Abstract: The paper presents a preliminary analysis of the kinetics of bacterial pretreatment of arsenical gold ore concentrate from Banbishan,Hebei.The batchwise bioprocessing of the concentrates was carried out in a 10L gas-lift loop reactor with 1 kg load using a mixed strain of Thiobacillus ferrooxidans and Thiobacillus thiooxidans.The level of dearsenication reached above 80% in 5 days of leaching.Comparison of the modelling with experimental data on dearsenication indicates that the bacterial growth can be described by the Monod equation,and modification is also necessary to reflect the inhibition due to the accumulated arsenic in the leaching solution.The leaching of arsenic and iron may be approached with the shrinking-core model,and the dearsenication rate seems to be limited by intraparticle diffusion of Fe~(3+) iron when the mechanism of indirect oxidation of arsenopyrite during bacterial pretreatment is assumed.