Leaching Of Chromium Research Articles

Cementitious Behavior of Argon Oxygen Decarburization Stainless Steel Slag and Its Stabilization on Chromium

The study mainly aims at the potential of Argon Oxygen Decarburization Slag (AODS) as a supplementary cementitious material and explores the mechanisms of stabilization/solidification (S/S) of chromium in cement-based composite pastes. The basic cementitious parameters, such as water requirement, setting time, soundness, hydration characteristics, and strength indexes of composite binders, were examined through standard methods. The results showed that the most beneficial mineral phase in AODS for cementitious behavior was beta dicalcium silicate (β-C2S). The utilization of a higher AODS dosage in composite binders increased the water requirement and the setting time, while it decreased the hydration heat and the strength indexes. Although the AODS possessed limited cementitious properties, it conformed the Grade II steel slag powder qualified for concrete and cement. Sequential leaching tests were conducted targeting the leachability of chromium in the pastes with different AODS dosage and curing time. Results showed that with the lower AODS dosage and the longer curing time, the S/S efficiency for chromium leaching from the composite paste was better. Utilization of AODS as a cement substitute not only can recycle this solid waste and decrease the emission of CO2 concerning cement production, but also helps to effectively reduce the chromium leaching risk.

Partitioning, leachability, and speciation of chromium in the size-fractions of soil contaminated by chromate production

Soil particle size significantly affects the distribution and migration of chromium (Cr) in soil. Limited studies have investigated the impact of soil particle size on Cr partitioning at chromate contaminated sites. In this study, the physicochemical properties of coarse sand, medium sand, fine sand, and silt-clay were analyzed. And the particle size effects on partitioning, leachability, and bioaccessibility of total Cr and Cr(VI) were determined. The results showed the distribution factor (DF) of Cr(VI) in the coarse sand, medium sand, fine sand, and silt-clay fractions were 0.70, 0.79, 1.35, and 1.60, respectively. The total Cr DF values also had the similar result. The leached concentrations of total Cr and Cr(VI) in silt-clay (562.89 mg/L and 551.71 mg/L) was higher than in coarse sand (238.55 mg/L and 228.68 mg/L) fraction. The bioaccessibility of total Cr and Cr(VI) in silt-clay (77.72% and 88.58%) was higher than in fine sand (60.72% and 79.55%) fraction. The total Cr proportion of the exchangeable fraction (45.92%–73.67%) was relatively high in the four soil particle size fractions and gradually increased as soil particle size decreased. These implied that finer soil particles are more capable of enriching, mobilizing, and bioaccessibility of Cr and Cr(VI) than the coarse particles, which was related to the higher organic matter, cation exchange capacity, specific surface area, and clay components in smaller particles. The results suggested that higher environmental risk occurred in the finer fraction than in the coarser fraction for the chromate production contaminated soil.

Comparative study of Fenton, Fe2+/NaOCl and Fe2+/(NH4)2S2O8 on tannery sludge dewaterability, degradability of organics and leachability of chromium

In this work, a comparative analysis of Fenton, Fe2+/NaOCl and Fe2+/(NH4)2S2O8 assisted advanced oxidation processes was carried out to study its efficacy in enhancing tannery chemical sludge dewaterability. Experimental results showed that, after conditioning of sludge at optimum pH, oxidant and catalyst dosage, capillary suction time (CST) was decreased by 75 ± 5 % and moisture content of sludge cake (M.Ccake) was reduced to 74 ± 2 % for all processes at 10 min reaction time. Among the three processes, Fe2+/(NH4)2S2O8 process was noted to have larger impact on the breakdown of sludge cells, which is reflected in terms of its highest amount of total organic carbon, protein and total dissolved solids present in the separated sludge fractions. In addition, Fe2+/(NH4)2S2O8 process was also observed to leach out largest fraction say 73.3 % of chromium present in the raw sludge into the treated sludge filtrate. The investigation carried out through zeta potential and scanning electron microscopy reveals the role of a two-step mechanism, namely oxidation followed by coagulation in enhancing the sludge dewaterability. Further studies on the possibility of utilizing dried treated sludge as biomass fuel could be carried out.

Conductometric tests and total chromium leachability in aqueous solution, from tanned leather waste

Conductometric tests and total chromium leachability in aqueous solution, from tanned leather waste

Immobilization of high concentration hexavalent chromium via core-shell structured lightweight aggregate: A promising soil remediation strategy

Among industrially polluted soils, chromium contaminated sites, especially hexavalent chromium (Cr6+) contaminated C6+ sites, are particularly difficult to manage. The Cr6+ in such soils is usually at a high concentration. Several studies show that sintering and solidification are effective ways to treat Cr6+ in soil. In this study, a core-shell lightweight aggregate (CS-LWA) was prepared using Cr6+ contaminated soil as the core and clean bulk materials as a shell to seal the Cr6+ pollutant in the core, and the shell prevents it from leaching out. A reductant, pulverized coal, was added to assist the solidification and improve chromium immobilization . The results show that this method can effectively reduce the leaching of chromium in polluted soil with varying chromium content, and that chromium leaching can be further reduced by increasing the amount of coating material. The chromium in leachate from coated CS-LWA mixed with 8% pulverized coal was only 0.02 mg/L, much lower than 1042.8 mg/L in leachate from untreated chromium-contaminated soil. Moreover, the strength, density, and water absorption characteristics of CS-LWA met the Chinese national standards, enabling its use as a lightweight aggregate for construction.

Kinetic model of chromium release from argon oxygen decarburisation (AOD) slag in a neutral leachate

Valorisation of argon oxygen decarburisation (AOD) slag, a suitable recycling resource, is limited by the release of a notable amount of heavy metals, such as chromium. The mineralogical component of AOD slag was characterised by X-ray diffraction and scanning electron microscopy-energy-dispersive X-ray spectrometry. To explore the release kinetics of chromium from AOD slag, neutral leaching tests were performed at various temperatures. The results indicated the existence of two leaching stages: quick and slow leaching stages. In 2 h, the chromium release fraction increased sharply as the leaching time increased. As the leaching time increased, the chromium release rate gradually decreased. Based on the shrinking core model, chromium release kinetic models for the quick and slow leaching stages from the AOD slag were independently determined. The chromium release was controlled by solid product diffusion during the quick leaching stage and a complicated process in the slow leaching stage. The activation energy of chromium leaching was calculated based on the Arrhenius equation. Solid product diffusion was the velocity-determining step during the 2 h leaching process. In the slow leaching stage, chromium release was controlled by complicated hybrid control dominated by solid product diffusion.

Performance of organic substrate amended constructed wetland treating acid mine drainage (AMD) of North-Eastern India

A horizontal subsurface flow constructed wetland (HSSF-CW) was evaluated for the remediation of synthetic acid mine drainage (AMD) using an organic-rich substrate (cow manure and bamboo chips) planted with common cattail. The synthetic AMD simulated the source AMD generated in North Eastern Coalfield of Assam, India. The synthetic AMD was highly acidic (pH < 2.5) and contained heavy metals (Fe, Mn, Al, Co, Ni and Cr) and sulfate (900–1500 mg L–1). HSSF-CW was operated under varying levels of AMD concentration (10, 25, 40, 70 and 100%) during the acclimatization and thereafter continued to operate at full strength AMD at hydraulic retention time of 7 days. After the 6-month experiment, the results suggested the potential application of HSSF-CW due to its ability to raise the pH from 2.1 to 6.4 with the simultaneous removal of metals (except for manganese) and microbial sulfate reduction (44–75%). Metal removal efficiency in the order: chromium (99.7%) > nickel (97.8%) > cobalt (93.7%) > iron (91.6%) > aluminium (59.7%). Toxicity Characteristic Leaching Procedure test (TCLP) study suggested very negligible leachability of chromium for safe disposal. Common cattails exhibited poor bioaccumulation and translocation for all heavy metals except for manganese and cobalt.

Mechanisms Accompanying Chromium Release from Concrete.

The use of mineral additives from the power and metallurgy industries in the production of building materials still raises questions about the ecological safety of such materials. These questions are particularly associated with the release of heavy metals. The article presents research related to the leaching of chromium from concretes made of Portland cement CEM I and slag cement CEM III/B (containing 75% of granulated blast furnace slag). Concrete was evaluated for leaching mechanisms that may appear during tank test over the long term (64 days). It has been presented that the dominating process associated with the leaching of chromium from both types of concrete is surface wash-off. Between the 9th and 64th day of the test, leaching of Portland cement concrete can be diffusion controlled. It has been proven that the participation of slag in the composition of concrete does not affect the level of leaching of chromium into the environment from concrete.

Tailoring the FeO/SiO2 Ratio in Electric Arc Furnace Slags to Minimize the Leaching of Vanadium and Chromium

Based on recently published research on leaching control mechanisms in electric arc furnace (EAF) slags, it is assumed that a FeO/SiO2 ratio of around one leads to low leached V and Cr concentrations. This ratio influences the mineral phase composition of the slag toward higher amounts of spinel and a lower solubility of calcium silicate phases by suppressing the formation of magnesiowuestite and highly soluble calcium silicate phases. To evaluate this hypothesis, laboratory and scaled up tests in an EAF pilot plant were performed on slag samples characterized by elevated V and Cr leaching and a high FeO/SiO2 ratio. Prior to the melting experiments, the optimum FeO/SiO2 ratio was calculated via FactSageTM. In the melting experiments, the ratio was adjusted by adding quartz sand, which also decreased the basicity (CaO/SiO2) of the slag. As a reference, remelting experiments without quartz sand addition were conducted and additionally, the influence of the cooling rate of the slag was examined. The remelted (without quartz sand) and the remelted modified slags (with quartz sand) were analyzed chemically and mineralogically and the leaching behavior was investigated. The modification of the slags yielded a minimized release of V and Cr, supporting the hypothesis that the FeO/SiO2 ratio influences the mineralogy and the leaching behavior.

Microwave assisted leaching investigation for the extraction of copper(II) and chromium(III) from spent catalyst

Microwave (MW) assisted leaching of copper (Cu) and chromium (Cr) from Cu-Cr spent catalyst was investigated. The MW assistance have many advantages over the regular leaching process and in consequences, the leaching time has been significantly reduced from 240 min to 120 min. The optimum condition; 900 Watt MW power, 2.0 min MW treatment time, 10% H2O2(v/v) and 1.0 M sulphuric acid for during MW irradiation followed by leaching with a very low concentration of H2SO4 (1% (w/w)) was suitable for quantitative extraction of both metals from the spent catalyst phase. The role of either of the oxidants (H2O2, NaClO4, K2S2O8 and HNO3) appears to be critical on enhancing the leaching efficiency of both copper and chromium in addition to the MW treatment. The leaching kinetics study was examined to ascertain the extraction mechanism. The activation energies were obtained to be 3.49 kJ mol−1 and 3.33 kJ mol−1 for Cu and Cr, respectively, indicating on the shrinking-sphere diffusion control leaching behaviour. The linear dependence log kap on log 1/do plot and a first order dependence for kap with H2SO4 at 1.0 M was derived from the proposed leaching model. The FESEM characterization of spent catalyst before and after MW treatment showed a significant change of the particle morphology (shred type to porous type). The XRD and EDAX characteristics pattern of residue samples resulted at optimum leaching condition further ascertained on substantial extraction of copper (99.99%) and chromium (98.56%) from spent catalyst phase.

Recovery and Separation of Vanadium and Chromium by Two-Step Alkaline Leaching Enhanced with an Electric Field and H2O2.

This paper focused on the treatment of vanadium–chromium reducing residue with a two-step alkaline leaching process: electro-oxidation leaching of vanadium and H2O2 as well as oxidation leaching of chromium in an alkaline medium. The effects of experimental parameters on the leaching performance of vanadium and chromium were investigated. The experimental data showed that in the first alkaline leaching in stage I, the leaching efficiency of vanadium reached up to 95.32% under optimal conditions, while most of the chromium could not leach out (about 4% of chromium was leached out). Chromium was easily oxidized to high valence (CrO42–) with H2O2 in the second alkaline leaching stage II. Under optimal conditions, 96.24% chromium was leached out.

Chromium Leachability from Leather Waste and Eco-toxicity under Environmental Conditions

Chromium (III) is currently used in leather manufacture worldwide and the attention has been centered on the alleged environmental impact of chromium in leather waste. The effects of liquid-solid ratio, pH, contact time, rotational speed and temperature on the leachability of chromium from leather waste and the eco-toxicity were evaluated to investigate the ecological impact under environmental conditions. The characterization of leachate included the determination of total Cr and total organics (TOC), analysis of UV-visible absorption spectra, as well as the toxicity test with Photobacterium phosphoreum. The liquid-solid ratio, extractant pH, contact time and temperature significantly affected the leachability of chromium and toxicity of the leachate, whereas rotational speed slightly affected the leaching behavior when beyond 100 RPM. The toxicity of the leachate was related to both the amount of released substance which was mainly affected by contact time and liquid-solid ratio, and the species which was mainly affected by temperature and extractant pH. Finally, three samples from different tannery corresponding to leather waste were leached and characterized by total Cr, TOC and toxicity test under the environmental conditions of liquid-solid ratio 20:1(mL/g), pH 7.0, contact time 8 hours, rotational speed 100 RPM and temperature 25°C. These results contributed to the risk assessment of stacking field and waste management of chrome-containing leather.

Inhibition Kinetics of Chromium Leaching by Calcite Coating on the Surface of Stainless Steel Slag via the Gas–Solid Accelerated Carbonation Process

Chromium leaching from stainless steel slag should be dealt with when utilized them as construction materials, an original idea of increasing calcite coating compactness in slag matrix is proposed for solving this problem. The paper originally proposes a carbonation strategy balancing carbon dioxide sequestration efficiency and chromium leaching inhibition kinetics through forming calcite coating. 48–75 μm stainless steel slag is carbonated at 300 °C and 0.4 MPa for 120 min, carbonated slag and fresh slag are applied for chromium leaching tests, aiming to discuss the inhibition kinetics of calcite coating combining with XRD, SEM–EDS, FT-IR and EMPA analysis. The results show that 7.9% valorization degree can be achieved for stainless steel slag under the conditions, and a thin layer of calcite coating is formed in slag matrix. Diffusion rates of chromium are in the range from 1.32 × 10−11 to 2.12 × 10–11 min−1 and from 0.617 × 10−11 to 1.47 × 10−11 min−1 for fresh and carbonated slag, respectively. Inhibition efficiency of calcite coating on diffusion rate is about 30% to 53%, and diffusion active energies for fresh slag and carbonated slag are 6.84 kJ/mol and 12.51 kJ/mol, respectively, which represents that carbonation strategy is indeed valid for inhibiting chromium leaching, when stainless steel slag is utilized as construction materials or road-based aggregates.

Carbonation of argon oxygen decarburization stainless steel slag and its effect on chromium leachability

This study focuses on evaluating the carbonation potential of argon oxygen decarburization (AOD) slag and analyzing influence mechanism of carbonation on chromium leachability. Static thin-film accelerated carbonation and sequential leaching tests were carried out. Results show that the liquid to solid (L/S) ratio was the most influencing factor for AOD slag’s carbonation, and the maximum carbonation ratio of AOD slag was 50–52% (L/S = 0.4 mL/g, PCO2 = 7.5 bar, and t > 6 h). Dicalcium silicate’s carbonation resulted in the generation of amorphous calcium carbonate, crystalline calcite and silica gel. AOD slag’s smooth surface could be eroded by these products gradually with carbonation furthered. The mineral phase evolution clearly influenced the mineral phase hydrolysis and physical encapsulation, and thus affected the hydrolysis behavior of the primary phase and the generation behavior of the secondary phase in the carbonated slags. Chromium leachability (20 days) declined to its lowest value (1.7 mg/kg) as the carbonation ratio growing to 23% and then increased to its highest value (7.9 mg/kg) with the carbonation ratio increasing to 52%. Chromium leachability varies with the carbonation ratio. The optimal carbonation ratio that resulting in minimum chromium leaching risk must be taken full in mind before using AOD slag in carbonation-related production activities.

Application and mechanism of an ore-washing sludge in the remediation of chromium (III) and copper (II)-contaminated soils

Ore-washing sludge is a typical solid waste from metallurgical industry and needs proper treatment. For the first time, this kind of sludge was used as a stabilizer for heavy metal-contaminated kaolin. As a result, after Cu (3655 mg/kg) and Cr (430 mg/kg)-polluted kaolins were mixed with the stabilizer, only 7.98 ml/L of Cr and 8 mg/L of Cu were leached by the toxicity characteristic leaching procedure. These values were both lower than the limits for the leaching of chromium and copper (GB5085.3-2007). In a column leaching test, only 2.52 mg/L of Cr and 18.51 mg/L of Cu were detected in the leachate when the pH of the leaching solution was lower than 5.6. After the stabilizer was used in Cu/Cr stabilization, it showed solid phases of oxides, hydroxides, and layered double hydroxides. After detailed calculations, oxides in the stabilizer accounted for 54.82% of Cu and Cr stabilizations. Specifically, O-top sites in oxides played a main role in stabilizing Cu and Cr. Therefore, this work will help in the development of high-value-added utilization of solid waste, as well as the remediation of acidic and heavy metal-contaminated soils.

Immobilization of Chromium in Stainless Steel Slag Using Low Zinc Electric Arc Furnace Dusts

A new synergistic treatment of stainless steel slag and low zinc content electric arc furnace (EAF) dusts is proposed to immobilize harmful chromium in stainless steel slag. The effects of ZnFe2O4 addition on the mineralogic phase and chromium leachability of CaO-SiO2-MgO-Al2O3-Cr2O3 synthetic slag were investigated to explore the feasibility of this method. The mineralogic phases in stainless steel slag were investigated by scanning microscopy equipped with energy-dispersive spectroscopy and X-ray diffraction. The leaching concentration values of chromium and zinc were evaluated according to an alkaline digestion for the hexavalent chromium (US-EPA-3060A) and toxicity characteristic leaching procedure (TCLP, US-EPA-1311) method, respectively. It was found that all synthetic slags mainly contain α-Ca2SiO4, merwinite and spinel phase, in line with the calculation results by FactSage. The crystallization of spinel and merwinite phases was enhanced by the addition of ZnFe2O4 but suppressed the precipitation of α-Ca2SiO4. It was revealed that the leaching concentration of chromium was depressed by adding ZnFe2O4 and was far below the chemical limits defined in the French proposal for a criterion and evaluation methods for waste ecotoxicity (0.1 mg L−1). In addition, the zinc leaching concentration meets the sanitary landfill standard. The proposed synergistic treatment method was further validated on industrial stainless steel slags and EAF dusts. Experimental results indicated that the synergistic treatment method can immobilize chromium effectively and the final slags can be disposed of by sanitary landfilling or recycling as constructional materials. A schematic technologic route diagram of the synergistic treatment was also proposed.

A novel substitution-based method for effective leaching of chromium (III) from chromium-tanned leather waste: The thermodynamics, kinetics and mechanism studies

A substitution-based method for chromium (III) leaching from chromium-tanned leather waste (CTLW) without destroying the collagen matrix was proposed. The leaching efficiency of Cr (III) from CTLW using different organic salts was investigated and sodium oxalate (OA-2Na) was considered to be the best Cr leaching agent. The effects of leaching time, temperature, pH, concentration, shaking speed and leather thickness on Cr leaching rate were investigated and a Cr leaching rate of 98% was obtained. Thermodynamic parameters (ΔG0 < 0, ΔH0 > 0 and ΔS0 > 0) were obtained in this study. The kinetic data fitted well with the first-order kinetic equation. The apparent activation energy (Ea = 82.9563 kJ/mol) and the frequency factor (A = 2.96 × 1011) were obtained. The collagen matrix remained intact after Cr leaching by the characterization of SEM and FTIR. A substitution mechanism was proposed that Cr (III) in CTLW was complexed with oxalate and dissociated from the collagen matrix.

USE OF TANNERY SLUDGE IN CLAY BRICK MANUFACTURING

The paper analyses the possibilities of recycling tannery sludge (TS) in clay brick manufacture. The physico-mechanical properties and microstructure of clay brick and cement mortars vary depending on TS content in the mix. 2.5 % 15.0 . TS (by weight) was added to clay bricks fired at 1000 .C temperature and maintained at maximum heat for 1 hour. The tests revealed that 2.5 . TS addition had a positive effect on physical and mechanical properties of clay brick: reduce drying and firing shrinkage, reduce water absorption, and increase compressive strength. Chromium leaching values in clay brick (2.5 % TS) were found not to exceed the limit values set forth in 2003/33/EC.

A Novel Technology for Recovery and Separation of Vanadium and Chromium from Vanadium-Chromium Reducing Residue

This paper was to develop an efficient process for efficient recovery and separation of vanadium and chromium. The vanadium-chromium reducing residue was conducted by oxidation acidic leaching with MnO2, followed by selective adsorption of vanadium and precipitation of chromium, respectively. The results showed that 97.93% vanadium was leached out and then adsorbed by melamine at pH 1.8 at 90 °C for 60 min. Almost all chromium was leached out and efficiently recovered as Cr2O3. The leaching process was mainly controlled by surface chemical reaction, and its kinetic behaviors fitted well with the shrink core model. The apparent activation energy for vanadium and chromium leaching out wascalculated as 19.93 kJ·mol−1 and 21.26 kJ·mol−1, respectively.

Minimizing Chromium Leaching from Low-Alloy Electric Arc Furnace (EAF) Slag by Adjusting the Basicity and Cooling Rate to Control Brownmillerite Formation

Brownmillerite is connected to chromium leaching when present in steel slags. To prevent chromium leaching, brownmillerite in slag should be prevented. Two methods for decreasing brownmillerite content in low-alloy electric arc furnace (EAF) slag were investigated: decreasing the basicity and increasing the cooling rate. The methods were tried on both laboratory scale and in full-scale production. In the laboratory scale experiments, chromium leaching decreased as the basicity decreased until brownmillerite was no longer present, slower cooling resulted in increased chromium leaching, and faster cooling decreased chromium leaching. In full-scale production, basicity modified single batches, with a basicity below 2.2, generally leached less chromium than slag batches with higher basicity, thus verifying the correlation between basicity and chromium leaching seen in laboratory scale experiments. The cooling process in the full-scale experiments was achieved either by letting the slag cool by itself in the air or by water spraying. The water-sprayed slag, which cooled faster, had less chromium leaching than the air-cooled slag. The full-scale production experiments confirmed that both decreasing basicity below 2.2 and increasing the rate of cooling could be used to decrease chromium leaching.