Dowa Mining Co., Ltd.

Akita Zinc Co., Ltd.

Akita Zinc Col., Ltd.

Norihito Ishimori

Hideki Nagata

Shuji Kuramochi

Kaoru Saruta

Hitoshi Masuda

A method for directly leaching a zinc concentrate in one of the stages contained in the hydrometallurgical process for the production of electrolytic zinc. The method comprises: a neutral leach step, a zinc concentrate leach step, and an iron oxidation step. In the zinc concentrate leach step, a neutral leach residue and an iron sediment returned from the iron oxidation step are repulped by the spent electrolyte followed by adding thereto zinc concentrate to extract zinc from the zinc concentrate by carrying out a leaching under atmospheric pressure and at a temperature of not lower than 90&deg; C., but not higher than the boiling point of the solution. According to this method, the concentration of Fe(III) ions in the zinc concentrate leach solution is significantly increased. Due to this Fe(III) ion concentration, the leaching rate of the zinc concentrate is enhanced.

Method of leaching zinc concentrate

Metal impurities such as mercury, copper, lead, zinc, iron and cadmium that are contained in trace amounts in sulfur that have been recovered from zinc concentrates by direct pressure leaching or other hydrometallurgical processes are removed effectively by contacting the molten sulfur, as it is held at a temperature not lower than the melting point of sulfur, with activated alumina by passage through a packed layer of activated alumina or a filter coated with activated alumina, or by mixing with activated alumina under stirring or by passage through a fluidized layer of activated alumina. The method is capable of reducing the sum of metal impurities in the sulfur to 50 ppm or below, with contents of mercury being reduced to 1 ppm or less, to provide sulfur having a purity of at least 99.99%, which is advantageous for use as a raw material in the production of sulfuric acid and in other chemical processes.

Method of sulfur purification

Mercury in trace amounts in sulfur that has been recovered from zinc concentrates by direct pressure leaching or other hydrometallurgical processes can be removed effectively by bringing the molten sulfur, as it is held at a temperature not lower than the melting point of sulfur, into contact with activated alumina by passage through a packed layer of activated alumina or a filter coated with activated alumina, or by mixing with activated alumina under stirring or by passage through a fluidized layer of activated alumina. The method is capable of reducing the mercury content to 1 ppm or less, whereby sulfur having a purity of at least 99.99% that is advantageous for use as a raw material in the production of sulfuric acid and in other industries is manufactured at low cost on simple equipment.

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Akita, Japan

Norihito Ishimori