Extraction of lithium from micaceous waste from china clay production

The granites of South-West England are a potential source of lithium which is generally found within the mica mineral, zinnwaldite. It is mainly found in the central and western end of the St. Austell granite. When kaolin extraction occurs in these areas a mica-rich waste product is produced which is currently disposed of in tailings storage facilities. In this study a tailings sample containing 0.84% Li2O was upgraded by a combination of froth flotation, using dodecylamine as the collector, and wet high intensity magnetic separation (WHIMS) to 2.07% Li2O. The concentrate was then roasted with various additives, including limestone, gypsum and sodium sulphate, over a range of temperatures. The resulting products were then pulverised before being leached with water at 85 °C. Analysis of these products by XRD revealed that the water-soluble sulphates, KLiSO4 and Li2KNa(SO4)2, were produced under specific conditions. A maximum lithium extraction of approximately 84% was obtained using gypsum at 1050 °C. Sodium sulphate produced a superior lithium extraction of up to 97% at 850 °C. In all cases iron extraction was very low.Preliminary tests on the leach solution obtained by using sodium sulphate as an additive have shown that a Li2CO3 product with a purity of >90% could be produced by precipitation with sodium carbonate although more work is required to reach the industrial target of >99%.

► Froth flotation upgraded the mica-rich feed from 0.84% to 1.45% Li2O at a recovery of 98%.
► Wet high intensity magnetic separation produced a 2.07% Li2O concentrate at a recovery of 73%.
► The magnetic fraction was identified as being predominantly zinnwaldite.
► Roasting of zinnwaldite with gypsum and sodium sulphate produced lithium extractions of 84% and 90% respectively.
► Soluble lithium species (KLiSO4 and Li2KNa(SO4)2) were identified in the roasted products.