The Potential Role of Colloidal Silica as a Depressant in Scheelite Flotation

Abstract

The main challenge in scheelite flotation lies in the contamination of the concentrate by other calcium-bearing minerals, mainly calcite. To remedy this problem, sodium silicate is frequently used as a depressant. According to the literature, one hypothesis for the mechanism of water glass consists in its absorption onto calcite through colloidal silica formation, preventing hydrophobization by the collector. This short communication presents research conducted on the direct use of colloidal silica as a depressant in scheelite flotation. Colloidal silica is shown to have an impact on scheelite flotation, especially by depressing silicates.

Laboratory Testing of Scheelite Flotation from Raw Ore in Sangdong Mine for Process Development

“…Na2CO3 is ionized in the pulp, and CO3 2-reacts with Ca 2+ on the surface of Ca-based minerals and precipitates as CaCO3 like surface carbonation. In this process, the Ca-bearing gangue minerals such as calcite and fluorite, which have relatively high Ca surface site density, have been employed to precipitate on the surface by reacting earlier than scheelite with low Ca surface site density (Fluorite: 11.1-12.9 μmol/m 2 , Calcite: 8.24 μmol/m 2 and Scheelite: 5.06-6.58 μmol/m 2 ) [24,26,39]. To support this, there is a Ca-O (Ca-F) bond length.…”

“…It is known that the shorter the bond length, the larger the bond energy. Relatively short bond lengths of calcite and fluorite reacted with Na2CO3, which is likely to be depressed before scheelite due to the enhanced reactivity due to the larger bond energy (Calcite: 2.36 Å , Fluorite: 2.37 Å and Scheelite: 2.44-2.48 Å ) [15,24,26,40]. Furthermore, Na 2+ in Na2CO3 reduces the probability that Ca 2+ activates quartz and hereby silicates [26,41].…”

“…Corresponding to the preliminary experiment result, the pH of the pulp was adjusted to 11 and the experiments were conducted using NaOH, Na 2 S, CaO, and Na 2 CO 3 as pH modifiers. For a depressant and a collector of scheelite flotation, Na 2 SiO 3 and oleic acid were selected due to the preliminary experimental results and they are widely used in many conventional processes [5,23,24,34,[36][37][38]. Figures S1-S3 show the results of the experiment with the variable type of depressant, collector, and frother in this study.…”

“…Scheelite is often associated with other Ca-bearing salt-type minerals such as calcite and fluorite, which has similar characteristics [5][6][7]22,23]. Their dissolved mineral species in the pulp might be some reactions such as hydrolysis, precipitation and adsorption which can affect the interaction between reagents and minerals [5,24]. Therefore, it is desirable to select suitable modifiers and depressants for selective separation which is available through the flotation method [5][6][7][8]12,16,21,24].…”

“…Their dissolved mineral species in the pulp might be some reactions such as hydrolysis, precipitation and adsorption which can affect the interaction between reagents and minerals [5,24]. Therefore, it is desirable to select suitable modifiers and depressants for selective separation which is available through the flotation method [5][6][7][8]12,16,21,24]. In particular, the studies on various kinds of flotation reagents have been carried out, and most of them have focused on the development of new collectors and depressants [8,11,14,15,21,25].…”