Uncovering the Selectivity of 4-((2-Octyldodecyl)oxy)-4-oxobutanoic Acid for Flotation Separation of Fluorite from Calcite

Fluorite and calcite have identical calcium active sites, rendering their flotation separation challenging. Herein, a novel surfactant 4-((2-octyldodecyl)oxy)-4-oxobutanoic acid (TEUA) with double hydrophobic chains and an ester group was designed as a fluorite flotation collector. Microflotation results indicated that TEUA could selectively separate fluorite from calcite at pH ∼ 8.0, with much higher separation efficiency than oleic acid (OA). Surface tension, adsorption capacity, FTIR, surface energy, and contact angle tests demonstrated that TEUA owned higher surface activity and stronger adsorption affinity to fluorite, making the fluorite surface more hydrophobic and easier to attach bubbles than calcite. In situ AFM image, AFM force, and the extended Derjaguin–Landau–Verwey–Overbeek (E-DLVO) theory analyses confirmed that TEUA’s adsorption facilitated fluorite more hydrophobic than calcite at nanoscale. And dynamic foam stability tests indicated that TEUA’s lower foaming ability reduced the froth entrainment of calcite. TEUA’s selective hydrophobization to fluorite and reduced froth entrainment of calcite together rendered its superior flotation separation efficiency between fluorite and calcite compared to OA. These results exhibited important insights on the development of new efficient fatty acid collectors and understanding their selective adsorption and hydrophobicity toward mineral surface at the nanoscale.