Selective chemical extraction of carbonate-associated metals from recent lacustrine sediments

Acidic ion-exchanger was applied to the selective extraction of heavy metals in carbonate phases of recent lake sediments. Cr was not detected and Fe and Cu contents were reduced by factors of three to ten, relative to non-carbonate fractions of the sediment samples. Values obtained for Mn and Zn exemplify the effects of dilution was well as enrichment, both originating from increased carbonate percentages. Determinations on grain-sized fractions from Bodensee samples suggest that elevated inputs of dissolved Zn, which partly originate from human activities, may be immobilized by authigenic carbonate precipitation.     

Laboratory chalcopyrite oxidation by Acidithiobacillus ferrooxidans: Oxygen and sulfur isotope fractionation

Laboratory experiments were conducted to simulate chalcopyrite oxidation under anaerobic and aerobic conditions in the absence or presence of the bacterium Acidithiobacillus ferrooxidans. Experiments were carried out with 3 different oxygen isotope values of water (δ¹⁸O_H2O) so that approach to equilibrium or steady-state isotope fractionation for different starting conditions could be evaluated. The contribution of dissolved O₂ and water-derived oxygen to dissolved sulfate formed by chalcopyrite oxidation was unambiguously resolved during the aerobic experiments. Aerobic oxidation of chalcopyrite showed 93 ± 1% incorporation of water oxygen into the resulting sulfate during the biological experiments. Anaerobic experiments showed similar percentages of water oxygen incorporation into sulfate, but were more variable. The experiments also allowed determination of sulfate–water oxygen isotope fractionation, ε¹⁸O_SO4–H2O, of ~ 3.8‰ for the anaerobic experiments. Aerobic oxidation produced apparent ε_SO4–H2O values (6.4‰) higher than the anaerobic experiments, possibly due to additional incorporation of dissolved O₂ into sulfate. δ³⁴S_SO4 values are ~ 4‰ lower than the parent sulfide mineral during anaerobic oxidation of chalcopyrite, with no significant difference between abiotic and biological processes. For the aerobic experiments, a small depletion in δ³⁴S_SO4 of ~? 1.5 ± 0.2‰ was observed for the biological experiments. Fewer solids precipitated during oxidation under aerobic conditions than under anaerobic conditions, which may account for the observed differences in sulfur isotope fractionation under these contrasting conditions.     

Effect of oxidation potential and zinc sulphate on the separation of chalcopyrite from pyrite

The effects of oxidation potential (Eh) and zinc sulphate on the separation of chalcopyrite from pyrite were investigated at pH 9.0. The flotation recovery of these minerals is Eh dependent with maximum separation obtained at 275 mV SHE. Zinc sulphate addition improved this mineral separation at an Eh value of 275 mV by selectively depressing pyrite flotation. A different result was obtained at lower Eh values where zinc sulphate addition improved chalcopyrite flotation but had no or little effect on pyrite flotation. These opposite effects of zinc sulphate on mineral flotation were reconciled by examining the surface species of these minerals. The selective depression of pyrite flotation by zinc sulphate was also confirmed in the flotation of two copper ores.     

Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: Environmental implications

Total concentrations of chemical elements in soils may not be enough to understand the mobility and bioavailability of the elements. It is important to characterise the degree of association of chemical elements in different physical and chemical phases of soil. Another geochemical characterisation methodology is to apply sequential selective chemical extraction techniques. A seven-step sequential extraction procedure was used to investigate the mobility and retention behaviour of Al, Fe, Mn, Cu, Zn, Pb, Cr, Co, Ni, Mo, Cd, Bi, Sn, W, Ag, As and U in specific physical–chemical and mineral phases in mine tailings and soils in the surroundings of the abandoned Ervedosa mine. The soil geochemical data show anomalies associated with mineralised veins or influenced by mining. Beyond the tailings, the highest recorded concentrations for most elements are in soils situated in mineralised areas or under the influence of tailings. The application of principal components analysis allowed recognition of (a) element associations according to their geochemical behaviour and (b) distinction between samples representing local geochemical background and samples representing contamination. Some metal cations (Mn, Cd, Cu, Zn, Co, Cr, Ni) showed important enrichment in the most mobilisable and bioavailable (i.e., water-soluble and exchangeable) fractions due likely to the acidic conditions in the area. In contrast, oxy-anions such as Mo and As showed lower mobility because of adsorption to Fe oxy-hydroxides. The residual fraction comprised largest proportions of Sn and Al and to a lesser extent Zn, Pb, Ni, Cr, Bi, W, and Ag, which are also present at low concentrations in the bioavailable fractions. The elements in secondary mineral phases (mainly Fe, Mn, Cu, Zn, Cd, Pb, W, Bi, Mo, Cr, Ni, Co, As and U) as well as in organic matter and sulphides are temporarily withheld, suggesting that they may be released to the environment by changes in physico-chemical conditions.     

ToF-SIMS and SEM study on the preferential oxidation of chalcopyrite

Chalcopyrite is known to be slow reacting mineral in hydrometallurgical systems and is considered one of the most inert sulphide minerals with respect to leaching. Such character of chalcopyrite seems to be linked to a formation of a passive layer on its surface. This work reports that freshly fractured chalcopyrite surfaces exhibit highly selective reactivity depending on the exposed fracture planes. ToF-SIMS was used to qualitatively characterize various fracture planes in freshly fractured chalcopyrite particles, prior to and after hydrometallurgical treatment. It was found that, prior to treatment, certain areas exhibited pronounced contamination from atmospheric hydrocarbons; whereas, others were highly unreactive and remarkably free from adventitious hydrocarbon contamination. The positive ion spectra recorded from these areas were found to be dominated by peaks from Fe- and Cu-elements and related compounds. The negative ion spectra for the reactive areas on the other hand showed a high content of oxidized (sulphur) species.The differences between the areas of low and high reactivity, as detected after leaching, were more subtle than prior to leaching; whereas, SEM analysis showed clear evidence for selective attack of ferric sulphate to specific planes. Furthermore, it was shown that, when chalcopyrite is in intimate contact with pyrite, it experiences an enhanced oxidation compared to when there is no electric contact with pyrite.Attempts were made to explain the preferential oxidation observed based on the different chemistry of the fracture surfaces.     

Physical protection of lignin by organic matter and clay minerals from chemical oxidation

The role of organic matter (OM) concentration, structure and composition and how these relate to mineral protection is important for the understanding of long term soil OM dynamics. Various OM–clay complexes were constructed by sequential sorption of lignin and dodecanoic acid to montmorillonite. Humic acid–montmorillonite complexes were prepared at pH 4 and 7 to vary OM conformation prior to sorption. Results obtained with constructed OM–clay complexes were tested with isolated mineral fractions from two soils. Oxidation with an acidic NaClO₂ solution was used to chemically oxidize lignin in the OM–clay complexes, sand-, silt- and clay-size soil fractions to test whether or not it can be protected from chemical attack. Gas chromatography–mass spectrometry was used to analyze lignin-derived phenols, cutin OH–acid (after CuO oxidation), fatty acid and n-alkanol concentrations and composition. We found that carbon content was not solely responsible for lignin stability against chemical oxidation. Lignin was protected from chemical oxidation through coating with dodecanoic acid and sorption of humic acid to clay minerals in a stretched conformation at pH 7. Therefore, interactions between OM constituents as well as OM conformation are important factors that protect lignin from chemical oxidation. Lignin-derived phenol dimers in the Grassland-Forest Transition soil fractions were protected from chemical oxidation to a greater extent compared to those in Grassland soil fractions. Therefore, although lignin was protected from degradation through mineral association, the extent of this protection was also related to OM content and the specific stability of lignin components.     

Experimental replacement of chalcopyrite by bornite: Textural and chemical changes during a solid-state process

Chalcopyrite was reacted with covellite and with chalcocite, respectively, between 200°C and 500°C. The ensuing solid-state replacement of chalcopyrite by bornite was studied both texturally and chemically. The relatively oxidizing conditions of the reaction chalcopyrite+covellite result in massive replacement, lacking structural control, where bornite and pyrite form complex intergrowth textures in chalcopyrite. Bornite nucleates around growing pyrite aggregates because of the release of copper and a decrease in volume. Diffusion of sulphur along grain boundaries and fractures largely controls the textural development. Reaction under the relatively reducing conditions involving chalcopyrite+chalcocite results in replacement of chalcopyrite in the sequence where chalcopyrite is replaced by bornite, below about 355°C, and by intermediate solid solution (ISS) and later bornite, above 355°C. The textural development, changing from replacement, apparently uninfluenced by directional properties in the host, to semioriented replacement, is structurally controlled. This suggests that the process is governed by diffusion of copper and iron through a sulphur framework. It is suggested that the observed formation of oriented bornite lamellae in chalcopyrite and in ISS during the chalcopyrite+chalcocite reaction may be explained by replacement exsolution at constant temperature.     

Selective separation of pyrite from chalcopyrite and arsenopyrite by biomodulation using Acidithiobacillus ferrooxidans

This paper discusses the selective depression of pyrite from chalcopyrite and arsenopyrite by biomodulation using Acidithiobacillus ferrooxidans under natural conditions of pH. The effect of bacteria–mineral interaction on the surface charge of mineral and bacterial cell was studied by microelectrophoresis. Adhesion experiments were conducted to establish the relationship between cell adhesion to specific minerals and the electrokinetic behaviour of the minerals subsequent to interaction with cells. Effect of bacterial interaction on the xanthate-induced flotation of all the minerals was assessed. Adhesion of A. ferrooxidans on pyrite was rapid and tenacious and subsequent to interaction with cells, pyrite remained hydrophilic even in presence of xanthate collector. The collector, on the other hand, was able to render good flotability to chalcopyrite even after interaction with bacterial cells. Copper activated arsenopyrite was able to retain its hydrophobicity in presence of cells due to poor attachment kinetics of cells to the mineral surface. Thus, by suitably conditioning with the cells and collector, it was possible to effectively depress pyrite from chalcopyrite and arsenopyrite.     

A comparison between heavy metals released from soil and its efficient speciation extracted by sequential extraction procedure

A simulating experiment was carried out on the interaction between natural precipitation and soil. The results demonstrated that the contents of heavy metals （V, Co, Cr, and Ni） released from soil into the solution under Earth＇s surface conditions are higher than the contents of those metals bonded to exchangeable species, which were extracted by sequential extraction procedure recommended by Tessier and others in 1979. It is demonstrated that the metals bonded to other 3 species （carbonate, Fe-Mn oxide, and organic matter） except those bonded to the exchangeable species in efficient speciation can be released under the Earth＇s surface conditions, when pH=4 in the reaction system, and the higher correlation coefficient indicated that the concentrations of heavy metals released from soil into the solution vary approximately with reaction time in terms of index regulations.     

Oxidation of chalcopyrite by extended milling

Chalcopyrite has been milled for up to 50 h in oxygen, air and argon atmospheres using a laboratory ball mill. No phase changes were evident in argon but the XRD peaks were weaker and broader indicating crystalline refinement. In oxygen, even after 1 h milling peaks for CuSO₄·5H₂O were present and these became predominant after 20 h milling where the chalcopyrite peaks were absent. In air, partial oxidation to CuSO₄·5H₂O was evident after 50 h. Leaching of the resultant powders with water showed 80% dissolution after 50 h milling in oxygen, significantly greater than the 20% and 6% dissolution after milling for 50 h in air and argon respectively. Solution analyses showed the Cu/Fe ratio increased with milling time in oxygen suggesting selectivity may be possible. The insoluble residue was found to consist of haematite, elemental sulphur and unreacted chalcopyrite.     

Sulfide oxidation in brown coal overburden and chemical modeling of reactions in aquifers influenced by sulfide oxidation

With a mean annual flow of 5.9×10¹¹m³yr^–1 and sediment load of 1600x10¹²gyr^–1 the Ganges river ranks second and third, respectively, in terms of water flow and sediment load among the world's rivers. Considering the enormous sediment transport by Ganges to the Bay of Bengal, a study was conducted on the size distribution and mineral characteristics of the suspended sediments of the Ganges river and is reported here. Most of the sediment load has a size range between <4–5.75 ). The sediments are mostly medium to coarse silt and are poorly sorted. Mica dominates among the clay minerals, followed by chlorite, vermiculite, kaolinite, and smectite. Due to differences in geology, smectite becomes a major clay mineral in downstream rivers. At Calcutta, the clay mineral transport in millions of tons per year is 18,464, 8000, and 2147, for mica, smectite, and chlorite, respectively.     

氧化亚铁硫杆菌促进金川铜镍硫化矿尾矿砂提取有价金属实验研究

金川铜镍硫化矿尾矿砂数量巨大,其中Ni、Cu和Co等有价金属种类较多,含量较为丰富,蕴含着巨大的经济价值。本文研究了氧化亚铁硫杆菌对金川铜镍尾矿砂提取有价金属效果的影响,在选取金川新尾矿库中心钻孔尾矿砂样品与氧化亚铁硫杆菌作用不同时间的基础上进行化学酸溶,利用电感耦合等离子体发射光谱仪(ICP-AES)分析了溶液中Cu²⁺、Ni²⁺、Co²⁺含量,并通过离子浸出率来表征微生物对尾矿中有价金属提取的影响效果。结果表明,尾矿砂直接化学酸溶后Cu²⁺、Ni²⁺浸出率分别为73.78%和69.87%,Co²⁺浸出率仅为39.57%;而氧化亚铁硫杆菌先与尾矿砂作用后再进行硫酸酸溶,其Cu²⁺、Ni²⁺总浸出率均可达到90%以上,Co²⁺总浸出率也可达到70%以上。实验结果证明氧化亚铁硫杆菌的参与促进了尾矿砂中Cu²⁺、Ni²⁺、Co²⁺的浸出。     

Evaluation of trace element availability from secondary metallurgical slag generated in steelmaking by sequential chemical extraction

During carbon steel manufacture, slag residues are generated to remove material impurities from liquid metal and thus control the quality of carbon steel. As the utilization of secondary metallurgical slags is not as efficient as those of primary slags, a comprehensive characterization of steel ladle slag was performed. Pseudo-total concentrations of a wide range of elements were determined during a 6-week sampling period with relevant physical and chemical properties, sequential extraction of trace elements, and parallel mineralogical characterization of extraction residues from a representative combined sample. According to the results, only Cr and V occurred in elevated concentrations with respective 6-week mean values of 198 and 310 mg kg^?1 (d.w.). The residual standard deviation of the weekly pseudo-total concentration values of the aforementioned elements (24 and 31 %, respectively) indicated that significant variation in the concentration of trace elements can occur due to fluctuation in process conditions and/or slag characteristics. The sequential extraction procedure suggested potential phytoavailability of V (123 mg kg^?1, d.w., amounting to 41 % of the respective pseudo-total concentration) through, e.g., changes in prevailing redox conditions. Although the analytical approach was validated by the analysis of a certified reference material and the calculation of extraction recoveries, the mineralogical characterization of parallel extraction residues indicated non-selectivity of the procedure coupled with potential redistribution phenomena during extraction with hydrogen peroxide and ammonium acetate.     

Copper oxidation state in chalcopyrite: Mixed Cu d and d characteristics

The determination of the oxidation states of copper and iron in sulfides, and chalcopyrite (CuFeS₂) in particular, using 2p X-ray photoemission spectroscopy (XPS) and L_2,3-edge X-ray absorption spectroscopy (XAS) is revisited. Reassessment of the published spectra derived by these methods produces consistent results and reveals the ‘d count’ in the copper compounds to be intermediate between d⁹ and d¹⁰. Nevertheless, these covalent copper compounds can be divided into those nominally monovalent and those nominally divalent. The Fe L_2,3-edge XAS of chalcopyrite, along with Mössbauer data, confirm the presence of high-spin Fe³⁺. Chalcopyrite, despite recent published reports to the contrary, clearly belongs to the monovalent copper class.     

金川铜镍硫化物精矿中有价金属分离实验研究

本文以金川铜镍硫化物精矿为研究对象,对比研究了A.f.菌浸出与硫酸酸溶浸出对铜镍硫化物精矿中有价金属Co、Ni和Cu的提取效果。为了进一步优化硫化物精矿中有价金属Co、Ni和Cu浸出效果,考察了微生物-硫酸浸出与硫酸-微生物浸出对精矿中Co、Ni和Cu提取的影响。结果表明:Co2+、Ni2+、Cu2+微生物-硫酸浸出率可分别达到85.05%、98.32%和95.31%。微生物-硫酸浸出加速了硫化物矿物的溶解,促进了硫化物矿物中有价金属Co、Ni、Cu的浸出,大大提高了有价金属Co2+、Ni2+、Cu2+的浸出率。     

Speciation and solubility of heavy metals in contaminated soil using X-ray microfluorescence, EXAFS spectroscopy, chemical extraction, and thermodynamic modeling

Synchrotron-based X-ray radiation microfluorescence (μ-SXRF) and micro-focused and powder extended X-ray absorption fine structure (EXAFS) spectroscopy measurements, combined with desorption experiments and thermodynamic calculations, were used to evaluate the solubility of metal contaminants (Zn, Cu, Pb) and determine the nature and fractional amount of Zn species in a near-neutral pH (6.5-7.0) truck-farming soil contaminated by sewage irrigation for one hundred years. Zn is the most abundant metal contaminant in the soil (1103 mg/kg), followed by Pb (535 mg/kg) and Cu (290 mg/kg). The extractability of Zn, Pb, and Cu with citrate, S,S-ethylenediaminedisuccinic acid (EDDS), and ethylenediaminetetraacetic acid (EDTA) was measured as a function of time (24 h, 72 h, 144 h), and also as a function of the number of applications of the chelant (5 applications each with 24 h of contact time). Fifty-three percent of the Zn was extracted after 144 h with citrate, 51% with EDDS and 46% with EDTA, compared to 69, 87, and 61% for Cu, and 24, 40, and 34% for Pb. Renewing the extracting solution removed more of the metals. Seventy-nine, 65, and 57% of the Zn was removed after five cycles with citrate, EDDS and EDTA, respectively, compared to 88, 100, and 72% for Cu, and 91, 65, and 47% for Pb. Application to the untreated soil of μ-SXRF, laterally resolved μ-EXAFS combined with principal component analysis, and bulk averaging powder EXAFS with linear least-squares combination fit of the data, identified five Zn species: Zn-sorbed ferrihydrite, Zn phosphate, Zn-containing trioctahedral phyllosilicate (modeled by the Zn kerolite, Si₄(Mg_1.65Zn_1.35)O₁₀(OH)₂ · nH₂O), willemite (Zn₂SiO₄), and gahnite (ZnAl₂O₄), in proportions of ∼30, 28, 24, 11, and less than 10%, respectively (precision: 10% of total Zn). In contrast to Cu and Pb, the same fractional amount of Zn was extracted after 24 h contact time with the three chelants (40-43% of the initial content), suggesting that one of the three predominant Zn species was highly soluble under the extraction conditions. Comparison of EXAFS data before and after chemical treatment revealed that the Zn phosphate component was entirely and selectively dissolved in the first 24 h of contact time. Preferential dissolution of the Zn phosphate component is supported by thermodynamic calculations. Despite the long-term contamination of this soil, about 79% of Zn, 91% of Pb, and 100% of Cu can be solubilized in the laboratory on a time scale of a few days by chemical complexants. According to metal speciation results and thermodynamic calculations, the lower extraction level measured for Zn is due to the Zn phyllosilicate component, which is less soluble than Zn phosphate and Zn ferrihydrite.     

Origin and chemical partitioning of heavy metals in riverbed sediments

In the present investigation, bulk and chemical partitioning of elements in the Shefa-Rud riverbed sediments are studies. Higher concentrations of elemental concentrations have been observed in estuarine zone when compared with riverine sediments (except for AI, Fe, Pb and Mn). Manganese is mobilized under anoxic conditions prevailing in the Caspian Sea. Lithogenous materials are greatly diluted in the estuarine zone by various pollutants present in the Caspian Sea. Organic metallic bonds are not significantly present in the area of study. Geological units of the area of study have resulted in the lower concentrations of elemental concentrations of riverbed sediments when compared with published values for mean crust and world sediments ones. Though, cluster analysis has clearly shown the importance of alumina-silicates in controlling the distribution of Fe and Mn in riverbed sediments but it could not depict controlling mechanism for other studied elements. Geochemical Index (Igeo) and Enrichment Factor (EF) values are indicative of a clean environment throughout the river course. These values are in a well agreement with results of chemical partitioning data. Quantification of EF values is not logically possible and therefore Igeo values can be used more effectively.     

The geochemical role of phyto- and zooplankton in the extraction of chemical elements from water

This paper provides for the first time comparative assessment of the contents of 70 chemical elements occurring in the aquatic environment in water, phytoplankton, and zooplankton. The assessment was made using modern highly sensitive methods. The studies were performed at Beloyarskoe Reservoir, a manmade freshwater lake situated in the Middle Urals that has been studied in detail. The chemical elements were ranked in groups differing in the accumulation coefficient (AC) values for the phyto- and zooplankton. The comparison revealed that for the vast majority of chemical elements, the AC values were higher in zooplankton (53, or 76%) than in phytoplankton (17, or 24%). The average AC values for zooplankton (∼740 000) exceeded that for phytoplankton (∼68 000) by more than 10 times. It was found that some elements had very high AC values in zooplankton compared to phytoplankton. For instance for Nb, the ratio AC_zoo/AC_phyto was 1 200 000; for B, Ta, Sn, Lu, U, 300 000–500 000; for Sb and Y, 100 000–130 000; for La and Nd, 80 000–85 000; for Mo, Cd, Pr, Gd, Dy, Sc, Se, Bi, 20 000–30 000; and for Pd, Hf, Sm, Sb, Er, As, 10 000–20 000. It is concluded that zooplankton is sometimes more suitable for the biogeochemical indication of the pollution of natural water bodies, because the AC values for most elements are much higher in zooplankton than in phytoplankton and the total plankton. Considering the high assimilability of microelements and radionuclides, the plankton may serve not only as an indication but also as the mean of regulated purification of waterbodies from these elements.     

Collectorless flotation of chalcopyrite and sphalerite ores by using sodium sulfide

The flotation of chalcopyrite and sphalerite from copper and copper-zinc ores has been achieved without using thiol-type collectors. Typically, a sulfide ore sample is first treated with sodium sulfide either during grinding or during the preflotation conditioning period, and then the chalcopyrite is floated with frother alone. With a copper-zinc ore, sphalerite is subsequently floated from the chalcopyrite tailings by activating it with copper sulphate. Results of the collectorless flotation tests are comparable to those obtained by using thiol collectors. The mechanisms of selective collectorless flotation are discussed on the basis of differences in the solubilities of sulfide minerals.     

Correlations between heavy metals and organic carbon extracted by dry oxidation procedure in urban roadside soils

The organic fraction in soils has a significant influence on heavy metal transport. In this study, the organic carbon content was measured by dry oxidation procedure from 21 Xuzhou urban roadside soils to assess the relationships between the concentrations of heavy metals (Pb, Cu, Zn, and Cr) and the amount of organic carbon. The anthropogenic heavy metals (e.g. Pb, Cu, Zn) were strongly correlated with organic carbon (denoted by C_org−c) extracted by dry oxidation while natural heavy metal (e.g. Cr) showed no correlation to the C_org−c. The anthropogenic heavy metals were also strongly correlated with the amount of the total carbon. These results show that the anthropogenic heavy metals are mainly enriched in the organic matter in the Xuzhou urban roadside soils.