Calcium phosphate neoformation and behavior of phosphorus solubilization in Humifert process

Abstract

The Humifert process is an alternative method for manufacturing fertilizer compounds and for the better utilization of phosphate rock, a non-renewable natural resource. The advantage of this process is that it does not have limitations regarding P2O5 content, which makes the exploitation of phosphate deposits and/or mining waste economically viable. The process uses phosphate and organic materials to produce organophosphate compounds. In this study, compounds generated from a mixture of phosphatic rock and sewage sludge showed a nonlinear trend of increased phosphorus solubility during reaction time, probably related to the dynamics of biogeochemical processes. Analysis by X-ray diffraction and scanning electron microscopy showed neoformation of phosphate phases. Solubility is lower in stages in which phosphorus and calcium are mainly immobilized in inorganic neoformation, such as a synthetic phase similar to brushite. On the other hand, when phosphorus is not strongly fixed, extraction is facilitated. This complex situation involves reaction kinetics, not yet controlled by reactor operating procedures, which may result in different degrees of attack. The results indicate that the Humifert process may be an efficient way to turn less soluble phosphorus into soluble forms, which associated with organic matter may form compounds that are more economically interesting and more environmentally friendly.