Chromium Sorption Capacity Research Articles

Nanoscale Zero-Valent Iron and Chitosan Functionalized Eichhornia crassipes Biochar for Efficient Hexavalent Chromium Removal.

Sorption is widely used for the removal of toxic heavy metals such as hexavalent chromium (Cr(VI)) from aqueous solutions. Green sorbents prepared from biomass are attractive, because they leverage the value of waste biomass and reduce the overall cost of water treatment. In this study, we fabricated biochar (BC) adsorbent from the biomass of water hyacinth (Eichhornia crassipes), an invasive species in many river channels. Pristine BC was further modified with nanoscale zero-valent iron (nZVI) and stabilized with chitosan (C) to form C–nZVI–BC. C–nZVI–BC adsorbent showed high hexavalent chromium sorption capacity (82.2 mg/g) at pH 2 and removed 97.34% of 50 mg/L Cr(VI) from aqueous solutions. The sorption capacity of chitosan–nZVI-modified biochar decreased while increasing the solution pH value and ionic strength. The results of a sorption test indicated that multiple mechanisms accounted for Cr(VI) removal by C–nZVI–BC, including complexation, precipitation, electrostatic interactions, and reduction. Our study suggests a way of adding value to biomass waste by considering environmental treatment purposes.

Enhanced Chromium Sorption and Quick Separation of Magnetic Hydrotalcite Anchored Biopolymeric Composites Using the Hydrothermal Method

The magnetic hydrotalcite supported biopolymeric composites were synthesized by hydrothermal (Hydro) and in situ precipitation (in situ) methods for selective chromium removal. A comparative evaluation of chromium sorption capacity (SC) of both hydrothermal and in situ synthesized magnetic biocomposites namely Fe3O4@alginate/hydrotalcite (Fe3O4@AlgHT) composite, Fe3O4@chitosan/hydrotalcite (Fe3O4@CSHT) composite, and Fe3O4@gelatin/hydrotalcite (Fe3O4@GelHT) composite was carried out. The hydrothermally synthesized magnetic biocomposites demonstrated greater chromium SC than in situ method. The synthesized materials were characterized by Fourier transform infrared spectrometer, X-ray diffraction, Brunauer–Emmett–Teller, ultraviolet–visible spectrophotometer, vibrating sample magnetometer, transmission electron microscope, scanning electron microscope, and energy dispersive X-ray analysis. The equilibrium data of the synthesized magnetic biocomposites were explained by Langmuir, Freundlich, and Dubinin–Radushkevich (D-R) isotherms. The thermodynamic result shows that the nature of chromium sorption onto the magnetic biocomposites is spontaneous and endothermic. The kinetic models suggested that the chromium sorption behavior follow pseudo-second-order and intraparticle diffusion models. The chromium sorbed magnetic biocomposites can be easily regenerated using NaOH and can be effectively used up to five cycles. The suitability of the magnetic biocomposites at field conditions was inspected by field water sample.

One pot synthesis of metal ion anchored alginate–gelatin binary biocomposite for efficient Cr(VI) removal

Biopolymers are widely used for the removal of chromium from aqueous medium but it possesses limitations like poor sorption capacity and low stability. To overcome the limitations of biopolymers and to improve their properties, the present study was designed in such a way to develop a novel sorbent with enhanced chromium sorption capacity and better stability by synthesizing metal ion cross-linked binary biocomposites using biopolymers like alginate and gelatin cross-linked with Ca2+, Ce3+ and Zr4+ ions namely Ca@AlgGel, Ce@AlgGel and Zr@AlgGel composites. The functional groups, agglomeration, surface area, surface morphology, elemental analysis and thermal stability of the composites were investigated by FTIR, TEM, BET, SEM with EDAX and TGA analysis. The chromium removal studies of the biocomposites were carried out in batch mode. The sorption process was optimized by varying the influencing aspects like contact time, dosage, presence of common ions, pH, initial chromium concentration and temperature. The maximum sorption capacity of Ca@AlgGel, Ce@AlgGel and Zr@AlgGel composites were found to be 19.40, 24.50 and 25.40mg/g, respectively. The sorption data was fitted by using Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. Thermodynamic parameters indicate the nature of chromium sorption. The suitability of the composite materials was also tested under the field conditions.

Effects of phosphorus concentration on Cr(VI) sorption onto phosphorus-rich sludge biochar

To investigate effects of phosphorus content on Cr(VI) sorption onto phosphorus-rich biochar, sewage sludge of different phosphorus concentrations from 4 to 60 mg·g−1 by dry weight were prepared and carbonized to make biochar for batch sorption experiments. Test results revealed that different phosphorous concentration of raw sludge had respective impacts on surface area, pore surface area, average pore diameter and pH value of derived biochar. The adsorption kinetics of phosphorus-rich biochar could be described by the pseudo-second-order model. The sorption isotherm data followed Langmiur model better than Freundlich model. Biochar produced from sludge with phosphorus concentration of 20 mg·g−1 gave the largest chromium sorption capacity, which could be attributed to its largest surface area and pores surface area comparing with those of biochars from sludge with other phosphorus concentrations. The chromium loaded biochar was analyzed using Fourier Transform Infrared Spectroscopy and X-ray Diffraction measurement. The results indicated that chemical functional groups hydroxyl and methyl on surface of biochar were involved in Cr(VI) binding and its reducing to Cr(III). Then, a portion of Cr (III) in form of various phosphate precipitates was bound onto biochar surface and the rest was released into the solution. The experimental results suggested that phosphorus played an important role in pore and surface area development of sludge biochar during pyrolytic process. It also could react with Cr(III) on the biochar surface that impacted on capacity of Cr(VI) removal from solution by sludge biochar. Therefore, phosphorus concentration in sludge should be considered when sludge pyrolytic residue would be reused for heavy metals sorbing.

An assessment and characterization for biosorption efficiency of natural dye waste

The local natural dyeing house run by a women’s self-help group was generating a huge amount of dye extracted pulp. We thought of using this pulp for an alternative use other than just composting it. This biomaterial was found to be excellent heavy metal adsorbents and was demonstrated to be very effective in remediation of groundwater and surface water of chrome metals in contaminated sites of tannery operations. In this article, sorption efficacy studies were carried out on selected biomaterials known for their potential usage as natural dyes. Canna indica flower, Portulaca olecera flower and stem, Hibiscus rosa sinensis flower and Trapa natans fruit skin (exocarp) were used for sorption studies. These plant parts, after the extraction of natural dye, were dried and evaluated for biosorption of heavy metal from effluent. Batch tests indicated that hexavalent chromium sorption capacity (qe) followed the sequence qe(Trapa) >qe(Hibiscus) >qe(Portulaca) >qe(Canna). Due to high sorptive capacity, Trapa fruit skin (exocarp) was selected. The optimization studies were carried out by taking the Trapa exocarp in powdered form, and of particular mesh size. Sorption kinetic data have shown first order reversible kinetic model for all the sorbents, however the biosorption of chromium by T. natans biomass occurred in two stages. In the first stage, 95% sorption was reported for Chromium (VI) in 15 min followed by a slower second stage. It reached equilibrium in 1 h at which 90–98% of the Chromium (VI) was biosorbed by T. natans. Experimentally reported equilibrium data fitted well with both the Langmuir and Freundlich Isotherms. The FT-IR, XRD and XPS analysis showed that the main mechanism of Chromium (VI) biosorption onto Trapa dried powder was through the binding of Chromium ions with amide group of the biomass.

Treatment of chromium‐bearing wastewaters with constructed wetlands

AbstractChromium can have detrimental effects on most organisms, including humans. The present study focused on the effect of treating chromium‐bearing, organic‐rich wastewater on constructed wetland performance. Eight laboratory‐scale systems were used to study organic matter and chromium removals, with three features tested in duplicate: media with proven chromium sorption capacity, vegetation presence and intermittent influent loading. A set of two wetlands acted as the base design. Average BOD5 and chromium removal rates were 13.4 g/m2 day and 135 mg Cr/m2 day, respectively. From an influent chromium concentration of 5 mg/L, <0.5 mg/L could be detected at the outlet during the study in all systems. Chromium removal efficiencies were statistically different for all systems (P<0.01), except when comparing the base design against the intermittent feed systems (P>0.05). Overall treatment performance of all systems was remarkably good in spite of significant chromium content and salinity.

Sorption studies of chromium(VI) onto new ion exchanger with tertiary amine, quaternary ammonium and ketone groups

A new acrylic anion exchanger with both tertiary and quaternary ammonium as well as ketone groups in the structural unit has been prepared by the nucleophilic substitution reaction of aminolyzed vinylacetate:acrylonitrile:divinylbenzene copolymer of porosity structure in the swelling state with 2-chloroacetone as a halogenated compound. The new compound exhibits better qualities of strong base exchange capacity than the weak base anion exchangers. The obtained acrylic anion exchanger was used to remove Cr(VI) from the aqueous solution. Batch adsorption studies have been carried out to determine the effect of contact time, concentration of hexavalent chromium in the solution and pH on the sorption capacity. The kinetic parameters were determined on the basis of the static results. The thermodynamic parameters of Cr(VI) sorption process on the anion exchanger were calculated based on the Langmuir and Freundlich isotherms. Sorption was studied in the pH range of 1.5–7 and it was found that it depends on the solution acidity. At the pH values of 3.5 and 7 the anion exchanger exhibited large values of chromium sorption capacity. The speciation of chromium was investigated in the studied pH range by the Diffuse Reflectance Spectroscopy (DRS) method. Reduction of chromium(VI) to chromium(III) under acidic conditions was observed. The performed acrylic strong base anion exchanger is superior compared to the conventional one based on the styrene:divinylbenzene matrix due to its ability for reposition of the long spacer arm for providing exchange sites, hydrophilic character of matrix, and possible hydrogen bonds provided by carbonyl functional groups.

Preparation and application of alumina/chitosan biocomposite

A new chitosan based biocomposite was prepared using alumina and used for the removal of chromium from the aqueous solution. The synthesized alumina/chitosan (AlCs) composite possesses an enhanced chromium sorption capacity (SC) of 8.62 mg/g than the original alumina and chitosan flakes that possess the SCs of 3.7 and 0.67 mg/g respectively, with a minimum contact period of 30 min. The sorption experiments were carried out in batch mode to optimize various parameters viz., contact time, initial chromium concentration, pH, co-ions and temperature that influence the sorption. The sorbents were characterized by FTIR, AFM, BET and SEM with EDAX analysis. The composite removes chromium by means of electrostatic adsorption coupled reduction and complexation. The adsorption data were fitted with Freundlich, Langmuir and Dubinin–Radushkevich (D-R) isotherms. The calculated values of thermodynamic parameters indicate the nature of chromium sorption. The dynamic studies demonstrate that the sorption process follows pseudo-second-order and intraparticle diffusion models.

Selective recovery of Cr and Cu in leachate from chromated copper arsenate treated wood using chelating and acidic ion exchange resins

The purpose of this study was to selectively remove chromium and copper from CCA-treated wood acid leachates (initial concentrations of 447–651 mg As l −1, 374–453 mg Cu l −1 and 335–622 mg Cr l −1) using ion exchange resins and precipitation techniques. Batch experiments revealed that the chelating resin Dowex M4195 had a high copper selectivity in the presence of chromium while the Amberlite IR120 resin had a high chromium sorption capacity. Combining M4195 and IR120 resins in four successive columns, made with Plexiglas tube, led to 96% copper extraction and 68% chromium extraction. NH 4OH (4 M) efficiently eluted copper from the chelating resin while H 2SO 4 (10% v/v) was used for IR120 resin elution. Copper and chromium recovery by elution reached 94% and 81%, respectively. Successive sorption and elution steps using M4195 and IR120 ion exchange resins presented similar metal removal capacities over the five cycles. No resin deterioration was observed but the results suggested arsenic bulk diffusion into the M4195 resin. Successive treatments of CCA-treated wood leachate with M4195 and IR120 allowed for copper and chromium removal while arsenic could be extracted by coagulation treatment with ferric chloride and precipitation with Ca(OH) 2 at pH 5.7. This final process led to 99.9% arsenic removal. The final effluent contained less than 1 mg l −1 of arsenic, chromium and copper.

Biosorption of aqueous chromium(VI) by Tamarindus indica seeds

The effectiveness of low cost agro-based materials namely, Tamarindus indica seed (TS), crushed coconut shell (CS), almond shell (AS), ground nut shell (GS) and walnut shell (WS) were evaluated for Cr(VI) removal. Batch test indicated that hexavalent chromium sorption capacity ( q e) followed the sequence q e(TS) > q e(WS) > q e(AS) > q e(GS) > q e(CS). Due to high sorptive capacity, tamarind seed was selected for detailed sorption studies. Sorption kinetic data followed first order reversible kinetic fit model for all the sorbents. The equilibrium conditions were achieved within 150 min under the mixing conditions employed. Sorption equilibria exhibited better fit to Freundlich isotherms ( R > 0.92) than Langmuir isotherm ( R ≈ 0.87). Hexavalent chromium sorption by TS decreased with increase in pH, and slightly reduced with increase in ionic strength. Cr(VI) removal by TS seems to be mainly by chemisorption. Desorption of Cr(VI) from Cr(VI) laden TS was quite less by distilled water and HCl. Whereas with NaOH, maximum desorption achieved was about 15.3%. When TS was used in downflow column mode, Cr(VI) removal was quite good but head loss increased as the run progressed and was stopped after 200 h.

Chromium Adsorption by Chitosan Impregnated with Microemulsion

Removal of chromium(III) from aqueous solutions by chitosan impregnated with a microemulsion was investigated. The modified chitosan showed a remarkable increase in chromium sorption capacity as compared to an untreated sample. Dynamic column experiments were performed to study the influence of pH, concentration, and the presence of others metal ions (copper and nickel) in the chromium solutions. The adsorption process is pH-dependent, and the amount of Cr(III) retained increases with increasing heavy metal initial concentration. It can be observed that the best bed efficiency was for copper, followed by chromium and then nickel. The nature of chromium(III) adsorption equilibrium at different temperatures (30, 40, and 50 °C) was investigated, and the Freundlich and Langmuir isotherm models were applied to fit the experimental data. The uptake process obeys the Langmuir isotherm. Following the adsorption step, the desorption process was carried out using several eluant solutions. The best results were obta...

Removal of chromium from aqueous solutions by diatomite treated with microemulsion

In order to evaluate the sorption of heavy metals, a crude diatomite was impregnated with a microemulsion which showed remarkable increase in chromium sorption capacity as compared to untreated diatomite. Samples with two different granulometries were investigated, both yielding practically complete adsorption. The adsorption process is pH dependent and the best results for the initial Cr (III) concentration of 1.5 g/L were obtained at pH 2.95. The effect of the concentration of the chromium synthetic solution was also investigated. The adsorption isotherms were obtained (30, 40 and 50°C) and the Freundlich and Langmuir models were used to determine the adsorption capacity of the adsorbent. Following the adsorption step, a desorption process was carried out using several eluant solutions. The best results were obtained using hydrochloric acid (100%) as eluant.

Chromium removal in tannery wastewaters “polishing” by Pinus sylvestris bark

The possibility of using ground, dried and classified Pinus sylvestris bark for trivalent chromium removal in tannery wastewater “polishing” was studied. Tests were carried out with synthesized solutions whose chromium concentrations (5 and 20 mg/l) were similar to those found in some effluents of Portuguese tannery industries after physico-chemical treatment. Bark concentrations of 1 and 2 g/l were used (higher concentrations would have no practical value) and chromium removals ⩾ 90% were achieved in a 4.5–5.0 pH range. Agitation was accomplished by means of both air bubbling and vibrating plate. Slight differences occurred. Bark wetting was achieved either by simple bark/solution contact or vacuum application. No marked differences were observed. From an industrial point of view air bubbling agitation and simple bark/solution contact certainly look more interesting. The presence of other ions decreased the chromium removal though this decrease was never greater than about 20%. Pretreatments of bark were carried out and, in some cases, an increase of about 6–11% in the chromium sorption capacity of bark was observed.