Lithium Extraction: A Question of Being in the Right Neighbourhood

SRK News | Issue 53: Metallurgy and Mineral Processing

   
    
A4   |   Letter

One of the few positive commodities in 2015 was lithium. Improvements in the performance and durability of lithium powered batteries have made electric cars a reality. The search for suitable raw materials has galvanised many junior mining companies to switch from uranium, gold, nickel or copper to searching for lithium.

Lithium is the lightest metal in the periodic table and the lightest solid. Its chemistry is similar to sodium and displays an aggressive reaction with water. This reactive chemistry and light weight reflect the fact that lithium has only one layer (or shell) of electrons around the atom’s core thus, it has virtually no insulation (or loss of conductivity) as other elements. This makes it an ideal battery component. Lithium batteries are lighter, smaller, provide more power than lead, copper, vanadium or nickel-zinc alloys, and they last longer. Lithium is relatively abundant in nature. It occurs mainly in silicate minerals in hard rocks often as a trace component, or it occurs as a chloride salt in brines and evaporates when associated with volcanically active areas. Lithium can be extracted from its mineral hosts by: water soluble extraction from salts; and acid leaching from resistant silicate minerals.

Obviously, the brine-associated lithium is easier to extract from lithium bearing salts. However, magnesium and chloride are also extracted. For use in batteries, lithium carbonate requires several steps of concentration, separating the salt components, purifying the lithium to remove impurities and carbonation to produce a useable high-purity lithium carbonate product. When processing calcium, sodium, potassium and particularly magnesium must be separated for product purity.

Broadly, two styles of hard rock lithium exist, pegmatite and volcanic-associated rocks. Lithium occurs in pegmatites often as attractive, collectable crystals showing a wide range of colour from white through pink to a purple and even forming gemstones such as kunzite.

Extraction begins with physically separating the ore-bearing minerals through crushing and milling.  

Once separated, the lithium minerals require destabilisation at high temperatures with an aggressive leaching agent, such as sulfuric acid. The lithium sulfate produced is segregated from the acid by ion exchange or solvent extraction before finally being neutralised and exposed to air and carbon dioxide to form lithium carbonate. As with brines, other constituents such as magnesium and chloride are removed to avoid contaminating the product.  

Selecting a suitable process for lithium requires good understanding of the geological occurrence of the element and its neighbours. Some, like tin and tantalum, can be valuable by-products; others, such as magnesium, are undesirable neighbours that need to be separated to avoid contamination.

Rob Bowell: rbowell@srk.co.uk

SRK Turkey