Cr Removal Efficiency Research Articles

Application of coconut shell activated carbon filter in vertical subsurface flow constructed wetland for enhanced multi-metal bioremediation and antioxidant response of Salvinia cucullate

Coconut shell activated carbon (CNSAC) was applied as a filter layer in hybrid vertical subsurface flow constructed wetland (H-VSSF-CW), in order to enhance the multi-metal removal efficiency of the constructed wetland (CW) and to reduce heavy metal accumulation on Salvinia cucullata. Treatment P + AC, (having CNSAC filter layer), showed 32, 21 and 34% more Cd, Cr, and Pb removal efficiency than treatment P (without CNSAC layer). CNSAC activated carbon adsorbed Cd and Pb and Cr by functional groups –NH, -NO2, -C-O, –OH and –CO, and significantly reduced Cd and Pb exposure to S. cucullate. Chromium adsorption by CNSAC filter layer was half (just 25% of total input) of the Cd and Pb. In treatment P, due to high Cd, Pb and Cr accumulation in S. cucullate, the antioxidant defense mechanism of the plant was collapsed and cell death was observed, which in turn has resulted reduced biomass gain (5% reduction). On the other hand, in treatment P + AC, an antioxidant defense mechanism was active in the form significantly (p ≤ 0.05) increased of SOD, CAT and proline content while reduced MDA, EL, %EB and soluble sugar. So, the application of CNSAC increased the heavy metal removal efficiency of H-VSSF-CW by adsorption of a considerable share of heavy metal and hence, reduced the heavy metal load/exposure to S. cucullate.

Integration of galvanic reactions and engineered nanoconfinement in iron-copper nanocomposites for highly-efficient remediation of Cr(VI)-contaminated acidic/alkaline water

To eliminate trace toxic hexavalent chromium (Cr(VI)) from water with different pHs, researchers focused on adsorption, reduction of Cr(VI) to trivalent chromium with followed precipitation while the complex and costly reactivity regulations via adjusting pHs was inevitable. Here we exploit Fe-Cu nanocomposites (CnZVI/Cu) with galvanic reactions and engineered nanoconfinement effect for removing Cr(VI) from acidic/alkaline water directly, consisting of phosphorylated cracked nanoscale zero-valent iron (CnZVI, crack width of 1–2 nm) anode and Cu aggregates cathode. The formed primary battery exhibits strong electrostatic interactions towards ions and outstanding reactivity of reduction and precipitation at acidic/alkaline conditions. The pH inside the cracks at neutral or alkaline conditions is calculated to turn lower for enhancing the dynamics relevant to remediation. Benefiting from those two effects, the removal efficiencies of Cr(VI) through CnZVI/Cu attain more than 99.5 % at pH ≤ 8 and even 96 % at pH of 12 in only 30 min, outperforming the previous works. Its protection on beings (water spinach, zebrafish, and cell) from suffering poisonous Cr(VI), control of adsorbed Cr from migration, and magnetic collectability demonstrate the admirable removal performance, biosafety, and stability, respectively. This work proposes highly-efficient, eco-friendly, convenient, and low-cost technology to scavenge Cr(VI) from acidic/alkaline water.

Promoted iron corrosion and subsequent hexavalent chromium removal in zero-valent iron systems by oxidant activation

Zero-valent iron (ZVI), as an effective medium, is widely used to eliminate heavy metal ions in filter tanks. However, it will react with Cr(VI) to generate Fe–Cr precipitates with low conductivity on its surface, resulting in slow iron corrosion and low Cr(VI) removal efficiency. In this study, three oxidants (KMnO4, NaClO, and Na2S2O8) were employed to promote iron corrosion in ZVI systems for enhanced Cr(VI) removal at a concentration of 5 mg/L through batch tests and column experiments. The ZVI/KMnO4, ZVI/NaClO, and ZVI/Na2S2O8 systems achieved significantly higher Cr(VI) removal rates of 31.5%, 52.8%, and 65.9% than the ZVI system (9.8%). Solid phase characterization confirmed that these improvements were attributed to promoted iron corrosion and secondary mineral formation (e.g., lepidocrocite, ferrihydrite, and magnetite) by oxidants. Those minerals offered more reaction sites for Cr(VI) reduction, adsorption, and sequestration. Cycle experiments indicated that ZVI/oxidant systems could stably remove Cr(VI). In long-term column experiment, the ZVI/NaClO column showed a much longer life-span and exhibited a 34.8 times higher Cr(VI) removal capacity than that of the ZVI column. These findings demonstrated that ZVI in combination with a reasonable amount of oxidants was a promising method for removing Cr(VI) in practical filter tanks and provided a new insight to enhance Cr(VI) removal.

One-step synthesis of ferrous disulfide and iron nitride modified hydrochar for enhanced adsorption and reduction of hexavalent chromium in Bacillus LD513 by promoting electron transfer and microbial metabolism

Microbial immobilization technology is effective in improving bioremediation efficiency and heavy metal pollution. Herein, Bacillus LD513 with hexavalent chromium (Cr(VI)) tolerance was isolated and immobilized on a novel ferrous disulfide (FeS2)/iron nitride (FeN) modified hydrochar (Fe3-SNHC) prepared from waste straws. The prepared Fe3-SNHC-based LD513 (FeLD) significantly improves Cr(VI) adsorption and reduction by 31.4 % and 15.7 %, respectively, compared to LD513 alone. Furthermore, the FeLD composite system demonstrates efficient Cr(VI) removal efficiency and good environmental adaptability under different culture conditions. Microbial metabolism and electrochemical analysis indicate that Fe3-SNHC is an ideal carrier for protecting LD513 activity, promoting extracellular polymer secretion, and reducing oxidative stress. Additionally, the carrier serves as an electron shuttle that accelerates electron transfer and promotes Cr(VI) reduction. Overall, FeLD is an environmentally friendly biocomposite that shows good promise for reducing Cr(VI) contamination in wastewater treatment.

Efficient nitrate and Cr(VI) removal by denitrifier: The mechanism of S. oneidensis MR-1 promoting electron production, transportation and consumption

When Cr(VI) and nitrate coexist, the efficiency of both bio-denitrification and Cr(VI) bio-reduction is poor because chromate hinders bacterial normal functions (i.e., electron production, transportation and consumption). Moreover, under anaerobic condition, the method about efficient nitrate and Cr(VI) removal remained unclear. In this paper, the addition of Shewanella oneidensis MR-1 to promote the electron production, transportation and consumption of denitrifier and cause an increase in the removal of nitrate and Cr(VI). The efficiency of nitrate and Cr(VI) removal accomplished by P. denitrificans as a used model denitrifier increased respectively from 51.3% to 96.1% and 34.3% to 99.8% after S. oneidensis MR-1 addition. The mechanism investigations revealed that P. denitrificans provided S. oneidensis MR-1 with lactate, which was utilized to secreted riboflavin and phenazine by S. oneidensis MR-1. The riboflavin served as coenzymes of cellular reductants (i.e., thioredoxin and glutathione) in P. denitrificans, which created favorable intracellular microenvironment conditions for electron generation. Meanwhile, phenazine promoted biofilm formation, which increased the adsorption of Cr(VI) on the cell surface and accelerated the Cr(VI) reduction by membrane bound chromate reductases thereby reducing damage to other enzymes respectively. Overall, this strategy reduced the negative effect of chromate, thus improved the generation, transportation, and consumption of electrons. SynopsisThe presence of S. oneidensis MR-1 facilitated nitrate and Cr(VI) removal by P. denitrificans through decreasing the negative effect of chromate due to the metabolites’ secretion.

Efficient removal of Cr(III) from wastewater by photo-responsive mesoporous silica

Efficient removal of Cr(III) from wastewater by photo-responsive mesoporous silica

Sequestration of chromium by Ananas comosus extract–coated nanotubes: synthesis, characterization, optimization, thermodynamics, kinetics, and antioxidant activities

AbstractHerein, a superior adsorbent was fabricated via immobilizing Ananas comosus juice extract on nanotubes (MWPJ) for the removal of chromium (VI) from simulated wastewater. The batch adsorption technique was used to establish the influence of solution pH, adsorbent dosage, solution temperature, initial Cr(VI) concentration, and contact time on the adsorption of chromium (VI). To comprehend the surface properties and to confirm chromium (VI) adsorption onto MWPJ and MWCNTs, TGA, SEM, and FTIR analyses were performed for MWPJ and MWCNTs before and after the adsorption process. These spectroscopic techniques revealed the temperature and surface characteristics responsible for the effectiveness of MWPJ. MWPJ and MWCNTs demonstrated optimum removal potential at solution pH 2, 0.05 g adsorbent dosage, and 180 min contact time. The MWPJ and MWCNTs had a maximum adsorption potential of 44.87 and 33.38 mg g−1 at 25 °C respectively. The reaction rate kinetics data for MWPJ and MWCNTs fitted well with Elovich and the pseudo-first-order kinetic model, respectively, while the saturated equilibrium data were best described by Freundlich isotherm. The thermodynamics analysis revealed that the uptake of Cr(VI) onto MWPJ and MWCNTs was a spontaneous and exothermic process. After five adsorption–desorption cycles of MWPJ, about 80% removal efficiency of Cr(VI) ions was sustained. Hence, MWPJ has demonstrated a superior capacity for practical applications in environmental remediation practice.

Efficient Removal of Cr(VI) from Wastewater by Magnetic Biochar Derived from Peanut Hull

Efficient Removal of Cr(VI) from Wastewater by Magnetic Biochar Derived from Peanut Hull

Taguchi method for optimization of Cr(VI) removal, isotherm, kinetic and thermodynamic studies

In this study, Taguchi optimization method was applied to determine the optimum operating conditions for batch adsorption of Cr(VI) from aqueous solution. Initial pH of solution, adsorbent dose, initial hexavalent chromium concentration, contact time and adsorbent type were selected as the variables, and the removal efficiency of Cr(VI) was chosen for the designated response. L18(35) orthogonal array, signal-to-noise (S/N) ratio and analysis of variance statistical procedures were applied to identify the effect of each operating parameter on the removal of Cr(VI) from aqueous solution. The signal-to-noise (S/N) ratio results showed that the optimal combination for Cr(VI) removal was at pH 1.0, adsorbent dose of 3.6 g.L−1, Cr(VI) concentration of 30 mg.L−1, contact time of 95 min and olive leaves as adsorbent type. A removal of 95.09% was obtained at these optimum conditions. The analysis of variance of the data revealed that initial pH of solution was the most dominant parameter affecting Cr(VI) removal efficiency, followed by adsorbent type, adsorbent dose, contact time and initial metal concentration. Under optimal conditions, adsorption kinetic of Cr(VI) was studied and modeled using the pseudo first-order, pseudo-second-order and intraparticle diffusion models. It was found that the pseudo-second-order model fitted the adsorption data most with the highest determination coefficient (R2 = 0.996). Freundlich isotherm model, with regression coefficient R2 of 0.953, fit well with the equilibrium isotherm data. The Langmuir maximum adsorption capacity was found to be 62.5 mg.g−1. The experimental values of ΔH°, ΔG° and ΔS° revealed that the adsorption process was spontaneous and endothermic.

Fabrication of abundantly functionalized dendritic biochar composites as adsorbents for the high-efficiency removal of heavy metal ions and dyes

A novel polymer modified biochar composite material (MNBC@p(HGMA-co-PSS-b-AA)) with dendritic structure, abundant functional groups and easy recovery was synthesized, which exhibited excellent removal capacity for Cr(VI), Lemon-Yellow (LY) and Malachite Green (MG). The prepared MNBC@p(HGMA-co-PSS-b-AA) was characterized via thermogravimetric analysis (TGA), scanning electron microscope (SEM) and Fourier transmission infrared spectra (FT-IR), proving to be with abundant functional groups and pore structure. The adsorption capacities for Cr(VI), LY and MG were 421.79, 1169.14 and 1231.53 mg/g, respectively, surpassing the capacities of most previously reported materials in recent years. Additionally, the effects of many factors on adsorption performance were explored. Experimental results indicated that the adsorption of Cr(VI), LY and MG on MNBC@p(HGMA-co-PSS-b-AA) followed pseudo-second-order and Langmuir models. Furthermore, MNBC@p(HGMA-co-PSS-b-AA) still displayed excellent removal capacity for Cr(VI), LY and MG after five reuse cycles. Moreover, different real water samples such as lake water, tap water were used to measure removal efficiency of Cr(VI), LY and MG. The results indicated that removal rates of Cr(VI), LY, and MG were not less than 86.26 %, 98.25 %, and 97.98 %. Meanwhile, MNBC@p(HGMA-co-PSS-b-AA) could maintain removal rate of 85.35 % even after continuously filtering a large number of pollutants solution in adsorption column, revealing its promising applicability for efficient removal of dyes and heavy metal ions. Surprisingly, MNBC@p(HGMA-co-PSS-b-AA) not only quickly adsorbed Cr(VI), but also enabled the concentration of Cr(VI) after adsorption to meet the World Health Organization standard for drinking water. Additionally, FT-IR and X-ray photoelectron spectroscopy (XPS) analysis suggested that adsorption mechanisms for Cr(VI) were hole filling, redox reaction and electrostatic interaction and adsorption mechanisms for LY and MG were hole filling, π–π interaction, π–π electron donor–acceptor (π–π EDA) interaction, electrostatic interaction and hydrogen bond.

Structural, optical, dielectric and magnetic behaviour of Cu1-xCoxO (x = 0.2-0.10) nano-composites and their applications in efficient removal of Cr (VI) ion from water

Hexavalent Chromium (VI) is one of the main pollutants coming from industrial waste, dyes, paints, and plastics. It is one of the major concerns due to the adverse effects associated with Cr (VI) including respiratory cancer, skin irritation, kidney damage, liver damage and perforated eardrums. Many physico-chemical techniques used for the removal of Cr (VI) are not environment-friendly and cost-effective because of the large number of chemicals used. In the present study polyvinylpyrrolidone (PVP) capped Pure and Cu1−xCoxO (x = 2, 4, 6, 8 and 10) nanocomposites synthesized by the chemical co-precipitation method were investigated for their structural, optical, magnetic, and dielectric and for the effective removal of Cr (VI) ions from contaminated water. The monoclinic structure of synthesized materials was confirmed from detailed X-ray powder diffraction (XRD) analysis and Fourier transfer infrared (FTIR) measurements. High-resolution transmission electron microscope (HRTEM) analysis confirmed the synthesis of elongated nanoparticles with an average crystalline size of ∼12–30 nm. The optical properties were determined from the analysis of diffused reflectance spectroscopy (DRS) and results showed a decreasing trend in bandgap values from 2.56 to 2.03 eV with an increase in Co2+ ion content. The presence of Cr (III) ions resulting from reduction of Cr (VI) to Cr (III) was confirmed by high-resolution X-ray photoelectron spectroscopy (XPS) analysis. The vibrating sample magnetometer (VSM) measurements revealed weak room temperature ferromagnetism in all synthesized nanocomposites tailored by Co2+ ion substitutions. The dielectric constants and dielectric losses of synthesized nanocomposites exhibit significant variation with frequency (∼1 kHz–5 MHz) and temperature (∼25 °C–300 °C) due to inter-granular activities and grain boundary effects. The adsorption capacity of the synthesized materials for the removal of Cr (VI) ions was evaluated for different initial Cr (VI) ion concentrations and adsorbent doses at room temperature. The fitted adsorption data were found to be in good agreement with the Langmuir isotherm model relative to the Freundlich and Temkin models.

Biosorption and desorption of chromium using hybrid microalgae-activated sludge treatment system

This study utilised a mixed culture of Chlorella vulgaris and bacteria from sludge to treat synthetic tannery wastewater (STWW) in modified stirred-tank photobioreactors (MSTPBRs). The MSTPBRs were fabricated locally and operated at irradiance value of 580 µmol/m2s supplied by red light-emitting diodes at 12:12 light–dark cycles and 100 ± 1 rpm continuous stirring. In each case, 50, 100 and 150 mg/L concentrations of STWW were inoculated with mixed culture of microalgae and bacteria in three MSTPBRs, with the control MSTPBR operating at 50 mg/L of STWW. Chromium concentrations were measured using colorimeter whilst Fourier transform infrared spectroscopy (FTIR) indicated possible Cr biosorption. Maximum Cr (VI) and total Cr removal efficiencies of 93 and 94% were achieved, with more than 78% total Cr recovery. Results from FTIR suggested involvement of Chlorella vulgaris in the Cr biosorption. The hybrid microalgae-bacteria system efficiently treated tannery wastewater with considerable Cr removal efficiencies. The potentials of the system in treating tannery wastewater in larger scale may require further investigation.

Novel montmorillonite/jute composites functionalized with polyethyleneimine and cetyltrimethylammonium bromide for Cr(VI) adsorption

Industrial wastewater containing heavy metal ions of Cr(VI) has drawn increasing attention because of extreme toxicity and detrimental effects on human health. This paper reported a novel nanocomposite adsorbent for Cr(VI) removal from water, consisting of montmorillonite (Mt), jute and the functional modifiers of polyethyleneimine (PEI) and cetyltrimethylammonium bromide (CTAB), i.e., Mt/Jute-PEI-CTAB. The Mt/Jute-PEI-CTAB adsorbent was synthesized via a synergistic method of ultrasonic treatment and sand milling. Various methods were used to characterize the Mt/Jute-PEI-CTAB adsorbent, and the effects of different components on Cr(VI) adsorption behaviors were systematically investigated. The adsorption experiments indicated that Mt/Jute-PEI-CTAB exhibits an excellent Cr(VI) adsorption performance, with a maximum adsorption amount of 59.3 mg/g, 4 times higher that of the Mt/Jute adsorbent without PEI or CTAB. A high Cr(VI) removal efficiency of 99% was achieved, and it is superior to most of clay/biomass-based adsorbents reported. The significantly improved Cr(VI) adsorption capacity can be attributed to the amino functional groups in Mt/Jute-PEI-CTAB through the modification of biomass, CTAB and PEI. The Cr(VI) adsorption process on Mt/Jute-PEI-CTAB can well be described using the pseudo-second order kinetic model and the Langmuir isotherm model. This work provides a novel and environmentally friendly method to design high-performance Cr(VI) adsorbents using clay minerals and biomass for environmental remediation.

Synergistic effect of adsorption-photocatalytic reduction of Cr(VI) in wastewater with biochar/TiO2 composite under simulated sunlight illumination.

Photocatalysis, which is an alternative technology to conventional methods, utilizes solar energy as the driving force to address environmental concerns and has attracted widespread attention from chemists worldwide. In this study, a series of photocatalytic materials composed of agricultural waste and titanium dioxide (TiO2) nanomaterial was prepared for the synergistic adsorption-photocatalytic reduction of hexavalent chromium in wastewater under mild conditions. The results showed that the TiO2 nanomaterial exhibited a higher photogenerated carrier separation efficiency and performance for the adsorption-photocatalytic reduction of Cr(VI) after loading straw biochar (BC). When the loading amount of BC was 0.025 g (i.e., TBC-3), the removal efficiency of Cr(VI) was as high as 99.9% under sunlight irradiation for 25 min, which was 2.9 and 3.5 times higher than that of pure TiO2 and BC samples, respectively. Additionally, after four cycles of experiments, the removal efficiency of Cr(VI) by TBC-3 remained at about 93.0%, proving its good chemical ability in our reaction system. Its excellent adsorption-photocatalytic performance is mainly attributed to the synergistic effect of the strong adsorption of BC and the outstanding photocatalytic performance of TiO2. Finally, the possible mechanism for the synergistic adsorption-photocatalytic reduction on BC/TiO2 to remove the highly toxic Cr(VI) in wastewater was proposed.

Study on the behavior of impurity removal from lithium-iron-phosphate slag using the ultrasonic-assisted sulphuric acid leaching

The recovery of iron phosphate from the leaching slag of used lithium iron phosphate cathode materials is a crucial step to achieve closed-loop recovery of lithium iron phosphate, which has not yet been effectively accomplished. In the study, ultrasonic-assisted sulfuric acid leaching was used to remove impurities in the iron phosphate, to meet the stringent impurity content requirements for battery-grade iron phosphate regarding impurity content. Optimization of leaching conditions involved a sulfuric acid concentration of 0.2 mol?L-1, acid-leaching time of 30 min, power of 50 W, and reaction temperature of 80?. Under these conditions, the removal efficiencies of Cr, Cu, Ni, and Zn in iron phosphate were 26.09%, 83.0%, 75.9%, and 96.3%, respectively. Simultaneously, the content of impurity elements Cr and Zn concurred with the standard for battery-grade iron phosphate (HG/T 4701-2021), with both 50 ppm and 10 ppm contents. The leaching results indicated the effectiveness of ultrasound in enhancing the removal of impurity elements in iron phosphate within a sulfuric acid solution. Further analyses, including XRD, particle size, TEM, and XPS indicated that the surface of the iron phosphate particles cavitated after ultrasonic acid leaching, resulting in the formation of numerous pores. Additionally, particle collisions led to a reduction in particle size, with no generation of by-products during the process. This innovative approach not only contributed to the removal of impurity elements but also provided insights into the reuse of leaching slag (iron phosphate) and offered guidance for the recovery of metals from waste lithium iron phosphate cathode materials.

The use of banana peel as a low-cost adsorption material for removing hexavalent chromium from tannery wastewater: optimization, kinetic and isotherm study, and regeneration aspects.

When the concentration of hexavalent chromium (Cr(vi)) in the environment is greater than a certain limit, it becomes a global concern. Thus, the aim of this study was to use banana peel as an adsorbent to remove heavy metals, specifically Cr(vi) ions from wastewater. Banana peel (BP) was activated in a furnace for 2 h (h) at 450 °C and 50% humidity. Subsequently, the activated BP was characterized by proximate analysis, elemental analysis, scanning-electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer Emmett Teller (BET) analysis, and thermogravimetric analysis (TGA). According to the characterization results, the activated BP possessed a porous surface and high surface area of 200 m2 g-1, which are important adsorption parameters. Additionally, the removal efficiency for Cr(vi) was evaluated in terms of pH, contact time, initial concentration, and adsorbent dose. Consequently, the optimal operating conditions for removing 94% of Cr(vi) were found to be an adsorption time of 92 min, adsorbent dose of 1.5 g L-1, pH of 3, and initial Cr(vi) concentration of 38 mg L-1. In addition, the adsorption kinetics and isotherms were examined. The pseudo-first-order model with an R2 of 0.996 and the Langmuir isotherm with an R2 of 0.997 were found to be the most effective mathematical representations of the rate and nature of Cr(vi) adsorption on the surface of the activated BP, respectively. Furthermore, it was discovered that the activated BP could be reused six times before its removal efficiency was reduced to less than 70%.

Investigating the Optimization of Magnetic Biochar Production from Rubber Seed Shells for Enhanced Cr(VI) Removal Efficiency

This study aimed to utilize agricultural and produce low-cost magnetic biochar from rubber-seed shells using ferric chloride (FeCl3) as a transition metal. The study employs Response Surface Methodology (RSM) based on the Box-Behnken Design (BBD) to determine optimal production conditions for removing chromium (Cr(VI)). The effect of preparation conditions such as pyrolysis temperature (500-700 °C), duration (90-180 min), and impregnation (1-3 M) on the produced magnetic biochar was examined. The optimal condition was demonstrated based on yield percentage and Cr(VI) removal efficiencies. The study revealed that the optimal conditions for producing magnetic biochar from rubber seed shells were a pyrolysis temperature of 580 °C, a pyrolysis time of 130 min, and a FeCl3 concentration of 3 M. Under these conditions, a yield of 48.63% was achieved, and the removal efficiencies for Cr(VI) were 41.29%. This research suggests that utilizing agricultural waste products from rubber seed shells may be a viable and economical method for producing magnetic biochar, which can serve as an efficient adsorption agent.

Ferrocenylselenoether and its cuprous cluster modified TiO2 as visible-light photocatalyst for the synergistic transformation of N-cyclic organics and Cr(vi).

In this study, fcSe@TiO2 and [Cu2I2(fcSe)2]n@TiO2 nanosystems based on ferrocenylselenoether and its cuprous cluster were developed and characterized by X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX), and electron paramagnetic resonance (EPR). Under optimized conditions, 0.2 g L-1 catalyst, 20 mM H2O2, and initial pH 7, good synergistic visible light photocatalytic tetracycline degradation and Cr(vi) reduction were achieved, with 92.1% of tetracycline and 64.5% of Cr(vi) removal efficiency within 30 minutes. Mechanistic studies revealed that the reactive species ˙OH, ˙O2-, and h+ were produced in both systems through the mutual promotion of Fenton reactions and photogenerated charge separation. The [Cu2I2(fcSe)2]n@TiO2 system additionally produced 1O2 from Cu+ and ˙O2-. The advantages of the developed nanosystems include an acidic surface microenvironment provided by Se⋯H+, resourceful product formation, tolerance of complex environments, and excellent adaptability in refractory N-cyclic organics.

Removal of Cr(vi) in wastewater by Fe-Mn oxide loaded sludge biochar.

Sludge biochar loaded with Fe-Mn oxides (FMBC) was prepared and employed to remove Cr(vi) from wastewater. The influences of solution pH, co-existing ion, contact time, adsorption temperature and Cd(vi) concentrations on removing Cr(vi) by FMBC were investigated. The Cr(vi) adsorption on FMBC had strong pH dependence. Additionally, Na+, Mg2+, Ca2+, SiO32-, NO3- and Cl- ions exhibited no influence on Cr(vi) removal efficiency for FMBC, whereas there were inhibition effects of Pb2+, Cu2+, Ni2+, CO32-, SO42-, and PO43- on removing Cr(vi). The Cr(vi) adsorption from solution for FMBC was well described by models of pseudo-second-order and Langmuir, and the largest Cr(vi) removal capacity of FMBC reached 172.3 mg g-1. FMBC had good capacity for treating electroplating wastewater and mineral dissolving wastewater containing Cr(vi). After five regenerations, the 50 and 5 mg L-1 Cr(vi) removing efficiency of FMBC was 82.34% and 97.68%, respectively. The Cr(vi) removal for FMBC involved adsorption-reduction and re-adsorption of Cr(iii) generated by reduction. These results indicated that FMBC has good prospects for remediating Cr(vi)-containing wastewater.

Performance and mechanism of Cr(VI) removal by sludge-based biochar loaded with zero-valent iron

In this work, sludge-based biochar was prepared from municipal sludge as raw material and coupled with zero-valent iron to obtain sludge-based biochar loaded with zero-valent iron (ZVI@SBC) for treating Cr(VI)-containing wastewater. Batch adsorption experiments were carried out to investigate the effects of adsorbent dosage, solution pH, adsorption time, adsorption temperature and pollutant concentration on the Cr(VI) removal by ZVI@SBC, and the potential mechanism of Cr(VI) removal by ZVI@SBC was investigated by characterization techniques. The optimum values of Cr(VI) removal efficiency and adsorption capacity by ZVI@SBC were achieved at the dosage of 25 mg. The Cr(VI) removal performance by ZVI@SBC existed strongly pH-dependent. Moreover, increasing the adsorption temperature promoted the Cr(VI) removal by ZVI@SBC. Notably, the Cr(VI) removal by ZVI@SBC was consistent with the pseudo second order kinetic model and the Langmuir model. The adsorption experiments showed that the maximum Cr(VI) adsorption capacity by ZVI@SBC was 150.83 mg/g at initial Cr(VI) concentration of 50–150 mg/L and adsorption temperature of 298 K. The Cr(VI) removal process by ZVI@SBC was homogeneous and chemical adsorption. The removal mechanism of Cr(VI) by ZVI@SBC was a complex process involving adsorption-reduction of Cr(VI) and release-adsorption of Cr(III). This work demonstrated that the sludge-based biochar loaded with zero-valent iron hold a better removal ability for Cr(VI) wastewater and provided a reference for the removal of Cr(VI) wastewater.