Partially acidulated phosphate rocks made from phosphoric acid using direct acidulation-granulation techniques

Abstract

Partially acidulated phosphate rocks were produced by spraying phosphoric acid onto North Carolina phosphate rock of three finenesses (unground, medium, or finely ground) in a pan or drum granulator. This ‘direct acidulation-granulation’ procedure resulted in free-flowing granular products using laboratory acid up to stoichiometric levels of 30% (unground), 45% (medium) and in excess of 50% (fine). However, when less pure works grade acids were used the maximum levels of acidulation were reduced to 15%, 30% and 45% respectively with a corresponding greater difficulty in producing good granules.

Mature product analyses indicated an analytical bias with granule size, the larger granules containing greater quantities of soluble phosphate in most instances. Physical tests on mature products indicated that all granules produced were inferior to those of the ‘traditional’ New Zealand fertiliser single superphosphate.