Papers by Author: Koichi Suto

Abstract: In a series of studies, various aspects of thermophilic bioleaching of chalcopyrite minerals and concentrates have been analyzed. Although the main objective was the elucidation of the catalytic effect of thermophiles in leaching chalcopyrite, various other new findings contributed to a better understanding of interactions among chemical, physicochemical and biological factors, which influence the bioleaching of chalcopyrite with thermophiles. Additionally, in order to bridge laboratory results and field applications, novel mathematical models as well as an alternative method to efficiently leach chalcopyrite without thermophiles are the contributions of this research.

Abstract: This paper describes about microbial diversity in an iron oxidation tank of an AMD treatment plant established at an abandoned sulphur mine in Japan. Since the mining operation was stopped, this mine has produced strong acidic mine drainage, pH 1.8, including a high concentration of ferrous iron, 301mg/L, and the flow rate was about 4m3/min. In 2006, a pilot scale microbial iron oxidizing system was installed to remove total iron more easily from the AMD by oxidizing ferrous iron to ferric iron. From the start of this pilot operation, microbial diversity in the iron oxidation tank was investigated using a PCR-DGGE method for about two months. In the PCR, V3 region of 16S rRNA gene for Bacteria was amplified. The profiles of DGGE showed that there were three dominant species in the iron oxidation tank through the experimental period. Number of bands on DGGE profiles decreased with dates of sampling so that the microbial population became less diverse because of the iron oxidizing operation. There was a wide variety of bacterial species of even though conditions were strongly acidic.

Abstract: A model was prepared to study the performance of a thermophilic bioleaching heap that employs mixed mesophilic and thermophilic microbes for copper extraction from CuFeS2. Mesophiles’ preference for and ease of dissolving additional FeS2 provided to the heap enables the transition from a mesophilic to a thermophilic bioleaching state without the necessity of additional energy supply. In this sense, the mathematical description of the bioleaching process is done taking into consideration the dependency of both microbes’ biological states on physicochemical factors such as the temperature and O2 availability. With regard to the flow rates of the liquid and air phases, simulation results have shown that these flow rates govern not just the heat transfer and variation of cell distribution, but also the leaching rate regardless of the fraction of CuFeS2 per FeS2 leached (FCP) which is the other variable influencing to the heat accumulation in the heap.