en Research Paper Research Paper In this paper, gold leaching of a refractory sulfide concentrate by chloride–hypochlorite solution was investigated and effects of stirring speed, temperature and particle size on the leaching rate were reported. Experimental data for leaching rate of gold were analyzed with the shrinking–core model. Results were consistent with chemical reaction control mechanism in the first 1 h of leaching and diffusion control mechanism in the second 1 h. Apparent activation energy also was found to be 22.68 kJ/mol in the first step and 3.93 kJ/mol in the second step of leaching. Gold concentrate, Non–cyanide leaching, Chloride–hypochlorite, Kinetic. 37 47 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-127-50&slc_lang=en&sid=1 M. Ghobeiti Hasab 180031947532846002540 180031947532846002540 No F. Rashchi rashchi@ut.ac.ir 180031947532846002541 180031947532846002541 Yes Sh. Raygan 180031947532846002542 180031947532846002542 No