Kinetics and mechanism study of lithium extraction from alkaline solution by HFTA and TOPO and stripping process using Lewis cell technique
The kinetics of forward extraction of lithium from alkaline solution is investigated using a Lewis cell. Different parameters such as lithium concentration, HFTA concentration, TOPO concentration, pH value of aqueous phase, type of anion ion, as well as temperature are studied separately to examine their effect on lithium extraction rate, and an initial rate equation is deduced based on the experiment results. By changing the agitation speed and interfacial area of the Lewis cell, controlling mechanism of the extraction process is determined. Experimental results suggest that lithium extraction is controlled by chemical reaction at the interface rather than in the bulk phase. Further data analysis demonstrates that the lithium extraction is first order with respect to lithium ion concentration, HFTA concentration, and TOPO concentration. Different types of anion ions in aqueous phase show almost no effect on lithium extraction rate according to the experiments. Rate equation of lithium extraction by HFTA and TOPO is proposed as R Li,0 = 10 −4.33±0.1 [Li + ][HFTA][TOPO]. The rate-determining step of lithium extraction is the formation of final complex at the interface and the deduced extraction mechanism justified the experiments results well. For stripping process, effect of lithium concentration in organic, hydrogen ion concentration stirring speed and interfacial area on stripping rate are investigated. Analysis of the experimental data reveal that lithium stripping from organic phase is mainly controlled by chemical reaction and the reaction takes place at the interface rather than phase bulk. Linear regression of the plot of log[HCl] and log[Li + ] org versus logR Li,st reveals that the reaction orders with respect to HCl and lithium in organic are both 1, namely the stripping process is first order with HCl and lithium concentration in organic. Rate equation of lithium stripping from organic phase by HCl is proposed as R Li,st = 10 −4.0±0.1 [Li + ] org [HCl].
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