An evaluation of a hybrid ion exchange electrodialysis process in the recovery of heavy metals from simulated dilute industrial wastewater

Hybrid ion exchange electrodialysis, also called electrodeionization (IXED), is a technology in which a conventional ion exchange (IX) is combined with electrodialysis (ED) to intensify mass transfer and to increase the limiting current density and therefore to carry out the treatment process more effectively. It allows the purification of metal-containing waters, as well as the production of concentrated metal salt solutions, which could be recycled. The objective of this paper was to investigate the ability of the IXED technique for the treatment of acidified copper sulphate solutions simulating rinsing water of copper plating lines. A single-stage IXED process at lab-scale with a small bed of ion exchanger resin with a uniform composition was evaluated, and the treatment performance of the process was thoroughly investigated. The IXED stack was assembled as a bed layered with the ion exchanger resin (strong acid cation-exchange Dowex™) and inert materials. The stack configuration was designed to prevent a non-uniform distribution of the current in the bed and to allow faster establishment of steady-state in the cell for IXED operation. The influence of operating conditions (e.g. ion exchanger resin with a cross-linking degree from 2 to 8% DVB, and current density) on IXED performance was examined. A response surface methodology (RSM) was used to evaluate the effects of the processing parameters of IXED on (i) the abatement yield of the metal cation, which is a fundamental purification parameter and an excellent indicator of the extent of IXED, (ii) the current yield or the efficiency of copper transport induced by the electrical field and (iii) the energy consumption. The experimental results showed that the performance at steady-state of the IXED operation with a layered bed remained modest, because of the small dimension of the bed and notably the current efficiency varied from 25 to 47% depending on the conditions applied. The feasibility of using the IXED in operations for removal of heavy metals from moderately dilute rinsing waters was successfully demonstrated.     

Coregionalization analysis of heavy metals in the surface soil of Inner Mongolia

Due to potential problems associated with their deficiencies or toxicities, heavy metals in soils are of great environmental concern. To evaluate heavy metal contents and their relationships in the surface soil of Inner Mongolia, soil samples were collected from 344 sites and contents of copper, lead, zinc, cadmium, nickel, chromium, mercury, cobalt, vanadium and manganese were determined. In this article, coregionalization of these ten heavy metals is investigated using factorial kriging. Vegetation type, parent material type and soil pH, with respective characteristic ranges of 200, 400 and over 1000 km, are identified as the primary factors that control the spatial distribution of soil heavy metals. At the scale of 200 km, heavy metal relationships mainly reflect the result of biocycling. Their relationships at the intermediate scale (400 km) are thought to be derived from the atomic substitution of metals in the parent materials. Effects of soil pH on the adsorption of heavy metals by soil organic materials could explain their relationships at the large spatial scale (over 1000 km).     

Distribution of heavy metals in the sediment of an unpolluted estuarine environment

The distribution of cadmium, cobalt, copper, lead, manganese, mercury, nickel and zinc in the sediments of Urr Water, an estuary relatively free of industrial and sewage pollution, has been investigated.The aim of this study was to provide baseline information for comparison with similar geochemical areas which are subject to pollution.     

Adsorption of heavy metals on Na-montmorillonite. Effect of pH and organic substances

Clays (especially montmorillonite and bentonite) are widely used as barriers in landfills to prevent contamination of subsoil and groundwater by leachates containing heavy metals. For this reason it is important to study the adsorption of metals by these clays. The sorption of seven metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) on Na-montmorillonite was studied as a function of pH and in the presence of ligands, forming complexes of different stabilities with the metals of interest. The continuous column method was used as it better simulates natural conditions. The total capacity of Na-montmorillonite towards these metals was determined. The pH variations influence to a higher extent the concentrations of Cu, Pb and Cd in the effluent. Moreover the results suggest that complex formation hinders the sorption of the metals on the clay, with an increasing influence in the order: Mn < or = Pb < or = Cd < or = Zn < Ni < Cu < Cr. The evaluation of the total capacity of Na-montmorillonite shows that this clay is a good sorbent towards all examined metals.     

Enhanced phytoextraction of uranium and selected heavy metals by Indian mustard and ryegrass using biodegradable soil amendments

The applicability of biodegradable amendments in phytoremediation to increase the uptake of uranium (U), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) by Indian mustard (Brassica juncea) and ryegrass (Lolium perenne) was tested in a greenhouse experiment. Plants were cultivated during one month on two soils with naturally or industrially increased contaminant levels of U. Treatments with citric acid, NH₄-citrate/citric acid, oxalic acid, S,S-ethylenediamine disuccinic acid (EDDS) or nitrilotriacetic acid (NTA) at a rate of 5 mmol kg^− 1 dry soil caused increases in soil solution concentrations that were up to 18 times higher for U and up to 1570 times higher for other heavy metals, compared to the controls. Shoot concentrations increased to a much smaller extent. With EDDS, 19-, 34-, and 37-fold increases were achieved in shoots of Indian mustard for U, Pb and Cu, respectively. The increases in plant uptake of Cd, Cr and Zn were limited to a factor of four at most. Ryegrass generally extracted less U and metals than Indian mustard. Despite a marked increase of U and metal concentrations in shoots after addition of amendments, the estimated time required to obtain an acceptable reduction in soil contaminant concentrations was impractically long. Only for Cu and Zn in one of the studied soils, could the Flemish standards for clean soil theoretically be attained in less than 100 years.     

A study on stack configuration of continuous electrodeionization for removal of heavy metal ions from the primary coolant of a nuclear power plant

This study investigated the production of high-purity water in the primary coolant of a nuclear power plant via the continuous electrodeionization (CEDI) process, using ion exchange resins as ion-conducting media between ion exchange membranes. The effectiveness of this method was examined with respect to the removal of heavy metals. The study was carried out on a laboratory scale with an effective area of 20 cm(2). The CEDI system was operated with a layered bed of cation exchange resins, anion exchange resins, and mixed-bed ion exchange resins. The stack configuration was designed to prevent a reaction between metal ions and hydroxide ions. The CEDI operation with the layered bed removed more than 99% of the ions at 30% of the current efficiency. The results showed that, with an inlet conductivity of 40 microScm(-1), a linear velocity of 4.17 cms(-1), and an applied current density of 17 mAcm(-2), the CEDI process yielded an outlet conductivity of 0.5 microScm(-1), thereby preventing the precipitation of metal ions. This study therefore successfully demonstrated the feasibility of the CEDI operation for the removal of heavy metals at a very low concentration.     

Accumulation of heavy metals in a lake ecosystem

The concentrations of Cu, Zn, Fe, Mn, Ni, Cd, Pb and Co have been determined in water, bottom sediments, plankton, zoobenthos and ichthyofauna of mesotropic Lake Piaseczno located in eastern Poland. In water, sediments, plankton and benthos the most abundant heavy metals were Fe, Zn and Mn, whereas in fish Zn, Cu, and Mn were most abundant. The amount of heavy metals in the biotic components was dependent upon their concentration in water and partly upon the concentration in bottom sediments. A considerably less important role in the translocation of heavy metals is probably played by trophic interactions.     

A laboratory model for evaluating the behavior of heavy metals in an aquatic environment

A dynamic biological system capable of simultaneously distinguishing between bioaccumulation and biomagnification through successive trophic levels in an aquatic ecosystem is described. The organisms used in the system were algae, predominantly Scenedesmus sp., Daphnia magna, fresh water mussels (Ligumia sp. and Margaritifera sp.) and the fathead minnow, Pimephales promelas.Thiosulfate complexed mercury and silver were each studied at two concentrations. The water and organisms were analyzed for the metals periodically during the 10-week tests. Both mercury and silver can be bioaccumulated by fish. The concentration factors for mercury are greater than for silver. Further, mercury is biomagnified by fish whereas silver is not. Fresh water mussels were found to be poor indicator species for metal contamination.     

Adsorption of heavy metals by a sorbent based on pine bark

Sorption properties of the pine bark treated with a 5% urea solution have been studied with respect to heavy metals Cu(II), Ni(II), Zn(II), and Pb(II). The bark subjected to treatment has higher sorption properties and retains several times as many metals as the untreated bark. Parameters of the Langmuir and Freundlich sorption isotherms were obtained. The possible mechanisms of the bark interaction with urea and reasons for an enhanced metal adsorption on the bark treated with urea solution have been also discussed.     

Short-term effects of biosolid and municipal solid waste applications on heavy metals distribution in a degraded soil under a semi-arid environment

Digested biosolid (SS) and municipal solid waste (MSW) were surface-applied to a degraded carbonated soil, under semi-arid environment, at rates of 0 and 80 Mg/ha, to determine the changes in organic matter and in the distribution of heavy metals in the topsoil, 1 year after its application. Waste application slightly increased the organic matter content and improved the composition of humic fractions in the treated soils, mainly in the MSW amended plots. A sequential extraction method (Tessier et al., 1979) was used to determine the distribution of Cd, Cr, Cu, Ni, Pb and Zn in both the waste and the amended.soils. Waste application had little effect on the total concentration of Ni and Cr in the treated soils as a consequence of the low availability of these metals in the wastes. A considerable increase of Cd, Cu, Pb and Zn was observed as a consequence of the high content and/or high availability of these metals in the wastes. The more labile fraction (exchangeable fraction) of all metals studied increased slightly (< 1.5 mg/kg) when SS and MSW were added. However, a remarkable increase in the Fe/Mn oxide fraction of Cd, Cu and Pb and in the organic fraction of Zn were noted in treated plots, this increase being higher in the MSW treated soils.     

The influence of weathering and organic matter on heavy metals lability in silicatic, Alpine soils

We investigated the effect of organic matter and weathering on the lability and solid phase speciation of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in two contrasting subalpine regions in the Italian Alps. Cr, Ni and Cu could be linked to weathering. This was not the case for Pb. Since organic matter (OM) influences the solid phase speciation of heavy metals, the total organic C and N content, the C and N content of different density fractions of OM and also of the labile (oxidised by H₂O₂) and stable (H₂O₂-resistant) fractions were determined. Soil OM stocks were high and soils on north-facing slopes had more OM than the south-facing sites to which they were paired. Density measurements and the H₂O₂ fractionation indicated that the higher OM content on north-facing sites was due to an accumulation of weakly degraded organic material. Due to higher weathering intensity on north-facing sites, the abundance of the EDTA-extractable heavy metals was higher than on south-facing sites. All EDTA-extractable heavy metals showed a good correlation to the water-soluble phenolic concentrations which indicates that the metals were probably translocated as metal-organic complexes. Pb and Cu correlate not only to the light (density < 1 g/cm³) and labile, organic fraction but also to the heavy (density > 2 g/cm³) and stable fraction. High-mountain ecosystems like the Alps are sensitive to changing environmental conditions such as global warming. A warmer climate and the more favourable conditions it brings for biological activity, especially at cooler sites, will probably lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM. As the Pb and Cu content is significantly related to the labile organic matter pools, the risk exists that an increase in OM mineralisation could affect the storage capacity and mobility of these metals in soils.     

Determination of heavy metals in natural water by the sorption-atomic-absorption method

The procedure for determining Hg, Cd, Pb, Zn, Cu elements in fresh water based on the preconcentration of these metals as complexes using poly-3-pyridyl-5-thioxo-4-allyl-4,5-dihydro-1H-1,2,3-triazole-1-carbodithionic acid with further measurement of atomic adsorption are proposed. The detection limits for metals are 5, 8, 20, 5 and 20 ng/dm³ respectively.     

ICP-MS法测定复方龙血竭胶囊中5种有害元素的残留量

目的:建立复方龙血竭胶囊中铅、镉、砷、汞、铜5种重金属及有害元素含量的测定方法。方法:采用电感耦合等离子体质谱法(ICP-MS),样品经微波消解后测定,在线引入内标以校正基体效应。结果:各元素在一定浓度范围内线性关系良好(r≥0.9990);检测限为0.389 ng·g-1³.548ng·g-1;加样回收率为87.5%3.548ng·g-1;加样回收率为87.5%¹09.4%,RSD(n=9)均小于9.1%。结论:该方法较简便、快速、准确,可用于复方龙血竭胶囊中有害元素的测定。     

Stabilization of heavy metals in sludge ceramsite

This paper attempts to investigate the stabilization behaviours of heavy metals in ceramsite made from wastewater treatment sludge (WWTS) and drinking-water treatment sludge (DWTS). Leaching tests were conducted to find out the effects of sintering temperature, (Fe₂O₃ + CaO + MgO)/(SiO₂ + Al₂O₃) (defined as F/SA ratios), pH, and oxidative condition. Results show that sintering exhibits good binding capacity for Cd, Cr, Cu, and Pb in ceramsite and leaching contents of heavy metals will not change above 1000 °C. The main crystalline phases in ceramsite sintered at 1000 °C are kyanite, quartz, Na-Ca feldspars, sillimanite, and enstatite. The main compounds of heavy metals are crocoite, chrome oxide, cadmium silicate, and copper oxide. Leaching contents of Cd, Cu, and Pb increase as the F/SA ratios increase. Heavy metals in ceramsite with variation of F/SA ratios are also in same steady forms, which prove that stronger chemical bonds are formed between these heavy metals and the components. Leaching contents of heavy metals decrease as pH increases and increase as H₂O₂ concentration increases. The results indicate that when subjected to rigorous leaching conditions, the crystalline structures still exhibit good chemical binding capacity for heavy metals. In conclusion, it is environmentally safe to use ceramsite in civil and construction fields.     

Modelling of chloride ingress into concrete from a saline environment

A mathematical model previously developed for the simulation of electrochemical chloride removal (ECR) process is utilised to predict the ionic mass transport associated with chloride ingress into concrete or hydrated cement paste from a saline environment by incorporating the convection of pore solution. Compared to the existing models, the present model has advantages in the aspect of numerical calculations as it avoids the difficulty of solving the Poisson equation about electrostatic potential. The significant effects of ionic interaction and the convection of pore solution on the chloride ingress are examined. Simulation results are compared with those obtained from the models using Fick's second law. The comparison shows that the present model is more detailed and accurate. It can be applied to various different cases with unified ionic diffusivities.     

A study of nitrate in Tehran ground water and a method of its removal

This study investigates the concentration of nitrate in groundwater in the province of Tehran. It also proposes the combination of ion exchange and biological denitrification as an effective way of removing nitrate from drinking water. The concentration of nitrate was measured in more than 200 deep and semi‐deep wells spread throughout urban and rural areas in Tehran. The result proved the presence of nitrate in a wide area in the province, especially in the southern part of the city of Tehran, and areas next to industrial or agricultural centers. The results show that there is a linear relationship between R (the proportion of nitrate ion concentration to total nitrate and sulfate ion concentrations in the influent) and the amount of each nitrate and sulfate ion derived from total capacity of resins. The last step in this study included denitrification of the spent regenerant by SBR and BPBR. At high concentrations of salt and nitrate, BPBR performed well while SBR showed an average performance.     

Selective removal of arsenate from drinking water using a polymeric ligand exchanger

The new maximum contaminant level (MCL) of 10 μg/L for arsenic in the US drinking water will take effect on January 22, 2006. The compliance cost is estimated to be $ 600 million per year using current treatment technologies. This research aims to develop an innovative ion exchange process that may help water utilities comply with the new MCL in a more cost-effective manner. A polymeric ligand exchanger (PLE) was prepared by loading Cu²⁺ to a commercially available chelating ion exchange resin. Results from batch and column experiments indicated that the PLE offered unusually high selectivity for arsenate over other ubiquitous anions such as sulfate, bicarbonate and chloride. The average binary arsenate/sulfate separation factor for the PLE was determined to be 12, which were over two orders of magnitude greater than that (0.1–0.2) for commercial strong-base anion (SBA) exchangers. Because of the enhanced arsenate selectivity, the PLE was able to treat 10 times more bed volumes (BVs) of water than commonly used SBA resins. The PLE can operate optimally in the neutral pH range (6.0–8.0). The exhausted PLE can be regenerated highly efficiently. More than 95% arsenate capacity can be recovered using 22 BVs of 4% (w/w) NaCl at pH 9.1, and the regenerated PLE can be reused without any capacity drop. Upon treatment using FeCl₃, the spent brine was recovered and reused for regeneration, which may cut down the regenerant need and reduces the volume of process waste residuals. The PLE can be used as a highly selective and reusable sorbent for removal of arsenate from drinking water.     

Movement of heavy metals into a shallow aquifer by leakage from sewage oxidation ponds

The concentrations of Mn, Ni, Cu, Cd and Cr were measured in a shallow perched groundwater aquifer which underlies the Dan Region Sewage Reclamation Project (Israel). The contribution of effluents to the groundwaters has been evaluated on the basis of chloride concentration. Groundwater which are estimated to contain more than 60% effluents showed a hundred-fold decrease in Cu and Mn at a distance of 650 m away from the ponds, as compared with the near ponds samples. Ni and Cd showed only a small decrease in concentration over a distance of 150 m, and then stayed constant. The concentrations of Cu and particularly of Mn in the groundwaters near the oxidation ponds is equivalent to or greater than in the ponds themselves. It is suggested that Cu and Mn are mobilized from the precipitated sludge into the interstitial waters. They percolate into the groundwater near the ponds and then are precipitated by increasing aeration during the movement of the water away from the pond area. Cd and Ni form stable soluble organic chelates which are only slightly removed by interaction with the sandy soil of the aquifer.