Studies on Separation of Heavy Metals from Acidic Solutions by Foam Fractionation with Respect to an Application on Acidic Soil Extracts

An experimental investigation is presented on the batch foam fractionation of the heavy metal cations Pb²⁺, Cd²⁺, Cu²⁺, Sb³⁺ and As⁵⁺ from diluted aqueous solutions with hexamethylenedithiocarbamate (HMDC) as complexing agent and sodiumdodecylsulfate (SDS) as surfactant. Among the considered pH-values of 2,4 and 7 the pH 2 experiments allow a direct application of foam fractionation on acidic extracts from heavy metal contaminated soil. The experiments at pH 2 and pH 4 show better results than those at neutral pH. Although a simple device was used, a maximum enrichment factor of 13.8 and a minimum removal factor of 0.01 have been measured. The flotation with weak organic acids like citric acid (CA) and acetic acid (AA) show about 50–70% smaller enrichment factors than those acidified with hydrochloric acid. The dissolution and mixing of the reacting components as well as the concentration of the detergent and the gaseous volume flow can be regarded as basic parameters of foam fractionation.     

Langzeitprognosen zum Sickerwasseraustrag von Schwermetallen aus Deponien von Müllverbrennungsschlacken

Long‐term Assessment for the Leachate Release of Heavy Metals from Municipal Solid Waste Incineration Bottom Ash Monofills Municipal solid waste incineration (MSWI) bottom ash was investigated by chemical, mineralogical, and microbiological methods as well as leaching‐ and laboratory lysimeter tests. Compared to geological material bottom ash shows a high content of soluble salts, organic carbon, and heavy metals. The heavy metals are mainly bound in alloys and glas. Addition of oxic and acetic solutions quickly oxigenize the metal‐phases and alloys. Only fixation in newly formed phases like carbonates or hydroxides prevents heavy metal release till pH 7 in case of pH‐reduce. In the long‐term the acid buffer is reduced by the environmental acid input in combination with the release of buffering phases (mostly calcite). Internal acid producing processes like decay of organic matter or oxidation of sulfides are not important for the pH‐decrease. Cu, Ni, and Zn are first released between pH 7 and 6 (mainly Zn) and a second time at pH values below 5 (mainly Cu). Pb is significantly released at pH values below 5, Cr only at pH < 4. Mainly metals, alloys, and the rims of glas are destroyed by leaching. Phases like metal hydroxides (mainly Fe‐phases) or amorphous, water bearing Fe‐Al‐Si‐oxides are finally formed. Long‐term leaching by acetic fluids increases the total availability of heavy metals (except Cr) with increasing time. Kinetic effects including changing of metal binding forms seem to be responsible for this development. Within deposit conditions of limited gas exchange (closed system) the pH of the carbonate buffering zone can drop below pH 7 in case of very strong acid input and quickly cause an enhanced metal release. But in reality such a strong acid input is not to be expected. Calcite will buffer between pH 8 and 7 for a long time. Depending on the environmental conditions (water balance, acidity of rain) and landfill design (compaction, permeability, cover, thickness) it can take hundreds till thousands of years until metal release will start. The long‐term metal release of matter with an acid buffer like carbonates can be approximately determined only by short‐term tests with powder (e.g. pH_static tests at pH 4).     

Evaluation of geochemical behavior and heavy metal distribution of sediments：The case study of the Tirumalairajan river estuary,southeast coast of India

The purpose of this study was to assess the chemical partitioning of selected heavy metals(Fe,Mn,Cu,Zn,Pb,Cr,Co and Ni) in 10 surface sediments at Tirumalairajan River Estuary in the southeastern coast of India.A five-step sequential extraction technique was used to assess the environmental status of heavy metals.Most of metals were considered to be immobile due to the high availability in the residual fraction of heavy metals.The sediments of Tirumalairajan River estuary had not been polluted by heavy metals,and they didn’t pose any high ecological risk.The seasonal variations of heavy metals were slightly higher in summer than in monsoon season.Factor analysis was also carned out to understand the associations of metals in different fractions with sand,silt,clay,organic matter,pH,salinity and other metals.The relationship between the Q-mode and R-mode cluster analyses was useful for identifying the pollution levels in both seasons.It was proved that the enrichment of heavy metals was related with geogenic and anthropogenic sources.The information on total metal concentrations in sediments was not sufficient for assessing the metal behavior in the environment,but the sequential extraction technique was more effective in estimating the environmental impact of contaminated sediments.     

Heavy metals mobility in harbour contaminated sediments: the case of Port-en-Bessin

Metallic contaminants associated with sediments showed various behaviours depending on physicochemical conditions. A contaminated sediment core from a harbour in the Bay of Seine was sampled to derive information about metal solubilization from anoxic sediment. In these anaerobic surroundings, physicochemical processes depended on the organic matter cycle, on vertical variation of redox conditions and on precipitation conditions of iron and manganese. In the studied core, anoxic conditions were developed at -15 cm depth. A three-step sequential extraction procedure, modified from the BCR method (now the SM&T), was applied to the anoxic sediment in order to evaluate the potential mobility of fixed metals. Zinc was the most labile metal, recovered in the first extraction stages, and was associated with the non-residual fraction of sediment. Lead was the least labile metal, with up to 70% associated with the residual fraction of the sediment. Copper was associated with organic matter, and its mobility was controlled by the concentration and degradation of the organic fraction. Discharge of organic-rich dredged sediments at sea results in degradation of contained organic matter and may affect the environmental impact of these metals significantly. These results therefore help to improve the waste management of such contaminated sediments.     

Simplification of a Sequential Extraction Scheme To Determine the Mobilisable Heavy Metal Pool in Soils

This investigation had the purpose of evaluating the reliability of a sequential extraction procedure according to Zeien and Brümmer (1989) which is performed routinely to analyse the distribution of heavy metals to different soil phases. Reliability was tested by two hypotheses. According to the first hypothesis an error propagation increased during a morefold extraction of heavy metals from a single soil sample to such an extend that it does not allow a statistical comparison of different analyses. This assumption was confirmed in an interlaboratory study of five participants applying the sequential extraction scheme on two different soils. The heavy metal amounts extracted by the different partners were of the same magnitude, but from the results no statistical correspondence at the 95% confidence level could be observed. The second hypothesis stated that also weak extraction agents were able to release metals from the more immobile soil fractions, especially if the amount of easily soluble metals was comparatively small. To answer this question the sequential extraction was modified by carrying out selected weak extraction steps several times. As expected the intensified extraction conditions caused a decrease of the element content within the more resistant phases. However, the additional release in the first four extraction steps of Pb, Mn, Fe, and Zn was only in the range of 5 to 10%. Furthermore, it was observed that a single EDTA extraction (step four within the sequential extraction scheme) was capable to extract the same amount of metals as the first four extraction steps of the original scheme at a variation of about 15%. From these results it was concluded that the EDTA step alone already represents a reliable pool of mobilisable metals. Thus it can be maintained that such a simple single EDTA extraction can be used to assess the environmental risk from heavy metal contaminated soils or to predict the potential heavy metal release of soil remediation processes.     

Bioavailability of heavy metals in soil of the Tieguanyin tea garden,southeastern China

The bioavailability of 22 heavy metals was investigated at 19 sampling sites in Tieguanyin tea garden in Anxi County,Fujian Province,southeastern China.Heavy metal concentrations were determined by inductively coupled plasma-mass spectrometry(ICP-MS)and evaluated by geo-accumulation index(I_(geo)).Dilute nitric acid extraction was used to evaluate biological activity.Cu,Pb,and Cd were highly bioavailable and most easily absorbed by tea trees.Heavy metal bioavailability in the surface soil was as the ratio of the effective state to the total amount.Cd had the highest I_(geo)values,and the respective samples and sites were classified as moderately/strongly contaminated.Cd element is considered the main factor of heavy metal pollution in the tea garden in Anxi.The other heavy metals studied were present in lower concentrations;thus,the samples were classified as uncontaminated or slightly contaminated.     

Speciation of heavy metals on suspended sediment under high flow conditions in the River Aire,West Yorkshire,UK

Concentrations of heavy metals (Cd, Cu, Pb and Zn) on suspended sediments during a flood event at Thwaite Mills, River Aire, were analysed using a five step sequential extraction technique to determine their major chemical associations (exchangeable, surface oxide and carbonate, Fe and Mn oxides, organic and residual metal ions). Total metal concentrations were lowest at higher discharges, resulting from dilution by clean sediment. The major transport fractions are the Fe and Mn oxides, which carry 29% of the total metals. Knowledge of the chemical forms of heavy metals on suspended sediment is essential for estimating their biological availability and physicochemical reactivity. © 1998 John Wiley & Sons, Ltd.     

Laboratory scale study of an industrial phosphate and thermal treatment for polluted dredged sediments

Dredged sediments are being chemically treated with phosphoric acid on an industrial scale.The effectiveness of the treatment was evaluated by performing the chemical reaction in a tubular reactor, followed by convective drying and maturation of the treated sediment at ambient temperature and finally thermal destruction of the organic matter by calcinations(500℃-900℃).The influence of acid concentration and calcination temperature on the specific surface area of the sediment was investigated. The stabilization of the heavy metals was evaluated by leaching tests and sequential extraction procedures.The phosphoric acid treatment is effective in reducing heavy metal mobility,a prerequisite for recycling the sediments in various construction materials.     

Comprehensive assessment of heavy metal contamination in sediment of the Pearl River Estuary and adjacent shelf

Total metal concentrations (Cr, Ni, Cu, Zn, and Pb), acid volatile sulfide and simultaneously extracted metals (AVS-SEM), and heavy metal fractionation were used to assess the heavy metals contamination status and ecological risk in the sediments of the Pearl River Estuary (PRE) and adjacent shelf. Elevated concentrations at estuarine sites and lower concentrations at adjacent shelf sites are observed, especially for Cu and Zn. Within the PRE, the concentration of heavy metals in the western shore was mostly higher than that in the middle shore. The metals from anthropogenic sources mainly occur in the labile fraction and may be taken up by organisms as the environmental parameters change. A combination of total metal concentrations, metal contamination index and sequential extraction analysis is necessary to get the comprehensive information on the baseline, anthropogenic discharge and bioavailability of heavy metals.     

Column Bioleaching of Arsenic and Heavy Metals from Gold Mine Tailings by Aspergillus fumigatus

A column bioleaching experiment was carried out to compare the effectiveness of the fungus Aspergillus fumigatus to bioleach arsenic (As) and heavy metals from the tailings using two different methods. In the first method, which is named as distribution method (DM), the fungus was distributed in the column by means of vertical and horizontal layers of coarse sand. In the other method, named as surface applied method (SAM), the fungus was cultivated on the surface of the tailings, which was covered with a few centimeters of coarse sand. Results showed that in the DM, oxalic acid production was stimulated and maximum removal of As, Fe, Mn, and Zn was 53, 51, 81, and 62%, respectively. However, Pb removal was low (8%), which might be due to the precipitation of Pb as its oxalates. On the other hand, the maximum removal of As, Fe, Mn, Pb, and Zn were 22, 28, 37, 64, and 34%, respectively, for the SAM. Results of the sequential extraction study showed that the DM was effective in removing the water soluble, exchangeable, carbonate, and Fe/Mn oxide fractions of As, Fe, Mn, and Zn. Our study suggested that A. fumigatus has a potential to be used in remediation of heavy metal contaminated sites. Distributing the fungus throughout the entire tailings columns improved the bioleaching of heavy metals by the fungus.     

Studies of a contaminated brackish marsh in the Hackensack Meadowlands of northeastern New Jersey: an assessment of natural recovery

Eight-Day Swamp is known to be contaminated with heavy metals, especially mercury. Sediment cores were collected to approximately 32 cm at 17 sites on four transects and analyzed at 1 or 2 cm intervals for seven metals and organic matter. Very high metal levels were found throughout the site. Long and Morgan's "effects range-median" (ER-M) was exceeded in more than 50% of slices for all elements except As. Hg had the highest concentration relative to ER-M; median Hg concentration was 72 times its ER-M. On the marsh plain, all metals showed enrichment at 14-20 cm depth of 10-40X over surficial sediments. 137Cs analysis showed sedimentation rates ranging from 0.33 to 0.50 cm yr(-1) over the last approximately 40 yr. These rates indicate that metal contamination peaks occurred in sediments deposited in the early 1960s. Thus, newer, less contaminated sediments are burying older, more contaminated layers and peak levels of contaminants are becoming less available to benthos.     

Untersuchungen zur Abtrennung von Schwermetallen aus Abwasser mit frisch hergestelltem Magnetit Studies for Separation of Heavy Metals from Wastewater with Freshly Precipitated Magnetite

The separation of heavy metals from wastewater may be improved by precipitation/flocculation with iron- or aluminium salts. Often, the resulting products are voluminous, water-containing, amorphous hydroxides which show only limited flocculation properties and may possibly pose problems with the technical separation from the aqueous phase. The application of magnetite could be advantageous because magnetite is ferromagnetic and can be separated very quickly in a magnetic field. First of all, a simple preparation method for magnetite was studied. Pure magnetite could be prepared by mixing an iron(II) salt solution with an equivalent amount of sodium hydroxide at room temperature without oxidation by air. The required reaction time was only 3 hours. For the precipitation of heavy metals from an electroplating wastewater, a better metal elimination and smaller sludge volumes resulted with that artificially produced magnetite in comparison with a precipitation by NaOH. Thereby not only the adsorption of metals was established but also coagulation effects of the magnetite sludge with small metal hydroxide particles. By means of the experimental results. sorption of nickel and chromium was compiled as function of pH and precipitation time. Because freshly precipitated magnetite shows very good sorption and flocculation properties, and pH of precipitation may be lower, its use in high gradient magnetic separation (HGMS) could be more effective for metal elimination than magnetite powder.     

Assessment of heavy metal contamination and mineral magnetic characterization of the Asopos River sediments (Central Greece)

The content and distribution of heavy metals in sediments of the intermittent and contaminated Asopos River, located in Central Greece, was assessed by means of total dissolution, dilute acid and sequential extraction procedures. Mineral magnetic properties were used as proxy parameters of transport mechanisms of land-derived material to the sea. The combination of enrichment factors estimated against local background levels and the levels of labile metals revealed that surface sediments are enriched in Cu, Cd, Ni and Cr. The low flow of the system allows particles and organic matter to accumulate in the estuarine shallow “pools” where they undertake a series of redox reactions, authigenic formation, etc. The most fine of these particles, which are metal rich, are transported to relatively long distances off the Asopos River mouth, even under low energy conditions, converting the system to a secondary source of pollution for the adjacent marine environment.     

Enhancement of Limestone Defluoridation of Water by Acetic and Citric Acids in Fixed Bed Reactor

Limestone defluoridation by fixed bed reactor has been studied with water pre‐acidified with edible organic acids, viz. acetic acid (AA) and citric acid (CA). The study has been carried out by varying acid concentration, contact time (t), number of repeated use of the same limestone bed (n), and chip size of the crushed limestone using fixed fluoride concentration of 10 mg/L in distilled water and groundwater amended to that concentration of fluoride. The presence of both the acids considerably improved the fluoride removal and the removal increased with increase in the acid concentration. Fluoride removal to less than 0.5 and 1.0 mg/L from initial 5 and 10 mg/L, respectively, have been achieved by the method on treatment with single reactor. The mechanism of fluoride removal in the process thought to be the increase in Ca²⁺ activity by dissolution of limestone, which precipitates as CaF₂. XPS analysis reveals that adsorption also contribute to the fluoride removal along with precipitation. The final pH of water remained within acceptable range for drinking water. Initial concentration of fluoride, effects the removal ability of the limestone particles only to some extent. The influence of other anions on fluoride removal process has a little influence which follows the order phosphate > sulfate > bromide > chloride > nitrate.     

Brown algae overproduce cell wall polysaccharides as a protection mechanism against the heavy metal toxicity

Brown algae are often used as heavy metal biomonitors and biosorbents because they can accumulate high concentrations of metals. Cation-exchange performed by cell wall polysaccharides is pointed out as the main chemical mechanism for the metal sequestration. Here, we biochemically investigated if the brown alga Padina gymnospora living in a heavy metal contaminated area would modify their polysaccharidic content. We exposed non-living biomass to Cd and Pb and studied the metals adsorption and localization. We found that raw dried polysaccharides, sulfate groups, uronic acids, fucose, mannose, and galactose were significantly higher in contaminated algae compared with the control ones. Metal concentrations adsorbed by non-living biomass were rising comparatively to the tested concentrations. Electron microscopy showed numerous granules in the cell walls and X-ray microanalysis revealed Cd as the main element. We concluded that P. gymnospora overproduces cell wall polysaccharides when exposed to high metal concentrations as a defense mechanism.     

Accumulation of Metals in Naturally Grown Weeds (Aquatic Macrophytes) Grown on an Industrial Effluent Channel

The ability of seven hyperaccumulator macrophytes which grow naturally in the heavy metal contaminated channels of three different industries (Hindustan Aeronautical Ltd., Eveready Ltd., and Scooter India Ltd.) to accumulate heavy metals was recorded. All these industries use electroplating processes in their manufacturing and are located in the inner area of Lucknow City, U.P., India. Of the three industries monitored, effluent released from Eveready Ltd. contained the highest concentration of heavy metals. In general, accumulations of heavy metals depend upon the plant species and the metal concentration in the media. All plant samples showed heterogeneous metal accumulations, except for Fe or Cd. It was observed that some plant species accumulated high level of metals, e. g., Eichhornnia crassipes for Fe (4052.44 μg/g), Mn (788.42 μg/g), and Cu (315.50 μg/g), and Spirodela polyrhiza for Cd (12.75 μg/g), Pb (20.25 μg/g), and Cr (128.27 μg/g), even when the metal concentrations were not high in the effluent. In summary, these two plants were found to be the best accumulators at each contaminated site. The results will be helpful in the selection of plant species which can be used as bioaccumulators or bioindicators.     

Preparative isolation and characterization of heavy metal complexes from acid mine drainage and surface wastewater

A preparative method was developed to sample dissolved organic carbon (DOC) and heavy metals (Ni, Mn) from polluted surface waters. Main focus was set on the preparative production of freeze‐dried samples mainly composed of organic ligands from heavy metal complexes. First characterizations were done in the aqueous phase. Finally, freeze‐dried samples provide stable organic matter for multiple characterizations. Acid mine drainage of the former mining area of Ronneburg (Germany) hold elevated concentrations of heavy metals and low concentrations of DOC. Municipal wastewater, passing the spoil pile, held elevated concentrations of DOC and low concentrations of heavy metals. Dissolved components smaller than 0.45 μm and larger than 1 nm were concentrated by nanofiltration. Organic heavy metal complexes were isolated from this solution by size‐exclusion chromatography (SEC). Different size classes of molecules were collected from the column effluent, depending on their elution time, and were characterized by UV spectroscopy, ICP‐OES, and DOC measurements. All samples held organic heavy metal compounds with different retention times. The organic heavy metal complexes in acid mine drainage had higher retention times than complexes from municipal wastewater. Most interestingly, we found different affinities of heavy metals to different size classes of DOC. This affinity of the heavy metals differs with size and origin of the DOC.     

Equilibrium approaches to natural water systems—Part 4

The contribution of organic bases to the alkalinity of the anoxic hypolimnetic water of a small lake has been studied. By means of potentiometric titrations the presence of a protolyte, best described as a one-protonic acid (HL) could be shown. The pka of HL was found to be 4.24±0.08 (3σ) and it reached a concentration of 0.4 mM close to the sediment surface. Because of precipitation reactions titration experiments could not be performed above pH≈6.8, but indications of additional bases having a pka >8were found. The results indicate the presence of low molecular weight carboxylic acids and free amino acids originating from bacterial decomposition of organic material. Polarographically measured Fe²⁺ concentrations, in situ pH measurements and various model ligands were used to assess the metal speciation in the hypolimnion. Although strong metal complexing agents such as citrate and glutamine may be present, the total concentrations of both Fe²⁺ (up to 0.6 mM) and ligands are too low to bind more than at maximum 20% of the ferrous iron.     

藻类对重金属的耐性与解毒机理

重金属是一类具有潜在危害的重要污染物,越来越多的重金属被排入水体,对水生生态环境构成严重威胁.藻类在长期响应重金属胁迫过程中,建立起一系列的适应机制.藻类通过控制重金属的吸收、富集、转运与解毒,使不同细胞组分中的重金属维持在正常浓度范围内.这些保护机制主要包括藻细胞的某些胞外组分与重金属结合,从而减少重金属进入胞内;在重金属诱导下藻细胞可合成金属结合蛋白或多肽;重金属诱导藻细胞合成一些代谢物使其免受伤害或修复由重金属胁迫造成的损伤;藻细胞通过液泡区室化作用使重金属远离代谢;藻细胞对重金属具有排斥与排出作用.