Application of a novel and eco-friendly metal ion-carbohydrates mixed depressant for efficient separation and enrichment of phosphate ores

To address the low flotation separation efficiency between apatite and calcite, a novel fucose–CuSO 4 complex depressant was developed. This study elucidated the selective depression mechanism of the fucose–CuSO 4 complex on calcite. Micro-flotation results demonstrated that under optimized conditions—pH 9, CuSO 4 concentration of 3 × 10 −4  mol/L, and a molar ratio of CuSO 4 to fucose of 1:3—the recovery of apatite and calcite were 95.78 % and 14.71 %, respectively. Experimental findings revealed that when CuSO 4 is used alone, Cu 2+ preferentially adsorbs onto the apatite surface, whereas SO 4 2− selectively binds to Ca sites on the calcite surface. In the presence of both fucose and CuSO 4 , a ternary bridging structure—CO 3 2− –Cu 2+ –O (fucose)—is formed via oxygen atoms in carbonate groups on calcite surface. The adsorbed species included CuC 6 O 5 H 10 + complexes, with an adsorption layer thickness of 20–40 nm. In contrast, no characteristic ion fragments of fucose were detected on the apatite surface, the adsorption layer thickness ranged from 5 to 10 nm, with significantly lower density. DFT calculations confirmed effective orbital overlap between fucose and Cu(OH) 2 , indicating strong interaction. The adsorption energy of fucose on calcite in the presence of Cu(OH) 2 was calculated as −191.57 kJ/mol, substantially higher than that on apatite, thereby validating the selective depression mechanism. This study elucidates the depression behavior of fucose–Cu 2+ complex depressants and provides a new idea for the selective suppression of calcium-bearing gangue minerals.