Study On Preparation Of Specific Sodium Ion Absorbent And Its Application To Remove Sodium From Ammonium Tungstate Solution

Abstract:In the process of tungsten metallurgy, tungsten minerals are firstly decomposed by NaOH or Na2CO3leaching. Then, the obtained Na2WO4is converted into (NH4)2WO4by ion exchange technique. As is known, the requirement for the sodium content in final tungsten products is very strict. The sodium content must be depressed to10ppm. Therefore, the sodium concentration in (NH4)2WO4solution should be strictly controlled during the ion exchange process. For this reason, a large quantity of pure water has to be used to rinse the sodium remained in pregnant resin, which will produce a lot of wastewater. The remaining tungsten in the wastewater is hard to be efficiently recovered. In addition, NH4Cl with low sodium content need be used to prepare the desorption agent, and the cost is high. If we can remove Na+efficiently from the (NH4)2WO4solution, the requirements of Na+concentration in ammonium tungstate solution in the ion exchange process could be reduced, which will be beneficial to energy-saving emission reduction.In order to separate Na+in ammonium tungstate solution containing large amount of NH4+, sodium specific absorbent Na1+xAlxTi2-x(PO4)3(NATP) was prepared. Experiments were conducted to investigate the adsorption performance of the prepared Na1.6Al0.6Ti1.4(PO4)3. The Na+adsorption experiments showed that the maximum amount of adsorption was achieved at about10min and the apparent exchange capacity was25.24mg·g-1. Increasing of pH value is preferable for increasing the Na+adsorption. Batch sorption kinetics and the equilibrium data can be described by Pseudo-second-order kinetic equations and Langmuir isotherm equations, respectively. The processes of Na+uptake by NATP ion sieve were spontaneous and endothermic, also, the diffusion may control the uptake process. Furthermore, the cycle experiments show that NATP has a good cycling performance.Sodium can be efficiently removed from commercial (NH4)2WO4by as-prepared NATP. When reagent amount of NATP is1.0times of theoretical amount, reaction temperature is25℃and reaction time is15 min, the removal rate of sodium from commercial (NH4)2WO4are higher than98%and the adsorbent is applicable towards wide range of Na+concentration. The spectrographic analyses for sodium concentration showed that all products accorded with the APT-0standard. Therefore, NATP can be used as the high-efficiency reagent to remove sodium from the commercial (NH4)2WO4solution.