PROCESS FOR THE SIMULTANEOUS TREATMENT OF RESIDUES OF THE NON-FERROUS METALLURGICAL INDUSTRY TO PRODUCE PIGMENTS BASED ON IRON OXIDES AND OTHER VALUED PRODUCTS, IN ACCORDANCE WITH CIRCULAR ECONOMY STRATEGIES

摘要

Described is a process for the simultaneous treatment of residues of the non-ferrous metallurgical industry, in particular Waelz slag and residues deriving from thermal fuming processes of jarosite, goethite or KSS slag, comprising the following steps: - possible initial pre-treatment (A) of the material to be treated, to obtain homogeneous particle size characteristics; - thermal pre-treatment (B) by the addition of ammonium sulphate (or nitric acid and/or sulphuric acid mixed with ammonium sulphate or with another reagent capable of promoting a reaction with the Waelz slag which makes it possible to obtain firstly the formation of the reaction intermediate ammonium hydrogen sulphate, (NH4)HSC>4 and, subsequently and in sequence, the formation of soluble iron and manganese sulphates and the development of ammonia) and gradual increase in temperature from ambient temperature to a final temperature in the range 200 °C to 600 °C, in a neutral/oxidising environment, to obtain the conversion of the iron, and manganese if present in the material, into compounds such as iron sulphates, and, possibly, manganese sulphates, soluble in water, with the formation of ammonia; and - hydrometallurgical treatments (C), according to the following sub- steps: - addition of water and mixing, - correction of acidity up to a pH of 2 to 8 in an oxidising environment, to obtain the precipitation of the iron in the form of mixed oxyhydroxides. The invention also relates to the use of the precipitate thus obtained, after separating from the solution and purification, for the production of pigments based on iron oxide.