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Nymphodora Papassiopi Katerina Vaxevanidou Ioannis Paspaliaris 《Minerals Engineering》2010,23(1):25-31
Current study investigates the possibility of obtaining the removal of iron from bauxite ores, by exploiting the metabolism of iron reducing microorganisms. The experiments were carried out using the microorganism Desulfuromonas palmitatis. The effectiveness of the treatment was evaluated on six different bauxite samples, containing the alumina oxide in the form of diaspore or boehmite. The Fe2O3 content of the samples varied between 16.3% and 22.3% and occurred mainly in the form of goethite or hematite, with one sample containing also chamosite. For comparison reasons the same treatment was also applied on three samples of synthetic Fe(III)-oxides, namely ferrihydrite, goethite and hematite. The removal of iron from the six bauxite samples was found to vary between 7% and 29% and the highest extraction corresponded to the sample containing the Fe(II) rich compound, chamosite. The bioavailability of Fe in the three synthetic oxides was highly dependant on their crystallinity. The amorphous ferrihydrite was almost completely dissolved, up to 95%, whereas dissolution of crystalline goethite and hematite did not exceed 9% and 1.2% respectively. 相似文献
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Removal of contaminant metals from fine grained soils, using agglomeration, chloride solutions and pile leaching techniques 总被引:1,自引:0,他引:1
A leaching process based on the use of a HCl-CaCl2 solution, with total chloride concentration 4M, was investigated for the removal of contaminant metals from fine acidic soils. The possibility to apply this treatment on piles constructed on-site was also examined as a low cost treatment option. The soil sample used in the study was fine in texture, i.e. clay loam, acidic (pH 5.6), and contaminated mainly with Pb, up to 16000mg Pb/kg dry soil, due to past mining activities. The experimental work comprised all the treatment stages, including agglomeration of fine soil particles to increase the permeability of soil, leaching of the agglomerated soil in a laboratory column, removal of metals from the leachate, regeneration and recycling of the leaching solution and final washing of the treated soil. The initial agglomeration treatment resulted in the formation of coarse aggregates and the percolation of leaching solution through the soil column was maintained at high levels, i.e.75ml/cm(2) per day, during the whole treatment. A low amount of HCl acid was required for the removal contaminants from this particular soil, i.e. 0.44mol HCl/kg soil, due to the absence of acid consuming minerals. The extractions achieved were 94% for Pb, 78% for Zn and more than 70% for Cd. The co-dissolution of soil matrix was very limited, with a total weight loss about 3.5%. The final pH of the soil after washing was found to be 5.15, i.e. slightly lower compared to the initial pH of the soil. The results of this study indicate that chloride leaching, in combination with agglomeration and pile leaching techniques, can be a cost effective option for the removal of metal contaminants from fine acidic soils. 相似文献
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Assessment of chromium biostabilization in contaminated soils using standard leaching and sequential extraction techniques 总被引:1,自引:0,他引:1
Papassiopi N Kontoyianni A Vaxevanidou K Xenidis A 《The Science of the total environment》2009,407(2):925-209
The iron reducing microorganism Desulfuromonas palmitatis was evaluated as potential biostabilization agent for the remediation of chromate contaminated soils. D. palmitatis were used for the treatment of soil samples artificially contaminated with Cr(VI) at two levels, i.e. 200 and 500 mg kg− 1. The efficiency of the treatment was evaluated by applying several standard extraction techniques on the soil samples before and after treatment, such as the EN12457 standard leaching test, the US EPA 3060A alkaline digestion method and the BCR sequential extraction procedure. The water soluble chromium as evaluated with the EN leaching test, was found to decrease after the biostabilization treatment from 13 to less than 0.5 mg kg− 1 and from 120 to 5.6 mg kg− 1 for the soil samples contaminated with 200 and 500 mg Cr(VI) per kg soil respectively. The BCR sequential extraction scheme, although not providing accurate estimates about the initial chromium speciation in contaminated soils, proved to be a useful tool for monitoring the relative changes in element partitioning, as a consequence of the stabilization treatment. After bioreduction, the percentage of chromium retained in the two least soluble BCR fractions, i.e. the “oxidizable” and “residual” fractions, increased from 54 and 73% to more than 96% in both soils. 相似文献
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Dimitrios Filippou Nikolaos Katiforis Nymphodora Papassiopi Katerina Adam 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1999,74(4):322-328
High‐quality magnesium hydroxide powders can be produced by hydrating slow‐reacting magnesia in dilute magnesium acetate solutions. The kinetics of this process are very crucial for process design and control, and for the production of a powder with desirable particle morphology. In this work, industrial heavily‐burned magnesia powders were hydrated in 0.01–0.1 mol dm−3 magnesium acetate solutions at temperatures ranging between 333 and 363 K. Examination of the magnesium hydroxide produced and the analysis of the kinetic data suggest that the hydration of heavily burned magnesia in magnesium acetate solutions is a dissolution–precipitation process controlled by the dissolution of magnesia particles. The activation energy was estimated to be 60 kJ mol−1, while the reaction order with respect to acetate concentration was found to be about one. © 1999 Society of Chemical Industry 相似文献
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C. T. Kiranoudis N. G. Voros T. Kritikos Z. B. Maroulis D. Marinoskouris N. Papassiopi O. Dimitropoulou I. Paspaliaris A. Kontopoulos 《Metallurgical and Materials Transactions B》1997,28(5):785-793
The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of the Bayer process flowsheet. It consists of the digestor/flash section as well
as the precipitation and washing circuits. Advanced hydrometallurgical process models for the specific unit operations involved
were developed and are appropriately described. The simulation studies mainly focus on studying the overall effects of certain
design parameters on the entire plant efficiency. The overall performance of the bauxite digestion section is greatly and
positively affected by the free-soda concentration of the feed liquor, the corresponding concentration of solid particles,
and the operation temperature of the circuit. Precipitation of alumina in crystallizers is greatly affected by the corresponding
soda concentration of the washing unit product stream, indicating the importance of this section. Furthermore, ambient temperature
is important to the precipitation kinetics, influencing negatively the quantitative precipitation but resulting in particle
populations of higher mean diameter. 相似文献
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C. T. Kiranoudis N. G. Voros T. Kritikos Z. B. Maroulis D. Marinoskouris N. Papassiopi O. Dimitropoulou I. Paspaliaris A. Kontopoulos 《Metallurgical and Materials Transactions B》1997,28(5):795-804
The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of sulfuric acid pressure leaching of laterite ores for the extraction of nickel
and cobalt, and aqueous pressure oxidation of pyrites for the recovery of gold. Advanced hydrometallurgical process models
for the specific unit operations involved were developed and are appropriately described. The simulation mainly focuses on
studying the overall effects of certain design parameters on the entire plant efficiency. In the case of pyrites, the autothermal
performance of the pressure autoclaves can be maintained by means of the oxidized recycle stream that greatly influences the
fundamental heat balances of the reactor. Flashing the reactor pulp at the exit of the autoclaves results in further precipitation
of solids related to ionic equilibrium reactions. The effect of grinding is important since most reactions are facilitated
by small particle diameters. The ratio of feed pyrites influences the amount of precipitation of solids in the autoclave. 相似文献
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Evaluation of monobasic calcium phosphate for the immobilization of heavy metals in contaminated soils from Lavrion 总被引:18,自引:0,他引:18
The objective of this work was to evaluate the efficiency of monobasic calcium phosphate for the stabilization of heavy metals in contaminated soils. The treatment was applied on a soil sample from the Lavrion mining area, Greece, heavily contaminated with Pb, Zn, Cd and As and characterized as toxic in respect to Pb according to the US EPA toxicity characteristics leaching procedure (TCLP). The efficiency of stabilization was evaluated based on two criteria: (a) the reduction of metals mobility below the TCLP regulatory limits; (b) the reduction of phytoaccumulation. Phytoaccumulation was evaluated both indirectly by applying leaching tests using EDTA, DTPA and NaHCO(3) solutions and directly by carrying out pot experiments with Phaseolus vulgaris as plant indicator. This treatment was found to immobilize Pb and Cd, whereas As and Zn were slightly mobilized. No effect on phytoaccumulation was observed. Moreover, the treatment had a negative effect on plants growth, which was combined with a strong deficiency of Ca in the tissue of leaves. 相似文献
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