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Experimental Study on Chromium Containment by Admixed Soil Liner
Abstract
Chrome tanneries generate large quantities of chromium-laden sludge that require proper disposal in engineered landfills to prevent contamination of subsurface soils and groundwater and reduce the risk to public health and the environment. This study investigates the feasibility of using a fine-grained soil as a suitable landfill liner material for the effective containment of chromium in the sludge leachate. Several series of laboratory permeability, adsorption, and column tests were conducted using soil without and with selected additives (rice husk, bentonite, and fly ash) to determine permeability and adsorption and transport of chromium in the soil. Permeability tests showed that the field soil amended with 17% rice husk and 2% bentonite provides the desired hydraulic conductivity of 10-7 cm/s (or less) to minimize the leachate migration into the surrounding subsurface environment. The rice husk and bentonite admixtures significantly reduced the hydraulic conductivity of the soil from 3×10-7 to 2.8×10-9 cm/s, and this admixture was further tested for its effect on the adsorption and transport of chromium in the soil. The batch kinetics and column tests results showed that the soil possesses relatively high chromium adsorption capacity under natural or slightly alkaline condition. The batch tests showed that the amendment marginally improved the chromium adsorptive capacity of the soil. The column tests showed a slight increase in breakthrough time due to the presence of the amendment. The inclined base column tests showed that a mildly inclined liner configuration has a marginal effect on the chromium attenuation in the soil. Overall, this study showed that soil amended with 17% rice husk and 2% bentonite significantly decreased the hydraulic conductivity of the soil and slightly increased the adsorption of chromium, and therefore, has the potential for usage as a landfill liner in a landfill system to contain chromium contamination.
... He et al. (2004) monitored metal (i.e., Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn, Mn, and Mo) concentrations in surface runoff at 11 sites in Florida and documented a positive correlation between concentrations of the analysed metals in runoff and soil. Ghosh et al. (2012) found that Cr(VI) could be successfully adsorbed onto the fine-grained soil used as a liner material in a landfill. Núñez-Delgado et al. (2015) found that both pine sawdust and oak wood ash could be used (as biosorbents) to reduce the concentration of Cr(VI) released from soil to water. ...
... Advection is controlled by the mean flow rate of water, and dispersion is characterized by molecular diffusion and mechanical dispersion. Langmuir (1918), Freundlich (1906), and linear isotherm models are often used to simulate Cr(VI) adsorption experimental results under equilibrium assumption (e.g., Fifi, Winiarski, & Emmanuel, 2013;Ghosh et al., 2012;Li, Liang, & Du, 2014;Mendonca, Melo, & Alleoni, 2013;Núñez-Delgado et al., 2015;Sangiumsak & Punrattanasin, 2014). Gupta and Bahu (2009) successfully simulated breakthrough curves of Cr(VI) by combining the Langmuir model with a mathematical transport model. ...
We investigate our ability to assess transfer of hexavalent chromium, Cr(VI), from the soil to surface runoff by considering the effect of coupling diverse adsorption models with a two‐layer solute transfer model. Our analyses are grounded on a set of two experiments associated with soils characterized by diverse particle size distributions. Our study is motivated by the observation that Cr(VI) is receiving much attention for the assessment of environmental risks due to its high solubility, mobility, and toxicological significance. Adsorption of Cr(VI) is considered to be at equilibrium in the mixing layer under our experimental conditions. Four adsorption models, i.e., the Langmuir, Freundlich, Temkin, and the linear model, constitute our set of alternative (competing) mathematical formulations. Experimental results reveal that the soil samples characterized by the finest grain sizes is associated with the highest release of Cr(VI) to runoff. We compare the relative abilities of the four models to interpret experimental results through Maximum Likelihood model calibration and four model identification criteria (i.e., the information criteria AIC and AICC, and the Bayesian criteria BIC and KIC). Our study results enable us to rank the tested models on the basis of a set of posterior weights assigned to each of them. A classical variance‐based global sensitivity analysis is then performed to assess the relative importance of the uncertain parameters associated with each of the models considered, within sub‐regions of the parameter space. In this context, the modeling strategy resulting from coupling the Langmuir isotherm with a two‐layer solute transfer model is then evaluated as the most skillful for the overall interpretation of both sets of experiments. Our results document that (a) the depth of the mixing layer is the most influential factor for all models tested, with the exception of the Freundlich isotherm, and (b) that the total sensitivity of the adsorption parameters varies in time, with a trend to increase as time progresses for all of the models. These results suggest that adsorption has a significant effect on the uncertainty associated with the release of Cr(VI) from the soil to the surface runoff component.
... It could be seen from Table 1 that the Freundlich adsorption capacity in milligrams per gram gives consistently low values, even though the regression values were close to one. This shows that Freundlich isotherm is not suitable for these sorbents (Damikouka and katsiri 2009;Nemr 2009;Ghosh et al. 2012;Moghal et al. 2014b). ...
... The leaching results show that CuAl 2 O 4 is superior to CuO for the purpose of copper immobilization over longer leaching periods. However, the working temperature range in this study was too low to observe such a phenomenon (Ghosh et al. 2012;Massacci et al. 2000;Moghal et al. 2015b;Ozverdi and Erdem 2010). ...
The presence of xenobiotic (human induced) chemicals from mining, refining and electroplating industries causes significant damage to the natural soil system, altering its physico-chemical geochemistry. Most of these chemicals contain metal pollutants that are non-biodegradable and the only way to contain or limit their movement is through sorption. In this study, the sorptive response of two most commonly found metal contaminants, hexavalent chromium (Cr+6) and mercury (Hg+2), are studied using two semi-arid soils from Saudi Arabia. To enhance their retention capacity, these soils are amended with lime. The response to sorption at varying initial contaminant concentrations, pH conditions, temperature levels, and dilution ratios is investigated. Relying on empirical models (Langmuir and Freundlich), the nature of sorption (monolayer or heterogeneous) is ascertained. Further, kinetic models are employed to validate the type and nature of sorption occurring (whether pseudo first-order or second-order). It is found that the experimental results correlate well with the selected empirical models for both the Al-Ghat and Al-Qatif soils when amended with lime and attenuate Cr and Hg to satisfactory levels. The R2 values are close to 1 for all the tested models. The order of sorption was Cr>Hg for heavy metals considered, and also for soils and soil mixtures considered Al-Qatif soil amended with 6% lime >Al-Ghat soil with 6% lime >Al-Qatif >Al-Ghat. Lime treated soils sorbed 69% and 63% more than the untreated soils for Cr and Hg, respectively.
... Studies have shown that various stabilization processes have considerable influence on the plasticity, density-moisture relation, swell and shrinkage, strength and stability, as well as on the durability and weathering characteristics of the laterite soils used for landfills (e.g. [14,19,23,30]) ...
The environment is seriously being affected by the leachate release at the unconstructed
and badly constructed waste containment or landfill facilities around the globe. The worst
hit is the developing world where there is little or totally no waste management system
and facilities to receive waste released into the atmosphere. This research work is focused
on the leachate drain into the soil and the underground water from landfills, which
toxicifies both the soil and the water. Also, the construction of the liner or barrier with
cement poses serious threat to the environment due to oxides of carbon release and this
research also took this into account by replacing the utilization of cement with rice husk
ash (RHA), which has proven to have the potentials of replacing cement as a
supplementary binder. Laboratory tests were conducted to determine the hydraulic
conductivity (K) of lateritic soil ameliorated with different dosages of RHA. Other
hydromechanical properties of the treated blend were studied and multiple data was
generated for the artificial neural network (ANN) back-propagation (-BP), genetic
algorithm (-GA), & gradual reducing gradient (-GRG), genetic prohgramming (GP) &
evolutionary polynomial regression (EPR) prediction exercises. Results show that the
lateritic soil (LS) was a poorly graded A-2 sandy silt soil, which was subjected to three
different compaction energies with the minimum of the British standard light (BSL) and
derived k of 6.95E-10, 50.75E-10 and 32.33E-10 for BSL, west African standard (WAS)
and British standard heavy (BSH) respectively. The RHA addition improved the studied
properties of the ameliorated LS. Out of the five models, the ANN-GRG outclassed
others with a performance of 99% with minimal error compared to the rest. Potentially,
this research has shown that RHA with a PCM of 81.47% can replace cement in the
construction of ecofriendly and more efficient landfills and waste containemnt barriers to
save the soil and the underground water as well as the environment from leachate
contamination and carbon emissions.
... In recent studies, the geotechnicians and environmentalists have shown increasing interest and revealed satisfactory results in utilizing industrial by-products such as fly ash, red mud, waste wood ash, construction and demolition wastes and cement kiln dust as a landfill liner material (Daud et al., 2017;Ghosh et al., 2012;Kumar and Stewart, 2007;Moses et al., 2013;Mukherjee and Mishra, 2017;Narani et al., 2020;Pal and Ghosh, 2013;Rubinos and Spagnoli, 2019). From the works of literature, it was evident that usage of industrial by-products such as fly ash (FA) blended with expansive clays, bentonite-sand mixtures, and laterite soils etc. improved their engineering properties of soil and bulk utilization of these industrial byproducts found satisfactory results as a liner material. ...
This paper showcases the geotechnical and environmental engineering properties of ground granulated blast furnace slag (GGBS, a byproduct of iron-ore) admixed with local laterite soil (LS), bentonite (BT) and cement (CT) mixtures as landfill liner. The main aim of this study is to determine the effect of GGBS on LS (i.e. effect of binder material with filler material) and to study the effect of GGBS-LS blended with varied BT and CT mixtures (i.e. binder-filler material in partial replacements), to perpetrate as a landfill liner material. Overall, a wide range of fifteen unique mix proportions was chosen in this study and are categorized into five series. Laboratory tests such as consistency limits, free swell index (FSI), Proctor compaction, hydraulic conductivity (HC), leachate characteristics (LC) and unconfined compressive strength (UCS) with post-testing analysis were conducted to evaluate the optimum mix. From the test results, the consistency limits and FSI decreased with an increase in GGBS content for all the mixes. In compaction tests, the addition of GGBS increases the dry unit weights and reduces the water contents. The HC decreased with the addition of GGBS quantities when permeated with deionized water and diesel oil as permeant fluids. In the LC, the concentrations of heavy metals (i.e. Cr, Co, Cd, Fe and Pb) in diesel oil decreased and removal efficiencies increased for lower HC values than higher HC values. The UCS values increased with an increase in GGBS quantities and curing intervals for all the mixes. The microstructure and mineralogical analysis revealed the identification and confirmation of new cementitious products which ameliorated the UCS values. Hence, from this study, when GGBS admixed with filler and other binder material established to be an efficacious and eco-friendly solution which not only reduces the disposal problem but improves the engineering properties and prerequisite as landfill liner.
... There is a need for engineers to perform the geoenvironmental investigation as appropriate to their studies on the stabilizer used for the assessment to be sustainable. Reference [94] utilized 17% rice husk ash (RHA) and 2% bentonite mixed with clay as a liner landfill to diminish chromium leachate. Reference [95] used the sawdust-stabilized clay as a landfill liner to contain lead and cadmium leachate. ...
The presence of expansive soils on construction sites is problematic in geotechnical engineering. The swell-shrink behaviour makes these soils not suitable to be used in their natural state. The expansive soil damages cause financial loss yearly more than floods, hurricanes, tornadoes, and earthquakes combined. Moreover, the cost of cut to spoil of expansive soils during construction projects has continued to rise because of the high cost of earthworks, haulage, and the increasing scarcity of spoil areas because of the built environment. Nonetheless, a proper stabilization technique can significantly enhance the expansive soil's properties. The research project attempts to review, report the limits and merits of mechanical and chemical methods utilized to stabilize expansive soils in line with their efficiency, environmental concerns, and cost-effectiveness. A review of mechanical and chemical treatment techniques is conducted in this regard. Ultimately, each stabilization method exhibits its merits and limitations. The lack of standards for the treatment of swelling soils is a significant problem in engineering practice. Specialists in the domain of soil treatment must work together to obtain an optimized stabilization approach and protocol. Moreover, engineers should perform a geoenvironmental assessment appropriate for chemical stabilization methods and additives utilized. This research work contributes as a guideline in the selection and application of chemical and mechanical stabilization methods.
... The results of the soil classification tests, from which the soil samples were classified as clay of high plasticity (CH), indicate that the soil samples have the potential of being used as hydraulic barriers for waste containment [12]. ...
... These liners act as barriers to sorb heavy metals and thus prevent them from contaminating the groundwater. Ghosh et al. (2012) used 2% bentonite and 17% rice husk ash (RHA) mixed with clay as a landfill liner to curtail chromium leachate. Similarly, Akinwumi et al. (2016) used sawdust-stabilised clay soil as a landfill liner to contain lead and cadmium leachate. ...
Expansive soils are problematic due to the performances of their clay mineral constituent, which makes them exhibit the shrink-swell characteristics. The shrink-swell behaviours make expansive soils inappropriate for direct engineering application in their natural form. In an attempt to make them more feasible for construction purposes, numerous materials and techniques have been used to stabilise the soil. In this study, the additives and techniques applied for stabilising expansive soils will be focused on, with respect to their efficiency in improving the engineering properties of the soils. Then we discussed the microstructural interaction, chemical process, economic implication, nanotechnology application, as well as waste reuse and sustainability. Some issues regarding the effective application of the emerging trends in expansive soil stabilisation were presented with three categories, namely geoenvironmental, standardisation and optimisation issues. Techniques like predictive modelling and exploring methods such as reliability-based design optimisation, response surface methodology, dimensional analysis, and artificial intelligence technology were also proposed in order to ensure that expansive soil stabilisation is efficient. © 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences
... The results of the soil classification tests, from which the soil samples were classified as clay of high plasticity (CH), indicate that the soil samples have the potential of being used as hydraulic barriers for waste containment [12]. ...
The suitability of using lateritic clays from Aviele and Igarra has been investigated both in the Northern part of Edo state, Nigeria as liners of an engineered landfill and to adsorb metals in leachates. Geotechnical characteristics, pH, and elemental composition for the lateritic clay samples were determined. The chemical composition, pH, total dissolved solids and electrical conductivity were determined for leachates collected from two dumpsites. The capacities of the lateritic clay soils to adsorb heavy metals in the leachates were determined using the batch equilibrium adsorption technique. The unconfined compressive strength (UCS) of soils were found to be sufficient to resist damage. By both the standard and modified Proctor compaction tests, it was found that the coefficients of permeability for the soil samples were lower than 1×10-9 m/s that is widely recommended for soils that are to be used as landfill liners. Pb 2+ , Zn 2+ and Cr 2+ were the heavy metals in the leachates. The sorption selec-tivity order for tested soils depended on the soil type and properties.
... Cr may be present naturally at background concentrations and, thus the US Environmental Protection Agency (USEPA) specifies standards. An average concentration of 100 mg/kg of Cr is found in soils and that range can vary from 1 to 1000 mg/kg as safe in ordinary soils; in drinking water, it should be less than or equal to 0.1 mg/L [3,4]. The importance of different transitional states of chromium at different pH values and the challenge it poses for geoenvironmental engineers for treatment of chromium contaminated sites. ...
The presence of xenobiotic (human induced) chemicals from mining, refining and electroplating industries causes significant damage to the natural soil system, altering its physico-chemical geochemistry. Most of these chemicals contain metal pollutants that are non-biodegradable and the only way to contain or limit their movement is through sorption. In this study, the sorptive response of two most commonly found metal contaminants, hexavalent chromium (Cr+6) and mercury (Hg+2), are studied using two semi-arid soils from Saudi Arabia. To enhance their retention capacity, these soils are amended with lime. The response to sorption at varying initial contaminant concentrations, pH conditions, temperature levels, and dilution ratios is investigated. Relying on empirical models (Langmuir and Freundlich), the nature of sorption (monolayer or heterogeneous) is ascertained. Further, kinetic models are employed to validate the type and nature of sorption occurring (whether pseudo first-order or second-order). It is found that the experimental results correlate well with the selected empirical models for both the Al-Ghat and Al-Qatif soils when amended with lime and attenuate Cr and Hg to satisfactory levels. The R2 values are close to 1 for all the tested models. The order of sorption was Cr>Hg for heavy metals considered, and also for soils and soil mixtures considered Al-Qatif soil amended with 6% lime >Al-Ghat soil with 6% lime >Al-Qatif >Al-Ghat. Lime treated soils sorbed 69% and 63% more than the untreated soils for Cr and Hg, respectively.
... In recent times, environmentalists have also been concerned about the toxic metal adsorption capacity of materials to be used as landfill liners, in order to protect groundwater from such toxic metal. Ghosh et al. (2012) found out that a clay soil amended with 17% rice husk and 2% bentonite has the potential of being used as a landfill liner to contain chromium leachate. ...
Compacted clay soils are commonly used as landfill liners. This research work was aimed at investigating the suitability of sawdust amended lateritic clay as a landfill liner to adsorb Pb and Cd, thereby protecting underground water. Index properties, compaction, strength and permeability tests were conducted on the unstabilized and stabilized clay in order to determine the effects of the sawdust on the geotechnical properties of the lateritic clay. Batch kinetics tests were utilized to determine the capacity of the clay and sawdust-amended clay to adsorb Pb and Cd. The soil, classified as A-7-6 and CH by AASHTO and unified soil classification systems, respectively, was admixed with 0%, 5%, 10%, 20%, and 30% sawdust by dry weight of the soil. Test results show that the specific gravity, plasticity index, maximum dry unit weight and unconfined compressive strength of the soil decreased with increasing sawdust content while the optimum moisture content and hydraulic conductivity increased with increasing sawdust content. The stabilization of the lateritic clay with ≤10% sawdust content was recommended for use as landfill liners, as they meet the standard hydraulic conductivity requirement and present a good adsorption of Pb and Cd.
... Quantitative evaluation of migration behaviour of pollutants is necessary to determine the transport parameters such as distribution coefficient (K d ), coefficient of hydrodynamic dispersion (D) and retardation factor (R) through batch and column adsorption tests for rational estimation of the above parameters (Ghosh et al. 2012a). Further the attenuation property of a liner material (clayey soil) can be enhanced by using different admixtures (Ghosh et al. 2012b). ...
... Quantitative evaluation of migration behaviour of pollutants is necessary to determine the transport parameters such as distribution coefficient (K d ), coefficient of hydrodynamic dispersion (D) and retardation factor (R) through batch and column adsorption tests for rational estimation of the above parameters (Ghosh et al. 2012a). Further the attenuation property of a liner material (clayey soil) can be enhanced by using different admixtures (Ghosh et al. 2012b). ...
Hexavalent chromium (Cr6+) is released in the lithospheric environment through leachate pollution in chrome tanning industries. Transportation of Cr6+ containing plume through soil needs to be assessed by estimation of some mechanistic parameters such as diffusion coefficient (D), distribution coefficient (K
d) and retardation factor (R). An investigation was undertaken with three soil samples, S1, S2 and B, to examine their potential use as liner material for controlling Cr6+ pollution in soil environment. Batch adsorption kinetic test was carried out to estimate the K
d and R values of soil samples S1 and S2. A numerical solution technique was adopted for prediction of such transport parameters in simulated field condition using the finite difference method (FDM). The efficacy of the present numerical solution technique (FDM) is compared with subsequent column experiment data with Soil-B along with the analytical solution. It was observed that the experimental value of “D = 3.04 × 10−8 m2/s for Soil- B” by using the applied technique closely fitted to that value evaluated by the analytical method (r
2 = 0.98). The values of ‘K
d’ for Soils S1 and S2 were found to be 0.008 and 0.021 mL/g, respectively, using batch adsorption. The values of ‘R’ of the soil samples S1 and S2 were obtained as 1.037 and 1.053, respectively. All the above results were obtained in correspondence to the initial hexavalent chromium concentration level of 7.5 mg/L in the simulated leachate sample.
... Chromium is one of the heavy metals used by modern industries like plastic, pigment, wood preservative, electroplating, leather tanning, cement, mining, dyeing and fertilizer (Oladoja et al., 2013). Among them, chrome tanning industry contributes more chromium pollution in water and land environment (Sudipta et al., 2012). Chromium occurs in aqueous systems as trivalent and hexavalent forms. ...
Present study dealt the removal of Cr(VI) in a tannery industry wastewater using rice husk silica powder as an adsorbent.The experimental investigations have been carried out by using rice husk silica powder for different adsorption dosage, different contact time and different pH against the initial Cr(VI) concentration of 292 mg/L. The maximum percentage removal of Cr(VI) in the tannery industrial wastewater (88.3 %) was found at an optimum adsorbent dosage of 15 g, contact time of 150 min., and pH of 4. Further, the experimental data on removal of Cr(VI) from tannery industry wastewater was validated with the Cr(VI) aqueous solution of same initial concentration of tannery industry waster against the optimum process parameters. The results of the validation experiment showed that the experiments conducted for the removal of Cr(VI) in a tannery industry wastewater may be reproducing capability for analyzing various parameters along with Cr(VI) based water and industry wastewater. The experimental data were fitted to Langmuir and Freundlich isotherm models. Isotherm models result indicated that the equilibrium data fitted well with the Langmuir isotherm than Freundlich isotherm, because of higher correlation created between dependent and independent variables. Thus, the adsorption method using rice husk silica powder was used effectively for removing Cr(VI) in the tannery industrial wastewater, seems to be an economical and worthwhile alternative over other conventional methods, because of their abundant source, low price, multi-purposes and antimicrobial properties.
... Chromium is one of the heavy metals used by modern industries like plastic, pigment, wood preservative, electroplating, leather tanning, cement, mining, dyeing and fertilizer (Oladoja et al., 2013). Among them, chrome tanning industry contributes more chromium pollution in water and land environment (Sudipta et al., 2012). Chromium occurs in aqueous systems as trivalent and hexavalent forms. ...
Present study dealt the removal of Cr(VI) in a tannery industry wastewater using rice husk silica powder as an adsorbent.The experimental investigations have been carried out by using rice husk silica powder for different adsorption dosage, different contact time and different pH against the initial Cr(VI) concentration of 292 mg/L. The maximum percentage removal of Cr(VI) in the tannery industrial wastewater (88.3 %) was found at an optimum adsorbent dosage of 15 g, contact time of 150 min., and pH of 4. Further, the experimental data on removal of Cr(VI) from tannery industry wastewater was validated with the Cr(VI) aqueous solution of same initial concentration of tannery industry waster against the optimum process parameters. The results of the validation experiment showed that the experiments conducted for the removal of Cr(VI) in a tannery industry wastewater may be reproducing capability for analyzing various parameters along with Cr(VI) based water and industry wastewater. The experimental data were fitted to Langmuir and Freundlich isotherm models. Isotherm models result indicated that the equilibrium data fitted well with the Langmuir isotherm than Freundlich isotherm, because of higher correlation created between dependent and independent variables. Thus, the adsorption method using rice husk silica powder was used effectively for removing Cr(VI) in the tannery industrial wastewater, seems to be an economical and worthwhile alternative over other conventional methods, because of their abundant source, low price, multi-purposes and antimicrobial properties.
... Included within the experimental device, the glass column has an inside diameter of 85 mm and a total length of 350 mm. To simulate the density in the field (i.e., 90 % relative compaction), the tested bentonite was set in the main part of the column and compacted in layers (Ghosh et al. 2012). Below and above the compacted soil layers, two consecutive layers of filter paper and glass wool were placed. ...
Bentonite was modified with cationic surfactant hexadecyl trimethyl ammonium bromide (HTAB) as landfill liner to retard the transportation of bisphenol A (BPA) for the first time. The modification was confirmed to form a lateral bi-layer in the interlayer space of bentonite by scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy. The introduction of HTAB into the internal position of bentonite led to an increased interlayer space of bentonite from 15.0 to 20.9 Å and a higher sorption affinity for BPA (10.449 mg/g of HTAB-bentonite and 3.413 mg/g of raw bentonite). According to the Freundlich model, the maximum adsorption capacity of the HTAB-bentonite was found to be 0.410 mg/g. The sorption capacity of raw bentonite and HTAB-bentonite both decreased at alkaline conditions. Although the hydraulic conductivity of HTAB-bentonite was higher than that of raw bentonite, results of laboratory permeability and column tests indicated that HTAB-bentonite obviously extended the BPA breakthrough time by 43.4 %. The properties of the HTAB-bentonite revealed its notable advantages as components of landfill liners material to retain BPA in leachate.
This work examines the study of engineering properties and leachate characteristics of ground granulated blast furnace slag (GGBS) blended with laterite soil-bentonite mixtures as a bottom landfill liner. In this study, laterite soil is referred to as non-expansive and non-plastic clay; on the contrary bentonite is highly expansive and high plastic clay. Laboratory experiments were performed to quantify the effect of GGBS-laterite soil-bentonite mixtures on the liquid limit (LL), free swell index (FSI), compaction characteristics, unconfined compressive strength (UCS), hydraulic conductivity (k), and leachate tests. As GGBS percentage in the mix blend increases, the LL, FSI, optimum moisture content, k determined with deionized water/diesel oil contaminants and leachate concentration decreases, whereas maximum dry densities and UCS value increases. Furthermore, X-ray diffraction analysis and energy dispersive X-ray spectrometer was performed on UCS samples to determine the evidence of hydration reaction in mix blends at 0, 14, and 28 days curing period. The test results revealed that an increase in Ca: Si ratio and a decrease in Al: Ca ratios, augmented the UCS enhancement during the curing period. Consequently, 20% GGBS combined with laterite soil-bentonite mixes proves to be the ideal material for landfill bottom liners in waste containment systems.
Chromium(VI), a kind of migratory heavy metal pollutant, does not only accumulate in the soil in huge amount, but it can also migrate to the deep layer soil and even contaminate the groundwater. The migration pattern of water in the unsaturated silt loam is studied. Then the dynamic leaching characteristic of Cr(VI) is observed. Finally, through the indoor soil column leaching experiment, the influence of adding nano-aluminium oxide (Al2O3) into the soil column on the migration of Cr(VI) in the silt loam is analysed. In unsaturated silt loam, water in it apparently affects the Cr migration. The deeper the soil layer is, the lower the Cr(VI) concentration is. With the drip irrigation going on, the Cr(VI) concentration in the soil increases constantly until it fundamentally reaches the saturated adsorbance of the soil. With nano-Al2O3 added into the column, the migratory rate of Cr(VI) in the soil decrease obviously, which is probably because of the space steric effect and adsorption characteristics of nano-Al2O3. Therefore, nano-Al2O3 can be utilised as a preferable material to reduce the migration rate of Cr(VI) of soil and groundwater. The research results can supply the theoretical basis to the research of heavy metal pollution in the unsaturated soil.
An investigation in field scale was carried out in a common tannery effluent treatment plant site near Kolkata for evaluating hexavalent chromium migration through the fine-grained clayey soil, for disposal of chrome sludge emanated from cake filter press. The locally available soil was used in situ as a compacted clay liner material as adsorbing candidate. Laboratory batch adsorption results demonstrated about 70–80 % of hexavalent chromium removed after 120 min of equilibration time. Hydraulic conductivity of the soil was found to be decreased by two decimal place due to permeation of hexavalent chromium laden leachate. Field test results also exhibited 63 % of hexavalent chromium was sorbed after 120 days interval. Experimental results were also validated by mathematical analysis with good agreement to test data.
To assess the extent of leachate migration, continuous samples of clayey soils (about 9m) were obtained beneath a 17-year old uncontrolled landfill in southeastern China. The soil samples were sub sectioned and analyzed to determine the concentrations of chloride, sodium and COD in the pore water. Total nitrogen and soil organic matter content of the soil samples were also determined. Leachate-derived chloride was detected in the clayey soil to a maximum depth of 9m. Sodium and COD were found to migrate into the soils to depths of 3-4m due to the attenuation of solutes by the soil organic matter and clay minerals at the shallow soils. The estimated migration depths for the chloride are 3m in the case of pure diffusion. Advection and mechanical dispersion were found to be more important than molecular diffusion for this site with an 8m high leachate mound. By comparing the results obtained by the mathematical modeling for layered advection-dispersion problem with the measured concentration profiles, the ranges of the effective diffusion coefficient, retardation factor and dispersivity of the soils were estimated. Better fits are obtained by employing an artificial effective interface about 1m above the observed interface. The clayey soils showed a relatively high attenuation capacity for COD with the estimated retardation factor of 5.
Health-based regulatory limits and remediation strategies for chromate [Cr(VI)] in alkaline soils enriched with chromite ore processing residue (COPR) should be based on oxidation-reduction and solubility interactions of Cr. A laboratory study characterized the solubility of Cr(VI) by sequential batch equilibrations and leachings from two COPR-enriched soils using dilute salt and acid solutions. Batch equilibrations quantified reduction of soluble and insoluble Cr(VI) in the whole soils and extracted solutions. The soils, termed Low Hex and High Hex, contained 105 and 460 mg Cr(VI) kg-1, 1.8 and 10.4 g total Cr kg-1, and had pH values of 8.5 and 10.4, respectively. Total cumulative Cr(VI) removed by the extractions was 49 and 386 mg kg-1 by both the batch equilibrations and leaching methods in the Low and High Hex soils, respectively, and no differences were found among the extractants. Addition of Mn2+ resulted in 50 to 100% reduction of soluble Cr(VI) in both soils without pH adjustment, a new finding that is thermodynamically predictable at pH > 7.2, and it is in sharp contrast to the ability of Mn(III,IV) oxides to oxidize Cr(III) to Cr(VI) in more acidic soils and Mn oxide suspensions. Additions of Fe2+, steel wool (Fe), leaf litter, and lactic acid (a component of human sweat) also reduced various quantities of soluble and insoluble Cr(VI) in the soils, depending on pH, reducing agent, and soil. Soluble Cr(VI) in these COPR-enriched soils appeared to be controlled by dissolution of a moderately soluble chromate salt, such as CaCrO4, and not by sorption or oxidation-reduction equilibria.
Soil liners have traditionally been compacted in the field to a minimum dry weight over a specified range in water content. This approach evolved from the practice for structural fills for which strength and compressibility are of primary concern. With soil liners, hydraulic conductivity is usually of paramount importance. Hence, the approach used to ensure adequate strength and permissible compressibility is not neccesarily applicable to the construction of soil liners. Data are presented to show that the water content-density criteria for compacted soil liners can be formulated in a manner that is different from the approach currently used by many engineers. The recommended approach is based on defining water content-density requirements for a broad, but representative, range of compactive energy, and relating those requirements to hydraulic conductivity and other relevant factors. A case history illustrates the recommened procedure and its implementation. Hydraulic conductivity measurements were performed on three soils to develop an 'acceptable zone' on the compaction curve that was used for quality control during construction. As a result of implementing the recommended procedure, constructrion operations were significantly accelerated.
An empirical method is described for estimating maximum dry unit weight (γdmax) and optimum water content (wopt) of clayey soils at any rational compactive effort E. One variation of the method uses the liquid limit (LL) and one compaction curve, whereas the other uses only the LL. Linear relationships between γdmax and the logarithm of compaction energy (log E), and wopt and log E, both of which are a function of the LL, are used to extrapolate to different compactive energies. Data for 22 clayey soils were used to develop the method, and data for five additional soils were used for validation. Both variations of the method are unbiased and robust. The variation employing the LL and one compaction curve is slightly more precise, with typical errors of about ±1% for wopt and ±2% on γdmax. For the variation employing only the LL, typical errors are about ±2% for wopt and ±6% on γdmax.
A database consisting of 85 full-scale compacted clay liners was assembled to evaluate field hydraulic conductivity K{sub F}. Large-scale field hydraulic conductivity tests were conducted on each liner. All of the clay liners were intended to achieve K{sub F} ⤠1 à 10â»â· cm/s, but only 74% succeeded in meeting this objective. The important factors affecting K{sub F} are the soil wetness relative to the line of optimums and the number of lifts or the thickness of the liner. Poor correlation exists between K{sub F} and hydraulic conductivities measured in the laboratory (K{sub L}) on field-compacted samples (especially for liners with K{sub F} > 10â»â· cm/s compacted at lower water contents relative to the line of optimums), percent compaction, and index properties representative of composition (e.g., Atterberg limits and particle size fractions). The findings indicate that (1) compacted clay liners having K{sub F} ⤠10â»â· cm/s can be constructed with a broad variety of clayey soils; (2) the primary emphasis should be ensuring compaction is primarily wet of the line of optimums; (3) less emphasis should be placed on other traditional measures such as percent compaction, K{sub L}, and index properties; and (4) liners that are thicker or have a greater number of lifts tend to have lower K{sub F}.
A database is described that contains laboratory measurements of hydraulic conductivity and associated soil properties that were extracted from construction reports for compacted soil liners. The database contains measurements conducted on a wide variety of soils from 67 landfills in North America. The database was used to evaluate relationships between hydraulic conductivity, compositional factors, and compaction variables and to identify minimum values for soil properties that are likely to yield a geometric mean hydraulic conductivity [=]7, the percent fines (< No. 200 sieve) [>=]30%, and the percent clay (=]15%. A multivariate regression equation was also developed that can be used to estimate the geometric mean hydraulic conductivity as a function of soil composition and compaction conditions.
The successful design of a landfill liner requires that consideration be given to the hydraulic performance of the landfill. The hydraulic performance of a landfill liner system comprises control of leakage rate, contaminant travel time through the liner and attenuation of leachate contaminant species. Parameters such as the thickness, slope, permeability, construction method and chemical properties of liner materials can be varied during design to maximize the hydraulic performance of the landfill liner. The effect of varying each of these on the components of hydraulic performance is discussed. The hydraulic performance of three common types of liner are compared - single mineral liners, single geosynthetic liners and composite mineral/geosynthetic liners - using LandSim, a probabilistic computer model that simulates the performance of landfills. The results of the comparison are used to discuss the importance of design parameters in determining the hydraulic performance of the different types of liner.
A Cr(VI)-reducing culture was enriched from an anaerobic chemostat fed with synthetic media containing acetate and Cr(VI). The enriched culture was used for a series of batch tests to investigate several environmental factors affecting microbial Cr(VI) reduction. Under carbon-limiting
conditions, the extent of Cr(VI) reduction proportionally depended on the carbon concentration and no reduction of Cr(VI) was observed in the absence of acetate. Cr(VI) reduction was also dependent upon the initial biomass level and the type of organic compounds. The developed model predicted
Cr(VI) reduction well at different Cr(VI) concentrations.Sulfate at 120 mg SO4
2−/L or nitrate at 150 mg N/L slightly inhibited Cr(VI) reduction. Reduction of nitrate but not sulfate was observed along with Cr(VI) reduction. Cr(VI) was not reduced by the aerobically
growing culture, and it was found that oxygen inhibitory effects on Cr(VI) reduction were reversible. The optimum pH and temperature for Cr(VI) reduction were found to be 7.3 and 32°C, respectively. In addition, Cr(VI) reduction was sensitive to the metal ions that may coexist with Cr(VI)
in industrial wastes containing Cr(VI).
Geoenvironmental Engineering covers the application of basic geological and hydrological science, including soil and rock mechanics and groundwater hydrology, to any number of different environmental problems.
* Includes end-of-chapter summaries, design examples and worked-out numerical problems, and problem questions.
* Offers thorough coverage of the role of geotechnical engineering in a wide variety of environmental issues.
* Addresses such issues as remediation of in-situ hazardous waste, the monitoring and control of groundwater pollution, and the creation and management of landfills and other above-ground and in-situ waste containment systems.
Efforts are being made to devise technologies and treatment systems to remediate contaminated soil on site without generating significant wastes for off-site disposal. Heap leaching, a technique used extensively in the mining industry, has been investigated as a method for remediation of hazardous metal contamination of the vadose zone. In the mining industry, metal bearing ore is excavated and mounded on a pad. The metals are removed by passing a special leaching solution through the ore. In this study, the removal of Chromium (VI) from four New Mexico soils (sand, sandy loam, and clay) using heap leaching was evaluated at a column scale. The heap leaching study demonstrated greater than 99% removal of Cr(VI), using tap water as the leaching agent. The soils were typical of arid climate soils with low organic content (< 1%).
Chromate adsorption was measured with and without reactive cosolutes on four subsurface soil horizons differing in pH and mineralogy, and on clay fractions from two of the oxide-containing subsoils. Chromate adsorption was greatest in low pH materials enriched in kaolinite and crystalline iron oxides. The calculated site density and surface binding constants for Al-goethite were used in the Triple Layer Model to calculate the effect of ionic strength, cosolutes, solids concentration, and sorbate concentration on CrO42- adsorption. -from Authors
Coefficients of permeability, calculated using Terzaghi's theory of one-dimensional consolidation, are reported for smectite, illite, and kaolinite, in water, methyl and ethyl alcohol, benzene, and carbontetrachloride. When the pore fluid was water the clays were homoionized to either the sodium or calcium form and the pore water electrolyte concentration was varied. The coefficients of permeability are evaluated in terms of both mechanical and physico-chemical variables. It appears that the coefficients of permeability are mainly influenced by mechanical effects, particularly the distribution of void sizes and the tortuosity of the channels. The coefficient of permeability is maximized if the flow channels consist of many small channels and a relatively few large ones, through which the main flow occurs. Physico-chemical variables exert great influence on the coefficient of permeability through their influence on dispersion or aggregation of the clay particles.
The need to develop various offshore containment systems encourages the contaminant transport study in marine clays. In the present investigation, an attempt has been made to examine six cases of contaminant transport in marine clays. Adequate literature background on the chemical diffusion of soils, and the earlier reported modeling techniques relevant to the present work have been highlighted. These methods enable a rapid examination of the impact of contaminant physical properties on the environment over a period of time. The numerical results of this study help to understand the chemicals transport phenomena in the marine environment especially at sea bed.
The characteristics of the richness in silica and the high porosity of rice husk enable its application as a good, yet cheap, heavy metal adsorbent from wastewater. This study used rice husk to sorb Cr(VI) from wastewater that contained 2000 mg Cr(VI) l-1. Results of a scanning electron microscopy (SEM) experiment indicate a considerable morphology alteration of the rice husk after the sorption experiments. 13C-nuclear magnetic resonance (NMR) measurements show significant decrease in intensity of all the following peaks: carbonylic, carboxylic, aromatic, polysaccharides, carbohydrates and aliphatics. The X-ray absorption near edge structure (XANES) result indicates that about 70% and 90% of the Cr(VI) sorbed on the rice husk after the 12 and 48 h sorption experiments, respectively, were in Cr(III) forms. In the 12 h sorbed rice husk sample, the chromium species distribution is 41% organic Cr(III) +27%Cr(OH)3+32%CrO3, while in the 48 h sorbed one, it is 57% organic Cr(III) +31%Cr(OH)3+12%CrO3.
The hydraulic conductivity of calcium and sodium bentonites was investigated for sand-bentonite mixtures, a thin bentonite layer simulating a geosynthetic clay liner (GCL), and bentonite-cement mixtures simulating backfill for a vertical cutoff wall. The permeant liquids were tap water and distilled water containing 0.25 M calcium chloride. In general, the hydraulic performance of calcium bentonite was not significantly better than the performance of sodium bentonite for either the clay-amended sand or the GCL application, and was substantially worse than the performance of sodium bentonite in the bentonite-cement mixture. A drained angle of internal friction of 21° was measured for calcium bentonite, compared to 10° for sodium bentonite. Except for a larger drained shear strength, no advantage of calcium bentonite over sodium bentonite could be identified from the results of this study.
The use of a single extraction with dilute unbuffered silver-thiourea (AgTU) solution (0.01 M Ag+) for measuring exchangeable cations and the cation exchange capacity (CEC) of soils was compared with the conventional effective CEC method, which used N NH4OAc displacement for exchangeable "bases" (Ca, Mg, K, Na) and N KCI extraction for exchange acidity (Al + H). Fifty-seven selected surface and lower B horizon samples of Alfisols, Ultisols, and Oxisols with low-activity clays derived from a wide range of parent materials were used.
The two extraction methods gave essentially the same CEC values for all soils studied (R2 = 0.92). Good agreements were also obtained between the dilute AgTU-extractable bases (Ca, Mg, K, Na) and N NH4OAc-extractable bases. The dilute AgTU extraction gave slightly larger values of exchange acidity (Al + H) than the N KCl extraction for most soils.
The single-extraction method using unbuffered Ag-thiourea is suitable for rapid, routine measurements of effective CEC and exchangeable cations for soils dominating in variable-charge colloids.
(C) Williams & Wilkins 1980. All Rights Reserved.
The disposal of toxic metals [e.g., Cr(VI)] generated by the Department of Energy during the cold war era has historically involved shallow land burial in unconfined pits and trenches. The objectives of this study were to investigate the impact of coupled hydrologic and geochemical processes on the fate and transport of Cr(VI) in undisturbed soil cores obtained from a fractured, acidic inceptisol that are commonly used in the disposal of waste at the Oak Ridge National Laboratory. The mobility of Cr(VI) was significantly retarded relative to a nonreactive Br- tracer, and the mobility decreased with increased loading of the solid phase with natural organic matter (NOM). A significant portion of added Cr(VI) did not elute from the columns, and X-ray absorption near-edge structure (XANES) revealed that both Cr(VI) and Cr(III) resided on the soil mineral surfaces. The reduction of Cr(VI) to Cr(III) was dramatically more significant on soils with higher levels of surface-bound NOM. This indicated that NOM was serving as a suitable reductant during Cr(VI) transport even in the presence of potentially competing geochemical oxidation reactions involving Cr. The redox reaction was catalyzed by the presence of soil mineral surfaces, and the reduced product Cr(III) was immobilized as a tightly bound moiety. The effectiveness of surface-bound NOM to reduce toxic Cr(VI) to Cr(III) under acidic conditions has important implications regarding the design and implementation of in situ remedial strategies.
The kinetics of reduction and oxidation of soluble chromium in various soils (peat, clay, sand, and luvi-chromic cambisols) were studied at constant soil moisture and constant temperature. A total of 1500 g of each soil was incubated with different concentrations of aqueous solutions of K2Cr2O7 or CrCl3 [1−1000 μg (g of dry soil)-1]. The total exchangeable chromium and Cr(VI) were analyzed in soil extracts over a period of up to 10 days. The parameters influencing the reduction and oxidation of soluble chromium were studied. Reduction of soluble chromium was observed in all the soils examined. It depends mostly on the content of organic matter, on the concentration of the added chromium, and on the pH of the soil. Up to 3 days of the experiment, the reaction was found to be first-order with respect to Cr(VI). Oxidation of soluble chromium was observed especially in soils high in manganese(IV) oxides and low in organic matter. The oxidation of added soluble chromium did not occur in peat soil. The results indicate that the oxidation and reduction of soluble chromium added to soils depends on the soil structure and on the reduction/oxidation conditions in the particular soil.
Permeable-reactive redox walls, placed below the ground surface in the path of flowing groundwater, provide an alternative remediation approach for removing electroactive chemicals from contaminated groundwater. Four types of Fe-bearing solids, siderite [FeCO3], pyrite [FeS2], coarse-grained elemental iron [Fe0], and fine-grained Fe0, were assessed for their ability to remove dissolved Cr(VI) from solution at flow rates typical of those encountered at sites of remediation. Batch studies show that the rate of Cr(VI) removal by fine-grained Fe0 is greater than that for pyrite and coarse-grained Fe0. Results from column studies suggest that partial removal of Cr(VI) by pyrite and coarse-grained Fe0 and quantitative removal of Cr(VI) by fine-grained Fe0 occur at rapid groundwater flow velocities. The removal mechanism for Cr(VI) by fine-grained Fe0 and coarse-grained Fe0 is through the reduction of Cr(VI) to Cr(III), coupled with the oxidation of Fe0 to Fe(II) and Fe(III), and the subsequent precipitation of a sparingly soluble Fe(III)−Cr(III) (oxy)hydroxide phase. Mineralogical analysis of the reactive material used in the batch tests indicates that Cr is associated with goethite (α-FeOOH). These results suggest that Cr(III) is removed either through the formation of a solid solution or by adsorption of Cr(III) onto the goethite surface. The effective removal of Cr(VI) by Fe0 under dynamic flow conditions suggests porous-reactive walls containing Fe0 may be a viable alternative for treating groundwater contaminated by Cr(VI).
The driving mechanisms for flux occur at interface between the soil particles and solution during electrokinetic soil remediation
and the nature of this interface affects the electrokinetic response of the system. The pH-dependent adsorption of heavy metal
contaminants by kaolin and the sensitivity of kaolin zeta potential to the aqueous phase properties are two important aspects
that complicate the metal movement during electrokinteic soil remediation. This paper addresses these aspects and presents
an electrostatic adsorption model that describes the behavior of kaolin surface for Cr(VI), Cr(III), Ni(II), and Cd(II) under
various chemical conditions. This study showed that the aqueous properties: pH, ionic strength and the presence of the heavy
metals Cr(VI), Cr(III), Ni(II), and Cd(II) in the system affect the zeta potential of kaolin surface. The zeta potential of
kaolin shifts to a more negative value if the system pH increases. However, it shifts to a more positive value if the system
ionic strength or metal concentration increases. It was found that the amount of the heavy metal adsorbed by kaolin has a
pronounced sensitivity to the pH. As a result of the adsorption modeling, the constant capacitance protonation-dissociation
intrinsic constants of kaolin are: pK
+int=-3.8±0.5_{+}^{{\mathop{\rm int}}}=-3.8\pm 0.5
and
pK-int=9.4±0.5pK_{-}^{{\mathop{\rm int}}}=9.4\pm 0.5
. The ion-kaolin surface complexation constants (pK
int^{{\rm int}}
) of Cr(VI), Cr(III), Ni(II), and Cd(II) are: −12.5± 0.5, −5.0± 1.0, 2.6± 0.6, and 3.3± 1.0, respectively.
The adsorption of hexavalent chromium from aqueous medium by rice husk-based activated carbon (RHC) was studied. The extent of adsorption was studied as a function of pH, contact time, contact temperature, adsorbate concentration and adsorbent with different pore structure. The removal of Cr(VI) by RHC was first introduced. The adsorption of two carbons activated by KOH-activation and NaOH-activation was discussed. The difference was studied through pore size distribution, pore volume and the adsorption capacity.
Recently there has been increasing interest in the use of the frequency dependent dielectric properties of clay soils as a potential method of contaminant detection. The study of dielectric properties of contaminated clays at lower frequencies is of particular importance as this has been theoretically argued to be the range in which the interfacial polarisation and double layer polarisation occurs. These are phenomena which provide valuable information on the physical and chemical properties of clays and how these will change in the presence of contaminants.However, dielectric measurements are more difficult to obtain at low frequencies due to a number of phenomena that can cause measurement errors. Four terminal measurement systems are theoretically capable of reducing the error due to the phenomenon of electrode polarisation. A commercial probe that is normally used to measure the biomass of biological suspensions has been tested for its suitability to make dielectric measurements in clays. Preliminary results highlight some of the problems with calibrating such a system for this type of measurement and indicate that the problems of electrode polarisation can still persist.
A new model is proposed to describe the removal of volatile organic compounds (VOC) from a gas stream passing through a bed packed with activated carbon fibers (ACFs). Toluene was used as the test compound. Both pore diffusion and surface diffusion are considered in the model. The equilibrium behavior is shown to fit the Dubinin–Radushkevich isotherm with the values of parameters K and W0 of 1.101 × 10−9 and 57.73 kg/m3, respectively. The experimental results show that this model can predict VOC breakthrough curve very well.
Worldwide chromium contamination of soils has arisen predominantly from the common practice of land-based disposal of tannery wastes under the assumption that the dominant species in the tannery waste would be the thermodynamically stable Cr(III) species. However, significant levels of toxic Cr(VI) recently detected in surface water and groundwater in India, China, Australia, and elsewhere raise critical questions relating to current disposal criteria for Cr-containing wastes. It now appears that despite the thermodynamic stability of Cr(III), the presence of certain naturally occurring minerals, especially Mn oxides, can enhance oxidation of Cr(III) to Cr(VI) in the soil environment. This factor is of public concern because at high pH, Cr(VI) is bioavailable, and it is this form that is highly mobile and therefore poses the greatest risk of groundwater contamination.
A review of the current literature indicates that extensive research has been performed on the speciation of Cr in soil, the effect of pH on soil solution concentrations of Cr(III) and Cr(VI), soil adsorption phenomenon of Cr species, redox reactions, and transformation of Cr(III) and Cr(VI) together with remediation strategies to decontaminate Cr-contaminated soils. Most of the studies were conducted using an uncontaminated soil artificially spiked with Cr, and very limited research has been conducted in the contaminated soil environment. Furthermore, studies on tannery waste contaminated soils are limited, and obviously a serious gap of knowledge exists in understanding the influence of long-term tannery waste contamination on Cr behavior in soil.
Sludge, soil and leachate samples collected from a chromium-contaminated tannery waste dumping site in Kanpur, India, were found to contain considerable amounts of Cr(VI), despite the fresh tannery sludge containing little or no Cr(VI). Literature reports suggested that dry Cr(III) precipitates could be converted to Cr(VI) when heated in the presence of oxygen. Also, Cr(III) in aqueous phase could be oxidized through interaction with manganese dioxide (MnO2) surface to Cr(VI). Measurement of manganese in the sludge samples collected from the site showed concentrations up to 0.6 mg/g. Based on equilibrium calculations, it was determined that both dry phase Cr(III) oxidation by atmospheric oxygen and aqueous phase Cr(III) oxidation by MnO2 surface were thermodynamically feasible. It was further suggested that in aqueous phase, manganese may act effectively as an electron transporter between Cr(III) and dissolved oxygen during Cr(III) oxidation, leading to regeneration of MnO2 solid phase. Further, as dissolved Cr(III) is oxidized, dissolution of Cr(OH3) will take place to maintain the equilibrium between the dissolved and solid phases of Cr(III). In the pH range of 3-10, and at oxygen partial pressure (P(O2)) of 10(-6) atm or higher, equilibrium conditions stipulate nearly complete conversion of Cr(III) to Cr(VI). At P(O2) of 10(-20) atm or lower, very little Cr(VI) is expected to be present under equilibrium conditions. In the intermediate P(O2) regions, incomplete dissolution of the Cr(OH3) solid phase and only partial conversion of chromium from +3 to the +6 oxidation state is expected, especially at lower pH values.
In order to evaluate the chromium (Cr) contamination due to the discharge of waste waters from the tannery of Jijel in the Mouttas river (Algeria), samples of water, sediment and vegetation (Agropyrum repens) were collected during a 6 month period in four stations located upstream (control) and downstream of the tannery. The total chromium was measured by atomic absorption spectrophotometry. Metal inputs were clearly related to effluent discharges from the tannery into the river. Although only traces of chromium were found in water samples upstream of the tannery, very high concentrations (up to 860 times higher) were detected downstream. The contamination was not limited to water of Mouttas River because a same difference in chromium concentrations was also found in sediments and plants Agropyrum repens that were sampled upstream and downstream of the tannery. This work showed that the treatment process used in the wastewater treatment plant of the tannery of Jijel is not able to remove the chromium detected in their influents. The occurrence and chromium levels detected in the aquatic environment represent a major problem concerning drinking water resources and environmental protection of water bodies.
An evaluation of the performance of four clay lined landfills in Wisconsin
- M E Gordon
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- P Kmet
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Theory and practice of leather manufacturing
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in tannery sludge to Cr (VI): Field observations and theoretical assessment." J. Hazard. Mater., 121(1-3), 215-222.
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X-Ray adsorption spectroscopy study of chromium recovered from Cr 6þ containing water with rice husk
- M J Hu
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spectroscopy study of chromium recovered from Cr 6þ containing water
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