The removal of heavy metals from aqueous solution using a recoverable poly [N-(dithiocarboxylate)-iminioethene] column

Poly [N-(dithiocarboxylate)-iminioethene] dispersed on kieselguhr provides a highly effective column packing for the removal of toxic heavy metals from aqueous solution. Metal ions removed include iron(II), cobalt(II), rhodium(III), nickel(II), palladium(II), platinum(II), copper(II), silver(I), zinc(II), cadmium(II) and mercury(II). The high metal ion uptakes previously observed in batch operation are maintained in column operation. Feed solutions with temperatures between ambient and 45°C are tolerated. pH values as low as 0.5 are not harmful to the column so long as the acid is hydrochloric acid. Nitric and sulphuric acids can be used down to pH 3.5 without harming the polymer. The column can be regenerated using cyanide solution for all metal ions except iron(II), cobalt(II) and zinc(II); disodium ethylenediaminetetraacetate can be used for these three metal ions.     

Solvent extraction of heavy metals contained in phosphoric acid solutions by 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline in kerosene diluent

The solvent extraction of zinc, cadmium and chromium contained in 5.5 mol/L phosphoric acid solutions (30% P₂O₅) was investigated using 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline-Kelex 100® as extractant and treated kerosene as diluent. At organic-to-aqueous phase ratio (1/1) and at room temperature, 58% of zinc, 34% of chromium and 15% of cadmium were recovered in 240 min. In order to improve the kinetics of extraction, a modifier reagent was added to the organic phase. The addition of n-decanol (10 vol.%) increased the rate metals extraction by reducing the equilibrium time from 240 min to 30 min, along with 60% recovery of metals. Extraction of metal ions increased with increasing aqueous phase pH. The pH_0.5 values difference of 0.1 M with Kelex 100® indicates the possible separation of cadmium, zinc and chromium. Increasing the concentration of Kelex 100® increased the percentage extraction of metal ions. The loading capacity values were found to be 83%, 80% and 71% for zinc, chromium and cadmium, respectively, at 0.4 M Kelex 100® concentration, indicating that the extractant is highly selective for the metal ions considered.     

Electrochemical reduction of arsenic (III) with cadmium metal

The kinetics of aqueous arsenic (III) reduction to amorphous arsenic with cadmium metal are presented. Two reaction mechanisms are observed in this system. With arsenic concentrations greater than approximately 0.2 gm/1 in solutions containing one molar sulfuric acid, the reduction of arsenyl ion on the cadmium surface is rate controlling. When arsenic concentrations are less than this value, reaction rate is mass-transport controlled. The reduction of arsenic (III) with cadmium powder at pH 2 is also presented.     

Recovery of EDTA from Power Plant Boiler Chemical Cleaning Wastewater

The deposition of iron oxides, metallic copper, and other impurities on boiler tube surfaces causes loss of heat transfer efficiency at electrical power plants. Hence, the tubes are cleaned every 3–5 years in order to restore the heat transfer efficiency. Chelating agents, mainly ethylenediaminetetraacetate (EDTA) and its salts, have been extensively used for the removal of metal deposits from the boiler tube surfaces. Consequently, the boiler chemical cleaning wastewater (BCCW) contains large amounts of iron, copper, and chelating agents. An electrochemical reduction process that reduces metal ions to their elemental state is tested and evaluated in order to provide the potential option to recover EDTA for reuse from power plant BCCW. Results from controlled direct current electrolysis experiments show that the electroreduction process can successfully remove metal ions from the synthetic solution and field BCCW samples and can deposit elemental metals on the cathodic plate. At a current density of 15.5 mA∕cm2 and a temperature of 40°C, the percentage metal removal and current efficiency were 94.16 and 8.27%, respectively, with a cadmium cathodic plate. Moreover, results also indicate that the percentage of metal removal and overall current efficiency increase with increasing current density and temperature under the optimal condition (15.5 mA∕cm2 and 40°C). The electroreduction process is able to separate metal ions from their EDTA complexes. The free EDTA can be recovered from field power plant BCCW and be reused again as cleaning agent.     

Selective adsorption of uranyl ion on ion-imprinted chitosan/PVA cross-linked hydrogel

An interpenetration network (IPN) ion-imprinting hydrogel (IIH) was synthesized using uranyl ions as template for adsorption and removal of uranyl ions from aqueous solutions. The IIH was obtained via cross-linking of blended chitosan/polyvinyl alcohol (PVA) using ethylene glycol diglycidyl ether (EGDE). The ability of the IIH to adsorb and remove uranyl ions from aqueous solutions was assessed using a batch adsorption technique. The maximum adsorption capacity was observed in the pH range of 5.0-6.0. The adsorption process could be well described by both the Langmuir and Freundlich isotherms and the maximum adsorption capacity calculated from Langmuir equation was 156 mg/g. Equilibrium was achieved within 2 h. The kinetic data, obtained at optimum pH 5.0 could be fitted with to a pseudo-second order equation. The selectivity coefficient of uranyl ion and other metal cations on IIH indicated an overall preference for uranyl ions which was much higher compared with the non-imprinted hydrogel. This suggests that the IIH is a promising sorbent material for the selective removal of uranyl ions from aqueous solutions.     

能量色散X射线荧光光谱法对水溶液中多种重金属离子的检测方法探讨

使用小台式的能量色散X射线荧光光谱仪可以实现水溶液中多种痕量重金属离子的直接测试,不需要对溶液进行消解,且仪器简单,对环境要求低。通过对谱线能量不同的元素进行分组,对各组元素的滤光片进行选择:对于铬、锰、铁,使用0.2 mm Al滤光片;对于镍、铜、锌、铅、硒、砷、汞,使用0.5 mm Ti滤光片;对于锑,使用1.25 mm Mo滤光片。使用国家标准溶液配制铬、铁、锰、镍、铜、锌、铅、硒、砷、汞和锑的混合溶液,探讨仪器对水溶液中重金属的检测情况,各元素校准曲线的线性相关系数均达到0.99以上,检出限在0.04~0.39 μg/mL之间。对1 μg/mL的混合溶液进行多次测试,铬测定值的相对标准偏差(RSD)最大达到19.5%,锰、铜、铅、汞、锑的RSD在10%～15%之间,其余元素的RSD均小于10%。采用能量色散X射线荧光光谱法(EDXRF)可实现水溶液中多种重金属离子的快速检测,为水溶液中重金属离子的检测提供参考。     

锰粉代替锌粉去除硫酸锌溶液中铜镉研究

湿法炼锌过程中,溶液净化过程中需要进行除铜镉操作,传统除铜镉方法以锌粉为还原剂去除铜镉,锌粉耗量高,产出铜镉渣品位较低。为了降低除铜镉工序物料消耗,提高铜镉渣品位,研究了用锰粉替代锌粉进行硫酸锌溶液中铜镉的去除,研究结果表明,金属锰粉代替锌粉除铜镉工艺可行。除铜镉速率及去除效果均优于电炉锌粉,同时也达到了降低成本的效果,吨锌生产成本降低104.75~129.52元。     

The extraction of copper from dilute aqueous solutions using a liquid membrane process

A liquid surfactant membrane process is considered for the separation of copper ions from dilute aqueous solutions. The process is shown to work effectively, solutions ranging in concentrations from 2000 ppm copper as copper sulphate (typical of acid leach solutions) down to 100 ppm copper have been successfully processed. In the case of the very dilute solutions the copper concentration in the final raffinate can be taken down to less than 1 ppm in a single contact stage. The liquid membrane is made up of a chelating agent, in this work Shell SME 529, organic diluent and emulsifying agent. Factors influencing mass transfer, such as membrane composition, O/A ratio, pH of the aqueous feed solution and acid content of the strip solution, contacting condition etc., have been studied. Providing membrane breakdown is low the process can be represented as a pseudo first order rate process. It is shown that by using this form of facilitated transport transfer of copper ions against very adverse concentration gradients across the membrane can be achieved. Further pilot plant work is required to examine scale up features of this process. Compared with conventional solvent extraction the amount of solvent (reagent and diluent) required in the contacting stage(s) is very much reduced. In this work it is shown that successful extraction of copper can be achieved using over two orders of magnitude less solvent than with solvent extraction.     

Phytoremediation: a novel strategy for the removal of toxic metals from the environment using plants

Toxic metal pollution of waters and soils is a major environmental problem, and most conventional remediation approaches do not provide acceptable solutions. The use of specially selected and engineered metal-accumulating plants for environmental clean-up is an emerging technology called phytoremediation. Three subsets of this technology are applicable to toxic metal remediation: (1) Phytoextraction--the use of metal-accumulating plants to remove toxic metals from soil; (2) Rhizofiltration--the use of plant roots to remove toxic metals from polluted waters; and (3) Phytostabilization--the use of plants to eliminate the bioavailability of toxic metals in soils. Biological mechanisms of toxic metal uptake, translocation and resistance as well as strategies for improving phytoremediation are also discussed.     

Biological determinants of P300: the effects of a barbiturate on latency and amplitude

Resistance to a range of heavy metal ions was determined for lead-resistant and other bacteria which had been isolated from a battery-manufacturing site contaminated with high concentration of lead. Several Gram-positive (belonging to the genera Arthrobacter and Corynebacterium) and Gram-negative (Alcaligenes species) isolates were resistant to lead, mercury, cadmium, cobalt, zinc and copper, although the levels of resistance to the different metal ions were specific for each isolate. Polymerase chain reaction, DNA-DNA hybridization and DNA sequencing were used to explore the nature of genetic systems responsible for the metal resistance in eight of the isolates. Specific DNA sequences could be amplified from the genomic DNA of all the isolates using primers for sections of the mer (mercury resistance determinant on the transposon Tn501) and pco (copper resistance determinant on the plasmid pRJ1004) genetic systems. Positive hybridizations with mer and pco probes indicated that the amplified segments were highly homologous to these genes. Some of the PCR products were cloned and partially sequenced, and the regions sequenced were highly homologous to the appropriate regions of the mer and pco determinants. These results demonstrate the wide distribution of mercury and copper resistance genes in both Gram-positive and Gram-negative isolates obtained from this lead-contaminated soil. In contrast, the czc (cobalt, zinc and cadmium resistance) and chr (chromate resistance) genes could not be amplified from DNAs of some isolates, indicating the limited contribution, if any, of these genetic systems to the metal ion resistance of these isolates.     

Enhancing communication with the Passy-Muir valve

Effective copper and cadmium concentrations which limited the growth of two chlorophytes by 50%, EC(50)s, after 96 h of static exposure were determined. EC(50)s were 5.94 microM copper and 4.55 microM cadmium for Dunaliella salina, and 0.78 microM copper and 0.025 microM cadmium for Chlamydomonas bullosa. The relationship of the two cations was synergistic towards the growth of both species. Chronic exposure to 4.5 x 10(-6) microM cadmium or 4.9 x 10(-4) microM copper increased the sensitivity of C. bullosa by 26% and 29% towards cadmium and copper, respectively. Changes in co-tolerance were not observed. Cd-treated D. salina was 50% more tolerant towards this cation, whereas Cu-treated cultures showed extreme sensitivity towards copper and "co-sensitivity" towards cadmium. Furthermore, the phylogenetic hypothesis, predictive of toxic response, failed to hold at the familial level.     

Competition of Cd, Cu, and Pb Adsorption on Goethite

Competition of copper, lead, and cadmium adsorption on goethite was studied and found to be dependent on metal ion and oxide surface characteristics. In adsorption edges, ionic strength effects suggested copper, lead, and cadmium are specifically adsorbed on goethite. Metal capacity on the goethite surface was found to increase with metal electronegativity: Cu > Pb > Cd. On the other hand, the equilibrium constant for lead was greater than that of copper, which is in agreement with their hydrated radii (Pb < Cu < Cd). Modeling revealed that the single-site Langmuir isotherm described the Cu-Cd and Pb-Cd adsorption and competition results within the error of the model. Furthermore, although the model provided a good fit for Pb and Cd data in the Pb-Cu and Pb-Cu-Cd systems, it underpredicted copper adsorption. The difference in site densities between copper and lead revealed a set of sites not available for competition. Using this approach where copper affinity is equivalent for both sites, the model provided a good fit for copper adsorption and competition. This study confirms that adsorption competition plays a crucial role in contaminant mobility in the environment.     

碱添加量对金属离子的分布和pH变化的影响

提出了一种计算公式,定量地计算了既有氢氧化物沉淀又有氢氧配离子形成的化学反应体系中的金属离子的分布,考察了影响沉淀和配离子形成的各种因素.基于提出的公式,计算了锌、镉、铜、镍、铁(Ⅲ)、铁(Ⅱ)、铝、钙、镁的沉淀率,理论计算与实验结果一致.     

Incidence and pattern of liver involvement in haematological malignancies

Copper release from copper-bearing IUD's was studied in vitro and in vivo using atomic absorption spectrophotometry in deionized water, normal saline solution and normal ovulatory cervical mucus. In these media, copper release from a 375 mm2 DIU occurs without latency, showing comparable amounts for identical time intervals. Daily copper release was shown to be respectively 8 and 11 times higher in cervical mucus and normal saline solution than in deionized water. Although copper ions are detectable in ovulatory cervical mucus under physiological conditions, the copper content appears 5 to 6 times higher in women bearing a copper IUD. Obviously, the copper amount is dependent on the copper exposed surface: the daily in vitro release from a 250 mm2 IUD is 18% inferior to that observed from a 375 mm2 model. In vivo, the daily copper release in ovulatory mucus of 380 or 200 mm2 IUD users is respectively 5 and 3.5 times higher than in controls.     

针铁矿对重金属离子的吸附作用

对针铁矿合成试验和针铁矿吸附重金属离子进行了研究。试验结果表明，针铁矿可用铁矿废渣获得，通过酸碱中和的方式所获得的针铁矿是微细针状，针铁矿对重金属离子具有强烈的吸附作用，对Cu^2 、Zn^2 和Cd^2 的吸附边界pH值分别为4.3,5.8和7.3，且吸附率最高可达95％以上；尤其对Pb^2 的吸附作用更加强烈，在pH值为3.5时吸附率就达到95％，并且随着pH值的升高吸附率仍在95％以上。研究表明，铁矿废渣可被利用制备针铁矿，针件矿用于含重金属离子污水的处理，具有较好效果。     

混凝与电絮凝废水中多种金属离子协同沉淀机制研究

采用混凝和电絮凝工艺去除废水中的多种金属离子(Pb^2+、Cd^2+、Cu^2+、Ni^2+),研究混凝反应主要影响因素液相pH、混凝剂(PAC)投加量对各金属离子去除效率的影响,探讨废水pH、施加电流密度对各金属离子电絮凝去除效率的影响,阐明混凝和电絮凝多金属协同沉淀去除的机制。结果表明,PAC混凝去除废水中Pb^2+、Cd^2+、Cu^2+、Ni^2+的最佳pH为7.0,最佳投加量600mg/L,Pb^2+、Cu^2+去除效率远高于Cd2+、Ni2+;电絮凝反应金属离子去除的最佳pH为7.0,最佳电流密度为1.2~1.8mA/cm^2。混凝与电絮凝金属离子的去除效率与金属离子的半径、相对分子质量大小无关,而与金属离子的溶度积直接相关,金属离子的溶度积越低,混凝和电絮凝去除效率越高。电絮凝较混凝反应具有更高的金属离子去除效率。研究结果对于采用混凝和电絮凝工艺处理多金属污染废水具有借鉴和指导意义。     

The use of the optical disector to estimate the number of neurons, glial and endothelial cells in the spinal cord of the mouse--with a comparative note on the rat spinal cord

Poly(ethylene glycol) (PEG)-bound chelated metal ions partition preferentially into the top, PEG-rich, phase of a PEG-salt or PEG-dextran aqueous two-phase system. Extraction by this soluble affinity ligand of proteins is due to a selective interaction of the chelated metal ion with accessible histidine residues on the protein surface. Using Cu-iminodiacetate-PEG (Cu-IDA-PEG) the surface of lactate dehydrogenase (LDH) isoenzymes from different species was probed for the presence of metal chelate binding sites. It was demonstrated that the homotetramers (LDH-1)(H4) from rabbit, bovine and pig displayed weak binding to chelated copper whereas the M4-type isoenzymes (LDH-5) bound strongly to this ligand. The binding of the different heterotetramers increases as the number of M-type subunits increases. In contrast, the human isoenzymes are bound to chelated copper in a reversed sequence. The comparison of the affinity partitioning effect of Cu-IDA-PEG in PEG-salt and PEG-dextran systems revealed that the discriminatory effect of copper is promoted by high salt concentrations. Resolution of isoenzymes by multiple extraction using counter-current distribution provides valuable data on the partitioning of enzymes relative to that of the bulk proteins. The efficacy of metal chelate affinity partitioning for the purification of LDH from tissue samples by batchwise extraction was also demonstrated.     

The effect of surface dissolution on fatigue crack nucleation in polycrystalline copper

Axial tension-tension fatigue experiments were conducted on high purity polycrystalline copper specimens in laboratory air and in 0.5N NaCl solutions with applied anodic currents. Results show that, when compared to experiments conducted in air, applied anodic currents greater than ≈ 10 μA/cm² lower fatigue life, and cause slip intensification and broadening. Additionally, crack nucleation and growth are converted from a primarily transgranular mode in air to an intergranular mode in aqueous solutions. A similar shift in crack nucleation is observed in air after an intermediate electropolishing to remove initial surface connected fatigue damage. These results can be explained from a consideration of mobile dislocation/environmental interactions. Formerly Research Assistant, Materials Division, Rensselaer Polytechnic Institute, Troy, New York 12181     

Detection of heavy metal ions at femtomolar levels using protein-based biosensors

Sensors based on proteins (GST-SmtA and MerR) with distinct binding sites for heavy metal ions were developed and characterized. A capacitive signal transducer was used to measure the conformational change following binding. The proteins were overexpressed in Escherichia coli, purified, and immobilized in different ways to a self-assembled thiol layer on a gold electrode placed as the working electrode in a potentiostatic arrangement in a flow analysis system. The selectivity and the sensitivity of the two protein-based biosensors were measured and compared for copper, cadmium, mercury, and zinc ions. The GST-SmtA electrodes displayed a broader selectivity (sensing all four heavy metal ions) compared with the MerR-based ones, which showed an accentuated selectivity for mercury ions. Metal ions could be detected with both electrode types down to femtomolar concentration. The upper measuring limits, presumably due to near saturation of the proteins' binding sites, were around 10(-10) M. Control electrodes similarly constructed but based on bovine serum albumin or urease did not yield any signals. The electrodes could be regenerated with EDTA and used for more than 2 weeks with about 40% reduction in sensitivity.     

硝酸铵-丁二酮肟-百里酚酞体系分离富集镍

建立了一种以微晶百里酚酞作吸附剂分离富集镍的新方法。探讨了分离富集镍的行为及其与常见离子定量分离的条件, 详细讨论了Ni²⁺的富集机理。结果表明, 控制pH 8.0, 在硝酸铵-丁二酮肟-百里酚酞体系中, 镍与丁二酮肟(DMG)形成的螯合物沉淀[Ni(DMG)₂]可被定量吸附至微晶百里酚酞表面上, 形成界面清晰的液-固两相, 而锰、铜、镉、铝、锌等不被吸附, 实现了镍与这些金属离子的定量分离, 据此建立了分离富集镍的新方法。方法成功用于合成水样中微量镍的定量分离, 富集率为95.9%~106.5%。