Electrokinetic study of pyrochlore in the presence of calcium and magnesium electrolytes in the context of water reuse

Abstract

This paper aims to present an adequate methodology for pyrochlore from flotation process sample to be used in fundamentals surface properties studies based on zeta potential measurements under Ca and Mg electrolytes in chlorides and sulfate media. A niobium ore concentrate with small amount of fine particles (−38 µm < 2.5%), composed by 61.8% (Nb2O5), 16.5% (CaO), 7.19% (TiO2), and 6.30% (Na2O), being pyrochlore (92.8%) the Nb-bearing mineral was used. The association of acid leaching (HCl 0.1 mol/L, 70 °C, 120 min, 20 g/L and 300 rpm) and heat treatment (300 °C, 120 min and 5 g/crucible) reduced the sample's flotability by 94% which was suitable for fundamental studies. Ca and Mg ions modified the zeta potential curve of the pyrochlore without causing any changes in the pHPIE, which occurs at pH 3.1. Ca(OH)2 precipitation was not evidenced in the system containing calcium ions. Thermodynamic simulation predicted its precipitation above pH 12.3 which is outside of the range of pH studied (2.0 to 12.0). However, Mg(OH)2 precipitation associated to the formation of metal hydroxy complexes predicted by PHREEQC (version 3.7.3, llnl.dat database) contributed to the reversal in the zeta potential of the sample. The anion supporting the metallic cations also contributed to the zeta potential alteration mainly due to the ionic strength modification associated to sulfate and chloride anion charges. The alternation of chloride and sulfate sources for [Ca + Mg] system did not affect the zeta potential curves.