Study On Flotation And Separation Intensification Of Complex Refractory Scheelite And Its Reaction Mechanism

The flotation separation of scheelite from calcite and fluorite, and the recovery of micro-fine scheelite are always focuses in the field of minerals processing. It is difficult to solve some problems, such as the similar floatability of these minerals and interference among minerals with different sizes and among different minerals, which seriously decrease the recovery of minerals and selectivity of depressants. Therefore, this thesis systemically studied the effects of hydrophobic agglomerate, solid-liquid interface properties and mineral solution on the scheelite flotation using the new flotation chemical calculation method, combining with modern test technologies and flotation tests. Based on the above mentioned researches, the thesis presented the methods which strengthened the recovery and separation of scheelite by increasing the hydrophobic of scheelite surface, eliminating or weakening the influence of calcium-bearing minerals dissolution on the selectivity of depressant, and designing the collectors with good selectivity.Firstly, the thesis proposed and verified a new formula for the group electronegativity and researched the inductive and conjugation index for the study of structure-activity relationship of flotation reagents. As a result, a method named "Group electronegativity-inductive and conjugation index" was deduced. By this new method, the calculated results for the structure-activity relationship of flotation reagents are in accord with results of the quantum chemistry calculation, and these two methods are complement. Secondly, the thesis researched the surface properties and floatability of calcium-bearing minerals. The results showed that there were significant differences in zeta potential, calcium content on surface and group electronegativity of anions in the crystal lattice, which resulted in the flotation separation of scheelite from gangue minerals containing calcium. The flotation tests showed that combination of reagents can improve the scheelite recovery. The scheelite particle size had an influence on the optimum ratio of reagents, but had no effect on optimum addition order. The addition order exert obvious influence on the performance of combined reagents, and it was affected by reagents structures, pH values, reagent dosages and the ratio of combined reagents. The scheelite recovery decreased sharply with the increase of calcium ions concentration, but it can be restored by using sodium carbonate in the presence of calcite. It was found that the calcite and calcium ions could decrease the scheelite recovery and the selectivity of depressants.Based on the above studies, the influence of fine particles content on the recovery of coarse scheelite, hydrophobic agglomerate and sodium carbonate on scheelite flotation was studied using theoretical calculation, flotation tests and modern test technologies in light of the great amounts of micro-fine particles. The results showed that the floatability of scheelite had the positively correlated relationship with its size when sodium oleate was used as collector. The hydrophobic interaction plays a dominated role in the particles agglomerate of scheelite, and the interaction energy and fluid forces are associated with particles sizes, which result in that the agglomerate is more easily to de formed among fine particles and medium size particles compared with the coarse particles, and therefore the fine fractions (-10?m) decreased the recovery of coarse scheelite (38.5-125?m) while had little influence on the recovery of medium-size(10-38.5?m) scheelite. The exchange of tungstate ions and carbonate ions on the scheelite surface increased the adsorption of collectors that had stronger activity than HCO3/CO32-, and therefore improved the hydrophobic interaction among fine particles and medium size particles and decreased the negative effect of fine particles on the coarse particles, hence increased the flotation recovery and rate.In light of the similar floatability of scheelite, calcite and fluorite, and interference among minerals, the method to eliminate or reduce the effects of minerals interaction on the selectivity of depressants, and collectors with better selectivity has been designed and synthesized, so as to strengthen the separation of scheelite from calcite and fluorite. Based on the theoretical calculation and flotation tests, it was found that the separation effect of sodium silicate on scheelite and fluorite was better than that on shceelite and calcite. Depressant is better selectivity than sodium silicate should be applied to separate scheelite from calcite. The results of flotation tests and theoretical calculation showed that the dissolution of calcite is the main cause to decrease the selectivity of depressants, but sodium carbonate can be used to decrease the calcite dissolution, hence decrease the negative influence of calcite on the selectivity of depressants. Flotation tests results confirmed that CMC can accomplish the flotation of scheelite from calcite by using the sodium carbonate to reduce the negative effects of calcite on the selectivity of CMC, and the separation effect was better than sodium silicate, however, the dosage of sodium carbonate has an optimal range, and too much sodium carbonate would decrease the concentrate grade. Based on the new method of "Group electronegativity-inductive and conjugation index" and quantum chemistry calculation, a new reagent named dodecyl malonic acid (DCA) was designed and synthesized. The flotation tests indicated that the combined reagents of DCA and sodium oleate can separate the scheelite from calcite using CMC as depressant, and the selectivity of the combined reagents was better than that of sodium oleate. The sodium carbonate would reduce the concentrate grade. However, the addition of calcium not only reduced the negative effects of sodium carbonate on the grade of concentrate, but also further strengthened the separation of scheelite from calcite.Due to the low grade scheelite ore with only 0.15%?0.18% WO3 from Malipo in Yun Nan province, the thesis used sodium carbonate to adjust pH value, eliminate the influence of calcium-bearing minerals on scheelite flotation, improve the scheelite floatability and the recovery of auto-carrier flotation, employed sodium silicate as depressant, utilized the cooperative effect of combined reagents to improve the grade and recovery rate of rough concentrate, and a good flotation index has been obtained. The scheelite ore contains a great quantity of calcium-bearing minerals from Hu Nan province, and the content of calcium-bearing gangue minerals decreased and concentrate grade increased after the 731 was replaced by the combined reagents of DCA and sodium oleate.The research results of the thesis richened the system of scheelite flotation, provided the reference for researchers on the collection of fine scheelite and the separation of scheelite and calcium-bearing minerals.