Adsorption Of Hexavalent Chromium Research Articles

Feasibility and mechanism of adsorption and bioreduction of hexavalent chromium using Rhodopseudomonas palustris immobilized on multiple materials

Rhodopseudomonas palustris immobilized on multiple materials was used to invistigate Cr(VI) adsorption and bioreduction. The highest Cr(VI) removal (97.5%) was achieved at 276h under the opitimed conditions of 2.5% SA, 8% PVA, and 50% filling degree. The highest adsorption capacity was obtained at 11.75mg·g-1 under 300 mg·L-1 Cr(VI). Results from adsorption kinetics and isotherms indicated that Cr(VI) adsorption of immobilized photosynthetic bacteria (IPSB) was consistent with the Freundich model and the pseudo-second-order kinetic model (qe =14.00mg·g-1). SEM and FTIR analyses verified that the porous multilayer network structure of IPSB provided more adsorption sites and functional groups for the removal of Cr(VI). Furthermore, the maximum Cr(VI) reduction efficiency of IPSB was achieved at 10.80mg·g-1, which correlated with the up-regulation of chrR gene expressions at 100 mg·L-1 Cr(VI). This study demonstrated the dual mechanisms of Cr(VI) removal in IPSB-treated Cr wastewater, involving both chemisorption and bioreduction working synergistically.

Microscopic and macroscopic analysis of hexavalent chromium adsorption on polypyrrole-polyaniline@rice husk ash adsorbent using statistical physics modeling

This paper contributed with new findings to understand and characterize a heavy metal adsorption on a composite adsorbent. The synthesized polypyrrole–polyaniline@rice husk ash (PPY–PANI@RHA) was prepared and used as an adsorbent for the removal of hexavalent chromium Cr(VI). The adsorption isotherms of Cr(VI) ions on PPY–PANI@RHA were experimentally determined at pH 2, and at different adsorption temperatures (293, 303, and 313 K). Multi-layer model developed using statistical physics formalism was applied to theoretically analyze and characterize the different interactions and ion exchanges during the adsorption process for the elimination of this toxic metal from aqueous solutions, and to attribute new physicochemical interpretation of the process of adsorption. The physicochemical structures and properties of the synthesized PPY–PANI@RHA were characterized via Fourier transform infrared spectroscopy (FTIR). Fitting findings showed that the mechanism of adsorption of Cr(VI) on PPY–PANI@RHA was a multi-ionic mechanism, where one binding site may be occupied by one and two ions. It may also be noticed that the temperature augmentation generated the activation of more functional groups of the composite adsorbent, facilitating the interactions of metal ions with the binding sites and the access to smaller pore. The energetic characterization suggested that the mechanism of adsorption of the investigated systems was exothermic and Cr(VI) ions were physisorbed on PPY-PANI@RHA surface via electrostatic interaction, reduction of Cr(VI) to Cr(III), hydrogen bonding, and ion exchange. Overall, the utilization of the theory of statistical physics provided fruitful and profounder analysis of the adsorption mechanism. The estimation of the pore size distribution (PSD) of the polypyrrole-polyaniline@rice husk ash using the statistical physics approach was considered stereographic characterization of the adsorbent (here PPY–PANI@RHA was globally a meso-porous adsorbent). Lastly, the mechanism of Cr(VI) removal from wastewater using PPY-PANI@RHA as adsorbent was macroscopically investigated via the estimation of three thermodynamic functions.

Two-dimensional MXene and molybdenum disulphide for the removal of hexavalent chromium from water: A comparative study

Chromium is a carcinogenic heavy metal that accumulates in plant and animal bodies. New materials for efficient removal of chromium from water bodies are in high demand. MXene was synthesized from MAX phase by using ammonium fluoride as an etching agent while molybdenum disulphide was synthesized by hydrothermal method. The pseudo-second order kinetic model described the adsorption of hexavalent chromium on MXene and molybdenum disulphide whereas the Freundlich Isotherm model best fitted for Mxene, and Langmuir Isotherm model was more suitable in case of molybdenum disulphide. The adsorption capacity obtained by MXene for hexavalent chromium was 59.8 mg/g (At Dosage = 1 g/L, T = 298 K, Time = 9 h, pH = 2, Co = 30 mg/L) and 113.7 mg/g in case of molybdenum disulphide (At Dosage = 0.5 g/L, T = 298 K, Time = 1.5 h, pH = 2, Co = 30 mg/L). Thermodynamic investigations showed that the process was endothermic and spontaneous. The coexisting ions showed a decrease in removal percentage up to 70 % and 79 % in case of MXene and molybdenum disulphide, respectively, after fifth cycle. It can be inferred that these developed materials have the advantages of simplicity for reducing heavy metal pollution.

Influence of the iron-oxide mass fractions of magnetic powdered activated carbon on its hexavalent chromium adsorption performance in water

Magnetic powdered activated carbon (Mag-PAC) is an effective adsorbent to remove hexavalent chromium (Cr(VI)) from water and can be recovered for reuse. However, the tradeoff between the adsorption performance of Cr(VI) and magnetic properties of Mag-PAC remains unclear. Herein, we prepared a series of Mag-PAC adsorbents containing various iron-oxide mass fractions with FeSO4·7H2O as the precursor, using a facile wet-chemical precipitation route and conducted batch experiments to evaluate the Cr(VI) adsorption performance. Results revealed that Mag-PAC was functionalized by magnetic iron oxide comprising crystalline goethite and magnetite structures. Furthermore, its adsorption performance was highly dependent on pH and was most effective at an initial solution pH of 2. Both the sorption rate constant and Cr(VI) adsorption capacity were greatly influenced by magnetization, and they gradually decreased as the iron-oxide mass fraction increased. Among the prepared adsorbents, Mag-PAC-75 (∼32% wt iron) exhibited not only an excellent Cr(VI) adsorption performance (Langmuir adsorption capacity: 75.76 mg/g) but also effective magnetic properties (saturation magnetization: 9.66 emu/g). Coexisting anions had a negligible competitive effect on Cr(VI) removal by Mag-PAC-75 at an initial pH of 2, whereas the presence of tannic acid markedly improved the Cr(VI) elimination. The presence of trivalent chromium on the surface of Mag-PAC-75 confirmed via X-ray photoelectron spectroscopy indicated that some synergistic redox reactions may occur during the sorption process. After five regeneration cycles using NaOH, Mag-PAC-75 continued to exhibit a high Cr(VI) removal efficiency and magnetic stability. These findings indicate that optimizing the adsorption performance and magnetic properties is a key factor for realizing the practical application of Mag-PAC for Cr(VI) removal. Overall, Mag-PAC may have been a promising application prospect for Cr(VI) removal from water due to its high adsorption capacity and magnetic properties, coupled with its good reusability and magnetic stability after regeneration cycles.

Histidine-Functionalised Polypyrrole Hybrid Nanocomposite for Adsorption of Toxic Hexavalent Chromium from Water

Histidine-Functionalised Polypyrrole Hybrid Nanocomposite for Adsorption of Toxic Hexavalent Chromium from Water

Synthesis of the to enhance synergistic adsorption and reduction of hexavalent chromium from wastewater

The polyethyleneimine functionalized magnetic NH2-MIL-125(Ti) composite (PFMC) is successfully synthesized for Cr6+ removal from wastewater with remarkable selectivity. The influence of adsorption parameters such as adsorption time and initial concentration on Cr6+ removal is investigated. The Cr6+ adsorption behavior is analyzed using Hill and pseudo-second-order model with adsorption capacity of 302.09 mg/g, which can meet the emission standard of the WHO allowable value (50 μg/L). Moreover, PFMC exhibits excellent selectivity for Cr6+ adsorption in coexisting ions wastewater and stability in the different water systems. The Cr6+ removal mechanism is analyzed, which includes electrostatic attraction and reduction reaction. The present work demonstrates that PFEM has promising potential in Cr6+ removal from wastewater.

Comparison of Hexavalent Chromium Adsorption Behavior on Conventional and Biodegradable Microplastics

Microplastics are omnipresent in aquatic environments and can act as vectors to carry other pollutants, modifying their pathway through the systems. In this study, the differences in the adsorption capacity and mechanism for Cr(VI) sorption with polyethylene (PE, a conventional microplastic) and polylactic acid (PLA, a biodegradable microplastic) were investigated via characterization of the MPs, the determination of kinetic behavior (pseudo-first- and second-order model, the Elovich model), and the degree of fit to Langmuir and Freundlich isothermal models; the adsorption behavior was also studied under different solution conditions. The results indicated that when the dose of MPs was 1 g/L, the adsorption capacity of Cr(VI) on MPs reached the highest value, the adsorption capacities were PLA(0.415 mg/g) > PE(0.345 mg/g). The adsorption of Cr(VI) on PE followed the Langmuir isotherm model, while PLA had a stronger fit with the Freundlich model. Sorption in both cases followed a pseudo-first-order kinetics model. The maximum adsorption capacity of Cr(VI) on PLA (0.54 mg/g) is higher than that on PE (0.38 mg/g). In addition, PLA could reach adsorption equilibrium in about 8 h and can adsorb 72.3% of the total Cr(VI) within 4 h, while PE required 16 h to reach equilibrium, suggesting that PLA adsorbs at a significantly faster rate than PE. Thus, biodegradable MPs like PLA may serve as a superior carrier for Cr(VI) in aquatic environments. When the pH increased from 2 to 6, the adsorption of Cr(VI) by PE and PLA decreased from 0.49 mg/g and 0.52 mg/g to 0.27 mg/g and 0.26 mg/g, respectively. When the concentration of sodium dodecyl sulfate in the Cr(VI) solution was increased from nil to 300 mg/L, the adsorption of Cr(VI) by PE and PLA increased by 3.66 and 3.05 times, respectively. In addition, a higher temperature and the presence of Cu2+ and photoaging promoted the adsorption of Cr(VI) by MPs, while higher salinity inhibited the adsorption. The desorption efficiencies of Cr(VI) on MPs were PLA(57.8%) > PE(46.4%). The characterization results further confirmed that the adsorption mechanism could be attributed to electrostatic attraction, hydrogen bonding, and surface complexation. In sum, PLA could potentially serve as better vectors for Cr(VI) than PE, but the risk associated with PLA might be higher than that with PE.

Efficient adsorption of hexavalent chromium in water by torrefaction biochar from lignin-rich kiwifruit branches: The combination of experiment, 2D-COS and DFT calculation

A biochar (KBC) enriched with O functional groups was prepared by torrefaction using lignin-rich kiwifruit branches (KBM) as a raw material, which was characterized, and then KBC was used to adsorb hexavalent chromium (Cr6+) from water. The results showed that KBC contained more functional groups compared to KBM. The maximum adsorption of Cr6+ by KBC could reach 143.64 mg·g−1 and also had better adsorption performance than other adsorbents reported in some other reports. Cr6+ absorption by KBC was mainly a mechanism of electrostatic interaction and adsorption-reduction coupling. FTIR and XPS revealed that -OH, -COOH, CO and CC on KBC participated in Cr6+ adsorption and new groups (C=O) were generated during the process of adsorption, which implied that a redox reaction occurred. 2D-COS and DFT calculations showed that the order of functional groups on KBC interacting with Cr6+ was -OCH3 > -COOH > -OH > phenolic hydroxyl, and the binding tightness of the different functional groups to Cr6+ was -OCH3 (the shortest displacement of both groups after the adsorption) > -COOH > -OH > phenolic hydroxyl. KBC has good regeneration performance, and it is a good adsorbent for Cr6+.

Effect of coexisting trivalent aluminum on the adsorption of hexavalent chromium on sp2 carbon

The analysis of the influence of coexisting ion impurities on the adsorption behavior of Cr6+ on activated carbon at microscopic interfaces should be highlighted. Based on the research background on the adsorption treatment for waste solutions of chromic anhydride, this study reveals that coexisting Al3+ affects the adsorption behavior of Cr6+ on sp2 carbon structure-containing defects, as evidenced by density functional theory calculations. After conducting electronic environment analyses based on isolated Al3+–Cr2O72− coordination and its adsorption models, the Al3+ ion acts as an electron relay station that srapidly transfer the electrons of the 2p orbital of the ortho-carbon atoms to Cr2O72− owing to the saturation of its own p orbital. These findings lead to two conclusions: (i) the facilitated reduction of Cr6+ and its positive charge neutralized by approximately 0.16 Coulomp, and (ii) the increased adsorption energy of Cr2O72− by 3.0 % and 14.6 % on the unelectron-neutralized and electron-neutralized (002) plane of sp2 C-containing defects, respectively, owing to the presence of Al3+. This is attributed to the decreased in 0.089 Hartree Gap value resulting from the energy change of the molecular orbital after Al3+ stable coordination with Cr2O72−. Therefore, the reduced energy barrier facilitates the electron transfer from the 2p orbital of the edge carbon atom to the O–Al–O bridge via the Al3+ bridge.

Hexavalent chromium adsorption from aqueous solution utilizing activated carbon developed from Rumex abyssinicus

The indiscriminate release of chromium-saturated effluent into water bodies has raised concerns regarding its effect on human health and environmental ecology. Therefore, this research aimed to remove hexavalent chromium from an aqueous solution utilizing activated carbon developed from Rumex abyssinicus. The adsorbent was prepared through chemical impregnation with H3PO4 and then thermally activated at 500 °C for 2 h. The optimization of the adsorption experiments was performed using the Box‒Behnken approach of response surface methodology. The characterization of the prepared activated carbon revealed good quality in terms of its amorphous structure, maximum specific surface area of 1722.9 m2/g and porous surface. Furthermore, the optimization results showed that a maximum removal efficiency of 95.97 % was attained at an optimum working pH of 3, a contact time of 60 min, an initial chromium concentration of 70 mg/L and an adsorbent dosage of 0.6 mg/100 mL. The Langmuir isotherm model was found to have the best fit with the experimental data. Moreover, the kinetics study revealed that a pseudo-second-order model fit the data best, indicating the occurrence of chemisorption. Overall, this study suggested that Rumex abyssinicus could be an effective adsorbent for removing hexavalent chromium from aqueous solutions.

Adsorption of Hexavalent Chromium on KOH Activated Carbon Derived from Water Hyacinth Leaf Coated with Polyaniline/Polypyrrole

KOH-Activated carbon derived from Water Hyacinth (KOH-WHL-AC) was prepared and coated with Polyaniline-Polypyrrole (PANI/PPY) copolymer for the removal of hexavalent chromium (Cr(VI)) from wastewater. The prepared material was characterized by FT-IR and XRD. The effect of pH, contact time, dosage, and initial Cr(VI) concentrations were optimized using batch adsorption experiment. The adsorption kinetics was found to fit better to pseudo-second-order than the pseudo-first order model. Langmuir and Freundlich isotherm models were analyzed using linear fitting. It was found that the Langmuir adsorption model gives the best fit indicating that the monolayer adsorption of Cr(VI) on the KOH-WHL-AC. The highest adsorption capacity of 409.83 mg/g was achieved at pH 1.0, and equilibrium was achieved within 420 min. The reuse efficiency of the synthesized material was also found to be greater than 54% for five consecutive cycles. Thermodynamic studies have also been carried out and the adsorption was found to be spontaneous and endothermic

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.

Sorption of hexavalent chromium adsorption and its subsequent removal from Aqueous Environment using algae Sargassum myriocystum

The present study focuson the adsorption of hexavalent chromium with Sargassum myriocystum, algae and the outcomes of various parameters such as size of sorbent, contact time, temperature, sorbent dosage and agitating speed were enhanced with aid of response surface methodology. The maximum adsorption of hexavalent chromium in its optimized conditions were determined as solution temperature of 35oC, size of sorbent for 0.5284 mm 36 BSS mesh ,contact time (1 hour), agitating speed (50 rpm) and sorbent dosage (4.309 g).The utmost removal was 99% . Isotherm studies revealed that Langmuir model is fitting the algae with a hexavalent chromium uptake of 61.5384mg/g. Thermodynamic study revealed that it is endothermic in nature and values of Gibb’s free energy, enthalpy and entropy change are in accordance. The sorbents were characterized with FTIR and SEM. FTIR studies revealed the presence of a few functional groups like carboxylic acid, amino and hydroxyl in hexavalent chromium adsorption. Pseudo I order kinetics are in accordance for this process. From above studies it can be concluded that Sargassum myriocystum had good removal capacity for hexavalent chromium from fabricated solutions.

Synthesis of a starch-composite magnetic material modified with polyethyleneimine for enhanced adsorption of diclofenac sodium, methyl orange, Amaranth, and hexavalent chromium

This study introduces Magnetic Starch (MAST), an innovative material designed for the efficient and rapid removal of water contaminants. MAST is synthesized by integrating polyethyleneimine and magnetic Fe3O4 nanoparticles into a starch composite. It exhibits a saturation magnetization of 7.3 emu/g and a functional surface area of 3.55 m² g−1. MAST's amine group density is 12.03 mmol/g, indicating a strong affinity for pollutants. Notably, MAST demonstrates exceptional adsorption capacities for various hazardous substances, including diclofenac sodium (620.51 mg g−1), methyl orange (470.85 mg g−1), amaranth (193.71 mg g−1), and hexavalent chromium (164.62 mg g−1). Thermodynamic studies reveal that the adsorption process is spontaneous and endothermic, with increased efficiency at higher temperatures, indicating suitability across various thermal conditions. MAST achieves rapid equilibrium within 20 minutes, conforms to pseudo-second-order and Langmuir models, and exhibits selective adsorption in complex matrices. These attributes underscore its potential for broad environmental remediation applications. Furthermore, MAST can be easily separated from water using magnets and retains 60 % of its effectiveness after five usage cycles, endorsing its feasibility for repeated use.

Hexavalent chromium adsorption by watermelon peels from tannery wastewater

Hexavalent chromium adsorption by watermelon peels from tannery wastewater

Removal of hexavalent chromium using one-step synthesized metal-polyphenol composites epigallocatechin gallate/titanium: Performance, interference, and mechanisms

Chromium-containing wastewater intensifies the shortage of water resources, and how to solve the problem has become a research hotspot. In this study, epigallocatechin gallate and titanium salt were combined to prepare epigallocatechin gallate/titanium composites by one-step synthesis, and the effectiveness and mechanisms of removing hexavalent chromium from wastewater were studied. Based on the characterization results, the epigallocatechin gallate/titanium nanometer-scale materials were irregularly spherical, and their surface was rich in phenolic hydroxyl groups. The average particle size, average pore size, and BET surface area were 448 nm, 6.23 nm, and 15.40 m2/g, respectively. The Freundlich isothermal model for adsorption and pseudo-second-order adsorption kinetics were both applicable to the hexavalent chromium adsorption. The maximum adsorption capacity of hexavalent chromium was 105.8 mg/g, and the adsorption process was more inclined to endothermic reaction. The salinity resistance of epigallocatechin gallate/titanium materials to different salts was sodium chloride > magnesium sulfate heptahydrate. In the organic acid-coexisting system, the removal efficiency of epigallocatechin gallate/titanium materials for hexavalent chromium with 20 mg/L fulvic acid and citric acid was 82.7% and 81.5%, respectively. The epigallocatechin gallate/titanium materials also showed excellent removal ability for hexavalent chromium, lead(II), copper(II), and nickel(II), with removal efficiencies all above 95%. Hexavalent chromium was first adsorbed and then reduced to trivalent chromium with the help of phenol hydroxyl groups on the materials. The trivalent chromium was further immobilized through electrostatic attraction and complexation. This work aimed to provide a new idea for handling hexavalent chromium-contaminated wastewater by using green and versatile polyphenol nanomaterials.

Extracting lignin from sugarcane bagasse for methylene blue and hexavalent chromium adsorption in textile wastewater: a facile, green, and sustainable approach.

This study presents the process of extracting lignin from sugarcane bagasse collected in the Mekong Delta, Vietnam by the alkali method. NaOH has been used as an effective, environmentally friendly chemical to enhance the extraction process. The obtained lignin was applied for methylene blue (MB) and hexavalent chromium (Cr(vi)) removal. Factors influencing lignin extraction and adsorption processes of MB and Cr(vi) were investigated, showcasing the sustainable reusability of lignin extracted from sugarcane bagasse. Lignin characterization was also carried out by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) techniques. The results showed that the extracted lignin content reached 38.61% under optimal conditions (NaOH concentration of 10%, reaction temperature of 90 °C and reaction time of 90 min). The adsorption efficiency and capacity of lignin reached 90.90% and 9.09 mg g-1 for MB and 80.10% and 28.04 mg g-1 for Cr(vi), respectively, under optimum adsorption conditions (pH, adsorption time, initial methylene blue concentration, and used lignin content). The adsorption process obeyed Langmuir adsorption and was principally physical adsorption. These findings prove sugarcane bagasse based lignin as a cheap and efficient adsorbent for MB and Cr(vi) removal, which contributes to the utilization of the abundant agricultural by-product for wastewater treatment.

Adsorption of hexavalent chromium from aqueous solution onto corn cobs – activated carbon

This study evaluated the performance of a new activated carbon (CCs-AC) produced from corn cobs by boric acid activation for the effective removal of hexavalent chromium, a heavy metal with high potential to pollute the environment, from wastewater. For this purpose, with the help of parameters such as solution pH, contact time, initial Cr(VI) concentration, CCs-AC dose, desorption and temperature, the removal of Cr(VI) ions from aqueous solution by adsorption on CCs-AC was investigated from equilibrium, kinetic and thermodynamic point of view. As a result of the experiments, it was determined that the optimum solution pH was 2.0, the contact time was 4 hours, and the desorption solution was 3.0 M NaOH. From the kinetic data, it was determined that the adsorption was compatible with the pseudo-second order kinetic model and the maximum Cr(VI) adsorption capacity (123.7 mg/g) obtained from the Langmuir isotherm model showed that CCs-AC was of competitive quality with the literature. From the thermodynamic data, the positive ΔH value indicates that the adsorption is endothermic and the value of 12.00 kj/mol indicates that the adsorption is rather chemically driven. The negative ΔG value indicates that the process proceeds spontaneously with an increase in temperature, while the ΔS value indicates an increase in the amount of unused energy.

Pineapple Stalk-Based Synthesized Activated Carbon for Effective Adsorption of Hexavalent Chromium in Aqueous Solutions

World industrial expansion fueled significant economic growth. Environmental deterioration is currently the main cause for concern. Human health is negatively impacted by the heavy metals in the waste water. The methods and their costs are more important in this heavy metal removal. The main method for getting rid of heavy metals like chrome, lead, nickel, etc. is adsorption. This study proposes a novel approach of eliminating hexavalent chromium since treatment methodologies need for creative, low-cost solutions. A straight method of activation including treatment with NaOH solution was utilized to produce activated carbon (ACs) with nanopores from pineapple stalk fruit waste. The NaOH solution reagent used for activation was easily cleared from the pre-treated pineapple stalks for recycling, which significantly reduced pollution during the carbonization process. The shape and arrangement of the ACs were assessed using SEM and FT-IR. The created adsorbent was employed in a batch adsorption procedure to remove Cr (VI). We further investigated the effect of the NaOH solution absorption on the structure, shape, and performance of the synthesized ACs in terms of Cr (VI) removal. According to the results of the characterization, treating the pineapple stalks with a NaOH solution removed some functional groups and resulted in the creation of micro-meso porous structures. At a dose of 1.0 g/ 100 mL and a pH of 6.3, the greatest adsorption capacity of the PSAC produced by triggering with 4% NaOH solution was 7.4 mg g-1, and the ACs displayed exceptional Cr (VI) adsorption ability.

Cauliflower stem-derived biochar for effective adsorption and reduction of hexavalent chromium in synthetic wastewater: A sustainable approach

Contamination with hexavalent chromium (Cr(VI)) has drawn immense interest of national and global regulatory authorities due to its toxic and carcinogenic threat. Although various approaches have been applied for Cr(VI) removal from aqueous solution, adsorption has been proven to be the most promising method. Biochar, a cost-effective adsorbent, is one of the prominent adsorbents for environmental remediation that can be produced from different biowaste precursors. Cauliflower (Brassica oleracea) is one of the common vegetables around the world. The cauliflower stem is not commonly edible and therefore discarded as waste. In this work, the cauliflower waste-based biochar, with and without chemical modification, was prepared from a simple oxygen-limited pyrolysis. With the assistance of TGA, DSC, and SEM-EDS, the effect of pyrolysis temperature on the generation of biochar, reaction energy as well as reaction temperature, and morphology of the prepared biochar were analyzed. Pyrolytic temperature of 450°C was found to be the best for tailoring biochar. Chromium(VI) removal from the synthetic solution was performed by using biochar as an adsorbent. H3PO4-activated biochar (PBC) performs better than other biochar. The adsorption kinetics, isotherm, and thermodynamic parameters were studied in batch-wise experiments by varying the contact time, initial Cr(VI) concentration, and operating temperature. The Cr(VI) removal on PBC biochar follows a pseudo-second-order kinetics and fits with Langmuir isotherm resulting in Cr(VI) adsorption capacity of 64.10 mg/g. The thermodynamic parameters and XPS analysis of spent biochar adsorbent reveal that Cr(VI) reduction to Cr(III) happens simultaneously during the removal process. The spent biochar can be regenerated using 0.1 M NaCl and used for several cycles. Thus, the cauliflower stem-derived biochar can be effectively applied for Cr(VI) removal for multiple cycles through regeneration, which would contribute to the circular economy for environmental purposes.