Efficient flotation separation mechanism of scheelite from calcite and fluorite using carboxymethyl sulfonated lignin as environmentally friendly depressant

Scheelite is an important strategic resource and often associated with calcium-bearing minerals (calcite and/or fluorite), which pose a challenge to flotation separation due to their similar surface properties. The development of highly selective depressants is essential to effectively achieving flotation separation. In this work, carboxymethyl sulfonated organic solvent lignin (CSOL) with varying degrees of carboxylation was synthesized to serve as an organic depressant. Flotation results showed that with the addition of CSOL, the recoveries of calcite and fluorite significantly decreased from 70.98 % to 9.34 % and from 91.8 % to 8.00 %, respectively, while the recovery of scheelite dropped slightly, from 94.9 % to 91.62 %. The contact angle, zeta potential and XPS results demonstrated that hydrophilic CSOL could adsorb onto the calcite sites on the surfaces of calcite and fluorite through carboxyl and sulfonic groups, thus increasing their hydrophilicity and decreasing their floatability. Negatively charged CSOL had a small amount of adsorption on the negatively charged scheelite surface due to strong electrostatic repulsion, thus it had no great effect on the further adsorption of collector sodium oleate (NaOL) and flotation of scheelite. This work provides valuable insights into the flotation performance and mechanisms of lignin-based environmentally friendly depressants for flotation separation of scheelite from calcium-containing gangue minerals.