Abstract:The objective of this study was to assess the effect of Al³⁺ dissolution induced by pre-agitation on the flotation of ultra-fine diaspore with the addition of NaOl. The results of flotation tests show that the addition of a small amount of Al³⁺ into the pulp is helpful for flotation, however, after Al³⁺concentration is higher than 1×10^-5 mol/L, the addition of Al³⁺ has a detrimental effect on flotation. A short time of pre-agitation can improve the recovery of diaspore, while the recovery decreases gradually when the miners are agitated more than 10 min. ICP measurements, adsorption capacity measurements, contact angle measurements and the analysis results of flotation solution chemistry show that Al³⁺ exists mainly as a form of hydroxy complexes in solution with a small additive quantity, which promotes the adsorption of NaOl on the mineral surface and enhances the hydrophobicity of diaspore. With a big additive quantity, the amount of hydrophilic hydroxide precipitation increases gradually, and the hydrophobicity of minerals becomes worse so that the floatability is decreased. Zeta potential measurements and particle size measurements show that the electronegativity of particles decreases and the particle size increases after pre-agitation, the results indicate the formation of flocculation. Compared with the direct addition of Al³⁺, an appropriate pre-agitation is beneficial to the formation of hydrophobic flocculation in pre-agitation, which is also an important reason for the higher recovery.

Key words: pre-agitation; diaspore; ultra-fine particle flotation; ions dissolution; hydrophobic flocculation