Removal of Cr(VI) from Aqueous Solutions Using Thermal Power Plant Gas Purification Waste (Reduction and Adsorption of Hexavalent Chromium), Interpretation of Mechanism: Disposal of Waste and Residues

Activated carbon impregnated by zero-valent iron nanoparticles (AC/nZVI) optimized for simultaneous adsorption and reduction of aqueous hexavalent chromium: Material characterizations and kinetic studies

Simultaneous adsorption and reduction of hexavalent chromium on biochar-supported nanoscale zero-valent iron (nZVI) in aqueous solution.

Cauliflower stem-derived biochar for effective adsorption and reduction of hexavalent chromium in synthetic wastewater: A sustainable approach

Mechanistic insights into adsorption and reduction of hexavalent chromium from water using magnetic biochar composite: Key roles of Fe3O4 and persistent free radicals

Ferrous disulfide and iron nitride sites on hydrochar to enhance synergistic adsorption and reduction of hexavalent chromium

Enhanced reduction and adsorption of hexavalent chromium by palladium and silicon rich biochar supported nanoscale zero-valent iron

Simultaneous adsorption and reduction of hexavalent chromium on the poly(4-vinyl pyridine) decorated magnetic chitosan biopolymer in aqueous solution

In the current work, we have reported a cationic surfactant-modified Ethiopian kaolin for improved adsorption of Cr(VI) from aqueous solution. The raw kaolin was modified by treating with CTAB to enhance the adsorption properties. The crystal structure and vibrational analysis of CTAB–kaolin were investigated by Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (p-XRD) techniques. The successful modification of kaolin by CTAB through intercalation and coating was investigated by XRD and FTIR. p-XRD confirms the raw kaolin obtained from Belesa, Tigo kebele is kaolinite mineral. The study has also focused on the application of kaolin–CTAB for adsorption of hexavalent chromium. The percent removal of Cr(VI) was investigated at different parameters such as pH, contact time, concentration of Cr(VI) and adsorbent dosage. CTAB–kaolin shows 99% removal of Cr(VI) at the adsorption equilibrium (time = 180 min, 100 mg CTAB–kaolin, 10 ppm/100 ml). The Langmuir and Freundlich isotherm models were used to investigate the adsorption process of chromium onto kaolin–CTAB composites. The equilibrium data obeyed Langmuir model than Freundlich, which shows that the adsorption process proceeds through monolayer adsorption and maximum adsorption capacity was found to be Qo = 22.72 mg/g. The pseudo-second-order kinetics model is found to be well fitted than Pseudo-first-order kinetics, which implies that the adsorption mechanism more favors electrostatic interaction between chromium and kaolin–CTAB composites. In conclusion, CTAB–kaolin was found to be a promising adsorbent for the efficient removal of Cr(VI) from the aqueous solution.

The uptake and reduction of Cr(VI) by Aspergillus niger and A. parasiticus was studied. After 96 hours of growth, the culture solutions spiked with an initial dichromate concentration of 20 mg/l, were completely decolorized and had residual Cr(VI) concentrations of only 0.74 ± 0.55 and 1.69 ± 0.29 mg/l in A. niger and A. parasiticus cultures representing Cr(VI) removal of 96.3% and 91.6%, respectively. In the A. niger culture, significantly (P < 0.01) lower Cr(VI) concentrations were observed within 72 hours of growth compared to those of A. parasiticus, but in both cultures complete removal was almost achieved by 144 hours of growth. The rate of Cr(VI) removal was 0.21 ± 0.09 mgl-1hr-1 and 0.20 ± 0.07 mgl-1hr-1 for A. niger and A. parasiticus, respectively. Cellular concentrations of Cr(VI) in the two fungi increased significantly (P < 0.05 – 0.001) with increasing concentrations of the dichromate treatments. Although tannic acid as sole source of carbon and energy gave significantly lower Cr(VI) removal than glucose (P < 0.001) and acetate (P < 0.01), it supported the removal of about 85.0% and 68.8% of the metal ion by A. niger and A. parasiticus, respectively. The active mycelia of both fungi showed significantly (P < 0.001) higher Cr(VI) removal than inactivated mycelia after incubation at 30°C for 72 hours. Incubation of cell – free extracts of both fungi with NADH at 30°C for 2 hours showed Cr(VI) reduction of 68.0% and 55.5% for A. niger and A. parasiticus, respectively. These findings suggest that uptake and metabolic reduction may be the process by which the two fungi are able to tolerate the toxic effects of hexavalent chromium. However, Cr removal via uptake by the two fungal biomass was observed to be in the range of 0.5 – 1.78% only, for all the concentrations applied, which is insignificant when compared with the initial Cr concentration in the culture medium. The results obtained through this investigation indicate the possibility of treating waste effluents containing hexavalent chromium using Aspergillus niger and A. parasiticus.

Adsorption of hexavalent chromium from aqueous solutions by bio-chars obtained during biomass pyrolysis

This study evaluated the performance of a new activated carbon (CCs-AC) produced from corn cobs by boric acid activation for the effective removal of hexavalent chromium, a heavy metal with high potential to pollute the environment, from wastewater. For this purpose, with the help of parameters such as solution pH, contact time, initial Cr(VI) concentration, CCs-AC dose, desorption and temperature, the removal of Cr(VI) ions from aqueous solution by adsorption on CCs-AC was investigated from equilibrium, kinetic and thermodynamic point of view. As a result of the experiments, it was determined that the optimum solution pH was 2.0, the contact time was 4 hours, and the desorption solution was 3.0 M NaOH. From the kinetic data, it was determined that the adsorption was compatible with the pseudo-second order kinetic model and the maximum Cr(VI) adsorption capacity (123.7 mg/g) obtained from the Langmuir isotherm model showed that CCs-AC was of competitive quality with the literature. From the thermodynamic data, the positive ΔH value indicates that the adsorption is endothermic and the value of 12.00 kj/mol indicates that the adsorption is rather chemically driven. The negative ΔG value indicates that the process proceeds spontaneously with an increase in temperature, while the ΔS value indicates an increase in the amount of unused energy.

Effect of acid modification on adsorption of hexavalent chromium (Cr(VI)) from aqueous solution by activated carbon and carbon nanotubes

The influence of pH, co-existing ions, ionic strength, and temperature on the adsorption and reduction of hexavalent chromium by undissolved humic acid

Synergistic adsorption and reduction of hexavalent chromium using highly uniform polyaniline–magnetic mesoporous silica composite

Enhanced adsorption of hexavalent chromium from aqueous solutions on facilely synthesized mesoporous iron–zirconium bimetal oxide