Pergamon zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Minerals Engineering, Vol. 14, No. 3, 305-316, 2001 pp. 0 2001 Elsevier Science Ud All rights reserved zyxwvutsr 0892-6875(01)00003-6 0892-6875/01/S - see front matter BIO REACTOR SIMULATION AND MODELING FOR A GOLD BIO LEACHING PROCESS T. DAS and P.K. SEN Engineers India Limited, R&D Centre, Sector-16, Gurgaon, Haryana, India. E-mail: pks@eihnd.emet.in (Received 22 April 2ooO; accepted 6 November 2000) ABSTRACT Bio leaching is becoming increasingly used for the extraction of goldfrom refractory gold ore. It is established that in gold bio leaching two kinds of mechanism are involved namely indirect bio leaching and direct bio leaching. The reaction schemes involved in the different mechanisms and kinetic rate expressions for diflerent reactions have been reported in the literature. In the present paper an attempt has been made to develop an approach for simulation of a gold bio reactor leach circuit, For this purpose a mathematical model for bio leaching has been developed for process design of a gold bio reactor circuit. The salient features of the model are parameter estimation from experimental data and then scaling up the process for pilot size and industrial size bio reactor operation in continuous mode. Bio reactors can be simulated for various combinations of series-parallel modes of operation. Experimental data of the laboratory scale bio reactor collected for difSerent pulp densities and residence times have been simulated for parameter estimation. Experimental data of pilot size bio reactors, collected from the literature, have been used for vetting of the parameters estimated earlier. Analysis of the simulation results indicates the extent of conversion taking place due to indirect and direct mechanisms. The pe@ormance of the simulation model developed based on literature information has been confirmed by some experimental data collected, as well as by literature data. 0 2001 Elsevier Science Ltd. All rights reserved. Keywords Bio leaching; bio reactor; simulation INTRODUCTION Throughout the world, the need to process the more complex deposits of refractory gold in addition to free- milling ore is becoming a requirement due to economic pressures. Pinches et al. (1994) have reported that one third of the world’s total production of gold is estimated to be from refractory deposits. The sulfide-refractory gold ores contain gold in intimate association with sulfide minerals, typically pyrite and arsenopyrite. Gold is not liberated for recovery by conventional cyanide treatment even by very fine grinding. Sulfide-oxidizing bacteria, namely Zhiobacillus ferroxi&zns, solubilize the host minerals, exposing the gold for conventional recovery. Three technologies are used commercially to treat sulfide-refractory ores and concentrates, namely roasting, pressure oxidation and bio leaching. Barrett et aL (1993), Poulin et al. (1996) have reported that bio leaching is becoming more popular because it is economical, environmental friendly and easy to operate compared with other technologies. To date there are several pilot plants and at least six commercial plants involved in the bio leaching of gold ore or concentrate in the world, according to Morin et aL (1989) and Pinches et al. (1994). Efforts for modeling bio leaching of gold bearing ore have been scantily reported, although development of such models are vitally important for carrying out process design of bio leaching circuits. 30.5