Conference Dates

April 29-May 4, 2018


World reserves of high-grade, high-quality phosphate rock are steadily decreasing. As a result, lower quality rock is being increasingly evaluated to determine its potential for commercial exploitation. It is well known that the chemical and mineralogical composition of phosphate rock varies widely from deposit to deposit, and therefore, the conditions for processing different phosphate rock types also varies.

Unfortunately, most early stage phosphate feasibility studies tend to focus on the P2O5 content and neglect the other chemical constituents or impurities in the rock. It is the remainder of the chemical constituents that often define the quality of the P2O5 concentrate and its potential for conversion to phosphate fertilizers. Typically, when evaluating phosphate ore and subsequent concentrate as a raw material, the first step is to analyze the composition (P2O5 and impurities) to gain a preliminary understanding of how the rock may behave in downstream chemical processing or as a direct application fertilizer. In addition to %P2O5, the following chemical constituents, at a minimum, should be evaluated when assessing the suitability of any phosphate rock:

  • Calcium (%CaO)
  • Magnesium (%MgO)
  • Iron (%Fe2O3)
  • Aluminum (%Al2O3)
  • Silica (%SiO2)
  • Chlorine (%Cl)
  • Fluorine (%F)
  • Carbon Dioxide (CO2) and Organics
  • Sulfides
  • Sodium (Na2O) and Potassium (K2O)
  • Heavy metals, rare earths, and other elements.

Once the above chemical analyses of a representative phosphate rock product are known, it is often possible to predict the suitability of the rock as feed for conventional wet process phosphoric acid production. However, given the vast range in which these chemical constituents can be present, acidulation pilot plant testing must be carried out during the feasibility study project phase in order to properly assess the deportment of these constituents into the acid and/or gypsum.

This paper is presented to give a general understanding of the conventional wet acid process for conversion (acidulation) of phosphate rock as it relates to the presence and concentration of the major chemical constituents usually associated with phosphate rocks. Five case studies are presented.

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