reactions that can further inhibit Zn volatilization. ...
... There was an increase in this volatilization as temperature increased and, when the temperature reached 1150 • C, it decreased. As temperature increased, Zn could react with SiO 2 and Al 2 O 3 and form stable metallic species, such as Zn 2 SiO 4 /ZnAl 2 O 4 [16,34], which can also promote the immobilization of Zn. In addition, the production of liquid slag can also promote reactions that can further inhibit Zn volatilization. ...
Melting solidification experiments of municipal solid waste incineration (MSWI) fly ash were carried out in a high-temperature tube furnace device. An ash fusion temperature (AFT) test, atomic absorption spectroscopy (AAS), scanning electron microscope (SEM), and X-ray diffraction (XRD) were applied in order to gain insight into the ash fusibility, the transformation during the melting process, and the leaching behavior of heavy metals in slag. The results showed that oxide minerals transformed into gehlenite as temperature increased. When the temperature increased to 1300 °C, 89 °C higher than the flow temperature (FT), all of the crystals transformed into molten slag. When the heating temperatures were higher than the FT, the volatilization of the Pb, Cd, Zn, and Cu decreased, which may have been influenced by the formation of liquid slag. In addition, the formation of liquid slag at a high temperature also improved the stability of heavy metals in heated slag.
... Thermal processes can detoxify combustion ashes in a number of ways: (i) by destroying POPs (Lundin and Marklund, 2005;Song et al., 2008a;Vehlow et al., 2006); (ii) by removing Cd, Cl, Pb, and, to some extent, Zn by volatilisation (Jakob et al., 1995;Lane et al., 2020a,b); and (iii) by immobilising non-volatile or partly-volatile heavy metals (Iretskaya et al., 1999;Sørensen et al., 2001). Previous studies (Jakob et al., 1995(Jakob et al., , 1996Lane et al., 2020b) have shown that Zn and other valuable elements can be separated from MSWI fly ash by means of volatilisation. Volatilised metals and metalloids, except Hg, can generally be condensed by rapid cooling of the hot product gases (Lane et al., 2020a;Sippula et al., 2012). ...
... A recent study has demonstrated production of metal concentrates containing commercial grades of Zn from MSWI fly ash containing only 1.6% w/w Zn (Lane et al., 2020a). Several elements can, in certain processing conditions, simultaneously volatilise with Zn during ash heating (Jakob et al., 1995(Jakob et al., , 1996Ludwig et al., 2001) and consequently follow Zn to the product zinc concentrate. This can have an adverse impact on the tradability and financial value of the concentrate (Sinclair, 2005). ...
... Several studies (e.g. Jakob et al., 1996;Lane et al., 2020b;Yu et al., 2015) have investigated the influence of ash composition on the partitioning of elements at different reaction temperatures. These studies have shown that several major elements in MSWI fly ash, including, but not limited to Cl and S, exert a particularly strong influence on the extent of heavy metal (and metalloid) removal. ...
Development of thermal processes for selective recovery of Zn and other valuable elements from municipal solid waste incineration (MSWI) fly ash requires comprehensive knowledge of the impact of gas atmosphere on the volatile behaviour of the element constituents of the ash at different reaction temperatures. This study assesses the partitioning of 18 elements (Al, As, Bi, C, Ca, Cd, Cl, Cu, K, Mg, Na, P, Pb, S, Sb, Sn, Ti, and Zn) between condensed and gaseous phases during thermal treatment of MSWI fly ash in both oxidising gas and reducing gas atmospheres, at different temperatures spanning the range 200-1050°C. The operating atmosphere had major impacts on the partitioning of the following elements: As, Bi, C, Cd, Cu, Na, Pb, S, Sb, Sn, and Zn. The partitioning of these elements cannot be accurately predicted over the full range of investigated operating conditions with global thermodynamic equilibrium calculations alone, i.e. without also considering chemical kinetics and mass transfer. In oxidising conditions , the following elements were predominately retained in condensed phases, even at high temperatures: As, Bi, Sb, Sn, and Zn. All these elements, except As, were largely released to the gas phase (>70%) at high temperatures in reducing conditions. The impact of gas atmosphere on the volatility of Cd and Pb was greatest at low reaction temperatures (below~750°C). Results for volatile matrix elements, specifically C, Cl, K, Na, and S, are interpreted in terms of the mechanisms governing the release of these elements to the gas phase.
... The intensity of the characteristic peaks of the chlorine-and calcium-containing mineral phases in the raw ash was high, which was consistent with the results of its elemental composition test. Chlorides had been reported to readily bind to heavy metals, and metals contained in MSWIFA form metal chlorides such as CdCl 2 ·H 2 O, CuCl 2 ·H 2 O, PbCl 2 and ZnCl 2 (Gu et al., 2021;Jakob et al., 1996). Heavy metals may also bind to various forms of organic matter or sulphides in MSWIFA (Zhu et al., 2011). ...
... Heavy metals may also bind to various forms of organic matter or sulphides in MSWIFA (Zhu et al., 2011). Furthermore, the alkali metal chlorides such as NaCl in the MSWIFA can convert metal oxides into volatile metal chlorides according to chemical reaction Eq. 2 (Jakob et al., 1996). Pretreatment of raw ash by different alkaline reagents decreased the peak intensities of NaCl, KCl and CaSO 4 , indicated that washing pretreatment can easily remove soluble metal chlorides and sulphates. ...
Municipal Solid Waste Incineration Fly Ash (MSWIFA) contains and organic toxic pollutants, which cause secondary pollution to the environment such as water and soil, and pose a threat to human health. Its suitable treatment of the MSWIFA as a secondary use of the solid waste resources is a hot spot of the current research. This paper aims to investigate the behavior of alkaline reagent pretreatment of MSWIFA, different kinds of alkaline reagents were used to pre-treat MSWIFA. The particle size, microstructure change, element composition, phase change and leaching toxicity of heavy metal ions were studied the MSWIFA, respectively. The following conclusions were mainly obtained: after pre-treatment of MSWIFA with alkaline reagents, the average particle size tends to decrease (down to 13.98 μm). The increasing of intergranular repulsion leads to a uniformly dispersed and dense microscopic morphology of MSWIFA. The increasing of SiO2 and Al2O3 content resulted in a decreasing in MSWIFA alkalinity (minimum value of 9.24) and an increasing in both its volcanic ash activity. The leaching concentration of the four heavy metal ions, namely Pb, Zn, Cu and Sr were decreased. Overall, alkaline solution pretreatment of MSWIFA was more effective, while 0.35 mol/L Na2CO3 had the best effect. The lowest leaching concentrations of Pb, Zn, Cu, and Sr were 3.97 mg/L, 1.58 mg/L, 4.13 mg/L, and 4.6 mg/L respectively. Alkaline reagent pretreatment of MSWIFA mainly includes: alkaline environment effect, chemical reaction effect and particle size effect. This study can provide theoretical basis for MSWIFA pretreatment and effective secondary application.
... For it, a reaction with alkali chlorides is necessary. In most cases, it is pointed out that NaCl, KCl and CaCl2 are responsible for removing heavy metals such as Zn and Pb since those chlorides are already present in the fly ash [4,[18][19][20][21][22][23]. Jakob et al. [22] described the possible reaction that can lead to the vaporisation of the heavy metals (as gaseous chlorides), in which M represents a heavy metal. ...
... In most cases, it is pointed out that NaCl, KCl and CaCl2 are responsible for removing heavy metals such as Zn and Pb since those chlorides are already present in the fly ash [4,[18][19][20][21][22][23]. Jakob et al. [22] described the possible reaction that can lead to the vaporisation of the heavy metals (as gaseous chlorides), in which M represents a heavy metal. ...
Disposing of fly ash from Waste to Energy plants is standard practice today. However, there are concerns associated with this option. First is the contamination impurities such as chlorides, sul-fates and heavy metals can impose on the environment. Second, the cost of ash landfills is increasing all over Europe. In partnership with EEW Energy from Waste, the current research aims to develop industrial separation processes to valorise fly ashes from waste incineration. A viable alternative is using fly ash as an additive to cement clinker. For the current process, hydrometallurgical and pyro-metallurgical steps are proposed. The fly ash sample was initially treated in a water-leaching step aimed the chloride removal. Optimum parameters were researched in the scope of the current project (60 ºC, liquid/solid = 5, 60 minutes of residence). The Cl removal reached more than 90 % of efficiency (with an error of less than 2.0 %), leading to a solid residue with a chlorine content of < 1 wt.-%. The leached fly ash was directed to the pyrometallurgical step, and different experiments were performed to develop a treatment protocol to remove the other impurities. In the pyrometallurgical step, the results obtained with the fly ash sample pointed out that using sand to promote a molten slag
... This means they are not stabilized in the treated product, posing more stringent requirements for the treatment of secondary fly ash [20,21]. A lot of studies have shown that the high chloride content in FA is a significant factor in causing heavy metal volatilization [22][23][24][25], making dechlorination an important process in FA thermal treatment [26]. At high temperatures, chlorides in FA react with SiO 2 and Al 2 O 3 to produce chlorine gas, which further reacts with heavy metal oxides leading to volatilization [27,28]. ...
... At around 1000 • C, the volatilization rates for Pb and Cd can reach 80% to near complete volatilization, whereas for Zn and Cu, the rates are slightly lower, between 40% and 60% [27,32]. The kinetics of volatilization at high temperatures can be described by a simple first-order rate model, with the rate coefficient exponentially related to temperature [25,33]. Given that the contents were below the economic extraction threshold, the separation and recovery of heavy metals from FA were not economically viable at present [19]. ...
... The effect was outstanding with the combined two-step pretreatment method which achieved rates of over 97 % and 88 % for chloride and sulfate respectively. It was reported that chloride could readily combine with heavy metals contained in the MSWIFA forming metal chlorides such as CdCl 2 ⋅H 2 O, CuCl 2 ⋅H 2 O, PbCl 2 and ZnCl 2 (Jakob et al., 1996). Heavy metals may also be bound by various forms of organic matter or sulfide in MSWIFA (Zhu et al., 2011). ...
... Heavy metals may also be bound by various forms of organic matter or sulfide in MSWIFA (Zhu et al., 2011). Besides, alkali chlorides such as NaCl in MSWIFA could convert metal oxides (MO) into volatile metal chlorides via the chemical reaction xMO + 2xNaCl + ySiO 2 → xMCl 2 + xNa 2 O-•ySiO 2 (Jakob et al., 1996). XRD analyses (Section 3.4) showed that chloride crystals mostly existed in the forms of NaCl, KCl and Na 3 K 6-Ti 2 Al 2 Si 8 O 26 Cl 3 , whilst crystalline sulfates existed predominantly as FeS 2 , ZnS and PbSnS 3 . ...
Swelling caused by gas generated from municipal solid waste incineration fly ash (MSWIFA) when it is mixed with alkali limits its uses. Besides, the leaching of anion salts and heavy metals contained in MSWIFA poses a high risk to environment. This study presents the feasibility of a one-step alkaline washing, one-step thermal quenching and two-step combination of alkaline washing and thermal quenching pretreatment methods in altering the key properties of MSWIFA for promoting its reusability. It was found that apart from H 2 (gas), NH 3 (gas) was also generated during the alkaline washing of the MSWIFA. Besides, pretreatments led to the reduction in particle size, the increase in pore volume and specific surface area of the MSWIFA, as well as the removal of chloride and sulfate anions. All the pretreatment methods were effective in reducing leaching of heavy metals to below levels of nonhazardous waste except Cd and Pb with alkaline washing. Furthermore, both the chemical Frattini test and the mechanical activity index test showed improvement in pozzolanic activities of the MSWIFA after the pretreatments. Overall, the combined pretreatment method was most effective in eliminating gas emission, and reducing leaching of metal ions and anions from the ash, while enhancing the pozzolanic activity of the ash.
... Experimental studies (e.g. Jakob et al., 1996;Nowak et al., 2012) have demonstrated substantial volatilisation of Zn, Pb, and Cu, from fly ash below the melting temperature of the ash. Two commercially available processes have been developed, the CT-Fluapur® process and the ASH DEC process (Lindberg et al., 2015), to separate and then recover Zn, Pb, and Cu from fly ash. ...
... To date most scientific studies have focused on the thermal behaviour of fly ashes in oxidising or inert gas atmospheres (e.g. Jakob et al., 1996;Nowak et al., 2010;Yu et al., 2015). Relatively few studies have compared the behaviour of fly ashes in reducing atmospheres to that in oxidising atmospheres (Jakob et al., 1995;Ludwig et al., 2003). ...
Municipal solid waste incineration fly ashes can contain high concentrations of Zn and other valuable elements including Cu, Pb, Sn, and Sb. These elements can potentially be separated from fly ashes by selectively volatilising and condensing them in thermal processes. This study presents a thermal process for production of zinc concentrates from fly ashes and assesses the impact of the reducing gas atmosphere used in the process on the volatility of Zn, Pb, and Cu. Concentrates were produced by heating samples of municipal solid waste incineration fly ash in a reducing atmosphere, consisting of 10% H2 and 90% N2, and selectively condensing elements which volatilised from the ash at 900 and 1100 °C. Thermodynamic equilibrium calculations were used to predict the volatile behaviour of Zn, Pb, and Cu in the reducing atmosphere and in an oxidising atmosphere (air). The extent of volatilisation of these elements was also determined experimentally for both the reducing atmosphere and the oxidising atmosphere by means of mass balances based on elemental analyses of untreated and heat-treated ashes. The concentrate produced at 900 °C contained high concentrations of Zn (55.9 ± 12.5% w/w) and Pb (4.7 ± 1.1% w/w). These metals and other higher value elements, specifically, Sn, Sb, and Bi, were greatly enriched in the concentrates when compared with the untreated fly ash, showing a high potential for the developed process to separate multiple valuable elements from ashes. However, several deleterious impurities, particularly K, Na, and Cd, also reported to the concentrates in significant concentrations. Further refinements to the process are needed to separate these elements from Zn. The reducing gas atmosphere substantially increased the volatility of Zn, but suppressed the volatility of Cu and, to a lesser extent, the volatility of Pb. The equilibrium calculations overestimated the release of Cu in oxidising conditions and the release of Zn and Pb in both oxidising and reducing conditions.
... Zn, and low levels of deleterious impurities, e.g. Cd and Cl, is challenging since many elements can simultaneously volatilise when fly ash is heated (Jakob et al., 1996;Ludwig et al., 2001). Design of thermal processes for selective volatilisation and condensation of Zn requires comprehensive knowledge of the volatile behaviour of the major, minor, and trace element constituents of fly ashes, in a range of operating temperatures and gas atmospheres. ...
... The two-step process was evaluated at 880°C. This temperature was estimated to be sufficiently high for substantial volatilisation of Cd and Cl and partial volatilisation of K and Na based on previous studies on the release of these elements during heat-treatment of MSW incineration plant ashes in an air gas atmosphere (Jakob et al., 1996;Yu et al., 2015). The volatilisation of metals and metalloids in the two-step process is compared to that obtained in one-step processes in oxidising and reducing gas atmospheres (see Fig. 6). ...
This study assesses the volatility of 15 elements (As, Bi, C, Cd, Cl, Cu, K, Mn, Na, P, Pb, S, Sb, Sn, and Zn) during thermal processing of fly ashes obtained from four waste-to-energy plants and one wood-combustion plant. Differences in volatility in oxidising and reducing atmospheres (air and 10% H 2 /90% N 2) were assessed at two temperatures, 700 and 1000 °C. P and Mn were predominately retained in all ashes regardless of the operating atmosphere and temperature. Other elements showed significant variation in volatility depending on the type of fly ash, atmosphere, and temperature. Heat-treatment of the wood-combustion fly ash in the air atmosphere resulted in low release of K, Na, and all investigated heavy metals and metalloids. Several valuable elements, including Zn, Sb, Sn, and Bi, were significantly more volatile in the reducing atmosphere than in the oxidising atmosphere, particularly at 1000 °C. Other elements were either less volatile, equally volatile, or only marginally more volatile when the ashes were heated at 1000 °C in the reducing atmosphere. These elements include C, Cl, Cu, and, in the case of fly ashes derived from municipal solid waste, Cd and Pb. A two-step process, in which municipal solid waste incineration fly ash is first heated in an oxidising atmosphere and then in a reducing atmosphere, is proposed for production of a chloride-free zinc concentrate. Evaluation of the two-step process at 880 °C shows good potential for selective volatilisation of Zn with other valuable elements, including Sn, Sb, and Bi.
... [19][20][21] Positively charged MB can injure human eyes and cause respiratory issues on inhalation; ingesting MB through the mouth can cause vomiting, mental confusion, a burning sensation, profuse sweating, and nausea. 22,23 Different technologies and approaches are used to remove heavy metals from wastewater, such as ion exchange, evaporation, chemical precipitation, adsorption, reverse osmosis, membrane ltration, otation, electrochemical deposition, and coagulation-occulation. [24][25][26][27][28][29][30][31][32][33] These approaches have some aws, such as high operating costs, hazardous byproducts, insufficient removal efficiency, sludge formation, high energy requirements, and difficulties in disposal. Sorption strategies offer advantages over other techniques, such as ease of operation, an outstanding elimination efficiency, affordability, and the ability to regenerate the sorbent. ...
The synthesis of polymeric magnetic composites is a promising strategy for the rapid and efficient treatment of wastewater. Lead and methyl blue are extremely hazardous to living organisms. The sorption of Pb 2+ and the dye methyl blue (MB) by biochar is an ecologically sustainable method to remediate this type of water pollution. We functionalized Shorea faguetiana biochar with Fe 2 O 3 and MXene, resulting in Fe 2 O 3 /BC/MXene composites with an efficient, rapid, and selective adsorption performance. Based on X-ray photoelectron and Fourier transform infrared spectrometry, we found that the Fe 2 O 3 /BC/MXene composites had an increased number of surface functional groups (F − , C]O, CN, NH, and OH −) compared with the original biochar. The batch sorption findings showed that the maximum sorption capacities for Pb 2+ and MB at 293 K were 882.76 and 758.03 mg g −1 , respectively. The sorption phenomena obeyed a pseudo-second-order (R 2 = 1) model and the Langmuir isotherm. There was no competition between MB and Pb 2+ in binary solutions, indicating that MB and Pb 2+ did not influence each other as a result of their different adsorption mechanisms (electrostatic interaction for Pb 2+ and hydrogen bonding for MB). This illustrates monolayer sorption on the Fe 2 O 3 /BC/MXene composite governed by chemical adsorption. Thermodynamic investigations indicated that the sorption process was spontaneous and exothermic at 293-313 K, suggesting that it is feasible for practical applications. Fe 2 O 3 /BC/MXene can selectively adsorb Pb 2+ ions and MB from wastewater containing multiple interfering metal ions. The sorption capacities were still high after five reusability experiments. This work provides a novel Fe 2 O 3 /BC/MXene composite for the rapid and efficient removal of Pb 2+ and MB.
... Heavy metals such as lead (Pb), zinc (Zn), copper (Cu), and cadmium (Cd) evaporate between 670°C and 1000°C only in the presence of residual chloride. In the absence of chloride, heavy metals are incorporated into an alumina-silicate complex matrix that limits their evaporation [52]. Temperature above 1200°C triggers the evaporation of metal oxides [50]. ...
Soil amendment has recently been addressed as one of the promising applications of torrefied biomass, where the distribution of nutrients is a significant parameter of interest. The present study uses an x-ray fluorescence technique to elucidate the influence of torrefaction severity on the nutrient composition of biomass (e.g. rice husk). An increase in the extent of process severity leads to an enhancement in the fixed carbon content. Hence, the variation in nutrient composition is analyzed with respect to changes in the fixed carbon content. Results reflected that variation of nutrients with increasing fixed carbon content does not follow a uniform trend. It signifies the need for understanding the effect of process conditions, chemical forms, and interactions among the elements on the release of compounds containing nutrients. Enrichment of P, Fe, Mn and Zn, and reduction of K, Ca, S, Cl, Cu, Ni, Si, Sr, Ti, and Br have been observed in the solid product obtained after torrefaction. Concentration of Si followed K and P are maximum in all samples. K, Cl, S, and Br loss occurs significantly because of relatively lower stability in the torrefaction temperature range. The present findings would be helpful in selecting the conditions required to produce torrefied biomass to amend a specific soil type for a particular crop.
... Heavy metal fractionation between IBA and FA depends on the composition of MSW, the binding form of the metals and the operating conditions of the incinerator. Metal transfer to FA is favoured by higher furnace temperatures and thus increasing amounts of dust particles as well as elevated chlorine and sulfur concentrations in the flue gas (Jakob et al., 1996;Morf et al., 2000). Ash particles are collected at different stages during the flue gas cleaning process. ...
The current paper discusses some selected developments for efficient management of the globally increasing quantity of waste. Incinerator bottom ash (IBA), the heavier ash generated during incineration of municipal waste, is currently utilised in two distinct ways. One pathway is not to fragment IBA and use it as a building material in road construction. This results in reduced landfilled residual but low metal recovery. The other way is to crush the mineral aggregate, thus maximising metal recovery but resulting in higher landfilled, end material. Here emphasis is placed on the second approach as implemented in Switzerland together with the economics and need for improvement of metal recovery from IBA and fly ash. The second theme reports on the viability of recycling mussel shells as a partial substitute for cement to stabilise dredged marine sediments mechanically. This can reduce the consumption of natural resources and lower the amount of binders used in sediment stabilisation practices. Finally, the adequacy of EU’s requirements regarding monitoring of groundwater pollution from landfills is assessed, and recommendations are provided to use bioindicators to determine the impact of landfills on surrounding vegetation.
... Consequently, the chlorination of a certain part of lead by the reactions (3-6) and its evaporation in the chloride form during the calcination of EAFD is also possible. This assumption is confirmed by authors [60,61], who has found out a high rate of Pb removal as lead chlorides at the temperature range of our study, as well as a possibility of lead vaporization at the temperatures even below 850 °C. After the main part of chlorides contained in the EAFD has been vaporized, a lead evaporation mechanism is also changed. ...
A behavior of zinc, lead, and iron during the processing of EAFD (electric arc furnace dust from steelmaking) by the promising method based on its calcination with lime was studied. The chemical and mineralogical composition of the EAFD were analyzed in detail by X-ray fluorescence, X-ray diffraction, and Mössbauer analyses, as well as using methods of chemical phase analysis. It was found that EAFD contains 29.95% Zn consisting of 15.9% of ferrite and 13.81% of free oxide, as well as 0.77% Pb, which is mainly in silicate form. It was shown that calcination of EAFD with CaO in the mass ratio of 1:0.3 at 1000 °C for 120 min led to the conversion of 90.2% Zn into the highly soluble form of ZnO and the removal of 95% Cl and 87% Pb that resulted to obtaining the calcine suitable for further leaching and electrolysis in zinc plants. Based on the obtained thermodynamic, kinetic, and analysis data, the behavior of zinc, lead, and iron during the calcination was discussed.
... The most common one is to use fly ash as one of the raw materials for cement production (Aubert et al. 2006;Guo et al. 2014). Some researchers have used the characteristics of heavy metals in fly ash to be volatile during high-temperature treatment to conduct high-temperature thermal separation of heavy metals such as high content of Cd, Cu, Pb, and Zn in fly ash (Jakob et al. 1996;Syc et al. 2020). The fly ash processed by high-temperature thermal separation technology can be used as ordinary waste landfill or construction raw materials. ...
Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.
... There are various heavy metal removal technologies and methods such as chemical precipitation [26], ion-exchange [27], membrane filtration [28,29], evaporation [30], reverse osmosis [31], flotation [32], Coagulation-flocculation [33], electrochemical deposition [34], and adsorption [35]. These methods have their drawbacks, for instance, insufficient removal, high operational cost, high energy requirements, difficulties in disposal, toxic byproduct, and sludge formation. ...
Lead (Pb) is a concerning water pollutant worldwide as it is highly toxic to living organisms. In this research, adsorption studies were carried out for the removal of Pb from water. Graphene oxide (GO) was used as adsorbent, which was synthesized by modified hummers method using graphite from waste dry cell battery. The prepared GO was characterized by FESEM, TEM, XRD, BET, Raman, FTIR, and Elemental analysis which revealed that the highly porous GO was successfully prepared from graphite rod of waste dry cell battery. Batch experiments were performed to investigate the effects of pH, contact time, adsorbent dose on the adsorption process, and optimum condition for adsorption was determined. Experiments showed 98.87% removal of Pb (10 ppm) in a very short time (20 min) at pH 4 while adsorbent dose was 0.25 gL⁻¹. The oxygenated groups on the surface of GO played a crucial role in the adsorption of Pb on GO. Experimental data were tested against kinetic and adsorption isotherm models. The adsorption process followed pseudo-second-order kinetics, Langmuir isotherm at lower temperature (20 and 30 °C), and Freundlich isotherm at higher temperature (40 °C). The maximum adsorption capacity was calculated to be 55.80, 54.03, and 51.83 mg g⁻¹ at 20, 30, and 40 °C, respectively. Thermodynamic studies suggested the adsorption was exothermic and spontaneous under 20–40 °C, which indicates that adsorption was feasible. Therefore, this study represents a rapid and efficient method in reducing water contamination caused by Pb.
... Herein, silicon nanoparticles were firstly prepared from i n d u s t r i a l w a s t e f l y a s h v i a a s o l i d -s t a t e a n d magnesiothermic reaction with molten salt, which shows great potential for the large-scale preparation of Si anodes for LIBs. Hence, compared with reported methods [13,34], this route enjoys four merits: (i) the scalability under mild conditions free of expensive Si precursors; (ii) industrial trash to silica treasure from waste (silica content up to ∼50 % [35]) is much green, environmentally friendly, and cheaper to other silicon resources, such as SiCl 4 , SiO 2 , commercial Si, SiC and Mg 2 Si; (iii) high Si yield; (iv) Si NPs can alleviate the volume change of Si during Li-Si alloying, promoting the overall structural stability. The synthesized Si NPs as anode for LIBs, exhibited excellent electrochemical performance, due to fine nanocrystalline characteristics. ...
Silicon nanoparticles were firstly prepared from industrial waste fly ash via a solid-state and magnesiothermic reaction with molten salt. The entire progression is feasible, green, economical, and scalable. Si nanoparticles served as anode materials for lithium-ion batteries (LIBs), delivering high specific capacity of around 3173.1 mAh g⁻¹, and outstanding cycling stability up to 500 cycles at 1 C. The work here will shed light on the idea of transforming trash, industrial waste fly ash, to treasure, silicon nanoparticles, for sustainable energy conversion.
Graphical Abstract
Industrial waste fly ash derived silicon nanoparticles were firstly synthesized via a coupled solid state-magnesiothermic reaction in a molten salt, which exhibited superb Li⁺ storage properties.
... The primary sources of Ca 2+ are soil erosion and construction (Nieberding et al., 2018), and its high proportion indicates that local fog may be affected by human activities. The high proportion of Cl may be related to domestic emissions from local villages; for example, combustion releases fly ash with an extremely high chlorine salt content in the air (Jakob et al., 1996;Wang et al., 2010). When long-wave radiative cooling leads to SS at night, some of the aerosols with Cl act as CCN, thereby activating fog droplets; activated fog droplets in turn adsorb Cl from the atmosphere, leading to a high proportion of Cl in the fog water. ...
We conducted a three-month field experiment focusing on the physical and chemical characteristics of fog in a tropical rainforest in Xishuangbanna, Southwest China, in the winter of 2019. In general, the fog would form at midnight and persist because of the increased long-wave radiative cooling combined with the high relative humidity, gentle breeze, and a relatively low aerosol number concentration in the forest; the fog would dissipate before noon due to the increasing turbulence near the surface. This diurnal cycle is typical for radiation fog. The microphysical fog properties included a relatively low number concentration of the fog droplet, large droplet size, high liquid water content, narrow droplet number-size distribution, and high supersaturation. The chemical properties showed that the fog water was slightly alkaline with low electrical conductivity, whereas the highest proportions of anions and cations therein were Cl− and Ca2+, respectively; the chemical components were enriched in small fog droplets. In addition, we indirectly calculated the fog supersaturation according to the κ-Köhler theory. We found that condensation broadens the droplet number-size distribution at relatively low supersaturation, which is positively correlated with the fog-droplet number concentration and negatively correlated with the droplet mean-volume diameter; this affects the key microphysical processes of fog.
... During incineration, volatile compounds from waste materials are transformed into the gas phase that form the flue gas. The transfer of heavy metals to the gas phase is thereby favored by higher furnace temperatures, as well as elevated chlorine and sulfur concentration in the flue gas (Verhulst et al. 1996;Abanades et al., 2002;Morf et al. 2000;Belevi and Moench 2000;Jakob et al. 1996). The first solid residue from the flue gas path is the ash arising at the 2nd and 3rd pass, also called the empty pass ash (EA), which is often disposed together with the bottom ash ( Fig. 1). ...
This study reports on detailed chemical and mineralogical characterization of the different municipal solid waste incineration ashes forming along the flue gas path of plants with separate dust removal and neutralization. In pursuit of optimizing heavy metal recovery through acid leaching, the metal extractability from empty pass ashes (EA), boiler ashes (BOA) and the electrostatic precipitator ashes (ESPA) was evaluated and compared. The focus was laid on matrix phases affecting leachability (e.g. alkalinity, oxidation–reduction potential), as well as on distribution and concentration of recoverable heavy metals and their binding forms. The data showed, that EA and BOA are geochemically similar and are essentially composed of two different materials: the heavy metal poor airborne ash particles and the Zn- and Pb-rich sulfate deposits that condensate on heat exchanger surfaces. Variation in relative amount and chemical composition of the deposits is responsible for fluctuations in bulk composition of EA and BOA. The ESPA shows different chemical and mineralogical characteristics than EA and BOA. The ESPA is enriched in the volatile heavy metals Zn, Pb, Cu, Cd and Sn, which are mainly incorporated in chlorides and sulfates. The high content of salt-bound and thus easily soluble heavy metals together with the lower alkalinity and lower oxidation–reduction potential indicates, that ESPA has a better leachability compared to EA and BOA. The EA and BOA, on the other hand, do not show any significant differences in leachability. The data may contribute to a basis for re-evaluating disposal routes of ash fractions with poor extraction properties.
... These results show that the metals are most probably emitted as chloride after reacting with Cl available as alkali salts. For high contaminated soils and biomass materials, the addition of chlorine compounds can boost their release utilizing thermal treatment (Jakob et al., 1995(Jakob et al., , 1996. However, the matrix and locally generated redox conditions can also affect the release of these metals. ...
In this study, leaf and soil samples were used as bio-monitors for different alkali and heavy metals at six different locations in Kyiv city. Using x–y plots of the inductively coupled plasma optical emission spectroscopy (ICP-OES) data measured the discrepancy level in elemental composition between the different investigated areas; the correlation between the concentrations in tree leaves and the samples from the surrounding soils were investigated. While the concentration of essential mineral elements and metals was found to be similar in several leaf and soil samples, in other samples, their concentration spread up to more than one order of magnitude. The concentration of metals was found to be higher in soil samples than in leaves. Thermo-gravimetric analysis (TGA) data helped to further characterize both types of samples. The metal removal during the incineration of the leaves was investigated by coupling a thermo-gravimetric analyzer to an inductively coupled plasma optical emission spectrometer (TGA-ICP-OES). The release of Cd, K, Na, Pb, and Zn during incineration at temperatures up to 960 °C was online monitored, and some insights were drawn about the behavior of such metals and the chemistry involved in the volatilization process.
... During co-combustion or co-gasification with biomass [4,5] or wastes like plastics, rubbers and especially scrap tyres [6,7] higher zinc concentration in the off-gas must be expected. Condensation behavior of zinc under combustion conditions has been extensively studied [8][9][10][11]. Few studies indicate that the condensation is affected by the oxygen partial pressure, e.g. in oxyfuel conditions [12], but it is important since gasification-based processes exhibit more advantages on controlling emissions of pollutants than conventional combustion [13,14]. ...
Fuels used in combustion and gasification, such as coal, biomass and wastes, yield large amounts of trace elements , which can cause both technological and environmental concerns. This work provides an in-depth insight into the condensation behavior of the trace element zinc under gasification-like conditions in atmospheres containing the HCl and H2S trace gases. A lab-scale quartz reactor with a multi-stage cooling zone was used to determine the condensation content and species distribution of the zinc deposition in different gasification atmospheres. The Scheil-Gulliver cooling model was used to simulate the zinc condensation process, since it provides a good reference to analyze the degree of supercooling during the condensation process. Competition of the gaseous species HCl and H2S with respect to the ZnO condensation behavior has been observed. HCl leads to significant supercooling of the ZnO condensation. It is shown that this can be compensated by ZnS acting as nucleation sites for ZnO if significant amounts of H2S are present. It is further shown that there is a significant bypass effect, i.e. even after nucleation has started there is a significant amount of Zn remaining in the gas phase which significantly extends the condensation regime to lower temperatures. To visualize both effects, a H2S-temperature-transition diagram is proposed. The potential applications including the prevention of problematic depositions (slagging and fouling) and sorbent selection as well as design for removal of trace element zinc from the syngas in IGCC power plants are proposed and discussed in the light of developing clean power technologies.
... A possible explanation for the greater volatility of Bi, K, Na, Pb, and Zn in the FA could be the higher concentration of Cl in the FA (5404 ± 100 mg of Cl per kg in the FA vs. 88.4 ± 1 mg of Cl per kg in the BA). Chlorine can form gas phase metal chlorides with all these metals at temperatures below 1000°C (Costa et al., 1983;Jakob et al., 1996;Lane et al., 2020b). Another possible explanation is differences in the chemical speciation of Bi, K, Na, Pb, and Zn in the FA and the BA. ...
This study assesses the potential of thermal processing for detoxification of wood-combustion ashes that contain high levels of Cr and Cd. Thermal treatment (1000 °C) of bottom ash and fly ash in an oxidising gas (air) atmosphere resulted in: low volatilisation of Cd and most other heavy metals, oxidation of Cr in the ashes to Cr (VI), and, in the case of the fly ash, significantly increased leaching of Cr and Mo. Thermal treatment in a nitrogen atmosphere resulted in local reducing conditions due to oxidation of ash-derived carbon to CO (g). Thermal treatments in this atmosphere and in a reducing atmosphere consisting of 10 % H2 and the balance N2 detoxified the ashes in at least two ways: (i) by substantially removing Cd, Pb, Bi, Tl, and, in the case of the fly ash, Zn from the ashes by volatilisation; and (ii) by thermal reduction of Cr (VI) in the ashes. There was at least a 100-fold reduction in the leaching of total Cr from both the bottom ash and the fly ash following the thermal treatments in reducing conditions. Chromium only leached from the detoxified bottom ash to a significant extent in acidic conditions (pH < 4).
... Previous works have shown that the volatilisation rate of heavy metals in FA is mainly affected by heat treatment temperature and chloride ion concentration, and the volatilisation rate of zinc (Zn) and copper (Cu) is the lowest. Meanwhile, heavy metals, SiO 2 and Al 2 O 3 tend to form aluminosilicates at high temperature to inhibit the volatilisation of heavy metals (Jakob et al., 1995(Jakob et al., , 1996. Wang et al. (2006) and Tian et al. (2012) have reported separating heavy metals at high temperature by solid phase high temperature volatilisation and adding a chlorinating agent. ...
This research investigated the heavy metal leaching property and cementitious material preparation by treating municipal solid waste incineration fly ash through the molten salt process. The results indicated that the heavy metal thermal evaporation of fly ash in the molten salt was related to molten salt composition, heat treatment temperature and atmosphere. After treatment with sodium chloride molten salts (contains 10–50 wt% calcium chloride) from 900°C to 1000°C for 2 h, the leaching concentrations of lead, cadmium, copper, zinc and other heavy metals in fly ash were decreased more than 90% and they could fully meet with the landfill standard. Moreover, after molten salt treatment, the weight fraction of fly ash was reduced by 50 wt% than the original one, and the fly ash has been changed as a kind of cementitious material, which has excellent cementitious property. The X-ray diffraction result indicated that the main crystal mineral composition of cementitious materials obtained was alite, belite, alinite and calcium sulphate.
... Some studies [109,111,112] have doubted the direct reaction of inorganic chlorine (NaCl) with heavy metals. The idea is that, since Na has a higher affinity for chlorine than heavy metals, direct chlorination is less likely to happen, and therefore, it has been suggested that NaCl can enhance the release of heavy metals, in the presence of SiO 2 , Al 2 O 3 , SO 2 , or H 2 O, according to the following reactions: ...
Municipal solid waste (MSW) Waste to energy (WtE) Thermal behavior Corrosion a b s t r a c t Municipal solid waste (MSW) incineration plays an important role in waste treatment systems throughout the world, due to the advantages of fast volume reduction by 80-90%, heat recovery, and power generation. However, waste-to-energy (WtE) plants have low electrical efficiency of 15-25%, due to the low steam temperature and pressure used in order to minimize boiler deposition and corrosion problems. Undoubtedly, the high Cl-content in MSW is the reason for the severe corrosion problem. Chlorine also forms volatile compounds with trace metals (e.g., Zn, Pb), and, influences the fate of other key elements, e.g., Na, K, and S. Different from alkali metals in biomass, which have been thoroughly investigated, the behavior of chlorine during MSW incineration has not been systematically and comprehensively studied. Up until now, there are few in-depth studies that have been conducted on the thermal behavior of chlorine or on the remedial measures against Cl-induced problems. An up-to-date review on the behavior of chlorine from incineration via freeboard chemistry to corrosive attack is therefore needed, in order to provide knowledge on process optimization and reactor design, thereby enabling high-efficient energy utilization and safe operation of large-scale WtE units. This review provides a critical summary of the progress of research on chlorine in MSW (ori-gins, species, and analytical methods); the thermal behavior of chlorine, including chlorine vaporization, aerosol formation and transformation (freeboard chemistry), deposit formation, and Cl-initiated corrosion mechanisms. In addition, the interrelationship of chlorine with other key elements (S, Na, K, Zn, Pb), and, the chlorine roadmap in the incineration process is presented, along with the influence of feedstock composition and the temperature of both the flue gas and boiler tube metal on chlorine-induced deposition and corrosion. Mitigation measures against Cl-initiated problems such as Segher boiler prisms, mixed secondary air injection, and eco-tube systems, are also thoroughly discussed. Finally, challenges and further research questions, are identified.
... A possible effect of chlorides on HMs evaporation must also be considered. Indeed, the presence of alkali chlorides can lead to the formation of volatile heavy metal chloride forms which may exhibit a certain immobilization and a limitation of evaporation because of the occurrence of chemical transformation to oxides or aluminates/ silicates compounds (Jakob et al. 1996). For instance, a significant influence of competition occurred between ZnCl 2 evaporation and ZnO hydrolysis and immobilization in silica and/or alumina matrices on the Zn separation from FA (Stucki and Jakob 1998). ...
The present work aims to provide a comprehensive review of the experimental studies focusing on municipal solid waste incineration fly-ash (FA) treatments that are required before the application of advanced processes aimed at their final reuse or safe disposal. The investigated pre-treatments are divided into three categories: (1) water washing/chemical leaching; (2) electrodialysis; and (3) thermal separation. Analysed aspects include: (1) process efficiency; (2) effect on FA physical–chemical characteristics; and (3) process applicability as a function of secondary FA treatment steps which are generally required for final disposal or reuse of the remediated waste. Investigations related to these elements allows a determination of the efficacy and the operational convenience of a specific pre-treatment to achieve a proper FA remediation level. A comparison of studies in the literature provides a thorough source and a useful basis for correctly addressing future experimental activities and research efforts. The discussion of the results provides the basis for the development of a suitable methodology to optimize the environmentally sustainable reuse or safer disposal of treated FA.
... Another plausible mechanism is the presence of chlorides which prevents the incorporation of the heavy metal into the matrix (Jakob et al. 1996) favored as it contains excessively high Ca content ). However, solidification using a binder results in an increase in the mass of the secondary waste which has to be disposed of. ...
Municipal solid waste incineration (MSWI) generates bottom ash, fly ash (FA), and air pollution control (APC) residues as by-products. FA and APC residues are considered hazardous due to the presence of soluble salts and a high concentration of heavy metals, and they should be appropriately treated before disposal. Physicochemical characterization using inductively coupled plasma mass spectroscopy (ICP-MS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) have shown that FA and APC have potential for reuse after treatment as these contain CaO, SiO2, and Al2O3. Studies conducted on treatment of FA and APC are categorized into three groups: (i) separation processes, (ii) solidification/stabilization (S/S) processes, and (iii) thermal processes. Separation processes such as washing, leaching, and electrochemical treatment improve the quality and homogeneity of the ash. S/S processes such as chemical stabilization, accelerate carbonation, and cement solidification modify hazardous species into less toxic constituents. Thermal processes such as sintering, vitrification, and melting are effective at reducing volume and producing a more stable product. In this review paper, the treatment processes are analyzed in relation to ash characteristics. Issues concerning mixing FA and APC residues before treatment, true treatment costs, and challenges are also discussed to provide further insights on the implications and possibilities of utilizing FA and APC as secondary materials.
Pozzolanic materials, known for their superior performance in enhancing the strength and integrity of well cements along with their significantly reduced carbon footprint, have been receiving much attention. The elemental characterization of pozzolanic materials is crucial because it affects the reactivity of cementitious fluids and thus the overall efficiency of a cementing job. This study investigates the elemental analysis correlation between inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray fluorescence (XRF) spectrometry techniques using machine learning (ML) algorithms.
ICP-OES is known for its high accuracy and low detection limit, but it can be labor-intensive and time-consuming because of the tedious sample preparation involved, which also raises chemical safety concerns. In contrast, XRF requires minimal sample preparation and offers quick analysis. However, the XRF results are subject to matrix effects. The goal of this study is to harness the power of ML to recognize and reduce the matrix interference in XRF, enabling the substitution of ICP-OES with XRF in practical well cementing applications.
A comprehensive dataset of over 100 unique pozzolanic materials, sourced from various suppliers worldwide, was compiled using ICP-OES, XRF, and other material characterization techniques. A family of ML regression models was optimized, primarily focusing on the simple and efficient principal component regression (PCR) and partial least squares (PLS) algorithms, while also exploring other linear, nonlinear, kernel-based, and decision tree-based ML models. These models were trained using full XRF spectra (both raw and after preprocessing), with ICP-OES measurements serving as the ground truth. Model predictions on an independent test set were critically evaluated and compared, resulting in the development of an optimal ML workflow. Rigorous reproducibility analysis was also conducted for both analytical techniques. The ML models demonstrated prediction errors of less than 5% (range-normalized root mean square error) for the 12 main elements of interest when applied to the XRF spectra. This suggests that ML-enhanced XRF spectrometry can effectively replace ICP-OES, significantly reducing the labor and time required for the elemental analysis of pozzolanic materials.
This study, pioneering the use of ML to enhance the elemental analysis of pozzolanic materials, offers a robust framework for future practical applications of XRF material characterization in the oilfield industry and beyond. The proposed approach will lead to informed decision-making regarding the formulation of pozzolan-based well cementing slurries. Leveraging advanced analytical techniques to ensure their effective use in cementing applications aligns with the industry's ambition to use environmentally benign materials.
Inadequate municipal solid waste (MSW) management threatens public health and the environment. The waste-to-energy (WtE) route allows the production of electricity, heat, and other valuable chemical products. WtE consists of incineration, gasification, pyrolysis, and some emerging technologies. This study applies the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to conduct a bibliometric analysis of WtE technologies for MSW management research. Scopus-indexed articles were examined between 1971 and 2023. Four periods were determined and analyzed in terms of their most significant results. In addition, the most pertinent journals, Waste Management, Chemosphere, and Waste Management & Research, were ranked first, second, and third, respectively. Moreover, the top contributor countries are one in America (the United States), three in Asia (China, Japan, and India), and five in Europe (Spain, Italy, Germany, Sweden, and the United Kingdom). Throughout a Life Cycle Assessment (LCA) case study, the environmental performance of gasification and incineration as relevant technologies for treating MSW were contrasted. Gasification excelled in seven environmental parameters, suggesting that developing strategies for MSW gasification on a commercial scale should prioritize this aspect. Finally, the energy potential was assessed, which provided valuable information on the societal benefits of WtE technologies in various sectors, such as education, health, and electromobility. Under their respective contexts, stakeholders should enhance MSW sorting policies, pretreatment methods, and emerging valorization options. Increasing global interest in WtE requires a social, environmental, and economic evaluation before implementation.
B2O3 was used as a fluxing agent can reduce the melting temperature of municipal solid waste incineration (MSWI) fly ash which related to the formation of the minerals Ca3(BO3)2, Ca2B2O5 and CaB2O4 during vitrification process. However, the relationship between immobilization of heavy metals and borates transformation during melting process remains unclear. In this study, the immobilization of heavy metal Pb inside Ca3(BO3)2, Ca2B2O5 and CaB2O4 based on density functional theory (DFT) were comparatively studied in this paper. The results showed that the defect formation energies for substitutional doping model are higher than interstitial model which is the more favorable the immobilization model for Pb. Pb cause a volume expansion in all borates. In the substitution doping model, Pb can replace Ca to balance the electronegativity of O atom and form chemical bonds with the surrounding O atoms, and the covalency of Pb–O is stronger than that of Ca–O. In addition, the order of covalency between Pb and surrounding O atoms is as follows: Ca3(BO3)2 > Ca2B2O5 > CaB2O4. In the interstitial doping model, bonds of O–Pb and B-Pb exhibited negative population values, revealing that filling of electrons into the antibonding states was the major orbital contribution. In addition, B 2s and 2p orbital and Pb 6p orbital form hybridization near the Fermi level in the CaB2O4 (I) doping model.
Safe and sustainable treatment of municipal solid waste incineration fly ash (MSWI FA) is urgently needed worldwide because of its high heavy metals, dioxin, and chlorine (Cl) contents. Thermal treatment is widely considered as a promising method for treating MSWI FA owing to its high toxic content removal efficiency and resource recovery; however, residual Cl is a concurrent critical problem faced during reutilisation of thermal treatment products. This review summarises the innovative thermal treatment methods of MSWI FA, such as those employed in production of cement, lightweight aggregates, glass slag, and metal alloys. The characteristics of Cl in MSWI FA, removal rate, transformation of water-soluble Cl into water-insoluble Cl, and the effect of different influencing factors such as temperature, composition, superheated steam, and mechanical pressure were analysed. The volatilization and decomposition of NaCl, KCl and CaClOH dominates Cl removal; however, the degradation of organic Cl and heavy metal chlorination volatilization process that generate HCl and heavy metal chlorides, respectively, also contributed to Cl removal. To promote the reutilisation of MSWI FA-based products, the leaching behaviour of residual Cl in products obtained by different thermal treatments was investigated.
The amount of incineration ash (IA) is expected to increase in South Korea from the rapidly rising numbers and operation capacities of incineration facilities; therefore, it remains necessary to establish measurements for the enhanced recycling and circularity of IA. This study established a database of hazardous substances in IA by compiling discharge data and survey results from domestic incineration facilities, along with literature survey values. The recycling potential of IA was assessed considering leaching reduction efficiency of various pretreatment methods. In particular, 98.2% of bottom ash and 49.0% of fly ash satisfied the IA recycling criteria after melting. Also, when mixed at a ratio of ∼ 78:22 natural soil to IA, the resulting material was usable for media-contact recycling by meeting the heavy metal content criteria of the Soil Environment Conservation Act.
Incineration industrial by-products can be used as supplementary cementitious materials (SCMs) to degrade the cement output, thereby reducing fossil-fuel combustion and contributing to the utilization and management of waste resources. This paper summarizes the state-of-the-art uses of incineration industrial by-products (coal ash, waste incineration ash, and biomass incineration ash), which are used as SCMs in partial cement replacement. It also summarizes alkali-activated by-products as cementitious materials that replace all cement with controlled low-strength material (CLSM). After introducing the general situation and physicochemical characteristics of these pozzolanic incineration ashes, the influences and mechanisms of the by-products on the performance of CLSM are summarized and analyzed. The discussions and analyses in this paper are expected to inspire further research and provide a basis for the sustainable development of CLSMs from incineration industrial by-products as cementitious materials.
This study explores the current state-of-the-art in the detoxification and valorization of solid residues from municipal solid waste incineration (MSWI), especially fly ash, using plasma vitrification. The principles and advances in hazardous material elimination, resource recovery, and system integration using plasma vitrification for MSWI fly ash are identified. The global production and the characteristics of MSWI fly ash are first reviewed. Then, the features and principles of plasma technologies used for MSWI fly ash treatment from the thermodynamic and physical aspects are provided. The mechanisms of detoxification of MSWI fly ash from the perspectives of dioxins destruction and metal separation by plasma vitrification are also discussed. Moreover, the recovery methods of valuable elements for vitrified slag are introduced. Finally, the improvement pathways of plasma vitrification processes from the domains of engineering performance, environmental impact, and economic viability are suggested.
Incineration is becoming a promising and effective approach to dispose the increasing municipal solid waste, while the fly ash produced is another urgent problem needed to be addressed. Municipal solid waste incineration fly ash (MSWI-FA) contains heavy metals and organic pollutants, which exert huge threat to human health and environmental safety. This paper analyzed the current situation of MSWI-FA, summarized the technologies of hazard-free treatment and resourceful utilization, expounded its future development trend. The latest thermal detoxification technologies of MSWI-FA were reviewed, including melting/vitrification, hydrothermal treatment and thermal plasma technology. The organic pollutants can be efficiently decomposed during the thermal treatment process, and the heavy metals can be stabilized, which was currently the most effective hazard-free treatment technology. The resource utilization technologies of MSWI-FA related to thermal treatment, including the application of MSWI-FA in the production of asphalt, cement, and glass ceramics, were reviewed. The life cycle assessment of various MSWI-FA treatment technologies were summarized and compared. The main principle was to make full use of the physicochemical characteristics of MSWI-FA, with its purpose to realize value-added utilization, and to decompose and stabilize the hazardous components during high-temperature process. The mechanism and technical characteristics of treating MSWI-FA through thermal detoxification and resource utilization were deeply summarized, and the future research work that needs to be further strengthened was proposed, thereby promoting the safe and effective treatment of MSWI-FA and realizing the green and sustainable development of the city.
High contents of heavy metals and Cl are major challenges for incineration residue disposal. Classification by the Chinese government and the coronavirus disease 2019 pandemic have changed the characteristics of incineration residues, thereby increasing the difficulty of disposal. In this study, medical waste incineration fly ash (MWI FA) was proposed as an additive to promote chlorination volatilization of heavy metals from municipal solid waste incineration fly ash (MSWI FA) and medical waste incineration slag (MWI S). When the mixing ratio of MWI FA to MSWI FA was 1:3, the chlorination volatilization efficiencies of Cu, Zn, Pb, and Cd at 1000 °C for 60 min were 50.2%, 99.4%, 99.7%, and 97.9%, respectively. When MWI FA was mixed with MWI S at a ratio of 1:1, the chlorination volatilization efficiencies of Cu, Zn, Pb, and Cd at 1200℃ for 40 min were 88.9%, 99.7%, 97.3%, and 100%, respectively. Adding MWI FA can replenish Cl in MSWI FA and MWI S while increasing the surface area and forming pore structures by sublimation of NaCl and decomposition of CaSO4, or can reduce the melting point and viscosity by Na2O destroying the glass matrix. Therefore, MWI FA can be co-disposed with MSWI FA and MWI S respectively to enhance the chlorination volatilization of heavy metals.
Al2O3 is regarded as an effective sorbent to capture lead from flue gas. The adsorption behaviors of different species of lead (Pb, PbO, PbCl and PbCl2) on the Al2O3 surfaces were explored based on density functional theory. The results show that the chemisorption mechanism is responsible for the adsorption of lead species on the Al2O3 surface. The high reactivity of Pb adsorption on the α-Al2O3 (110) surface is mainly attributed to the existence of unsaturated Al atoms. The Al hollow sites are identified as the effectively active sites for Pb adsorption on the (110) surface. The adsorption energies of different species of lead on the Al-terminated (110) surface are in the range of -4.20 to -6.30 eV. PbO adsorption at the Al hollow site of the Al-terminated (110) surface shows the highest adsorption energy (-6.30 eV), suggesting that Al2O3 prefers to capture PbO among different species of lead. The strong interactions of PbO, PbCl and PbCl2 molecules with the unsaturated Al atoms of the α-Al2O3 (110) surface are responsible for PbO, PbCl and PbCl2 capture by Al2O3. Al2O3 has a good ability to capture different species of lead, and the adsorption capacity follows the order: PbO > Pb > PbCl > PbCl2.
As the world races toward its urban future, the quantity of wastes, one of the vital by-products of an enhancement in the standards of living, is exponentially rising. The treatment of wastes employing plasma is an upcoming area of research and is globally used for the simultaneous processing of diverse wastes coupled with the recovery of energy and materials. Ground-breaking and cost-effective thermal plasma technologies with high efficiencies are a prerequisite for the growth of this technology. This paper delivers an evaluation of the fundamentals such as the generation and characteristics of the thermal plasma along with the various types of wastes treatable by thermal plasma and the related issues. Furthermore, the authors discuss different types of advanced technologies as well as the material and energy recovery techniques and their present status worldwide, at lab-scale and industrial scale. The application of different thermal plasma technologies is discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. Mathematical modeling studies are also assessed with an objective to derive ideal conditions and permissible limits for the reactors and to test a variety of waste materials. A strategy to improve the feasibility and sustainability of waste utilization is via technological advancement and the minimization of environmental effects and process economics. This paper sheds light on diverse areas of waste utilization via thermal plasma as a potentially sustainable and environmentally friendly technology.
Typical biomasses (wheat straw, maize straw and rice straw) were used for studying the carbonization of biomass, preparation and performance characterizations of charcoal briquettes. The combustion with charcoal briquettes was conducted on a self-built platform and the emission characteristics of sulfur and nitrogen pollutants were investigated. The results indicated that it is optimal for biochar preparation as a fuel with 450–500 °C of carbonization temperature, 180 min of holding time and 5 °C·min⁻¹ of heating rate. Biochar briquettes will have strong mechanical strength at briquetting pressure of 25 MPa, particle size of less than 1 mm and the ratio of modified corn starch of 4.32 wt%. Compared with biomass burning, biomass charcoal briquettes had better combustion performance and the emissions of pollutants were reduced.
Like conventional material products, waste is the last stage of the life cycle of engineered nano-materials, which are then incinerated or stabilized before disposal. However, because of their special physical characteristics, the fate of the thermally treated nano-materials may differ or not from the conventional ones. In this study the thermal release of metals from three nano-materials, namely CuO, ZnO and TiO2, embedded in matrices containing organic and inorganic compounds was investigated by using an in-house developed setup. This later, which combines a TGA (Thermogravimetric Analyzer) and an ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer) offers the possibility to gain simultaneously thermogravimetric and elemental information. It is shown that the matrix composition, such as chlorine and silicon, play a key role in the evaporation of Cu and Zn at temperatures above 700°C, while at relatively low temperatures (250 to 450°C) the nano-materials are most probably entrained in the flue gas independently of their chemical properties. Incineration experiments using a tubular furnace and subsequent ICP-MS (ICP Mass Spectrometry) analysis of the obtained residues allowed to quantify the metal evaporation from the three nano-materials.
Zinc fuming processes are used to volatilize heavy metals from slags and produce a clean slag. Since alternative fuel sources containing plastics are explored, the effect of chlorides becomes relevant. In this paper, the influence of Cl additions to a zinc fuming process on the Zn volatilization is investigated. Thermodynamic calculations were carried out on available industrial data from three different installations. The effects on the fuming performance of the α-value (mol O2/ mol C, in a range of 0.5 to 0.75), chloride source (Cl2, KCl, NaCl, MgCl2, and CaCl2), and added chloride amounts (50, 150, and 500 ppm Cl/min) were investigated. Although the α-value is still the most influential parameter for the overall zinc fuming rate, chloride additions can have positive effects as well. They make ZnCl2 volatilization possible, which supplements the Zn volatilization. Large additions of CaCl2 and MgCl2 improve the fuming rate the most since they cause the largest formation of the volatile ZnCl2 and they do not negatively influence Zn volatilization.
Removal of some heavy metals during thermal treatment of a model solid waste under different ambient gases (carbon monoxide [CO], nitrogen [N2], and air) was studied. Compared with the removal under N2 and air, removal of cadmium was significantly enhanced by CO at temperatures of 700°C and 800°C. Nickel removal was highest at 700°C, whereas removal of lead and zinc was highest at 800°C, also under CO. The enhancement trend correlated with the evaporation temperatures of the zero-valent forms of the metals. These show the potential of thermal treatment with a reducing CO gas in removing some heavy metals from solid wastes.
A comprehensive approach was used to characterize speciation and leaching behavior of major, minor, and trace elements in electrostatic precipitator (ESP) ash from a Canadian MSW incinerator. Neutron activation analysis (NAA), X-ray powder diffraction (XRPD), scanning electron microscopy/X-ray microanalysis (SEM/XRM), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS) were used to quantify elements, describe particles and phase associations, identify bulk and surface mineral phases, and identify the speciation of elements. SEM/XRM showed a complex polycrystalline material covering aluminosilicate spheres. XPS, as a surface technique, provided information on speciation at the particle surface where leaching first occurs. SIMS showed molecular fragments indicative of speciation and enrichment of volatile species (K, Zn, Cl, S, Pb) in the fine polycrystalline material. Many of these phases readily dissolve during leaching. Dissolution behavior and pH-dependent leaching could be modeled with the geochemical thermodynamic equilibrium model MINTEQA2. The ability to model leaching behavior provides an opportunity to examine possible disposal or treatment behavior.
Some kinetic aspects of the inactivation of poliovirus by chlorine in water have been observed in experiments with both HOCl and OCl - using virus preparations in which no less than 99% of the virions were free single particles. In this manner any influence of virion aggregation on the reaction rates observed was minimized. Under these conditions HOCl was clearly superior to OCl - as a disinfecting agent for this virus. Inactivation rates for both agents increased with increasing concentration, but in neither case did this increase continue in a linear fashion. Both forms of free chlorine became less efficient as the concentration was increased. While the decline in log plaque titer was not strictly linear with time for either HOCl or OCl -, HOCl was nearly linear below 0.6 log survival ratio. However, the OCl - inactivation rate slowed significantly below a 10 -2 survival level. These observations suggest that the mechanisms of viral inactivation by these two agents were not the same. Physical evidence of change has been detected by electron microscopy in negatively stained preparations of HOCl-treated poliovirions, even though inactivation occurred first. Some of the virions appeared to retain physical integrity after plaque titer indicated that they must have been inactive.
Adsorption was observed by measuring the weights of microporous alumina adsorbents as a function of time while they were exposed to varying partial pressures of NaCl and KCl in a stream of Ar. Despite the high experimental temperatures, the results exhibited the characteristics of physical adsorption. Adsorption and desorption were reversible without hysteresis. The kinetics appeared to be limited by transport through the adsorbent pores. The steady-state weight gains were readily described by the BET isotherm. The values of the weight gains at monolayer coverage, deduced from both the steady state and the rate data, were of the size expected from the adsorbent surface areas and estimated molecular cross sections. The phenomenon promises to be useful for removing trace amounts of these corrosive salts from hot combustion gases.
Data from the U.S. Department of the Interior, Bureau of Mines, and the University of Maryland on metal concentrations in municipal solid waste and in incinerator residues have been examined in three different ways to distinguish between combustible and noncombustible sources of the metals in the bottom ash, fly ash, and atmospheric particles from a municipal incinerator. Silver, Cd, Cr, Mn, Pb, Sn, and Zn were found to be derived from the noncombustible components of refuse as well as from the combustibles. Eight of the other 13 metals examined may also have significant noncombustible sources. Separation of the combustible components of municipal solid waste prior to use as a fuel should reduce the concentrations of these metals in the effluent streams from combustion processes.
Since strict regulations have been placed prohibiting the placement of hazardous wastes in landfills, incineration is emerging as the principal and most attractive alternative for disposal of hazardous wastes. Incineration of waste offers various advantages including conversion of toxic organic components of hazardous wastes to harmless or less harmful forms, reduction in volume, and means of energy recovery. Unfortunately, since metals are not destroyed during the incineration process, toxic metal particles or vapors are generated as byproducts when wastes containing these metals are incinerated. A significant fraction of volatile compounds of toxic metals like lead, mercury, cadmium, arsenic, and selenium, are emitted as vapor or fine particles. Nonvolatile toxic metal compounds are released with the ash and also require safe disposal.
Kaolinite, bauxite and emathlite have been found suitable for alkali removal from hot flue gases in coal conversion systems. The effect of temperature on the kinetics and mechanism of alkali adsorption/reaction on these sorbents was studied under a simulated flue gas atmosphere. Kaolinite and emathlite reacted irreversibly with the alkali; however for bauxite, 10% of the total weight gained was due to physisorption. Kaolinite was found to have the highest capacity and the largest activation energy for alkali removal. The overall sorption process is not just physical and non-selective, but rather a combination of physical and chemical processes, which are dependent on the temperature and sorbent chemistry. The reaction product of alkali with emathlite has a melting point of approximately 1270 K, while kaolinite and bauxite form compounds with a melting point of about 1870 K. Consequently, kaolinite and bauxite are more suitable for in situ removal of alkali, while all three can be used for downstream alkali removal.
Thermal treatment is a promising way for the decontamination and inertization of residues from waste incineration. The evaporation of heavy metals thereby is of great significance. It is the goal of this work to investigate the fundamental aspects of the evaporation of heavy metals in the heat treatment process and to determine the process parameters leading to complete evaporation of the relevant heavy metals. Evaporation experiments in different atmospheres were carried out with filter ash from municipal solid waste incineration. The quantities of the heavy metals Zn, Pb, Cd, and Cu evaporated as a function of time were measured at temperatures between 670 and 1300 degrees C; evaporation turned out to be most effective at temperatures just below the melting range of the residue (i.e., at 1000-1100 degrees C) and decreased drastically above this temperature range. The amounts of evaporation (relative to the contents in untreated filter ash) at about 1100 degrees C were 98-100% of Pb, Cd, and Cu and 50% of Zn in air and 98-100% of Ph, Cd, and Zn and 10% of Cu in argon atmosphere, respectively. Results of experiments using model systems indicate that the decre ase in the Zn evaporation at high temperatures is caused by the formation of compounds like Zn2SiO4 and ZnAl2O4. The results of the experiments in argon atmosphere are explained thermodynamically by the reductive potential of the carbon, contained in the residue.
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