Analysis of the solubility of phosphate rock from Aipe (Colombia) via formation of 2Na-EDTA complex.

Phosphate rock (PR) is the main source of phosphorous used in fertilizers for Colombian soils. In many regions of Colombia, PR is applied directly to the soil, which affects eutrophication problems and phosphorus losses due to runoff, because to the low solubility of phosphorus in this georesource. In this article, phosphate rock samples from Colombia were treated with ethylenediamine tetra-acetic acid disodium salt dihydrate (2Na-EDTA) at different concentrations. PR obtained from the Media Luna Mine, located in Aipe, Huila (Colombia), was characterized using Infrared Spectroscopy, X-ray Diffraction and Scanning Electron Microscopy. Carbonate fluorapatite Ca9.74(PO4)5.45F2.05(CO3)0.53 (0.5%-61.5 %), hydroxyapatite - Ca5(PO4)3OH (26.6 %-84.0 %) and quartz- SiO2 (13.2 %) were the minerals found in the largest composition in the two samples of PR. The PR was crushed to powder (~125 µm) and it was treated with disodium EDTA dihydrate solutions at different concentrations [0.0025-0.1000 M]. Water-soluble phosphate was determined by UV-Vis spectrophotometry based on the ASTM -4500P method. The modified absolute solubility index (ASI*) was calculated for each EDTA treatment used in the phosphate rock, considering the total phosphorus solubilized in H2SO4 (40 % v/v) at 30 °C. The statistical analysis showed that there were significant differences between the treatments used, where (16.87 %) was presented highest ASI* for the treatment with 2Na-EDTA (0.353 M).