Extraction of impurities from phosphorite ore in concentration and processing

Abstract

The article presents a review of the reports on the composition and properties of phosphorite ore from the Polpino deposit and on the problems connected with the ore processing by dry fractional crushing–sifting separation. The content of impurities in this ore exceeds the standard, which eliminates technological capability of straight sulfuric acid treatment of the ore for wet-process phosphoric acid production. The attempted wet processing of the ore by solutions of weak organic acids, selected because of their availability, regenerative capacity and environmental safety, is described. It is found that the organic acids are lo w-effective in extraction of alkaline-earth metal impurities: extraction is not higher than 3.5 and 9.5 % with acetic and formic acids, respectively; total recovery of Al2O3 and Fe2O3 is not higher than 2.0 and 8.0 %, and is factually independent of concentration of the acids. The authors prove straight processability of phosphorite ore by sulfuric acid treatment with production of compound fertilizers, including selective removal of impurities and carbonate minerals, and controlled recovery of iron and aluminium. The optimization parameters of the process are concentration of nitric acid, the acid–ore interaction time and temperature. These parameters should ensure complete extraction of the target component to solution (99.0 %), as well as controlled removal of iron impurities (18.0–20.0 %) and aluminium impurities (31–32 %), which have an adverse influence on rheological properties of suspensions. Thus, the article proves technological capability of straight processing of Polpino phosphorite resources containing Р2О5–15.3 %, CaO–27.42 %, MgO–0.95 %, Fe2O3–2.58 % and Al2O3–3.65 % without pretreatment.