Effect of mechanical activation on thiosulfate leaching of gold from complex sulfide concentrate Mohsen HASHEMZADEHFINI 1 , Jana FICERIOVÁ 2 , Emad ABKHOSHK 3 , Behrouz Karimi SHAHRAKI 1 1. Iran Mineral Processing Research Center, Karaj, Iran; 2. Institute of Geotechnics of Slovak Academy of Sciences, Watsonova 4504353 Košice, Slovakia; 3. Department of Mining Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran Received 14 March 2011; accepted 8 June 2011 Abstract: The use of mechanical activation to enhance gold recovery from a CuPbZn complex sulfide concentrate was investigated. The effects of milling time, ball size, sample to ball ratio and milling speed on thiosulfate leaching were studied. Under optimum conditions of milling time 1 h, ball size 20 mm, sample to ball ratio 1/15 and mill speed 600 r/min, nearly 78% of sample is amorphized, particle size decreases from d 100 =30 µm to d 100 =8 µm, specific surface area increases from 1.3 m 2 /g to 4.6 m 2 /g and gold recovery enhances from 17.4 % in non-activated sample to 73.26 %. Key words: mechanical activation; thiosulfate leaching; refractory ore; extraction of gold 1 Introduction Dissolution of gold from raw materials is mainly performed using cyanide leaching [1], though at present interest in the use of noncyanide processes for recovery of gold is a target due to the increasing concern regarding the hazardous character of cyanide. Thus, several leachants for gold recovery based on the stability of the corresponding gold complexes such as thiosulfate, thiourea, chloride, thiocyanate, ferric chloride and bromide have been proposed. Among them, ammoniacal thiosulphate leaching is considered a promising and nontoxic alternative to cyanidation [2]. The thiosulphate leaching and recovery of gold have been reviewed [2]. With depletion of the oxidized free-milling gold reserves close to the earth surface, most of the important new deposits being mined today do not respond to direct leaching. It is found that the gold is very finely disseminated and encapsulated in host matrices that are inert and/or impermeable to the leaching solution. In many cases, the host matrices are sulfide minerals, which exhibit a strong association with finely disseminated gold particles in many ore bodies [3]. Several attempts have been made to process efficiently those raw materials [4−9]. In order to overcome the refractory character, a pre-treatment is required to breakdown the sulfide matrix and renders the gold amenable for recovery prior to the application of any conventional treatment. The traditional route to treat these types of raw materials is by oxidative roasting of the sulfides before leaching. Alternative viable methods of oxidation such as pressure oxidation, bio-oxidation and electrooxidation have been developed to eliminate pollution problems caused by the emission of toxic gases (SO 2 and As 2 O 3 ) during oxidative roasting [10]. The relatively new process of mechanochemical pretreatment is being successfully applied in both fundamental research and plant operations [11]. In this process, which is also called mechanical activation, the minerals are subjected to high-intensity grinding. This grinding results in particle size reduction and causes chemical or physicochemical transformations, which significantly affect the subsequent hydrometallurgical process [12−17]. Currently, mechanical activation has been widely applied to the pretreatment of minerals [18−21]. Several investigators studied the effect of mechanical activation on sulfide minerals dissolution [22−26]. Many researchers studied the effect of mechanical activation on the extraction of metals in refractory Corresponding author: Mohsen HASHEMZADEHFINI; Tel: +98-9376715705, Fax: +98-2619208360; E-mail: hashemzadehmohsen@gmail.com DOI: 10.1016/S1003-6326(11)61118-7