1-Hydroxyethylidene-1,1-diphosphonic acid used as pH-dependent switch to depress and activate fluorite flotation I: Depressing behavior and mechanism

Fluorite is usually separated from calcite by froth flotation method using large amounts of sodium silicate depressant, which can cause trouble in the loss of fluorite and wastewater treatment. In this study, green and low-cost 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP or H 4 L) was used as pH-dependent switch to initially depress fluorite for calcite pre-removal at pH 6.0, and then activate fluorite for further upgrading fluorite concentrate at pH 8.0. The depressing behavior and mechanism were reported in this work. H 2 L 2− was the dominant form of HEDP, and a stronger chemical adsorption of H 2 L 2− on fluorite hindered the subsequent adsorption of sodium oleate (NaOL), while that of the calcite showed the opposite result. Two active O atoms in H 2 L 2− could well match in interatom distance with two Ca sites on fluorite to form Ca-H 2 L complexes. The pH-dependent switch reagent reported here may open a new avenue for more selective separation among mixed mineral systems.