Abstract
Mechanochemical treatment of phosphate rock is considered as an effective and ecologically clean way of treating the medium- and low-grade phosphorite which could be used as fertilizer instead of the high-grade phosphorite. In order to investigate the effects of different milling times on the mechanochemically activated phosphorite (lower total phosphorus content) by more efficient milling equipment with enhanced milling speed, phosphorus solubility in citric acid and structural characteristics of natural and mechanochemically activated phosphorite from Yichang, China were studied using scanning electron microscope, infrared spectroscopy and X-ray diffraction. Phosphorus solubility in citric acid increased proportionately with the milling time until 30 min (57.51%), but then gradually reached an equilibrium with the maximum (59.03%) in 50 min. These changes were mainly manifested in considerably reduced particle size, decreased crystallinity and increased structural defects of phosphorite due to substitution of PO43- with CO32- and the incorporation of OH-. With the incorporation of CO32- and OH-, the non-activated carbonate-fluorapatite (type B) was transformed into a mixture of carbonate-fluorapatite, hydroxyapatite, fluorocarbon hydroxyapatite and/or carbonate apatite, respectively during the process of mechanochemical activation. As a result of the structural and phase transformations after mechanochemical activation, phosphorus solubility remarkably increased.
Highlights
70–80% of high-grade phosphorite (P2O5 30%) in the world has been used to produce phosphorus fertilizer to ensure enough nutrition for crops
Besides the total phosphorus content (P2O5total), phosphorus solubility in citric acid is one of the most important factors to evaluate whether the phosphorite can be used as fertilizers
Our results showed that the solubility of phosphorus from apatite ores in citric acid increased proportionately with the grinding time, and it nearly reached the maximum level (59.03%, 50 min) at 30 min (57.51%) and gradually reached an equilibrium, under the condition of the constant other processing parameters
Summary
70–80% of high-grade phosphorite (P2O5 30%) in the world has been used to produce phosphorus fertilizer to ensure enough nutrition for crops. The depletion of high-grade phosphorite as well as the ecological problems caused by the wet treatment with acid have intensified the problem of finding a more efficient ways of producing phosphorus fertilizers. Medium- and low-grade phosphorite (P2O5
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