Effect of metal phenolic networks constructed via tannic acid coordination with Fe³ ⁺ on scheelite/calcite flotation selectivity

Metal-phenolic networks (MPNs) offer a promising, environmentally compatible strategy for cleaner, more efficient tungsten resource utilization due to their tunable structures and efficient interfacial regulation. This paper investigates the structural regulation effect of a self-assembled Fe(Ⅲ)-tannic acid (TA) MPN, formed through the coordination of TA and Fe 3 + , on the flotation separation of scheelite and calcite. The adsorption mechanisms were elucidated through contact angle, adsorption capacity, zeta potential and XPS analyses, while TEM, UV–vis spectroscopy and DFT calculations were employed to probe the micro- and coordination structures. The results demonstrated that the Fe(Ⅲ)-TA MPN formed at pH= 4 with TA:Fe= 1:1/2 exhibited minimal inhibition of scheelite but strong suppression of calcite, yielding a tungsten concentrate with a WO 3 grade of 71.35 % and recovery of 86.94 %. This behavior was attributed to the formation of a mono-coordination network (Fe:TA=1:1), which adsorbed onto both mineral surfaces through Fe-mediated interactions. In contrast, the tris-coordination network (Fe:TA=1:3) displayed the highest intrinsic reactivity but was limited by Fe(OH) 3 colloid deposition, hindering collector adsorption. The bis-coordination network (Fe:TA=1:2) remained stable over pH= 3–8 and selectively adsorbed on calcite via synergistic electrostatic attraction, hydrogen bonding, and chemical bonding, forming stable hydrophilic films. However, strong electrostatic repulsion hindered Fe(Ⅲ)–TA MPN adsorption on scheelite, thus maintaining its floatability. This study elucidates the structure-function relationship of Fe(III)-TA MPNs, offering new perspectives for designing environmentally friendly inhibitors for selective tungsten flotation.