Synthesis And Properties Of Aluminum Salt Based Lithium-Adsorbent

China is rich in brine resources,while most are hard developing high Mg/Li salt lakes.The adsorption technique,because of its unique advantages such as non-pollution and environment-friendly and suitable for lower concentration solutions,it has been used in the industrial lithium extraction from salt lakes.However,the adsorption and desorption performance,recycling,selectivity,mechanical properties and stability of the adsorbent still need to be further improved,and the production cost also needs to be reduced.The aluminum salt based adsorbent is a lithium adsorbent with a good application prospect because it`s lower preparation cost and simple process than other lithium adsorbent such as manganese-based or titanium-based.At present,the main problem is that the adsorption capacity is lower than other lithium adsorbents,and the dissolution loss is large and the recycling property is poor.These problems are urgently needed to be studied and improved.In this paper,a new process for the synthesis of aluminum salt based adsorbent was carried out,and the adsorption,desorption performance and selectivity of the adsorbent were systematically studied.In order to further improve the adsorption performance of the adsorbent,many pore formation explorations were explored.The main work carried out and the results obtained are as follows.Three kinds of crystalline Al（OH）₃（Gibbsite,Boehmite and amorphous Al（OH）₃） and poly aluminum chloride（PAC）were used as raw materials to synthesize adsorbent.Experimental results show that only the adsorbent synthesized by amorphous Al（OH）₃and PAC has certain adsorption for lithium ions,while the adsorbent prepared by amorphous Al（OH）₃ has large dissolution loss.The single adsorption has a dissolution loss of more than 50%.It is finally determined to adopt a synthetic scheme using PAC as a raw material.The synthetic process of synthesizing with PAC as raw material was studied.The single-factor experimental method was used to study the feeding mode,reactant ratio,reaction temperature,reaction time and feed rate.The results show that the most important factor affecting the synthesis of the adsorbent is the reactant ratio,and the optimum process conditions are obtained.Based on the comprehensive analysis and characterization results,it is considered that the adsorbent components are mainly composed of Li Cl·2Al（OH）₃·n H₂O with different crystallinity,and contain Al（OH）₃,Ca CO₃,（Ca O）₃Al₂O₃·6H₂O and Li Cl·H₂O etc.The lower the crystallinity of Li Cl·2Al（OH）₃·n H₂O,the better the adsorption performance.The adsorption,desorption performance and selectivity of the synthesized adsorbent were systematically studied.The results showed that the adsorbent was completely saturated in Li Cl solution after 15 h;the adsorption capacity was 6.1 mg/g,compared with the literature reported aluminum-based salt adsorbent.The adsorption amount is increased by 20%～50%,at higher temperature,the adsorption amount can be further improved;the suitable solution p H range is 3～5;the adsorbent is selective for lithium in Li-Na,Li-Ca and Li-K solution system.Among them,Li and Ca have the best separation effect,and the separation coefficient S_Li/Ca reaches 10 or more.In the complex solution system,the separation coefficient S_Li/Ca is as high as 78,the separation effect of lithium and calcium is splendidly.The adsorption process accords with the Freundlich isotherm model,the adsorption kinetics fits the quasi-secondary kinetic model,the optimal desorption conditions are determined.The adsorption mechanism was explored.XRD patterns and Infrared spectras of the adsorbent,before and after adsorption and desorption were compared.The structure of the adsorbent did not change significantly before and after adsorption.There are inserting and extracting of lithium ion in the adsorption and desorption process.And the intercalation and extraction of lithium ions is ion exchange with hydrogen ions.In order to further improve the adsorption performance,three pore-forming schemes were explored.The pores were prepared by surfactant,and the obtained adsorbent contained mesopores.The specific surface area was increased by 3～5 times compared with the unporosed adsorbent,and the adsorption capacity was increased by 30%.The mesoporous adsorbent was prepared by alginate.The gel adsorbent has a specific surface area that is 4 times higher than that when the pores are not formed.When the mass percentage of the main component of the adsorbent is reduced by 50%compared with the original adsorbent,the adsorption amount is only decreased by 15%～47%.It is expected that the adsorption capaticy can be improved through synthesizing in optimizing ratio.The porogen is used for pore-forming,and the specific surface area of the synthesized product is about 6 m²/g,which is basically a non-porous granular structure.Since the porogen is involved in the synthesis reaction of the adsorbent,the final product of the reaction is basically does not contain Li Cl·2Al（OH）₃·n H₂O,so it has no adsorption capacity for lithium.It is not feasible to use a porogen to make pores to improve adsorption performance.