Abstract:

Phosphate rock flotation is a widely used method in phosphate rock processing in which aimed minerals are selectively separated from gangue minerals based on the difference in surface wettability. Due to its associated minerals in phosphate rock, there is always a lot of Mg²⁺, Al³⁺ and Fe³⁺ in phosphate rock slurry. The existence of metal ions, whose forms are changed with slurry pH, can affect the flotation operation by adsorption on the mineral surface. The surface properties of minerals are the main factors affecting their dispersion, aggregation, and flotation behavior. Herein, the influences of unavoidable metal ions, including Mg²⁺, Al³⁺ and Fe³⁺, on the surface properties of fluorapatite （FAP） in pulp were studied by solution chemical calculation, turbidity, contact angle and Zeta-potential test. The results showed that the forms of metal ions in solution vary with pH. FAP is a hydrophilic mineral, and the influence of adding Fe³⁺ ions on the wettability of FAP was greatly affected by pH. In acidic environment, Fe³⁺ ions could promote the hydrophilicity of FAP, while in neutral and alkaline environment, Fe³⁺ ions could inhibit the hydrophilicity of FAP. The effects of Mg²⁺ and Al³⁺ ions were less affected by pH, and both Mg²⁺ and Al³⁺ ions inhibited the wettability of FAP in neutral environment. In the range of pH 3-11, Mg²⁺ mainly existed as divalent ions, which compressed the double layer on the FAP surface. Al³⁺ and Fe³⁺ mainly generated hydroxide precipitation through hydrolysis to cover the surface of FAP. Mg²⁺, Al³⁺ and Fe³⁺ ions would destroy the dispersity of FAP and promote the coagulation of FAP.

Key words: phosphate rock, fluorapatite, wettability, dispersibility, metal ion, surface property