| A large amount of rare earth wastewater is generated in the process of rare earth mining and extraction.If it is allowed to flow into the area around the mining area,it will not only pollute the soil and water,but also lead to serious loss of rare earth resources.At the same time,rare earth is refractory and bio-enriched,which can enter the human body through the food chain and thus affect health.Therefore,the study of rare earth wastewater treatment has profound practical significance.Based on the application potential of clay minerals in the treatment of rare earth wastewater,vermiculite was used as the adsorption raw material for expansion modification and sodium modification,and the single factor influence experiment of La(Ⅲ)and Y(Ⅲ)in the adsorption solution was carried out.Combined with different characterization results,the adsorption behavior and mechanism were discussed.The main conclusions are as follows:(1)Natural vermiculite(Ve)has an irregular layered structure,and the structure is not destroyed after the adsorption of La(Ⅲ)and Y(Ⅲ).Under the conditions of temperature 45℃,p H value 5.5,initial solution concentration 40 mg/L,adsorption time 2 h,and the dosage of Ve for La(Ⅲ)and Y(Ⅲ)adsorption 2.5 g/L and 3.5 g/L,respectively,the removal rates of La(Ⅲ)and Y(Ⅲ)can reach 97.04% and 96.96%.The adsorption of La(Ⅲ)and Y(Ⅲ)by Ve is a spontaneous endothermic process that follows the quasi-second-order kinetic equation.The main process is chemisorption.The experimental data of Ve for La(III)and Y(III)were consistent with Langmuir isothermal adsorption model,and the maximum adsorption capacities obtained by fitting were 21.32 mg/g and 13.63 mg/g,respectively.(2)Expanded vermiculite material(Ev)was prepared by chemical and heat treatment composite modification of Ve.Ev retains the original layered structure of natural vermiculite,but the original compact layered structure is stretched out,and the surface becomes more rough and curly,and there is an irregular mesoporous structure.The specific surface area,pore volume and average pore size of Ev are improved compared with Ve.At the same time,the expansion process will lead to changes in the group and crystalline structure of vermiculite surface.The optimal dosage of Ev materials for La(Ⅲ)and Y(Ⅲ)adsorption was1.5 g/L and 2.5 g/L,respectively.The decrease of the dosage compared with Ve(2.5 g/L,3.5g/L)indicated that the expansion modification was successful and effective.The adsorption capacity of Ev for La(Ⅲ)and Y(Ⅲ)increased with the extension of contact time,the increase of p H value,the increase of initial concentration and the increase of reaction temperature.The adsorption of La(Ⅲ)and Y(Ⅲ)on Ev materials is an endothermic process,which conforms to the quasi-second-order kinetic model and follows the Langmuir isothermal adsorption model.The fitted maximum adsorption capacities of La(III)and Y(Ⅲ)on Ev surfaces are 29.28 and17.54 mg/g,respectively.Compared with Ve,they increased by 37.4% and 28.7%respectively.(3)The adsorption material Na-Ev modified by Ev sodium modification still retains its original layered structure,and sodium ions are successfully inserted into the Ev layer.The NA-modification process does not affect the composition of the original surface functional groups,and its specific surface area decreases and the average pore size increases.The optimal dosage of Na-Ev for the adsorption of La(Ⅲ)and Y(Ⅲ)was 1 g/L and 1.5 g/L,respectively,indicating that the adsorption effect was better than Ve and Ev.The increase of Na-Ev dosage,the extension of reaction time,the increase of p H value,the decrease of initial concentration and the increase of system temperature all have positive effects on the adsorption rate of Na-Ev.The adsorption of La(Ⅲ)and Y(Ⅲ)by Na-Ev is a forward heat absorption process,which conforms to the quasi-second-order kinetic equation and follows the Langmuir model.The theoretical maximum adsorption capacity of La(III)and Y(Ⅲ)on the surface of Na-Ev is 40.0 and 24.27 mg/g,respectively,which is 36.6% and 38.4% higher than that of Ev.(4)The adsorption mechanism of vermiculite-based adsorption materials for La(Ⅲ)and Y(Ⅲ)includes pore fixation,ion exchange and electrostatic attraction,in which ion exchange plays a major role in the adsorption process... |
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