Toxicity characterization and long-term stability studies on copper slag from the ISASMELT process

Detailed studies on the toxicity and long-term stability of copper slag of varying heavy metal concentration generated over a 14-week period in an Indian copper plant through the ISASMELT process was carried out using USEPA's toxicity characteristic leaching procedure (TCLP), multiple extraction procedure and sulfuric acid leaching of granulated and mechanically activated slag as a function of pH at two different temperatures. The TCLP, acid leaching and multiple extraction test results carried out on a large number of slag samples of varying compositions derived from the use of several copper concentrates indicate poor leachability of the heavy metals and assures long-term stability even in extreme atmospheres. Leaching tests on mechanically activated samples gives an idea of the resistance to leaching of the heavy metals even upon weathering. The multiple extraction leaching tests indicate that the heavy metals present in the slag are stable and are not likely to dissolve significantly even through repetitive leaching under acid rain in a natural environment. The highest concentration of all the elements is far below the prescribed limits in USEPA 40CFR Part 261

Arsenic removal by magnetite-loaded amino modified nano/microcellulose adsorbents: Effect of functionalization and media size

Comparative adsorption study related to benefits of parent media size, i.e. microfibrillated cellulose (MC) versus nanocellulose (NC) support, for the preparation of magnetite (MG) based high performance adsorbent for arsenic removal was conducted. Precipitation of MG on amino terminal branched organic structure, L, either linked by maleic acid residue on NC surface (NC-MA/L) or linked by oxalyl bridge on MC surface (MC-O/L) produced NC-MA/L-MG and MC-O/L-MG adsorbents, respectively. Precipitation of nanosized MG on amino functionalized NC-MA/L and MC-O/L, performed according to optimized procedure, contributed to improved textural properties and adsorptive/kinetic performances of novel adsorbents. Adsorption capacity of arsenate, As(V), was in favor of NC-MA/L-MG (85.3 versus 18.5 mg g(-1)) while MC-O/L-MG exhibited faster kinetics (0.541 versus 0.189 g mg(-1) min(-1)). Lower capacity of arsenite, As(III), removal, 68.3 mg g(-1) for NC-MA/L-MG and 17.8 mg g(-1) for MC-O/L-MG, were obtained. Calculated activation energies, 13.28 and 10.87 kJ mol(-1) for NC-MA/L-MG and MC-O/L-MG with respect to As(V), respectively, suggest, in accordance with results of Weber-Morris fitting, that internal mass transfer controls adsorption process. Model free adsorption kinetics confirmed beneficial uses of MC-O/L-MG due to low activation energy dependence on the extent of adsorption

Studies on the electrochemical decontamination of wastewater containing arsenic

The arsenic removal from aqueous solutions by electrocoagulation (EC) using mild steel electrodes was studied. Effect of electrolytes such as NaCl, NaNO3 and Na2SO4 on anodic dissolution of iron and in turn the arsenic removal was deliberated. The arsenic removal was observed to be 98% in the presence of NaCl whereas it is around 75% in the presence of Na2SO4 and NaNO3. The removal of arsenic by EC process was found to be almost similar irrespective of its oxidation state. Almost 95% of the total arsenic was removed within 5 min from its initial concentration of 10 mg L−1. The precipitates formed during EC were characterized using FT-IR, SEM-EDAX, XRD, XPS and magnetometer. The iron oxy-hydroxide precipitate formed during EC was identified as maghemite and lepidocrocite. The magnetic property, particle size and surface properties of the iron oxy-hydroxide precipitate were found to be influenced by arsenic adsorption. The oxidation state of arsenic and iron in EC products was ascertained by XPS. It was observed that some amount of As3+ was converted to As5+ during EC. The electrokinetic and FT-IR measurements revealed the co-precipitation of arsenic by specific chemical interaction between arsenic species and iron oxide precipitate. The effect of initial As3+concentration and current density on arsenic removal was also discussed. The TCLP test (USEPA method-1311) was conducted on EC products to assess their toxicity. It was confirmed that the solid waste generated during EC process is non-hazardous and can be safely disposed

Adsorption of arsenate on synthetic goethite from aqueous solutions

Goethite was synthesized from the oxidation of ferrous carbonate precipitated from the double decomposition of ferrous sulfate doped with sodium lauryl sulfate (an anionic surfactant) and sodium carbonate in aqueous medium. The specific surface area and pore volume of goethite were 103 m(2) and 0.50 cm(3) g(-1) . Batch experiments were conducted to study the efficacy of removal of arsenic(V) using this goethite as adsorbent for solutions with 5-25 mg l(-1) of arsenic(V). The nature of adsorption was studied by zeta-potential measurements. The adsorption process followed by Langmuir isotherm and diffusion coefficient of arsenate was determined to be 3.84 x 10(11) cm(2) s(-1). The optimum pH of adsorption was found to be 5.0. The kinetics of adsorption was evaluated with 10 mg 1(-1) and 20 mg 1(-1) of As(V) solutions and activation energy of adsorption, as calculated from isoconversional method was in the range of 20 U mol(-1) to 43 U mol(-1). This suggests that the adsorption process is by diffusion at the initial phase and later through chemical control. FT-IR characterization of arsenic treated goethite indicated the presence of both As-O-Fe and As-O groups and supported the concept of surface complex formation. (c) 2005 Elsevier B.V. All rights reserved

Stability of copper smelter slag in sea water

The long-term stability of the slag in sea water is an essential requirement for its use in marine environment. Because no specific standards exist for studying the leachability of slag in sea water, its long-term stability was assessed through four types of indigenously designed extraction tests: (i) extraction tests on the slag similar to that specified in the multiple extraction procedure USEPA 1320, however, using sea water as the leachant; (ii) mechanical activation of the slag followed by extraction test using sea water as leachant; (iii) pressure leaching of the slag (at 1000 psi) in N2 and O2 for 4 h at different temperatures up to 120 degrees C; and (iv) mechanical activation of slag followed by pressure leaching of the slag in the temperature range of 40120 degrees C. In all these four tests, the leachability of the copper smelter slag was found to be higher in sea water compared to that in the Toxicity Characteristic Leaching Procedure medium and in acids. However, the highest concentration of all the relevant elements in the leachate was below the prescribed limits in USEPA method 1311. (C) 2010 American Institute of Chemical Engineers Environ Prog, 201

Adsorption studies of arsenic on Mn-substituted iron oxyhydroxide

: Mn-substituted iron oxyhydroxide (Mn0.13Fe0.87OOH) was prepared by the oxidation of ferrous carbonate precipitated from ferrous sulfate and sodium carbonate solutions. X-ray diffraction analysis led to the conclusion that the sample was basically iron manganese hydroxide with bixbyite structure. The sample exhibited a surface area of 101 m(2) g(-1) and a pore volume of 0.35 cm(3) g(-1). Batch experiments were conducted to study the adsorption of arsenite and arsenate species onto Mn-substituted iron oxyhydroxide (MIOH) and adsorption equilibrium time was evaluated. The temperature of adsorption was varied from 30 to 60 degrees C. The maximum uptake of arsenite and arsenate was found to be 4.58 and 5.72 mg g(-1), respectively. Zeta potential measurements and FT-IR spectral studies were also conducted to study the nature of adsorption. In both cases. adsorption was best described by Langmuir isotherm and activation energies as calculated from a model-free isoconversional method were found to be on the order of 15-24 and 45-67 kJ mol(-1) for arsenate and arsenite, respectively. (c) 2006 Elsevier Inc. All rights reserved

Removal of Cr (VI) by electrochemical reduction

Removal of Cr (VI) from aqueous solutions by electrochemical reduction was studied using steel rods connected in unipolar mode. An aqueous solution of potassium dichromate was used as the model contaminant. Three different supporting electrolytes, viz. NaCl, NaNO3 and Na2SO4 were used during electrolysis. Only NaCl was found to be effective to arrest the passivation of electrodes by Cr (VI). The effect of initial concentration of Cr (VI) and current density on chromium removal was investigated. The rate of conversion of Cr (VI) to chromite is fast at higher current densities and the sludge is contaminated with more iron oxide. X-ray diffraction studies have revealed the formation of chromite (FeCr2O4) as main product in the electrochemically precipitated sludge. Though chromite is a predominant species other products such as Cr2O3, Fe2O3 are also formed during the process. At low current densities the electrochemical reduction of Cr (VI) was found to be initially under current control and turns to diffusion control after certain time. (c) 2007 Elsevier B.V. All rights reserved

Studies on electrochemical detoxification of trichloroethene (TCE) on Ti/IrO2–Ta2O5 electrode from aqueous solution

Anodic oxidation of trichloroethene (TCE), a toxic chlorinated water contaminant, is carried out using Ti/IrO2–Ta2O5 electrode. The redox behaviour of TCE molecule, fouling of electrodes and generation of oxygen was studied by cyclic voltammetry. The studies on cyclic voltammetry reveals that the TCE oxidation takes place directly on electrode surface at the potential region above 0.3 V vs. SCE by direct electron transformation and oxygen evolution from anode. The effect of the electrolyte, pH of the aqueous medium and applied current density on the mineralization behaviour of TCE is also investigated. The degradation of TCE is monitored in terms of TOC and TCE concentration with electrolysis time and corresponding chloride evolution. The complete mineralization of TCE is achieved using Na2SO4 as supporting electrolyte. Conversely, the mineralization of the TCE molecule was observed to be poor because of the electrode fouling in the presence of NaNO3. The dechlorination of TCE is found to increase with electrolysis time and the complete dechlorination is observed at all Iappl studied. The kinetics of TCE degradation was found to follow pseudo-first order reaction whose rate constant was calculated to be 0.0081 cm s1 at Iappl value of 13.39 mA cm2. The performance of Ti/IrO2–Ta2O5 anode was proved to be better compared to Pt under similar experimental conditions