Synergistic Depressive Mechanism of Cu ²⁺ /Salicylic Acid in the Flotation Separation of Apatite and Dolomite

Apatite and dolomite exhibit similar floatability due to their analogous calcium ion active sites, posing significant challenges for their flotation separation. The selection of efficient depressants is crucial for effective separation. The microflotation experiment is a core laboratory method in the field of mineral processing for studying the flotation behavior of single minerals/artificial mixed ores, optimizing reagent systems, and revealing the mechanism of action. This study employed copper ions (Cu²⁺) and salicylic acid (SA) as a combined depressant to investigate their selective depression effects on the two minerals through flotation experiments. The depression mechanism was elucidated using contact angle measurements, zeta potential analysis, adsorption capacity tests, X-ray photoelectron spectroscopy, and ToF-SIMS tests. Flotation results demonstrated that at pH 9.5 with a Cu²⁺:SA molar ratio of 1:1 (5 × 10^-4 mol/L), apatite recovery reached 92.23%, while dolomite recovery was significantly depressed to 19.88%, achieving remarkable selectivity. Mechanistic studies show that SA exhibits stronger adsorption on the surface of dolomite than on apatite, and the introduction of copper ions (Cu²⁺) further amplifies this difference. Cu²⁺ preferentially adsorbs on the dolomite surface to provide active sites and bridges SA to form a stable adsorption layer; this not only effectively occupies the adsorption sites of the collector and hinders the interaction between the collector and dolomite, but also the synergistic effect of these processes is the key to achieving selective inhibition. This study reveals the combined depressant's selective adsorption on dolomite via multiple characterizations. With clean and efficient properties, it not only optimizes phosphate ore flotation enrichment but also matters greatly for efficient clean phosphate utilization and securing strategic resources in agriculture and new energy.