The fundamentals

Historically, lithium was mined from pegmatite deposits in North Carolina, Zimbabwe, Portugal, Brazil and China. With the advent of cheaper production of lithium from brines in South America (and to a lesser extent China) in the 1980s, hard-rock production in the above-mentioned countries dwindled. From the 1990s on, production of spodumene concentrate came to be dominated by the Greenbushes mine in Western Australia, a situation that persisted until the commissioning of new production in that state by the likes of Galaxy, Pilbara Minerals, Altura, Minres, Neometals, etc.

More recent developments in Western Australia (Wadgina, Pilgangora, Mt Marion, Bald Hill, Mt Cattlin and Earl Grey, as well as the expansion of Greenbushes) will result in considerable extra feed, as will new projects in Canada and southern Africa, but requirements are still likely to outstrip supply longer term.

Spodumene deposits mined to date have shown yields to commercial lithium concentrate of 50-70%, with some operations targeting optimised recoveries of 75%. But where is the rest reporting?

Lithium pegmatites are often characterised by complex mineralogy, with the lithium occurring in more than one mineral phase. Product specifications for commercial spodumene concentrates preclude other lithium mineral contaminants, meaning that lithium micas, petalite, amblygonite, eucryptite, etc. are rejected as tailings. Under some circumstances this can result in lithium losses as high as 30%.

The situation is exacerbated by the requirement to meet quality specifications for commercially traded spodumene concentrates. Not only is liberation (to achieve chemical specifications) an issue but specified critical particle size for conventional ‘converter’ feed also reduces yield, the principal factor being acceptable sizing to feed counter-current rotary kilns.

Without radical departures from current processing technologies, lithium supply is most likely to be enhanced by greater exploitation of abundant sources, and of materials discarded during the processing of other resources. Ergo, the best targets are:

  • waste generated during the processing of spodumene;
  • the lithium micas found in pegmatites and greisen, and
  • spent batteries.

In line with a major push by consumers and legislators for greater sustainability and protection of the environment, the ubiquity of the above-mentioned sources renders each an ideal focus in the quest for improvement.

The spodumene conversion dilemma

Given the ways in which spodumene mineral separation circuits perform, and how commercial concentrates are produced, most pegmatite orebodies produce only a low lithium yield. Partly, the issue revolves around the product specifications for spodumene converters in China (and soon Australia); these involve spodumene concentrates being fed into rotary kilns for the first stage of the lithium extraction process.

The kilns convert α-spodumene (unreactive with sulphuric acid) to β-spodumene, from which the lithium is recovered by a sulphation bake and subsequent water leach. Lithium is extracted as a sulphate solution, which is purified prior to the manufacture of lithium carbonate or lithium hydroxide.

While such ‘conversion’ processes are well established they have a number of shortfalls: not only are they energy-intensive but feed rates are dependent on particle size (as gas flow is counter-current to the flow of concentrates being converted from α to β-spodumene).

Such systems are best suited to relatively coarse feed material, but producers have to deal with the trade-offs of:

  • liberation;
  • concentrate purity, and
  • product size specifications.

To date, trade in spodumene concentrates has been a ‘buyers’ market’, in which China dominates downstream conversion activities and the production of lithium chemicals. However, that is about to change as refining facilities in Australia (Tianqi, Albemarle, Minres and SQM/Kidman) come online.

Although these companies will have greater flexibility in terms of product specifications, from a practical point of view refining will still entail commercial trade-offs in that much fine spodumene will be discharged to tailings.

LieNA® and spodumene tailings – an opportunity

Lithium Australia has been working with ANSTO Minerals to solve the fine-spodumene dilemma and also provide a less energy-intensive alternative to conventional conversion processes. To that end, Lithium Australia has developed the LieNA® process, a caustic digest of spodumene. In effect it generates a phase change analogous to conventional ‘conversion’ processes, except that it occurs in solution rather than a furnace.

During the LieNA® process, fine spodumene is fed into an autoclave, where it reacts with caustic soda to form a synthetic lithium sodalite. Most of the lithium partitions into the newly formed sodalite, which is recovered via a simple, solid/liquid separation step. The lithium within the sodalite is weakly bound, so an exchange reaction that substitutes H+ for Li+ allows it to be recovered from the solid by leaching in weak acid. A simplified pictorial flow sheet is provided below.

The LieNA® process, rather than being sensitive to fine spodumene, requires fine spodumene as a feed source to achieve acceptable kinetics.

So, what are the ramifications of a process designed to recover lithium from fine spodumene? If we assume that Western Australian spodumene concentrate production will soon eclipse 5 million tonnes per annum (Mtpa), and that the average recovery will result in a fine discharge of 1.7 Mtpa of spodumene, of which 75% is recoverable, that leaves around 1.3 Mtpa spodumene fines available for LieNA® processing.

That quantity of fines could produce about 170,000 tpa LCE. Such is the waste inherent in the lithium industry. Adoption of a LieNA® processing strategy could also allow utilisation of many years’ worth of stored tailings containing fine spodumene.

The ability to process such sources of fine spodumene would create a new market for concentrate producers, allowing them to better utilise resources. That in turn would improve sustainability and help meet the rapidly escalating demand for lithium.

Lithium Australia seeks partners to assist in evaluating the recovery of lithium from fine spodumene in both current tailings discharge and historic tailings in storage facilities.