Browsing by Author "Ahmadi, Ali"

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    Conventional and electrochemical bioleaching of chalcopyrite concentrates by moderately thermophilic bacteria at high pulp density
    (Elsevier, 2011) Ahmadi, Ali; Schaffi, Mahine; Petersen, Jochen; Schippers, Axel; Ranjbar, Mohammad  
    Conventional and electrochemical bioleaching were investigated to extract copper from Sarcheshmeh chalcopyrite concentrate at high pulp densities. Experiments were conducted in the presence and absence of a mixed culture of moderately thermophilic iron- and sulphur oxidizing bacteria using a 2-L stirred electro-bioreactor at 20% (w/v) pulp density, an initial pH of 1.4–1.6, a temperature of 50 °C, a stirring rate of 600 rpm and Norris nutrient medium with 0.02% (w/w) yeast extract addition. The results of 10 day leaches showed that, when using electrochemical bioleaching in an ORP range of 400 to 430 mV, copper recovery reaches about 80% which is 3.9, 1.5 and 1.17 times higher than that achieved in abiotic electrochemical leaching, conventional bioleaching, and electrochemical bioleaching at 440–480 mV ORP, respectively. It appears that applying current directly to the slurry optimises both, the biological and chemical subsystems, leading to an increase in both, the dissolution rate and the final recovery of copper from the concentrate. Mineralogical analysis of the solid residues of electrochemical leaching in both, biotic and abiotic media, showed the formation of chalcocite and covellite minerals on the surface of not leached chalcopyrite. It is postulated that the reduction of refractory chalcopyrite to more soluble minerals such as chalcocite and covellite is achieved through both, electron transfer upon electrode contact and by ferrous reduction at the low ORP of the slurry. These secondary minerals are then rapidly dissolved through bioleaching, while at the same time a formation of a passive layer of jarosites is minimised. This process also appears to promote an increased bacteria–solid ratio due to favourable growth conditions.
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    Kinetic modeling of bioleaching of copper sulfide concentrates in conventional and electrochemically controlled systems
    (Elsevier, 2012) Ahmadi, Ali; Ranjbar, Mohammad; Schaffie, Mahin; Petersen, Jochen
    In this paper a model of conventional and electrochemical bioleaching of high grade complex copper sulfide ores or flotation concentrates in isothermal stirred tank reactors is presented and compared to experimental data. Experiments were conducted in an electrobioreactor using a mixed culture of moderate thermophile microorganisms at pulp density 20% (w/v), leaching time 10 days, stirring rate 600 rpm and temperature 50 °C. The behavior of conventional and electrochemical bioleaching processes was described with a combined reaction-based kinetic model. The model considers the effects of mineralogical composition of the feed, the properties of the initial solution, the presence of iron- and sulfur oxidizing microorganisms and both the passivation and electroreduction of chalcopyrite on the values of copper recovery, pH and redox potential during the processes. Comparing the values obtained from the integrated semi-empirical model with the experimental data showed that the model results are in good agreement with the real leaching data of copper recovery, ORP (oxidation reduction potential) and pH for the mentioned processes under different experimental conditions.