Lithium Uptake Properties Of Nano-Lithium Ion Sieve Doped With Magnesium

Recently the demand for lithium has risen for their promising use in many fields, such as high-performance batteries, heat-resistant ceramics, flux for welding, pharmaceuticals and so on. Lithium mainly exists in mines, seawater and salt lakes. But it is very difficult and costly to extract lithium from the mineral resources because the minerals are low-grade, heterogeneous and limited. Therefore, more and more scholars focus on the technologies for extracting lithium from seawater, brine and ground water with low concentrations. Adsorption has been considered a promising method to uptake lithium from solutions owing to economic and environmental considerations. And there is growing concern about the spinel-type manganese oxide as adsorbent because of its high selectivity and adsorption capacity of lithium.In this paper, magnesium (II) doped spinel lithium manganese oxide (LMS) was synthesized by soft chemical method and ion-sieve manganese oxide (HMS) was prepared by extracting lithium and magnesium from LMS. The characteristics of HMS were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area, determination of pH at the point of zero charge (pHPZC) and infrared spectroscopy measurements (FT-IR). Batch experiments were carried to study the selective and cycled performance, effects of initial pH, Li+concentration, contact time, adsorbent dose and temperatures on lithium uptake. The equilibrium, kinetics and thermodynamics of lithium uptake were investigated under different conditions. The intraparticle diffusion kinetic, pseudo-first-order and pseudo-second-order models were applied to describe the experimental kinetics. Langmuir and Freudlich isotherms were used to describe the experimental thermodynamics in buffer system. In addition, the competitive model was used to describe the competition between Li+-H+.It can be seen from the characterization that HMS obtained from LMS preserved the original spinel structure and presented nanosized particles. In the adsorption process, HMS has high selectivity and adsorption capacity of Li+and it presents better stability with doping of magnesium. The batch experiment results suggested that the sorption of Li+showed a highly pH and initial concentration dependent profile. The adsorption capacity increased with the increase of initial pH and concentration and reached up to 37.4 mg/g at pH 12 with initial concentration 200 mg/L. The adsorption process followed the pseudo-second order model and intraparticle diffusion and boundary diffusion control the adsorption together. The results of Li+uptake in pH 8.0 buffer solution revealed that the equilibrium process could be well described by Langmuir model and the adsorption process was spontaneous, entropy increase and endothermic. In non-buffer system involving H+variation, competitive model could be used to predict the effects of pH on Li+adsorption over a continuum of pH values. XRD, FT-IR, adsorption behavior and composition of samples indicated that Li+-H+exchange was preponderant in the lithium extraction/insertion process.