REMOVAL OF MAGNESIUM FROM PHOSPHATES AND PHOSPHORIC ACID

摘要

Among the impurities present in sedimentary phosphate rocks, magnesium is especially troublesome. Its removal depends on its status in the ore. Three examples of treatment of poor phosphates are related, each one being adapted to the mineralogy of MgO species and distribution. Abu Tartar Phosphate, containing 1.82% MgO, is characterized by the presence of ferriferous dolomite as subautomorphic crystals. High gradient Magnetic Separation can lead to a final concentrate grading 32.9% P_2O_5 and 0.4% MgO. The recovery of P_2O_5 attains 79%. Kalaat Khasba phosphate (1.38% MgO) contains well crystallized dolomite. Flotation using N-alkyl (coprah) amino-propionic acid is performed in two steps. The dolomite is first floated at pH = 7/7.5 and, after, the silica is removed at pH = 5, without changing the water. The final concentrate assays 31.83% P_2O_5 and 0.22% MgO, with P_2O_5 recovery of 84%. Djanatass phosphate, a deposit of Kara Tau Basin, features a high level of MgO (2.6%). The intimate mineralogical association of the individual components does not allow a flotation concentrate assaying more than 29.5% P_2O_5 nor less than 1.2% MgO. However, after sulphuric attack of that concentrate, a crude phosphoric acid is obtained, containing 27% P_2O_5 and 1.2% MgO. Further extraction of Magnesium from this weak phosphoric acid by using a strong acid cation exchange resin is able to reduce MgO content to 0.2%.