DEVELOPMENT OF A TECHNOLOGY FOR PROCESSING IRON HYDRATE NICKEL-CONTAINING CAKE FOR ITS INVOLVEMENT IN STEEL PRODUCTION

Abstract

The article addresses the utilization problem of a nickel-containing iron hydroxide cake, a by-product formed during the hydrolytic precipitation of iron from a bleed electrolyte in the process of cathode nickel electrowinning. The relevance of the study is due to the accumulation of significant volumes of this waste, which contains valuable components (iron, nickel, copper, cobalt) as well as residual sulfur (up to 3 wt.%), limiting the possibility of its direct use in ferrous metallurgy, increasing the environmental burden, and necessitating the development of special processing technologies. The aim of the work was to study the physicochemical properties of the raw material, identify the limitations of its direct use in steelmaking, and develop a technology for producing a conditioned product. A three-stage processing technology has been proposed. In the first stage, the cake was dried to a moisture content of 6–8 %, as a result of which the material becomes free-flowing and capable of self-disintegration into aggregates sized 0–20 mm. In the second stage, the dried raw material was pelletized in a disc pelletizer with the addition of 1 % bentonite clay as a binder to obtain strong granules larger than 5 mm suitable for subsequent thermal roasting. In the third stage, oxidizing desulfurizing roasting of the pellets was carried out in a rotary tube furnace in a continuous mode with open flanges to ensure an oxidizing atmosphere. The optimal process parameters were determined: a temperature of 1000 °C and a duration of 30–60 min. Under these conditions, a degree of desulfurization of 98–99.3 % was achieved, and the final sulfur content in the pellets was reduced to 0.021–0.057 %. Simultaneously, iron is transformed from the hydroxide phase (goethite) into the oxide phase (hematite), which ensures an increase in the total iron content from 59.1 % to 64.7 %. For industrial implementation of the process, the use of a rotary kiln is recommended to ensure intensive mixing of the material and acceleration of desulfurization. As a result of the study, a pelletized product with a fraction of 8–20 mm and a low sulfur content was obtained, suitable for use in steelmaking as a cooling raw material and a source of iron and the alloying element nickel. The developed technology makes it possible to efficiently utilize iron hydroxide cake from nickel production, reduce the negative impact on the environment, and return valuable metals to the industrial circuit, contributing to the transition of enterprises to zero-waste production.