Remediation Of Hexavalent Chromium Research Articles

Single step synthesis of sulfidated nanoscale iron modified kaolin clay for hexavalent chromium remediation from groundwater

Remediation of dissolved hexavalent chromium [Cr(VI)] is often achieved by iron nanoparticles [nZVI], sulfidated nZVI [SnZVI], and adsorption on clay minerals. Although different types of nZVI effectively removed Cr(VI), performance evaluation of nZVI modified with low-cost and naturally available kaolinite clay was not thoroughly studied. In the present research, kaolin was modified with nZVI (K-nZVI) and SnZVI (K-SnZVI) at two different kaolin to iron mass ratios (kaolin: Fe). Both K-nZVI and K-SnZVI were synthesized by a simple one-step process, avoiding complicated amalgamation methods of modified nZVI. Effects of ionic strength, pH, major cations, and anions in Cr(VI) remediation efficiencies were probed. Kinetics of Cr(VI) removal was quantified from sacrificial batch studies. Further experiments were performed in Cr(VI)-spiked synthetic groundwater matrix in the respective pH and initial Cr(VI) ranges of 5.5–8 and 2–100 mg L−1. With maximum Cr(VI) remediation efficiencies of 100% (K-nZVI) and 98% (K-SnZVI) in synthetic groundwater contaminated with 2–100 mg L−1 Cr(VI), both of these materials might be effectively used for groundwater treatment. The usage of kaolin—an analog of the natural kaolinite clay—with relatively decreased Fe content in the nanoparticles would reduce the treatment cost and provide insight into a sustainable solution for Cr(VI) contamination.

Efficient and low-cost mesoporous magnetic carbon composites derived from date palm stones for environmental remediation of hexavalent chromium

This study was performed to achieve two important scientifically challenging goals, environmental remediation of toxic heavy metals and utilization of agricultural lignocellulosic wastes. In this work, a series of mesoporous magnetic carbon (MMC) adsorbents were synthesized by carbothermic reduction at different temperatures employing date palm (Phoenix dactylifera L.) stones as the carbon source. The synthesized adsorbents were characterized by different technquies and the results confirmed the presence of zero-valent iron (ZVI) nanoparticles and other iron oxides as products of the carbothermal reduction. The nature of phases present, crystallite size and the surface properties were found to be dependent on the calcination temperature. The adsorbent MMC700 exhibited the smallest (ZVI) crystallite size 36 nm and the largest SBET 341 m2/g. All adsorbents showed mesoporous structure with mesopore average diameter lower than 6 nm. The performance was evaluated in the removal process of toxic Cr(VI) in an aqueous medium, and the optimum conditions of the process were reported. The removal process was dependant of solution pH where best results was achieved at pH = 2. Complete removal of chromium was achieved in less than 5 min by MMC700. The results were better fitted with pseudo-second-order kinetics and followed the Freundlich model isotherm. The maximum adsorption capacity was found to be 265.25 mg/g for MMC700, suggesting its application as an efficient, low-cost, and easily separable adsorbent for the toxic Cr(VI) removal process. The prepared adsorbents exhibited superior performance in the removal process compared to other agricultural wastes or biomass - derived adsorbents reported in literature.

Optimizing Typha biochar with phosphoric acid modification and ferric chloride impregnation for hexavalent chromium remediation in water and soil

Considering the persistent and covert nature of heavy metal soil contamination, the sustainable development of ecological environments and food safety is at significant risk. Our study focuses on remediating soils contaminated with chromium (Cr); we introduce an advanced remediation material, iron oxide phosphoric acid-loaded activated biochar (HFBC), synthesized through pyrolysis. This HFBC displays greater microporosity, fewer impurities, and enhanced efficiency for the remediation process. Our research utilized a comprehensive set of analytical techniques, including Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS), alongside adsorption studies to elucidate the Cr removal mechanism. The effectiveness of HFBC in remediation was influenced by several factors: the pH level, dosage of HFBC, the initial concentration of Cr, and the ambient temperature. Our results indicated an optimal chromium (VI) adsorption capacity of 55.5 mg/g by HFBC at a pH of 6.0 and a temperature of 25 °C, with the process adhering to the pseudo-second-order kinetic model and the Langmuir adsorption isotherm, thus suggesting spontaneity in the uptake method. Moreover, this mechanism encompasses both adsorption and reduction reactions. Using HFBC in pot experiments with cabbage indicated not only an increase in soil pH and cation exchange capacity (CEC), but also a surge in bacterial community abundance. Significant reductions in bioavailable chromium were also recorded. Interestingly, HFBC addition bolstered the growth of cabbage, while concurrently diminishing chromium accumulation within the plant, particularly notable as the HFBC application rate increased. In summation, the HFBC produced in our study has demonstrated convincing efficacy in removing chromium from aqueous solutions and soil. Moreover, the positive agronomic implications of its use, such as enhanced plant growth and reduced heavy metal uptake by plants, indicate its high potential for operational value in the domain of environmental remediation of heavy metals.

Reaction Thermodynamics of Zerovalent Iron and Hexavalent Chromium at the Solid-Liquid Interface and in Solution.

Zerovalent iron (Fe0) is a promising candidate for remediating hexavalent chromium (Cr(VI)) via adsorption and (or) reduction. Herein, the reaction between Fe0 and Cr(VI) at the solid-liquid interface and in solution under varying pHs was inspected using the methodology of equilibrium thermodynamics. First, species distribution functions of aqueous Cr(VI), Cr(III), Fe(III), and Fe(II) are deduced to illuminate the quantitative distribution of aqueous metal species. Second, the plausible reaction at pH = 0-14 either at the solid-liquid interface or in solution is determined according to the species distribution function. Third, the spontaneity of each reaction is evaluated via a thermodynamic calculation based on the van't Hoff equation. The results present the following. (1) At the solid-liquid interface, the redox reaction 2Cr(VI) + 3Fe0 → 2Cr(III) + 3Fe(II) is spontaneous, inducing complete Cr(VI) → Cr(III) reduction at pH = 0-14. Especially, the high spontaneity of the redox reaction is mainly ascribed to Fe0 oxidation, which serves as a highly spontaneous subreaction. (2) In solution, the redox reaction Cr(VI) + 3Fe(II) → Cr(III) + 3Fe(III) is nonspontaneous at pH = 6 and 7, whereas it is spontaneous at pH = 6-7, 0-5, and 8-14. Accordingly, no Cr(VI) → Cr(III) reduction at pH = 6-7 and complete Cr(VI) → Cr(III) reduction at pH = 0-5 and 8-14 are expected. Particularly, the nonspontaneity of the Cr(VI) reduction at pH = 6-7 is majorly attributed to water ionization, which is involved as a highly nonspontaneous subreaction. On the contrary, the spontaneity of the Cr(VI) reduction at pH = 0-5 and 8-14 is mainly owing to acid-base neutralization, which is involved as a highly spontaneous subreaction. This work may deepen our knowledge about the chemistry involved in hexavalent chromium remediation by the zerovalent iron.

Remediation of Cr(VI) using a radiation functionalized green adsorbent: Adsorption modelling, mechanistic insights and prototype water purifier demonstration

The work reports remediation of hexavalent Chromium (Cr(VI)) in water using a radiation functionalized cellulose based green adsorbent, fabricated via gamma radiation assisted Mutual Irradiation Grafting Process (MIGP), wherein poly(2-Trimethylammoniumethyl methacrylate chloride) (PTMAEMC) was grafted onto Woven Cotton Cellulose Fabric (WCCF). The grafted adsorbent “ChromClear” efficiently sequestered Cr(VI) from water and demonstrated a maximum adsorbent capacity of ∼55 mg.g−1, successfully curtailing Cr(VI) concentrations to <20 μg.L−1. Characterization of samples was performed using 13C NMR, XPS, SEM-EDS, FTIR, TGA, and BET analysis. The equilibrium adsorption, kinetic, and breakthrough curve data were analysed using various theoretical models to infer the adsorption mechanism and extract important process parameters. Artificial Neural Network (ANN) modelling was used to predict adsorption capacity and % Cr(VI) removal in continuous flow column mode under different operational conditions, with a high degree of agreement (R2 > 0.99) between experimental and modelled data. Density Functional Theory (DFT) calculations established the interaction between CrO42− and PTMAEMC groups of ChromClear to be occurring in a 1:2 ratio. ChromClear could be regenerated for over five recycled iterations with >88 % retention in adsorption capacity. Concept based prototype water purification systems were also developed for pump as well as gravity driven continuous flow operations, and successfully demonstrated for remediation of Cr(VI) contaminated ground water samples. The efficacy and simplicity of the process provides ample scope for further upscaling and deployment for community level water treatment applications, with a special emphasis on compliance with drinking water norms in affected areas.

Chitosan-based foam composites for hexavalent chromium remediation: Effect of microcellulose and crosslinking agent content

Potentially toxic metal ions, such as hexavalent chromium (Cr6+), present in water concern the population's health due to their persistence, bioaccumulation potential, and high toxicity. Highly porous materials based on polysaccharides are promising technologies for metal removal due to their high surface area, biodegradability, and low toxicity. This study evaluated the effect of concentrations of microcellulose (0.5, 1, and 1.5 %) and glutaraldehyde (1, 2, and 3 %) in the adsorption capacity and mechanical properties of chitosan foams. The developed foams exhibited a three-dimensional structure with interconnected pores. Compared to foams without microcellulose, adding 1.5 % microcellulose increased up to 180 % in maximum stress supported by the foams and up to 135 % in Young's modulus. However, Cr6+ sorption capacity decreased with increasing microcellulose and crosslinking agent content due to the occupation of amino groups. Still, the foams exhibited a highly favorable sorption behavior, and the Sips isotherm model provided the best fit to the experimental data. The maximum sorption capacity reached approximately 1.4 mmol·g−1 at pH 4.0 and 25 °C. The foam structural integrity, enhanced mechanical properties, and efficient sorption capacity make them viable alternatives for environmentally friendly and cost-effective treatment of water contaminated with Cr6+ ions.

A Review of the Latest Advances in Nanoparticle-Mediated Processes for Hexavalent Chromium Remediation from Water Bodies.

Hexavalent chromium (Cr(VI)) is a well-known carcinogen, and hence its removal from aqueous media is an important area of research in the field of environmental engineering. Adsorptive removal and catalytic reduction are the two most common techniques applied for this purpose. In this regard, nanoparticle-mediated technology has contributed significantly. In the current review article, a systematic investigation has been carried out to find the latest developments that took place in the domain of Cr(VI) removal by nanotechnology. The major portion deals with the advancement and application of the new-age materials, such as carbon nanotubes (CNTs), g-C3N4, MXenes, zero-valent iron (ZVI), and their composites, for the Cr(VI) remediation purpose. Various interesting mechanisms, as proposed by different research groups, have been covered. Applications of the nanocomposites in the real wastewater scenario have also been highlighted. Different characterization techniques often conducted in order to get insight into Cr(VI) removal process have been mentioned. Some patents related to this field have been discussed. Lastly, the future scope of the nanomaterials, current challenges, feasibility of using these nanomaterials in large-scale treatment plants, etc., have been addressed before concluding the article.

Molybdate modified nano zero-valent iron via green synthesis enhances Cr(VI) reduction during their cotransport in water-saturated porous media

The in situ remediation of hexavalent chromium (Cr(VI)) pollution in groundwater and soil using nano zero-valent iron (nZVI) has garnered great attention. However, Cr(VI) remediation, particularly its reduction remains limited in the subsurface due to the poor migration of nZVI materials to contaminated sites. Herein, we successfully prepared a series of Mo/nZVI@GT materials with varying Mo/Fe synthesis molar ratios using green tea extracts and molybdate and efficiently improved the transportability of Mo/nZVI@GT. The pronounced size-selective retention of Mo/nZVI@GT in water-saturated porous media also favors for the effective reaction with Cr(VI) during their cotransport. Moreover, Cr(VI) reduction capacity of Mo/nZVI@GT was remarkably improved at pH 6.0, especially in the presence of phosphate. Mechanistically, X-ray absorption near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) revealed that tea polyphenols promoted the production of Mo(IV) species in Mo/nZVI@GT, which enhanced the conversion of Cr(VI) to Cr2O3 rather than Cr(OH)3. Additionally, the increased Mo(IV) and Fe(II) active sites might mitigate phosphate disturbance. This study elucidated the mechanisms of Cr(VI) reduction and removal by green synthesized nZVI@GT with Mo modification during their cotransport and highlighted the potential application of Mo/nZVI@GT composites in efficient in situ remediation of Cr(VI)-contaminated groundwater and soil.

Effective Cr(VI) reduction and immobilization in chromite ore processing residue (COPR) contaminated soils by ferrous sulfate and digestate: A comparative investigation with typical reducing agents

Chemical reduction combined with microbial stabilization is a green and efficient method for the remediation of hexavalent chromium (Cr(VI)) contaminated soil. In this study, the combination of ferrous sulfate with kitchen waste digestate was applied to reduce and immobilize Cr(VI) in chromite ore processing residue (COPR) contaminated soils, and systematically evaluated the remediation performance of Cr(VI) compared with several typical reducing agents (i.e., ferrous sulfate, zero valent iron, sodium thiosulfate, ferrous sulfide, and calcium polysulfide). The results showed that the combination of ferrous sulfate and digestate had superior advantages of a lower dosage of reducing agent and a long-term remediation effect compared to other single chemical reductants. Under an Fe(II):Cr(VI) molar ratio of 3:1% and 4% digestate (wt), the content of Cr(VI) in the soil decreased to 5.07 mg/kg after 60 days of remediation. Meanwhile, the leaching concentrations of Cr(VI) were below detection limit, which can meet the hazardous waste toxicity leaching standard. The risk level of Cr pollution was decreased from very high risk to low risk. The X-ray photoelectron spectroscopy (XPS) results further demonstrated that the combined treatments were beneficial to Cr(VI) reduction and stabilization. The abundance of bacteria with Cr(VI) reducing ability was higher than other treatments. Moreover, the high abundance of carbon and nitrogen metabolism in the combined treatments demonstrated that the addition of digestate was beneficial to the recovery and flourishing of Cr(VI)-reducing related microorganisms in COPR contaminated soils. This work provided an alternative way on Cr(VI) remediation in COPR contaminated soils.

Characterization and application of Fe-modified biochar alleviating Cr(VI) stress in pak choi seedling cultivated in Cr-polluted hydroponics

Chromium (Cr) is one of the common environmental pollutants, which causes severe health hazards on human health and environmental security. In this study, we characterized two biochars, a raw biochar (RBC) and a Fe-modified biochar (MBC) made from poplar wood chips and determined the effect of the two biochars on remediation of hexavalent chromium (Cr(VI)) in hydroponic system by monitoring Pak choi growth. Results showed the surface area, pore number and pore volume were significantly higher in MBC than in PBC, but the pore size was larger in PBC than in MBC. When compared to the control, low concentrations of Cr(VI) (≤2 mg L−1) promoted the growth and biomass production of Pak choi by 10–78%. In contrast, the high concentrations of Cr(VI) (≥4 mg L−1) showed a significantly reduction of the growth and biomass production of Pak choi by 10–28%. Fe-modified biochar (MBC) had a more significant impact than RBC on the remediation of Cr in the Cr(VI) pollution and improved growth and biomass production of Pak choi to a greater extent. Our study indicated that MBC has a better effect on degrading Cr(VI) pollution. The findings provide scientific basis and reference for the remediation of heavy metals in aquatic ecosystems by using biochar.

Porphyrin-based conjugated microporous adsorbent material for the efficient remediation of hexavalent chromium from the aquatic environment.

The encapsulation and eradication of anions from water have received a lot of scrutinize and are extremely important for virtuous production and environmental treatment. To prepare extremely efficient adsorbents, a highly functionalized and conjugated microporous porphyrin-based adsorbent material (Co-4MPP) was synthesized using the Alder Longo method. Co-4MPP featured a hierarchical microporous and mesoporous layered structure containing nitrogen and oxygen-based functional groups with a specific surface area of 685.209 m2/g and a pore volume of 0.495 cm3/g. Co-4MPP demonstrated a greater Cr (VI) adsorption empathy than the pristine porphyrin-based material did. The effects of various parameters such as pH, dose, time, and temperature were explored on the Cr (VI) adsorption by Co-4MPP. The pseudo-second-order model and the Cr (VI) adsorption kinetics were in agreement (R2 = 0.999). The Langmuir isotherm model matched the Cr (VI) adsorption isotherm, demonstrating the optimum Cr (VI) adsorption capacities: 291.09, 307.42, and 339.17 mg/g at 298K, 312K, and 320K, correspondingly, with remediation effectiveness of 96.88%. The model evaluation further revealed that Cr (VI) adsorption mechanism on Co-4MPP was endothermic, spontaneous, and entropy-rising. The detailed discussion of the adsorption mechanism suggested that it could be a reduction, chelation, and electrostatic interaction, in which the protonated nitrogen and oxygen-containing functional groups on the porphyrin ring interacted with Cr (VI) anions to form a stable complex, thus remediating Cr (VI) anions efficiently. Moreover, Co-4MPP demonstrated strong reusability, maintaining 70% of its Cr (VI) elimination rate after four consecutive adsorptions.

Comparison of biosorption efficiency for hexavalent chromium remediation in synthetic wastewater using unmodified and chemically modified chicken feathers

The aim of the present study was to compare the effectiveness of raw chicken feathers (RCFs), NaOH and ethylenediamine-modified chicken feathers (MCFs), and xanthate-modified chicken feathers (XMCFs), treated with both NaOH, ethylenediamine, and carbon disulfide. The physicochemical characteristics of the biosorbents were analyzed using attenuated total reflection Fourier transform infrared spectrophotometry (ATR-FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), adsorption of N2 at −196°C and point of zero charge determination (pHpzc). The biosorption of Cr(VI) using MCFs and XMCFs was evaluated through various parameters, namely, pH, biosorbent amount, and contact time in batch experiments. The results showed a significant increase in the biosorption capacities of MCFs (90.90 mg/g) and XMCFs (100 mg/g) compared to RCFs (52.63 mg/g). The batch adsorption experiments indicated that the optimal conditions for biosorption were pH 2.0, with an equilibrium contact time of 90 min for RCFs, and 60 min for both MCFs and XMCFs. The optimal biosorbent concentrations were 16 g L−1 for RCFs and 12 g L−1 for both MCFs and XMCFs. The biosorption behavior was well described by the Langmuir isotherm and pseudo-second-order kinetic models. The thermodynamic parameters indicated that the biosorption of Cr(VI) onto the biosorbents was a spontaneous and endothermic process. Desorption analysis was carried out using a 0.1 M NaOH solution.

Remediation of hexavalent chromium and pharmaceuticals from aquatic environments by employing an oxygen-doped porous carbon adsorbent and its antifungal activity

The existence of emerging pollutants, including hexavalent chromium and pharmaceuticals in water, presents a severe hazard since the degree of their effects on the ecology and public health remains unknown.

Effect of electrolyte, potential gradient and treatment time on remediation of hexavalent chromium contaminated soil by electrokinetic remediation and adsorption

Effect of electrolyte, potential gradient and treatment time on remediation of hexavalent chromium contaminated soil by electrokinetic remediation and adsorption

Three chambered fuel cell for desalination coupled urea oxidation and hexavalent chromium remediation

Proof-of-concept of a fuel cell type electrochemical cell is demonstrated for simultaneous wastewater treatment and desalination. The electrochemical desalination cell (EDC) utilized the potential difference and concentration gradient between three chosen waste streams to convert their inherent chemical energy into electrical energy. Urea/cow urine was chosen as a potential electron donor, Cr(VI) was an electron acceptor, and synthetic NaCl/seawater solution (in the middle chamber) established a three-compartment EDC. The effect of a wide range of brine (5 to 35 g/L) and Cr(VI) concentrations (200 to 1000 mg/L) on desalination performance and Cr(VI) reduction were comprehensively investigated. When fed with urea, Cr(VI) reduction of 96.2 ± 0.4 % (with an initial concentration of 1000 mg/L) and salt removal of 63.1 ± 0.2 % (with brine concentration of 35 g/L) were observed (in 4 h) with a maximum power of 15.2 mW (for 21 cm2 electrode). A 12 L benchtop prototype with six anode-cathode configurations was demonstrated. Cr(VI) reduction of 95.2 ± 2 % and desalination of 70.7 ± 0.2 % (in 20 h) with power generation of 55.2 mW was recorded. The economic analysis projection of the EDC presents a significant step toward the application of this technology in real systems.

Potential use of Chlorella vulgaris KCBAL01 from a freshwater stream receiving treated textile effluent in hexavalent chromium [Cr(VI)] removal in extremely acidic conditions

Remediation of hexavalent chromium with conventional chemical and physical methods is a costly process, while replacing some critical steps in physiochemical remediation with self-sustaining bioremediation agents are expected to be cost-effective and environmentally friendly implementation. In this study, a microalga isolated from a freshwater stream receiving treated textile wastewater was identified up to its molecular level and investigated its ability to tolerate and remove hexavalent chromium from extremely acidic conditions under different temperatures. The ability of microalgae to tolerate and remove Cr(VI) was investigated by growing it in BG11 media with different pH (1, 2, 3 & 7), amended with several concentrations of Cr(VI) and incubated under different temperatures for 96 hrs. Microalga was identified as Chlorella vulgaris and found that the isolated strain has a higher hexavalent chromium removal potential in extremely acidic conditions than in neutral pH conditions at 25 °C. In contrast, its Cr(VI) removal potential is significantly influenced by the pH and temperature of the growth medium. Furthermore, it exhibited a permanent viability loss at extreme acidic conditions (pH 1 − 3) and prolonged exposure to the higher chromium content. The microalga investigated will be a highly useful bioagent in hexavalent chromium remediation in high acidic conditions.

Possible remediation of hexavalent chromium by native fungi of Sukinda mining area: a review

The expeditious industrialization is helping the world to give a new modern era with all sorts of amenities. But the consequences are following great risks that might result in a terrifying future. Heavy metal pollution and its hazardous effects are one of them. Though India is the 3rd largest chromium producing country and the Sukinda valley of Odisha, is the chief source for chromium, hence here the threat of chromium pollution is at a high point. Countermeasures to this problem have become of prime importance. Among several remedial measures, bioremediation is an approaching process to control the accelerated growth of heavy metal contamination including chromium. In the world of microorganisms, the congenital characteristics of fungi have great importance as they can grow easily in polluted habitats. Again, there is evidence of native fungi having the potential to bind with heavy metals and remove toxic agents from natural environments. The pathway of chromium toxicity and its possible remediation potential by fungi have been studied extensively in the Sukinda area. This study signifies some positive aspects that can be practised in the future as a convenient option for bioremediation. Fungal bioremediation improved with biotechnology tools will be suitable output for rapid remediation which is vital for this moment.

Effect of ionic Fe(III) doping on montmorillonite for photocatalytic reduction of Cr(VI) in wastewater

The potential photocatalytic activity of Mt (montmorillonite) after Fe(III) doping was measured for the photocatalytic remediation of hexavalent chromium (Cr(VI)). Mt was modified with Fe(III) at pH = 2 with IAP ≤ 1.5 ∙ 10–38 <Ksp(Fe(OH)3) = 6.0 ∙ 10 -38 to prevent the precipitation of Fe(OH)3. Doped ionic Fe(III) was located mainly in the interlayer space but presented partially on the Mt layers. XRD, FTIR, XPS and XANES/EXAFS analyses suggested that Fe(III) should exist in the cationic form. The photocatalytic characterization of the obtained Fe/ Mt suggests that Mt gained photocatalytic activity after Fe(III) ion doping. The photocatalytic transformation of Cr(VI) to harmless trivalent chromium (Cr(III)) on Fe/ Mt was also dominated by Fe(III) doping on the Mt interlayer and Mt aluminosilicate layers. Higher Fe(III) doping correlated with higher photocatalytic efficiency with the Fe(III) adsorbed on Mt at a ratio lower than 0.274 mmol/g. A further intercalation of Fe(III) reduced the photocatalytic efficiency, which could be attributed to the excess Fe(III) providing a recombination state for the electrons, trapping the electrons from the Cr(VI) reduction, and the extra Fe(III) overlapping with the active sites receiving irradiation. Based on the characterization and photocatalytic activity test, the mechanism of the photocatalytic property of Fe(III)-doped Mt was revealed for the first time. The new Fermi level formed between the forbidden bands narrowed the band gap of Mt, endowing the Mt with photocatalytic activity. This finding may contribute to explaining the role of Fe/ Mt in Fe/ Mt-based photocatalytic composites.

A stepwise processing strategy for treating manganese residue and the remediation of hexavalent chromium in water and soil by manganese residue-derived (Fe,Mn)C2O4

This work provides a new approach for effective treatment and utilization of manganese residue (MR), including leaching, desulfurization, and recycling of iron and manganese. The secondary residue and the acidic filtrate (pH = 0.94) composed of H2SO4 and H2C2O4 could be used as a cement material and the medium and reductant for manganese sulfate production system, respectively. Approximately 94.5% of Fe and 97.5% of Mn were recovered to produce (Fe,Mn)C2O4 composite, which had a capacity of 122.7 mg g−1 for removing Cr(VI) and a good performance in a wide pH range of 2–9. The removal of Cr(VI) by (Fe,Mn)C2O4 was attributed to adsorption, reduction, and co-precipitation. What's more, the control experiment of FeC2O4 and MnC2O4 affirmed the synergism between Mn and Fe in (Fe,Mn)C2O4 composite, attributed to that the accelerated reduction of Mn(III) by Fe(Ⅱ) and the co-reduction effect of Fe with Mn on Cr(VI) synergistically promoted the reduction of Cr(VI). Furthermore, the ability of (Fe,Mn)C2O4 for immobilizing Cr(VI) in the soil was investigated, and the result proved that (Fe,Mn)C2O4 significantly reduced the leaching and releasing risk of Cr(VI). This strategy for treating and utilization of MR has great economic and ecological benefits.

Temperature Impact on Reverse Osmosis Permeate Flux in the Remediation of Hexavalent Chromium

Reverse osmosis technique was applied in removing hexavalent chromium ions from artificial wastewater. Different operating conditions were studied to monitor the separation process using commercial Reverse Osmosis BW30XFR membrane. Different concentrations of hexavalent chromium; 5, 30, and 100 ppm were tested. Samples were subjected to incrementally increasing operating pressure; 10, 30, and 45 bar and flow rates; 2.2, 3.4, and 4.5 L/min under various temperatures; 25, 35, 45, and 55 °C. Collected permeate and concentrations were measured after each experiment using a UV spectrophotometer. Results obtained presented a higher rejection percentage at lower feed concentrations with a value up to 99.8% for 5 ppm in comparison to 94.3% for 30 ppm and 77.2% for 100 ppm concentration due to concentration polarization; however, it showed no effect of increasing operating flow rates. Moreover, the increase in feed temperature from 25 to 55 °C had positively increased permeate flux to more than 300 times. The permeate flux at 25 °C is recorded for all tested samples in the range of 30 to 158 kg/h·m2, this range has risen at 55 °C under the same conditions to the range of 70 to 226 kg/h·m2, indicating alteration within the membrane pore size due to temperature increase and high applied pressure concluding high sensitivity of polymeric membranes towards changing permeate flow rate with increasing temperatures.