Bioleaching behaviour of chalcopyrite in the presence of silver at 35 degrees and 68 degrees C

Chalcopyrite bioleaching kinetics has been improved by using catalytic ions able to modify the mechanism of electrochemical dissolution of chalcopyrit e through its fixation on the sulphide surfaces. Among these cations, silve r has been proven to be the most effective ion for chalcopyrite dissolution with mesophilic microorganisms (35 degrees C). In this way, bioleaching kinetics has been accelerated by means of thermoph ilic microorganisms (68 degrees C). However, different studies with these b acteria and in the presence of silver have shown no improvement in the copp er recovery. This scattered behaviour of the silver-catalysed chalcopyrite bioleaching a t 35 degrees and 68 degrees C leads to several questions, such us: is there a different mechanism of the silver attack at each temperature?, is there any problem associated with the toxic effect of the catalytic ion on the th ermophilic microorganisms? or simply, the surface film formed by the intera ction between Ag+ ions and chalcopyrite is different? In an attempt to answer these questions, the influence of the catalyst conc entration on chalcopyrite bioleaching at 35 degrees and 68 degrees C has be en examined at first place. Furthermore, the composition of the different p hases formed on the mineral surface during the attack has been analysed by EDX and electron microprobe. Finally, the bacterial attack on the chalcopyr ite has been simulated in an electrochemical cell. The results show that the chalcopyrite attack at 35 degrees and 68 degrees C takes place through different mechanisms, as a consequence of the formati on of different compounds during the interactions between silver ions and c halcopyrite. At 35 degrees C a thin layer of silver sulphide was formed, wh ereas at 68 degrees C a thicker film, mainly formed by metallic silver, was detected. Evidence of a high silver penetration through chalcopyrite crack s at 35 degrees C compared to a silver deposition only on the surface at 68 degrees C was obtained.