Removal of hexavalent chromium with a lignocellulosic substrate extracted from wheat bran

In this paper, a new recovery system of the toxic hexavalent chromium Cr(VI) is proposed that uses a lignocellulosic substrate derived from the industrial treatment process of wheat bran. We studied the adsorption mechanism of Cr(VI) onto the lignocellulosic substrate and showed that the adsorption reaction consumes a large amount of protons goes along the reduction of Cr(VI) into Cr(III). The oxidation of lignin moieties takes place concurrently to the chromium reduction and leads to the formation of hydroxyl and carboxyl functions. The latter contribute to an increase in the number of ion-exchange sites for the reduced chromium. The maximum adsorption capacity for hexavalent chromium was found at about 35 mg g(-1) in an acidic medium. This is comparable to other natural substrates and ordinary adsorbents.     

Co-removal of hexavalent chromium through copper precipitation in synthetic wastewater

The mechanisms of hexavalent chromium [Cr(VI)] co-removal with copper [Cu(II)] during homogeneous precipitation were studied with batch tests using a synthetic solution containing Cr(VI) and Cu(II). Metal precipitation was induced by adding Na2CO3 stepwise to different pH, and the respective removals of Cu(II) and Cr(VI) were measured. At the same time, the relative quantities of Cu(II) and Cr(VI) in the precipitates were also analyzed to establish their stoichiometric relationship. The results indicated that, in a solution containing 150 mg/L Cu(II) and 60 mg/L Cr(VI), the initial co-removal of Cr(VII with Cu(II) began at pH 5.0 and completed at pH 6.2. At pH 5.0-5.2, coprecipitation took place through the formation of copper-chromium-bearing solids [such as CuCrO4 and/or CuCrO4 x 2Cu(OH)2]. Thereafter, the remaining soluble copper started to react with carbonate in a heterogeneous environment to form the negatively charged basic copper carbonate precipitates [CuCO3 x Cu(OH)2], which subsequently adsorbed additional Cr(VI) (or HCrO4-) at pH 5.2-6.2. The maximum Cr(VI) co-removal took place at pH 6.2. Between the two mechanisms, co-precipitation accounted for about 29% of the total chromium's co-removal while the remaining 71% was attributed to surface adsorption, mainly through electrostatic attraction and ligand exchange. When the solution pH was increased to beyond 7.5, a surface charge reversal took place on the basic copper carbonate solids, and this led to some Cr(VI) desorption. Thus, the extent of Cr(VI) adsorption is highly pH dependent.     

Removal of hexavalent chromium by biosorption process in rotating packed bed

Removal of hexavalent chromium ions from an aqueous solution by crude tamarind (Tamarindus indica) fruit shell was examined in a rotating packed bed contactor by continuously recirculating a given volume of solution through the bed. Reduction of Cr(VI) to Cr(III) within the biosorbent appeared to be the removal mechanism. Depletion rate of Cr(VI) from, and release of reduced Cr(III) ions into the aqueous phase, was influenced by mass transfer resistance besides pH and packing depth. A mathematical model considering the reduction reaction to be irreversible and incorporating intraparticle and external phase mass transfer resistances represented the experimental data adequately. The study indicated that the limitations of fixed bed contactor operating under terrestrial gravity in intensifying mass transfer rates for this system can be overcome with rotating packed bed due to liquid flow under centrifugal acceleration.     

基于金属有机框架化合物的非织造复合材料制备及其对废水中六价铬的去除

为解决水体中重金属六价铬(Cr(Ⅵ))的污染问题,利用聚氨酯(PU)对锆基金属有机框架化合物(UiO-66-NH2)进行接枝改性,将改性所得PU/UiO-66-NH2负载于聚丙烯(PP)非织造布上制备PU/UiO-66-NH2/PP非织造布复合材料,最后将其用于Cr(Ⅵ)的吸附与可见光催化还原.探讨UiO-66-NH2...     

壳聚糖/铝矾土复合絮凝剂处理染色废水的研究

利用壳聚糖/铝矾土复合絮凝剂对活性艳红X3B和还原大红R模拟废水进行絮凝脱色处理。考察了复合絮凝剂用量、pH值、搅拌速率、搅拌时间等因素对脱色率的影响。实验结果表明,复合絮凝剂的脱色效果明显优于单独使用壳聚糖或铝矾土。在染料质量浓度为100 mg/L,pH值为5的条件下,用量为1.25 g/L时,3种质量比的复合絮凝剂对活性艳红X3B的脱色率分别达到75%、90%和97%以上;而在用量为0.5 g/L时,3种质量比的复合絮凝剂对还原大红R的脱色率均可达到100%。同时铝矾土具有很好的可重复利用性,重复使用3次的铝矾土复合絮凝剂对活性艳红X3B的脱色率仍高于94%。     

Removal of natural steroid hormones from wastewater using membrane contactor processes

Growing demands for potable water have strained water resources and increased interest in wastewater reclamation for potable reuse. This interest has brought increased attention to endocrine-disrupting chemicals (EDCs) as emerging water contaminants. The effect of EDCs, and in particular natural steroid hormones, on humans is of heightened interest in the study of wastewater reuse in advanced life support systems (e.g., space missions) because they are excreted in urine and have high endocrine-disrupting potencies. Direct contact membrane distillation (DCMD) and forward osmosis (FO) are being investigated for wastewater treatment in space. Retention of two natural steroid hormones, estrone and 17beta-estradiol, by these two processes was evaluated in the current investigation. DCMD provided greater than 99.5% hormone rejection; DCMD also provided constant flux, greater than 99.9% urea and ammonia rejection, and high water recovery. FO provided from 77 to 99% hormone rejection depending on experiment duration and feed solution chemistry.     

Extraction of hexavalent chromium from chromated copper arsenate treated wood under alkaline conditions

Information on chromium (Cr) oxidation states is essential for the assessment of environmental and health risks associated with the overall life-cycle of chromated copper arsenate (CCA) treated wood products because of differences in toxicity between trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium compounds. Hypothetical Cr(VI) fixation products were investigated in CCA type C treated sawdust of aspen and red pine during or following preservative fixation by extraction with Cr(VI)-specific extractants. Cr(VI) was found only in alkaline extracts of treated wood. A major source of Cr(VI) was method-induced oxidation of fixed Cr(III) during alkaline extraction, as confirmed by demonstrated oxidation of Cr(III) from CrCl3 treated wood. Oxidation of nontoxic and immobile Cr(III) to toxic and mobile Cr(VI) was facilitated by the presence of wood at pH > 8.5. Thermodynamic equilibrium between Cr(III) and Cr(VI) is affected by pH, temperature, rates of dissolution of CrIII) compounds, and oxygen availability. Results of this study recommend against alkaline extraction protocols for determination of Cr(VI) in treated wood. This Cr oxidation mechanism can act as a previously unrecognized route for generation of hazardous Cr(VI) if CCA treated wood is exposed to alkaline conditions during its production, use, or waste management.     

Removal of chlorophenols from wastewater using red mud: an aluminum industry waste

Removal of toxic substances from wastewaters using low-cost alternatives to activated carbon is an important area in environmental sciences. Efforts have been made to convert red mud, an aluminum industry waste, into a low-cost potential adsorbent, and the final material has been used for the removal of phenol, 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol from wastewater. It is pertinent to mention that phenol and chlorophenols are highly carcinogenic and an priority class of pollutants which needs to be removed from effluents before discharge into water bodies. 2,4-Dichlorophenol and 4-chlorophenol are sorbed by the developed adsorbent up to 94-97%, while the removal of 2-chlorophenol and phenol was up to 50-81%. The removal of phenols and its derivatives was achieved up to 98% by column experiments at a flow rate of 0.5 mL/min. The order of removal was 2,4-dichlorophenol > 4-chlorophenol > 2-chlorophenol > phenol, and the removal takes place through a particle diffusion mechanism. The adsorption was found to be endothermic in nature and follows both Langmuir and Freundlich models. Estimation of the phenols was carried out by capillary electrophoresis, and the adsorbent has been successfully tried for the removal of chlorophenols from a wastewater. The developed process is very useful, economic, rapid, and reproducible for the removal of phenols.     

皮革中六价铬的研究进展

对国内外有关皮革中六价铬形成的原因、检测方法和预防措施的研究现状进行了总结 ,并提出了一些自己的观点     

Evaluation of hexavalent chromium extraction method EPA method 3060A for soils using XANES spectroscopy

Hexavalent chromium (Cr(VI)) occurrence in soils is generally determined using an extraction step to transfer it to the liquid phase where it is more easily detected and quantified. In this work, the performance of the most common extraction procedure (EPA Method 3060A) using NaOH-Na(2)CO(3) solutions is evaluated using X-ray absorption near edge structure spectroscopy (XANES), which enables the quantification of Cr(VI) directly in the solid state. Results obtained with both methods were compared for three solid samples with different matrices: a soil containing chromite ore processing residue (COPR), a loamy soil, and a paint sludge. Results showed that Cr(VI) contents determined by the two methods differ significantly, and that the EPA Method 3060A procedure underestimated the Cr(VI) content in all studied samples. The underestimation is particularly pronounced for COPR. Low extraction yield for EPA Method 3060A was found to be the main reason. The Cr(VI) present in COPR was found to be more concentrated in magnetic phases. This work provides new XANES analyses of SRM 2701 and its extraction residues for the purpose of benchmarking EPA 3060A performance.     

HPLC法测定纺织品中可萃取六价铬

建立了柱前衍生高效液相色谱测定纺织品中可萃取六价铬的方法.用二苯基碳酰二肼与纺织品水萃取液中的六价铬在酸性条件下进行衍生反应,以甲醇和10 mmol/L H3PO4水溶液为流动相,ZORBAX SB-C18柱分离,采用高效液相色谱于540nm波长处对衍生物进行检测.该方法可有效消除颜色的干扰,且精确、可靠、快速、重现性好、灵敏度高,在0 ～ 1.2 mg/kg织物的范围内,线性相关系数r=0.99982,检测限达0.02 mg/kg织物.     

深色皮革中六价铬含量测定方法的研究

在不改变DIN5 3 3 1 4检测方法的前提下 ,采用特效脱色剂对深色皮革的提取液进行脱色 ,解决了深色皮革中六价铬含量的测定难题     

Reduction of hexavalent chromium with the brown seaweed Ecklonia biomass

A new type of biomass, protonated brown seaweed Ecklonia sp., was used for the removal of Cr(VI). When synthetic wastewater containing Cr(VI) was placed in contact with the biomass, the Cr(VI) was completely reduced to Cr(III). The converted Cr(III) appeared in the solution phase or was partly bound to the biomass. The Cr(VI) removal efficiency was always 100% in the pH range of this study (pH 1 to approximately 5). Furthermore, the Cr(VI) reduction was independent of the Cr(III) concentration, the reaction product, suggesting that the reaction was an irreversible process under our conditions. Proton ions were consumed in the ratio of 1.15 +/- 0.02 mol of protons/mol of Cr(VI), and the rate of Cr(VI) reduction increased with decreasing the pH. An optimum pH existed for the removal efficiency of total chromium (Cr(VI) plus Cr(III)), but this increased with contact time, eventually reaching approximately pH 4 when the reaction was complete. The electrons required for the Cr(VI) reduction also caused the oxidation of the organic compounds in the biomass. One gram of the biomass could reduce 4.49 +/- 0.12 mmol of Cr(VI). From a practical viewpoint, the abundant and inexpensive Ecklonia biomass could be used for the conversion of toxic Cr(VI) into less toxic or nontoxic Cr(III).     

番茄红素中总铬和六价铬本底值分析及健康风险评估

了解保健品中化学污染物的本底水平,有利于科学地进行综合判定,为制定相关的标准和法规提供理论依据。本文采用微波消解-离子交换分离-石墨炉原子吸收法对12种番茄红素胶囊中铬本底值水平进行测定和分析。结果表明,番茄红素样品中Cr本底值为401⁴521μg/kg,Cr(VI)本底水平为0.74521μg/kg,Cr(VI)本底水平为0.7²66μg/kg,仅占Cr的0.9%266μg/kg,仅占Cr的0.9%⁷%,番茄红素中的铬主要以Cr(Ⅲ)形式存在;Cr、Cr(VI)暴露健康风险指数分别为0.007和0.0006,无健康风险。本研究为正确认识番茄红素中铬天然水平及健康风险评估提供了数据支持。     

Treatment of hexavalent chromium in chromite ore processing solid waste using a mixed reductant solution of ferrous sulfate and sodium dithionite

We investigated a method for delivering ferrous iron into the subsurface to enhance chemical reduction of Cr(VI) in chromite ore processing solid waste (COPSW) derived from the production of ferrochrome alloy. The COPSW is characterized by high pH (8.5-11.5) and high Cr(VI) concentrations in the solid phase (up to 550 mg kg(-1)) and dissolved phase (3-57 mg L(-1)). The dominant solid-phase minerals are forsterite (Mg2SiO4), brucite (Mg-(OH)2), and hydrocalumite [Ca4(Al, Fe)2(OH)12X x 6H2O), X = (OH)2(2-), SO4(2-), CrO4(2-)]. The method utilizes FeSO4 in combination with Na2S2O4 to inhibit oxidation and precipitation of the ferrous iron, thereby preventing well and formation clogging. Laboratory batch tests using a 0.05 M FeSO4 + 0.05 M Na2S2O4 solution indicated effective treatment of both dissolved and solid-phase Cr(VI). Contrary to treatments with FeSO4 and FeCl2 alone, the combination resulted in both complete removal of Cr(VI) from solution and sustained Fe(ll) concentrations in solution after a 24 h period. A field test involving injection of 5700 L of a 0.07 M FeSO4 + 0.07 M Na2S2O4 solution into a COPSW saturated zone (pH 11.5) indicated no well and formation clogging during injection. Examination of a core collected 0.46 m from the injection well following injection indicated effective treatment of the solid phase Cr(VI) based on analysis of water, phosphate solution, and high temperature alkaline extracts. The combined reductant solution also imparted a residual treatment capacity to the COPSW allowing for subsequent treatment of dissolved phase Cr(VI); however, dissemination of the iron in the highly alkaline environment appeared to be impeded by the inability to sufficiently lower the pH with distance from the injection well to avoid precipitation of Fe(OH)2 and likely also FeCO3. Injection of a 0.2 M FeSO4 + 0.2 M Na2S2O4 solution into another COPSW saturated zone (pH 9) indicated much more effective dissemination of the injected iron.     

Effect of set potential on hexavalent chromium reduction and electricity generation from biocathode microbial fuel cells

Setting a biocathode potential at -300 mV improved the subsequent performance of an MFC for Cr(VI) reduction compared to a control (no set potential). With this set potential, the startup time was reduced to 19 days, the reduction of Cr(VI) was improved to 19.7 mg/L d, and the maximum power density was increased to 6.4 W/m(3) compared to the control (26 days, 14.0 mg/L d and 4.1 W/m(3)). Set potentials of -150 mV and -300 mV also improved system performance and led to similarly higher utilization of metabolic energy gained (PMEG) than set potentials of +200 mV and -450 mV. We observed putative pili at -150 and -300 mV potentials, and aggregated precipitates on bacterial surfaces in both poised and nonpoised controls. These tests show that there are optimal potentials that can be set for developing a Cr(VI) biocathode.     

Behavior of hexavalent chromium in a polluted groundwater: redox processes and immobilization in soils

This work describes the chemical mechanisms governing transport and reduction of hexavalent chromium in soils of a contaminated industrial waste landfill. Groundwater and soil analyses indicate that the main source of chromium is a slag heap essentially consisting of mill tailings. In the groundwater, downstream migration of Cr(IV) is limited thanks to a redox mechanism involving chromate ions and ferrous ions or Fe(II)-bearing minerals. High Fe2+ concentrations in the groundwater are a result of pyrite residues from old activities at the site. Analyses of soil samples reveal that chromium is preferentially located in the soil profile at the fluctuation of the groundwater level. Grain size fractionation of four soil samples was performed, and fraction analyses show that chromium is preferentially accumulated in the clay fraction (<2 microm) and more specifically associated with montmorillonite particles. This work is a demonstration of the reduction of Cr(VI) by Fe(II) studied previously in the laboratory (Buerge, I. J.; Hug, S. J. Environ. Sci. Technol. 1997, 31, 1426-1432; Fendorf, S. E.; Li, G. Environ. Sci. Technol. 1996, 30, 1614-1617; Sedlak, D. L.; Chan, P. G. Geochim. Cosmochim. Acta 1997, 11, 2185-2192) in a field setting. Cr(VI) migration into the groundwater is stopped vertically by the very thick green clay unit and horizontally by the presence of Fe(II) acting as a chemical barrier. The specific site conditions safely prevent any extension of the Cr pollution.     

Determination of hexavalent chromium reduction using Cr stable isotopes: isotopic fractionation factors for permeable reactive barrier materials

Cr stable isotope measurements can provide improved estimates of the extent of Cr(VI) reduction to less toxic Cr(III). The relationship between observed (53)Cr/(52)Cr ratio shifts and the extent of reduction can be calibrated by determining the isotopic fractionation factor for relevant reactions. Permeable reactive barriers (PRB) made of Fe(0) and in situ redox manipulation (ISRM) zones effectively remediate Cr-contaminated aquifers. Here, we determine the isotopic fractionations for dominant reductants in reactive barriers and reduced sediments obtained from an ISRM zone at the US DOE's Hanford site. In all cases, significant isotopic fractionation was observed; fractionation (expressed as ε) was -3.91‰ for Fe(II)-doped goethite, -2.11‰ for FeS, -2.65‰ for green rust, -2.67‰ for FeCO(3), and -3.18‰ for ISRM zone sediments. These results provide a better calibration of the relationship between Cr isotope ratios and the extent of Cr(VI) reduction and aid in interpretation of Cr isotope data from systems with reactive barriers.     

Removal of arsenic from Laminaria japonica Aresch juice using As(III)-imprinted chitosan resin

An As(III)-imprinted chitosan resin (As-ICR) was successfully prepared to selectively remove arsenic from Laminaria japonica Aresch (LJA) juice. Batch adsorption experiments and column adsorption experiments were performed to evaluate the adsorption conditions, selectivity, and reusability. The results showed that the minimum total arsenic concentration of the juice was 4.16 mg/L at pH 6.0, 40 °C, with equilibrium time 4 h. The selectivity of As-ICR for arsenic was much higher than that of non-imprinted chitosan resin. As-ICR could be reused for 10 times with only about 13% regeneration loss. FTIR spectra demonstrated that the adsorption of As-ICR for arsenic occurred on amino and hydroxyl groups. Total arsenic concentration of the juice decreased significantly, while the other metal ions decreased except Zn²⁺ insignificantly. This suggests that As-ICR is a very promising sorbent for selective removal of arsenic from the juice.