Process for making phosphoric acid

Abstract

A phosphate rock slurry, which may be used in the production of wet process phosphoric acid, is provided by wet grinding the rock with partially neutralized, acid water. In one aspect, wet process phosphoric acid is made by advantageously recycling mineral acid waste water effluent of the process. All or a portion of the effluent can be at least partially neutralized with neutralizing agent, e.g., by contact with the base-forming constituents of phosphate rock or extraneous neutralizing agent, e.g., preferably ammonia, to provide a mixture which is wet ground to produce a processable slurry. In one particularly preferred aspect, all of the acid water is at least partially neutralized with phosphate rock and a portion of this acid water is advantageously further neutralized with an extraneous neutralizing agent. The slurry is provided by such neutralization at a pH compatible with the milling, e.g., grinding, media utilized. The use of acid water permits the use of mixtures having high solids content in the mill and thus also reduces the amount of water required to wet grind the mixture. The wet ground processable phosphate rock slurry is advantageously used in the production of phosphoric acid and recycle mineral acid waste water effluent from the process is used in wet grinding phosphate rock and as part of the overall water balance control of the process.