Studies of adsorption behavior of crosslinked chitosan for Cr(VI), Se(VI)

In this work, it was found that crosslinked chitosan (CCTS) had strong adsorption ability for some anions under certain conditions. Cr(VI) and Se(VI) existed in anion forms in aqueous solution, and their adsorption rates by CCTS were 97% for Cr(VI) at pH 3.0 and 95% for Se(VI) at pH 4.0. In addition, the adsorption balance time and isotherm of CCTS for Cr(VI) and Se (VI) were discussed and adsorption mechanism was explained. This research will be useful for designing CCTS‐based adsorption for metallic toxin removal and preconcentrating Cr(VI) and Se(VI) in their trace analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3216–3219, 2000     

Efficient removal of Cr(VI) and Pb(II) from aqueous solution by magnetic nitrogen-doped carbon

The magnetic nitrogen-doped carbon (MNC) was prepared from polypyrrole by a simple high temperature calcination process in this paper. The structure and properties of MNC were analyzed by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, Brunner-Emmet-Teller, vibrating sample magnetometer, and X-ray photoelectron spectroscopy. The capacity of MNC to adsorb Cr(VI) and Pb(II) was evaluated. The effects of the initial pH, dosage, concentration and temperature on the adsorption capacity of MNC were measured. MNC had a large specific surface area and a special porous structure. Its nitrogen and carbon sources were rich, and the ratio of carbon to nitrogen was fixed. The maximum Cr(VI)-adsorption capacity and maximum Pb(II) adsorption capacity of MNC could reach 456.63 and 507.13 mg∙g⁻¹ at 318 K, respectively. The pseudo-second-order model was used to describe the adsorption kinetics of MNC, and the Freundlich model was employed to discuss its isotherms. The adsorption process was affected by the electrostatic force, the reducing reaction, pores and chelation. The results of this study suggest that MNC is a material with superior performance, and is very easily regenerated, reused, and separated in the adsorption process.     

Removal of Cr(VI) from aqueous solution using magnetite/non-oxidative graphene composites: Synergetic effect of Cr(VI) on dyes removal

Non-oxidative graphene (nOG) synthesized from natural graphite powder was modified with magnetite (Fe₃O₄) for removal of Cr(VI) and dyes in aqueous solution. The adsorption behavior of Cr(VI) on Fe₃O₄/nOG (M-nOG) was systematically investigated, and the simultaneous adsorption of Cr(VI) and dyes such as methylene blue (MB) and rhodamine B (RhB) was evaluated. Adsorption kinetic and isotherm of Cr(VI) were fitted well with pseudo-second-order model and Sips model, respectively. For the binary system, Cr(VI) removal was not affected with increasing the dye concentration, whereas the adsorption capacity of both MB and RhB was enhanced with increasing the concentrations of Cr(VI).     

A Study in the Adsorption Behaviors of Cr (VI) on Crosslinked Cationic Starches

The adsorption behaviors between Cr (VI) and crosslinked cationic starch with quaternary ammonium group were investigated in various conditions. The adsorption processes are found to be dependent on the initial pH of the solution, the dose of the absorbents, initial concentration of Cr (VI), and adsorption temperature. The adsorption reaches equilibrium in a short time, and follows the Langmuir isotherm. The adsorption capacity increases with the increasing cationic groups. The adsorption thermodynamics study shows that adsorption processes are exothermic, and lower temperature is favorable to the adsorption of Cr (VI).     

Enhanced adsorptive removal of Cr(VI) in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine (PEI) modified palygorskite (Pal) was used for the adsorption of Cr(VI) in aqueous solution. The absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Characterized results confirmed that the Pal has been successfully modified by PEI. The modification of PEI increased the Cr(VI) adsorption performance of the Pal by the adsorption combined reduction mechanism, and amino groups of the adsorbent play the main role in the enhanced Cr(VI) adsorption. The maximum adsorption capacity was 51.10 mg·g⁻¹ at pH 4.0 and 25 °C. The adsorption kinetics of Cr(VI) on the adsorbent conforms to the Langmuir isotherm model. The maximum adsorption occurs at pH 3, and then the adsorption capacity of PEI-Pal was decreased with the increase of pH values. The adsorption kinetics of Cr(VI) on PEI-Pal was modeled with pseudo-second-order model. The addition of Cl⁻, SO₄²⁻ and PO₄³⁻ reduced the Cr(VI) adsorption by competition with Cr(VI) for the active sites of PEI-Pal. The Cr(VI) saturated PEI-Pal can be regenerated in alkaline solution, and the adsorption capacity can still be maintained at 30.44 mg·g⁻¹ after 4 cycles. The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI) in aqueous solutions.     

Mechanisms of Cr(VI) removal from water by various types of activated carbons

The removal mechanisms of Cr(VI) from water using different types of activated carbons, produced from coconut shell, wood and dust coal, were investigated in this project. Different types of activated carbons have different surface characteristics. The coconut shell and dust coal activated carbons have protonated hydroxyl groups on the surface (H‐type carbons), while the surface of the wood‐based activated carbon has ionised hydroxyl groups (L‐type carbons). The adsorption kinetics of chromium onto the activated carbons at pH values ranging from 2 to 6 were investigated. It was found that the optimum pH to remove total chromium was 2 for wood‐based activated carbon, while for coconut shell and dust coal activated carbons, the optimum pH was around 3–4. The difference in the optimum pH for different activated carbons to remove Cr(VI) from water can be explained by the different surface characteristics and capacity of the activated carbons to reduce Cr(VI) to Cr(III). © 1999 Society of Chemical Industry     

Removal of Cr(VI) from Model Solutions by a Combined Electrocoagulation Sorption Process

The elimination of hexavalent chromium from synthetic effluents in a batch stirred electrocoagulation cell with aluminum electrodes coupled with a sorption process using red onion skin adsorbent is addressed. The effect of process variables such as medium pH and adsorbent concentration was investigated in an attempt to optimize the removal capacity. Adsorption and electrocoagulation were first considered separately, with maximum Cr(VI) removal yields of 47 % and 78 %, respectively, at pH 2. When combining the two processes, a removal of 97 % of the total Cr(VI) in a pH range of 3–6 was achieved. The almost total elimination observed for the considered pollutant demonstrated the feasibility and the synergistic effect of the coupled process.     

光催化法处理含Cr(VI)废水的研究

采用P 25 TiO2作为光催化剂,研究了废水的pH值、Cr(VI)的初始浓度、气氛及有机物等因素对含铬废水中Cr(VI)去解率的影响。结果表明,在pH值为3.0时,光催化反应速率最大;反应气氛对该体系中Cr(VI)的光催化还原无明显影响;苯酚、葡萄糖等有机物的存在能有效地促进Cr(VI)的光催化还原,当加入与Cr(VI)等物质的量的苯酚或葡萄糖时,150 mL反应液[Cr(VI)浓度为0.96 mmol/L],0.15 g光催化剂,经12 W紫外灯照射反应120 m in,Cr(VI)完全被去除,相对于在反应体系中不加有机物时,Cr(VI)光催化还原效率提高了近100%;Cr(VI)的光催化还原符合L-H动力学规律。     

Application of nitrogen-enriched nanobiopolymer for the effective removal of Cr(VI) from tannery effluent

Nitrogen-enriched nanobiopolymer has been fabricated using (2,3-epoxypropyl) trimethylammonium chloride (EPTMAC) and explored for the removal of Cr(VI) from tannery effluent. The removal efficiency of nanobiopolymer was found to be 23.99 mg g^?1 (95.94%) under optimized conditions. The sorption data agrees well with the Langmuir and pseudo-second-order model. Equilibrium parameter (R_L) and sorption energy show the favorability and physical binding of Cr(VI) on the nanobiopolymer’s backbone. The values of ?G° (?7.84 kJ mol^?1), ?S° (65.97 J mol^?1K^?1) and ?H° (11.82 kJ mol^?1) reflect the feasible nature of the sorption process. Reusability study was also conducted to state the performance of the nanobiopolymer.     

Separation of Cr(VI) from Water by Green Reduction Reaction and Adsorptive Removal on Gelatin-Grafted-Yeast Biosorbent

A green chemical method was explored and described for separation and extraction of the toxic hexavalent chromium from aqueous solutions and real water samples. A green reduction reaction for the transformation of toxic hexavalent chromium into the nontoxic trivalent chromium ion was performed by using hydrogen peroxide. The produced Cr(III) was then extracted by biosorption on the surface of a novel and eco-friendly gelatin-grafted-baker’s yeast (Gelatin-Yeast) biosorbent. The investigated biosorbent was characterized by high capacity value of the reduced trivalent chromium species in pH 6.0 as 1.120 mmol g^?1. The biosorption processes were examined, monitored, and optimized in different experimental and controlling parameters. The potential applications of Gelatin-Yeast for separation and removal of Cr(VI) from real industrial and sea water samples were also studied.     

Chromium electrodeposition from Cr(VI) low concentration solutions

This work presents a study of a hard chromium plating process using low concentration H₂CrO₄ baths. In particular, the effect of different values of CrO₃/H₂SO₄ ratio on coating properties such as adhesion, hardness, surface roughness, apparent density and microstructure were considered. To increase the solution conductivity, avoiding long deposition times and low throwing power typical of dilute solutions, the behaviour of various inorganic compounds was investigated. Specifically, the compounds suitable for obtaining brighter coatings with lower surface roughness values than those obtained using Fink’s solutions were Na₂SO₄ and Al₂(SO₄)₃ × 18H₂O. A bath composition was identified, with a limited use of Cr(VI) in a solution able to produce coatings with a better surface roughness than those of conventional industrial baths.     

Removal of Cr(VI) from aqueous solution by surfactant-modified kaolinite

Removal of Cr(VI) from aqueous solution by hexadecyltrimethylammonium chloride (HDTMA) modified kaolinite (HMK) was investigated, where the maximum adsorptive capacity reached 27.8 mg/g Cr(VI) using HMK compared with only 0.7 mg/g using unmodified natural kaolinite (NK). The adsorption of Cr(VI) on HMK can be well described by the Langmuir isotherm, and the kinetic adsorption of Cr(VI) on both HMK and NK fitted a pseudo-second-order model. FTIR analysis showed that surface modified HDTMA was responsible for the high adsorptive capacity of Cr(VI). HMK was used to remove Cr(VI) from an electroplating wastewater.     

Uptake of Cr (VI) by Sphingomonas paucimobilis Biomass from Aqueous Solutions

The Sphingomonas paucimobilis biomass has been successfully utilized to degrade several persistent organic pollutants (POPs). However, few studies have been conducted to use it to remove heavy metals from aqueous solutions. In the present study, biosorption experiments for Cr (VI) were investigated using nonliving biomass of S. paucimobilis isolated from activated sludge, Lianyungang Dapu sewage treatment plant, China. The effects of several parameters including solution pH, contact time, and ionic strength, etc. on Cr (VI) uptake were studied. The biomass was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared spectrometer (FTIR). The applicability of the Langmuir and Freundlich models was tested. The correlation coefficients (R) of both models were greater than 0.95. The maximum adsorption capacities were found to be 28.5 mg/g for Cr (VI) at 20°C. The adsorption process was quick and found to follow the pseudo-second-order equation. The optimum adsorption was achieved at pH 2. The adsorption was also NaCl concentrations dependent.     

啤酒酵母吸附Cr（VI）的动力学及热力学研究

研究啤酒酵母对溶液中铬(VI)的吸附效果和机理,通过红外对吸附前后菌体表面特征分析,表明Cr (VI)与菌体表面基团发生配位络合反应.结果表明,在温度为35 ℃,pH=2,Cr(VI)初始浓度为20 mg/L时达到最大吸附量,最大吸附量为4.19 mg/g.酵母菌对Cr(VI)的吸附行为基本符合Langmuir方程,并且在 25,30和35 ℃条件下的理论最大吸附量qmax分别为4.472,4.533,4.702 mg/g.动力学研究表明,反应在240 min吸附基本达到平衡状态,准二级动力学模型能够更好的描述吸附过程.不同温度下的吸附热力学显示,该吸附过程为自发的吸热反应.     

Removal of Cr(VI) from aqueous solution by London plane leaves

The effect of initial metal concentration, contact time and solution temperature on the removal of Cr(VI) from solution by waste London plane leaves, generated by the pruning of street trees, was investigated in batch mode conditions. The removal of Cr(VI) was highly concentration‐dependent and mainly governed by physico‐chemical adsorption under the weak acidic conditions studied. The equilibrium data fit well in the Langmuir isotherm model. The Langmuir constants were calculated at different temperatures and both the adsorption capacity and adsorption intensity increased with rising temperature. The endothermic nature of the Cr(VI) adsorption was confirmed by the thermodynamic parameters. The study has shown that the waste leaves can be used as an effective adsorbent for removal of Cr(VI) from wastewater. Copyright © 2003 Society of Chemical Industry     

Modelling of Cr(VI) removal from polluted groundwaters by ion exchange

This work reports the viability and modelling of the removal of Cr(VI) from polluted groundwaters by means of ion exchange using the resin Lewatit MP‐64. Feed groundwaters that contained Cr(VI) at an average concentration of 2431 mg dm^?3 and 1187 mg dm^?3 of chloride and 1735 mg dm^?3 of sulfate as main anions were acidified to a pH of 2.0 prior to the removal process. Dynamic experiments were carried out in a fixed bed column with feed waters at flow rates in the range of 2.78 × 10^?7 m³ s^?1 to 5.55 × 10^?7 m³ s^?1. Regeneration was achieved with NaOH (2 mol dm^?3). From the experimental results, the equilibrium of the ion exchange reaction was successfully modelled, obtaining an equilibrium constant (K′_AB) = 44.90. Finally, a mass balance that included mass transfer resistances in the liquid and solid phases was developed and from the comparison between simulated and experimental data the value of the effective intraparticle diffusivity (D_s) was determined as 1.43 × 10^?12 m² s^?1. Copyright © 2004 Society of Chemical Industry     

铁盐共沉淀泡沫浮选法去除废水中Cr(VI)的应用研究

采用铁盐共沉淀泡沫浮选法去除废水中Cr(VI),用FeSO4将六价铬还原成三价状态,考察了还原剂用量、捕捉剂品种及pH对总铬去除率的影响。结果表明,对浓度为10 mg/L的含Cr(VI)模拟废水,使用FeSO4作还原剂,LAS作捕捉剂,铁铬摩尔比为7∶1,pH=10,鼓泡10 min的条件下,Cr(VI)去除率可达99.1%。     

铜渣基化学键合陶瓷材料吸附Cr(VI)的性能及机理

以富含铁的铜渣（CS）为原料，在碱激发条件下制备了铜渣基化学键合陶瓷材料（CSCBC），对废水中的Cr(Ⅵ)进行吸附处理。考察了吸附剂添加量、Cr(Ⅵ)初始浓度及pH等因素对Cr(Ⅵ)吸附效果的影响，并通过吸附动力学和热力学分析，结合吸附前后吸附材料结构表征，对其吸附机理进行了探讨。结果表明，当Cr(Ⅵ)初始质量浓度为200 mg/L、pH=1、吸附剂投加量为0.4 g时，在240 min内达吸附平衡，Cr(Ⅵ)去除率可达93%以上，最大理论吸附容量25.3 mg/g。与生物炭基铁氧化物复合材料、FeS复合材料、铁掺杂吸附剂等同类型吸附剂相比，Cr(Ⅵ)吸附容量明显提高。CSCBC对Cr(Ⅵ)的吸附过程符合准一级动力学模型和Langmuir等温吸附模型。其吸附机制主要是还原、吸附等双重作用的结果。 6次吸附-解吸实验后，其吸附容量保持初次吸附容量的75%以上 。