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Abstract: Natural dolomite was calcined at 700–900°C under air and an Ar gas flow atmosphere to characterize its sorbency potential for borate. A sequential decarbonation occurred with increase in calcination temperature, that is, transformation of CaMg(CO3)2 to MgO and CaCO3 up to 700°C and CaCO3 to CaO from 700 to 900°C. The surface molar ratio of Ca/Mg decreased from 1.6 to 0.6 by calcination at more than 700°C, owing to the crystal growth of MgO toward the surfaces. MgO crystal growth is responsible for hydration leading to borate co-precipitation. The sorption density of borate was greater with the calcined products at 700°C than 800–900°C and under an Ar gas flow system rather than for static air at the same temperatures. The surface reactivity of the calcined dolomite with borate in the aqueous phase was affected by CO2 emitted in the decarbonation at higher temperatures. [Copyright &y& Elsevier]

Abstract: The surface reactivity of biogenic birnessite is attributed to its structure. However, structural control of heavy metal adsorption on biogenic birnessite is not well understood. Here a poorly-crystalline birnessite was produced by the fungus Paraconiothyrium sp. WL-2 strain under ambient pH and temperature conditions. The structure was characterized by X-ray absorption spectroscopy and X-ray diffraction. Sorption behaviors of Co2+ were compared with Zn2+. The primary product of the Mn bio-oxidation is hexagonal birnessite with a turbostratic structure. XAFS analysis demonstrated that the biogenic birnessite consists of octahedral sheets with Mn(IV) as the central metal and some vacant sites. Mn(III) atoms are coordinated to some of the vacant sites in the interlayer. The adsorption of Co2+ by the biogenic birnessite is higher than Zn2+. The excess adsorption of Co2+ than Zn2+ is nearly the same as the excess release of Mn from the biogenic birnessite. These results strongly suggested that the interlayer Mn(III) can oxidize the adsorbed Co2+ to Co3+, resulting in excess adsorption of Co2+ compared to Zn2+ by biogenic birnessite. [Copyright &y& Elsevier]

Abstract: The effect of calcination temperature during production of magnesium oxide-rich phases from MgCO3 on the sorption of F− ions in the aqueous phase has been investigated. Magnesium oxide-rich phases were formed by calcination at over 873K for 1h. Higher calcination temperatures produced more crystalline MgO with smaller specific surface area and provided larger values of the total basicity per unit surface area. The higher calcination temperatures lead to slower F− removal rate, and lower equilibrium F− concentrations, when the equilibrium F− concentrations are less than 1mmoldm−3. Larger total basicity per unit surface area made the reactivity with F− ions in aqueous phase more feasible, resulting in a greater degree of F− sorption. For equilibrium F− concentrations more than 1mmoldm−3, lower calcination temperatures favored the co-precipitation of F− with Mg(OH)2, probably leading to the formation of Mg(OH)2−x F x , and the achievement of larger sorption density. This is the first paper which describes the relationship between the solid base characteristics obtained by CO2-TPD for MgO with different calcination temperatures as a function of the reactivity of F− sorption in the aqueous phase. [Copyright &y& Elsevier]

Abstract: Chalcopyrite (CuFeS2) occurs sometimes in association with As-bearing copper ores, such as enargite (Cu3AsS4) and tennantite (Cu12As4S13), especially in deep ore bodies. To employ oxidative pretreatment for recovering copper resources from these minerals, it is important to characterize the surface properties of enargite and tennantite as well as chalcopyrite. The minerals were oxidized in 0.013% H2O2 with O2 bubbling at pH 2, 5, and 11 followed by analysis with X-ray photoelectron spectroscopy. Elemental sulfur was formed most significantly at pH 2 in all sulfide mineral samples. Enargite was the most stable under the oxidative conditions. Arsenic in enargite was partly oxidized at pH 5. Substantial proportion of copper in tennantite was oxidized from Cu(I) to Cu(II) at pH 11. The dissolution rate of Cu from tennantite at pH 2 was by far the fastest, and incongruent dissolution of Cu occurred with suppression of As and S in tennantite. These selective differences in the oxidation may be of use in designing a flotation process for separation of these sulfide minerals. [Copyright &y& Elsevier]

Abstract: A TACUB jig was applied to separate waste plastics [polystyrene (PS), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate (PET)] used in copy machine. The effect of water pulsation including amplitude and frequency on the separation performance was investigated for the feeds containing three plastics. Good results were obtained under suitable conditions. Grades of 99.8% PS, 99.3% ABS, and 98.6% PET were recovered as the products in the top, middle and bottom layers, respectively. Based on these results, a processing pilot plant for recycling of plastics from scrapped copy machines was constructed. Two cells of a TACUB jig were used in the plant to separate the plastics containing PS, ABS and PET, where PET was recovered from the first cell as bottom layer product, and ABS and PS from the second cell as bottom and top layer products, respectively. A monitor and control system of the jig operation was developed. High recoveries of PET, ABS, and PS with high grades were achieved, and the Newton''s efficiency of the first cell was 0.99. [Copyright &y& Elsevier]

Copper extraction during the oxidative leaching of chalcopyrite (CuFeS2) by ferric ions or by dissolved oxygen in sulfuric acid solutions is known to be faster at low redox potentials but slower at potentials above a critical value. The present study shows that this phenomenon occurs only when cupric and ferrous ions coexist, based on electrochemical measurements.Using a chalcopyrite electrode prepared from an ore lump sample, effects of the addition of 0.1 kmol m-3 cupric and ferrous ions on anodic polarization curves and AC impedance spectra were investigated in 0.1 kmol m-3 sulfuric acid with stirring at 298 K in nitrogen. Without cupric and/or ferrous ions, the anodic current increased monotonically with increasing applied potential. When cupric and ferrous ions coexisted, active-passive behavior was observed, i.e., the current increased with increasing potential to reach a maximum and it suddenly decreased at a certain potential, whereby the current became less dependent on the potential. In the active region, i.e., at low potentials, the anodic current with coexisting cupric and ferrous ions was larger than that without these ions. These results agree well with the results of leaching experiments reported previously, and indicate that coexisting cupric and ferrous ions promote the anodic dissolution of chalcopyrite at low potentials. The analysis of the AC impedance spectra indicates that a high-resistance passive layer grows on the chalcopyrite surface without cupric and/or ferrous ions, and that coexistence of these ions causes a formation of another product layer and inhibits the passive layer growth in the active region. To interpret the active-passive behavior of chalcopyrite, a reaction model, assuming the formation of intermediate Cu2S in the active region, is discussed based on the experimental results. [Copyright &y& Elsevier]

Chalcopyrite leaching in sulfuric acid solutions depends on the redox potential determined by the concentration ratio of ferric to ferrous ions, and the leaching rate is higher at redox potentials below a critical value. Previously, the authors have proposed a reaction model to interpret this phenomenon. The present study applied the model to interpret the catalytic effect of silver ions on chalcopyrite leaching.The model assumes that at lower potentials, chalcopyrite leaching proceeds in two steps: first, chalcopyrite is reduced by ferrous ions to form Cu2S that is more rapidly leached; next, the intermediate Cu2S is oxidized by ferric and/or dissolved oxygen to release cupric ions. During the chalcopyrite reduction, hydrogen sulfide is released to the liquid phase. Silver ions react with the hydrogen sulfide to form silver sulfide precipitate and decrease the concentration of hydrogen sulfide in the liquid phase, causing a rise in the critical potential of Cu2S formation and broadening of the potential range where rapid copper extraction takes place.To confirm the model, the redox potential dependence of chalcopyrite leaching was investigated in the presence of various concentrations of silver ions with 0.1 kmol m−3 sulfuric acid containing known concentrations of ferrous and ferric ions at 298 K in air. The critical potential increased with increasing concentrations of silver ions. This agrees with the model proposed here but cannot be explained by the conventional model proposed by Miller et al. [Copyright &y& Elsevier]

The extremely acidophilic, Fe(III)-reducing heterotrophic bacterium Acidocella aromatica strain PFBC was tested for its potential utility in bioreduction of highly toxic heavy metal, hexavalent chromium, Cr(VI). During its aerobic growth on fructose at pH 2.5, 20 µM Cr(VI) was readily reduced to Cr(III), achieving the final Cr(VI) concentration of 0.4 µM (0.02 mg/L), meeting the WHO drinking water guideline of 0.05 mg/L. Despite of the highly inhibitory effect of Cr(VI) on cell growth at higher concentrations, especially at low pH, Cr(VI) reduction activity was readily observed in growth-decoupled cell suspensions under micro-aerobic and anaerobic conditions. Strain PFBC was not capable of anaerobic growth via dissimilatory reduction of Cr(VI), such as reported for Fe(III). In the presence of both Cr(VI) and Fe(III) under micro-aerobic condition, microbial Fe(III) reduction occurred only upon complete disappearance of Cr(VI) by its reduction to Cr(III). Following Cr(VI) reduction, the resultant Cr(III), supposedly present in the form of cationic Cr (III) (OH2) 6 (3+) , was partially immobilized on the negatively charged cell surface through biosorption. When Cr(III) was externally provided, rather than microbially produced, it was poorly immobilized on the cell surface. Cr(VI) reducing ability was reported for the first time in Acidocella sp. in this study, and its potential role in biogeochemical cycling of Cr, as well as its possible utility in Cr(VI) bioremediation, in highly acidic environments/solutions, were discussed.