Efficient Removal Of Hexavalent Chromium Research Articles

Efficient Solar-Powered Bioremediation of Hexavalent Chromium in Contaminated Waters by Chlorella sp. MQ-1

Microalgae are known for their efficient removal of hexavalent chromium (Cr(VI)) through biosorption and bioaccumulation, yet the subsequent release of Cr(VI) upon cell death remains a challenge. The reduction of Cr(VI) to the less toxic trivalent chromium [Cr(III)] is another critical remediation strategy that mitigates the risk of Cr(VI) re-release, but research on microalgal reduction of Cr(VI) is scarce. In this study, a microalgal strain designated as MQ-1 was isolated from chromium-contaminated mine effluent, demonstrating the capability to tolerate and remove Cr(VI). Phylogenetic analysis revealed that MQ-1 is closely related to the genus Chlorella; hence, it is classified as Chlorella sp. MQ-1. This strain exhibited robust growth at Cr(VI) concentrations below 2 mg/L, achieving a removal rate higher than 82% for initial Cr(VI) concentrations between 0.5 and 1 mg/L after a 5-day incubation period. Mechanistic studies revealed that MQ-1 promoted the removal of Cr(VI) mainly through intracellular bioreduction and bioaccumulation processes, in which more than 60% of Cr(VI) was reduced to the less toxic Cr(III) and stocked in the cells. A two-stage cultivation strategy, involving initial biomass accumulation followed by Cr(VI) treatment, significantly enhanced the removal efficiency, which was further accelerated under illuminated conditions. Notably, MQ-1 cultures with initial OD680 values of 4 and 6 accomplished 84.28% and 91.31% Cr(VI) removal from 2 mg/L solutions, respectively, within 30 hours under light exposure. These findings highlight the potential of MQ-1 to utilize renewable solar energy to reduce Cr(VI) and to mitigate the risk of its re-release into the environment. This characteristic positions MQ-1 as a potentially sustainable and cost-effective solution for Cr(VI) remediation and suggests its significant potential for large-scale implementation in bioremediation strategies aimed at Cr(VI)-contaminated waters.

Efficient removal of hexavalent chromium from wastewater using a novel sodium alginate-biochar composite adsorbent

Discharging hexavalent chromium (Cr(VI))-containing wastewater has become a critical environmental and ecological concern. Coffee grounds biochar (CGB), rich in oxygen-containing functional groups, can reduce Cr(VI) to the less toxic trivalent chromium (Cr(III)) without secondary contamination. This study developed a composite adsorbent by incorporating sodium alginate (SA) into CGB, exploiting their synergistic adsorption and ion exchange reduction effects for efficient Cr(VI) removal. The maximum adsorption capacity of SACGB, fitted by the Langmuir isotherm model, was 30.66 ± 1.89 mg/g. Under optimal conditions (pH = 2, SA: CGB mass ratio = 3:2, Cr(VI) concentration = 50 mg/L), SACGB achieved 99.79 % Cr(VI) removal from synthetic wastewater. Significant Cr(VI) reduction to Cr(III) (58.97 % removal) occurred at an SA:CGB ratio of 1:1. The adsorption mechanism involved hydrogen bonding, electrostatic interactions, and ion exchange reduction. Removal of Cr(VI) retained 93 % removal despite interference from coexisting Cu(II), Zn(II), and Ni(II) ions, and the ions promoted Cr(VI) adsorption onto SACGB. In actual wastewater, SACGB exhibited excellent Cr(VI) removal (99.26 %), meeting the Chinese industrial effluent discharge standard (0.2 mg/L). After 6 recycling cycles, SACGB demonstrated stable removal performance and contained no biotoxic components. The cost of preparation and adsorption process was analyzed and also compared with earlier studies to evaluate and highlight the economic feasibility of the adsorbent for a truly green removal method. This study highlights SACGB as an economical and efficient adsorbent with practical application potential for Cr(VI) removal from industrial wastewater.

Efficient removal of hexavalent chromium from aqueous solutions by lanthanum crosslinked chitosan/polypyrrole composite

In this work, in order to improve the adsorption capacity of chitosan for Cr(VI), a chitosan-based composite co-modified with lanthanum and polypyrrole (CS-La-PPy) was prepared and its effectiveness in removing Cr(VI) from aqueous solution was investigated. CS-La-PPy was characterized by FT-IR, XRD, BET, SEM, EDS and XPS. The successful synthesis of CS-La-PPy was confirmed by the presence of C=C (pyrrole ring) and La-O in the FT-IR spectrum. The effects of different adsorbent materials, dosage, initial pH, coexisting ions, adsorption time and temperature on the removal of Cr(VI) were investigated by batch experiments. The removal efficiency of 50 mL Cr(VI) with concentration of 150 mg L−1 by CS-La-PPy is 95.28 % at pH=2.0, T = 298 K. The adsorption process is spontaneous, which is consistent with pseudo-second-order kinetic model and Freundlich adsorption isotherm model. The maximum adsorption capacity is 321.96 mg g−1. XPS analysis showed that the removal mechanism of Cr(VI) by CS-La-PPy was mainly based on the electrostatic adsorption between Cr(VI) and lanthanum, -NH2+, and -NH3+, the ion exchange between Cr(VI) and Cl−, the reduction of Cr(VI) to Cr(III) by PPy0 and -OH groups, and the complexation between Cr(III) ions and COO- groups. This work provides a reference for the design and preparation of efficient chitosan-based adsorption materials.

Preparation of a cationic hydrogel microsphere adsorbent for efficient removal of hexavalent chromium from aqueous solution

AbstractHerein, a cationic hydrogel microsphere (CHMS) was prepared by inverse suspension polymerization and freeze‐drying and was applied to the adsorptive removal of hexavalent chromium (Cr(VI)) from aqueous solution. Morphological characterization shows that there are lots of folds and pores on the surface of CHMS with a unique petal‐like appearance. According to the chemical structure analysis, CHMS contains plenty of functional groups such as amine and hydroxyl groups. These features give CHMS a larger specific surface area, faster adsorption rate, and higher adsorption capacity than the conventional cationic hydrogel microparticle (CHMP) adsorbent. The adsorption of Cr(VI) in water by CHMS is mainly based on the combination of electrostatic adsorption and redox reaction, with the electrostatic interaction between the protonated amine and Cr(VI) serving as the predominant adsorption mechanism. Experimental results reveal that CHMS can efficiently remove Cr(VI) from simulated wastewater in both batch and continuous adsorption modes, which is primarily due to its distinctive surface morphology and rich functional groups. Furthermore, the common coexisting metal ions in Cr(VI)‐containing wastewater have no substantial negative influence on the adsorption. Therefore, it can be concluded that CHMS has a promising application prospect in the treatment of Cr(VI)‐containing wastewater.

Activated sodium bentonite as an adsorbent for efficient removal of hexavalent chromium: Statistical optimization using Box–Behnken design

AbstractAt present, developing countries, including Ethiopia, are undergoing a phase of industrial transformation. As a result, there has been a significant rise in the presence of harmful pollutants in groundwater. The release of deleterious heavy metals, such as Cr (VI), into the surrounding ecosystem is a result of various industrial operations. The present investigation utilized activated sodium bentonite clay as an adsorbent agent to facilitate the elimination of Cr (VI). The clay was subjected to acidification and thermal modification techniques to enhance its adsorption capacity. The investigation involved an examination of the particular surface area, capacity for cation exchange, crystalline properties, functional groups on the surface, and structural morphology. The methylene blue test method was employed to ascertain the maximum specific surface area and cation exchange capacity of the adsorbent, which were found to be 512 m2/g and 65.5 meq/100 g, respectively. The clay mineral composition was analyzed using X‐ray diffraction, which indicated that the primary constituent was montmorillonite. The presence of impurities such as quartz, feldspar, muscovite, cristobalite, and hematite was also detected. The study employed response surface methodology, Box–Benkhen design (RSM‐BBD) to investigate the impact of operational parameters, including agitation time, initial Cr (VI) concentration, and adsorbent dosage. Under the optimal conditions, a removal efficiency of 98.05% was achieved for Cr (VI) for a contact duration of 120 min, a dosage of 3.913 g/L, and an initial concentration of 50 mg/L. The sodium bentonite clay that was activated demonstrated a maximum capacity for adsorption of 22.72 mg/g in regards to the adsorption of Cr (VI). The experimental data were best fitted by the Langmuir isotherm, which exhibited a correlation coefficient of 0.9699. The adsorption kinetics were assessed and determined to adhere to a pseudo‐second‐order pattern, exhibiting a coefficient of determination (R2) value of 0.999. Furthermore, the activated sodium bentonite clay demonstrated remarkable potential for repeated utilization in the adsorption of Cr (VI) ions in aqueous solutions.

Effect of the electrode geometry on the performance of a batch electrochemical reactor used for Cr(VI) removal

The efficient removal of hexavalent chromium from aqueous media is a problem that has found a solution by electrochemical methods. In this work, the effect of electrode geometry on the performance of a stirred tank electrochemical reactor designed for this purpose is evaluated. Two electrode configurations are evaluated: static rings (SR) and electro baffles (EB). The electrodes installed in the batch reactor are static, so the stirring is done with a system of two impellers, whose distance between them is also a variable studied. Five cases are assessed. The evaluation of the cases contemplates experimental tests of Cr(VI) reduction to know its effect on the reaction rate and energy consumption. Computational fluid dynamics analysis is also performed to assess the hydrodynamic environment inside the reactor and relate it to experimental performance. The results show that the electrode geometry affects the Cr(VI) reduction rate as it promotes the process to be controlled by mass transfer. The hydrodynamic analysis shows that the process requires two aspects: an efficient circulation of the fluid inside the tank and homogeneous flow conditions in the vicinity of the electrode surface.

The Ce-Fe loaded biochar for efficient removal of hexavalent chromium: Broad pH adaptation and mechanisms

The adsorption as a convenient, effective and economical method has been widely used for the removal of highly toxic Cr(VI) from aqueous solution in recent years. However, the adsorption for Cr(VI) was usually more effective under acidic conditions and less effective in neutral and alkaline environments, and there are few studies on the response sequence of the functional groups on the biochar participating in the Cr(VI) removal process. The biochar CeFe-SPBC prepared in this work not only showed a great removal efficiency (85.7%) for Cr(VI) at pH= 3, but also exhibited a removal efficiency close to 70% for Cr(VI) at pH= 9, which reflected that the CeFe-SPBC had an excellent adaptability to changes in pH. The characterization results displayed the large specific surface area (296 m2/g) and various functional groups as well as metal oxides of CeFe-SPBC. And, the response sequence of the main functional groups was identified as follows: Ce-O > Fe-O > aromatic CC > C-OH > -COO-. On this basis, the adsorption-enhanced reduction-immobilization mechanisms of Cr(VI) on the surface of the CeFe-SPBC were discussed in detail.

Efficient removal of hexavalent chromium by nano-cerium-based adsorbent: The critical role of valence state and oxygen vacancy

Cerium-based adsorbents have been gradually used for the adsorption removal of highly toxic Cr(VI) from wastewater due to their low toxicity and wide working pH. However, the intrinsic properties of adsorbents contribute significantly to their adsorption performance, and the relationship between them needs to be clarified. Herein, series of nano-cerium based adsorbents (Ce@Cs) with different surface defects and Ce(III) content were prepared to explore their effects on the Cr(VI) adsorption capacity. Results showed that the optimal Ce@C performed well over a wide pH range of 2.0–12.0, and the calculated Cr(VI) adsorption capacity reached 302.43 mg/g at 45 ℃. Ce(III) and surface defects in cerium-based adsorbents exhibited an important influence on the Cr(VI) adsorption performance of Ce@Cs, and their contents showed a good positive correlation with the Cr adsorption capacity (R2 =0.988 and 0.827). A series of evidences confirmed that the generated Ce(III) and oxygen vacancies could provide more sufficient coordination number to promote Cr(VI) complexation with Ce@Cs and lower the impedance of Ce@Cs to improve the reduction of Cr(VI) to low-toxic Cr(III). This work provides new insights into the Cr(VI) adsorption using cerium-based adsorbents, which helps to improve their potential in the purification of Cr(VI)-containing wastewater.

Green synthesis of lignin-directed palladium nanoparticles/UiO-66-NH2 paper-based composite catalyst for synergistic adsorption-catalysis removal of hexavalent chromium

A combination of multiple methods can greatly intensify the removal efficiency of hazardous substances. Herein, the synergistic utilization of adsorption and catalysis achieved for the highly efficient removal of hexavalent chromium (Cr6+). A paper-based palladium nanoparticles/UiO-66-NH2 (PdNPs/UiO-66-NH2/LP) composite catalyst was prepared using lignocellulose paper-based material (LP) for the loading of UiO-66-NH2 MOFs materials, with the lignin in LP as the reducer for the in-situ synthesis of PdNPs (12.3 nm) on UiO-66-NH2 MOF materials. Lignocellulose paper-based materials with high strength (82 N·m/g) realized low-cost and environmentally friendly preparation and guaranteed the practicability of PdNPs/UiO-66-NH2/LP composite catalyst. The prepared PdNPs/UiO-66-NH2/LP achieved high-efficiency catalytic activity for hazardous Cr6+ removal through a constructed adsorption-catalytic synergistic system, in which the removal efficiency of Cr6+ in 10 min was increased by 2 times compared with a composite catalyst without MOFs loading. Finally, the PdNPs/UiO-66-NH2/LP composite catalyst demonstrated the great efficiency and practicality of water pollution treatment through synergistic adsorption enrichment and catalytic reduction.

Efficient removal of hexavalent chromium (Cr(VI)) from wastewater using FeCl3-modified Chlorella-based biochar

Efficient removal of hexavalent chromium (Cr(VI)) from wastewater using FeCl3-modified Chlorella-based biochar

Protonated-amino-functionalized bamboo hydrochar for efficient removal of hexavalent chromium and methyl orange

Hydrochar has great potential for wastewater treatment and the functional modification can significantly improve the ability of hydrochar to remove pollutants. Herein, a novel protonated amino-modified bamboo hydrochar (PAHC) was synthesized by the reaction of bamboo hydrochar first with acryloyl chloride, then with amine and finally with hydrochloric acid, and employed to adsorb methyl orange (MO) and Cr(VI). The PAHC was observed by BET, SEM-EDX, FTIR, elemental analysis, and zeta potential to monitor its textural properties before and after adsorption. The amino groups were effectively grafted onto the hydrochar by the Aza-Michael addition reaction through characterization. Adsorption results showed the PAHC possessed high MO/Cr(VI) adsorption amounts (515.35/523.57 ​mg ​g−1 ​at 298 ​K) because the introduction of protonated amine was pivotal in eliminating anionic pollutants by electrostatic interaction. The Langmuir/Freundlich model can well describe MO/Cr(VI) adsorption, which proves the removal process belongs to MO monolayer/Cr(VI) multilayer adsorption. The PAHC also exhibited a good regeneration performance. These results indicate the PAHC is a green and efficient adsorbent with potential application in wastewater treatment.

Facile elaboration of arginine-functionalized PANI@graphitic carbon nitride for efficient removal of hexavalent chromium

Facile elaboration of arginine-functionalized PANI@graphitic carbon nitride for efficient removal of hexavalent chromium

Efficient removal of hexavalent chromium from water by Bacillus sp. Y2-7 with production of extracellular polymeric substances

ABSTRACT Bioremediation is an environmentally friendly technology for the treatment of chromium-contaminated sites. Here, a hexavalent chromium [Cr(VI)]-resistant strain was isolated from oil-contaminated soil and designated as Bacillus sp. Y2-7 based on 16S rDNA sequence characterization. The effects of various factors including inoculation dose, pH value, glucose concentration, and temperature on Cr(VI) removal rates were then evaluated. Based on the response surface methodology, optimal Cr(VI) removal efficiency (above 90%) could be achieved at an initial Cr(VI) concentration of 155.0 mg·L−1, glucose concentration of 11.479 g·L−1, and pH of 7.1. The potential removal mechanisms of Cr(VI) by strain Y2-7 were also supposed. The contents of polysaccharide and protein in extracellular polymer (EPS) of strain Y2-7 decreased slowly after cultured with Cr(VI) of 15 mg·L−1 from 1 to 7 days. We thus inferred that EPS bonded with Cr(VI) and underwent morphological changes in water. Molecular operating environment (MOE) analysis suggested that macromolecular protein complexes in Bacillus sp. Y2-7 and hexavalent chromium could establish hydrogen bonds. Collectively, our findings indicate that Bacillus sp. Y2-7 is an excellent bacterial candidate for chromium bioremediation.

Asymmetric Alternative Current Electrochemical Method Coupled with Amidoxime-Functionalized Carbon Felt Electrode for Fast and Efficient Removal of Hexavalent Chromium from Wastewater

A large amount of Cr (VI)-polluted wastewater produced in electroplating, dyeing and tanning industries seriously threatens water ecological security and human health. Due to the lack of high-performance electrodes and the coulomb repulsion between hexavalent chromium anion and cathode, the traditional DC-mediated electrochemical remediation technology possesses low Cr (VI) removal efficiency. Herein, by modifying commercial carbon felt (O-CF) with amidoxime groups, amidoxime-functionalized carbon felt electrodes (Ami-CF) with high adsorption affinity for Cr (VI) were prepared. Based on Ami-CF, an electrochemical flow-through system powered by asymmetric AC was constructed. The mechanism and influencing factors of efficient removal of Cr (VI) contaminated wastewater by an asymmetric AC electrochemical method coupling Ami-CF were studied. Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) characterization results showed that Ami-CF was successfully and uniformly loaded with amidoxime functional groups, and the adsorption capacity of Cr (VI) was more than 100 times higher than that of O-CF. In particular, the Coulomb repulsion effect and the side reaction of electrolytic water splitting were inhibited by the high-frequency anode and cathode switching (asymmetric AC), the mass transfer rate of Cr (VI) from electrode solution was increased, the reduction efficiency of Cr (VI) to Cr (III) was significantly promoted and a highly efficient removal of Cr (VI) was achieved. Under optimal operating conditions (positive bias 1 V, negative bias 2.5 V, duty ratio 20%, frequency 400 Hz, solution pH = 2), the asymmetric AC electrochemistry based on Ami-CF can achieve fast (30 s) and efficient removal (>99.11%) for 0.5-100 mg·L-1 Cr (VI) with a high flux of 300 L h-1 m-2. At the same time, the durability test verified the sustainability of the AC electrochemical method. For Cr (VI)-polluted wastewater with an initial concentration of 50 mg·L-1, the effluent concentration could still reach drinking water grade (<0.05 mg·L-1) after 10 cycling experiments. This study provides an innovative approach for the rapid, green and efficient removal of Cr (VI) containing wastewater at low and medium concentrations.

Coconut power: a sustainable approach for the removal of Cr6+ ions using a new coconut-based polyurethane foam/activated carbon composite in a fixed-bed column.

To attain efficient removal of hexavalent chromium (Cr6+) from aqueous solutions, a novel polyurethane foam-activated carbon (PUAC) adsorbent composite was developed. The composite material was synthesized by the binding of coconut shell-based activated carbon (AC) onto a coconut oil-based polyurethane matrix. To thoroughly characterize the physicochemical properties of the newly developed material, various analytical techniques including FTIR spectroscopy, SEM, XRD, BET, and TGA analyses were conducted. The removal efficiency of the PUAC composite in removing Cr6+ ions from aqueous solutions was evaluated through column experiments with the highest adsorption capacity of 28.41 mg g-1 while taking into account variables such as bed height, flow rate, initial Cr6+ ion concentration, and pH. Experimental data were fitted using Thomas, Yoon-Nelson, and Adams-Bohart models to predict the column profiles and the results demonstrate high breakthrough and exhaustion time dependence on these variables. Among the obtained R2 values of the models, a better fit was observed using the Thomas and Yoon-Nelson models, indicating their ability to effectively predict the adsorption of Cr6+ ions in a fixed bed column. Significantly, the exhausted adsorbent can be conveniently regenerated without any noteworthy loss of adsorption capability. Based on these findings, it can be concluded that this new PUAC composite material holds significant promise as a potent sorbent for wastewater treatment backed by its excellent performance, cost-effectiveness, biodegradability, and outstanding reusability.

A facile, green and scalable approach to fabricate hierarchical ZnAl-LDH for efficient removal of hexavalent chromium

A feasible, green and scalable approach for the synthesis of hierarchical ZnAl-LDH with well adsorption capacity to Cr(vi).

Highly efficient removal of hexavalent chromium by magnetic Fe-C composite from reed straw and electric furnace dust waste.

Reed straw and electric furnace dust (EFD) waste were used to prepare magnetic Fe-C composite (EFD&C) by co-precipitation and high-temperature activation method to remove Cr(VI) from water. The magnetic EFD&C owned a large specific surface (536.61m2/g) and a porous structure (micropores and mesopores), and had an efficient removal capacity for Cr(VI). Under conditions of pH (2), the addition amount of EFD&C (1g/L), the adsorption time (760min), and the temperature (45°C), the maximum adsorption capacity reached 111.94mg/g. The adsorption mechanism mainly attributed to chemical adsorption (redox), Cr(VI) reduced to Cr(III) by Fe(II) and Fe(0) (from Fe3O4 and Fe components in EFD) and surface functional groups of -OH, C = C, C-C and O-C = O (from biochar), and secondary attributed to physical adsorption, Cr(VI) and Cr(III) (from reduced Cr(VI)) adsorbed into the porous structure of EFD&C. This study provided a feasible solution for the preparation of adsorbents for adsorbing heavy metals from iron-containing metallurgical solid waste and biomass waste, which contributed to reducing the environmental pollution and lowering the cost of adsorbent preparation.

Highly efficient removal of hexavalent chromium from electroplating wastewater by ferrous/ferric hydroxide complex: From lab-scale to pilot-scale study

Low electron-transfer efficiency and cumbersome processes are widely known to negatively affect the application of Fe-based materials for treating electroplating wastewater. In this study, ferrous/ferric hydroxide complex (FHC) was successfully synthesized to greatly improve the electron-transfer efficiency for Cr(VI) removal; meanwhile, the effect of the interlayer type on Cr(VI) removal and the possible removal mechanisms were well investigated. The sulfate interlayer of FHC was shown to strongly promote Cr(VI) removal, with 10.4 % and 29.0 % improvements over those achieved by chloride and carbonate interlayers, respectively, in close association with the amounts of surface structural Fe(II), surface –OH, and adsorbed water. The initial pH value was demonstrated to exert almost no effect on Cr(VI) removal by FHC(SO42−) owing to the buffering effect of the surface –OH. These results were different from some previously reported Cr(VI) removal of Fe-based materials. Moreover, the results of characterization and lab-scale experiments indicated that most of Cr(VI) binds rapidly with the surface –OH owing to electrostatic attraction. The peak at 618 cm−1 in the FT-IR spectra shifted to 549 cm−1 and new peaks at 576.79 and 586.39 eV in the XPS spectra were observed after the reaction, which was attributed to the formation of CrOOH and FeCr2O4 owing to reduction and coprecipitation. Pilot-scale experiments revealed that the chemical cost and sludge yield during the FHC process decreased by 71.3 % and 54.1 %, respectively, compared with those in the NaHSO3 process. These findings provide new insight for utilizing different interlayers to improve the reactivity of FHCs in remediating electroplating wastewater containing Cr(VI).

One-step synthesis of nitrogen-functionalized graphene aerogel for efficient removal of hexavalent chromium in water.

The efficient removal of hexavalent chromium (Cr(VI)) with high toxicity has attracted widespread concern since it causes serious harm to ecological environment and public health. Herein, we report a novel nitrogen-functionalized graphene aerogel with stereoscopic structure through a simple hydrothermal method and freeze drying for Cr(VI) removal from water. Graphene oxide (GO) and nitrogenous organics polyethyleneimine (PEI) and pyrrole are used as raw materials for preparing PEI/polypyrrole/GO aerogel (PPGA) adsorbent. PEI and pyrrole act as nitrogen sources to introduce nitrogenous functional groups, and also take on the role of cross-linkers for helping GO sheets to form stereoscopic structure. The obtained PPGA has a fast adsorption rate, excellent reusability, and shows a remarkable adsorption capacity for Cr(VI) up to 458.24mg/g under the optimal conditions (pH 2.0, 298K, Cr(VI): 600mg/L, dosage: 0.4g/L). The adsorption process of Cr(VI) on PPGA can fit the pseudo-second-order kinetic model well. Analysis of intraparticle diffusion shows that the Cr(VI) removal process is a multi-step process. Adsorption thermodynamic and isotherm results demonstrate Cr(VI) adsorption on PPGA is a spontaneous endothermic process. The adsorption mechanism involves electrostatic attraction, redox, and chelation. In general, this work provides a simple and eco-friendly way to prepare PPGA, which has a great potential for actual application of Cr(VI) removal in effluent.

Efficient removal of Cr(VI) from aqueous solutions by polypyrrole/natural pyrite composites

Easily agglomeration of polypyrrole (PPy) significantly limits its practical applications. In this study, natural pyrite (NP) was applied to disperse PPy and overcome this agglomeration; a novel composite of PPy/NP was synthesized and applied for the efficient removal of hexavalent chromium [Cr(VI)] from aqueous solutions. Results showed that the PPy/NP composites exhibited better Cr(VI) removal performance than PPy alone. This enhanced removal capacity is attributed to the addition of NP, which prevents PPy agglomeration and reduces Cr(VI) to trivalent chromium[Cr(III)]; Cr(VI) removal was significantly dependent on the solution’s pH. The sorption kinetics of Cr(VI) with PPy/NP was described by the pseudo-second-order model and Elovich models, which highlight the chemicalsorption process. The sorption isotherm was well simulated by Langmuir model and the maximum adsorption capacity of Cr(VI) on PPy/NP was 261.78–395.26 mg/g at 303 – 323 K, which is significantly higher than that of PPy alone (124.84–194.17 mg/g). Thermodynamic analyses confirmed that this adsorption process was spontaneous and endothermic. PPy/NP composites could be used as a recyclable absorbents for four Cr(VI) reduction cycles without any evident loss in adsorption performance. The mechanism Cr(VI) removal by PPy/NP composites is attributed to ion exchange (9.47 %), adsorption (31.03 %), and reduction (59.50 %).