SiLeach and LPD, page-29

US Patent #3189407

From Li-Technology's patent application

Page 5

[0006] US Patent 3,189,407 describes a process in which lithium is said to be recovered from lithium minerals, such as lepidolite, by reaction of the mineral with sulfuric acid and lithium is ultimately precipitated from solution. In this process, lepidolite is first pulped with acid and heated to a temperature of between 140C and 200C, preferably 150C to 170C (an acid bake) in what is said to an effort to react only with the lepidolite and not the gangue that may be present. The bake is run over a period of up to hours and only small levels aluminium and potassium are said to be dissolved. Most of the water present evaporates during the bake, leaving product substantially the form of a thick paste, not what might typically described as a slurry. This paste is then repulped in water. Aluminium is then precipitated through the addition of an alkali or alkali earth carbonate to increase the pH to between 3.5 to 4.5. The recovery process of the present invention has as one object thereof to substantially overcome the problems associated with the prior art or to at least provide a useful alternative thereto.