Optimization of combined mechanical activation-leaching parameters of low-grade α-spodumene/NaF mixture using response surface methodology

Abstract

This paper studied the optimization of the Li extraction process by mechanical activation of low-grade α-spodumene ore with NaF followed by leaching with NaF/H2SO4 solution at low temperatures (≤90 °C). The effects of mechanical activation on the structural and microstructural parameters (crystallite size and lattice strain) of the mineral/NaF mixture were analyzed. In addition, the investigated operating parameters were mechanical activation time, reaction temperature, and leaching time. The response surface methodology based on a D-optimal design was used to comprehend the effect of the process parameters on the leaching efficiency of Li. The results indicated that the milling time, the temperature, and the leaching time had a positive effect on the lithium extraction. The temperature, the leaching time, and their interaction had the greatest effect on the lithium extraction. The optimum Li extraction value achieved was 81% working with a sample activated 600 min, and a temperature and leaching time of 90 °C and 240 min, respectively. The characterization of the products showed that Al and Si were recovered as Na3AlF6 and Na2SiF6 during the leaching process. The presence of albite and quartz indicated that the leaching reaction was highly selective on α-spodumene, allowing to work with mineral samples with low Li content.