A novel mixed depressant for the flotation separation of scheelite and cassiterite: Adsorption mechanism and performance

Abstract

Citric acid (CA) exhibits weak inhibitory on some oxidized gangue minerals owing to its relatively few hydrophilic polar groups (OH and COOH). This study investigate the synergistic mechanism of ferrous ions (Fe²⁺) to enhance both the selective adsorption capacity and stability of CA. The separation of scheelite and cassiterite through a flotation process was successfully achieved using a Fe²⁺/CA mixed depressant. Micro-flotation test results revealed that with the addition of Fe²⁺/CA, 84.60 % of scheelite and 23.64 % of cassiterite were recovered in the foam concentrate, with grades of 66.26 % and 17.73 %, respectively. Fe²⁺/CA had a strong depressing effect on cassiterite, resulting in a 69.30 % decrease in its recovery and a 20.33 % decrease in its grade. This indicates the effective separation of scheelite from cassiterite. Fe²⁺/CA exhibited a high adsorption affinity for the cassiterite surface, which mainly comprised L^3–, Fe²⁺, and FeOH⁺ components. Additionally, the FeOH⁺ complex, formed from the pre-reaction between Fe²⁺ and CA, exhibited significant chemical adsorption at the Sn active sites, thereby depressing cassiterite. The high-intensity adsorption peaks at cracks and the significant increase in the normalized intensity of FeOH⁺ on the cassiterite surface indicated that the FeOH⁺ complex had stronger adsorption on cassiterite and selectively depressed cassiterite. This enhanced both the selective adsorption capacity and stability of CA on the cassiterite surface. The Fe²⁺/CA mixed depressant achieved efficient flotation separation of scheelite and cassiterite.