Surface modification of typical calcium-containing minerals by aluminum ion and its effect on adsorption of citric acid

In this study, aluminum ion surface modification was used to improve the depressive performance of citric acid on calcite. The micro-flotation experiment showed that the mixed depressant of aluminum ion and citric acid displayed a higher separation effect on the two minerals than the single citric acid, the recovery of scheelite was 90.6 %, but that of calcite was 4.3 % using the mixed depressant. The artificial mixed mineral experiment confirmed that the mixed depressant exhibited an efficient separation effect, and an excellent scheelite enrichment index with WO3 grade of 67.36 % and scheelite recovery of 83.95 % was obtained using 1.0 x 10-4 mol/L aluminum ion and 1.0 x 10-4 mol/L citric acid. The surface characterization methods indicated that the aluminum ion complex was selectively adsorbed on the CO32- sites of the calcite surface in the form of aluminum citrate and monohydrogen aluminum citrate radical. The calculation result of thermodynamic and conditional stability constants revealed that the aluminum species complex aluminum citrate was more easily formed and more stable than monohydrogen aluminum citrate radical. Atomic force microscopy images showed that aluminum ion complexes were selectively adsorbed on the calcite surface in the form of clusters and sheets with higher adsorption height and density than scheelite. This study provides an excellent reagent system using for enriching scheelite.