Sulfuric acid-based partially acidulated phosphate rock -- its production, cost, and use

Many of these deposits have had little commercial significance in the past because they were either too low in grade, too unreactive, or associated with excessive quantities of unwanted impurities. One means of utilizing these indigenous phosphates to the benefit of countries having such deposits is to increase the plant- available phosphate by chemical conversion to a partially acidulated phosphate rock (PAPR) product. The partial acidulation concept, indicating the use of less acid than that needed to convert the rock to superphosphate, often makes it possible to process problem ores into useful fertilizer products when the use of conventional processing methods is not feasible. The PAPR products may be especially attractive to producers who rely upon imported sulfur or sulfuric acid because less acid is used and a significant saving in foreign exchange can be realized. The process technology, production cost estimates, and agronomic performance of a number of sulfuric acid-based PAPR (SAB-PAPR) products described in this bulletin often compare favorably with those of conventional superphosphate fertilizers. The factory-gate cost of phosphate oxide obtained from SAB-PAPR is estimated at about 80% of that obtained from single superphosphate. Likewise, the agronomic performance of the SAB- PAPR products is comparable to that of conventional superphosphate under the appropriate conditions (acid soils with high phosphorus-fixation capacities). (Author abstract)