Apatite and dolomite present challenges in their separation due to their similar surface chemistry. To achieve flotation separation of apatite and dolomite, depressants are required, but conventional depressants have several drawbacks. Hence, the development of effective and environmentally friendly depressants is of great importance. This study aimed to investigate the depressive effect of gallic acid (GA) on the flotation separation of apatite from dolomite using sodium oleate (NaOL) as the collector. The floatability of apatite and dolomite was examined through micro-flotation. The findings revealed that, with 1.0 × 10⁻⁴ mol L⁻¹ NaOL, the recovery rates of apatite and dolomite were 86.29% and 77.42%, respectively. After introducing 2.0 × 10⁻⁴ mol L⁻¹ GA, the recovery of apatite remained at 83.42%, while that of dolomite drastically decreased to only 14.33%. The selective depression mechanism of GA in the flotation separation of apatite from dolomite was investigated using various techniques, including zeta potential, contact angle, UV-vis, FTIR, XPS, ToF-SIMS, and AFM analyses. The results demonstrated that GA increased the hydrophilicity of the dolomite surface and impeded the adsorption of NaOL on that surface without affecting the apatite. GA was found to bind to Ca and Mg sites on the dolomite surface through –OH and –COOH groups. The adsorption of GA on the dolomite surface was substantial, with the adsorption height primarily concentrated in the range of 10–30 nm. GA exhibited selective depression on dolomite, thus, enabling successful flotation separation of apatite from dolomite.

This review mainly discusses the evaluation criteria for green depressants, their application in typical salt and silicate gangue minerals, and a comparative analysis between novel green depressants and traditional depressants.