ABSTRACT:

A unique bioprocess is proposed for extracting metals from marine manganese nodules. In this bioleaching, sulfurous acid and sulfuric acid are biologically produced from elemental sulfur and simultaneously used as leaching agents to manganese nodules. In the leachability aspect of nodules, the thermophile Acidianus brierleyi growing on elemental sulfur at 65°C is more effective than the mesophile Thiobacillus species at 30°C. Leaching experiments with A. hrierleyi were undertaken to optimize the conditions under which valuable metals in nodules are solubilized during the bacterial growth on elemental sulfur.

INTRODUCTION

There have been many investigations into the recovery of valuable metals from marine manganese nodules because of their potential importance for mineral resources in future (Fuerstenau and Han, 1983). Although physical and chemical processes have been extensively developed for extracting the metals from manganese nodules, another possible process is the leaching of nodules by microbial means. In the area of hydrometallurgy, a large amount of work has been conducted in the application of microorganisms to the recovery of base and precious metals from various sulfide mineral resources, but little attention has been given to the microbial treatment of manganese nodules. The primary microorganisms in sulfide leachings is acidophilic mesophile Thiohacillus tlziooxidans and Tiziohacillus ferrooxidans, which grow optimally at 30°C and low pH 1-2. Moreover, the acidophilic thermophile Acidianus hrierleyi, which has a temperature optimum for activity at 65°C, is a candidate microbe for sulfide leachings. Although these acidophilic sulfur-oxidizing bacteria obtain their growth energy from the oxidation of inorganic sulfur compounds, they have no ability to attack directly manganese nodules which are comprised mainly of oxides of manganese and iron. Alternatively, there is a unique treatment of manganese nodules with the sulfur-oxidizing bacteria growing on elemental sulfur. The microbial treatment is induced in a combined process.

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