Abstract
The conventional processing of fl-spodumene involves decrepitation at about 1100 degrees C, digestion with concen-trated sulfuric acid at 250 degrees C, and several purification stages that identify the process with high energy, feed-stock, and by-product intensity. In addition to the low-value by-product of sodium sulfate (Na2SO4), the disposal cost of another by-product, hydrogen aluminosilicate (HAlSi2O6, aka keatite-HAlSi2O6), drives the research to avoid its formation in lithium refineries or converting this material into marketable products such as zeolites. Two processes are developed to leach lithium from fl-spodumene in a single digestion step using solutions of NaCl, with and without the addition of NaOH, operating at up to 200 degrees C. The optimised processes extract at least 92.9% of Li by varying the leaching time, temperature, liquid to solid mass ratio, NaCl/fl-spodumene mass ratio, solution pH and agitation. The two processes are simple, prevent using concentrated sulfuric acid and preclude forming HAlSi2O6 and Na2SO4 by-products, resulting in significantly lower amounts of impurities in the leach liquor, and high selectivity for lithium extraction. The keatite process functions at circumneutral pH, high NaCl/ fl-spodumene and L/S ratios and generates sodium aluminosilicate (keatite-NaAlSi2O6) as a by-product. The analcime process requires alkaline pH to produce analcime (NaAlSi2O6 center dot H2O) as a by-product. The study dem-onstrates a shift in the mechanism between circumneutral and alkaline conditions from ion exchange to dissolution-precipitation (i.e., recrystallisation). In an analogy to keatite and analcime processes for NaCl, we also investigate the extraction of lithium from fl-spodumene with KCl with and without KOH but find both re-actions to be ineffective in recovering Li. The analcime process offers a cleaner and less hazardous alternative to the conventional sulfuric acid process while maintaining a high lithium extraction effectiveness, rapid reaction rates and high concentration of Li in the leach.
