Synthesis and characterization of Fe-MCM-41 from rice husk silica by hydrothermal technique for arsenate adsorption

Rice husk (RH) agro-waste was used as a raw material for synthesizing mesoporous molecular sieves, MCM-41. The Fe-MCM-41 was prepared by the hydrothermal technique (HT), resulting in a higher surface area and crystallinity than when prepared under ambient conditions. In addition, a hexagonal structure was clearly seen with hydrothermal technique (HT) preparation. The adsorption of arsenate by HT-Fe-MCM-41 was investigated. The factors studied affecting arsenate adsorption capacity were ferric content in MCM-41, contact time, pH of solution, and initial arsenate concentration. It was found that HT-Fe-MCM-41 at the Si/Fe mole ratio of 10 gave the highest adsorption capacity. Arsenate adsorption reached equilibrium within 4 h. The adsorption capacity of HT-Fe-MCM-41 (Si/Fe = 10) was affected by the initial pH value and the initial arsenate concentration. The adsorption capacity was highest at pH 3 and decreased thereafter with increases in the pH of solution value. The Langmuir model fit the arsenate adsorption isotherm well. The maximum adsorption capacity for arsenate was 1,111 μg g⁻¹.     

Adsorption and removal of antimony from aqueous solution by an activated Alumina

The adsorption of Sb(V) ions from aqueous solutions onto commercially available activated alumina (AA) was investigated. AA has a much higher adsorption capacity than presently used adsorbents. Sb(V) ions are likely adsorbed through electrostatic attraction and/or specific adsorption mechanism, while the optimum pH is found in the range of 2.8–4.3. The Sb(V) ions adsorption capacities increase with increasing temperature. The addition of nitrate, acetate, arsenite, chloride, and silicate ions affected Sb(V) ions adsorption only slightly, while the coexisting ascorbate, arsenate, phosphate, sulfate, EDTA, tartrate, and citrate ions substantially depressed Sb(V) ions adsorption.     

Removal of arsenic by Acidothiobacillus ferrooxidans bacteria in bench scale fixed-bed bioreactor system

In the present study arsenic contaminated simulated water and groundwater was treated by the combination of biological oxidation of tri-valent arsenite [As (III)] to penta-valent arsenate [As (V)] in presence of Acidothiobacillus ferrooxidans bacteria and its removal by adsorptive filtration in a bioreactor system. This method includes the immobilisation of A.ferrooxidans on Granulated Activated Carbon (GAC) capable of oxidising ferrous [Fe (II)] to ferric [Fe (III)]. The Fe (III) significantly converts the As (III) to As (V) and ultimately removed greater than 95% by the bed of GAC, limestone, and sand. The significant influence of Fe (II) concentration (0.1–1.5?gL^?1), flowrate (0.06–0.18?Lh^?1), and initial As (III) concentration (100–1000?µgL^?1) on the arsenic removal efficiency was investigated. The simulated water sample containing the different concentration of As (III) and other ions was used in the study. The removal of other co-existing ions present in contaminated water was also investigated in column study. The concentration of arsenic was found to be <10?µgL^?1 which is below Maximum Contaminant Level (MCL) as per WHO in treated water. The results confirmed that the present system including adsorptive-filtration was successfully used for the treatment of contaminated water containing As (III) ions.     

集胞藻(Synechocystis sp. PCC6803)对砷吸收转化特性的初步研究

砷是一种广泛存在于环境中的有毒物质.集胞藻属于单细胞藻类,广泛分布在淡水生态环境中.采用营养液培养的方法探讨了集胞藻(Synechocystis sp.PCC6803)对砷的累积和转化特性.当集胞藻分别暴露于2和100 μM的无机As(Ⅲ)和As(Ⅴ)14 d后,体内的砷形态均以As(Ⅴ)为主,并且在100 μM浓度处...     

砷形态在湖水中垂直分布的研究

本文以天津水上公园湖泊作为研究现场，通过采样分析，研究了湖水中砷酸盐、亚砷酸盐、一甲基胂酸盐和二甲基胂酸盐的垂直分布及其影响因素。结果表明水上公园湖泊中砷酸盐是溶解态砷的主要存在形式，其垂直分布与悬浮物、叶绿素ａ、磷酸盐的浓度、水文等诸因素密切相关；一甲基胂酸盐含量保持相对稳定；光致转化是影响水中亚砷酸盐垂直分布差异的一个因素。     

The removal of arsenic from water with natural and modified clinoptilolite

The presence of increased arsenic concentrations in Eastern Croatia is a consequence of the geological composition of the soil. Because of its known harmful effects, arsenic removal is of high importance and adsorption represents an attractive and economically efficient approach to arsenic removal. The use of zeolites obtained from the Donje Jesenje deposit, Croatia (CZ) and the Zlatokop deposit in Vranjska Banja, Serbia (SZ) in Na- and Fe–Na-modified forms was investigated in order to effectively remove arsenate and arsenite from aqueous solutions. The adsorption kinetics of arsenic was studied as a function of the initial arsenate and arsenite concentrations (30–300 μg · L^?1), equilibration time (3–48 h), pH (5–10) and in the presence of sulfate and phosphate at initial concentrations of 0.2–0.5 mg · L^?1. In order to estimate sorption constants designating the sorption capacity and affinity of the zeolites samples, the experimental results were fitted to the Langmuir and Freundlich sorption isotherms. Desorption tests conducted with 1–3 mol · L^?1 HCl indicated that arsenate sorption was irreversible. The results obtained indicated that use of the Serbian zeolite in the Fe–Na-modified form (Fe–Na-SZ) was favourable for arsenate removal from water containing up to 30 μg As · L^?1.     

Use of fly ash agglomerates for removal of arsenic

The aim of this work is to investigate the application of fly ash adsorbent for removal of arsenite ions from dilute solution (100–1,000 ppm). Experiments were carried out using material from the “Turów” (Poland) brown-coal-burning power plant, which was wetted, then mixed and tumbled in a granulator to form spherical agglomerates. Measurements of arsenic adsorption from aqueous solution were carried out at room temperature and natural pH of fly ash agglomerates, in either a shaken flask or circulating column, to compare two different methods of contacting solution with adsorbent. Adsorption isotherms of arsenic were determined for agglomerated material using the Freundlich equation. Kinetic studies indicated that sorption follows a pseudo-second-order model. Preferable method to carry out the process is continuous circulation of arsenite solution through a column.     

Cr (VI) and Fe (III) removal using Cajanus cajan husk

Husk of tur dal (Cajanus cajan) was investigated as a new biosorbent for the removal of Fe (III) and Cr (VI) ions from aqueous solutions. Parameters like agitation time, adsorbent dosage and pH were studied at different initial Fe (III) and Cr (VI) concentrations. The biosorptive capacity of the Tur dal husk was dependent on the pH of the chromium and iron solution, with pH 2 and 2.5 respectively being optimal. The adsorption data fit well with Langmuir and Freundlich isotherm models. The practical limiting adsorption capacity (qmax) calculated from the Langmuir isotherm was 96.05 mg of Cr(VI)/ g of the biosorbent at an initial pH of 2.0 and 66.65 mg/g at pH 2.5. The infrared spectra of the biomass revealed that hydroxyl, carboxyl and amide bonds are involved in the uptake of Cr (VI) and Fe (III) ions. Characterisation of tur dal husk has revealed that it is an excellent material for treating wastewaters containing low concentration of metal ions.     

Simultaneous removal of arsenate and fluoride from water by AI-Fe （hydr）oxides

A1-Fe （hydr）oxides with different A1/Fe molar ratios （4：1, 1：1, 1：4, 0：1） were prepared using a co- precipitation method and were then employed for simultaneous removal of arsenate and fluoride. The 4A1 ： Fe was superior to other adsorbents for removal of arsenate and fluoride in the pH range of 5.0-9.0. The adsorption capacity of the A1-Fe （hydr）oxides for arsenate and fluoride at pH 6.50.3 increased with increasing A1 content in the adsorbents. The linear relationship between the amount of OH released from the adsorbent and the amount of arsenate or fluoride adsorbent by 4A1 ： Fe indicated that the adsorption of arsenate and fluoride by A1- Fe （hydr）oxides was realized primarily through quantita- tive ligand exchange. Moreover, there was a very good correlation between the surface hydroxyl group densities of A1-Fe （hydr）oxides and their adsorption capacities for arsenate or fluoride. The highest adsorption capacity for arsenate and fluoride by 4A1 ： Fe is mainly ascribed to its highest surface hydroxyl group density besides its largest pHpzc. The dosage of adsorbent necessary to remove arsenate and fluoride to meet the drinking water standard was mainly determined by the presence of fluoride since fluoride was generally present in groundwater at much higher concentration than arsenate.     

Higher sorption of arsenate versus arsenite on amorphous Al-oxide, effect of ligands

Arsenic pollution is currently a major health issue because As is toxic for human beings, animals, and plants. Knowledge of As mobility is therefore important to assess health risk. The sorption of arsenite and arsenate on metal oxides in the presence of various anionic ligands is closely linked to the mobility, bioavailability, and risk. It was reported that the sorption mechanisms and characteristics of arsenite and arsenate on Al-oxides were different from that on Fe-oxides. Previous work reports the sorption of arsenite and arsenate on Fe-oxides in the presence of ligands. Whereas there is few knowledge on the sorption of arsenite and arsenate by Al-oxides in the presence of ligands. Here, we studied the sorption of arsenite and arsenate on amorphous Al-oxide by batch experiments. We tested the effect of organic ligands: oxalate, malate, tartrate, citrate; and inorganic ligands: sulfate, phosphate, selenate, selenite. Results show that amorphous Al-oxide has more sorption affinity for arsenate than arsenite. The inhibition of As sorption by ligands at pH 6 is higher for arsenite than arsenate. For arsenite, the As sorption inhibition decreases in the order phosphate, citrate, malate, selenite, oxalate, tartrate, sulfate, and selenate. For arsenate, the As sorption inhibition decreases in the order phosphate, malate, citrate, selenite, tartrate, oxalate, sulfate, and selenate.     

Species-level study on arsenic availability from dietary components

Arsenic (As) contaminated water and foodstuffs are of major concern. Samples of drinking–cooking water (n = 50), raw rice (n = 50), common vegetables (eight types), and common pulses (three types) were collected from households in the endemic region. The study found up to 70% As reduction by using safe water for cooking of rice and vegetables. Speciation study reflected more arsenate than arsenite and other organic arsenicals in all the types of samples. Male intake of 293 μg As through drinking water contained 38 μg arsenite and 246 μg arsenate, and female intake of 199 μg As contained 167 μg arsenate and 25 μg arsenite. In cooked rice, 108 μg As contained 69 μg arsenate and 17 μg arsenite with 9 μg dimethylarsonic acid (DMA). Total As consumption from cooked vegetables was 45 μg with 34 and 4 μg of arsenite and arsenate, respectively, and 5 μg of DMA. Data indicate that cooking with As-free water removes arsenic in already contaminated foodstuffs but without interconversion of the As species, from toxic inorganic to less toxic organic forms.     

Non-carcinogenic effects of inorganic arsenic

This review will focus primarily on ohe effects of the inorganic arsenicals (arsenate and arsenite forms) that are present in drinking water. They are acutely toxic to both humans and animals, an effect that may be related to their bioavailibility. In humans, arsenicals have been reported to cause dermatitis and mucous membrane irritation upon exposure. They have also been reported to cause skin lesions and peripheral neurotoxicity in smelter workers and in patients treated with Fowler's Solution. When humans are exposed to arsenic in drinking water, effects such as hyperkeratosis, electromyographic abnormalities and vascular effects have been reported. In experimental animals, arsenic has been demonstrated to affect the liver and kidneys. In mice, arsenic has also been reported to decrease the animal's resistance to certain viral infections. The arsenite (+3) and arsenate (+5) forms have different modes of action. Arsenite binds to sulphhydryl groups and has been reported to inhibit over 100 different enzymes, while the arsenate can substitute for phosphate in various high energy intermediates, resulting in arsenolysis. In addition, when arsenate is reduced to arsenite in the body, it can also cause toxicity as that species.     

砷酸盐的溶解度及其稳定性随pH值的变化

本文讨论了铁、钙和钡的砷酸盐在水环境中的溶解度与稳定性，着重分析了砷酸盐在水中发生不一致性溶解与稳定性的关系。同时藉助PHREEQC程序，探讨了砷酸铁溶解时，其溶解度、砷的存在形式与pH值的关系，以及共存的氢氧化铁对稳定性的影响，并作出了Ca-As-水和Ba-As-水体系的Ig[As]-pH相图。     

Enhanced adsorption of phosphate by loading nanosized ferric oxyhydroxide on anion resin

Ferric oxyhydroxide loaded anion exchanger （FOAE） hybrid adsorbent was prepared by loading nanosized ferric oxyhydroxide （FO） on anion exchanger resin for the removal of phosphate from wastewater. TEM and XRD analysis confirmed the existence of FO on FOAE. After FO loading, the adsorption capacity of the hybrid adsorbent increased from 38.70 to 51.52mg.g-1. Adsorption processes for both FOAE and anion resin were better fit to the pseudo first order model. Batch adsorption experiments revealed that higher temperature （313K）, higher initial phosphate concentration （50 mg.L-1） and lower solution pH （pH value of 2） would be more propitious to phosphate adsorption. Competition effect of coexisting anions on phosphate removal can be concluded as sulfate 〉 nitrate 〉 chloride. Freundlich isotherm model can describe the adsorption of phosphate on FOAE more accurately, which indicated the heterogeneous adsorption occurred on the inner-surface of FOAE.     

Biosorption of Cu(II) and Zn(II) onto a lignocellulosic substrate extracted from wheat bran

We studied the removal of copper and zinc ions from aqueous solutions using a lignocellulosic substrate obtained by an acido-basic treatment of wheat bran. The sorption capacity of this material was investigated through batch and column experiments. Batch experimental results showed that the retention capacity of the lignocellulosic substrate was 0.20×10^–3 mol g^–1 at pH 4.5 for copper(II) and 0.24×10^–3 mol g^–1 at pH 6.5 for zinc(II). Column experiments showed a reduced sorption capacity for both ions compared to batch experiments. Batch and column data were analysed using the Langmuir equation in order to determine the affinity constant and the binding capacity of the sorbent and to compare both retention processes.     

Arsenic removal using natural biomaterial-based sorbents

Arsenic contamination of water is a major problem worldwide. A possible solution can be approached through developing new sorbents based on cost-effective and environmentally friendly natural biomaterials. We have developed new sorbents based on biomaterial impregnation with iron oxyhydroxide. In this study, raw peat material, iron-modified peat, iron-modified biomass (shingles, straw, sands, cane and moss) as well as iron humate were used for the removal of arsenate from contaminated water. The highest sorption capacity was observed in iron-modified peat, and kinetic studies indicated that the amount of arsenic sorbed on this material exceeds 90 % in 5 h. Arsenate sorption on iron-modified peat is characterised by the pseudo-second-order mechanism. The results of arsenic sorption in the presence of competing substances indicated that sulphate, nitrate, chloride and tartrate anions have practically no influence on As(V) sorption onto Fe-modified peat, whereas the presence of phosphate ions and humic acid significantly lowers the arsenic removal efficiency.     

树脂D001负载纳米Pd/Fe双金属脱溴2,2’,4,4’-四溴联苯醚(BDE-47)的研究

采用大孔树脂D001交换吸附Pd2+、Fe2+并在厌氧条件下以硼氢化钠溶液还原吸附的钯铁离子制备成负载纳米Pd/Fe双金属树脂。利用该树脂对2,2’,4,4’-四溴联苯醚(BDE-47)进行脱溴反应,探讨了该法的可行性和特性。结果表明:当大孔树脂D001、氯化钯、硫酸亚铁用量分别为0.75 g、2μg和0.2 g时所制备的双金属树脂脱溴水-乙醇溶液中的BDE-47效果最佳,反应遵循准一级动力学,速率常数k约为0.161 d-1,半减期为1.21 d。负载Pd/Fe的D001连续3次脱溴反应都有较好的效果,水-乙醇溶液中超过90%以上的BDE-47在反应6 d后被降解。负载Pd/Fe双金属的树脂可以重复活化再生,但再生2次后其脱溴效率变差,反应6 d只有47.3%的BDE-47被降解。用气相色谱-质谱联用仪和离子色谱仪跟踪Pd/Fe双金属树脂脱溴BDE-47反应,可知产物包括溴离子、三溴联苯醚、二溴联苯醚、一溴联苯醚和联苯醚。     

树脂D001负载纳米Pd/Fe双金属脱溴2,2＇,4,4＇-四溴联苯醚（BDE-47）的研究

采用大孔树脂D001交换吸附Pd2＋、Fe2＋并在厌氧条件下以硼氢化钠溶液还原吸附的钯铁离子制备成负载纳米Pd/Fe双金属树脂。利用该树脂对2,2＇,4,4＇-四溴联苯醚（BDE-47）进行脱溴反应,探讨了该法的可行性和特性。结果表明：当大孔树脂D001、氯化钯、硫酸亚铁用量分别为0.75 g、2μg和0.2 g时所制备的双金属树脂脱溴水-乙醇溶液中的BDE-47效果最佳,反应遵循准一级动力学,速率常数k约为0.161 d-1,半减期为1.21 d。负载Pd/Fe的D001连续3次脱溴反应都有较好的效果,水-乙醇溶液中超过90%以上的BDE-47在反应6 d后被降解。负载Pd/Fe双金属的树脂可以重复活化再生,但再生2次后其脱溴效率变差,反应6 d只有47.3%的BDE-47被降解。用气相色谱-质谱联用仪和离子色谱仪跟踪Pd/Fe双金属树脂脱溴BDE-47反应,可知产物包括溴离子、三溴联苯醚、二溴联苯醚、一溴联苯醚和联苯醚。     

砷、矾与镉交互作用及其对土壤吸附镉的影响

研究了砷、矾与镉交互作用及其对土壤吸附镉的影响 .结果表明 :江西红壤、海南砖红壤、湖南红壤和北京褐土等四种土壤吸附镉的等温线符合Freundlich方程 ,吸附常数K的大小顺序为 :北京褐土 >湖南红壤 >江西红壤 >海南砖红壤 .pH值是决定土壤吸附镉的关键因素之一 ,砷和矾的存在可促进土壤对镉的吸附     

大同盆地富砷地下水的水化学与地球化学研究

为弄清大同盆地地下水中影响砷的迁移、富集的主要地球化学与生物地球化学过程,为区域供水安全提供指导作用,针对高砷地下水系统开展了水文地球化学与含水层沉积物全岩地球化学研究;并在此基础上探讨了研究区高砷地下水成因。结果表明,研究区高砷地下水为偏碱性、强还原环境,砷含量为0.31～452μg·L-1,主要以砷酸盐形式存在,地下水中砷与三价铁的浓度有显著的相关性。高砷含水层沉积物中有机质、铁与砷含量表现出显著相关性。以上结果说明,碱性还原环境有利于地下水中砷的富集;微生物参与下,沉积物相有机质的氧化和Fe氧化物/氢氧化物的还原过程是本区高砷地下水形成的主控因素。