| Lithium and its compounds are widely used in various fields,including ceramics,glass,metallurgy,aluminum production,medicine and so on.In recent years,with the rapid developments of electronic devices and electric vehicles,the rapid application of lithium-ion batteries have greatly increased the demand for lithium resources,leading to unharmonious of supply and demand of lithium.Therefore,the development and recovery of lithium resources become a hot research topic.The adsorption method as a kind of economic,environmentally friendly and effective separation method was considered as a potential method to extract lithium ions from salt lake brines with high Mg/Li ratio However,the conventional adsorbents show low selectivity for lithium ions.Ion imprinting technology can significantly increase the selectivity by specific recognition of target ions.Thus,in this paper,two lithium-ion imprinted adsorption materials were prepared by bulk polymerization and surface imprinting methods.First,lithium ion-imprinted polymers(Li(Ⅰ)-IIPs-1)were prepared with lithium ion as template ion,acrylic acid(AA)as functional monomer,calix[4]aromatic hydrocarbon(C4)as selective ligand,ethylene glycol dimethacrylate(EGDMA)as cross-linking agent,and azo diisobutyronitrile(AIBN)as initiator in methanol and N,N-dimethyl formamide(DMF)solvent.Since hole size of C4 is close to the size of lithium ion,the coordination complexation between Li(Ⅰ)and C4 can be realized.At the same time,since intermolecular hydrogen bond between C4 and AA can be formed,thus by free radical crosslinking polymerization reactions to polymer inside,the existence of C4 can realize the adsorption processby specific recognition after cross-linking by polymerization Then the effects of preparation and adsorption conditions on adsorption performance of Li(Ⅰ)-IIPs-1 were investigated.The results showed that the adsorption equilibrium could be reached in 25 min and the maximum adsorption capacity of Li(Ⅰ)-IIPs-1 was approximately 29 mg.g-1 at pH 10.The adsorption process agreed better with Freundlich adsorption isotherm and pseudo-second-order kinetic models.Li(Ⅰ)-IIPs-1 showed good selectivity for Li(Ⅰ)in the presence of Rb(Ⅰ),Na(Ⅰ)and K(Ⅰ).The selectivity coefficiencies of Li(Ⅰ)for Li/Rb,Li/Na and Li/K binary solutions were 1.427,2.476 and 1.582,respectively.In addition,after 10 sorbing-desorption processes,the adsorption capacity of Li(Ⅰ)-IIPs-1 only decreased by 12.14%after repeating adsorption-desorption processes for ten times,demonstrating good reuse performance.In order to increase the selectivity of polymers for lithium ions,lithium ion-imprinted polymers(Li(Ⅰ)-IIPs-2)were prepared by surface imprinting method with SBA-15,Li(Ⅰ),C4,APTES,TEOS as the carrier,target ion,selective ligand,functional monomer and cross-linking agent,respectively.SBA-15 was modified by HCl to make its surface rich in hydroxyl for convenient loading.Then the effects of preparation and adsorption conditions on adsorption performance of Li(Ⅰ)-IIPs-2 were investigated.The results showed that the adsorption equilibrium of Li(Ⅰ)-IIPs-2 could be quickly reached in 20 min and the maximum adsorption capacity of Li(Ⅰ)-IIPs-2 was approximately 15 mg·g-1 at pH 5.5.The adsorption process agreed better with Langmuir adsorption isotherm and pseudo-second-order kinetic models.Li(Ⅰ)-IIPs-2 showed good selectivity for Li(Ⅰ)in the presence of Rb(Ⅰ),Na(Ⅰ),K(Ⅰ)and Mg(Ⅱ).The selectivity coefficients of Li(Ⅰ)for Li/Rb,Li/Na,Li/K,Li/Mg binary solutions were 2.385,3.604,2.547 and 1.283,respectively.In this paper,two kinds of lithium ion-imprinted polymers were prepared by two imprinting polymerization methods and both the lithium ion-imprinted polymers showed good selective adsorption performances for lithium ions,providing certain technology support for ultimate realization of adsorption of lithium ion from salt lake brines with high Mg/Li ratio. |
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