Adsorption And Desorption Mechanism Of Ammonium And Lanthanum On Kaolin

Ionic rare earth ores contained heavy and medium rare earth elements as national strategic resources have attracted more and more attention.The rare earth elements in ionic rare earth ores are mainly adsorbed on the surface of fine particles by the ion exchangable phase.At present,the in-situ leaching method of ammonium sulfate is mainly used for mining.The rare earth ions adsorbed on the surface of the mineral particles enter the solution through the ion exchange with the ammonium ions.The solution containing rare earth and ammonium ions moves in the ore body and constantly interacts with the ore body particles.Finally,the leaching liquor is collected and treated in a specific part of the mine.Therefore,the adsorption and desorption of rare earth ions and ammonium ions between the solid particle surface and the solution,and the competitive adsorption regularity between rare earth ions and ammonium ions on the solid particle surface,is of great theoretical and practical significance for the resource exploitation and related environmental protection of the ionic rare earth ores.In this study,lanthanum nitrate and ammonium sulfate were used as adsorbents and kaolin as adsorbents.Firstly,the related physical and chemical properties of kaolin adsorption were determined;secondly,the batch adsorption experiment of lanthanum and the desorption experiment of lanthanum extracted continuously were carried out;secondly,the batch adsorption experiment of ammonium sulfate and the desorption experiment of ammonium ion extracted continuously were carried out;finally,the competitive adsorption experiment of lanthanum and ammonium ion on kaolin surface was carried out.The results show that:(1)The adsorption of lanthanum on the surface of kaolin was divided into three stages,first increased,then gentle,and last increased with the increase of solution concentration.When the pH of the solution increased from 3 to 6,the lowest concentration of lanthanum ion on the surface of kaolin decreased from 9.95 mmol/L to 2.69 mmol/L.According to the regularity of adsorption and desorption of "threephase lanthanum",it is found that the rare earth in water-soluble phase is easy to be adsorbed and desorbed by water flow,so it is difficult to mineralization,the formation of rare earth in colloidal phase needs to be realized under specific conditions.Therefore,in reality,the rare earth elements in ionic rare earth ore are mainly in ion-exchangeable phase.(2)The adsorption of ammonia nitrogen on the surface of kaolin conforms to Langmuir isotherm adsorption model,which can be divided into physical adsorption,ion exchange adsorption and chemical adsorption.When pH increased from 3 to 6,the adsorption capacity of physical adsorption,ion exchange adsorption and chemical adsorption increased from 0.2 umol/g to 0.85 umol/g,0.7 umol/g to 3.7 umol /g,0.6 umol/g to 3.4 umol/g,respectively.PH affects the adsorption amount of ammonia nitrogen on the surface of kaolin by affecting the charged groups on the surface of kaolin.(3)Under the condition of pH=3~6,the competitive adsorption experiment of ammonium ion and lanthanum on the surface of kaolin was carried out.It was found that the order of adding ammonium ion and lanthanum to kaolin was different,the ratio of the maximum adsorption amount of lanthanum and ammonium ion by kaolin which was the adsorption selectivity coefficient "?" of kaolin was different,because the cations added first occupy the empty adsorption site on the surface of kaolin.In the competitive adsorption experiment of lanthanum and ammonium ion," ?=1.5 ",compared with ammonium ion,the adsorption of lanthanum by kaolin shows a selective advantage.