Mineralogical; micromorphological and geochemical characterization of the phosphatic phase from organo-phosphatic compounds obtained by the Humifert process

Abstract

Brazilian phosphatic ores are mainly the lateritization products of apatite-rich carbonatitic igneous bodies. Lateritic weathering plays a double role in phosphatic ore concentration, because, after concentrating the ore mineral, in the early phase of weathering, it modifies and destabilizes the residual apatite, generating low quality materials, although still rich in P2O5 (TOLEDO et al. 1999). These rejected materials can be valuable in alternative processes, as the Humifert process (STERNICHA 1988), in which a mixture of discarded phosphatic materials and wet organic matter are treated with nitric acid formed by the reaction between N oxides and the humidity, forming products with higher solubility than that of the initial natural phosphates but not as soluble as traditional phosphated fertilizers. The Humifert process was applyed to Brazilian phosphatic materials for the first time by OBA (2000), and the products then obtained are characterized in the present work, in order to understand the changes in apatite grains, the interactions between the constituents, the neoformations and the properties acquired by the transformed materials. Moreover, this research tried to correlate all these characteristics with original phosphatic materials, from Catalão I (GO), Jacupiranga (SP), and Patos de Minas (MG), and with the different agronomic results observed by OBA (2000). Microscopic studies showed phases within the products corresponding to neoformed compounds and different apatite grains as compared to the initial grains. Thermal analyses indicated an exothermic event at about 490-520ºC, related to the new compounds. P solubility measures with different substances (water, 2% citric acid, and amonium neutral citrate) showed increasing solubility in the products, related to the original phosphatic materials. The best agronomical results among the products were obtained from the more weathered original materials, having apatite not related to quartz.