Hydrometallurgical processes for the recovery of lithium from silicates

Lithium Australia NL has been developing a number of hydrometallurgical process flowsheets for the recovery of lithium from silicates. The most advanced of these, the halogen-based SiLeach™ process, was developed specifically for the digestion of spodumene, a refractory lithium pyroxene previously able to be processed only by roasting, followed by sulphation bake and water leach. The SiLeach™ process, which relies on the reaction of halogens with silicon-oxygen bonds, is widely applicable to the dissolution of all categories of silicate minerals and has found practical application in the processing of lithium micas. SiLeach™ is currently being commercialised, utilising pilot facilities established at ANSTO Minerals (a division of the Australian Nuclear Science and Technology Organisation). With SiLeach™, the halogens can be added to the process slurry in a number of ways. However, the preferred method is via the addition of ground fluorine minerals (which may include the lithium micas themselves) to the process slurry prior to the addition of sulphuric acid. Due to the kinetics of competing reactions, this sequence allows the momentary generation of fluoride in solution – and its almost instantaneous reaction with the silicates – without any accumulation of hydrogen fluoride ('HF') in the slurry. Process plant operations can be accomplished without the hazards often considered a risk with fluorine-based processes.The SiLeach™ process is capable of recovering a wide range of by-products, as all metals in the target silicate are dissolved. The low energy requirements of the process, as well as by-product credits, enhance the economics, which may result in lithium production costs using SiLeach™ to be among the lowest currently experienced. SiLeach™ has the potential to provide access to a wide range of plant feed previously not considered viable. Such feed includes low-grade spodumene concentrates and micas as primary feed sources. Furthermore, vast quantities of lithium minerals currently discharged as tailings from non-lithium mining operations create very attractive targets for the application of this type of technology. Utilisation of these materials as lithium sources will greatly enhance the sustainability of the lithium industry.