Initial Cr Concentration Research Articles

Fabrication, Characterization and Adsorption Investigation of Nano Zinc Oxide–Sodium Alginate Beads for Effective Removal of Chromium (VI) from Aqueous Solution

Alginate–zinc oxide (Alg–ZnO) biocomposite was synthesized and tested as a chromium ions Cr(VI) adsorbent for environmental applications. Alg–ZnO biocomposite was prepared by the interaction between sodium alginate biopolymer and zinc oxide nanoparticles (ZnO–NPs), prepared by modified wet chemical method. The solid adsorption characteristics of the synthesized Alg–ZnO biocomposite were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–Vis spectroscopy. Adsorption isotherms of chromium ions on the prepared Alg–ZnO biocomposite were investigated with varying the initial concentration of Cr(VI) under different application conditions such as pH, contact time, adsorbent dosage, and temperature. Adsorption of Cr(VI) was investigated by different isotherm models such as Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. Maximum adsorption capacities (31.09 and 34.63 mg/g) were achieved by ZnO–NPs and Alg–ZnO, respectively at 25 °C. The results of isotherm models indicate the perfect applicability of Langmuir and Dubinin–Radushkevich models, revealing the dominance of monolayer and the physisorption of chromium ions onto the studied adsorbents.

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

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

Adsorption of hexavalent chromium from aqueous solution using cationic modified rice husk: Parametric optimization via Taguchi design approach

The current work study the adsorption capacity of modified rice husk for the removal of Cr(VI) from aqueous solution. The rice husk was prepared and modified cationicaly. The cationic modified risk husk (cRH) was characterized by scanning electron microscopy (SEM) and fourier transform infrared (FTIR) spectroscopy. Also, point-of-zero pH (pHzero), specific surface area (m2/g) and bulk density (g/cm3) of the cRH were determined. The adsorption process was optimized by considering four independent process parameter at three variation levels using Taguchi design approach. The results showed the bulk density (0.392 g/cm3) and surface area (192 m2/g) which revealed the presence of numerous sorption sites on the cRH. Also the SEM micrograph showed the pores of different sizes which favoured the adsorption of Cr(VI). Taguchi experimental design predicted initial Cr (VI) concentration of 25 mg/L, contact time of 90 min, 2 g cRH dosage and pH of 2 as the optimum conditions to achieve 91.48% removal efficiency. The optimized condition was verified and 91.13% removal efficiency was achieved. The experiment data fitted well to Langmuir model indicating anion species monolayer adsorption on the cRH homogeneous surface. Also, the process is in better agreement with pseudo-second-order kinetic model, indicating a chemisorption controlled process. Thus, the study revealed that cationic modified rice-husk is suitable for the removal of Cr(VI) from aqueous solution.

Hexavalent Chromium Removal from Water and Wastewaters by Electrochemical Processes: Review

Hexavalent chromium (Cr(VI)) is a toxic, mutagenic, teratogenic, and carcinogenic species. Its origin is in industrial activities. Therefore, its effective control is realized on a source basis. Although chemical methods proved effective in removing Cr(VI) from wastewaters, more economic solutions with a minimum sludge production have been sought. Among them, the use of electrochemical processes has emerged as a viable solution to the problem. Much research was conducted in this area. The aim of this review paper is to make a critical evaluation of the literature on Cr(VI) removal by electrochemical methods, particularly electrocoagulation with sacrificial electrodes, and to assess the present data as well as to point out the areas that need further elaboration. Following the review of the theoretical concepts of electrochemical processes, the literature on the electrochemical removal of Cr(VI) was evaluated on the basis of important elements of the system. Among them are initial pH, initial Cr(VI) concentration, current density, type and concentration of supporting electrolyte, and the material of electrodes and their operating characteristics and process kinetics. Dimensionally stable electrodes that realize the reduction process without producing any sludge were evaluated separately. Applications of electrochemical methods to a wide spectrum of industrial effluents were also assessed.

Modeling and Optimization of the Adsorption of Cr (VI) in a Chitosan-Resole Aerogel Using Response Surface Methodology.

In this paper, a model for Cr (VI) removal and optimization was made using a novel aerogel material, chitosan-resole CS/R aerogel, where a freeze-drying and final thermal treatment was employed to fabricate the aerogel. This processing ensures a network structure and stability for the CS, despite the non-uniform ice growth promoted by this process. Morphological analysis indicated a successful aerogel elaboration process., FTIR spectroscopy corroborated the aerogel precursor's identity and ascertained chemical bonding after adsorption. Owing to the variability of formulations, the adsorption capacity was modeled and optimized using computational techniques. The response surface methodology (RSM), based on the Box-Behnken design using three levels, was used to calculate the best control parameters for the CS/R aerogel: the concentration at %vol (50-90%), the initial concentration of Cr (VI) (25-100 mg/L), and adsorption time (0.3-4 h). Analysis of variance (ANOVA) and 3D graphs reveal that the CS/R aerogel concentration and adsorption time are the main parameters that influence the initial concentration of CS/R aerogel metal-ion uptake. The developed model successfully describes the process with a correlation coefficient of R2 = 0.96 for the RSM. The model obtained was optimized to find the best material design proposal for Cr (VI) removal. Numerical optimization was used and showed superior Cr (VI) removal (94.4%) under conditions of a CS/R aerogel concentration of 87/13 %vol, with an initial concentration of Cr (VI) of 31 mg/L, and an adsorption time of 3.02 h. These results suggest that the proposed computational model can obtain an effective and viable model for CS material processing and for optimization of the uptake of this metal.

Application of multi-gene genetic programming technique for modeling and optimization of phycoremediation of Cr(VI) from wastewater

BackgroundRemoval of Cr(VI) from wastewater is essential as it is potentially toxic and carcinogenic in nature. Bioremediation of heavy metals using microalgae is a novel technique and has several advantages such as microalgae remove metals in an environmentally friendly and economic manner. The present study deals with modeling and optimization of the phycoremediation of Cr(VI) from synthetic wastewater. The initial concentration of Cr(VI), initial pH, and inoculum size were considered as input factors, and the percentage removal of Cr(VI) was chosen as a response.ResultsAn accurate data-driven genetic programming model was developed with the experimental data of other scientists to find a relation between the percentage removal of Cr(VI) and all input parameters. To maximize the removal of Cr(VI), the grey wolf optimization technique was applied to determine the optimal values of input parameters.ConclusionThese optimum input parameters are difficult to get through experimentation using the trial-and-error method. The established modelling and optimization technique is generic and can be applied to any other experimental study.Graphical

Agro-waste-based functionalized and economic adsorbents for the effective treatment of toxic contaminants from tannery effluent

The present investigation explored two novel adsorbents, i.e., hydroxyapatite (HAP) and moringa-modified activated carbon (MMAC) from eggshell and moringa (Moringa oleifera) seeds, respectively, for the treatment of tannery effluents (TE). Particular emphasis was given to Cr(VI) adsorption when varying equilibration time, effluent pH, initial concentration of Cr(VI) and temperature. The adsorbents' characteristics suggested significant Cr(VI) accumulation onto the adsorbent's surface, whereas adsorption modelling recommended pseudo-second-order (PSO) and Langmuir models fitted well with the experimental data based on the regression coefficient (R2) values with minimum errors. The surface complexation model (SCM) indicated that speciation of Cr(VI) sorbed complexes formed an inner-sphere compound dominated by acidic pH, validated by pHpzc. The maximum adsorption capacities (qmax) of Cr(VI) were accounted to be 295 and 280 mg/g for HAP and MMAC, correspondingly. Interestingly, both adsorbents effectively removed other metallic ions; Fe, Pd, Cu and Zn removal was 85 %, while Cd, Ni, and Mn removal was 70 %. The Cr(VI) adsorption processes followed chemisorption mechanisms dominated by the surface complexation phenomenon. The performance of a 100 L packed-bed reactor was evaluated, and the breakthrough time of Cr(VI) adsorption for both adsorbents was 15 min. The adsorbents had splendid regeneration capacities and could be re-used numerous times. In essence, the present study concludes that both adsorbents are highly effective at removing Cr(VI) and other contaminants. The adsorbents are innovative and economical and can be one of the breakthrough feasible options for treating toxic contaminants in a large-scale TE.

Crosslinked modified chitosan biopolymer for enhanced removal of toxic Cr(VI) from aqueous solution

Two new crosslinked modified chitosan biopolymers, namely (CTS-VAN) and (Fe3O4@CTS-VAN) bioadsorbents were prepared starting from chitosan and 4-hydroxy-3-methoxybenzaldehyde (VAN) in presence of epichlorohydrin. The analytical techniques FT-IR, EDS, XRD, SEM and XPS besides BET surface analysis were utilized for full characterization of the bioadsorbents. Batch experiments were conducted to study the effect of various influencing parameters in Cr (VI) removal such as initial pH, contact time, adsorbent amount and initial Cr (VI) concentration. The adsorption of Cr (VI) was found out to be maximum at pH = 3 for both bioadsorbents. Langmuir isotherm fit well the adsorption process with a maximum adsorption capacity of 188.68 and 98.04 mg/g for CTS-VAN and Fe3O4@CTS-VAN, respectively.The adsorption process followed pseudo second-order kinetics with R2 values of 1 and 0.9938 for CTS-VAN and Fe3O4@CTS-VAN, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that Cr(III) accounted for 83 % of the total Cr bound to bioadsorbents surface, which indicated reductive adsorption was responsible for Cr(VI) removal by the bioadsorbents. Cr(VI) was initially adsorbed on the positively charged surface of the bioadsorbents and reduced to Cr(III) by electrons provided by oxygen-comprising functional groups (e.g., CO), and consequently part of the converted Cr(III) stayed on the surface and the rest released into solution.

Optimization of Cr (VI) removal from aqueous solution with activated carbon derived from Eichhornia crassipes under response surface methodology

Tannery industries’ effluent contains a high concentration of Cr (VI) which has the potential to affect the environment and public health. Therefore, this study aimed to investigate the optimization of Cr (VI) adsorption by activated carbon (AC) derived from Eichhornia crassipes from an aqueous solution. The adsorbent was activated with dilute sulfuric acid followed by thermal activation. AC was characterized using proximate analysis, SEM, FTIR, X-ray diffraction, and the BET method. The Cr (VI) removal optimization process was performed using a central composite design under the response surface methodology. The proximate analysis showed that the moisture content, volatile matter, ash content, and fixed carbon of the activated carbon were 5.6%, 18.2%, 14.4%, and 61.8% respectively. The surface areas of the Eichhornia crassipes before activation, after activation, and after adsorption were 60.6 g/m2, 794.2 g/m2, and 412.6 g/m2 respectively. A highly porous structure with heterogeneous and irregular shapes was observed in the SEM micrograph. In the FTIR analysis, different peaks are indicated with various functional groups. The intensity of XRD peaks decreased as 2 theta values increased, which indicates the presence of an amorphous carbon arrangement. The point of zero charge (pHpzc) of the activated carbon was found to be 5.20. A maximum Cr (VI) removal of 98.4% was achieved at pH 5, contact time 90 min, adsorbent dose 2 g, and initial Cr (VI) concentration of 2.25 mg/L. Statistically significant interactions (P < 0.05) were observed between the initial Cr (VI) concentration and adsorbent dose as well as the initial Cr (VI) concentration and contact time. Langmuir adsorption isotherm fitted the experimental data best, with an R2 value of 0.99. The separation constant (RL) indicates that the adsorption process is favorable. The kinetic experimental data were best fitted with the pseudo-second-order model with an R2 value of 0.99 whereas the adsorption rate is controlled by intraparticle and extragranular diffusion processes. Generally, the AC has the potential to be a strong adsorbent candidate for wastewater treatment at the industrial level.

Study of the hydraulic correlation in the removal of pollutants from synthetic wastewater by means of a filter with Musa Paradisiaca

Background: The objective of this work was to decontaminate synthetic sewage from fouracid blue (BRL) dye, with characteristics similar to those of the textile industry, to determine the correlation between flow rate, permeability and removal of hexavalent chromium (Cr+ 6), Cupper (Cu), chemical oxygen demand COD and color using Paradise Muse filter bed. Methods: three concentrations of BRL synthetic wastewater were prepared, determining the initial concentrations of Color, pH, COD, Cr +6 and Cu. In addition, the hydraulic characteristics of the fiber were determined in four types of fiber cut. The synthetic wastewater was filtered in a filtration cell with the three fiber cuts, using three speeds, the time used for these tests was 180 minutes. Water samples were collected every 5 minutes and then analyzed in the laboratory. Simple exponential smoothing was performed on the data obtained, and the statistical analysis of variance ANOVA of 2 factors. Results: The results show that flow velocity and permeability are correlated with color removal, COD and Cr+ 6, determining that the best treatment was to use 1 cm fiber and high flow velocity in which 77.92% and 70.01% for color and COD respectively. In contrast, for Cr+ 6 the best treatment was fiber at 1 cm and low flow velocity removing up to 80% of the concentration of this contaminant and for Cu the best treatment was fiber at 3 cm and low flow velocity removing up to 88.69%. Conclusions: It was determined that the Musa Pardisiaca fiber is capable of absorbing contaminants, but the effectiveness of the treatment depends on the initial conditions of the synthetic water, the cut of the fiber and the velocity. In addition, it is important to mention that, in order to lower heavy metal concentrations, low flow rates should be used.

Reduction of Hexavalent Chromium from Soil of the Relocated Factory Area with Rice Straw Hydrothermal Carbon Modified by Nano Zero-Valent Iron (nZVI).

In order to reduce the content of Cr(VI) in the soil of the relocated chromium salt factory, the rice straw-derived hydrothermal carbon was prepared by hydrothermal method and loaded with nano zero-valent iron generated by liquid phase reduction, which effectively alleviated the self-aggregation problem of nano zero-valent iron (nZVI) in the treatment of Cr(VI) and improved the Cr(VI) reduction rate without changing the soil structure. The reduction effect of Cr(VI) in soil by key influencing factors such as carbon-iron ratio, initial pH value, and initial temperature was investigated. The results showed that nZVI modified hydro-thermal carbon composite (named RC-nZVI) had a good reduction effect on Cr(VI). Scanning electron microscope (SEM) and energy spectrum analysis showed that nZVI was evenly distributed on the surface of hydrothermal carbon, which effectively reduced the agglomeration of iron. Under the conditions of C/Fe = 1:2, 60 °C, with pH of 2, the average Cr(VI) content in soil decreased from 182.9 mg kg-1 to 21.6 mg kg-1. Adsorption kinetics of Cr(VI) by RC-nZVI fit well with the pseudo-second-order model, and the kinetic velocity constant revealed that Cr(VI) reduction rate decreased with increasing initial Cr(VI) concentration. Cr(VI) reduction by RC-nZVI was mainly dominated by chemical adsorption.

Development of nitrogen-doped graphene/MOF nanocomposites towards adsorptive removal of Cr(VI) from the wastewater of the Herbert Bickley treatment works

Industrial effluents laden with Cr(VI) pose considerable health risks to human and animal life if left untreated. Hence, in this work, metal–organic framework-5/nitrogen-doped graphene (MOF-5/NGO) nanocomposites bearing Cr(VI) adsorption properties were fabricated. These unique materials were produced with increasing NGO loadings (0.05, 0.10 and 0.15 wt%) to investigate the role of NGO content on the chemical and physical properties of the composites. The FTIR spectra show the nanocomposites be to be rich in surface –OH and –COOH functional groups. Raman spectroscopy confirmed bond formation between the MOF-5 and NGO through downshift of the G- and 2D-bands. XRD analysis showed MOF-5/NGO nanocomposites, MOF-5 and the NGO to be highly crystalline while thermogravimetric analysis indicated the thermal stabilities of the composites to be enhanced. SEM studies revealed the NGO flakes to be dispersed on the MOF-5 microstructures prior to adsorption and the disappearance of microstructures post adsorption. The as-synthesized nanocomposites exhibited BET surface area in the range 384.55–395.56 m2.g−1 which is a significant increase from that of MOF-5 261.00 m2.g−1. The optimal conditions for maximum Cr(VI) adsorption were determined to be: pH = 2, contact time of 60 min, adsorbent dosage of 6 mg.L−1, initial Cr(VI) concentration of 0.5 mg/L and temperature of 30 °C. A maximum adsorption efficiency of 46.1 % was achieved by the composite MOF-5/NGO (0.05 wt%) and not significantly compromised by competing metal ions. The Cr(VI) removal on MOF-5/NGO nanocomposites is well described by the Langmuir isotherm, confirming a chemisorption process. In addition, the thermodynamic studies confirmed the adsorption process to be favorable, spontaneous and endothermic. The Cr(VI) removal % on MOF-5/NGO from real water was found to be 52.1 %. Therefore, the novel MOF-5/NGO nanocomposite can be applied for efficient Cr(VI) removal from industrial wastewater due to synergistic surface morphologies between NGO and MOF-5 units characterized by better adsorption capacity not met by pristine materials.

Magnetite-impregnated biochar of parthenium hysterophorus for adsorption of Cr(VI) from tannery industrial wastewater

The tannery industry inevitably generates toxic and catastrophic wastewater, which results in a huge threat to public health and water resources. Therefore, this work aimed to synthesize parthenium hysterophorus-based biochar–Fe3O4 composite for removal of Cr(VI) from tannery wastewater under 34 full factorial experimental designs of the Box–Behnken, which was analyzed using response surface methodology under four independent factors of pH (3, 6, and 9), initial Cr(VI) concentrations (40, 70, and 100 mg/L), contact times (30, 60, and 90 min), and adsorbent doses (20, 60, and 100 mg/100 mL). This composite adsorbent was described by a high BET surface area of 237.4 m2/g, XRD prominent peaks, SEM morphology corroborate and FTIR multifunctionalities of O–H at 3296 cm−1, the vibration of ketone C–OH at 1240 cm−1, and the vibration of C–O–C at 1147 cm−1 and Fe–O stretching at 542 cm−1. The maximum Cr(IV) removal efficiency of 91.8% was recorded at an initial Cr(VI) concentration of 40 mg/L, pH of 3, adsorbent dose of 100 mg/100 mL, and a contact time of 90 min, whereas the minimum Cr(VI) removal of 17.3% was observed at an initial Cr(VI) concentration of 100 mg/L, 20 mg/100 mL of adsorbent dose, pH of 9, and contact time of 30 min. The concentration of Cr(VI) in real wastewater was determined to be 85.13 mg/L and its remediation was found to be 81.8%. Langmuir’s model was the best fit with experimental data at R2 0.99 and qmax 400 mg/g, showing that the adsorption process was homogenous and monolayer. In conclusion, the adsorption results were encouraging, and biochar–Fe3O4 appears to be a potential candidate for Cr removal from wastewater.

Chromate Removal by Enterobacter cloacae Strain UT25 from Tannery Effluent and Its Potential Role in Cr (VI) Remediation.

An indigenous chromate-resistant bacterial strain isolated from tannery effluent was identified based on morphological, biochemical, and 16S rRNA gene sequencing, as Enterobacter cloacae UT25. It was found to resist heavy metal ions such as Cr (VI), Pb (II), Cu (II), Co (II), Ni (II), Hg (II), and Zn (II) and antibiotics. The strain was able to remove 89 and 86% chromate, after 24h of incubation in a Luria-Bertani (LB) medium at an initial Cr (VI) concentration of 1000 and 1500µg/ml, respectively. Minimum inhibitory concentration (MIC) was observed for chromate to be 80,000 and 1850µg/ml, after 48h of incubation in LB and acetate minimal media (AMM), respectively. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis showed discrete cells with intact and smooth cell walls and homogenous cytoplasm in the absence of metal stress, whereas chromate stress caused cell lysis and reduction in size, which was a characteristic response to Cr (VI) toxicity. Energy Dispersive X-Ray Spectroscopy (EDX) confirmed the adsorption of oxyanions to the cell wall which was one of the Cr (VI) removal mechanisms by the bacterium. Atomic Force Microscopy (AFM) micrographs of chromate-untreated and treated cells revealed Root Mean Square roughness (Rq) values of 16.25 and 11.26nm, respectively, indicating less roughness in the presence of stress. The partial gene sequence of class 1 integrons (intI1) of strain UT25 showed 94% homology with intI1 gene of strain Enterobacter hormaechei strain ECC59 plasmid pECC59-1. The present analysis highlighted the potential of E. cloacae UT25 as a promissory bacterium that could be applied in removing chromate from polluted environments.

Effective removal of hexavalent chromium by novel modified alginate-based biocomposites: Characterization, kinetics and equilibrium studies

This study aims to synthesise novel biocomposites by combining fungal hyphae (Aspergillus oryzae or Penicillium roqueforti) and reduced graphene oxide to evaluate their adsorption potential for hexavalent chromium (Cr(VI)) from synthetic solutions and real wastewater. Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analyses were used to characterize the effects of the carbon-based materials on microbial structure. In addition, independent variables including with a contact time (1–11 h), reduced graphene oxide concentration (0.1–1 g.L−1), and initial Cr(VI) concentration (10–50 mg L−1) were tested in batch-scale laboratory experiments by response surface methodology. Accordingly, maximum adsorption was achieved at 11 h contact time, 1.0 g L−1 rGO, and 50 mg L−1 Cr(VI) with a removal rate of 98.9%. The pseudo-first-order and Freundlich isotherm models were well fitted. The results show that these biocomposites can serve as novel adsorbent for the removal of Cr(VI) from wastewater.

Cu(II) and Cr(VI) Removal in Tandem with Electricity Generation via Dual-Chamber Microbial Fuel Cells

Microbial fuel cells (MFCs) have shown great advantages in electricity production, heavy metal removal, and energy recovery. However, the impact and mechanism of conflicting effects of numerous electron acceptors on heavy metal removal remain unknown. The effects of different initial heavy metal concentrations, cathodic dissolved oxygen, and electrode materials on the electricity generation and heavy metal removal efficiencies of Cu(II) and Cr(VI) were investigated in this study. When the initial concentration of Cr(VI) increased from 10 mg/L to 150 mg/L, the maximum voltage, coulomb efficiency, and maximum power density declined from 99 to 44 mV, 28.63% to 18.97%, and 14.29 to 0.62 mW/m2, and the removal efficiencies of Cu(II) and Cr(VI) decreased dramatically from 98.34% and 99.92% to 67.09% and 37.06%, respectively. Under anaerobic cathodic conditions, the removal efficiency and removal rate of Cu(II) and Cr(VI) were lower than those under aerobic conditions. When the cathode electrode was titanium sheet and graphite plate, the coulomb efficiency and maximum power density increased to 38.18%, 50.71%, 33.95 mW/m2, and 62.23 mW/m2. The removal efficiency and removal rates of Cu(II) and Cr(VI) were significantly increased to 98.09%, 86.13%, and 0.47, 0.50 mg/(L h) with a graphite plate, respectively. The pH of the cathode varied considerably greater as the MFC current increased. Cu(II) and Cr(VI) were removed and reduced to elemental Cu, Cu2O, and its oxides as well as Cr(OH)3 and Cr2O3 precipitates on the cathode electrode by cathodic bioelectrochemical reduction.

Adsorptive removal of anionic azo dye by Al3+-modified magnetic biochar obtained from low pyrolysis temperatures of chitosan.

Magnetic γ-Fe2O3/Al3+@chitosan-derived biochar (m-Fe2O3/Al3+@CB) was prepared by introducing magnetic maghemite (γ-Fe2O3) nanoparticles and aluminum sulfate [Al2(SO4)3] into chitosan-derived biochar (CB) obtained at low pyrolysis temperatures. m-Fe2O3/Al3+@CB was used to remove typical anionic azo dye (Congo red, CR). Effects of initial CR concentration, contact time, initial pH value, background electrolytes, and temperature on CR adsorption by m-Fe2O3/Al3+@CB were studied. Compared with magnetic chitosan-derived biochar (m-Fe2O3@CB), m-Fe2O3/Al3+@CB exhibited excellent performance for a wider range of pH values (pH 1-7) and in the presence of background electrolyte. The introduction of Al3+ is an effective method for improving the properties of magnetic chitosan-derived biochar. High CR adsorption capacity (636.94mgg-1) of m-Fe2O3/Al3+@CB could result from collaborative effect of flocculation/coagulation and electrostatic attraction. These results demonstrated that m-Fe2O3/Al3+@CB is a potential adsorbent for effective removal of organic dyes from aqueous solution due to its high adsorption capacity and convenient magnetic recovery and stronger anti-interference ability against coexisting anions in wastewater.

Water Cleaning by a Continuous Fixed-Bed Column for Cr(VI) Eco-Adsorption with Green Adsorbent-Based Biomass: An Experimental Modeling Study

In this study, chromate adsorption onto red peanut skin (RPS) was investigated in a fixed-bed column; FTIR, PZC, SEM, DLS, and BET were used to evaluate its adsorption properties. The experiments were conducted to determine the effect of physical parameters, including the inlet initial Cr(VI) concentration (100–500 mg L−1), bed height (10–20 cm), and feed flow rate (13.59–23.45 mL min−1). They were carried out to predict breakthrough curves. The adsorption capacity coefficients were determined using the most widely used Bohart–Adams model. It was tested to fit experimental data, for a better understand the dynamic behavior, and for further optimize column performance. It was found that the Cr(VI) uptake decreases when increasing the flow rate and that high chromate concentration and bed height consequently increase the column’s life span. A high column adsorption capacity can be achieved with a higher Cr(VI) concentration due to the higher driving force. The results indicated that the Bohart–Adams model provides a good description (R2 &gt; 0.98) of the experimental data of the Cr(VI)’s removal from the aqueous solution on the RPS suggesting that the surface diffusion is the rate-limiting step in the continues adsorption process.. Breakthrough adsorption capacity is crucial for comparing RPS with other similar materials. Indeed, possible mechanisms have been suggested for illustrating adsorption onto RPS. The obtained results showed significant potential of 26.23 mg g−1 of RPS on Cr(VI) elimination at a natural pH of 5.35. Furthermore, this global investigation allowed for the design of a promising low-cost material for the future scale-up of cleaning wastewater polluted by metal and determine the properly conditions for operating column adsorption. This material provides an economical, efficient means of eliminating pollutants, thus meeting the main aims of the UN Sustainable Development Goals (UN SDGs).

Formation and mechanism of nanoscale zerovalent iron supported by phosphoric acid modified biochar for highly efficient removal of Cr(VI)

The effect of phosphoric acid modified biochar on activity of nanoscale zero valent iron particles is not clear until now. In this research, Egeria najas powder driven biochar-supported nanoscale zero valent iron was modified by phosphoric acid (P-BC/nZVI) for highly effective removal of Cr(VI) from wastewater. The TEM and XRD of P-BC/nZVI indicated that nZVI particles were successfully immobilized on the P-BC surface. The batch experiment results show that the Cr(VI) removal efficiency by P-BC/nZVI was higher than that of BC/nZVI, nZVI, P-BC and BC. Moreover, the optimal ratio of nZVI to P-BC lies at 3:1 with fixed P-BC/nZVI dosage of 0.75 g/L, initial Cr(VI) concentration of 20 mg/L, solution pH of 2, and reaction temperature of 333 K. Additionally, Cr(VI) removal capacities by nZVI, BC/nZVI and P-BC/nZVI aged for 15 days in water were 12.9 %, 28.55 % and 99.35 %, respectively. Furthermore, corresponding reaction kinetics fitted well with pseudo-second order model, and adsorption isotherm fitted to Sips isothermal model. The SEM-EDS and XPS confirm that Cr(VI) was participated in the reaction, and about 63.43 % of Cr(VI) was reduced to Cr(III), and the rest was adsorbed on the surface of P-BC/nZVI. The removal mechanism of Cr(VI) by P-BC/nZVI was complex, including adsorption, reduction and surface complex formation.

Removal of Hexavalent Chromium in Aqueous Solution by Cellulose Filter Paper Loaded with Nano-Zero-Valent Iron: Performance Investigation and Numerical Modeling.

Cr(VI) pollution in water bodies is very harmful to human health and the environment. Therefore, it is necessary to remove Cr(VI) from water. In this study, the composite (FP-nZVI) was prepared by loading nano-zero-valent iron (nZVI) onto cellulose filter paper (FP) using a liquid-phase reduction method to improve the dispersibility and oxidation resistance of nZVI. In batch experiments, the effects of iron loading of FP-nZVI, initial concentration of Cr(VI), temperature, and pH on Cr(VI) removal were particularly investigated. The maximum removal rate of 98.6% was achieved at 25 °C, pH = 5, initial concentration of Cr(VI) of 20 mg/L, and FeCl3·6H2O solution concentration of 0.8 mol/L. The removal of Cr(VI) by FP-nZVI conformed to a pseudo-second-order kinetic model and Langmuir isotherm model. The mechanism of Cr(VI) removal was a multi-step removal mechanism, involving adsorption, reduction, and coprecipitation. Column experiments investigated the effect of flow rate (1 mL/min, 3 mL/min, and 5 mL/min) on Cr(VI) removal. We found that increasing flow rate slightly decreased the removal rate of Cr(VI). The transport of Cr(VI) in composite porous media was simulated using HYDRUS-1D, and the results show that the two-site model can well simulate the reactive transport of Cr(VI). This study may provide a useful reference for the remediation of groundwater contaminated with Cr(VI) or other similar heavy metals using FP-nZVI.