Modeling, simulation, and optimization of bacterial leaching reactors

Bacterial leaching represents an unusual problem in biochemical engineering , because the substrate for bacterial growth is not supplied directly, but is a product of another reaction, the leaching of mineral particles. In add ition, leaching is a heterogeneous reaction dependent on the particle-size distribution in the feed and on the kinetics of particle shrinkage. In this study, these effects are incorporated in the material balance for each min eral by the number balance. Examination of the number balance gives rise to a novel analysis of the competing technologies for leaching. The model is completed by the addition of material balances for the ferrous and ferric i ons, the dissolved oxygen, and for each bacterial species to the number bal ance for each mineral present in the feed. The model is compared with pilot plant data for three different ores. It is shown that the model is in exce llent agreement with the data. The performance of a bacterial leaching reac tor is explored using the model, and the washout and sensitivity criteria a re determined. It is shown that there are three washout conditions, in whic h the leaching conversion drops to zero. The washout conditions are depende nt on the growth rate of the bacteria, on the rate of dissolution of the mi neral, and on the rate of mass transfer of oxygen to the reactor. The criti cal washout condition is that arising from the rate of mineral dissolution. The optimization of a plant in which continuous tank reactors are configur ed in series is addressed. This analysis shows that the primary reactor sho uld be between 1.5 and 2 times the size of each of the secondary reactors i n a series combination. (C) 2001 John Wiley & Sons, Inc.