New insights into the depressive mechanism of citric acid in the selective flotation of scheelite from fluorite

Abstract

The effects of citric acid (CA) as a depressant in the separation of scheelite and fluorite were evaluated by microflotation test. The underlying selective separation mechanism was revealed via wetting analysis, Fourier transform infrared (FTIR) spectroscopy, thermodynamic calculations, adsorption amount tests, inductively coupled plasma–optical emission spectroscopy (ICP–OES) and atomic force microscopy (AFM). Microflotation tests showed that CA strongly depressed the flotation of fluorite but not of scheelite. Artificial mixed mineral separation tests showed that scheelite and fluorite achieved a good flotation separation effect in the presence of CA as the depressant. Mineral surface wettability analyses and adsorption amount tests indicated that CA was more strongly adsorbed onto the surface of fluorite than onto the surface of scheelite. FTIR spectroscopy proved that CA had a strong chemical adsorption on fluorite surface. Thermodynamic calculations indicated that CA could spontaneously form the organic complex CaL− on the surface of fluorite but not on the surface of scheelite. ICP–OES revealed that a strong dissolution behaviour occurred on the surface of fluorite that caused more calcium ions to dissolve into the slurry, thereby decreasing the number of adsorption sites of calcium ions on the surface of fluorite. AFM intuitively confirmed the intense adsorption and the strong dissolution behaviour of CA on the surface of fluorite.