Study On The Selection And Mechanism Of Separation Inhibitors Of Scheelite And Calcium - Containing

The floatability of scheelite is very similar to its in common calcium gangue, such as fluorite and calcite. At present, our country still has some ore dressing workshop with high calcium content of gangue, used heating flotation with mature technology, but this method in the process of production can lead to process operation difficulties, poor environment and high cost.Studies on the crystal structures of scheelite, calcite, and fluorite reveal that the Ca-0 bonds of scheelite, calcite, and fluorite, are 0.09,0.12, and 0.07, with bond lengths of 2.48,2.36,and 2.37A, respectively. The similar crystal structures cause dissociating surfaces of the three kinds of minerals against the surface dominated by metallic ions upon crushing, and considerable calcium ions in high-energy state appear on the mineral surfaces. Effective separation of scheelite, calcite, and fluorite from ore pulps is difficult because of the similar chemical characteristics of the mineral surfaces.Sodium silicate is a common inhibitor for gangue minerals that is used to inhibit calcite and fluorite in scheelite flotation at room temperature. This study explores the mechanisms of action of the inhibitor systematically from the aspects of single-mineral flotation behaviors, solution chemistry, zeta potential, infrared (IR) spectra, and photoelectron spectra. The study aims to explore differences between the mineral surfaces in the adsorption form and capacity of sodium silicate in the process of inhibiting Ca-bearing gangue, to find new rational agent regimes, and to intensify inhibitory actions on Ca-bearing gangue. The main findings are as follows:In single-mineral flotation tests, the effects of sodium silicate, hexametaphosphate, sodium fluorosilicate, oxalic acid, tannins, carboxymethyl cellulose, and sodium lignosulfonate on the flotation behaviors of Ca-bearing minerals under different solution conditions (concentration and pH value) are confirmed. Studies show that the sequence of sodium silicate inhibition of the three kinds of Ca-bearing minerals is fluorite>calcite>scheelite;the sequence of sodium fluorosilicate inhibition is calcite>fluorite>scheelite;the sequence of hexametaphosphate inhibition is fluorite>calcite-scheelite;the sequence of oxalic acid inhibition is fluorite>scheelite>calcite; the sequence of tannin inhibition is fluorite>scheelite>calcite; the sequence of carboxymethyl cellulose inhibition is fluorite>calcite>scheelite; and the sequence of sodium lignosulfonate inhibition is fluorite>calcite-scheelite. Tests on strengthening the inhibitory effects of sodium silicate with metallic ions showed that, within a pH value range of 7.0～11.0, three kinds of metallic ions, namely Al3+, Fe2+ and Pb2+, can affect the recovery rates of scheelite, calcite, and fluorite. Among the ions, Fe2+ slightly affects the recovery rate of scheelite while efficiently strengthening the inhibitory effects of sodium silicate on calcite and fluorite. This finding indicates that Fe2+ ions not only act as an "adjuvant inhibitor" but also enhance the selectivity of sodium silicate.Studies on solution chemistry show that calcium ions are preferentially separated or dissociated from ore pulps into scheelite, calcite, and fluorite at the optimal pH for flotation. Moreover, at this the pH value, the dominant hydrophilic group in sodium silicate and sodium silicate hydrolysates is [SiO(OH)3-].Studies on zeta potential show that the three kinds of minerals, namely, scheelite, calcite, and fluorite, had the mineral surface zeta potential decreased to varying degrees (scheelite<calcite<fluorite) under the actions of sodium silicate. This finding indicates that the adsorption of hydrophilic groups [SiO(OH)3-] produced in the hydrolysis of sodium silicate within the pH value range on the three kinds of minerals are also sequenced as follows:scheelite<calcite<fluorite. Under a suitable condition, sodium silicate is proven to realize the separation of scheelite, calcite, and fluorite.Comparison of the IR spectra of the three kinds of single minerals (such as scheelite, fluorite, and calcite) before and after acting with sodium silicate show that the vibration peaks of the Si-0 bonds in the sodium silicate groups had shifted in the IR spectra of scheelite, fluorite, and calcite. This result indicates the absorption of sodium silicate on the surfaces of the three kinds of minerals. After sodium silicate interacts with scheelite, new absorption peaks did appear in the spectral analysis results, and no remarkable peak displacement occurred. However, ions produced in the hydrolysis of sodium silicate exhibited more evident chemical adsorption on fluorite and calcite, with new absorption peaks in the IR spectrum. The inhibitory actions of sodium silicate on scheelite, calcite, and fluorite are sequenced as fluorite>calcite>scheelite; that is, the inhibitory actions of sodium silicate can facilitate the separation of scheelite, fluorite, and calcite under the preferred experimental conditions. However, the inhibitory effects on calcite with sodium silicate alone are poorer than those on fluorite. Thus, other agents with the inhibitory effects should be used to improve high-grade tungsten concentrates.X-ray photoelectron spectroscopy shows that the three kinds of minerals, namely, scheelite, calcite, and fluorite, exhibit Si-O absorption peaks on the mineral surfaces under the actions of sodium silicate; the molar percentages of Si 2p follows the order:scheelite<calcite<fluorite. This trend verifies the significant differences in the adsorption of sodium silicate on the mineral surface. These differences lead to differences in the floatability and enable the separation of minerals. Moreover, a Si-O binding energy of 102.13 eV is detected in the photoelectron spectra of scheelite, calcite, and fluorite. This binding energy is not ascribed to the Si-O binding energy in sodium silicate. Studies show that, in standard Si-O binding energy in CaSiO3, the calcium ions dissociate preferentially, and [SiO(OH)3-] produced during the hydrolysis of sodium silicate may produce CaSiO3 in the ore pulp. Moreover, the ions turn mineral surfaces hydrophilic after being absorbed due to strength differences. Third, in the process of FeSO4 (as the adjuvant inhibitor) inhibition of gangue after synergistic action with sodium silicate, only the calcite surface showed a significantly increased molar percentage of Si2p. This finding indicates that the adjuvant inhibitor can increase the adsorption of hydrophilic ions produced in the hydrolysis of sodium silicate on the calcite surface, thus further reducing the floatability of calcite. Finally, after synergistic action with sodium silicate, FeSO4(as the adjuvant inhibitor) exhibits molar percentages of Fe2p on the surfaces of the three kinds of minerals in the following order:calcite>fluorite>scheelite. After the addition of the adjuvant inhibitor, the O1s peak value of calcite is markedly increased, indicating the possible formation of new compounds. A new binding energy of 531.9eV is detected after the peak fitting of the O1s spectrum of calcite. Studies show that the binding energy is attributed to the 0-0 binding energy of FeOOH. The hydrophilic FeOOH is selectively absorbed onto the calcite surface, thereby reducing the calcite floatability.On the basis of the preliminary research on the mechanism, in view of the scheelite resources in Yunnan wenshan for flotation experiment, adopting the combination of sodium silicate+FeSO4inhibitors, slurry pH 10.5 and collector for 733 agents obtained under the condition of scheelite concentrate containing WO363.17%, recovery was 86.32%, from the experimental results verified the accuracy of the mechanism.