Ratchaburi phosphate rock (Rat-PR), Kanchanaburi-PR (Kan-PR), and Roi-Et-PR (Roi-PR) from Thailand, and North Carolina-PR (NCR-PR), were evaluated in the laboratory for agronomic use. NCR-PR consisted mostly of apatite (unit-cell a-value 9.336 Å, c-value 6.889 Å). Rat-PR contained apatite (a-value 9.428 Å and c-value 6.882 Å) and calcite as the main minerals. Kan-PR consisted mostly of apatite (a-value 9.406 Å and c-value 6.888 Å), crandallite, and calcite. Roi-RP consisted mostly of quartz and variscite. Dissolution kinetics of PRs in 2% formic acid (2% FA), 2% citric acid (2% CA), neutral ammonium citrate (NAC), alkaline ammonium citrate (AAC), and deionized (DI)-water were determined. The dissolution rate of phosphate from PRs in 2%FA, 2%CA, NAC, and DI-water was NCR-PR > Rat-PR > Kan-PR > Roi-PR. As Roi-PR is very poorly soluble, it is clearly unsuitable for direct application to soil. © 2013 Japanese Society of Soil Science and Plant Nutrition.
Charanworapan, C., Suddhiprakarn, A., Kheoruenromne, I., Wiriyakitnateekul, W., & Gilkes, R. (2013). An evaluation of three Thai phosphate rocks for agronomic use based upon their chemical and mineralogical properties. Soil Science and Plant Nutrition, 59(4), 522-534. https://doi.org/10.1080/00380768.2013.810546