Elimination Of Cr Research Articles

Synthesis of novel Ag-doped ZnFe based-oxides nanocomposite for wastewater treatment, self-cleaning, and corrosion resistance

To tackle the critical environmental and industrial challenges, this research endeavors to develop nanomaterial with enhanced photocatalytic function, corrosion resistance, self-cleaning capabilities, and optimal effluent treatment. This research successfully synthesized Ag@ZnFe2O4 nanocomposite to activate peroxymonosulfate (PMS) for the removal of Congo red from water. The structural composition and morphology of the materials were examined by the utilization of XRD, FTIR, XPS, SEM with EDS and TEM. The study examined the impacts of catalyst dosage, concentrations of PMS, pH, and simultaneous ions on the experiment, as well as the ability of the nanocomposites to be reused and their stability. The photocatalytic degradation process was hypothesized to operate using free radical trapping tests. Results indicated that the heterostructure junction flanked by ZnFe2O4 nanoparticles and Ag promoted charge transfer, reducing electron-hole recombination. By adding 5mg of Ag@ZnFe₂O₄ nanocomposite, Congo red degradation was optimized at 98.7% due to the huge surface area of Ag microflowers, which boosted active sites and CR elimination. Due to nanoparticle surface charge, PMS speciation, and radical interactions, CR degradation was most efficient at pH 7.3 and less efficient at pH 9.5. CR degradation rates rose with PMS concentration, reaching 34.7%, 67.9%, and 97.9% at 0.3, 0.6, and 1mM, respectively. The order of the inhibitory action was CO32− > H2PO4− > Cl− > NO3−. Free radical entrapment experiments show that hydroxyl (•OH) and sulfate radicals (•SO₄⁻) are key in CR photodegradation, with h+ and •O₂ being the main active species. ESR tests revealed radicals, while electron transfer between ZnFe₂O₄ and Ag boosted carrier migration, driving redox cycles and CR breakdown into stable byproducts like CO₂ and H₂O. Light-induced reaction eliminated 45.8% of TOC, indicating CR partial mineralization. Mechanism of PMS-based photodegradation of CR removal was proposed. This study underscores the promising potential of Ag@ZnFe2O4/nanocomposites for PMS activation in degrading Congo red-contaminated wastewater. Electrochemical impedance spectroscopy (EIS) showed that a polymeric nanocomposite coating greatly improves the ability to resist corrosion in steel substrates when exposed to a 3.5% NaCl solution. This is achieved by reducing the corrosion current density and boosting corrosion resistance. Superhydrophobic nanocomposite coatings repel water and pollutants, safeguarding various substrates from soil residues.

Sustainable Removal of Cr(VI) from Wastewater Using Green Composites of Zero-Valent Iron and Natural Clays

Composites for efficient removal of hexavalent chromium Cr(VI) from industrial wastewater were obtained by deposition of nano-zero-valent iron (nZVI), synthesized by environmentally friendly synthesis using oak leaf extract, on inexpensive, natural, readily available and cheap natural raw materials, sepiolite (SEP) or kaolinite/illite (KUb) clay, as support. nZVI particles were deposited from the FeCl3 solution of different concentrations, with the same volume ratio extract/FeCl3 solution (3:1), and with different masses of SEP or KUb. Physico–chemical characterization (SEM/EDS, FTIR, BET, determination of point of zero charge) of the composites and nZVI was performed. The results of SEM and BET analyses suggested more homogeneous deposition of nZVI onto SEP than onto KUb, which ensures greater availability of the nZVI surface for Cr(VI) anions. Therefore, the higher Cr(VI) removal at all investigated initial pH values (pHi) of the solution (3, 4 and 5) was achieved with the SEP composites. The adsorption results indicated that the elimination of Cr(VI) was achieved via the combined effect of reduction and adsorption. The removal of total chromium at pHi = 3 was approximately the same as that of Cr(VI) removal for the KUb composites, but lower for the SEP composites, indicating lower removal of Cr(III) compared to the reduced Cr(VI). The SEP/nZVI composite with the highest removal efficiency was applied for Cr(VI) removal from real wastewater at pHi = 3 and pHi = 5. The results demonstrated the high Cr(VI) removal capacity, validated the assumption that a good dispersion of nZVI particles is beneficial for Cr(VI) removal and showed that the produced green composites can be efficient materials for the removal of Cr(VI) from wastewater.

Enhanced photocatalytic reduction of Cr (VI) using porous hierarchical Bi2O3/Bi2S3 high-low heterojunctions: Novel strategies and charge transfer mechanisms

High-low heterojunctions derived from metal-organic frameworks (MOFs) have promising applications in photocatalytic wastewater treatment because of their high photo-redox ability and boosted charge separation efficiency. Herein, Bi-MOF derived porous hierarchical Bi2O3/Bi2S3 nanoflower-like heterojunctions were prepared by the calcination-hydrothermal method. The optimized Bi2O3/Bi2S3-2 composite showed a higher degradation rate of Cr (VI) (99.79 % in 30 min) than the pure substance. Moreover, comprehensive studies were conducted on the kinetics, stability and recycling of Bi2O3/Bi2S3, as well as optical characteristics. The active species trapping experiments confirmed that e- plays a dominant role in the elimination of Cr (VI). These findings provided novel strategies for construction of porous hierarchical heterojunctions with advanced visible-light-induced degradation performance. The enhanced photo-degradation efficiency of the optimal nanocomposite was assigned to the higher visible-light absorbance, separation of photogenerated carriers, reduced recombination of photo-induced carriers, and enhanced redox capability owing to the construction of porous hierarchical heterojunctions amongst the components.

Polypyrrole/waste molasses composites as a superior adsorbent for highly efficient and selective removal of Cr(VI) from aqueous environments

Reduction of Cr(VI) to Cr(III) or elimination of Cr(VI) from aqueous environments is the most commonly used method to address Cr(VI) contamination. Waste molasses (WM) is a by-product from the sugar industry, if discharged arbitrarily without treatment can lead to waste of resources and cause serious environmental pollution. In this study, the modification of polypyrrole (PPy) with WM (PPy/WM) not only provided PPy with good dispersibility and higher specific surface area, but it can also enrich the functional groups on the surface of PPy. The findings indicated that PPy/WM composites can serve as superior adsorbent materials for highly efficient and selective removal of Cr(VI) when different interfering ions are present. e.g., 150 mg/L of Cr(VI) can be eliminated completely within 6 h under the condition of PPy/WM amount of 0.8 g/L, temperature of 303 K, and pH of 2.0. PPy/WM showed excellent performance for removal of Cr(VI) in a wide pH range (2.0 - 10.0). PPy/WM exhibited excellent reusability for five cycles without obvious loss of its adsorption capacity. The maximum Cr(VI) adsorption capacity of PPy/WM was 662.25 mg/g at 323 K, evidently higher than that of unmodified PPy (194.17 mg/g). Cr(VI) removal by PPy/WM was chiefly accomplished by electrostatic adsorption, ion exchange and in-site reduction. This study not only provides a new technology for efficient adsorption and in-situ reduction of Cr(VI), but also realizes the resource utilization of WM and solves the WM pollution problems.

Microwave-assisted Chitosan Based Activated Bentonite (CAB) for Cr (VI) Removal from Acid Mine Drainage

Background: Acid Mine Drainage (AMD) causes widespread environmental problems including the contamination of land and water bodies. The low-cost adsorbent synthesis from regional resources can be used for removal of toxic metals such as Cr (VI) from AMD. Objectives: Rapid synthesis of Chitosan based Activated Bentonite (CAB) nanocomposite adsorbent using microwave-assisted method for the removal of Cr (VI) from the acidic environment. Methods: The compositional and surface morphological characterization was conducted using FTIR, XRD, and FEG-SEM-EDS analysis. The Synthesized adsorbents were used to removal of Cr (VI) ion under different experimental conditions including initial concentration (45 to 120 mg L-1), contact time (0 to 180 min), dose (0.25 to 4 g L-1), solution pH (2 to 6). Findings: The optimum removal was 73.14 % at room temperature (27 ℃), pH 2, concentration 90 mg L-1 and 2.0 g L-1­ dose of CAB adsorbent. The field evaluation parameters such as ionic strength under various acids and regeneration ability show the potential applicability of the adsorbent in remediation of AMD. The kinetics models and adsorption isotherm were fitted with pseudo first order model (R2 > 0.86) confirmed 49.62 mg g-1 maximum adsorption capacity by Langmuir isotherm (R2 > 0.93). Novelty : Novel microwave assisted rapid synthesis of CAB nanocomposites adsorbent has the possibility to use for large scale synthesis and elimination of Cr (VI) from the AMD. Keywords: Chitosan, Activated bentonite, Cr (VI) removal, Adsorption isotherm, Kinetics rate models

Cr(VI) adsorption on activated carbon, sludge derived biochar, and peanut shells derived biochar: Performance, mechanisms during the reuse process and site energy distribution analysis

The reusability of adsorbents for Cr(VI) removal and the related mechanism are important to practical application. In this study, commercial activated carbon (AC), sludge-derived biochar (SBC), and peanut shell-derived biochar (PBC) were reused to the tenth round on Cr(VI) removal and then characterized to analyze the ongoing adsorption mechanisms involved during the reuse process. The site energy distribution theory was used to analyze the changes in site energy during the reuse of synthesized adsorbents. Batch adsorption experiments revealed that Cr(VI) removal efficiency decreased from 99.97 % to 43.37 %, 47.22 %, and 40.13 % when reusing AC, SBC, and PBC, respectively, from the first to the tenth round at optimum conditions. The adsorption capacity decreased with each reuse round due to a decrease in -OH, CO, O=C-O, and CO on the surface of adsorbents. The site energy (E*) values decreased as adsorption capacity (qe) increased, indicating that HCrO4− and Cr2O72− first occupied high-energy adsorption sites and then the low-energy adsorption sites. Reduction of Cr(VI) to Cr(III) was identified as significant in the elimination of Cr(VI). These findings offer new insights into the reusability behavior and interaction mechanisms of adsorbents during Cr(VI) elimination from wastewater.

Efficiency of FeSO4.7H2O as a Coagulant on Chromium Hexavalent Removal Using Coagulation-Flocculation Process: Optimization Using Response Surface Methodology

Response Surface Methodology-Central Composite Design (RSM-CCD) is widely employed in the process of optimizing the applications of coagulants for wastewater treatment. The experiment aims to evaluate the effect of the FeSO4.7H2O concentration and settling time on removing the chromium hexavalent (Cr (VI)) from wastewater by coagulation-flocculation using RSM-CCD. This experiment was carried out based on the results of the model and optimization using the RSM-CCD to obtain the removal efficiency of Cr (VI) as well as determine the influence of the concentration of FeSO4.7H2O (X1) and settling time (X2). The RSM-CCD experimental design uses a two-factor and two-level design with 13 experimental runs and 5 center points. Inter-variable regression coefficients are also produced with the elimination of Cr (VI). The ANOVA test results showed a fairly significant figure for the assembled model. The model validation results show that the proposed model is compatible with the experimental results. RSM optimization shows optimum conditions based on experimental FeSO4.7H2O coagulant concentration variables and coagulation time at 150 mg/L coagulant concentration and 60 minutes of time, and the prediction results based on RSM-CCD optimization using Design Expert show the most optimum condition at 165,562 mg/L coagulant concentrations and 60,527 minutes of time.

Interaction between Cr(VI) and Tubificidae in sludge reduction system: effect, reduction, and redistribution of Cr(VI).

The treatment of heavy metals in sewage treatment systems has gained more attention with the increase in heavy metal hazards. Tubificidae in sludge reduction have been widely studied; however, little is known about the effect of Tubificidae in the treatment of Cr-containing wastewater. In this study, the mechanism of Tubificidae in the sludge reduction system with Cr stress was studied. Predation experiments by Tubificidae in a Cr-containing sludge reduction system were conducted to investigate the changes in enzyme activities in the Tubificidae under different concentrations of Cr, and the distribution of Cr in the sludge reduction reactor was analyzed. The kinetic model of uptake and elimination of Cr in Tubificidae was established. The results showed that the maximum activation multiplier factor of superoxide dismutase (SOD) activity was 1.95 under the low concentration of Cr(VI), which indicated that Tubificidae had a certain detoxification. After the effect of Tubificidae on Cr(VI) experiments, the Cr concentrations in Tubificidae, sludge, and feces increased first and then decreased with exposure time, and the proportion of total Cr and Cr(VI) in the sludge decreased from 71.98% and 42.7% to 29.18% and 6.82%, respectively. The detoxification mechanism of the Tubificidae could be activated with Cr stress, and 63.22% of the Cr(VI) was converted to Cr(III). The bioconcentration factor (BCF) for theoretical equilibrium was 446, the maximum bioaccumulation factor (BAF) reached 0.97 on the 15th day. It can be seen that Tubificidae could be considered a good scavenger of environmental Cr(VI). The hyperbolic model fits the process of Cr uptake and elimination well and can be used as a predictive tool for Tubificidae accumulation.

Effective removal of hexavalent chromium with magnetically reduced graphene oxide bentonite

AbstractWater pollution by hexavalent chromium (Cr(VI)) is widespread and problematic. As a result, more research into economic Cr(VI) removal is needed. In this study, we created and employed an adsorption–reduction mechanism to remove Cr(VI). Magnetically reduced graphene oxide bentonite (MrGO-BT) is acid resistant and can undergo magnetic separation. The hydroxyl group of chitosan (CS) condensed with the functional groups on the surface of bentonite (BT), and the MrGO-BT sandwich has been fabricated and constructed from an Fe3O4 core layer sandwiched by reduced graphene oxide (rGO) and a BT shell, with CS acting as a crosslinker. Cr(VI) elimination by MrGO-BT was exothermic and spontaneous according to thermodynamic analyses. The adsorption kinetics and adsorption isotherms were characterized by the pseudo-second order kinetic theory and the Langmuir model, respectively. Regarding the elimination of Cr(VI), the greatest adsorption ability for Cr(VI) elimination achieved was 91.5 mg g–1. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy suggested that Cr(VI) was reduced by C–O–H on MrGO-BT to produce Cr(III) and H–C=O, and that Cr(III) chelated with amino groups or exchanged with BT after intercalation. In addition, the introduction of Cu2+ increased the positive charge of MrGO-BT and amplified the electrostatic interaction between Cr2O72− and HCrO4–, which is what caused Cr(VI) to be eliminated. Cu2+ and reduced Cr(III) combined with -NH2 on the surface of MrGO-BT to form -NH-Cr(III) or -NH-Cu2+, and Cr(VI) elimination via chelation and ion exchange was confirmed. MrGO-BT is shown to be an adsorbent with high acid resistance and good magnetic responsiveness and stability.

Efficient removal of Cr(VI) by the modified biochar with chitosan schiff base and MnFe2O4 nanoparticles: Adsorption and mechanism analysis

Cr(VI) contained the characteristic of water solubility, mobility and cell permeability in aqueous solution. As a result, the treatment of Cr(VI) in aqueous solution was very necessary before it was discharged into water body. A novel adsorbent of the modified biochar with chitosan schiff base and MnFe2O4 nanoparticles (CsSB/MnFe2O4@BC) was prepared, characterized and applied into the elimination of Cr(VI) by batch adsorption process. CsSB/MnFe2O4@BC composites were characterized by some technologies (Such as SEM, TEM, XRD and FT-IR). The results showed that it was an irregular, wavy and heterogeneous surface, and it contained MnFe2O4 nanoparticles and functional groups of C−H, O−H and C−O−C stretching vibrations. The operational parameters (For example, pH, concentration of Cr(VI), contact time and temperature) had an important influence on the adsorption capacity of Cr(VI) removal. The adsorption processes were best fitted to Pseudo-second order model and Freundlich model. Additionally, the maximum uptake capacity of Cr(VI) ions reached 125.34 mg/g. The possible mechanisms were ion exchange, surface complexation, electrostatic attraction, and pore adsorption. After five cycles, adsorption capacity of Cr(VI) by CsSB/MnFe2O4@BC still remained high, and reached 102.45 mg/g. Therefore, it was a simple, economical, efficiency and reuse adsorbent and could be used as an high efficient adsorbent in the treatment of Cr(VI) in aqueous solution.

Secondary resource utilization of exhausted copper slags (ECSs): Efficient removal of Cr (VI) from aqueous solutions and removal mechanism

Exhausted copper slags (ECSs) are secondary slags produced in the reusing process of copper smelting fly ashes and have the potential to synthesize adsorbent for the elimination of toxic elements. This study focuses on the potential of the original ESCs for the detoxication and removal of Cr(VI) from aqueous solutions. Batch adsorption experiments showed that ESCs present an excellent performance on Cr(VI) eliminate, and the maximum adsorption capacity is 110.50 mg∙g−1 at acid solutions (pH = 2) with a mild temperature condition (308 K). Furthermore, the adsorption efficiency of Cr was barely effected by the comment co-existing elements, such as NO3– and SO42-, indicating its specific adsorption capacity for Cr. The elimination of Cr onto ESCs fits well with the Langmuir adsorption model, indicating that the adsorption process was controlled by monolayer adsorption. Moreover, Cr(VI) adsorption onto ESCs also followed the Pseudo-second-order kinetics with the adsorption rate constant k at 2.65 × 10-3 g·mg−1·min−1. Mechanistic analysis indicated that ECSs eliminated Cr(VI) by electrostatic adsorption and flocculation precipitation, and reduced Cr(III) by Fe2+, Mo2+, S2-, and SO32-. The environmental risks during its adsorption implication process were also accessed and the toxic elements, such as Cu, As, and Pb in the materials were barely detected in the residue solutions. Thus, ECSs could be used as a facile and cost-effective adsorbent for Cr(VI) removal, even without any further pre-treatment process, which is meaningful to the disposal of this typical industrial waste.

Chromium(III) Removal from Nickel(II)-Containing Waste Solutions as a Pretreatment Step in a Hydrometallurgical Process.

This paper presents Cr(III) removal from nickel sulfate waste solutions as a pretreatment step for the modification of hydrogen storage alloys. Adsorption with two cation exchange resins, Dowex G26 (strongly acidic) and MAC-3 (weakly acidic), and precipitation with various solutions were chosen as simple operations for Cr(III) removal from waste solutions. The adsorption of Cr(III) was investigated for both model and real waste nickel solutions. Dowex G26 appeared to be more efficient in Cr(III) removal (RCr(III) from 43 to 80%) than MAC-3 (RCr(III) from 40 to 53%). However, the adsorption from multi-component solutions (presence of Co(II), Ni(II) and Cr(III)) showed no selectivity in Cr(III) adsorption in comparison to those of Co(II) and Ni(II). Cr(III), Ni(II) and Co(II) were removed at a comparable level (30–36%) from a three-component solution of 10 g/dm3 of each metal ion, and a 56–72% removal of these ions was achieved from the real solution. Therefore, the precipitation of Cr(III) was carried out from a real waste nickel solution to compare its performance with adsorption. The best precipitation solution appeared to be 3 and 30% NaOH due to the quantitative precipitation of Cr(OH)3 at pH 5 and relatively small co-precipitation of Ni(II) and Co(II) hydroxides (PCo(II) = 20–52%, PNi(II) = 0–54%). Based on the results of the research, it can be concluded that precipitation with a NaOH solution is an efficient pretreatment operation of an electrolyte for further steps of the hydrometallurgical process of nickel electrodeposition and appears to be more selective in the elimination of Cr(III) than adsorption with Dowex G26 resin.

Removal of Chromium (VI) from the Steel Mill Effluents Using the Chemically Modified Leaves of Pteris vittata as Adsorbent

Chromium (Cr), a metal that is released in appreciable amounts from the steel industry into water bodies, is not only the main causative agent of lung cancer in human but also negatively affects the metabolic activities of plants. Keeping in view the hazardous effects of Cr(VI), the present study was aimed to eliminate it from industrial effluents of steel mills installed in Dargai District Malakand, Pakistan, using chemically modified Pteris vittata plant leaves as an adsorbent. The instrumental techniques such as FTIR, surface area analysis, SEM, TGA and EDX were used to evaluate surface functionality, morphology, thermal stability and elemental composition of the modified leaves. To identify the ideal conditions for the biosorption process, batch adsorption tests were carried out under varied conditions of pH, contact time, initial metal concentration, biosorbent dose, as well as temperature. Various models, such as those of Freundlich, Jovanovich, Temkin, Langmuir, and Harkins–Jura, were utilized to explain the isothermal experimental data. The high value of R2 (0.991) was exhibited by the Langmuir model. Pseudo-first-order, power function, pseudo-second-order, intraparticle diffusion, and Natarajan–Khalaf models were employed to obtain an insight into kinetics of the process. The highest R2 value, close to unity was recorded with pseudo-second order. At pH = 2, the best elimination of Cr was observed with maximum uptake capacity qmax(66.6 mg/g) as calculated from the Langmuir isotherm. The thermodynamic analysis, which was conducted at different temperatures, showed that the nature of this sorption process was exothermic and spontaneous. The modified leaves-based biosorbent could be used as an alternative adsorbent for effective Cr elimination from water, and its use could be extended to other heavy metals and organic pollutants as well, and further experimentation are needed in this regard.

Exchanged zeolite adsorbent for removing Cr(VI): Kinetics, thermodynamics and adsorption mechanism

ABSTRACT In this work, copper-exchange-zeolite was prepared as appropriate material for the elimination of Cr(VI). The materials were characterised by SEM/EDX, N2 adsorption-desorption, and FTIR. pH effects, initial Cr(VI) concentration, contact time, and temperature on adsorption efficiency were evaluated. The materials have uniform and regular crystal shapes indicating an unmodified morphology according to SEM findings. The amount adsorbed is optimal at pH = 10 for all zeolites. The Pseudo-second-order model describes best kinetic adsorption. The adsorbed quantity decreases with temperature whatever the material. The maximum adsorption capacity was 9.30 mg g−1. The effect of competing anions on adsorption was examined, it was discovered that the CO3 2- had a significant impact on adsorption efficiency. The activation energy value of Cr(VI) adsorption on exchanged zeolite was 0.120 kJ mol−1. The electrostatic interaction between CrO4 2- and Cu2+ inserted in the zeolite explains the adsorption mechanism The result was confirmed by the diffusion Boyd and D-R model. The present study indicates that this material is efficient adsorbent to eliminate Cr(VI) in Industrial rejects.

A study on the utilization of rice husk as a biosorbent material for Cr (VI) removal from industrial effluent


 
 
 
 Purpose: To study Cr (VI) removal from waste water using chromium-resistant bacterial strains in combination with rice husk.
 Methods: Two strains of Exiguobacterium sp. resistant to chromium (VI) were applied in the present work. Rice husk (RH) was used as an agricultural waste for Cr (VI) removal. The elimination of Cr from the husk was chemically facilitated using hydrochloric, sulphuric and citric acids, as well as formaldehyde and potassium dihydrogen phosphate Investigation of optimum physical factors such as pH, temperature, shaking speed and biomass concentration on Cr (VI) removal was carried out using citric acid-processed rice husk alone, and in combination of bacterial strains. Fourier transform infra-red (FTIR) spectroscopy was performed to determine the contributions of different functional groups involved in Cr (VI) binding. Scanning electron microscopy (SEM) of treated and untreated RH was also performed.
 Results: Citric acid-processed RH was most effective in the removal of chromate (97.3 %). The two bacterial strains combined with rice husk proved highly efficient in Cr (VI) removal from sterile and non-sterile industrial effluents. FTIR spectra showed the involvement of esters, amines and aliphatic functional groups in Cr (VI) binding, while SEM displayed the damaging effects of Cr (VI) on the surface of RH; however, bacterial inoculation minimized the damage.
 Conclusion: Exopolysaccharides from Exiguobacterium strains and citric acid-processed rice husk demonstrated high efficiency for Cr (VI) removal. Hence, RH with these bacterial strains are potential biosorbents for control of heavy metal contamination arising from industrial effluents.
 
 
 

Utilization of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) Impregnated Activated Carbon for Removal of Hexavalent Chromium

Chromium (Cr) is a toxic heavy metal present in industrial effluent which could cause degenerative diseases on ingestion. Therefore, elimination of Cr from contaminated water becomes essential to preserve and sustain the quality of life. In this study, superparamagnetic iron oxide nanoparticles (SPIONs) were impregnated on activated carbon and checked for enhanced removal of Cr(VI). Thus, granular activated carbon (N‐GAC) of mesh size 8∗20 was impregnated with SPIONs to produce SPIONs impregnated activated carbon (Sp‐GAC) and characterized using UV‐VIS spectrophotometer, FT‐IR, SEM‐EDX, XRD, and VSM. Sp‐GAC was found to be possessing superparamagnetic behavior, and it was used in batch adsorption study where the adsorption parameters like pH, concentration of adsorbent, and adsorbent‐adsorbate were optimized. It was found that Cr(VI) adsorption was predominant at acidic pH (pH 3) for both cases; moreover, N‐GAC showed better adsorption comparatively. Both the N‐GAC and Sp‐GAC adsorption were found to be obeying to Langmuir.

Insight into the performance and mechanism of persimmon tannin functionalized waste paper for U(VI) and Cr(VI) removal

Herein, using dialdehyde waste paper (DAWP) as a cross-linking agent to immobilize persimmon tannin (PT) was first used to remove the U(VI) and Cr(VI) via the “waste control by waste” concept. The microscopic and macroscopic surface properties of the as-prepared adsorbent was characterized by the advanced characterization techniques. Factors that affected the elimination process such as variable pH, coexistence ions and equilibrium time were investigated by batch techniques. The results showed that the maximal removal capacities of U(VI) and Cr(VI) on DAWP-PT were 242.3 mg/g (pH = 6.0) and 178.7 mg/g (pH = 2.0) at 298 K, which exhibited competitiveness with most of the reported solid materials. Meanwhile, adsorption data were fitted perfectly to the Langmuir and Pseudo-second-order equations, which indicated that the monolayer and homogenous chemisorption dominated the removal process. The SEM-EDX, DFT and XPS analysis conformed that adsorption of U(VI) was mainly via surface complexation, while the elimination of Cr(VI) was a redox reaction process, and about 65.33% of Cr(III) and 34.67% of Cr(VI) co-existed onto the surface of DAWP-PT. Thus, this study would provide a high-efficiency and low-cost adsorbent for radionuclide and heavy metal treatment.

A collaborative strategy for elevated reduction and immobilization of Cr(VI) using nano zero valent iron assisted by schwertmannite: Removal performance and mechanism

A novel collaborative strategy for enhanced removal of Cr(VI) using nano zero valent iron (nZVI) assisted by schwertmannite (Sch) with two synthesis methods was designed. Batch experiments demonstrated that nZVI/Sch-AP (synthesized by abiotic precipitation of Fe3+ species) exhibited excellent removal performance for Cr(VI) than nZVI/Sch-CO (synthesized by chemical oxidation of Fe2+ species). The results indicated that the removal efficiencies of Cr(VI) by nZVI/Sch-AP and nZVI/Sch-CO were highly pH-dependent and achieved to be 99.99% and 98.01% under the optimal conditions of 10 mg L−1 Cr(VI) concentration, a pH of 6.3 and a Fe(0)/Cr(VI) molar ratio of 12. But nZVI/Sch-AP emerged greater k of 0.1097 min−1 than that of nZVI/Sch-CO (0.0485 min−1). Humic acid exhibited promotion effect on the Cr(VI) removal in low concentration of 1 mg L−1. Results of XRD and XPS demonstrated that α-FeOOH was the dominant products in both incubations of nZVI/Sch-AP and nZVI/Sch-CO, accompanied with FeCr2O4 and CrFe mixed (oxy)hydroxides, and γ-FeOOH was found alone in the incubations of nZVI/Sch-CO. We proposed a consecutive and simultaneous process involving surface absorption-reduction and co-precipitation/immobilization for the removal. This study provides new insights into the elimination of Cr(VI) from wastewater by nZVI/Sch, especially in acid mine drainage.

Efficient adsorption and reduction of Cr(VI) and U(VI) by nanoscale zero-valent iron supported on polydopamine-decorated SBA-15

Herein, a composite material (nZVI@SBA-15-PDA/PEI) was developed by loading nanoscale zero-valent iron (nZVI) on polydopamine-decorated SBA-15 for Cr(VI) and U(VI) removal. The structure, morphology and composition of the as-prepared composites were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffractometer (XRD) and fouriertransforminfraredspectroscopy (FT-IR) techniques. The experimental results demonstrated that the water environmental conditions played an important role in elimination of Cr(VI) and U(VI), such as pH values, pollutantconcentrations and equilibriumtime. Meanwhile, the fitted data displayed that the elimination process could be more accurately explained by the Langmuir and pseudo-second-order kinetic models, and the maximum removal capacities for Cr(VI) and U(VI) were 44.05 mg/g (pH = 3.0) and 57.78 mg/g (pH = 6.0) at 298 K, respectively. The characterizationanalysis conformed that the elimination mechanisms were proposed as a two-step interaction. Namely, both Cr(VI) and U(VI) were firstly attached onto the surface of composite materials via electrostaticinteraction or surface complex reaction, and subsequently about 47.1% of U(VI) and 55.7% Cr(VI) were reduced to U(IV) and Cr(III) by nZVI. Thus, this nZVI composites exhibited a high potential to eliminate Cr(VI) and U(VI) from polluted water environment.

New insights into colloidal GO, Cr(VI) and Fe(II) interaction by a combined batch, spectroscopic and DFT calculation investigation

In this paper, a variety of experimental techniques including batch equilibrium reactions, density functional theory (DFT) theoretical calculation, and X-ray spectroscopic techniques, were utilized to investigate the colloidal GO, Cr(VI) and Fe(II) interaction. The results indicated that a Cr(III)-Fe(III) precipitate could be formed when Fe(II) was added in Cr(VI) solution, and then Cr(VI) was adsorbed on the neoformed precipitate. The kinetics for all systems can be described by the pseudo-second-order model the best, suggesting chemical reaction mainly contributed to colloidal GO, Cr(VI) and Fe(II) interaction. There co-existed reductive and oxidative functional group on GO surfaces simultaneously, leading to the reduction Cr(VI) into Cr(III), and/or oxidation of Fe(II) into Fe(III), when Fe(II) and Cr(VI) were adsorbed on GO, individually. Furthermore, in comparison with individual GO and Fe(II) in solution, more Cr(VI) could be reduced into Cr(III) via Fe(II)-treated GO, due to the much higher reactivity of GO adsorbed Fe(II). So, GO demonstrated excellent adsorption and reduction capacity for Cr(VI) in the presence of Fe(II). These findings are vital to apply GO in the elimination of Cr(VI) from wastewater.