Research On Resource Utilization Of Lithium From Concentrated Seawater

With the rapid development of high-tech industries, e.g. energy conversion and aerospace, terrestrial brine resources are insufficient for human long-term development, thus more and more researchers around the world have focused their studies on the development of seawater resources. Among lithium extraction methods, adsorption is considered as the most promising one for industrial application, nevertheless, the fairly low lithium concentration is still a critical process difficulty. Consequently, it is urgently demanded to concentrate seawater before extracting lithium. Meanwhile, in the chain of seawater utilization process, there exist some concentrated feed liquids, in which plenty of elements including lithium have been enriched, and they are in fact ideal raw material for lithium. Regretfully, these concentrated liquids have not been effectively utilized, and some of them were discharged as wastes, which brought about not only varying degrees of environmental pollution, but also serious waste of valuable resources.Therefore, aiming at the utilization of lithium resource in concentrated seawater, this research firstly optimized the lithium ion sieves after comprehensive comparison, and then substituted desalinated seawater, bittern from salterns and mother liquor after bromine extraction for natural seawater, to carry out static and dynamic experiments of lithium extraction. Through optimizing these concentrated liquids and process conditions of lithium adsorption, desorption and precipitation, effective ways to solve the problems of long adsorption cycle, big treatment volume and high equipment load during industrialized lithium extraction, were systematically discussed. Besides, against the ecological imbalance problems in utilization process of the concentrated liquids, optimization research on the technology of blending desalinated seawater with salt-bond brine was performed from the standpoint of ecological restoration. The main conclusions of this study are as follows:Two synthetic methods(hydrothermal- two stage heat treatments, colloidal crystal template treatment) were used for preparing lithium ion sieves MnO2·0.5H2 O. Furthermore, the crystal structure, surface morphology of the ion sieves were studied by XRD, SEM, HRTEM, TG-DTA, and then adsorption properties were analysed according to adsorption isotherm, kinetics and ionic selectivity models. It can be drawn that, under the systems of desalinated seawater, bittern from salterns and mother liquor after bromine extraction, the two ion sieves had better Li+ adsorption performance, and their adsorption processes were in accordance with Lagergren kinetics equation and Langmuir isotherm equation, and meanwhile showed fairly high selectivity to Li+.Dynamic adsorption/desorption experiments were performed with these concentrated liquids, then the results of above static tests, operability and economics of the techonologies were also taken into consideration, and consequently bittern from salterns was chosen as the raw liquid for lithium extraction. Moreover, after comprehensive comparison towards the two ion sieves in respects of adsorption performance, stability and preparation cost, ion sieve synthesized by hydrothermaltwo stage heat treatments was optimized as the adsorbent for lithium extraction. Following that, optimization experiments of dynamic adsorption process were carried out to ascertain the relative optimum technological conditions: pH value was 8.5, temperature was 298 K, flow velocity was 5.0 mL/min, and circulating mode of superposition adsorption was adopted. Similarly, optimization experiments of dynamic desorption were performed to ascertain the relative optimum conditions: the concentration of acid was 0.5 mol/L, temperature was 298 K, flow velocity was 2.0 m L/min, and 5 times circulating desorption was adopted to improve the enrichment factor of Li+.Taking lithium-rich fluid after desorption as raw material, crude product of lithium carbonate was prepared successively by purification, evaporation, deeper removal of magnesium, precipitation. And then technologies of washing and carbonation-decomposition were applied to obtain the high purity lithium carbonate. In above processes, energy consumption, production cycle and operability of the techonologies were taken into consideration overall on the premise of guaranteeing product purity and Li+ recovery rate, and finally technological conditions above were optimized separately.