Beneficiation of phosphate ore / Обогащение фосфатной руды

Phosphate rock is an important mineral commodity used in the production of phosphoric acid. The majority of phosphoric acid is produced by the “wet process,” in which phosphate rock is reacted with sulfuric acid to produce phosphoric acid and gypsum (calcium sulfate dihydrate). The wet process demands a phosphate rock feed that meets certain specifications in order to produce phosphoric acid efficiently and economically.
Traditionally, relatively high-grade sedimentary phosphate reserves have been mined. These reserves usually contain only clays and silica as significant gangue minerals (Lawver et al. 1978; Houot 1982; Dibble 1990; Herring and Fantel 1993; Guan 2009a). Clay slimes are removed using log washers and hydrocyclones, whereas silica is removed using the well-established Crago double float process. However, as the high-grade reserves begin to diminish, there is a need to consider processing lower-grade reserves that contain significant amounts of carbonates (Lawver et al. 1982; Llewellyn et al. 1982; Wiegel 1999). Low-grade sedimentary phosphate reserves that are high in carbonates are not isolated to Florida; they are abundant worldwide (Abouzeid et al. 1980; Vaman Rao et al. 1985; Abu-Eishah et al. 1991; Al-Fariss et al. 1991; Al-Fariss 1993; Zafar et al. 1996a; Ozer 2003; Sengul et al. 2006). These high-carbonate sedimentary phosphate reserves pose particular problems because of their dolomite (CaMg(CO3)2) content. If not removed, dolomite hinders the wet process in two ways: it increases sulfuric acid consumption, and it increases fluid viscosity, which lowers filtration rates when separating solid gypsum crystals from the valuable phosphoric acid. Removing dolomite from sedimentary phosphates has proven to be very difficult because of the mineralogical similarities between dolomite and phosphates. <...>