Abstract
A detailed investigation of two phosphate rock acidulation modes has been carried out in batch acidulators. The classical dihydrate process rate is affected by the coating of the rock particle by gypsum. The clean phosphoric acid process using phosphoric acid as an acidulation agent does not suffer from this inhibitory coating effect, however it is affected by the increasing viscosity of the solution during acidulation. Under practical conditions the rate of acidulation using phosphoric acid is much higher than that of the dihydrate process using sulfuric acid as an acidulation agent.