Studies On Preparation And Properties Of Novel Sodium Specific Adsorbent Li_1+xM_xN_2-x(PO₄)₃ (M=Al,Cr,La;N=Ti,Zr)

Lithium chloride is an industrial raw material, from which lithium compounds and in particular metallic lithium are produced. To make further processing of the lithium chloride more economic and efficient, it is very necessary to provide the raw material as pure as possible. It is very difficult to separate small quantities of sodium with the method of extraction. Adsorption is a simple way to separate Na+ in theory. In recent years, the extensive exploitation of lithium source in salt lakes needs to separate the impurity sodium ion in lithium chloride effectively. So it has an practical significance to develop a bargain sodium ion adsorbent with excellent effect.In this work, we report the synthesis of the adsorbent Li_1+xAl_xTi_2-x(PO₄)₃ by solid state reaction method. The physical and chemical performances are investigated. It is found that they show a high absorption capacity towards Na+. Compared with the other methods, the new Na specific adsorbent Li_1+xAl_xTi_2-x(PO₄)₃ described here is a simpler and more convenient way to remove Na+ from LiCl solution and shows the favorable prospective to its application. Results are as follows:1. The adsorbent Li_1+xAl_xTi_2-x(PO₄)₃ is synthesized by solid state reaction method. The analysis of TG-DTA shows this process is consistent with the following reaction: (1+x)Li₂CO_3+xAl₂O₃ + (4-2x)TiO₂ +6NH₄H₂PO₄ = 2Li_1+xAl_xTi_2-x(PO₄)₃+9H₂O+6NH₃+(1+x)CO₂2. Analysis of powder XRD spectra indicates that, LiTi2(PO₄)₃ crystal whisker belongs to rhombohedral system with the rhomb-centered lattice, space group R 3c and the cell parameters of a=0.8518nm,b=0.8518nm,c=2.087nm,α=90°,β=90°,γ=120°. It shows that trifle Al³⁺ dopant did not affect the structure of the material.3. Raman and FT-IR spectroscopic studies for these materials were carried out and the vibrational bands were assigned. The infrared characteristic adsorption peaks are 642.19 cm^-1; 584.39 cm^-1; 677.05 cm^-1. The Raman characteristic adsorption peaks are 1097.27 cm^-1; 1070.27 cm^-1; 989.28 cm^-1; 969.99 cm^-1; 595.86 cm^-1; 580.44 cm^-1; 445.44cm^-1.4. The investigation of the adsorption properties showed that the low concentration Al dopant (x≤0.4) made Li_1+xMxN2-x(PO₄)₃ (M=Al,Cr,La; N=Ti,Zr) adsorb sodium selectively, and also confirmed that the Al ion dopant is an effective method to improve the adsorption properties. The exchange capacity of Li1.4La0.4Zr1.6(PO₄)₃ was 49.83 mg/g, under pH =10.0¹1.0 in LiCl solution.