| The content of lithium is very high and rich in brine. It accounts about70%～80%of the total lithium resources. And the extraction cost is lower simultaneously. So it will gradually replace lithium pyroxene to become the main resource in lithium industry. The Ion-sieve adsorbent method is currently accepted that the most promising method of extracting lithium from brine. The lithium manganese oxide’s ion-sieve, which is the optimal inorganic lithium absorbent with good comprehensive properties, is investigated mostly. In this thesis, it was mainly studied on the lithium ion-sieve precursor (Li1.6Mn1.604) by a solid-phase method and the adsorption performance of MnO2·0.5H2O after pickling.It was preliminarily determined that the synthesis temperature of LiMnO2should be controlled above500℃by thermal gravimetric analysis for the mixture of Mn2O3and LiOH·H2O. Several important influence factors for LiMnO2synthesis was investigated, respectively. And the optimal experimental conditions were for lithium manganese mole ratio for1.03, roasting temperature for600℃and calcination time for8h. Then LiMnO2was calcinated in the air for Li1.6Mn1.6O4. The effects of calcination temperature and time on the synthesis of Li1.6Mn1.6O4were investigated. The optimal conditions for synthesis were:calcination temperature for470℃and time for6h.The lithium ion-sieve MnO2·0.5H2O was obtained after Lii6Mn1.6O4pickling with hydrochloric acid. The influencing factors that pickling temperature, stirring speed, pickling time, hydrochloric acid concentration and liquid-solid ratio were investigated, respectively. The optimal pickling conditions were:pickling temperature for70℃, stirring speed for500r/min, pickling time for24h, hydrochloric acid concentration for0.5mol/L and liquid-solid ratio for400. At the optimal experimental condition, the extracting rate of lithium was96.28%and the rate of dissolved loss of manganese reached7.46%.Several influence factors on MnO2·0.5H2O adsorption Li+such as pH, temperature, initial concentration of lithium were studied, respectively. It shows that at the beginning, the adsorption capacity of ion-sieve for lithium increase slowly with the rise of pH, but to increase significantly after10. The alkaline more stronger, the adsorption capacity more bigger. At certain temperature, the adsorption capacity increases with the extension of adsorption time. The adsorption capacity increased sharply at the beginning short time, and then the adsorptive reaction is to achieve balance basically after8h. The adsorption capacity also increases with the increase of initial concentration of lithium. As at the low concentration range, the increasing range of adsorption capacity is bigger with the increase of lithium concentration. While the initial lithium concentration reaches800mg·L-1or more, the increase of adsorption capacity is slower and to reach a basic equilibrium. So the effect of lithium concentration on adsorption capacity has been inconspicuous.Langmuir and Freundlich adsorption isotherm equation, pseudo-first-order and pseudo-second-order kinetic models were applied to make the linear fitting for the adsorption data that MnO2·0.5H2O adsorbed in the simulation lithium liquid. ΔGθ、 ΔHθ、 ΔSθ、 Ea was calculated with the related fitting parameters at different temperature by Langmuir equation and pseudo-second-order kinetic models. And the control steps of adsorption process was also investigated by using move boundary model. The results show that the adsorption process of ion-sieve adsorbing Li+follows Langmuir and single adsorption; the adsorption process also complies with pseudo-second-order kinetic models and is chemical adsorption process; adsorption process is spontaneous and endothermic; the control steps of adsorption process are not decided by a single process, but several process joint action.The separation characteristics of ion-sieve for the main metal ions in the brine and its circulation adsorption performance were inspected detailedly. It shows that the adsorption priorities for the metal ions are Li+>> Na+> K+> Mg2+, and the separation coefficients of Li+to Mg2+, K+Na+are all far bigger than1. This shows that the ion-sieve has good specific selectivity for Li+. During the process of cyclic experiment, the quantity of adsorption and desorption of ion-sieve are little difference, and the adsorption capacity reduces very slowly with the increase of cycling times; the dissolve loss rate of manganese is lowering along with the increase of cycling times, and when the cycle times arrives to5times later, the dissolve loss rate of manganese is stable around2.4%; the average valence of manganese almost does not change, and maintains+4prices; the actual adsorption capacity of Ion-sieve in the brine is20mg-g-1or so, and nearly a third of its theoretical capacity. Which suggests that the ion-sieve does not reached its maximum saturation adsorption capacity, and the mole ratio Li/Mn has a great difference with its theoretical value. |
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