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Abstract

The invention relates to a method for preparing a sulphidic concentrate which is intended for further processing to copper and/or precious metals and which contains high percentages of arsenic and/or antimony, and possibly also bismuth in quantities likely to disturb subsequent processing stages, by partially roasting the concentrate in a fluidized bed, so as to eliminate substantially all the arsenic present and a major part of the antimony and/or bismuth. According to the invention, the concentrate and gas are supplied to a fluidized-bed reactor, and are there heated to a minimum temperature above the splitting or decomposition temperatures of the complex minerals containing arsenic and/or antimony and bismuth present in the concentrate. The oxygen potential in the reactor is regulated, so as to prevent the formation of non-volatile compounds of said impurities. The residence time of the concentrate in the reactor is controlled in a manner to ensure a given minimum elimination of the impurities. The gas and solids are withdrawn from the reactor and passed to a separating means, in which substantially impurity-free solids can be separated from the gas. The aforesaid minimum temperature and said regulated oxygen potential are maintained while the solids are in contact with said gas, and at least a part of the separated solids is returned to the reactor, for controlling the residence time, and an end product is removed from the fluidized bed and/or the separating means. The method is suitably carried out in one stage in a fluidized-bed reactor having a circulatory fluidized bed, although in certain cases the method can be carried out in two stages, in mutually separate reactors.

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First Claim