The effect of dissolution kinetics on flotation response of apatite with sodium oleate

Abstract

Different flotation strategies are used to concentrate apatite from phosphate rock around the world. There is evidence that the flotation performance of apatite can be influenced by its dissolution kinetics. The objective of this study was to investigate the effect of dissolution kinetics parameters on the flotation response, with sodium oleate, of apatite samples from different origins and genesis. The samples were firstly purified and characterized by X-Ray Fluorescence (XRF) and the Rietveld method applied to X-Ray Diffraction data (RXD). Surface area, specific mass and porosity were also determined. Apatite dissolution experiments were carried out in an automated reactor. The apatite flotation responses were determined by means of microflotation experiments. Both types of tests were performed at pH8 and 10. By means of exponential adjustment of the dissolution curves (accumulated amount of dissolved Ca2+ ions as a function of time) it was possible to calculate the maximum amount of dissolved Ca2+ ions (Ca2+MAX) and the kinetic constant (k). The initial dissolution rate (Ri) was determined by linear adjustment of the first minutes of reaction. It was observed that the initial dissolution rate, as well as the floatability, is greater at pH8 than at pH10. In addition, by comparing apatites from different origins it was found that the floatability increases with Ri and Ca2+MAX. The results indicate that the flotation performance is improved by the increase in the amount of Ca2+ ions that are available to interact with oleate molecules. This result supports the relevance of the surface precipitation mechanism governing the adsorption of oleate on the apatite surface.