Micro-morphology and phase composition of lithium slag from lithium carbonate production by sulphuric acid process

The phase composition of lithium slag has important guiding significance for its potential pozzolanic activation and resource utilization. In order to improve the recycling rate of lithium slag, its phase composition was studied in this paper. The morphology of lithium slag samples from three representative origins was observed by back scattered electron image under scanning electron microscope. The elements composition and phase characteristics in 844 micro-regions of these phases were analysed by energy dispersive X-ray spectrometry, statistical analysis method and X-ray diffraction. The relative contents of main phases in the lithium slag were determined by quantitative method based on scanning electron microscope coupled with Image-ProPlus 6.0 software. The results showed that the lithium slag contained the dark grey polygonal and flat cake-shaped crystalline aluminosilicate phase, off white irregularly polygonal alkali and alkaline-earth compounds phase, black grey amorphous phase without fixed morphology, grey clubbed gypsum phase, and a small amount of bright approximatively hexagonal and round granular iron-bearing phase. According to the gray distribution curve, the main phases of the lithium slag were composed of 39.78–42.65% amorphous aluminosilicate phase (amorphous Al₂O₃·4SiO₂), 6.46–9.83% alkali and alkaline-earth compounds phase (CaCO₃, KAlSi₃O₈ and CaAl₂Si₂O₈, a little NaAlSi₃O₈), 34.41–44.74% crystalline aluminosilicate phase (Al₂Si₄O₁₀(OH)₂, a little quartz), 3.96–7.10% gypsum phase (CaSO₄·2H₂O), etc.