Initial Cr Concentration Research Articles

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

Removal of chromium using rhamnolipid biosurfactant, ferrous sulfate and cationic tannin‐based flocculant in a dissolved air floating system using a central composite design (CCD)

AbstractThis research studied the wastewater chromium removal efficiency by dissolved air flotation (DAF) using a rhamnolipid (RL) biosurfactant as a collector. An experimental flotation DAF apparatus with 6 vessels of 2 L containing a coupled saturator injecting compressed air at 5.88 kPa in the vessels was used. The total RL concentration of the broth resulting from fermentation was 9 ± 1.0 g/L. This broth was used in nature in the DAF experiments. A central composite design (CCD) was used to optimize removal of Cr(VI) and total Cr with regards to two independent variables, pH (3.17–8.83) and iron concentration of the medium (0–225.0 mg/L), with a three assays performed at the conditions of the central point of the design. The experimental conditions for DAF were an initial hexavalent Cr concentration of 100 mg/L; RL broth volume of 500 mL; saturated with oxygen water volume of 200 mL; and a rapid mixing time of 6 min through stirring at 120 rpm. The results showed that under acidic pH conditions and with high iron concentrations, both the Cr(VI) and total Cr removal rates were highest. The optimal removal region determination was at a pH of 3.5 and iron concentration of 180 mg/L. Subsequently, cationic tannin‐based flocculant was also evaluated as a collector, and ferrous sulfate was used as a coagulant during Cr(III) removal. The best Cr(III) removal percentage was obtained at cationic polymer concentrations of 300 mg/L with Cr(III) removal of 50.8% and a pH of 5.5.

Optimizing Typha biochar with phosphoric acid modification and ferric chloride impregnation for hexavalent chromium remediation in water and soil

Considering the persistent and covert nature of heavy metal soil contamination, the sustainable development of ecological environments and food safety is at significant risk. Our study focuses on remediating soils contaminated with chromium (Cr); we introduce an advanced remediation material, iron oxide phosphoric acid-loaded activated biochar (HFBC), synthesized through pyrolysis. This HFBC displays greater microporosity, fewer impurities, and enhanced efficiency for the remediation process. Our research utilized a comprehensive set of analytical techniques, including Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS), alongside adsorption studies to elucidate the Cr removal mechanism. The effectiveness of HFBC in remediation was influenced by several factors: the pH level, dosage of HFBC, the initial concentration of Cr, and the ambient temperature. Our results indicated an optimal chromium (VI) adsorption capacity of 55.5 mg/g by HFBC at a pH of 6.0 and a temperature of 25 °C, with the process adhering to the pseudo-second-order kinetic model and the Langmuir adsorption isotherm, thus suggesting spontaneity in the uptake method. Moreover, this mechanism encompasses both adsorption and reduction reactions. Using HFBC in pot experiments with cabbage indicated not only an increase in soil pH and cation exchange capacity (CEC), but also a surge in bacterial community abundance. Significant reductions in bioavailable chromium were also recorded. Interestingly, HFBC addition bolstered the growth of cabbage, while concurrently diminishing chromium accumulation within the plant, particularly notable as the HFBC application rate increased. In summation, the HFBC produced in our study has demonstrated convincing efficacy in removing chromium from aqueous solutions and soil. Moreover, the positive agronomic implications of its use, such as enhanced plant growth and reduced heavy metal uptake by plants, indicate its high potential for operational value in the domain of environmental remediation of heavy metals.

Amino-Functionalized Lotus Stem Hydrochar for Rapid Adsorption and In Situ Detoxification of Cr(VI) from Water.

The development of low-cost, efficient, and environmentally friendly adsorbents is the key to highly toxic hexavalent chromium [Cr(VI)] removal by adsorption. In this paper, amino-functionalized lotus stem hydrochar (ALSHC) was prepared from an agricultural waste lotus stem (LS) for the adsorption removal of Cr(VI) from water. The effects of the initial Cr(VI) concentration, contact time, temperature, coexisting anions, and reusability of ALSHC on Cr(VI) removal were examined in detail. The adsorption mechanism was further discussed by investigating the impact of the solution's initial pH, the relation between the pH change in solution and Cr(VI) removal during the process, the changes of chromium (Cr) species in solution and on ALSHC during adsorption, and the XPS characterization. The results demonstrated that ALSHC effectively removed Cr(VI) from water with rapid adsorption (the removal rate reached 80.90% in only 10 min) and in situ detoxification. Most importantly, ALSHC still had better adsorption performance (adsorption capacity of 30.95 mg g-1) than commercially activated carbon, even at pH = 9.00. The adsorption of Cr(VI) by ALSHC accorded with the pseudo-second-order kinetic model and Langmuir isotherm model, indicating a monolayer chemisorption process. The adsorption process was shown to be spontaneous and endothermic based on the thermodynamic characteristics (ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0). The mechanism of Cr(VI) removal was mainly composed of three parts in sequence: Firstly, Cr(VI) in solution was quickly adsorbed onto ALSHC with protonated -NH2 through electrostatic attraction; subsequently, the adsorbed Cr(VI) on ALSHC was mostly detoxicated by in situ reduction; and finally, the reduced Cr(III) and the remaining Cr(VI) were fixed on the ALSHC surface by complexation. The prepared ALSHC displayed a certain superiority in Cr(VI) adsorption and had the prospect of further development.

Sustainable and integrated approaches for carbon capture and rapid remediation of Cr- and Zn-contaminated soils

Soil contamination is a growing concern for sustainable development worldwide. Conventional remediation approaches, such as using ordinary Portland cement (OPC) or lime are limited due to high CO2 emissions, energy consumption, and natural resource consumption. This paper proposes a sustainable method using CO2 and a waste from steel production (ladle slag, LS) for rapid remediation of Cr and Zn-contaminated soils. Contaminated soils spiked by Cr and Zn with various initial concentrations were treated with 10% LS and subjected to conventional and CO2 curing for different periods. The results demonstrated that LS with conventional curing could reduce leaching concentrations of Cr and Zn in contaminated soils. However, it necessitated 28 days to meet the criteria of inert waste and drinking water standards. In contrast, LS with CO2 curing required significantly less time (32 h for Cr and 8 h for Zn) to achieve lower leaching concentrations of Cr and Zn than those with 28-day conventional curing. After CO2 curing for 152 h for Cr- and 80–120 h for Zn-contaminated soils, leaching concentrations of Cr and Zn were 1.5–4 times and 6–72 times lower than those with 28-day conventional curing, respectively. Simultaneously, carbon capture was increased from 10.6% to 17.5% and 19.9%, respectively, with the initial Cr and Zn concentrations increased from 0 to 8000 mg/kg. The strength of Cr- and Zn-contaminated soils with CO2 curing also effectively enhanced up to around 3.3–3.6 times and 1.3–3.3 times higher than those with 28-day conventional curing, respectively.

Enhanced chromium and nitrogen removal by constructing a biofilm reaction system based on denitrifying bacteria preferential colonization theory

Understanding the developmental characteristics of microbial communities in biofilms is crucial for designing targeted functional microbial enhancements for the remediation of complex contamination scenarios. The strong prioritization effect of microorganisms confers the ability to colonize strains that arrive first dominantly. In this study, the auto-aggregating denitrifying bacterial Pseudomonas stutzeri strain YC-34, which has both nitrogen and chromium removal characteristics, was used as a biological material to form a stable biofilm system based on the principle of dominant colonization and biofortification. The effect of the biofilm system on nitrogen and chromium removal was characterized by measuring the changes in the quality of influent and effluent water. The pattern of biofilm changes was analyzed by measuring biofilm content and thickness and characterizing extracellular polymer substances (EPS). Further analysis of the biofilm microbiota characteristics and potential functions revealed the mechanism of strain YC-34 biofortified biofilm. The results revealed that the biofilm system formed could achieve 90.56% nitrate-nitrogen removal with an average initial nitrate-nitrogen concentration of 51.9 mg/L and 40% chromium removal with an average initial hexavalent chromium Cr(VI) concentration of 7.12 mg/L. The biofilm properties of the system were comparatively analyzed during the biofilm formation period, the fluctuation period of Cr(VI)-stressed water quality, and the stabilization period of Cr(VI)-stressed water quality. The biofilm system may be able to increase the structure of hydrogen bonds, the type of protein secondary structure, and the abundance of amino acid-like components in the EPS, which may confer biofilm tolerance to Cr(VI) stress and allow the system to maintain a stable biofilm structure. Furthermore, microbial characterization indicated an increase in microbial diversity in the face of chromium stress, with an increase in the abundance of nitrogen removal-associated functional microbiota and an increasing trend in the abundance of nitrogen transfer pathways. These results demonstrate that the biofilm system is stable in nitrogen and chromium removal. This bioaugmentation method may provide a new way for the remediation of heavy metal-polluted water bodies and also provides theoretical and application parameters for the popularization and application of biofilm systems.

Biodegradation of phenanthrene-Cr (VI) co-contamination by Pseudomonas aeruginosa AO-4 and characterization of enhanced degradation of phenanthrene

Microorganisms capable of simultaneously remediating heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) pollution hold significant importance in bioremediation efforts. In this study, we investigated the ability of Pseudomonas aeruginosa AO-4 to simultaneously degrade phenanthrene (PHE) and reduce Cr (VI). Specifically, it has the ability to reduce 100 % of Cr (VI) (30 mg/L) while degrading 43.8 % of PHE (50 mg/L). In batch experiments, it was observed that the presence of Cr (VI) can enhance the degradation of PHE by strain AO-4. The solubility of PHE in soluble extracellular polymeric substances (S-EPS) was found to be related to the initial concentration of Cr (VI), which could explain why Cr (VI) promotes the degradation of PHE. Additionally, XPS analysis confirmed that Cr (VI) was reduced to Cr (III) with S-EPS produced by Pseudomonas aeruginosa AO-4. GC–MS analysis was conducted to analyze the degradation metabolites of phenanthrene, di(2-ethylhexyl) phthalate and 2TMS derivatives of salicylic acid were detected, indicating that Pseudomonas aeruginosa AO-4 is capable of degrading phenanthrene through two distinct pathways. These findings demonstrate the potential of Pseudomonas aeruginosa AO-4 in the treatment of co-contamination scenarios involving PAHs and HMs.

Exploring the Role of Carbon Nanosheets for Detoxification of Cr(VI) from Aqueous Solution

Toxic pollutants in wastewater must be reduced in order to protect the aquatic ecosystem's stability and the public's health. Finding affordable and effective technologies for treating municipal, horticultural, aquacultural and industrial wastewater is urgently needed. Nitrogen-doped carbon nanosheets (N-CNS), which are produced by hydrothermal reaction from glycerol, sulfuric acid and melamine, have strong adsorptive behaviour against hazardous aqueous pollutants such as heavy metals and organic compounds. The overall elemental composition of CNS is altered by nitrogen incorporation, favouring CNS interaction with pollutants. The objective of the current investigation was to investigate the possibility for Chromium(VI) [Cr(VI)] adsorption on the CNS from a liquid solution. The ideal pH for Cr (VI) adsorption was noted to be 2.0. The Cr(VI) adsorption was enhanced when the starting metal concentration is more up to 700 mg L-1. A maximum removal of 256.41 mg g-1was seen when pH was 2.0 at 700 mg L-1 initial Cr(VI) concentration. We employed both the Freundlich and the Langmuir adsorption isotherms to determine the adsorption equilibrium constants. Using fitting curves and correlation coefficients (R2), it has been found that the model of the Langmuir isotherm is a best fit and it indicates homogeneous surface of CNS.

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

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

NFeS Embedded into Cryogels for High-Efficiency Removal of Cr(VI): From Mechanism to for Treatment of Industrial Wastewater.

Most studies have focused on complex strategies for materials preparation instead of industrial wastewater treatment due to emergency treatment requirements for metal pollution. This study evaluated sodium polyacrylate (PSA) as a carbon skeleton and FeS as a functional material to synthesize PSA-nFeS material. The characteristics and interactions of PSA-nFeS composites treated with hexavalent chromium were analyzed by means of various techniques, such as scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FTIR), and atomic absorption spectroscopy (AAS). Adsorption-coupled reduction was observed to be the predominant mechanism of Cr(VI) removal. The feasibility of PSA-nFeS composites in reducing toxicity and removing of Cr(VI) from real effluents was investigated through column studies and material properties evaluation. The continuous column studies were conducted using tannery effluents to optimize feed flow rates, initial feed Cr(VI) concentration, and column bed height. The results revealed that PSA-nFeS composites are ideal for filling materials in portable filtration devices due to their lightweight and compact size.

Activated sodium bentonite as an adsorbent for efficient removal of hexavalent chromium: Statistical optimization using Box–Behnken design

AbstractAt present, developing countries, including Ethiopia, are undergoing a phase of industrial transformation. As a result, there has been a significant rise in the presence of harmful pollutants in groundwater. The release of deleterious heavy metals, such as Cr (VI), into the surrounding ecosystem is a result of various industrial operations. The present investigation utilized activated sodium bentonite clay as an adsorbent agent to facilitate the elimination of Cr (VI). The clay was subjected to acidification and thermal modification techniques to enhance its adsorption capacity. The investigation involved an examination of the particular surface area, capacity for cation exchange, crystalline properties, functional groups on the surface, and structural morphology. The methylene blue test method was employed to ascertain the maximum specific surface area and cation exchange capacity of the adsorbent, which were found to be 512 m2/g and 65.5 meq/100 g, respectively. The clay mineral composition was analyzed using X‐ray diffraction, which indicated that the primary constituent was montmorillonite. The presence of impurities such as quartz, feldspar, muscovite, cristobalite, and hematite was also detected. The study employed response surface methodology, Box–Benkhen design (RSM‐BBD) to investigate the impact of operational parameters, including agitation time, initial Cr (VI) concentration, and adsorbent dosage. Under the optimal conditions, a removal efficiency of 98.05% was achieved for Cr (VI) for a contact duration of 120 min, a dosage of 3.913 g/L, and an initial concentration of 50 mg/L. The sodium bentonite clay that was activated demonstrated a maximum capacity for adsorption of 22.72 mg/g in regards to the adsorption of Cr (VI). The experimental data were best fitted by the Langmuir isotherm, which exhibited a correlation coefficient of 0.9699. The adsorption kinetics were assessed and determined to adhere to a pseudo‐second‐order pattern, exhibiting a coefficient of determination (R2) value of 0.999. Furthermore, the activated sodium bentonite clay demonstrated remarkable potential for repeated utilization in the adsorption of Cr (VI) ions in aqueous solutions.

Accelerated Cr (VI) removal by a three-dimensional electro-Fenton system using green iron nanoparticles.

Green-synthesized iron nanoparticles (GAP-FeNP) were used as particle electrodes in a three-dimensional electro-Fenton (3DEF) process to accelerate the removal of hexavalent chromium [Cr (VI)]. Removal was evaluated by varying the pH (3.0, 6.0, and 9.0) and initial Cr (VI) concentrations (10, 30, and 50 mg/L) at 5 and 25 min. These results demonstrated that GAP-FeNP/3DEF treatment achieved more than 94% Cr (VI) removal under all tested conditions. Furthermore, it was observed that Cr (VI) removal exceeded 98% under pH9.0 in all experimental parameters tested. The results of the response surface methodology (RSM) determined two optimal conditions: the first, characterized by a pH of 3.0, Cr (VI) concentration at 50 mg/L, and 25min, yielded a Cr (VI) removal of 99.7%. The second optimal condition emerged at pH9.0, with Cr (VI) concentrations of 10mg/L and 5min, achieving a Cr (VI) removal of 99.5%. This study highlights the potential of the GAP-FeNP to synergistically accelerate Cr (VI) removal by the 3DEF process, allowing faster elimination and expansion of the alkaline (pH9.0) applicability. PRACTITIONER POINTS: The required time for >99% of Cr (VI) removal by the GAP-FeNP/3DEF process was shortened from 25 to 5min. EF process with GAP-FeNP reduces the time necessary for Cr (VI) removal, which is 67% faster than conventional methods. EF process using GAP-FeNP removed >94% of Cr (VI) after 25 min for all initial Cr (VI) concentrations and pH treatments. Cr (VI) removal by the GAP-FeNP/3DEF process was >98% at a pH of 9.0, widening the solution pH applicability.

ADSORPTIVE REMOVAL OF HEXAVALENT CHROMIUM FROM AQUEOUS PHASE USING VEGETABLE-TANNED BUFFING DUST

Removal of hexavalent chromium from synthetic wastewater was performed by employing vegetable-tanned buffing dust, a byproduct of tanneries. Different analysis techniques such as SEM, BET, and FTIR were used to characterize the vegetable-tanned buffing dust. The experiment on adsorption was carried out in a batch manner. Investigations were conducted into the various operating parameters, such as the dose of adsorbent, contact period, and initial Cr (VI) concentration. At a dose of 1g/100 mL and a contact period of 280 minutes, the maximum adsorption capacity was noted. The Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherms were examined at various concentrations. With a maximum adsorption efficiency of 14.14 mg/g, the Langmuir isotherm model was found to be the most well-fitting for the current investigation. Kinetic analysis was performed for pseudo first and second order; the pseudo-second-order model demonstrated the most optimal fit with a regression coefficient (R2 ) of 0.9936.

Hydrothermal preparation of Nb5+-doped α-Fe2O3 nanorods for efficient visible light-driven photocatalytic reduction of hexavalent chromium

Nb5+ doped α-Fe2O3 (Nb-Fe2O3) nanorods with different Nb5+ contents were prepared using a low-temperature, short-time, one-pot hydrothermal method. All the prepared Nb-Fe2O3 products showed better photocatalytic activities than α-Fe2O3 nanorods in the reduction of aqueous Cr(VI) under visible light (wavelength > 420 nm). 4% Nb-Fe2O3 had the maximum photocatalytic activity, which was 2.24 times that of α-Fe2O3 nanorods and surpassed those of many newly reported visible light photocatalysts. Moreover, the photocatalytic efficiency of 4% Nb-Fe2O3 can be further improved by proper increasing its dosage, decreasing the initial pH and Cr(VI) concentration of K2Cr2O7 solution. Furthermore, 4% Nb-Fe2O3 showed rather good photocatalytic stability and reusability. Besides, 4% Nb-Fe2O3 was efficient in visible light-driven photocatalytic reduction of Cr(VI) in diluted black chrome plating solution. Nb5+-doping can efficaciously enhance the abilities of α-Fe2O3 in absorbing visible light and transferring and separating photogenerated carriers, thereby contributing to the elevated photocatalytic activity of Nb-Fe2O3.

Biosorption of hexavalent chromium by biochar prepared from the Ceratonia siliqua pod: Kinetic, equilibrium, and thermodynamics studies

Ceratonia siliqua pod biochar sample (CBC) was generated in this work from C. siliqua (carob pod waste) biomass (CBM) by slow pyrolysis for 5h at 400°C as an alternative low-cost biosorbent for the removal of Cr(VI). The biosorption parameters that were adjusted were the initial pH (2.0–10.0), temperature (30°C, 40°C, and 50°C), biosorbent dose (0.01–0.03 g/50 mL), initial Cr(VI) concentration (10–100 mg/L), and contact period (0–360 min). The interaction between the surface functional groups on the CBM and CBC and the Cr(VI) ions was found to be the primary mechanism for Cr(VI) sorption via surface complexation and electrostatic interactions, according to the investigation of the pH influence. The Langmuir isotherm was shown to be more well-fitting than the Freundlich and Dubinin-Radushkevich isotherms for the concentration range of 10 to 100 mg/L. The testing results indicated a sorption capacity of 90.909 mg/g of CBM and 131.579 mg/g of CBC. According to kinetic investigations, the absorption of Cr(VI) ions onto CBM and CBC was defined in pseudo-second order. The findings of thermodynamic investigations showed that the biosorption of Cr(VI) ions onto CBM and CBC was an exothermic, spontaneous process. These findings demonstrated that, even for high concentrations of Cr(VI) in industrial wastewater, CBM and CBC could be viable, affordable alternatives as adsorbents.

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

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

Adsorption of hexavalent chromium from wastewater using polyaniline-coated microcrystalline cellulose nanocomposites.

In this study, the effectiveness of microcrystalline cellulose (MCC) as an adsorbent for the removal of hexavalent chromium, Cr(vi), from synthetic wastewater was enhanced through functionalization with polyaniline (PANI). Scanning electron microscopy (SEM) showed that MCC was an effective scaffold for in situ chemical oxidative polymerization of aniline. Fourier transform infrared spectroscopy (FTIR) spectroscopy and X-ray diffraction confirmed successful PANI synthesis. The MCC/PANI nanocomposites exhibited relatively high specific surface areas, compared to that of the MCC (2.05 m2 g-1). Batch adsorption studies showed that the optimal conditions for the removal of Cr(vi) from wastewater using the MCC/PANI-69 wt% nanocomposite were an initial Cr(vi) concentration of 100 mg L-1, an adsorbent dosage of 4 g L-1 and a Cr(vi) solution pH of 7. The MCC/PANI-69 wt% required only 30 min to reach equilibrium and the equilibrium removal efficiency was 95%. FTIR spectroscopy and energy dispersive X-ray spectrometry results suggest that the Cr(vi) removal mechanism by the MCC/PANI-69 wt% nanocomposite at pH 7 was through electrostatic attraction of Cr(vi) species by PANI, reduction of Cr(vi) into Cr(iii) and precipitation of Cr(iii) on the nanocomposite surface. The kinetics for the removal of the Cr(vi) by the MCC/PANI-69 wt% nanocomposite were adequately described by the pseudo second order (PSO) kinetics model, whereas the Langmuir isotherm adequately described the equilibrium data. The MCC/PANI-69 wt% nanocomposite had a significantly improved maximum adsorption capacity of 35.97 mg g-1, at pH 7, in comparison to that of the MCC (3.92 mg g-1 at pH 1). The study demonstrated that, whereas most of the reported adsorbents for Cr(vi) are only effective at low pH values, the MCC/PANI nanocomposite synthesized in this study was effective at pH 7.

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

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

Bio-based iron oxide nanoparticles forming bi-functional chitosan composite adsorbent for Cr(VI) decontamination

Iron oxide nanoparticles (IONPs) synthesized in a bio-based route are viable contenders for the removal of Cr(VI) from contaminated water. However, recovery and reuse of these IONPs are challenging and could limit their practical applicability. Herein, reusable and bi-functional composite chitosan (CS) beads (CS/IONPs) are developed by infusing IONPs in the CS matrix and applied for Cr(VI) adsorption and detoxification from synthetic wastewater. CS/IONPs beads were characterized through various analytical techniques: X-ray diffraction, X-ray photoelectron spectroscopy and Scanning electron microscopy. The loading of IONPs varied from 0.1 to 0.25 (% w/v) with Fe(III)/Fe(II) in a molar ratio of 2. Mesoporous (11.65 nm) CS/IONPs beads with a size from 6.6 − 4.31 mm were formed with a specific surface area of 63.67 m2/g compared to 25.42 m2/g for CS beads. Cr(VI) removal of 98.71 % was achieved by CS/IONPs adsorbent within 480 min at the optimal conditions of initial pH 3, CS/IONPs dosage 2.5 g/L, temperature 25 °C, and initial Cr(VI) concentration 150 mg/L. The co-existing cations didn’t affect Cr(VI) adsorption capacity of CS/IONPs beads, though PO43− and SO42− competed slightly with Cr(VI) adsorption. Cr(VI) removal process was spontaneous and exothermic and followed the pseudo-first-order kinetic. CS/IONPs composite beads could adsorb a maximum of 345.53 mg Cr(VI) per g of IONPs as determined by Langmuir isotherm. The used CS/IONPs beads could be regenerated using NaOH for the initial 4 cycles, but about 15.7 % of active sites were reduced afterwards. Cr(VI) removal involves electrostatic interaction, Cr(VI) reduction to Cr(III), Cr(III) adsorption, Cr(III) surface complexation through abundant –NH2 group, and Cr(III) co-precipitation with Fe(III).

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.