Hydrometallurgical extraction of Al and Si from kaolinitic clays

Abstract

Herein is presented the results of a study on the hydrometallurgic extraction and recovery of aluminum and silicon by leaching of kaolinitic clays with HF. The studied extraction parameters were: temperature, reaction time, solid/liquid ratio, concentration, and precipitating agent mass. In the leaching process, mineral dissolutions near 100% were obtained when working at 348 K, solid/liquid ratio 2% w/v, HF 12% v/v, for 120 minutes. The HF leach liquor generated from the dissolution of kaolinitic clays contains H₂SiF₆and H₃AlF₆. Studies were conducted to recover the two valuable fluorides as K₂SiF₆and Na₃AlF₆by precipitation with alkaline salts from the leach liquor. Phases of precipitated fluorides were identified by XRD and surface morphology by SEM. The purity of the K₂SiF₆precipitate was 98.8%, whereas for Na₃AlF₆, it was 89.3%. Also, both synthesized solids are of high commercial value due to their industrial applications.

Keywords:
extraction; kaolinitic clays; aluminum; synthesis; cryolite.