The potential of Hazara phosphates for phosphoric acid manufacture

Abstract

The phosphate reserves in Pakistan are small. The largest ore body (Lagarban area) of Hazara Administrative Division located in the North East of the country has 3.25 (measured) and 6.71 (inferred) million tons phosphates rock of silicious and dolomitic nature with 25.8% average P₂O₅ contents besides high impurities of R₂O₃ (3.3%) and MgO (up to 6%).

The deposits are not beneficiable by dry and wet screening due to significant phosphate losses which take place. Phosphate flotation recoveries are also low. Heavy intensity magnetic separation removes iron after the removal of dust from classified fraction. Acid leaching is efficient for removing MgO (up to 84%) with low P₂O₅ losses. However, removal of iron and MgO by these methods is not considered feasible on economic grounds.

Laboratories and pilot plant processing trials showed that phosphoric acid of 23–25% P₂O₅ can be manufactured from Lagarban rock. As most of the impurities of the rock Fe₂O₃, Al₂O₃, MgO and part of SiO₂ are washed down during processing the resulting product acid is of poor quality with high viscosity.

Triplephosphates prepared from this acid are hygroscopic and have low P₂O₅ availability (86%).

To overcome the problem of these objectionable impurities in the product acid, removal of these impurities during the processing of phosphoric acid is required, i.e. aggolomeration with gypsum crystals-Pembrook pŕocess, Occidental process.