An alternative method for the recovery of lithium from spodumene
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METALLURGICALTRANSACTIONSB
screened to eliminate particles larger than 200 mesh. A chemical analysis showed the following composition: 62.9 24.4 6.8 0.7 0.5 0.53 0.13 0.11
SiO2 AI203
L%O K20
Na20 "Fe203 MgO CaO
pct pct pct pct pct pct pct pct
The tachyhydrite dried in an oven at 400 to 410 K for one hour was cooled in a desiccator and then crushed in a porcelain mortar and screened to separate and discard the particles larger than 200 mesh. The chemical analysis of this mineral revealed the following percentages in the dry sample: Na + K" Mg +ยง Ca ++ . C1SO4IR* * IR residue insoluble in
2.98 pct 1.44 pct 14.43 pct I0.19 pct 69.89 pct 0.26 pct 0.81 pct hot water
The two minerals were then mixed in a 50 ml capacity platinum crucible in the predetermined proportions, usually 1 g of spodumene and 8 g tachyhydrite. The crucible was then heated in a muffle furnace open to natural ventilation during two hours at the selected temperature which ranged from 923 K to 1473 K. The product in the form of a sinter was cooled in air and then ground in a porcelain mortar. It was observed that the grinding was more difficult at higher reaction temperatures. The ground sinter was then transferred to a 200 ml capacity Erlenmeyer flask and leached with distilled water maintained at the boiling temperature and with continuous magnetic agitation. The leaching continued for approximately 4 hours. The pulp was then filtered in a buchner, the residue washed with distilled water and the filterate completed with distilled water to 500 ml in a volumetric flask. The extracted lithium was analyzed by atomic absorption spectrometry. In some experiments a complete analysis was made of the leach liquor to determine the masses of all the ions present. The behavior of the two minerals, individually, during heating was investigated by the Differential Thermal Analysis technique. When a sample of tachyhydrite weighing 36 mg was heated in air at a steady heating rate of 20 K per minute, it was observed that it gradually loses its water of crystallization, becoming unhydrous at 573 K. Between 703 K and 823 K the weight loss suggests a decomposition of the MgC12 to MgO. This was confirmed by chemical analysis. Spodumene, on the other hand, is stable, showing a mass loss of 0.3 pct around 693 K and an endothermic reaction at 1323 K characteristic of the transformation a-spodumene /3-spodumene. At the reaction temperatures used in this study the mixture can then be regarded as a mixture of spodumene plus MgO and CaC12. VOLUME 15B, DECEMBER 1984--725
Table I.
Effect of Temperature on Lithium Recovery after Roasting for Two Hours
Temperature. K
Recoveries,Pct
823 973 1173 1273 1373 1423 1473
43 50 64 69 78 88 69
52 51 64 68 80 89 71
49 55 59 68 76 85
47 54 52 65 75 86
AverageValue
49 50 58 67 77 --
48 52 60 68 78 87 70
Element
Table I demonstrates the dependence of the quantity of lithium extracted from spodumene upon the reaction temperature. The data show the calculated average of five runs at each indicated temperature where the devi
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