Cr Removal Performance Research Articles

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

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

Efficient Removal of Chromium and Lead from Tanneries Effluent of Korangi Industrial Area Karachi Using Rotating Disk Mesh as Anode Electrode Electrocoagulation

The aim of this study was to examine the best electrode design for the electrocoagulation process with the best removal performance, reduced passivation on the electrode surface, and lower energy consumption requirements for removing Chromium (Cr) and Lead (Pb) from leather tannery effluent. Three different electrodes were compared: non-rotating disk electrode (NRDE), rotating disk electrode (RDE) and rotating disk mesh electrode (RDME). All electrodes were used to observe a reduction in passivation on the electrode surface and its effects on the removal performance of Cr and Pb. The material used for the electrodes was iron. The maximum removal efficiency obtained was Cr = 87.9% and Pb = 97.5% under the following operating conditions: pH = 7, treatment time = 90 min, current density = 6.57 mA/cm², and RPM = 80. The results show that the electrical energy requirement for treating chromium and lead using RDME was 4.5 kWh/m³, which was found to be lower than the energy requirement observed in various other studies for treating tannery effluent. According to the results, RDME shows the highest removal performance with lower specific energy consumption compared to NRDE and RDE. RDME can be efficiently employed at a larger scale for treating leather tannery effluent.

Insights into chromium removal mechanism by Ca-based sorbents from flue gas

Chromium is a typical toxic pollution in sewage sludge incineration flue gas. Cr removal from flue gas is a challenge due to the high toxicity and valence variability of chromium. Ca-based sorbents, including CG-CaO, CA-CaO, and CCi-CaO, were developed for Cr capture by calcining calcium D-gluconate monohydrate, calcium acetate hydrate, and calcium citrate tetrahydrate, respectively. CG-CaO, CA-CaO, and CCi-CaO exhibit better Cr removal performance than traditional CaO. CA-CaO shows superior Cr adsorption ability due to the large BET surface area and pore volume. The Cr adsorption efficiency of CA-CaO is up to 94.79 % at 1000 °C. XRD and XPS results reveal that the adsorbed Cr contains Cr(III) and Cr(VI), and exists in the form of CaCr2O4 and CaCrO4. Cr adsorption on Ca-based sorbents is mainly controlled by adsorption and oxidation mechanism. The adsorption process of Cr on different Ca-based sorbents was described by four typical adsorption kinetic models. For CaO and CG-CaO, pseudo-first order model and Elovich model are suitable for the description of Cr adsorption. For CA-CaO and CCi-CaO, pseudo-second order model, Elovich model and Weber and Morris model fit well with the experimental values of Cr adsorption, suggesting that Cr adsorption on CA-CaO and CCi-CaO is controlled by a combined mechanism of chemisorption and intraparticle diffusion. The saturated adsorption capacity of CaO, CG-CaO, CA-CaO and CCi-CaO are evaluated to be 39.77, 48.98, 102.22 and 104.52 mg/g, respectively. The effects of incineration flue gas components on Cr adsorption were also explored. O2 shows no obvious influence on Cr adsorption over CA-CaO. HCl, SO2, NO and CO2 can inhibit Cr adsorption because of the competitive adsorption, and the inhibitory effect of SO2 is the strongest.

Homogeneous dispersion of amorphous nanoscale zero-valent iron supported on chlorella-derived biochar: In-situ synthesis and application mechanism for Cr(VI) removal over a wide pH range

Novel recyclable chlorella pyrenoidosa-derived biochar (CP-BC) supported nanoscale zero-valent iron composite (nZVI@CP-BC) was developed via an in-situ liquid-phase chemical reduction-deposition method. The obtained adsorbent kept prominent hexavalent chromium (Cr(VI)) removal capacity with a broad pH range (3.0–11.0). Also, these findings revealed that the removal performance of Cr(VI) via nZVI@CP-BC was 1.37, 6.67 and 1.25 times more than that of pristine nZVI, unmodified CP-BC and nZVI + CP-BC, respectively. The exceptional Cr(VI) removal benefited from the combination of high-reactivity nZVI and CP-BC resulting in an effective synergy. The physicochemical property of the nZVI@CP-BC was systematically elucidated utilizing multiple characterizations. It is launched that the Cr(VI) molecules were converted into Cr(Ⅲ) mainly via surface adsorption and chemical reduction. And CP-BC may regulate beneficial conditions for Cr(VI) chemical reduction reaction via largely mediating solution pH and electron transfer, which showed a rational reaction mechanism of promoted removal of Cr(VI) under a broad working pH range. The corrosion mechanism of nZVI in the whole reaction was also studied thoroughly. This work indicates that this novel nZVI@CP-BC would be a prominent material for the preferable remediation of Cr(VI)-bearing wastewater.

Insights of mechanism into enhanced removal of Cr(VI) by Ginkgo biloba leaves synthesized bimetallic nano-zero-valent iron/copper

For purpose of green preparation of nano-zero-valent iron and copper (GB-nZVI/Cu), the use of Ginkgo biloba extract as a reducing agent is reported herein. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) analyzed the properties of nanoparticles. GB-nZVI/Cu exhibited a better Cr(VI) removal performance than nZVI/Cu materials synthesized by apricot leaves (Al-nZVI/Cu) and hawthorn leaves (Hl-nZVI/Cu). GB-nZVI/Cu could remove 97.2% Cr(VI) in 30 min. Low pH and 313 K promoted the reaction while humic acid (HA) had inhibitory effect. The promoting effects of coexisting anions were observed following the order: SO42->HCO3->Cl-. The rate constant K2 increased from 0.0303 to 4.8865 g·mg-1·min-1 as SO42− concentration increased. Na+ and low Mg2+ concentration promoted the removal of Cr(VI) while NO3−, K+, Ca2+ and high Mg2+ concentration had the negative effects. The removal reaction followed the pseudo-second-order kinetic model, with a chemical adsorption as a rate-controlling step. Visual MINTEQ models and mechanism studies showed that the removal of Cr(VI) by GB-nZVI/Cu was a combination of adsorption, reduction and precipitation. The Fe-Cu galvanic cell can accelerate the corrosion of Fe0, enhancing the reduction of Cr(VI). Cu0/Cu(I) could be oxidation into Cu(II) by receiving electrons from Fe3+, resulting in the generation of Fe2+. Cr(III) finally precipitated in the form of FeXCr1−X(OH)3 and Cr(OH)3. GB-nZVI/Cu had superior sedimentation behavior and more Fe2+ production to promote Cr(VI) reduction. GB-nZVI/Cu maintained a better removal performance of Cr(VI) than Al-nZVI/Cu and Hl-nZVI/Cu after five reuses.

Synthesis, characterization and removal performance of Cr (Ⅵ) by orange peel-based activated porous biochar from water

A novel high-active porous activated biochar (KC) has been successfully prepared through a two-step chemical activation method with KOH by using orange peel as raw materials. The KC demonstrates several remarkable advantages for Cr (VI) removal from water, including large specific surface area of 1998 m2/g, well-developed porous microstructure, rich oxygen-containing functional groups and abundant surface-active sites. With these merits, the KC exhibits an outstanding experimental absorption capacity of Cr (VI) of 285.5 mg g−1 for 2400 mins at pH 2.0. The influences of initial pH, contact time, concentration and temperature on the remediation are investigated. The adsorption behavior fit well to Elovich model, suggesting a chemical adoption process. The Langmuir model fits better than the Freundlich model in simulating the adsorption isotherm, which implies a monolayer adsorption reaction through chemical adsorption. Mechanism studies demonstrate that chemical adoption, reduction, ion exchange and complexation with the assistance of oxygen-containing functional groups and porosity are involved in removal process of Cr (VI). Our work offers a feasible approach to optimize microstructure of biochar with satisfactory adsorption performance.

Kinetic and Isothermal Investigations on the Use of Low Cost Coconut Fiber-Polyaniline Composites for the Removal of Chromium from Wastewater.

Pollution due to various heavy metals is increasing at an alarming rate. Removal of hexavalent chromium from the environment is a significant and challenging issue due to its toxic effects on the ecosystem. Development of a low-cost adsorbent with better adsorption efficiency is presently required. In this study, waste coconut fibers (CF) were used to prepare its composite with polyaniline (PANI) via in-situ oxidation. The obtained composites with varying loading of PANI (15, 25, 50, and 75% w/w) were characterized by FE-SEM, TGA, and FTIR spectroscopy. The prepared composites were evaluated for their adsorption performance for removal of Cr(VI). It was concluded that the composite with 50% w/w polyaniline loading on coconut fiber exhibited a maximum adsorption efficiency of 93.11% in 30 min. The effect of pH, dosage, and concentration of the aqueous solution of chromium on the Cr(VI) adsorption efficiency of the composite was also studied. From the optimization studies it was observed that the absorbents exhibited the best adsorption response for Cr(VI) removal with 0.25 mg/mL adsorbent at pH 4, in 30 min. The effect of pH, dosage, and concentration of the aqueous solution of chromium on the Cr(VI) adsorption efficiency of the composite was also studied. This study highlights the application of low-cost adsorbent as a potential candidate for the removal of hexavalent chromium. A detailed study on the adsorption kinetics and isothermal analysis was conducted for the removal of Cr(VI) from aqueous solution using coconut fiber-polyaniline composite. From the kinetic investigation, the adsorption was found to follow the pseudo second order model. The data obtained were best fitted to the Elovich model confirming the chemisorption of the Cr(VI) on coconut polymer composites. The analysis of the isothermal models indicated monolayer adsorption based on the Langmuir adsorption model.

Study on the Preparation of Nano-FeS Loaded on Fly Ash and Its Cr Removal Performance.

Chromium has been considered as one of the most hazardous heavy metals because of its strong and persistent toxicity to the ecosystem and human beings. In this study, fly ash-loaded nano-FeS (nFeS-F) composites were constructed with fly ash as the carrier, and the performance and mechanism of the composites for the removal of Cr(VI) and total chromium from water were investigated. The composite was characterized by X-ray diffraction and transmission electron microscopy. The effects of fly ash size, molarity of FeSO4, and flow rate of FeSO4 solution on the removal of Cr(VI) and total chromium were investigated by a single factor experiment. The interaction of various factors was studied by the Box-Behnken response surface methodology. The optimum conditions of removal of Cr(VI)and total chromium by nFeS-F were determined. The results show that ① the optimal preparation conditions for nFeS-F were an FeSO4 concentration of 0.45 mol/L, a fly ash particle size of 120–150 mesh, and a flow rate of 0.43 mL/s.② The response surface model provides reliable predictions for the removal efficiencies of Cr(VI) and total chromium.③ The removal efficiencies of Cr(VI) and total chromium were 92.87 and 83.53%, respectively, under the optimal preparation conditions by the experimental test. This study provides an effective method for the removal of Cr(VI) and total chromium.

Heavy metal removal from aqueous solutions by chitosan-based magnetic composite flocculants

In this study, three magnetic flocculants with different chelating groups, namely, carboxymethyl chitosan-modified Fe3O4 flocculant (MC), acrylamide-grafted magnetic carboxymethyl chitosan flocculant (MCM), and 2-acrylamide-2-methylpropanesulfonic acid copolyacrylamide-grafted magnetic carboxymethyl chitosan flocculant (MCAA) were prepared, synthesized, and characterized by photopolymerization technology. They were applied to the flocculation removal of Cr(III), Co(II), and Pb(II). The effect of flocculation condition on the removal performance of Cr(III), Co(II), and Pb(II) was studied. Characterization results show that the three magnetic carboxymethyl chitosan-based flocculants have been successfully prepared with good magnetic induction properties. Flocculation results show that the removal rates of MC, MCM, and MCAA on Cr(III) are 51.79%, 82.33%, and 91.42%, respectively, under the conditions of 80 mg/L flocculant, pH value of 6, reaction time of 1.5 hr, G value of 200 s−1, and precipitation magnetic field strength of 120 mT. The removal rates of Co(II) by MC, MCM, and MCAA are 54.33%, 84.99%, and 90.49%, respectively. The removal rates of Pb(II) by MC, MCM, and MCAA are 61.54%, 91.32%, and 95.74%, respectively. MCAA shows good flocculation performance in composite heavy metal-simulated wastewater. The magnetic carboxymethyl chitosan-based flocculant shows excellent flocculation performance in removing soluble heavy metals. This research provides guidance and ideas for the development of efficient and low-cost flocculation technology to remove heavy metals in wastewater.

Theoretical and experimental research of novel fluorine doped hierarchical Sn3O4 microspheres with excellent photocatalytic performance for removal of Cr(VI) and organic pollutants

The fluorine doped Sn 3 O 4 strengthened the redox potential. Moreover, the phenols and Cr(VI) acted as sacrificial agent of h + / OH and e − , respectively, which remarkably enables the efficient utilization of photoinduced electron-hole pairs. • The unique fluorine doped hierarchical Sn 3 O 4 microspheres were first reported. • F doping enhanced light harvesting and boosted active radical generation. • Low recombination rate of free charge carrier was obtained. • F-Sn 3 O 4 microspheres are promising for removing organic pollutants and Cr(VI). Here, novel fluorine doped Sn 3 O 4 microspheres with highly photocatalytic performance were reported. UV–vis diffuse reflectance spectrum (DRS) and transient photocurrent response test showed the enhanced light harvesting and photo-response. DRS and electron spin resonance (ESR) spectrum confirmed that the enhanced light harvesting could remarkably boost active radical generation. The low recombination rate of free charge carrier and the long lifetime of photon-generated carrier also made great contribution. The lifetime of photon-generated carrier of F 0.2 -Sn 3 O 4 was 1.38 μs, which was 2.76 times of Sn 3 O 4 (0.50 μs). F 0.2 -Sn 3 O 4 reduced 95% of 10 ppm Cr(VI) (pH = 7) under light irradiation (400 W metal halogen lamp, light intensity: 148.36 mW/cm 2 ) for 12 min, which was 3.6, 10.2 and 64.5 times higher than that of Sn 3 O 4 (25.83%), C 3 N 4 (9.25%) and commercial TiO 2 (1.47%), respectively. F 0.2 -Sn 3 O 4 could remove 98% of methyl orange within 4 min comparing with commercial TiO 2 (30%). The highly removing efficiency of phenols (phenol, bisphenol A and p-chlorophenol) was also obtained. Density functional theory (DFT) calculation, Powder X-ray diffraction (XRD) patterns and DRS revealed that the replacement of F − by O 2− enhanced the light harvesting. The work is promising for the synergistic treatment of industrial waste water with organic pollutants (phenols) and Cr(VI).

Isolation of Chromium Resistant Bacteria from Contaminated Soil and Its Performance Evaluation for Hexavalent Chromium Removal

The present study deals with the metal tolerance as well as metal resistance characteristic in bacteria isolated from mostly tannery effluent contaminated soil. Seven chromium resistant bacteria (CrRB 1-7) were isolated for this study in LB medium amended with 100 mg/L filter sterilized hexavalent chromium (Cr(VI)) solution. The minimum inhibitory concentrations (MIC) of these gram positive and gram negative bacteria were found in the range of 350 – 450 mg/L of Cr(VI) concentration. Cr(VI) removal potential of these seven isolates were also studied. One isolate CrRB 1 possessed the ability to remove 98.4% Cr(VI) within 24h in LB medium. The effect of hexavalent chromium on their biomass growth potential were further observed. For CrRB1 least differences were found in doubling time calculated from growth curve in presence and absence of Cr(VI). CrRB 1 was then further studied in real life wastewater i.e. tannery effluent to evaluate its performance for removal of Cr(VI).The favorable outcomes encourages for the use of this isolate in green bioremediation technology for tannery industry. The subsequent reactor studies requires to reveal its performance for in-situ application.

Preparation of FeS/iron oxide composite and flax stem‐based porous carbon and its Cr(VI) removal ability

Using flax stem and ferrous sulfate, a composite porous carbon material was prepared by means of high‐temperature roasting and a one‐step process in a muffle furnace. The samples were characterized using X‐Ray diffraction (XRD) and Scanning electron microscopy (SEM), and the effects of ferrous sulfate concentration, carbonization temperature, and pH values of Cr(VI) aqueous solution on the removal performance of Cr(VI) were studied. XRD and SEM analysis showed that the prepared samples were amorphous porous carbon loaded with FeS/Fe2O3/Fe3O4. High FeSO4 impregnation concentration, high carbonization temperature, and a low pH value of Cr(VI) aqueous solution were beneficial for Cr(VI) removal. When pH = 2, the amount of Cr(VI) removal was 99.93 mg/g by the sample obtained from 1 g flax powder impregnated in 4.5 mmol FeSO4/40 mL H2O solution and calcined for 2 hr at 800°C.

Scalable synthesis of wrinkled mesoporous titania microspheres with uniform large micron sizes for efficient removal of Cr(vi)

Scalable synthesis of wrinkled mesoporous TiO2 microspheres with uniform large micron sizes is achieved. They show excellent performance for removal of Cr(vi).

Novel green micelles Pluronic F-127 coating performance on nano zero-valent iron: Enhanced reactivity and innovative kinetics

Abstract The reactivity of nano zero-valent iron (NZVI) tends to be significantly reduced due to its aggregation in liquid phase. To address this problem, for the first time, NZVI was successfully modified by green micelles Pluronic F-127 for reduction of Cr(VI) from wastewater. Pluronic F-127, a nontoxic and biodegradable copolymer, exhibits enhanced reactivity for removal of Cr(VI) by being coated on NZVI. The systematic observation and characterizations of (including SEM, TEM, and XRD) illustrate that, compared with bare nano zero-valent iron particles (BNZVI), the particle size of Pluronic F-127 modified NZVI (FNZVI) was decreased, while the dispersity and antioxidizability of FNZVI were increased. Furthermore, C O band appeared in XPS and FT-IR pattern of FNZVI indicated successful coating of Pluronic F-127 micelles on NZVI. This study also demonstrated that FNZVI dosage, initial pH value, and reaction temperature played an important role in the removal efficiency of Cr(VI). The removal efficiency of Cr(VI) could be increased by 37.56% by using FNZVI under optimal condition. Studies on the kinetics of Cr(VI) reacted with NZVI implied that their behaviors didn’t match the first- or pseudo-first-order kinetics due to dispersants on FNZVI or the presence of oxidation phases on the surface of BNZVI that could influence the whole reduction process by affecting the diffusion of Cr(VI) onto reactive sites. Therefore, an innovatively revised kinetics of the Cr(VI) removal by dispersant modified NZVI were provided and followed well. More importantly, Pluronic F-127 can be easily biodegraded after being released into environment with FNZVI. Given an excellent performance for removal of Cr(VI), the environmentally friendly micelles Pluronic F-127 modified NZVI represents an effective way for the remediation of Cr(VI) pollution.

Preparation of Polyacrylonitrile/Ferrous Chloride Composite Nanofibers by Electrospinning for Efficient Reduction of Cr(VI).

In this study, A novel adsorbent material of polyacrylonitrile (PAN)/ferrous chloride (FeCl2) composite nanofibers is prepared by electrospinning, a simple and effective method. The obtained composite nanofibers have a non-uniform morphology and structure and a large specific surface area of 13.8 m2 g-1. Fourier transform infrared spectroscopy (FTIR) revealed that Fe2+ was successful introduced into the composite nanofibers. Furthermore, the PAN/FeC12 composite nanofibers exhibited excellent performance in Cr removal, especially when reacted with reduction from a Cr(VI) standard containing solution, which has much faster removal efficiency than the previous report of Lin et al. (2011). The results of the adsorption isotherm show that the data fitted well to the Langmuir isotherm model. The maximum adsorption of chromium ions composite nanofibers is 108 mgCr/gFeCl2. An attempted model prediction of the transient dynamics of adsorption-desorption elucidated the feasible kinetic analysis of Cr6+ from the PAN/FeCl2 composite nanofibers. This kinetic modeling can be used both for adsorption of heavy metals wastewater and for organic-adsorption and biosorption of diverse wastewaters. The PAN/FeCl2 composite nanofibers producted in this study exhibit high efficiency in Cr(VI) removal from wastewater, and may be used as a reference for future investigation.

A facile one-pot synthesis of TiO2-based nanosheets loaded with MnxOy nanoparticles with enhanced visible light–driven photocatalytic performance for removal of Cr(VI) or RhB

This paper reports a facile one-pot approach for MnxOy (Mn=Mn2+, Mn3+) loaded TiO2-based nanosheets (Mn–TNSs) with surface enrichment of MnxOy nanoparticles via a simple hydrothermal route. The as-synthesized samples showed clearly sheet-like structure, with high specific surface area (200–300m2/g) and small thickness (ca. 4nm). The small MnxOy nanoparticles with uniform size (1–2nm) were highly dispersed on the surface of the TNSs. Loaded MnxOy not only have influenced the crystal structure and surface area of the TNSs, but also resulted in considerable enhancement of visible-light absorption and red-shift for TNSs. The results of X-ray photoelectron spectroscopy showed that Mn2+ and Mn3+ co-exist in Mn–TNSs. The loading of MnxOy on TNSs resulted in changes in binding energies of Ti and O. The concentration of Ti3+ increased gradually with the amount of loaded MnxOy increasing. The photo-reactivity of the samples were evaluated by measuring the formation of photo-induced hydroxyl radical (OH) using coumarin (COU) as a probe molecule and photocatalytic degradation of Rhodamin B (RhB) and dichromate (Cr(VI)) under visible-light irradiation. It has been found that the Mn–TNSs photocatalysts showed better visible-light photocatalytic activity for aqueous RhB or Cr(VI) solution. The photocatalytic activity gradually increased with the content of MnxOy increasing initially, and then decreased after attaining a maximum value at an optimal content (2.5 at.%) of MnxOy in TNSs for degradation of aqueous RhB or Cr(VI) solution, respectively. The cyclic tests that performed five times demonstrated high stability and recyclable usability of the photocatalysts. A possible alternate mechanism for the enhancement of the photocatalytic activity under visible-light irradiation was also proposed.

Adsorption kinetic study: Effect of adsorbent pore size distribution on the rate of Cr (VI) uptake

Adsorbents were synthesized to obtain novel silica nanoparticles with a broad pore-size distribution (herein referred to as USG-41). The material demonstrated fast adsorption rates with highest adsorption capacities following Langmuir adsorption. Kinetic data best fit the intraparticle diffusion model demonstrating a two-step, surface and pore, adsorption process with pore diffusion being the rate determining step. This data provides key evidence of internal pore chelation of dichromate ions by USG-41. In contrast silica adsorbents (SBA-15 and MCM-41) prepared with similar average pore sizes to USG-41, but with narrow pore-size distributions, had lower adsorption capacities and their kinetic date best fit pseudo-second order diffusion models indicating a one-step, surface only, adsorption process. This study clearly demonstrated that pores size distribution, not the surface area or the average pore size, was central to ensure optimum adsorbent performance for removal of Cr (VI) from contaminated water.

Cr(VI) removal from synthetic wastewater using coconut shell charcoal and commercial activated carbon modified with oxidizing agents and/or chitosan

In this study, the technical feasibility of coconut shell charcoal (CSC) and commercial activated carbon (CAC) for Cr(VI) removal is investigated in batch studies using synthetic electroplating wastewater. Both granular adsorbents are made up of coconut shell ( Cocos nucifera L.), an agricultural waste from local coconut industries. Surface modifications of CSC and CAC with chitosan and/or oxidizing agents, such as sulfuric acid and nitric acid, respectively, are also conducted to improve removal performance. The results of their Cr removal performances are statistically compared. It is evident that adsorbents chemically modified with an oxidizing agent demonstrate better Cr(VI) removal capabilities than as-received adsorbents in terms of adsorption rate. Both CSC and CAC, which have been oxidized with nitric acid, have higher Cr adsorption capacities (CSC: 10.88, CAC: 15.47 mg g −1) than those oxidized with sulfuric acid (CSC: 4.05, CAC: 8.94 mg g −1) and non-treated CSC coated with chitosan (CSCCC: 3.65 mg g −1), respectively, suggesting that surface modification of a carbon adsorbent with a strong oxidizing agent generates more adsorption sites on their solid surface for metal adsorption.