Effects of alkaline treatment on the surface properties and flotation behavior of scheelite

Alkaline regulators can alter the surface properties of scheelite and thereby affect its interaction with collectors. This study compared the effects of NaOH and Na 2 CO 3 on the surface properties and morphology of representative crystal surfaces using microflotation tests, contact-angle measurements, atomic force microscopy (AFM), N 2 adsorption–desorption measurements, X-ray diffraction (XRD), and inductively coupled plasma atomic emission spectrometry (ICP-AES). At pH 11, the mean scheelite recoveries were 90.41 % in the NaOH system and 81.93 % in the Na 2 CO 3 system. The XRD patterns showed no appreciable change in the bulk crystal structure after either treatment. NaOH induced pronounced surface modification and increased the BET specific surface area from 0.0778 to 0.1696 m 2 ·g −1 ; these changes coincided with a stronger NaOL-induced hydrophobic response. By contrast, Na 2 CO 3 treatment was associated with surface flattening, a decrease in BET specific surface area to 0.0599 m 2 ·g −1 , and weaker NaOL-induced hydrophobic response. The combined AFM, BET, XRD, and ICP-AES results were consistent with localized surface modification in the NaOH system and carbonate-associated surface modification or passivation in the Na 2 CO 3 system. In single-run closed-circuit tests of the actual ore, the NaOH system produced a concentrate with a WO 3 grade of 66.43 % and a WO 3 recovery of 67.40 %, compared with 65.98 % and 64.89 %, respectively, in the Na 2 CO 3 system. Under the investigated conditions, NaOH caused more pronounced surface modification and a stronger NaOL-induced hydrophobic response than Na 2 CO 3 . The results suggest that regulator-dependent modification of the scheelite surface is associated with its subsequent response to NaOL, with the NaOH-treated surface exhibiting a stronger NaOL-induced hydrophobic response than the Na 2 CO 3 -treated surface.