In the case of production from pegmatites, assuming the most common acid leach process is used, they comprise mining, beneficiation to a moderate or high grade of concentrate, calcination to produce acid-leachable beta spodumene, reaction with sulphuric acid and the conversion of the lithium sulphate solution with sodium carbonate. The costs of acid, soda ash and energy are a very significant percentage of total costs but they can be partly offset if a market exists for the sodium sulfate by-product.
In the case of hectorite clays, geothermal brines and oilfield brines lithium recovery costs have not been developed but work is current on the first two of these potential sources.
In the case of continental brines which are the current major source costs, probably, vary greatly. As with the case of pegmatites the cost of soda ash to convert lithium chloride to lithium carbonate is very significant. Brine grades vary greatly ranging currently in the Andes, from approximately 0.3% Li at the SQM operation in Chile to 0.062% and 0.034% at the two Argentinian salares of Hombre Muerto and Rincon respectively.
The most deleterious element in the brine is magnesium and the magnesium/lithium ratio is relatively low at the Salar de Atacama, very low at the Salar de Hombre Muerto and high at the Salar de Rincon. The largest of the Chinese brine deposits also has a very high ratio and these brines need more complex processing.
The other important factor in the brine chemistry is the presence or not of other recoverable products.
In Chile, Rockwood Holdings, now the owner of Chemetall who purchased Foote/Cyprus recover moderate tonnages of potassium chloride as a co-product at their operation and SQM recover much larger tonnages together with potassium sulphate and boric acid. Most of SQM’s potassium chloride is converted to much higher value potassium nitrate using nitrates from company owned deposits located between the salares and the Pacific coast.
At the Salar de Rincon potash recovery is planned and most of the Chinese salars contain economic concentrations of potassium and boron.
Another factor affecting capital costs apart from brine grade is the net evaporation rate which determines the area of the evaporation ponds necessary to increase the grade of the plant feed. These are a major capital cost but not a factor at the FMC operation where the lithium chloride is recovered directly from the in situ brine.
In the case of the one geothermal source discussed later the brine is rich in zinc a co-product as well as lithium and is a major producer of electric power but, as is with the case of oil field brines and hectorites, lithium recovery costs have not been determined.
A final cost factor is location. Some deposits are extremely remote.