Abstract: The invention relates to method for leaching zinc-containing materials in connection with the electrolytic recovery of zinc. According to this method, the feed materials i.e. zinc calcine and zinc sulphide, are leached in three stages, in which he sulphuric acid content of the stages rises in accordance with the direction in which the solids are moving. The solids and solution formed in the leaching stages are routed throughout the process countercurrently in relation to each other.

Abstract: The invention relates to a method for the removal of mercury from gas containing sulphur dioxide and oxygen and from the sulphuric acid vapour contained in the gas. According to the method, the gas is washed with a water solution that contains selenium ions, whereby metallic selenium is formed in the presence of oxygen, which precipitates the mercury in the gas and vapour either as a selenide or in a chlorine-containing environment, as a dichloride of mercury and selenium. Gas washing occurs at a low temperature, below 50° C.

Abstract: This invention relates to a method for the removal of iron as hematite from a zinc sulphate solution in atmospheric conditions during the electrolytic preparation of zinc. According to the method, the pH of the iron-containing solution is adjusted to a value of at least 2.7, oxygen-containing gas is fed into the solution and part of the hematite thus formed is recirculated to the precipitation stage.

Abstract: The invention relates to method for leaching zinc-containing materials in connection with the electrolytic recovery of zinc. According to this method, the feed materials i.e. zinc calcine and zinc sulphide, are leached in three stages, in which he sulphuric acid content of the stages rises in accordance with the direction in which the solids are moving. The solids and solution formed in the leaching stages are routed throughout the process countercurrently in relation to each other.

Abstract: This invention relates to a method for the removal of iron as hematite from a zinc sulphate solution in atmospheric conditions during the electrolytic preparation of zinc. According to the method, the pH of the iron-containing solution is adjusted to a value of at least 2.7, oxygen-containing gas is fed into the solution and part of the hematite thus formed is recirculated to the precipitation stage.

Abstract: The present invention concerns equipment for the leaching of solid matter from a sludge with the aid of a gas containing oxygen, the said equipment comprising a tall reactor (1) equipped with a central pipe (2) and from the reactor bottom (3), an upward-directed double-action mixer (5). The mixer is situated in the vicinity of the lower edge of the central pipe: the upper blades (13) of the mixer produce a downward suction flow from the central pipe, and the lower blades (14) disperse the gas to be fed into the sludge in the form of small bubbles, thereby preventing the solid matter from settling to the bottom of the reactor.

Abstract: The invention relates to a method for the leaching of solid matter from a sludge with the aid of a gas containing oxygen, whereby the solid matter of the sludge is recirculated in a tall reactor equipped with a central pipe in the centre of the reactor and a double-action mixer located in the vicinity of the lower edge of the central pipe. A flow is formed with the aid of the mixer which sucks the sludge from the central pipe downward, and a gas to be conducted into the sludge in the bottom part of the reactor is dispersed in the form of small bubbles into the sludge outside the central pipe and the flow direction of the sludge is turned upwards in the outer casing of the reactor.

Abstract: The invention relates to a method for the removal of mercury from gas containing sulphur dioxide and oxygen and from the sulphuric acid vapour contained in the gas. According to the method, the gas is washed with a water solution that contains selenium ions, whereby metallic selenium is formed in the presence of oxygen, which precipitates the mercury in the gas and vapour either as a selenide or in a chlorine-containing environment, as a dichloride of mercury and selenium. Gas washing occurs at a low temperature, below 50° C.