4. Mechanical preparation of raw phosphates

The processing of raw phosphates always combines crushing with screening and classification. In all sedimentary phosphate processing schemes, it is imperative to avoid the formation of phosphate particles smaller than 100 µm, which would be irretrievably oriented towards clayey tailings, and therefore lost. In general, fine grinding is required to free phosphate nodules from their exogangue, but little or no endogangue is released.

The energy required for wet grinding varies from one phosphate to another. Bond Index (Wi ) values, determined for a closed grinding-classification circuit (table 1 ), range from 10 to 20 kWh/t for sedimentary phosphates and exceed 30 kWh/t for phosphates of igneous origin (e.g. South African carbonatites).

For dry grinding, the energy indices must be...