Lithium Processing

Processing

Processing routes for lithium will largely depend on the characteristics (e.g. mineralogy) of the deposit being exploited. For example, lithium recovered from brines are subject to a very different set of processes to lithium recovered from hard-rock sources.

Figure 1: Generalised flow diagram of the acid and carbonate leaching processes for chemical beneficiation of spodumene concentrate (Brown, 2016).

Hard-rock

After mining, lithium-bearing minerals, predominantly in the form of spodumene are processed to increase the Li content. This stage of initial concentration is generally performed at or near to the mine site and involves crushing the ore and separating the Li-bearing ore minerals from the gangue (uneconomic) minerals, using a range of physical (e.g. gravity separation, magnetic separation and froth floatation) processes. Chemical processes, such acid roasting and leaching, are used to separate the Li from the ore minerals and also remove unwanted impurities (e.g. iron). A series of chemical steps are then used to produce high-purity lithium carbonate (see Figure 1) (Brown, 2016).

Processing of Li ores and concentrates predominantly takes place in China, where high-purity lithium chemicals (i.e. Li2CO3 and LiOH) are produced chiefly for the manufacutre of batteries. However, lithium refining also takes place, albeit on a smaller scale, in Chile (Li2CO3 and LiOH), Argentina (Li2CO3 and LiOH) and Europe (LiOH), with future refining capacity planned in Australia (LiOH).

There is currently no commercial extraction of lithium from clay (hectorite)-bearing deposits nor from lithium-bearing micas (e.g. lepidolite); however, feasibility studies have shown this may be possible in the future, if the technologies can be scaled-up.

Brines

After extraction, ususally by pumping, the brine undergoes an initial stage of concentration to increase the lithium content. This is usually achieved by solar evaporation in a series of surface ponds. Lithium is highly soluble, therefore other compunds such as sodium chloride, potassium chloride or calcium sulfate will precipitate first leaving the brine increasingly concentrated in lithium. The lithium itself will eventually precipitate, typically as lithium chloride. The concentrated brine is further processed to remove impurities such as magnesium and boron. The resulting lithium chloride is reacted with sodium carbonate to precipitate a lithium carbonate slurry that is filtered, washed and dried to produce lithium carbonate with a >99% purity. After the extraction of lithium, brine is re-injected into the salar (see Figure 2) (Brown, 2016).

Figure 2: Generalised process for lithium extraction from brine deposits, with associated co-products. Sequence and exact chemical compounds produced will vary according to each deposit (Brown, 2016).

Emerging technology

Direct lithium extraction (DLE) is an emerging technology for fast processing of lithium, especially lithium extracted from brine deposits. The technology is a form of ion exchange where lithium (green circles in the below figure) is selectively extracted from a brine using a lithium-selective sorbent (orange hexagons in the below figure). Brine is passed through a tank and mixed with a lithium-selective sorbent, the lithium-rich brine is passed into a second tank for further refining, whilst the unwanted brine, now rich in impurities like Na, Mg and Ca is re-injected (Figure 3). DLE simultaneously increases the lithium content of the brine but also removes unwanted impurities (e.g. Ca, Mg and Na). DLE may prove particualrly useful where the lithium grade in the brine is low (10-100s ppm). The environmental impact of DLE is lower than other processing technologies, as it typically requires less energy, less water and has a smaller physical footprint (i.e. reduced land-take). However, complex brine chemistry can increase the time required to establish a system (i.e. increased testwork may be required), ongoing expenditure may be higher and there may be tehcnical risks associated with re-injection of brine.

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