Study On Flotation Process And Mechanism Of Low-grade Phosphate Ores

High-grade phosphate ores are almost exhausted in China.Low-grade phosphate ores are the focus of the current research.The demand of phosphorus chemical industry for the flotation of phosphate ore is increased.The collectors having high flotation properties are needed to prepare.Amino acid-based surfactants are new surfactants having one amino group,one carboxyl group and one hydrophobic group in their molecular structures.Such surfactants not only have good properties of foaming,emulsifying and wetting,but also easily adsorb on mineral surfaces.The surfactants have good safety to environment and organism and also show low irritation and toxicity and good biodegradability.Firstly,four amino acid-based anionic surfactants with different structures were synthesized.A surfactant(C12GlyNa)with the same alkyl chain length but with only one carboxylate group was also synthesized and evaluated.A series of dicarboxylate-based surfactants(C12Mal Na2,C12 Asp Na2,C12GluNa2)with varying distance between the carboxylate groups(one or two methylene groups)were synthesized,the structures of which were characterized by 1H NMR and IR spectroscopy.The surface activity,aggregation number and foam stability of four surfactants were studied.The results show that the surface tension of the critical micelle concentration(cmc)and the critical micelle concentration(gcmc)increase,the saturated adsorption amount decreases and the aggregation number decreases when the carboxyl group of the polar group is increased from one to two.Foaming ability and foam stability are decreased when the carboxyl group is increased.When methylene is added between the two carboxyl groups,the minimum surface tension of surfactants remains almost unchanged,but the cmc and ?max decreases,Amin increases,the aggregation number decreases,and the foaming ability decreases.The wettability of four amino acid-based anionic surfactants on the surfaces of apatite,calcite and dolomite was studied.The effect of surfactant concentration on contact angle,adhesion force,adhesion work and solid-liquid interfacial tension was discussed.The results indicate that the contact angle increases firstly with the increase of surfactant concentration and reaches the maximum value,and then decreases with the further increase of surfactant concentration.The maximum contact angle of the same anionic surfactant on the surface of apatite is lower than that on calcite and dolomite.The adsorption mechanism of the surfactants on the mineral surfaces was studied.The amino acid-based anionic surfactant,C12 GlyNa,was selected as a collector in the flotation process of phosphate ores.The optimized flotation conditions are shown as following.The grinding time is 12 min.The pulp p H is 5.0.The dosage of the inhibitor(YZ-1)is 400g/t.The dosage of the collector is 600g/t.The flotation time is 50 s.The grade of P2O5 for the phosphate ores is increased from 26.97% to 31.02%.The content of Mg O for the phosphate ores decreases from 5.28% to 1.27%.The recovery of P2O5 for the phosphate ores is 85.96%.The surfactant,C12 GlyNa,shows high flotation properties for phosphate ores.The flotation mechanism was studied by the experiments of floatation recovery,Zeta potential and adsorption.The results show that the four surfactants have different collecting abilities for the apatite,calcite and dolomite.The surfactants,C12 Mal Na2 and C12 GlyNa,have high flotation ability for calcite and dolomite.