The role of EDTA on rutile flotation using Al³⁺ ions as an activator

Rutile is a relatively stable mineral, due to its weakly specific adsorption to collectors. The development and application of a high efficiency and low-toxicity activator is the main challenge in rutile flotation. In this study, Al³⁺ ions and EDTA (ethylene diamine tetraacetic acid) as mixed activators were investigated using micro-flotation tests. The results of the micro-flotation tests showed that the flotation recovery was slightly increased (from 65.8% to 69.7%) using single Al³⁺ ions as the activator and surprisingly, the activating effect was sharply improved (from 69.7% to 80.6%) after adding EDTA. The activating mechanism of Al³⁺ ions and EDTA was revealed by adsorption capacity measurements, zeta potential measurements, FT-IR spectroscopy analysis and XPS analysis. Al³⁺ ions were adsorbed on the rutile surface in the form of Al(OH) ^3- (n = 0, 1, 2), which increased the zeta potential and the activating sites for anionic collector adsorption. The addition of EDTA removed the surplus Al³⁺ ions, and prevented the generation of hydrophilic colloidal Al(OH)₃ over the pH range of optimum flotation.