Flotation Performances And Mechanisms Of Benzyl Quaternary Ammonium Salt For Phosphogypsum Desilication

Phosphogypsum is a kind of chemical solid waste,which contains more than 80%gypsum and has potential value to replace natural gypsum.However,quartz is one of the main factors that affect the purity of phosphogypsum and restrict the resource utilization of phosphogypsum.Therefore,the desilication of phosphogypsum is the prerequisite for its comprehensive utilization.At present,flotation is a better method to separate quartz from gypsum,and the collector is the key to determine the flotation effect.In view of this,in this paper,benzyl quaternary ammonium salt was used as phosphogypsum reverse flotation desilication collector,and physical property analysis,flotation test,adsorption test,interface chemical analysis and quantum chemical calculation were carried out to reveal the desilication performance of benzyl quaternary ammonium salt and its mechanism.The main research contents are as follows:Firstly,the physical properties of phosphogypsum,gypsum and quartz minerals were studied,and the flotation tests of single mineral and phosphogypsum were carried out.The results show that the quartz and gypsum are extremely hydrophilic and negatively charged.The flotation performances of benzyl quaternary ammonium salt collectors with different chain lengths（DDBAC,TDBAC,HDBAC）and traditional desilication collector dodecylamine（DDA）on quartz and gypsum were studied by single mineral flotation experiments.The results show that the flotation ability of the four collectors is in the order of TDBAC>DDBAC>HDBAC>DDA,the flotation recovery of quartz was 93.59%,while that of gypsum was only 10.77%after optimized flotation conditions.The results of mixed ore flotation test show that under the optimized conditions,the flotation recovery of gypsum reaches 93.04%and the concentration of gypsum in concentrate is 90.66%.The results of phosphogypsum flotation test also show that the flotation desilication rate of phosphogypsum is 60.00%when the p H of pulp is 5.5 and the dosage of reagent is 150 g/t,the content of gypsum in concentrate is 96.93%and Si O₂ is 1.38%.Flotation experiments show that benzyl quaternary ammonium salt has good selectivity for quartz in phosphogypsum and can effectively separate quartz from gypsum.Secondly,the adsorption mechanism of benzyl quaternary ammonium salt on two minerals surface was studied by reagent property analysis and adsorption test.The surface tension test results show that TDBAC’s flotation ability is better than DDA’s because TDBAC has a lower CMC value and a larger polar group size.The reagent adsorption test shows that the adsorption capacity of TDBAC on quartz surface is much greater than that of gypsum,which is basically consistent with the flotation test results.The results of adsorption kinetics and adsorption isotherm showed that the adsorption process of TDBAC on quartz and gypsum accord with the quasi-second-order kinetic model,and the adsorption isotherm was more in line with the Freundlich isotherm model.Furthermore,the interaction mechanism between benzyl quaternary ammonium salts and the two minerals was studied by means of contact Angle,Zeta potential,Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）.Contact Angle and Zeta potential results show that the quartz surface hydrophilicity is decreased obviously after TDBAC treated,but gypsum surface wettability basic has not changed.TDBAC makes the surface of quartz and gypsum electrical reversal,but quartz surface potential to the moving direction was significantly greater than gypsum,which indicated that the electrostatic adsorption of TDBAC on quartz is stronger than that of gypsum;FTIR and XPS analysis showed that hydrogen bonding was also the mechanism of TDBAC interaction with quartz.Finally,the mechanism of interaction between benzyl quaternary ammonium salt and two minerals was studied from the microscopic level by using quantum chemistry theory.The results show that oxygen element has the highest activity among the exposed elements on quartz and gypsum.The electronegativity and exposure density of oxygen atoms on quartz surface are higher than those on gypsum,and it is easier to interact with cationic collector.Adsorption kinetics simulation show that TDBAC is easier to adsorb with quartz and has good selectivity to quartz,and H on the benzyl position of TDBAC is easy to hydrogen bond with O on quartz surface.In this paper,the flotation performance and action mechanism of benzyl quaternary ammonium salt on quartz in phosphogypsum were systematically studied through physico-chemical property analysis,flotation test,adsorption test,surface and interface analysis test and quantum chemical computation,which provided theoretical basis and experimental support for phosphogypsum flotation desilication.