Preparation Of Phenolic Resin-based Monolithic Lithium Ion-sieves For Lithium Ion Adsorption And Separation

Lithium and its compounds are widely used in various fields of national economy as an important strategic resource.Salt lake brine contains a large amount of lithium with low concentration,most of which are accompanied by high content of Mg²⁺.It is difficult to extract Li⁺with the traditional method due to the similar chemical properties,ion radius and ionic charge of Mg²⁺and Li⁺.However,nano lithium ion sieves have a highly selective adsorption performance for Li⁺while mesoporous phenolic resin has excellent chemical stability,mechanical properties,heat resistance,a large specific surface area and uniform pore size as a monolithic adsorbent,based on which,two types of monolithic adsorbent with hierarchical pore structure were constructed with phenolic resin and lithium ion sieves by the soft template method to solve the difficulty for the separation of nano lithium ion sieves after adsorption,meanwhile maintain the excellent selective adsorption performance for Li⁺.The main research contents and results are as follows:Nano lithium manganate was prepared by one step hydrothermal method as lithium ion sieves precursor,then compounded with phenolic resin by solvent-induced self-assembly via a soft template method,followed by cross-linking based on Friedel–Crafts alkylation reaction and soaking with ethanol and hydrochloric acid to remove the template and Li⁺.The as-prepared monolithic phenolic resin/λ-MnO₂ composite lithium ion sieves with hierarchical structure exhibit a high specific surface area(355 m²·g^-1)and a largeλ-MnO₂ loading（44.7%）and loading efficiency more than 80%),showing excellent adsorption performance(the maximum adsorption capacity is 32.08 mg·g^-1),fast kinetics（the adsorption equilibrium time is 6 h）.After6 cycles of regeneration by adsorption column operation,90%of the initial adsorption capacity was still maintained.Nano Li₂TiO₃ was prepared by two-step hydrothermal method as lithium ion sieves precursor and compounded with phenolic resin by solvent-free self-assembly via a soft template method,then cured at 160℃,followed by calcinating at 350℃to remove the template and soaking with hydrochloric acid to elute Li⁺.The preparation process is suitable for large-scale preparation on account of avoiding the use of a large amount of solvents,acid and alkali and highly toxic formaldehyde,the as-prepared monolithic phenolic resin/H₂TiO₃ composite lithium ion sieves with hierarchical structure exhibit a high specific surface area(246 m²·g^-1)and a large H₂TiO₃ loading（68.1%）,The maximum adsorption capacity of the ion-sieve to Li⁺is 29.56 mg·g^-1 and the adsorption equilibrium can be reached within 8 h.After cycling for 6times,the final adsorption capacity can still be maintained above 95%,showing excellent regeneration performance.