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- Lithium is probably the hottest market to go after in the current minerals market due the need for Li ion batteries. Li is found in very low concentration in igneous rocks. While there is only a handful of deposits in the US the majority can be found in Canada.
- The largest concentrations of lithium-containing minerals are found in granitic pegmatites. The most important of these minerals are spodumene (Li2O. Al2O3.4SiO2) and petalite (Li2O.Al2O3.8SiO2). Spodumene has a theoretical Li2O content of 8.03%. Due to its high lithium content, spodumene is considered the most important lithium ore mineral. A typical run of mine ore can contain 1-2% Li2O, while a typical spodumene concentrate suitable for lithium carbonate production contains 6-7% Li2O (75% – 87% spodumene). Higher grade concentrates with 7.6% Li2O and low iron content are used in ceramics and more demanding in the industry.
- Lithium can be extracted from spodumene concentrates after roasting and acid roasting operations. A concentrate with at least 6% Li2O (approximately 75% spodumene) is suitable for roasting. Roasting is performed in rotary kilns at about 1050°C (1922 F), during which spodumene goes through a phase transformation from α-spodumene to β-spodumene. The α-spodumene is virtually refractory to hot acids.
- As a result of the phase transformation, the spodumene crystal structure expands by about 30% decreasing its specific gravity from 3.1 g/cm3 (natural α-spodumene) to around 2.4 g/cm3 (β-spodumene) and making it amenable to hot sulfuric acid attack.
- After roasting, the material is cooled, mixed with sulfuric acid (95-97%) and the mixture roasted again at about 200°C (392 F) (in coolers). The latter roast is an exothermic reaction that begins at 170°C (338 F) whereby lithium is extracted from β-spodumene to form lithium sulfate, which is soluble in water.