Study On The Preparation Of Silicon-based Materials And The Absorption Properties Of Rare Earth Elements

Rare earth is a strategic metal resource that plays an important role in the new material industry,modern high-tech industry and national defense industry.China is a big country producing rare earths,but it is currently facing problems such as the reduction of rare earth reserves,uneven distribution of rare earth ore,and the difficulty of using associated ore.Expanding the sources of rare earths and improving the separation efficiency of rare earths has become a top priority.New rare earth sources mainly include associated ore tailings,brine,bauxite slag,fly ash,and electronic waste.The total amount of rare earth elements in these sources is large and there are many types.The enrichment,recovery and utilization of rare earth metals from new rare earth resources have important economic value.However,the concentration of rare earth elements in new resources is usually low.For example,the concentration of rare earth elements in the solution obtained by leaching is often at the ppm level;in addition,there are many other non-rare earth metal elements in these rare earth resources,such as When separating rare earth elements from bauxite tailings,fly ash and mining brine,the acid solution usually contains high concentrations of metal ions such as Al³⁺,Ca²⁺,Fe³⁺and Mg²⁺.All these have brought huge challenges to the recovery and utilization of different rare earth metals from alternative rare earth resources.The industry mainly uses liquid-liquid extraction to enrich and separate rare earth elements.The purity of the rare earth elements obtained by this method is relatively high,but there are many problems such as complicated processes,excessive waste liquid generation,and unfriendly environment.In contrast,solid-phase adsorption has relatively high separation efficiency for rare earth elements,simple process and environmentally friendly,and is currently an important means for the selective separation of low-concentration rare earth elements.The difficulty and core lies in the high-efficiency solid adsorbent material.Design and preparation.In view of the above problems,this paper uses the silicon element in fly ash as the inorganic silicon source,and prepares SBA-15 with good acid resistance and large specific surface area as the adsorbent carrier,and uses carboxylic acid ligands and phosphoric acid ligands respectively.A solid adsorbent was prepared by surface modification,and the effect of adsorption conditions on the adsorption of rare earth ions(Eu,Gd,Tb,Sm,Nd)was studied,adsorption kinetics and isothermal adsorption model fitting were explored,and typical competing ion pairs were explored.The effect of rare earth ion adsorption.The main research content and conclusions are as follows:(1)The structure of the SBA-15 adsorbent(PAA-SBA-15)modified by phosphonoacetic acid(PAA)was characterized by N₂-physical adsorption and TG.The results showed that the modified adsorbent had a specific surface area of 271.2 m²/g and an average pore size.The volume is 0.48 cm³/g,and the average pore diameter is 7.051nm.The effect of solution p H on adsorption was investigated.The results showed that the adsorption efficiency of the adsorbent for rare earth ions was the highest at p H=5,and the adsorption process reached equilibrium at 180 min.Kinetic studies show that the adsorption process conforms to the second-order kinetics and langmuir isotherm adsorption model,the adsorption process is a single-layer adsorption,and chemical adsorption controls the rate of the entire adsorption process.The influence of typical impurity ions Ca²⁺,Mg²⁺,Al³⁺,Fe³⁺on the adsorption performance of PAA-SBA-15 on five rare earth ions was investigated.The results show that Ca²⁺and Mg²⁺have little effect on the adsorption performance of rare earth ions;when the concentration of Al³⁺increases to 500 ppm,the adsorption efficiency of the five rare earth ions is reduced by 3.9%,5.2%,4.5%,7.8%,3.4%compared with uncompetitive ions.and when the Fe³⁺concentration increased to 500 ppm,the adsorption efficiency decreased by 50%,44%,49.8%,44.8%,and 50.2%,respectively.After four adsorption-desorption cycles of PAA-SBA-15adsorbent,the efficiency of the five rare-earth ion adsorbents can still be maintained at74.2%,76.1%,73.9%,75.1%,and 74.1%.(2)SBA-15 was functionalized with diethylenetriaminepentaacetic dianhydride(DTPADA)to prepare adsorbent DTPADA-SBA-15.The characterization results of N₂-physical adsorption showed that the specific surface area was 275.0 m²/g,the average pore volume was 0.44 cm³/g,and the average pore size was 6.49 nm.The adsorption experiments under different p H values(2.0-6.0)of the solution showed that the adsorbent had the highest adsorption efficiency for rare earth ions when the p H was 2.The adsorbent has a fast rate of adsorption of rare earth ions,and the adsorption equilibrium can be reached within 30 minutes.The kinetic study shows that the adsorption process conforms to the Langmuir isotherm adsorption model and the second-level kinetic simulation,and the chemical adsorption dominates the entire adsorption process.The infrared spectra of the adsorbent before and after adsorption showed that O atoms on the adsorbent surface coordinated with rare earth ions.When coexisting with four competing ions of Ca²⁺,Mg²⁺,Al³⁺,Fe³⁺,the adsorption effect of DTPADA-SBA-15 on rare earth ions all decreased;further study the effect of a single competitive ion on the adsorption of rare earth ions.,The results show that the presence of Ca²⁺,Mg²⁺and Al³⁺has little effect on the adsorption effects of the five rare earth ions;and when the Fe³⁺concentration reaches 100 times the rare earth ions,the adsorption efficiency of the five rare earth ions Eu³⁺,Gd³⁺,Tb³⁺,Nd³⁺,and Sm³⁺decreases respectively They dropped by 49.4%,49.6%,49.8%,49.2%,52.6%,respectively.The cyclic adsorption performance of the adsorbent was studied.After the adsorbent was subjected to 10 adsorption-desorption cycles,the adsorption efficiency of the adsorbent for the five rare earth ions could still be maintained above 80%.