Studies Of Intensive Collectting Of Silicates And Selective Depressing Of Diaspore

This article is based on the difference of the crystal structure and surface properties of the main minerals in bauxite, put emphasis on the selective depression of diaspore and intensive collecting of silicates, such as kaolinite, illite and pyrophyllite, according to the principles and technologies of bauxite reverse flotation. In order to study the flotation behavior and the interaction mechanisms between flotation agents and minerals in the system of dodecyl-amine or in the quaternary ammonium salt, the methods such as flotation tests, the measurements of zeta potential, the adsorption of flotation agents, Fourier transaction infrared, augor electronic spectroscopy, as well as the quantum chemistry calculation are used. As following have been shown:At first, the crystal structure and electrical properties of diaspore, kaolinite, illite and pyrophyllite were investigated. When the minerals are grinding, kaolinite is hydrophilic and has bad flotability because of its broken bonds on the surfaces, that is hydrogen on the basal siloxane and the Si-O, Al-O on the edges. Pyrophyllite has good hydrophobic and flotability since the predominant interlayer bonding forces are Van der waals. Illite has good hydrophilic and bad flotability because of its ionic bonds on the surfaces. The point of zero charge(PZC) of diaspore is pH6.2, kaolinite is pH4.2, illite is pH3.0 and pyrophyllite is pH3.0.The second, we studied the flotation behavior of minerals and the interaction mechanisms with quaternary ammonium DTAL as a collector: Diaspore had bad floatbility while silicates had excellent floatbility, especially in the acid condition, with DTAL as a collector. This is a basis of the separation of diaspore and other silicates. In order to enlarge the flotation difference of diaspore and silicates, the regulators were used. The tests showed that the fluoride, sodium chloride and SFL wereeffective regulators. These regulators activated the flotation of silicates while had no effects on the flotation of diaspore.The mechanisms of DTAL in the flotation separation of diaspore and silicates were also investigated by several kinds of methods. It indicated that: the adsorption of quaternary ammonium DTAL on the mineral surfaces was electrical interaction. DTAL had much more higher adsorption on the silicates surfaces than on the surface of diaspore because silicates had high cation exchang capacities and DTAL had strong electrical interaction with the silicates surface, so that it could overcome the steric hindrance which was from the adsorption of DTAL on the surface of minerals.Fluoride interacted with the minerals with the substitution of the hydroxyls on the mineral surfaces. Fluoride ions markedly adsorbed on the silicates surfaces and dispersed to the interlayers of the silicates, then resulted in decreasment of the zeta potentials, accordingly, this prompted the adsorption of the cationic surfactant. The adsorption of fluoride ions was little and had no effects on the zeta potentials of the diaspore. In the condition of sodium chloride, the activation to silicates was from the intercalation of the chloride and the "salt effects", which obviously decreased the zeta potentials of silicates or decreased the critical micelle concentration of the surfactant and prompted the adsorption the collector. While the adsorption of the chloride ions on the diaspore was little, and didn't affect the zeta potentials of diaspore, too. The SFL decreased the adsorption of the collector on the diaspore while increased the adsorption of the collector on the silicates, which resulted in the selective depression on the diaspore and intensive collecting of silicates.The flotation separation tests of artificial mixed minerals demonstrated that diaspore could be separated from silicates with the SFL as a regulator, DTAL as a collector. The A/S ratio of concentrateincreased with the increase of A/S ratio of the original minerals, and also the recoveries of the alumina.The third, in the reverse flotation system of dodecylamine:Diaspore had stated flotability in the acid condition and its flotability increased with the increasement of pH with dodecylamine as a collector. The flotability of silicates was good in the acid condition but decreased with the increasement of pH. The order of the flotabilities of the three silicates was: pyrophyllite>kaolinite>illite.The interaction were mainly physical electrical forces between the dodecyl-amine and the alumina-silicates, except for the weak hydrogen. Dodecyl-amine gived a rise to the zeta potential of the diaspore while almost didn't affect that of silicates. The results of quantum chemistry calculation showed that the adsorption of dodecylamine on the aluminous minerals was more than on the siliceous mineral. The adsorption of alkaline dodecylamine molecular was more than that of acid dodecylamine ion on the surface of aluminous minerals. These results were consistent to the flotation tests.In order to carry out the reverse flotation of bauxite, the selective depression of diaspore or the activation of silicates flotation are necessary. The results of flotation tests indicated that the sodium hexmetaphosphate has selective depression on the diaspore. The depressing mechanisms were that sodium hexmetaphosphate preferentially interacted with the alumina sites by the chemical interaction, while didn't interact with the siliceous sites on the surface. After the interaction, the diaspore was overlayed by the sodium hexmetaphosphate and complete hydrophilic, so that it couldn't continuously interact with the collector. The silicates had the siliceous sites on the surface which didn't interact with the phosphates and the siliceous sites could further interacte with the collector, named dodecylamine. Consequently, silicates still had some hydrophobic and could be floated.The simulation results showed that the electronic cloud density of the adsorption of phosphates on the aluminous was much more bigger than that on the silicates, and it was more closed to the surfaces of the aluminous than to that of siliceous. Except for that, phosphates competed for the surface sites with dodecyl-amine, resulted in the desorption of the collector.The flotation separation tests of artificial mixed minerals demonstrated that diaspore could be separated from silicates with the sodium hexmetaphosphate as a regulator, dodecyl-amine as a collector. After the flotation, the A/S ratio of the mineral was from 2.1 to 7.8.Finally, the practice and sheets of the reverse flotation of bauxite:According to the conditions and results of the experiments, a practice was carried out to the actual bauxite in Henan province. The original mineral was selectively dispersed and get rid of the slurry in the pH9.0 by sodium carbonate, then floated separation with the SFL as a regulator and DTAL as a collector. The A/S ratio of the concentrate is 10.04 and the recovery of A12O3 is 85.76%.