Research On The Performance And Mechanisms Of Depressants For Separating Scheelite From Calcareous Gangue Minerals By Flotation

The flotation separation of scheelite from fluorite and calcite is one of the interesting issues in the field of minerals processing. The separating difficulty of scheelite from fluorite and calcite is that the similar flotability of these minerals due to the similar crystal and surface chemical properties, therefore, it is necessary to strength the selective collecting of sheelite and the selective depressing of calcareous gangue minerals in the flotation prcess.The depressing behaviors and reaction mechanisms of different depressants on the flotation of scheelite, fluorite and calcite have been investigated by means of flotation test, zeta potential measurement, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. In order to reveal the microscopic mechanisms between depressants and minerals, the structure of minerals and the interaction between minerals and depressants have also been studied using the Quantum Chemistry and Band Theory. The major contents of this study are as follows:The depressing behaviors of sodium silicate, silica gel and the combined depressant of sodium silicate and silica gel on the flotation of scheelite, fluorite and calcite have been investigated by micro-flotation. In the presence of sodium oleate or731, the depressing effect can not be enhanced with increasing the dosage of silica gel in combined depressant for separating sheetite from fluorite and calcite by flotation within the pH range of9.7to10.3, and the optimum dosage of combined depressant is2.5g/L. The flotation recovery of three minerals changes according to the order:scheelite>calcite>fluorite while using combined depressant. In the presences of75mg/L731, the depressing effect of sodium silicate on the flotation of minerals can be strengthed with the addition of Al3+, Pb2+, K+and Ca2+over the pH range from9.7to10.3. The flotation separation of scheelite from artificial mixtures which composed with50%scheelite and50%calcite is easier than that from artificial mixtures which composed with50%scheelite and50%fluorite. The flotation separation of artificial mixtures composed with sheelite, calcite and fluorite had also shown some selectivity.The selective depressing effect of organic depressants on minerals falls in the following order:sodium poly acry late>citric acid>tannin extract>starch. The scheelite can be separated efficiently from fluorite and calcite by flotation in the pH range from8.7to9.3using5×10-4mol/L sodium oleate as collector and37.5mg/L PA-Na-2as depressant.Using75mg/L731as collector, fluorite and calcite can be depressed effectively by PA-Na-2and PA-Na-3in the pH range from8.7to9.3, and the flotation recoveries of these two minerals are below20%, while the flotation recovery of scheelite remaines at about70%. The optimum concentration of PA-Na-2and PA-Na-3for the flotation separation of scheelite from fluorite and calcite is37.5-50.0mg/L and22.5-30.0mg/L respectively. Pb2+can activate the floatability of scheelite in weak alkaline conditions when PA-Na-2is used as depressant, and then the flotation separating selectivity of the artificial mixtures can be improved.The FTIR spectra of minerals treated with sodium silicate were studied. The characteristic peaks of minerals shifted a little wavenumbers due to the stretching vibration of Si-O from sodium silicate, and it shows that sodium silicate adsorbed on three mineral surface. New antisymmetric vibration characteristic peaks and symmetric vibration absorption peaks of COO-were observed on the mineral surface after the reaction with sodium polyacrylate, and it indicates that sodium polyacrylate is bound to the three mineral surface by chemical adsorption.The results of zeta potential measurements show that the zeta potentials of scheelite shift negatively a little, however, the zeta potentials of fluorite and calcite shift to more negative values in the presence of sodium silicate and sodium polyacrylate. The zeta potentials shift negatively abide by the order:fluorite>calcite>scheelite with the adding of sodium silicate, and the order:fluorite≈calcite>scheelite with the adding of sodium polyacrylate, and these results are corresponding with the results of miroc flotation tests.The XPS measurments show that Ca2p binding energy of minerals surface move to the direction of high energy in the following order: calcite>fluorite> scheelite. It indicates that sodium silicate and sodium polyacrylate all adsorb on the surface of scheelite, fluorite and calcite, but the adsorption on the surface of scheelite is the weakest.The quantum chemical simulation indicates that the absolute value of adsorption energy abided by the oreder:fluorite (293.29eV)> calcite (178.54eV)> scheelite (133.57eV) when sodium polyacrylate adsorbs on the three mineral’s surface in aqueous solution. These results are consistent with the results of micro-flotation experiments.Batch flotation tests have been conducted for Jiangxi scheelite ore (WO30.55%) with pre-desulfurization. By adopting a circuit with one stage rougher flotation, five stages of cleaner and three stages of scavenger, the scheelite concentrate was produced with the grade of57.93%WO3and the recovery of62%WO3while using Na2SiO3as rough floatation depressant. When the depressant PA-Na-2was used for rough floatation, the result shows that the WO3grade of scheelite concentrate is53.06%and the recovery of WO3is52.75%by adopting a circuit with one stage rougher flotation, six stages of cleaner and three stages of scavenger. For both batch tests, the concentrate after the twice blank cleaning was condensed to50%wt, and stirred strongly for45min with the addition of6000g/t Na2SiO3.