天然膨润土还原吸附Cr（Ⅵ）

以天然膨润土为吸附剂,还原吸附处理含Cr（Ⅵ）模拟废水。实验结果表明：以（NH₄）₂FeSO₄为还原剂吸附效果最佳;在还原剂加入量为理论值的0.8倍、膨润土加入量为6 g/L、吸附时间为30 min、吸附温度为30 ℃、初始Cr（Ⅵ）质量浓度为1 mg/L的条件下,Cr（Ⅵ）去除率可达99.6%,处理后模拟废水中总铬质量浓度低至0.003 mg/L。天然膨润土对Cr（Ⅵ）的还原吸附符合准二级动力学模型及Freundlich等温吸附模型。     

碱熔融—微波晶化法合成粉煤灰沸石及其对Cd2+的吸附

以粉煤灰为主要原料,采用碱熔融—微波晶化法合成粉煤灰沸石。采用XRD,SEM,TEM等技术表征了粉煤灰沸石的微观结构,并对其吸附Cd²⁺的性能进行了研究。表征结果显示,粉煤灰沸石主要由X型沸石、P型沸石和铝组成,粉煤灰沸石中有排列规则、呈蜂窝状的孔穴和孔道存在,其孔穴和孔道大小分布均匀,致密。粉煤灰沸石的比表面积为108.49 m²/g,平均孔径为3.779 nm,孔体积为0.221 mL/g。实验结果表明,在溶液pH为7、吸附时间30 min的最佳吸附条件下,Cd²⁺去除率均大于94%。粉煤灰沸石对Cd²⁺的吸附可很好地用二级动力学方程进行拟合,相关系数为0.999 99。可用Langmuir等温吸附模型描述该吸附过程,该吸附过程是单分子层吸附,主要是化学吸附,粉煤灰沸石对Cd²⁺的饱和吸附量为49.261 mg/g。     

Bioremediation of Chromate by Sulfate-Reducing Bacteria, Cytochromes c3 and hydrogenases

The treatment of soils and ground waters polluted by heavy metals is of economical and environmental interest. Reduction of Cr(VI) to the less toxic Cr(III) associated to its precipitation is a potentially useful process for bioremediation. In order to develop ecological processes using micro-organisms, we have compared various sulfate-reducing bacteria for enzymatic reduction of chromate. The best Cr(VI) reductase activity was obtained with Desulfomicrobium norvegicum. Despite morphological changes induced by the presence of chromate, this strain can grow in the presence of up to 500 M Cr(VI) and can decontaminate waters polluted by Cr(VI) when seeded in bioreactors. We have demonstrated the ability of several metalloenzymes (cytochromes c ₃ and hydrogenases) to reduce chromate. Biophysical investigations of the chromate/protein interaction in order to get further informations on the mechanism of metal reduction by cytochromes c ₃ are under the way.     

THE IMPACT OF URBANIZATION ON THE DISTRIBUTION OF HEAVY METALS IN BOTTOM SEDIMENTS OF THE SADDLE RIVER1

ABSTRACT: A three-year study has been conducted on a 4.6 mile stretch of the Saddle River near Lodi, New Jersey. The primary objectives of this investigation were (1) to provide baseline information on the concentration and distribution of heavy metals in bottom sediments of the Saddle River; (2) to qualitatively evaluate which parameters affect this distribution; and (3) to determine the effect of urbanization on the concentration and distribution of these materials. Significant enrichments of several heavy metals were observed in bottom sediments of the lower Saddle River near Lodi, New Jersey, as compared to the upper Saddle River. Attempts to correlate metal concentrations in bottom sediments with chemical-oxygen demand were not successful in demonstrating a relationship between these two factors. Metal concentrations were found to be strongly dependent upon particle size. In general, metal concentrations in bottom sediments increased with decreasing partical diameter. However, metals enrichment was observed to be considerably greater in the larger sediment fractions studied (>420μ) than the smaller sediment fractions as one proceeded downstream through the urban area. Since the larger sediment fractions are least effected by scour and transport they may best reflect the effect of urbanization on the distribution of heavy metals over an extended period of time at a given location.     

皮革铬鞣废水回收利用中铬渣的铬量测定

本文研究了皮革铬鞣废水中铬的定性特征曲线。利用吸光度加合定律对大量实测数据进行统计处理。建立测定铬的实验室校准直线方程，相关系数γ＝０．９９６０．以此作为测定铬鞣废水及回收铬渣中铬量的实验室回归直线方程。并对本法的可靠性进行研究，结果令人满意。本法不仅大大简化了铬量测定的步骤．而且在提高分析效率的同时获得同等的检测结果。     

Pomegranate husk as an adsorbent in the removal of toxic chromium from wastewater

The use of a new sorbent developed from the husk of pomegranate, a famous fruit in Egypt, for the removal of toxic chromium from aqueous solution has been investigated. The batch experiment was conducted to determine the adsorption capacity of the pomegranate husk. The effects of initial metal concentration (25 and 50 mg l^-1), pH, contact time, and sorbent concentration (2-6 g l^-1) have been studied at room temperature. A strong dependence of the adsorption capacity on pH was observed, the capacity increased as the pH decreased, and the optimum pH value was pH 1.0. Adsorption equilibrium and kinetics were studied with different sorbent and metal concentrations. The adsorption process was fast, and equilibrium was reached within 3 h. The maximum removal was 100% for 25 mg l^-1 of Cr⁶⁺ concentration on 5 g l^-1 pomegranate husk concentration, and the maximum adsorption capacity was 10.59 mg g^-1. The kinetic data were analysed using various kinetic models—pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion equations—and the equilibrium data were tested using several isotherm models, Langmuir, Freundlich, Tempkin, Dubinin-Radushkevich, and Generalized isotherm equations. The Elovich and pseudo-second-order equations provided the greatest accuracy for the kinetic data, while Langmuir and Generalized isotherm models were the closest fit for the equilibrium data. The activation energy of sorption has also been evaluated as 0.236 and 0.707 kJ mol^-1 for 25 and 50 mg l^-1 chromium concentration, respectively.     

铬渣中铬的浸出行为

采用BCR法连续浸提研究铬渣中铬的存在形态,结果表明:铬渣中总铬和六价铬主要以残渣态和可氧化态形式存在;通过铬渣动态连续浸提实验与静态浸提实验研究了浸提剂和活性炭对铬渣中铬浸出行为的影响,研究发现p H值为3.1的醋酸浸提剂浸出液中铬浓度最低,且添加活性炭后的静态浸出液中铬的浓度有不同程度降低。     

Simultaneous photocatalytic treatment of Cr(VI), Ni(II) and SDBS in aqueous solutions: Evaluation of removal efficiency and energy consumption

Simultaneous photocatalytic reduction of poisonous Cr(VI) and Ni(II) ions, coupled with photocatalytic oxidation of sodium dodecyl benzene sulfonate (SDBS) were studied with a trace amount of commercial titania nanoparticles and by means of a direct-photo-irradiation reactor. The co-presence of metal ions and SDBS causes metal ions reduction as well as SDBS oxidation to enhance and energy efficiency to improve. XRD, XPS and FTIR analysis were used to characterize TiO₂ particles before and after usage with the aim of evaluating the mechanism of reactions. The effect of major operating parameters, pH and temperature, was investigated. Under conditions of [Cr(VI)]₀ = [Ni(II)]₀ = 5 mg/L, [SDBS]₀ = 10 mg/L, [TiO₂] = 40 mg/L, pH 6 and T = 35 °C; the removal efficiencies of 55.4%, 71.2% and 57.2% were obtained, respectively, for Cr(VI) and Ni(II) reduction, as well as for SDBS oxidation, after 110 min operation. The relevant kinetic model jointed with the Arrhenius equation was introduced. Pseudo-first-order reactions are relevant. Energy consumption (electrical and thermal) evaluations revealed that operations at higher temperatures provide significant cost reduction. Meantime, a criterion was proposed for a consistent assessment of this kind of processes.     

运行参数对水蚯蚓生物吸持六价铬性能影响研究

水蚯蚓能通过摄食剩余污泥而使污泥减量,但剩余污泥中常含有各种重金属污染物.本文以颤蚓科蠕虫(Tubificidae)为研究对象,以六价铬为典型重金属污染物,考察运行工艺参数:初始铬浓度、p H、水蚯蚓投加量和温度对水蚯蚓吸持六价铬的影响.实验结果表明,在研究浓度范围内(0.1~8.0 mg·L-1),水蚯蚓对六价铬的吸持速率随铬浓度的增大而加快,单位质量吸持量从14.4 mg·kg-1(以干重计,下同)增加到312.7 mg·kg-1,但六价铬的吸持率却随Cr6+初始浓度的增加而降低;p H从6.0增加到8.0,水蚯蚓对六价铬的吸持速率随p H的上升而提高,吸持率和单位质量吸持量先明显增强,p H达到7.5后逐渐趋于平衡,即吸持最佳p H为7.5;水蚯蚓投加量从1.0 g(以湿重计,下同)增加到5.0 g时,吸持速率及吸持率均上升,但单位质量吸持量却随着水蚯蚓投加量的增加而减少;当温度在10~20℃范围内时,水蚯蚓对六价铬的吸持速率相对较慢,到25℃时,吸持速率明显加快,吸持率和单位质量水蚯蚓的吸持量的变化趋势与吸持速率的变化相一致,但当温度达到30℃,水蚯蚓会大量死亡,综合考虑,处理系统最佳温度宜控制在25℃.     

Removal of Cr(VI) from Cr-contaminated groundwater through electrochemical addition of Fe(II)

The conventional chemical reduction-precipitation technique in the removal of Cr(VI) from contaminated groundwater involves a two-step process whereby Cr(VI) is first reduced to Cr(III) at an acidic pH by a reducing agent and in a subsequent step, Cr(III) is precipitated as insoluble hydroxide at an alkaline pH. In a variation of this method, Fe(II) is added electrochemically to the Cr(VI) containing water. From a pure iron electrode, Fe(2+) ions are released into the solution and bring forth the reduction of Cr(VI). At the cathode, H(2)O is reduced whereby the OH(-) ions entering the solution keep the pH of the solution in the alkaline range. This latter fact greatly facilitates simultaneous reduction of Cr(VI) to Cr(III) and co-precipitation of hydroxides of trivalent Cr and Fe. On the basis of a set of experimental data, it is shown that this process is both thermodynamically and kinetically efficient, meaning, with the electrochemical method, rapid and nearly complete removal of Cr(VI) from a groundwater source with both high and low levels of Cr-contamination can be achieved. These factors make the electrochemical process superior to the conventional chemical process in remediation of Cr-contaminated groundwater.