Simultaneous Removal Of Cr Research Articles

Mechanistic insight into the simultaneous removal of Cr(VI) and phosphate by a novel versatile bimetallic material

Industrial wastewater containing hexavalent chromium Cr(VI) and phosphate poses a great threat to human health and the aquatic ecological environment. In this study, a novel La(OH)3- and CaO2-fabricated CNT (La-Ca-CNT) material was developed for the simultaneous and highly effective removal of aqueous Cr(VI) and phosphate. Characterization results showed that synergistic effects existed between the CNT support and La and Ca species. La-Ca-CNT showed high phosphate and Cr(VI) removal rates in acidic conditions with high stability. Kinetic study suggested that the fast adsorption of phosphate on La-Ca-CNT was controlled by intraparticle diffusion. The removal of Cr(VI) and phosphate interacted with each other, and the removal of Cr(VI) went through a slow-fast-slow reaction, reaching a Cr(VI) removal rate of over 97% within 180min. La-Ca-CNT had a high phosphate adsorption capacity (174.3mg/g), and over 70% of the adsorbed phosphate could be recovered. The presence of co-existing anions showed negative effects on phosphate adsorption but negligible effects on Cr(VI) reduction, while organic carbon in natural water showed no effect on phosphate and Cr(VI) removal. A mechanistic study revealed that phosphate was removed by physical-chemical adsorption (outer-sphere complexation and ligand exchange) over La-Ca-CNT, while Cr(VI) was reduced by H2O2 generated from CaO2 or directly by surface CaO2.

Bidirectional extracellular electron transfers in Serratia marcescens and Stenotrophomonas sp. correlate to EPS and Cr(VI) removal in single‐chamber bioelectrochemical systems

AbstractBACKGROUNDElectrochemically active bacteria (EAB) capable of bidirectional extracellular electron transfer (EET), either outward or inward EET, largely control the efficiency of interactions and electrical communication between biofilm and electrode and, thus, control the performance of bioelectrochemical systems (BESs) for heavy metals removal. However, the behavior of such metallurgical EAB capable of bidirectional EET has yet to be investigated, and the role of extracellular polymeric substances (EPS) in these switchable EAB with bidirectional EET and in the presence of heavy metals remains unexplored in the single‐chamber BESs treating heavy metal‐based wastewaters that are limited by carbon/electron sources or electron acceptors.RESULTSThe biofilms of the Cr(VI)‐tolerant EAB Stenotrophomonas sp. YS1 and Serratia marcescens Q1 exhibited bidirectional EET metabolizing either organic (acetate) or inorganic (HCO3−) species with simultaneous removal of Cr(VI) in single‐chamber BESs. Q1 inward EET uptake of electrons was more efficient than that of YS1 (165 μA vs. 118 μA); meanwhile, YS1 outward EET was more efficient than Q1 (8.0 μA vs. 4.7–5.2 μA). The adaptive electrochemically‐tunable EPS in both biofilm strains was regulated by the direction of the EET (inward or outward) in the presence of Cr(VI) and circuital current.CONCLUSIONThis study demonstrates the switching properties of EAB, such as Stenotrophomonas sp. or S. marcescens, that are capable of bidirectional EET to or from the electrodes, and it displays the regulation of such responses with the amount and compositional diversity of the biofilms’ EPS, giving a comprehensive appreciation of tunable EPS for Cr(VI)‐wastewater treatment in single‐chamber BESs. © 2024 Society of Chemical Industry (SCI).

Simultaneous removal of Cr, Cu, Zn, and Cd by nano zero-valent iron modified sludge biochar in high salinity wastewater

Cr, Cu, Zn, and Cd commonly coexisted in the electroplating wastewater with high salinity and organics, while their removal was often investigated individually. In this study, the simultaneous removal of Cr, Cu, Zn, and Cd was investigated by nano zero-valent iron modified sludge biochar (nZVI@SBC). The results showed that nZVI@SBC could significantly improve the removal efficiency of the four heavy metals (HMs) in high salinity wastewater. NO3– (N-NO3–) and humic acid (HA) could promote the removal of Cr, Cu, Zn, and Cd, and PO43- (P-PO43-) could enhance the removal of Cd. EPR analysis demonstrated the generation of 1O2 in different water matrices. The 1O2 intensity increased in the presence of NO3– and HA, which indicated the acceleration of the nZVI corrosion and the promoted electron transfer in the system. To further understand the reaction mechanism, the variation of nZVI@SBC structures and compositions during the treatment process were characterized by SEM-EDS, XRD, BET, and XPS. Cr and Cu were removed through adsorption and co-precipitation after reduction by nZVI, while Cd and Zn were removed by alkali precipitation and complexation. This work improves the understanding of simultaneous removal of HMs by nZVI@SBC and provides a cost-effective approach for the electroplating wastewater treatment.

Simultaneous removal of Cr(Ⅵ) and tetracycline from wastewater by dielectric barrier discharge plasma coupled with TiO2/rGO/Cu2O composites: Performance and mechanism

In this study, dielectric barrier discharge (DBD) plasma combined with titanium dioxide/reduced graphene oxide/copper oxide (TiO2/rGO/Cu2O) composites for simultaneous removal of hexavalent chromium (Cr(Ⅵ)) and tetracycline (TC) from wastewater were explored systematically. The TiO2/rGO/Cu2O composites were successfully prepared to improve the specific surface area and charge carrier separation rate. When Cr(Ⅵ) and TC coexist, the two pollutants have better removal efficiency without changing the initial pH. Moreover, the removal efficiency of Cr(Ⅵ) and TC could be further improved in the DBD-TiO2/rGO/Cu2O system, indicating that the TiO2/rGO/Cu2O composites also exhibited good synergistic effects with the DBD plasma. The mechanism exploration showed that the TiO2/rGO/Cu2O composite catalyst could be activated in DBD system to produce various active species by photocatalytic reaction, among which photo-generated electrons and •O2− could significantly enhance Cr(Ⅵ) reduction, while photo-generated holes and •OH could improve TC degradation. More importantly, the intermediate products obtained from TC degradation can be oxidized to •CO2− by photo-generated holes, which can also facilitate the reduction of Cr(Ⅵ). This study shows that DBD combined with TiO2/rGO/Cu2O composites are capable of simultaneous Cr(Ⅵ) reduction and TC degradation, which would provide novel ideas for practical wastewater remediation.

Unveiling the role of biochar in simultaneous removal of hexavalent chromium and trichloroethylene by biochar supported nanoscale zero-valent iron

The simultaneous removal of hexavalent chromium (Cr(VI)) and Trichloroethylene (TCE) is facing great challenges, and the influences of the biochar on their removal by nanoscale zero-valent iron (nZVI) are poorly understood and seldom addressed in the literature. The rice straw pyrolysis at 700 °C (RS700) and their supported nZVI composites were investigated on the removal of Cr(VI) and TCE by batch experiments. The surface area and chromium bonding state of biochar supported nZVI with and without Cr(VI)-TCE loading were analyzed by Brunauer-Emmett-Teller analysis and X-ray photoelectron spectroscopy. In single pollutants system, the highest removal amounts of Cr(VI) and TCE were observed in RS700-HF-nZVI (76.36 mg/g) and RS700-HF (32.32 mg/g), respectively. The Cr(VI) removal was attributed to the reduction by Fe(II) with the adsorption by biochar primarily controlling the TCE removal. The mutual inhibition was revealed in simultaneous removal of Cr(VI) and TCE, in which the reduction of Cr(VI) was decreased due to the adsorption of Fe(II) by biochar, while the TCE adsorption was primarily inhibited owing to the blockage of surface pores of biochar supported nZVI by chromium‑iron oxides. Therefore, biochar supported nZVI could be potentially used for the combined contaminated groundwater remediation, but the mutual inhibition should be evaluated.

Simultaneous removal of Cr(VI) and 2,4-dichlorophenol from water using the zero-valent iron–aminotriacetic acid system

Zero valent iron (ZVI) can remove complex organic pollutants and heavy metals during water purification. However, the oxide film formed on its surface leads to passivation, which reduces the complete exposure of the reaction sites. Aminotriacetic acid (NTA) as a complexing agent is considered to be a good choice for inhibiting the surface passivation of ZVI due to its simple operation, economic feasibility and rapid reaction. The removal efficiency of pollutants and influencing factors (pollutant concentration, iron dosage, NTA concentration, and pH) were investigated in the ZVI/NTA system. Cr(VI) and 2,4-dichlorophenol (2,4-DCP) were simultaneously removed in the ZVI/NTA system with removal efficiencies of 98.1 % and 94.3 % within 120 min, respectively. Cr(VI) removal was mainly ascribed to the reduction ability of bare ZVI, whereas 2,4-DCP removal was ascribed to the •OH generated during the reaction between Fe(II) and H2O2. Quenching and molecular probe experiments confirmed the participation of •OH in 2,4-DCP removal. X-ray photoelectron spectroscopy analysis further confirmed the mutual conversion of Fe(II)/Fe(III) in the ZVI/NTA system, which contributes to the generation of •OH. In the ZVI/NTA system, Cr(VI) and 2,4-DCP were more easily removed under weak acidic conditions. Moreover, the TOC removal efficiency reached 75 % within 120 min, indicating decreased toxicity of this pollutant. As for the 2,4-DCP degradation, the intermediates 2-chlorohydroquinone, 1,2,4-trihydroxyphenol, hydroquinone, phenol, benzene, and acetic acid were detected. This research provides a new approach for simultaneously removing complex organic pollutants and heavy metals.

Simultaneous removal of Cr(VI) and phenol in a dual-chamber photocatalytic microbial fuel with NiCo2O4/MoS2/GF photocathode

Efficient treatment and resource utilization of sewage are of great value for global sustainability. In this study, a composite photocathode was prepared by loading NiCo2O4 nanosheets and MoS2 nanoflowers to a graphite felt (GF)-based electrode through a two-step hydrothermal and calcination method. A photocatalytic microbial fuel cell (PMFC) was constructed using the NiCo2O4/MoS2/GF photocathode and carbon felt (CF) anode in a dual-chamber H-type battery. Cr(VI) and phenol were employed as target pollutants in the cathode chamber. The photoelectric performance of the NiCo2O4/MoS2/GF photocathode and the removal efficiency of the battery system were studied systematically. When a mixed solution of Cr(VI) and phenol was used, the removal rates of Cr(VI) and phenol after 24 h of light exposure were 8.13 % and 12.65 % higher than those when Cr(VI) or phenol was used alone, respectively. At the same time, the output power density of the battery in the mixed pollutants was 362.7 mW/m3, which was 45.78 % higher than that in the single Cr(VI) solution (248.8 mW/m3). The excellent performance of the PMFC was attributed to three reasons: (1) NiCo2O4 and MoS2 were simultaneously excited as two narrow-bandgap semiconductors, and the utilization rate of light energy was increased; (2) The Z-scheme heterojunction between NiCo2O4 and MoS2 improved the separation efficiency of the photoelectric carriers and retained the high valence band of NiCo2O4 and low conduction band of MoS2 to the greatest extent, which is crucial for the PMFC to achieve electronic export and double contaminant removal; and (3) the NiCo2O4 nanosheet and MoS2 nanoflower structures enhanced the contact between the catalysts and the pollutants.

Cross-redox and simultaneous removal of Cr(VI) and As(III): Influences of Fe(II), Fe(III), oxalic acid, and dissolved organic carbon

Hexavalent chromium [Cr(VI)] and arsenite [As(III)] are hazardous to both human and ecosystem. While their cross-redox reaction decreases both their toxicities, the interferences from ubiquitous substances like Fe (Fe(II) and Fe(III)) and organic compounds (oxalic acid and soil-extracted dissolved organic carbon (DOC)) on such interaction are rarely reported; thence, inspires the investigation in this study. Results showed that the cross-redox, in the absence of interfering substances, only occurred at pH≤2.0, with reaction orders of 0.676 and 0.783 in respect to the concentration of Cr(VI) and As(III). The pseudo-reaction constant, k′, of such reaction was recorded at 0.087 m1.377/(mmol0.459 min). With the addition of Fe(II), the rate of Cr(VI) reduction is promoted in conjunction with suppressed As(III) oxidation. Upon neutralizing to pH 6.0, such reduced Cr can be entirely removed via Fe(II)-assisted adsorption and/or co-precipitation. Meanwhile, the elimination of aqueous As is relatively inferior (36 %), attributed to the largely preserved As(III), which is less susceptible to adsorptive/co-precipitative removal. Unlike Fe(II), Fe(III) did not alter Cr(VI)-As(III) cross-redox path, but triggered high adsorptive and/or co-precipitative removals of Cr and As (90 %). In contrast, both organically-altered systems exhibits plummeted As(III) oxidation, under distinctive mechanisms: oxalic acid competes with As(III) in the redox interactions while DOC reduces As(V) into As(III). Also, DOC would undergo complexion with metals and/or blocked the adsorption or co-precipitation sites, leading to even lower Cr and As precipitation. This study unravelled the interference from ubiquitous species in the co-removal of Cr(VI) and As(III), which provides insightful remediation for heavy metal contaminations.

Temperature-dependent carbothermally reduced iron and nitrogen doped biochar composites for removal of hexavalent chromium and nitrobenzene

Synthesizing new composites with better efficiency and stability from abundant sources offers an appealing prospect for removal of heavy metals and organic pollutants to address water pollution concerns. In this study, iron (Fe) and nitrogen (N) doped biochar (BC) composites were investigated for hexavalent chromium (Cr(VI)) and nitrobenzene (NB) removal. Specifically, temperature-dependent Fe1-N1-BC1 composites were synthesized with different mass ratios of FeCl3 as Fe, melamine as N, and pinewood sawdust (PWS) as BC precursors via carbothermal reduction at 300, 500, 700, and 900 °C. Detailed characterizations indicating low-temperature incorporated superior N and high-temperature incorporated more Fe species in Fe1-N1-BC1 composites. The Cr(VI) and NB were removed with Fe1-N1-BC1, and experimental results attested with standard isotherm and kinetic models. The N species (pyridinic-N, pyrrolic-N, graphitic-N, quaternary-N, and oxidized-N) and Fe species (Fe3C, Fe0, Fe 2p 3/2, and Fe 2p 1/2) in temperature-dependent Fe1-N1-BC1 composites participated in pollutants removal. Mass ratio of 1:1:1 of Fe, N, and BC was effective, and under optimum conditions, low-temperature (Fe1-N1-BC1-300) and high-temperature (Fe1-N1-BC1-700) composites completely removed Cr(VI) and NB, respectively. In comparison to pinewood sawdust BC (PWBC) and composite of FeCl3 with PWS (Fe-BC), melamine with PWS (N-BC), and FeCl3 with melamine (Fe-N), the Fe1-N1-BC1 was more efficient due to synergistic effect of Fe, N, and BC for better pollutant interaction and removal. Effect of different factors on pollutants removal with Fe1-N1-BC1 was studied to reveal removal mechanism insights. Additionally, Fe1-N1-BC1 showed better efficiency in simultaneous removal of Cr(VI) and NB, stability for > 4 months, reusability, and applicability for multiple pollutants. This study offers a benign approach for synthesizing and applying Fe1-N1-BC1 for pollutants removal and exploring reaction mechanisms.

Highly Efficient and Simultaneous Removal of Cr(VI) and Imidacloprid through a Ferrocene-Modified MIL-100(Fe) Composite from an Aqueous Solution.

A novel nanocomposite [Fc-MIL-100(Fe)] was constructed by combining ferrocene (Fc) with the porous structural metal-organic framework [MIL-100(Fe)]. The proposed composite material could simultaneously and efficiently remove hexavalent chromium [Cr(VI)] and imidacloprid and reduced strongly noxious Cr(VI) to weakly noxious trivalent chromium [Cr(III)]. The removal efficiencies of the composite material for Cr(VI) and imidacloprid could reach 95% after 15 h. The adsorption process was determined by kinetics, isotherms, and thermodynamics. The results demonstrated that the adsorption kinetics of Cr(VI) followed the pseudo-second-order model mainly by chemisorption; meanwhile, the adsorption of imidacloprid by the material conformed to the pseudo-first-order kinetics, which indicated that physical adsorption was the main process. Additionally, the intraparticle diffusion model revealed that the uptake of imidacloprid and Cr(VI) occurred via intraparticle diffusion at the composite material. The adsorption procedure for Cr(VI) was fitted to the Langmuir model (R2 = 0.995) via monolayer adsorption, and that for imidacloprid was fitted to the Freundlich model (R2 = 0.995) due to multilayer or heterogeneous adsorption. The thermodynamic research confirmed that the adsorption procedure was exothermic and spontaneous. Infrared spectroscopy, X-ray photoelectron spectra, and the pH effect implied that intermolecular hydrogen bonding and electrostatic interaction played a crucial role during the removal process. Fc-MIL-100(Fe) also exhibited long-term stability and satisfactory regeneration and reusability. Therefore, this method may enhance an environmentally friendly and prospective approach for concurrently removing imidacloprid and Cr(VI) from wastewater.

Simultaneous Removal of Cr(Vi) and Phenol in Dual-Chamber Photocatalytic Microbial Fuel with Nico2o4/Mos2/Gf Photocathode

Simultaneous Removal of Cr(Vi) and Phenol in Dual-Chamber Photocatalytic Microbial Fuel with Nico2o4/Mos2/Gf Photocathode

G-C3N4/Carbon spheres composite for efficient photoreduction and simultaneous removal of chromium

A hydrothermally prepared carbonaceous composite (GCNCS) of graphitic carbon nitride (g-C3N4) and carbon spheres with band gap in visible region is reported for simultaneous photoreduction and removal of Cr(VI) from water. After 4 h of visible light irradiation, the Cr(VI) removal with GCNCS is ∼ 100% and ∼ 82% from 10 to 75 and 100 ppm Cr(VI) solutions (pH 2), respectively. The maximum adsorption capacity for GCNCS is estimated to be 333.33 mg/g and the efficiency remained constant after five continuous cycles. The efficient photo-reduction and simultaneous removal of Cr(VI) with GCNCS is thus ascribed to the g-C3N4/carbon spheres heterojunction.

Simultaneous removal of Cr(VI) and orange G6 by polyaniline/attapulgite supported nano zero-valent iron activate persulfate

Simultaneous removal of Cr(VI) and orange G6 by polyaniline/attapulgite supported nano zero-valent iron activate persulfate

Simultaneous removal of Cr(VI), Cd, and Pb from aqueous solution by iron sulfide nanoparticles: Influencing factors and interactions of metals

• Cr(VI), Cd, and Pb may be removed from aqueous solutions simultaneously by FeS NPs. • Acidic pH values favor Cr(VI) removal, and alkaline pH values favor Cd and Pb removal. • Oxygen inhibits Cr(VI) removal, but does not influence Cd and Pb removal. • The interactions between Cr(VI), Cd, and Pb involve enhanced adsorption and precipitation. Cadmium (Cd), lead (Pb), and hexavalent chromium (Cr(VI)) are often found in soils and water affected by metal smelting, chemical manufacturing, and electroplating. In this study, synthetic iron sulfide nanoparticles (FeS NPs) were stabilized with carboxymethyl cellulose (CMC) and utilized to remove Cr(VI), Cd, and Pb from an aqueous solution. Batch experiments, a Visual MINTEQ model, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectrometer (XPS) analysis were used to determine the removal efficiencies, influencing factors, and mechanisms. The FeS NP suspension simultaneously removed Cr(VI), Cd, and Pb from an aqueous solution. The concentrations of Cr(VI), Cd, and Pb decreased from 50, 10, and 50 mg·L −1 to 2.5, 0.1, and 0.1 mg·L −1 , respectively. The removal capacities were up to 418, 96, and 585 mg per gram of stabilized FeS NPs, respectively. The acidic conditions significantly favored the removal of aqueous Cr(VI) while the alkaline conditions favored the removal of Cd and Pb. Oxygen slightly inhibited the removal of Cr(VI), but it had no significant influence on the removal of Cd and Pb. A potential mechanism was proposed for the simultaneous removal of Cr(VI), Cd, and Pb using FeS NPs. The interactions of the three heavy metals involved a cationic bridging effect on Cr(VI) by Cd, an enhanced adsorption effect on Cd by [Cr,Fe](OH) 3 , precipitation of PbCrO 4 , and transformation of PbCrO 4 to PbS. Therefore, FeS NPs have a high potential for use in the simultaneous removal of Cr(VI), Cd, and Pb from contaminated aqueous solutions.

Simultaneous removal of Cr(VI) and acid orange 7 from water in pyrite-persulfate system

As the industries advances at a fast pace, efficient and simultaneous removal of both heavy metals and organics from aqueous is essential to protecting public human health and environment. In this work, we used pyrite as reductant and catalyst for simultaneously reducing Cr(VI) and activating persulfate (PS) to degrade acid orange 7 (AO7). The results indicated that the simultaneous removal rate of AO7 and Cr(VI) by pyrite-PS was up to 100% within 60 min under acidic conditions. However, There was a competitive relationship between PS activation and Cr(VI) reduction for robbing Fe2+. At beginning of the reaction, the limited Fe2+ firstly activated persulfate rather than reduce Cr(VI). The effect of dosage of pyrite and PS on Cr(VI) reduction was more significant than that on AO7 degradation. Increased pyrite dosages from 1g·L−1 to 6 g L−1 resulted in enhanced Cr(VI) removal, and excessive PS (more than 0.4 g L−1) was not beneficial to Cr(VI) removal. Electron paramagnetic resonance (EPR) spectroscopy and radical scavenger studies demonstrated that sulfate (SO4−·), singlet oxygen (1O2) and superoxide radical (·O2−) were the crucial reactive oxygen species (ROS) in the pyrite-PS system rather than hydroxyl radical (·OH). This study showed that the pyrite-PS system could simultaneously remove AO7 and Cr(VI), which provided a new idea for the actual wastewater treatment.

Simultaneous removal of Cr(III) from high contaminated soil and recovery of lactic acid from the spent solution

It is proposed a closed-loop treatment cycle for Cr(III) removal from contaminated soils (2080 mg/kg). The treatment includes the use of lactic acid as washing agent, and the recovery of both Cr(II) and lactic acid from the spent solution. Results indicate that Cr(III) removal efficiency can be very high, passing 70% in all tested operative conditions. The metal forms strong complexes with lactic acid, and therefore cannot be eliminated through direct precipitation simply increasing the pH value. Therefore, lactic acid is preliminarily extracted from the solution using n-butanol at very acidic pH. The obtained extraction degree is generally high, varying between 0.5 and 1 according to the amount of used n-butanol solution. After lactic acid extraction, almost 100% of chromium can be recovered through precipitation in alkaline conditions. Lactic acid, in turns, can be purified and reused for a new washing treatment, separating it from n-butanol solution through water extraction. The extraction efficiency is once more satisfying (around 0.5), and not dependent on the operative pH.

Simultaneous removal of Cr(III) and V(V) and enhanced synthesis of high-grade rutile TiO2 based on sodium carbonate decomposition

Rutile TiO2 is widely applied as the raw material to produce titanium dioxide and titanium sponge, whereas the Cr (III) and V (V) impurities in rutile TiO2 significantly affect the performance of related products. In the present work, the sodium carbonate decomposition treatment on Panzhihua titanium slag was attempted, to improve the preparation process of rutile TiO2 with high crystallinity and simultaneously reduce the chromium (Cr) and vanadium (V) content as hazardous elements. Effects of sodium carbonate decomposition treatment on the crystal composition, microstructure of rutile TiO2 were determined using XRD, SEM and Raman characterization. The recovery of Cr(III) and V(V) was achieved through leaching the roasted titanium slag by dilute sulfuric acid, with the chromium and vanadium content in the residue decreasing up to 0.03 % and 0.04 %, respectively, followed by the final product rutile TiO2 was produced by the leaching residue calcined at 1323.15 K with a duration time of 120 min, with 85.56 % of TiO2 grade. The work highlights the feasibility of synchronously preparing rutile TiO2 and removing hazardous Cr (III) and V (V) impurities from titanium slag using sodium carbonate decomposition.

Simultaneous removal of Cr(VI) and triclosan from aqueous solutions through Fe3O4 magnetic nanoscale-activated persulfate oxidation

Triclosan (TCS) and Cr(VI), which are dangerous to human and ecological health, are frequently detected in surface waters. As a proposed solution, in this study, Cr(VI) and TCS were removed through an Fe3O4-activated persulfate (PS) oxidation process. At first, several influence factors on TCS degradation were investigated such as initial pH value, PS dose, temperature, Fe3O4 dosage and Cr(VI) concentration. 87.5% degradation of 5 mg L−1 TCS and 99.5% removal of 1 mg L−1 Cr(VI) were achieved within 120 min by using 2 g L−1 of Fe3O4 and 1 mM PS at 30 °C with a pH of 7. The degradation of TCS follows the pseudo-first-order kinetics under the given experimental conditions. Acid conditions were beneficial to TCS removal. TCS oxidation remained feasible at circumneutral pH. Moreover, CO32−, HPO42−, less than 10 mM of chloride ions and humic acid slightly inhibited the removal of Cr(VI) and TCS. Radical scavenger experiments indicated that sulfate radicals are the primary radical species responsible for TCS degradation. Then, three possible degradation pathways were proposed, including the breakage of ether bond, dechlorination and hydroxylation. This study indicates that the Fe3O4-activated PS oxidation process could be used as a novel treatment technique for the simultaneous removal of heavy metal and organic pollutants.

Simultaneous removal of chromium(VI) and phosphate from water using easily separable magnetite/pyrite nanocomposite

The treatment of multi-component pollutants in wastewater is a challenge. In this work, a novel nanoscale magnetite/pyrite (Fe3O4/FeS2) composite was successfully synthesized, characterized and applied in simultaneous removal of Cr(VI) and phosphate. Transmission electron microscopy, X-ray photoelectron spectroscopy, Vibrating sample magnetometer, Fourier transformed infrared spectroscopy, and X-ray diffraction analysis were applied in characterization of Fe3O4/FeS2 composites. The comparative experiments among FeS2, Fe3O4 and Fe3O4/FeS2 for the removal of Cr(VI) and phosphate were carried out. The Fe3O4/FeS2 composite with molar ratio of 1:4 exhibited remarkable performance on the removal of Cr(VI) and phosphate at initial pH 3.0. Compared with bare Fe3O4, Fe3O4/FeS2 exhibited an enhanced removal of Cr(VI). Cr(VI) removal includes electrostatic attraction and reduction. The removal of phosphate was due to electrostatic attraction and the formation of FePO4 precipitates. The efficient removal of Cr(VI) and phosphate and the great performance of solid-liquid separation show that Fe3O4/FeS2 nanocomposite is a promising material for Cr(VI) and phosphate contaminated wastewater treatment.

Hydrogen generation and simultaneous removal of Cr(VI) by hydrolysis of NaBH4 using Fe-Al-Si composite as accelerator

The present study reports a novel method for hydrogen generation and simultaneous removal of Cr(VI) from synthetic wastewater using NaBH4 as the reducing agent and Fe-Al-Si composite as accelerator. The results showed that the hydrogen generation yields of NaBH4 occurred at low pH, high temperature and stirring speed. The presence of Cr(VI) was found to inhibit hydrogen generation at the initial pH 3.0, especially at low temperature conditions. Increasing temperature resulted in the increase of hydrogen generation, whereas a higher reduction rate of Cr(VI) was obtained at low temperature. Therefore, to alleviate the contradiction between hydrogen generation and Cr(VI) removal with respect to temperature, we introduced reduction accelerator by preparing Fe-Al-Si composite using wasted fly ash as raw materials. The resultant hydrogen generation yield could be enhanced from 32.04 to 80.70%, and total Cr removal was increased from 46.72 to 98.96% at 30 °C. First, H+ produced by hydrolysis of Fe-Al-Si composite improves the hydrolysis ability of NaBH4, thus promoting its ability to reduce Cr(VI) and to produce hydrogen by itself. The Cr(VI) reduction and hydrogen generation process are competitive for H+, which is particularly evident at insufficient H+. Second, at low doses, Fe3+ exhibited a lower ability to promote hydrogen generation and simultaneous Cr(VI) removal than Al3+. One of the reasons for the low promotion ability of Fe3+ in the whole pH range was the formation of Fe0 at pH less than 3.0, and the other was the weaker hydrolysis ability of Fe3+ itself at pH greater than 3.0.