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Recovery of Rare Earth Metals and Precipitated Silicon Dioxide from Phosphorus Slag
Abstract
This article presents the results of a study conducted to investigate the recovery of rare earth metals and precipitated silicon dioxide from phosphorus slag. To determine the possibility and completeness of the studied processes, thermodynamic data was obtained through the determination of the Gibbs energy and equilibrium constant of the reactions of calcium metasilicate with different reagents, namely sodium hydroxide and carbonate as well as nitric, hydrochloric, and sulphuric acids. This article also presents the results of studies on the treatment of phosphorus slags via hydrometallurgical methods using alkaline agents (sodium hydroxide and sodium carbonate) and nitric acid. The recovery of silicon in solution by the autoclave leaching of phosphorus slag using solutions of sodium hydroxide and sodium carbonate resulted in recovery efficiencies of 1.1% and 16.6%, respectively. The nitric acid treatment of phosphorus slag was studied, and the recovery efficiencies of various elements were the following: rare earth metals, 98.3–98.6%; aluminium, 96.5–98.6%; iron, 94.9–96.5%; and calcium, 99.1–99.5%. Nitric acid (46.5%) was selected as the phosphorus slag recovery agent. The cake produced after the nitric acid treatment of phosphorus slag was leached using two processes based on the use of a sodium hydroxide solution: (1) in a temperature-controlled cell under normal conditions and (2) in an autoclave. The process of leaching under normal conditions was determined to be the most effective process, resulting in an efficiency of silicon recovery into solution of 97.7%.
... e majority of YPS particles compose of CaO and SiO 2 , accounting for approximately 85% of the slag mass [3]. Other components of the YPS are Al 2 O 3, Fe 2 O 3 , MgO, and some rare earth metals [4,5]. In Vietnam, the P 4 is mainly produced and supplied by Lao Cai Yellow Phosphorus JSC (Tang Loong Industrial Zone, Bao ang District, Lao Cai Province, Vietnam), with the productivity of 93,800 tons P 4 /year and about 750,000-1,031,000 tons of YPS waste are produced and released directly into the surrounding environment [6]. ...
... erefore, it is important to find different ways to utilize this waste product. Recent studies have been focusing on applying YPS into asphalt or asphalt binder [7,8], cemented backfilling [9], retarding the early hydration of cement [10] or recovering rare earth metals [5]. YPS had been treated by different technologies and methods [11][12][13]. ...
Yellow phosphorus is used widely in the world for production of phosphoric acid, various phosphates, flame retardant, detergent, water treatment, metal surface treatment, etc. After the production of yellow phosphorus, a large amount of phosphorus sludge is discharged to environment, causing environment pollution. This work focused on treatment of yellow phosphorus slag (YPS) and application of it as an absorbent for chromium (VI) ion and methylene blue. The YPS was first washed with water to remove phosphoferrite (FeP) and impurities and then being milled and transferred to a float sorting system to obtain YPS particles. The characteristics of YPS particles were determined by inductively coupled plasma-mass-spectrometry (ICP-MS), energy-dispersive X-ray spectroscopy (EDX), infrared spectroscopy (IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), zeta potential, and nitrogen adsorption methods. The YPS particles were retreated with NaOH, HNO3, and EDTA solutions to evaluate the influence of these agents on metal ion and organic compound adsorption ability by YPS. The adsorption parameters of chromium (VI) ion and methylene blue (MB) by treated YPS particles were recognized by the ultraviolet-visible (UV-Vis) spectrometer. The effects of temperature, pH solution, and initial concentration of absorbed substances on the adsorption ability were investigated. The adsorption isotherms and adsorption kinetics of chromium (VI) ion and MB by YPS particles were also determined. The obtained results confirmed that the green technology used to treat the YPS2 particles is suitable to obtain an effective absorbent. The adsorption efficiency of YPS2 particles for removal of chromium (VI) ions is smaller than that for removal of MB in aqueous solutions. The adsorption isotherm of MB adsorption process is complied with the Langmuir isotherm while the adsorption kinetic fits well with the pseudo-second-order reaction model. The thermodynamic parameters of MB adsorption processed on YPS2 were calculated and discussed.
1. Introduction
Yellow phosphorus slag (YPS) is a waste product of manufacturing yellow phosphorus (P4) using the electrical furnace method at 1400°C–1600°C [1]. The worldwide yellow phosphorus production yields an average of 1.5 million tons of P4 each year [2]. In which, the countries discharge a large YPS weight including Chinese (75%), Kazakhstan (13%), America (8%), Western Europe (6%), Russia (4%), and the rest of India. For each ton of manufactured P4, about 8 to 10 tons of yellow phosphorus slag are produced [1]. This waste product is often left accumulated in the landfills, proposing a potential pollution thread to the environment. The majority of YPS particles compose of CaO and SiO2, accounting for approximately 85% of the slag mass [3]. Other components of the YPS are Al2O3, Fe2O3, MgO, and some rare earth metals [4, 5]. In Vietnam, the P4 is mainly produced and supplied by Lao Cai Yellow Phosphorus JSC (Tang Loong Industrial Zone, Bao Thang District, Lao Cai Province, Vietnam), with the productivity of 93,800 tons P4/year and about 750,000–1,031,000 tons of YPS waste are produced and released directly into the surrounding environment [6]. Therefore, it is important to find different ways to utilize this waste product. Recent studies have been focusing on applying YPS into asphalt or asphalt binder [7, 8], cemented backfilling [9], retarding the early hydration of cement [10] or recovering rare earth metals [5].
YPS had been treated by different technologies and methods [11–13]. In German Auslegeschrift No. 1,804,172, the YPS particles were heat treated at 1000°C to 1100°C in a rotary furnace [11]. In German Offenlegungsschrift No. 2,211,505, a physical separation method, for example, by gravity separation with tetrabromoethane as the liquid phase, the refinement of silicate slag phase was reported [12]. US patent No. 4,243,425 presented a method for refining of silicatic slag phase with steam at a temperature between 600°C and softening temperature of the slag [13].
In this work, an effective method for treatment of YPS was developed. This is a combination of the water washing flotation system with milling and sorting flotation. The waste water system was treated to recover P2O5, F, and minerals for other applications. The advantages of this technology were low energy consumption, reduction of noise and dust pollution, closed technology, and environmental friendly and waste water can be easily processed and reused (about 80–90%). The minimized weight of chemicals was used, and treatment process was carried in room temperature. This approached to the green technology, the general trend of the world.
The study on metal ion adsorption ability of YPS in aqueous solutions has been limited in the research. Herein, the YPS was chosen as an absorbent due to its silicate structure with high content of silica. Moreover, the small size particle as compared with micrometer inorganic additives is an advantage of the YPS. Hence, the obtained YPS could be expected to use as an absorbent for removing toxicity substances in aqueous solutions. In this paper, chromium (VI) and methylene blue have been chosen as the model substances to study the adsorption ability of YPS. Chromium, commonly found in various sources of industrial waste water, is one of the most toxic metal ions, which influences seriously the biodiversity of the environment and causes several health issues to humans. Chromium often comes from discharge of industrial activities such as leather tanning, electroplating, or textiles [14]. It exists in water with various oxidation forms, but mainly in trivalent and hexavalent state [15], in which the hexavalent state is considered the most toxic because it is easily dilution and can bioaccumulate in human organs [16]. Some studies reveal that Cr (VI) ions can cause digestive system and lungs cancer, gastrointestinal and dermatological problems, severe diarrhea, and hemorrhage [17–19]. Many materials have been utilized to adsorb Cr (VI) ions in aqueous solutions including banana peel [20], coffee resins [21], fly ash [22], groundnut hull [23], or zeolite NaX [24] and showed good results.
Dye has been an important ingredient in many common daily industries such as textile, leather, cosmetics, plastics, and food production [25]. Nevertheless, colored dye waste water constitutes considerable issues to the environment and water sources [26]. Complex aromatic molecular structures of dyes make them nondegradable [27]. Dyes, which have high demand for chemical and biological oxygen, high toxicity, and capability to hinder sunlight penetration into water bodies, are harmful pollutants to the aquatic ecosystem [28]. Methylene blue (MB), a cationic dye, is widely used in biology, medical science, chemistry, and dye field. However, long-term exposure to MB can cause certain symptoms and illnesses such as increased heart rate, vomiting, nausea, anemia, cyanosis, and tissue necrosis [29, 30]. Various adsorbents have been used to adsorb MB in aqueous solutions with promising output such as activated carbon [29], natural clay [31], sea grass dead leaves [32], or modified pumice stone [33].
According to our calculation, the price of one tone of YPS at the Tang Loong Industrial Zone is only about 22 USD. This indicates that YPS product is cost-effective and promising for application not only as an absorbent but also as an additive for other fields (composites, paint, coating, etc.). Acids and bases are used for treatment of inorganic waste, for example, fly ash and gypsum, to improve the adsorption ability of these waste products [18, 20, 22, 23]. Besides, EDTA is known as a chemical used for both industrial and medical purposes. In the industry, it is mainly used to sequester metal ions in aqueous solution. Thanks to its high affinity for metal ions, EDTA can enormously enhance the chelation properties of the adsorbent. Therefore, in this work, NaOH, HNO3, and EDTA were chosen for retreatment of YPS particles to evaluate their adsorption ability. We mainly focused on the characterization of YPS products as well as investigation of the factors affecting on the adsorption ability of YPS products for removal of chromium (VI) ions and methylene blue in aqueous solutions.
2. Experiment
2.1. Materials
Yellow phosphorus slag (YPS0) is waste product of Lao Cai Yellow Phosphorus JSC (Tang Loong Industrial Zone, Bao Thang District, Lao Cai Province, Vietnam) with a particle size of 50–100 µm; density of 2.75 g/cm³; hardness of 1–3; compressive strength of 80–100 MPa; water absorption of 1–4%; and porosity of 10–12%. Ethylenediaminetetraacetic acid (EDTA); 1,5-diphenylcarbazide (DCP); potassium chromate; and methylene blue (MB) were purchased from Merck Co. HNO3 and NaOH are the commercial products which are used as received.
2.2. Surface Treatment of Yellow Phosphorus Slag
2.2.1. Treatment of Yellow Phosphorus Slag by Flotation System
Firstly, the washing flotation system was used to remove preliminary soluble impurities and to separate the particles for next stage. In this stage, the large content of FeP, P2O5, fluorine compounds, and some other impurities were removed and the YPS0 was then wet sieved down to prepare a granular material which is smaller than 100 µm in diameter (YPS1) (by sieve analysis). These particles could be applied for cement production or concrete directly. In the next stage, the particles were milled and transferred to a float sorting system to obtain particles in smaller size. The solid part was then rotated in a spinning double-drum composter and dried at 100°C until unchanged weight. The product was designed as YPS2 with the calcium silicate content in particles higher than 90%. The waste water system was treated to recover P2O5, fluorine compounds, and minerals for other applications. The BET surface area/t-plot micropore area, pore diameter, and pore volume of YPS2 product are 1.3145 m²g⁻¹/0.3024 m²g⁻¹, 21.4897 nm, and 0.000134 cm³g⁻¹, respectively (determined by the nitrogen adsorption method on a TriStar 3000 V6.07 A device).
2.2.2. Surface Treatment of Yellow Phosphorus Slag (YPS) Using NaOH and HNO3 Solutions
The YPS particles were retreated by NaOH or HNO3 solution as follows: 200 mL of NaOH 1 M (or HNO3 1 M) solution was added into a flask containing 20 g of YPS particles and stirred at 70°C for 3 hours. Then, the treated YPS particles by NaOH (or HNO3) solution were filtered and washed with distilled water until filtered aqueous solution reached to neutral medium (pH 7). After that, the treated YPS particles were dried in an oven at 100°C for 12 hours. The YPS0 particles and YPS2 particles which were treated with NaOH or HNO3 solution were designed as YPS0-NaOH, YPS2-NaOH, YPS0-HNO3, and YPS2-HNO3.
2.2.3. Surface Treatment of Yellow Phosphorus Slag (YPS) Using EDTA
In this research, YPS was modified by using EDTA as follows: 5 g of YPS was added into 100 mL distilled water in a 250 mL glass beaker containing 0.5 g of EDTA. This solution was then stirred on a magnetic machine at a speed of 500 rpm for 2 hours at 60°C. Next, the solution was filtered to obtain the solid part. Finally, the solid part was dried in an oven at 100°C for 3 hours.
2.3. Characterizations
2.3.1. Infrared Spectroscopy (IR)
IR spectra of YPS samples were recorded using a Nicolet iS10 spectrometer (Thermo Scientific, USA) in the range of wavenumbers from 4000 cm⁻¹ to 400 cm⁻¹, resolution of 8 cm⁻¹, and scan average of 32 times.
2.3.2. Energy-Dispersive X-Ray Spectroscopy (EDX)
EDX spectra of the YPS samples were carried out on a SEM/EDS device (Oxford Instruments, UK).
2.3.3. Inductively Coupled Plasma-Mass-Spectrometry (ICP-MS)
The element content of YPS samples was detected by NexION 2000 ICP-DRC-QMS (Perkin Elmer, USA).
2.3.4. Scanning Electron Microscopy (SEM)
Scanning electron microscopy (SEM) of YPS samples was taken on a SEM-S-4800 device (Hitachi, Japan). The samples were coated a Pt layer on the surface to enhance the resolution of images.
2.3.5. X-Ray Diffraction Analysis (XRD)
XRD patterns of YPS samples were performed on a Siemens D5000 X-ray diffractometer (XRD) with CuKα radiation source (λ = 0.154 nm) at 40 kV generator voltage with 0.03° step and 30 mA current by 0.043°/s scan speed in the range of 2θ from 2° to 70°.
2.3.6. Zeta Potential
Zeta potential of the YPS2 sample was conducted on a Zetasizer, ver. 6.2, Malvern Instruments, with zeta runs of 12, count rate (kcps) of 288.7, and measurement position of 4.5 mm at 25°C. The YPS2 was dispersed in water (pH ≈ 7) with its dispersant RI of 1.330, viscosity of 0.8872 cP, and dispersant dielectric constant of 78.5.
2.3.7. Ultraviolet-Visible (UV-Vis) Absorption Spectrometry
Spectra of samples were determined on a UV spectrophotometer (CINTRA 40, GBC, USA) in the range of wavelength from 200 to 800 nm.
2.4. Determination of Adsorption Ability of Yellow Phosphorus Slag in Aqueous Solution
An exact weight of the YPS samples was added into a 100 mL of Cr (VI) or MB solution. The solution was stirred on a magnetic stirrer at room temperature for 120 minutes. The solution was then filtered, and 25 mL of aliquots was withdrawn. For MB adsorption, the withdrawn solution was monitored by a UV-Vis spectrophotometer (CINTRA 40, GBC, USA) at λmax = 664 nm. For Cr (VI) adsorption, 1 mL of H2SO4 1M and 1 mL of DCP 0.5% solution were introduced into the withdrawn solution and this solution was kept for 10 minutes before taking on a UV-Vis spectrophotometer at λmax = 540 nm. All studies were performed in triplicate to increase accuracy.
2.5. Determination of Cr (VI) Ion and Methylene Blue Adsorption Isotherms and Adsorption Kinetics of Yellow Phosphorus Slag
2.5.1. Adsorption of Cr (VI) Ions and Methylene Blue Using YPS Samples
The amount of adsorbate per amount of adsorbent at equilibrium condition, Q (mg/g), was calculated as follows:where and are the concentration of adsorbate in solution at initial and equilibrium (mg/L), V is the solution volume (L), and W is the mass of YPS samples (g).
The percentage of metal ions removed, H (%), was calculated using the following equation:
2.5.2. Adsorption Isotherms
In this work, we study the adsorption behavior in the solid-liquid system using four adsorption isotherms: Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherms. Langmuir isotherm equation for ion adsorption: where is the maximum monolayer adsorption capacity (mg/g) and kL is the Langmuir isotherm constant representing binding energy of the adsorption system (L/mg). Freundlich isotherm equation: where is the Freundlich isotherm constant (mg/g) indicating adsorption capacity and is adsorption intensity. Temkin isotherm equation: where is the Temkin isotherm equilibrium binding constant (L/g), is the Temkin isotherm constant related to heat sorption (J/mg), T is absolute temperature (K), and R is the gas constant (8.314 J/mol/K). Dubinin–Radushkevich (DR) isotherm equation: where is the theoretical isotherm saturation capacity (mg/g) and is the Dubinin–Radushkevich isotherm constant (mol²/kJ²).
2.5.3. Adsorption Kinetics
Adsorption kinetics were studied using four reaction models: first-order, pseudo-first-order, second-order, and pseudo-second-order reaction models. First-order reaction model: Pseudo-first-order reaction model: Second-order reaction model: Pseudo-second-order reaction model: where is the maximum monolayer coverage capacity (mg/g); and are the amount of adsorbate adsorbed per gram of adsorbent at equilibrium time and testing time t (mg/g); and are the solution concentration at the initial time and the testing time t (mg/l); and are the rate constant (per minute) of the first-order reaction model, pseudo-first-order reaction model, second-order reaction model, and pseudo-second-order reaction model, respectively.
3. Results and Discussion
3.1. Characteristics of Yellow Phosphorus Slag (YPS) Samples
3.1.1. FTIR Spectra of YPS Samples
Figure 1 shows FTIR spectra of the YPS samples. It can be seen that the absorption peaks of YPS samples mostly appeared in the wavenumber range of 1500–500 cm⁻¹. In the low frequency region, the deformation vibration of bridge Si–O–Si and terminal O–Si–O groups and the metal-oxygen polyhedral (CaOn) results in the absorption bands of about 550 cm⁻¹. The adsorption peak at 699 cm⁻¹ assigned to the Al–O and Si–O bonds and showed the presence of pseudowollastonite α–CaSiO3 in the slag. The spectra from 750 cm⁻¹ to 1050 cm⁻¹ with the peak at 872 and 920 cm⁻¹ correspond to the stretching vibration of Si–O groups, indicating the presence of the glass-like earth silicon. Numerous unbridged connections of Si–O emerging are the result of breach of the polymer network Si–O–Si of the frame due to the introduction of Са atoms for replacement of Si atoms in the Si–O–Si network. Furthermore, the peaks at 1414 and 1484 cm⁻¹ represent the vibration of in calcite, one of main compositions of YPS samples. This result is similar to the report of Zinesh et al. [34].
... Phosphate rocks are an alternative source of scandium since they generally contain a non-negligible amount of this metal (22,29). However, phosphate rocks also contain many impurities such as As, Cd, Cu, Cr, Fe, Mg and Ti. ...
... Also monocarboxylic acids and basic amines have been studied for extraction from solutions with low acidity. The extraction efficiency and selectivity may be increased by the use of a mixture of reagents, selection of extraction conditions (pH, temperature, salting-out agents) or carrying out multistage processes (23,29,32,33). Scandium can be stripped from the organic phase by high concentrations of strong mineral acids, basic solutions or fluoride salts by forming ScF 3 precipitation. ...
Scandium and its compounds are used in many modern industrial fields due to its unique chemical and physical properties. It is mainly recovered from residues and wastes in the production of other metals. The exploitation of the ores and wastes could contaminate water and soil creating environmental problems. This paper discusses recent developments and tendencies in scandium separation, purification and preconcentration from different wastes, residues, environmental samples as well as in the production of radiopharmaceuticals for nuclear medicine, both in the laboratory and on the industrial scale. The period reviewed here mainly includes publications that have appeared, since 2010.
... The use of TBP is most suitable for extracting REMs from nitric acid solutions. In the preliminary studies carried out by Karshigina et al. (2015), nitric acid was selected for the primary processing of phosphorous slag (Table 1). Slag decomposition by nitric acid results in prevention of gypsum formation in the solid residue and possibility to obtain easy-processing cake with higher silicon concentration. ...
... Improvement of nitric-acid leaching (decrease in nitric acid consumption, increase of REMs concentration in the solution, and others) requires studies on the influence of different process parameters on dissolution of REMs and the associated components of aluminium, iron, and calcium. In addition, the possibility of obtaining REMs concentrate from solution (after leaching) containing macroimpurities of calcium, Table 1 Leaching phosphorus slag by nitric acid (Karshigina et al., 2015). aluminum and iron is also of considerable interest. ...
The present research is directed to processing of slag originating during the yellow phosphorus production. Slag was investigated using a complex of physical and chemical treatment methods. The presence of the following elements of rare earth group in phosphorus slag was identified as: Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Tm, Yb, Lu. Thermodynamic calculation of reactions probability of phosphorous slag components interaction with nitric acid was made. Nitric-acid leaching of phosphorus production slag for extraction of rare earth metals (REMs) was investigated. Silicon containing cake obtained after leaching was fond to be suitable for precipitated silicon dioxide production. Behaviour during the leaching of associated components such as calcium, aluminum, and iron were studied. The following optimum parameters were selected for leaching studies: nitric acid concentration is 7.5 mol/dm3; solid-to-liquid ratio is 1:2.6-3; temperature is 50-80 ºС; process duration is 1 hour; pulp stirring rate is 500 rpm and the recovery of rare-earth metals, calcium, aluminum and iron into the solution were seen to be 85 %, 98 %, 80.7 %, and 11.8 %, respectively. Cake produced as a result of leaching contained ~80-85 % of amorphous SiO2. A solution after phosphorus slag leaching was processed with the solvent extraction methods to concentrate and separate it from basic macroimpurities. After precipitating of REMs oxalates from strip liquor and calcination of the precipitate a concentrate had been obtained, which contained ~17% of ∑REMs oxides.
... In recent years, considerable attention has been paid to the chemical phosphorus slag processing to produce a number of valuable materials, e.g., precipitated nanosilica and rare-earth metal (REM) concentrate [9][10][11][12][13][14]. ...
The paper provides a flow sheet of the phosphorus slag processing to produce precipitated silica (white soot). The process conditions for opening phosphorus slag at the I stage of leaching have been selected: the nitric acid concentration is 3.5 mol/dm ³ ; the ratio S:L = 1:3.5; the temperature is 60 oС; and the process duration is 1 hour. The parameters of the white soot production II stage have been determined: the HNO 3 concentration is 6.5 mol/dm ³ ; the ratio S:L = 1:3.5; the temperature is 50 oС; and the process duration is 1 hour. The temperature effect on the white soot structure and the specific surface have been established. At optimal process parameters, the white soot batches have been obtained with the main SiO 2 component content of 88.2 and 90.5 %, and a specific surface of 170 and 182 m ² /g, respectively. The through recovery of silicon into a commercial product is 98.0 % of its initial content in slag.
... The extraction of rare-earth metals from phosphorus slag is of great interest along with the obtaining of precipitated silicon dioxide [18,19]. Acidic methods are more universal and common when extracting rare-earth metals from technogenic raw materials. ...
The thermodynamic calculation was performed for the probability of the main slag components leaching reaction ∆G°T with mineral sulfuric (H2SO4), phosphoric (H3PO4), hydrochloric (HCl) and nitric (HNO3) acids, taking into account a phase and chemical compositions of the initial product. Gibbs energies were calculated for the reactions in the temperature range from 20 to 100 °C. It was found that the reactions were thermodynamically favorable and were almost not-reversible. The interaction of Fe2O3 with hydrochloric acid was an exception. With the temperature increase from 60 to 100 °C, hydrolysis went due to the increase in the dissociation degree of water molecules affecting the results of hydrochloric acid treatment. Experiments on the phosphorus slag dissolution were performed with H3PO4, HCl and HNO3 solutions in the concentration of 2 mol/dm 3. The distribution of calcium, aluminum, and iron were analyzed over the slag leaching products. The choice of nitric acid as a leaching reagent was justified. A thermodynamic analysis of the reactions of the interaction of the slag rare-earth metals components with nitric acid was performed. The use of nitric acid in the analyzed temperature range from 50 to 100 °C was acceptable for all rare-earth components. For thermodynamic purposes reactions of rare-earth metals and their ions interaction with nitric acid were the most favorable for lanthanum sulfide, yttrium phosphate, lanthanum and neodymium phosphate, as well as for rare-earth metals carbonate ions. The Gibbs energy for these compounds was within from-424.93 to-36.16 kJ/mol. Rare-earth metals (REMs) remained in the cake by 85% when phosphoric slag was leached with a HNO3 solution in the concentration of 2 mol/dm 3. It was found that the use of nitric acid as an opening reagent was favorable for the decomposition of the main components of phosphorus slag.
... The energy-intensive process of yellow phosphorus production is highly challenging due to the consumption of 13,000-15,000 kWh electric energy per ton of yellow phosphorus [14,15]. A lower phosphorus yield is one reason why higher-power electricity consumption occurs in industrial phosphorus furnaces. ...
The phosphorus production industry is energy-intensive, which is one of the major reasons phosphorus has lower yields through furnace production. In this study, phosphorus conversion rate from phosphorus ore was investigated using four different fluxing agents: silica, potassium shale, potassium feldspar, and nepheline. Different holding times (10, 20, 30, and 40 min), acidity values (0.68, 0.88, 1.02, 1.42, and 2.02), coal surplus coefficients (1.05, 1.25, 1.5, 2, and 2.5), and calcination temperatures (1250 °C, 1300 °C, 1350 °C, 1400 °C, and 1450 °C) were studied. The results demonstrated that potassium shale, potassium feldspar, and nepheline as new fluxing agents improved phosphorus conversion rate under the same experimental conditions. To further ensure the significance of the experiment, the conversion rate of phosphorus from phosphorus ore was also investigated without an additive and with the addition of Na2CO3 and K2CO3. The slag viscosity of different fluxing agents and different additives at high temperatures was analyzed via the spread area method. To investigate the mechanism of phosphorus conversion, silica and nepheline as fluxing slag at different calcination temperatures were analyzed using X-ray diffraction.
... Finally, the specimens were quenched in water to preserve the equilibrium state. The equilibration time was determined by comparing the amount of Sc 2 O 3 dissolved in the glass phase after different equilibration times (12,18,24,36, and 48 hours). The solubility of Sc 2 O 3 in the glass phase was changed (14,18, and 24 hours) and the solubility of Sc 2 O 3 in the glass phase was consistent (24, 36, and 48 hours). ...
... PS comprised mostly of calcium and silicon oxides (Cao and Wang 2013;Karshigina et al. 2015) is less reactive than blast-furnace slag is (Chen et al. 2009;Li et al. 2000). Residual Р 2 О 5 has a strong decelerating effect on the hardening time of cement, while insufficient concentration of Al 2 O 3 affects the cement strength (Li et al. 2000). ...
We have investigated the effects of secondary raw materials content on the hydration of slag-cement mixtures. We focus on the important issue of studying cost-effective alkaline additives in binder mixtures based on phosphorus slag. We have analyzed the main phases in slag and ash and found that the most common phase was slag glass. This phase has considerable hydraulic properties due to high latent energy if we compare them to compare to those of the holocrystalline phase of the same compound. The process of adding small amounts of alkali and sulfates to vitreous slag activates its latent hydraulic properties. The effect of alkaline activators creates an alkaline environment required for the reactions between slag glass components. This article provides a way of determining the composition of raw mixtures and ensuring the possibility of correcting it, as well as a method for determining the proper (in terms of quality of concrete) pH value.
... And the results showed that it is a very useful tool to support the proper design of industrial yellow phosphorous tail gas purification unit. Zaure et al. [23] studied the recovery efficiencies of precipitated silicon dioxide and various elements from phosphorus slag via hydrometallurgical methods using alkaline agents and nitric acid. These authors' results showed that the recovery efficiencies of silicon could reach 1.1% and 16.6% using sodium hydroxide and sodium carbonate, and rare earth metals content was 98.3-98.6%; ...
Reducing energy and sustainable using of natural mineral resources offer challenges in energy production and environment. In this study, an efficient methodology is proposed for using K-feldspar as fluxing agent instead of silica in phosphorus furnace. Thermodynamic analysis of the process indicated the decomposition temperature of phosphate could be reduced by as much as 103 ∘C using K-feldspar. A series of experiments were conducted at the same acidity of 0.8. At the same potassium gasification rate of 96%, the high temperature melting results showed operating temperature of the silica system was 1300 ∘C while K-feldspar system operated at 1200 ∘C When phosphorus conversion rate was close, the residual flow temperature of the K-feldspar system was 180 ∘C lower than the silica. This was due to the residual quantity and different fluxing agents. The viscosity results indicated the spread out areas were similar at 1253 ∘C for K-feldspar while at 1432 ∘C for silica. This illustrated operating temperature was reduced about 180 ∘C and potash fertilizer was produced using K-feldspar in phosphorus furnace. The significance of this result will mean improved energy and cost savings for this process.
... In conventional carbothermic phosphorus production (as presented in Fig. 1), SiO 2 is used as a flux in order to achieve operating temperatures of the order of 1500°C, and it produces a low-phosphorus slag (\ 1 wt% P) [4], which should result in a similar outcome to the silicothermic extraction experiments presented in Part I of the present article, i.e., a low final concentration of REEs. Recently published work by Karshigina et al. [17] has disclosed a method using extremely concentrated nitric acid (due to the stability of the silicates) to recover REEs from high-silica discard slag produced as a by-product of the conventional carbothermic phosphorus process. The high-acid leach would seem to indicate difficulties in treating such slag, and the economics of such a process could be questioned particularly with the current low prices for REEs, as previously indicated in Fig. 1 of Part I of the article [13]. ...
Apatite, Ca5(PO4)3F, is a useful raw material for the production of both elemental phosphorus and phosphoric acid, and the mine tailings present at Luossavaara-Kiirunavaara AB (LKAB) in Kiruna, Sweden, represent a significant potential European source of apatite if upgraded to a concentrate. In the present study, pilot apatite concentrate made from the LKAB tailings has been pyrometallurgically treated using carbon to extract phosphorus without fluxing at temperatures exceeding 1800 °C, with the ultimate objective of recovery of rare earth elements (REEs) from the resulting slag/residue phases. Experimental behavior has been modeled using equilibrium thermodynamic predictions performed using HSC®. A process is proposed, and mass–energy balance presented, for the simultaneous production of P4 and CaC2 (ultimately for acetylene, C2H2, and PVC production) from apatite, producing a lime residue significantly enriched in REEs. Possible implications to kiln-based processing of apatite are also discussed.
... Phosphorus slag with the content of SiO 2 35-42 % can serve as a source for production of precipitated silica [2,3]. Developments for obtaining mineral fillers from wastes of the phosphoric industry were carried out at JSC "Institute of Metallurgy and Beneficiation" in collaboration with specialists from phosphorus plants [4]. ...
p class="TTPSectionHeading">The report presents a technological scheme of complex processing of man-made waste of phosphorus production - slag to produce highly dispersed silicon dioxide and a rare-earth metal concentrate. The technological parameters of each operation of the technology are chosen. Recovery of rare-earth metals from phosphorus slags during various operations was, %: leaching – 95.0; extraction - 90.2; stripping on the average ~ 93.2; the production of ∑ REM oxide concentrate is 93.9. The composition of some batches of "white soot" obtained during processing of the technological scheme is shown.</p
... Selection of a reagent for phosphorus slag decomposition considered a potential for extraction of both rare-earth metals and precipitated silicon dioxide. Considering the task statement, a decision was made to use nitric acid as a reagent for leaching phosphorus slag [12]. Moreover, along with recovery of rare-earth metals into the solution, cake with high concentration of silicon was produced which may be suitable for production of precipitated silicon dioxide. ...
The present research is devoted to the processing of slag generating during the yellow phosphorus production. In this paper are presented studies on leaching of phosphorus production slag by nitric acid with recovery of rare earth metals (REMs) into solution. REMs recovery into the solution achieved 98 % during the leaching process with using 7.5 mol/L of HNO3, liquid-to-solid ratio is 2.6:1, temperature is 60°C, process duration is 1 hour and stirrer speed is 500 rpm. Behaviour during the leaching of associated components such as calcium, aluminium, and iron was studied. After the leaching cake contains ~⃒75-85 % of SiO2 and it might be useful for obtaining of precipitated silicon dioxide. With the purpose of separation from the impurities, recovery and concentrating of REMs, the obtained solution after leaching was subjected to extraction processing methods. The influence of ratio of organic and aqueous phases (O: A) on the extraction of rare earth metals by tributyl phosphate (TBP) with concentrations from 20 up to 100 % was studied. The REMs extraction with increasing TBP concentration under changes O:A ratio from 1:20 down to 1:1 into the organic phase from the solutions after nitric acid leaching increased from 22.2 up to 99.3%. The duration effect of REMs extraction process was studied by tributyl phosphate. It is revealed that with increasing of duration of the extraction process from 10 to 30 minutes REMs recovery into the organic phase almost did not changed. The behaviour of iron in the extraction process by TBP was studied. It was found that such accompanying components as calcium and aluminium by tributyl phosphate didn't extracted. To construct isotherm of REMs extraction of by tributyl phosphate was used variable volume method. It was calculated three-step extraction is needed for REMs recovery from the solutions after nitric acid leaching of phosphorus production slag. The process of the three-steps counter current extraction of rare earth metals was modelled from the solutions after slag leaching with using 50 % of TBP in kerosene at the ratios O:A = 1:6 and 1:20. So, REMs recovery into the extract achieved 97.0 and 76.5 %, respectively. It was offered flowsheet of processing of phosphorus slag production with extraction of rare earth metals and obtaining silicon containing cake.
... Recent developments in REE mineral characterization and flotation reagents can be found in the works of Pradip and Fuerstenau (2013) and Lin, Hsieh and Miller (2013). Regarding secondary sources, extraction from phosphogypsum is explored in Al-Thyabat and , extraction from phosphorus slag in Karshigina et al. (2015) and extraction from red mud, or bauxite residue, in Borra et al. (2015). ...
Phosphate rock contains traces of rare earth elements (REEs) and can be a secondary source of these critical materials as large tonnages of phosphate rock are mined annually. Attention has mostly focused on the extraction of REEs from phosphogypsum, which contains more than 70 percent of the REEs reporting to phosphate concentrate, with only limited work conducted on REE extraction from sand tailings and slime even though they account for 16 percent and 15 percent, respectively, of REEs mined with phosphate matrix. In this work, phosphate flotation tailings were upgraded by gravity separation and froth flotation. Gravity separation was conducted using a laboratory shaking table, while flotation was conducted in a Denver D-12 flotation cell. The concentrated tailings were then leached by nitric acid followed by REE extraction with solvent and ion-exchange resin. The sand tailings were assayed as having 2.6 percent phosphate (P2O5) and 198.1 mu g/g REEs. It was found that the shaking table could produce tailing concentrate assayed as having 8.6 percent P2O5 and 616 mu g/g REEs but with only 20 percent REE recovery, while the froth flotation produced froth concentrate assayed as having 8.1 percent P2O5 and 368.2 mu g/g REEs with 63.5 percent REE recovery. Leaching the flotation concentrate with 5.2 M (25 percent) nitric acid followed by extraction with solvent and ion-exchange resin yielded precipitates with REE contents of 0.926 and 0.314 percent, respectively, compared with 0.716 and 0.213 percent when table concentrate was used.
Phosphorus slag is the most heavy-tonnage waste of yellow phosphorus production, which is stored in the dump fields for many years causing ecological problems in the regions. One of the relevant and priority directions is rare-earth metals (REMs) production, presence of which in the phosphorus slags allows considering the latter as an acceptable raw material source. Phosphorus slags contain about 30–40 wt % of silicon dioxide, therefore they can serve as a source of production of precipitated silicon dioxide highly required in different industries. The purpose of this work is studying the conditions for REMs recovery from phosphorus slag and further processing of silicon-containing cake to improve a quality of the obtained products. The work shows results of researches on the phosphorus slags’ chemical and phase compositions identification, processes of leaching of phosphorus slag and the obtained silicon-containing cake by nitric acid. Instrumental and chemical methods of phosphorus slag content analysis dive following data. It consists of 90–92 % of pseudowollastonite α-CaSiO3, and also there is gyrolite Ca4(H2O)4[Si6O15](OH)2, small amounts of serpentine Mg6[Si4O10](OH)8, hydrated calcium aluminosilicate impurities CaO∙2Al2O3∙2SiO2∙H2O, quartz α-SiO2, calcite CaCO3, hematite Fe2O3, iron phosphate FePO4 and metallic iron with manganese impurity. As a result of kinetic studies of leaching process of phosphorus slag, the apparent activation energy for ΣREMs, calcium, aluminum and iron was determined which amounted to 4.31, 8.53, 7.43 and 12.31 kJ/mol, respectively. This, in combination with value of the Pilling-Bedward Criterion CP-B = 1.1 for orthosilicate acid H4SiO4, indicates that the process is characterized by an intradiffusion region. With a decrease in temperature of nitric acid treatment from 90 to 70 °C, purification degree of precipitated silicon dioxide from iron and aluminium impurities increases. Results of the experimental data will serve as a basis for development of the technology of complex processing of production waste of phosphorus industry and for improving quality of obtained products as REMs concentrate and precipitated silicon dioxide.
The rare earth elements (REE) are vital to modern technologies and society and are amongst the most critical of the critical elements. Despite these facts, typically only around 1% of the REE are recycled from end-products, with the rest deporting to waste and being removed from the materials cycle. This paper provides an overview of the current and future potential of the recycling of the REE, including outlining the significant but currently unrealised potential for increased amounts of REE recycling from end-uses such as permanent magnets, fluorescent lamps, batteries, and catalysts. This future potential will require a significant amount of research but increasing the amount of REE recycling will contribute to the overcoming some of the criticality issues with these elements. These include increased demand, issues over security of supply, and overcoming the balance problem where primary mine-derived sources overproduces lower demand REE without necessarily meeting demands for the higher demand REE.
Systematic scientific studies for dephosphorization and acid leaching of Korean monazite are reported here. 50% NaOH (w/v) solubilizes 99.99% phosphate, at 170 degrees C, 100 g/L pulp density in 4 h. Kinetics of phosphate leaching fitted well with model "chemical reaction control," i.e. 1 - (1 - X)(1/2) = k(c)t, E-a = 58.04 kJ/mot. Further, rare earth hydroxides (REHs) was leached using 6 N HCl at 90 degrees C, 60 g/L pulp density for 2 h to recover similar to 95% REMs. Leach liquor generated can be further processed using solvent extraction/ion exchange techniques. From the pure solutions, metal/salts could be obtained using evaporation, precipitation, etc.
The article presents the results of studying the determination of the influence of the nature of a number of mineral reagents (solutions of hydrochloric, nitric, sulfur and phosphoric acids, as well as sodium hydroxide and carbonate) on silicon extraction in solution upon he leaching of phosphorus production slags. The results of studying the process of the breakdown of phosphorus production slag with sodium carbonate solutions depending on various physicochemical parameters are provided. The optimum conditions of main technological operations were found and the main parameters that influence the morphological structure and size of precipitated silica particles were established. The influence of the conditions of washing of carbonate-silicate cake on its chemical, phase, and granulometric composition has been studied. Scaled-up laboratory tests have been carried out and a technology for processing phosphorus production slags to produce mineral fillers was developed on their basis. Conclusions on the applicability of pilot batches of white soot in tire and paint industries and carbonate-silicate fillers in construction industry and agriculture were obtained.
The recycling of rare earth metals from phosphor powders in waste fluorescent lamps by solvent extraction using ionic liquids was studied. Acid leaching of rare earth metals from the waste phosphor powder was examined first. Yttrium (Y) and europium (Eu) dissolved readily in the acid solution; however, the leaching of other rare earth metals required substantial energy input. Ionization of target rare earth metals from the waste phosphor powders into the leach solution was critical for their successful recovery. As a high temperature was required for the complete leaching of all rare earth metals, ionic liquids, for which vapor pressure is negligible, were used as an alternative extracting phase to the conventional organic diluent. An extractant, N, N-dioctyldiglycol amic acid (DODGAA), which was recently developed, showed a high affinity for rare earth metal ions in liquid-liquid extraction although a conventional commercial phosphonic extractant did not. An effective recovery of the rare earth metals, Y, Eu, La and Ce, from the metal impurities, Fe, Al and Zn, was achieved from the acidic leach solution of phosphor powders using an ionic liquid containing DODGAA as novel extractant system.
The Hybin apatite concentrate is the most promising raw material for rare earth metal (REMs) producing a technology for extraction of REMs and yttrium from phosphogypsum, prepared during processing the Hybin apatite concentrate is elaborated. The REMs extracted are free from radioactive impurities. The sulfuric acid leaching technology shows reasonably high extraction of REMs from phosphogypsum at ratio of solution volume to solid mass equal to (5-10):1. The results of research of the physicochemical factors, causing transfer of REMs into solution in sulfuric acid leaching, are presented.
The present study uses a commercial heat cured silicone rubber formula (including a process aid) and mixing techniques to investigate the effect of varying fumed silica properties - including load, surface area, silica structure level, and surface pretreatment levels - on the rubber processing, curing, and cured physical properties. Based on the results, a simple silica network reinforcement model was developed to explain the changes in processing, curing, and vulcanizate properties of the silicone elastomers. The network is held together by silica-silica interactions and silica-polymer-silica bridge bonds between the silica aggregates. Increasing the silica loading, surface area, and structure level increases the number of interactions and hence the network strength. The pretreatment of the silica surface with organosilane molecules reduces the strength of silica-silica and silica-polymer interactions, therefore, weakening the silica network. Furthermore, the good interrelations between the initial plasticity, crepe hardening, curing modulus yield, and durometer values strongly supports the concept of the presence of a silica network within the compounds under the low strain conditions of the tests.
This paper describes the technology of producing precipitated silica, in which yellow phosphorus slag is leached by phosphoric acid and calcium is separated in form of calcium phosphate monobasic. The experimental results show that optimal technical conditions are: phosphoric acid concentration
31%, reaction time 0.5 hour, stirring speed 400rpm, liquid-solid ratio 5:1 and natural temperature.
The feasibility of manufacturing non-autoclaved aerated concrete using alkali activated phosphorus slag as a cementitious material was investigated in this paper. Liquid sodium silicate with various modules (the molar ratio between SiO2 and Na2O) was used as alkali activator and a part of phosphorus slag was replaced with fly ash which was used to control the setting time of aerated concrete. The influences of the fly ash, curing procedure, modulus of sodium silicate solution and concentration of alkalis on the compressive strength and bulk density of non-autoclaved aerated concrete have been studied. Moreover, the types of the hydration products were investigated using XRD and SEM. The results indicate that: the compressive strength of aerated concrete was influenced by concentration of alkalis obviously. The compressive strength of 11.9MPa and the bulk density of 806kg/m3 were obtained with an activator of 1.2 modulus of sodium silicate and 6% concentration of alkalis under the circumstance of 60°C curing for 28 days.
When precipitated silica was prepared from yellow phosphorus slag by the phosphoric acid leaching, the Fe content can not meet the quality requirements of the product. This article indicates the method of purifying precipitated silica with nitric acid solution, which may decrease the Fe content to about 0.02%. The purification optimum technical conditions are: the nitric acid concentration 8%, reaction time 2.0 hours, reaction temperature 343.15K, fluid solid ratio 4:1, stirring speed 300 rpm.
With an increase in number of waste nickel-metal hydride batteries, and because of the importance of rare earth elements, the recycling of rare earth elements is becoming increasingly important. In this paper, we investigate the effects of temperature, hydrochloric acid concentration, and leaching time to optimize leaching conditions and determine leach kinetics. The results indicate that an increase in temperature, hydrochloric acid concentration, and leaching time enhance the leaching rate of rare earth elements. A maximum rare earth elements recovery of 95.16% was achieved at optimal leaching conditions of 70 °C, solid/liquid ratio of 1:10, 20% hydrochloric acid concentration, −74 μm particle size, and 100 min leaching time. The experimental data were best fitted by a chemical reaction-controlled model. The activation energy was 43.98 kJ/mol and the reaction order for hydrochloric acid concentration was 0.64. The kinetic equation for the leaching process was found to be: 1−(1−x)1/3=A/ρr0[HCl]0.64exp−439,8008.314Tt. After leaching and filtration, by adding saturated oxalic solution to the filtrate, rare earth element oxalates were obtained. After removing impurities by adding ammonia, filtering, washing with dilute hydrochloric acid, and calcining at 810 °C, a final product of 99% pure rare earth oxides was obtained.
Current resource issues and the growing demand for metals used in advanced technologies have focused attention towards more efficient processing of end-of-life products and waste streams. Fluorescent lamp waste is a viable target for the recovery of rare earth metals (REMs); specifically cerium, europium, gadolinium, lanthanum, terbium, and yttrium. Waste originating from a discarded lamp processing facility was investigated using Scanning Electron Microscopy/Energy Dispersive Spectroscopy and X-ray Diffraction. Total dissolution experiments were carried out with aqua regia at elevated temperatures in order to estimate an average metal content and assess the recycling potential of the material.
The leaching of rare-earth elements, phosphorus, and alkali metals from phosphodihydrate, obtained in processing of the Khibiny
apatite concentrate into mineral fertilizers, with sulfate solutions with a sulfuric acid concentration c(H2SO4) = 0.5−4 wt % was studied.
A mixture of rare earth double sulfates was produced from a Turkish bastnasite-containing pre-concentrate (low grade concentrate) by sulfuric acid baking, subsequent water leaching and precipitation with sodium sulfate. The results of acid baking and leaching indicated that recoveries of rare earth elements up to 90% were readily obtained and the recovery of hydrofluoric acid as a by-product was also possible. Reasonable decontamination of the rare earth double sulfate salt from impurities such as Th, Fe, Al and Mg was possible by rapid precipitation at 50 °C using 1.25 times the stoichiometric amount of Na2SO4. The total rare earth double sulfate content (TREDS) was > 90% and analysed 17.3% La, 15.6% Ce, 3.2% Nd, 1.1% Pr, 0.3% Sm, 0.03% Eu, 0.01% Yb and 0.02% Y together with about 0.7% Ca, Fe, Al and other impurities.
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