The regulation mechanism of carboxylate/hydroxylate organic acid ligands coordinating with Fe3+ on the flotation separation of scheelite from calcite

Fe-organic complexes enabled selective flotation separation of scheelite and calcite. • Ligand structure governed Fe 3+ coordination stability and interfacial selectivity. • Fe-PA revealed higher calcite selectivity and depression efficiency than Fe-SA. • Fe-PA formed stable multidentate chelates with enhanced electronic delocalization. The similar surface physicochemical properties of scheelite and calcite hinder their selective separation due to the limited selectivity of depressants. In this study, Fe–organic complexes were prepared using succinic acid (SA) and pyrogallol (PA) as ligands to regulate scheelite/calcite flotation separation. Their coordination structures and interfacial mechanisms were elucidated using solution speciation analysis, UV–Vis spectroscopy, TEM, adsorption measurements, contact angle measurements, zeta potential analysis, XPS and DFT calculations. The Fe-organic complexes significantly enhanced flotation separation, with Fe-PA showing superior selective inhibition and yielding a tungsten concentrate with a WO₃ grade of 70.49% and recovery of 84.79%. Fe 3+ forms a stable coordination complex with ligands in a 1:2 ratio in weakly acidic conditions. SA interacted with Fe 3+ primarily through its carboxylate groups, whereas PA exhibited coordination behavior associated with its ortho-positioned phenolic hydroxyl groups. The stronger electron-donating ability of Fe-PA promoted Fe O coordination with active sites on calcite, giving an adsorption energy of −56.67 kJ·mol −1 , while its affinity toward scheelite was weaker. Consequently, Fe-PA selectively modified the calcite surface and inhibited BHA adsorption, resulting in different interfacial adsorption behaviors and providing insights into the relationship between ligand structure and interfacial adsorption behavior. Download: Download high-res image (234KB) Download: Download full-size image