ZimPhos makes two grades of superphosphate, Single Superphosphate (SSP) with 20% phosphate (P2O5) content and triple superphosphate (TSP) with 45% phosphate content.
The SSP is made by mixing phosphate rock with sulphuric acid while TSP is made from phosphate rock and phosphoric acid. The same equipment is used at different times to make the two products. Mono-Calcium Phosphate (MCP) is also produced in the same plant from phosphoric acid and limestone and is used as a source of phosphates in animal stock feed formulations.
ZimPhos traditionally produced sulphuric acid from two plants. The oldest plant used local iron pyrites as a source of sulphur while the other uses imported elemental sulphur. The pyrites burning plant was maintenance intensive and was closed down in 2010 when it became no longer viable. The sulphur burning plant was temporarily shut down during the economic meltdown era in the country but will be restarted in 2013 after a major revamp currently in progress. In the meantime the company is using imported acid. Most of the acid produced is used for phosphates production while a smaller proportion is used for aluminium sulphate production and sales, including exports, mainly to the mining industry.
Phosphoric acid is produced from phosphate rock concentrate and sulphuric acid. The ZimPhos phosphoric acid plant uses the so-called Prayon DiHydrate process. The plant was re-vamped in 1997 doubling its capacity to 40 000 tpa with modernized process controls
Large volumes of gypsum are produced as a byproduct in the phosphoric acid process and are stockpiled in massive tailing dams. Stockpiling is necessary because generally more gypsum is produced than is required by the various markets, mainly cement, plaster products and agricultural sectors.
Aluminium sulphate is used for drinking water treatment by the City of Harare and other municipalities in the region. It is produced at ZimPhos from bauxite and sulphuric acid in the plant shown above.