Increasing demand for effective energy storage used in personal devices, electrical cars, renewable energy storage facilities, boosted the global demand for lithium.
Lithium-ion batteries are not the only industrial use of lithium (e.g. catalysts, lubricants, heat-resistant glass and ceramics, alloys for aerospace), but undoubtedly, the most rapidly growing one.
Two main lithium production sources are hard-rock lithium deposits and lithium brines.
The later are lithium salts-enriched salines in the underground, which accumulate under the surface of dried lakebeds. A great advantage of lithium extraction from brines is lower production cost, which is a natural evaporation process, followed by further processing in a chemical plant. A natural evaporation assumes a low cost, but at the same time it is climate and weather dependent. The evaporation step can take up to a year and even longer, depending on the conditions. Only few regions in the world have economically valuably brine deposits (Chile, Argentina, Bolivia and China).
Lithium hard-rock deposits occur across the globe. The recovery process, although more costly, is not climate-dependent, which makes such deposits a more stable source of lithium. The three main countries producing lithium from hard-rock deposits are Canada, China and Australia. The latter is the leading producer with 18.7 million tons produced in 2018.
Lithium production from hard-rock deposits
Economically valuable lithium containing minerals that occur in hard-rock granite pegmatites deposits are spodumene, apatite, lepidolite, tourmaline and amblygonite of which spodumene is the most common lithium-bearing mineral.
Lithium ore is extracted either using open-pit or underground mining. The further processing can be broken down into the following key steps:
- crushing of the ore,
- concentration by froth floatation,
- thermal treatment in a rotary calcining kiln to convert α-spodumene into its β-modification.
Flotation and calcination efficiency are directly determined by the ore mineralogy. Therefore, frequent, fast and accurate mineralogy monitoring is essential for the optimized recovery rate and stable product quality.
In the introduction blog, we established that X-ray diffraction (XRD) is a fast, versatile and accurate mineralogy probe, which can be easily implemented in the process flow at mine operation and processing plant. In the following case study, we discuss the added value of XRD for the beneficiation of hard-rock lithium ore using samples from an operating lithium mine.
Monitoring of lithium ore feed, concentrates and tales by XRD
In the case study we used 14 samples from a lithium mine, representing the key steps in the lithium ore recovery: ten raw ore samples, one α–spodumen concentrate and one tailing after the froth flotation step, one β-spodumene concentrate and one residue of the thermal treatment process.
All samples were prepared as pressed pellets and measured on an Aeris Minerals benchtop diffractometer with a scan time of 10 minutes, followed by an automatic quantification of the mineral phases.
Figure 1 shows an example of a full-pattern XRD analysis of a hard-rock lithium ore.
Any XRD pattern is a set of diffraction peaks of different intensities, located at certain diffraction angles (2θ), specific to a certain mineralogical phase. Peak positions enable identification of present phases. The relative intensities of the peaks in the XRD pattern allow the determination of the relative amount of each present mineral. The method is called Rietveld refinement.
In the example shown in Figure 1, the main minerals present are spodumene LiAl(SiO3)2, quartz SiO2, albite NaAlSi3O8, anorthite CaAl2Si2O8, minor amounts of lepidolite K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2 and traces of orthoclase KAlSi3O8 and beryl Be3Al2(SiO3)6. The rest of the raw ore samples show similar mineralogy, some samples contain additionally traces of tourmaline (elbaite) Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4 and analcime NaAlSi2O6·H2O.
The mineral quantification of the whole sample set is shown in Figure 2. Even though the mineralogy of the ore samples is consistent, the relative mineral quantities differ from sample to sample.
This information is extremely important for blending the optimal mixture for consistent input towards the beneficiation plant for further froth flotation.
Samples 11 and 12 in Figure 2 represent spodumene concentrate and tailings after the flotation step. 90% of the concentrate sample (sample 11) is spodumene with the minor amounts of quartz, albite, anorthite and traces of lepidolite, beryl, orthoclase and analcime. The main fraction of the gangue minerals went to the corresponding tailing sample (sample 12), which primarily consists of albite, quartz and anorthite. The mineralogical composition of concentrate and tailing after the flotation step indicates a high efficiency of the flotation process.
The remaining samples in Figure 2, sample 13 and 14, represent β-spodumene and corresponding residue from the calcination of α-spodumene concentrate (sample 11). The mineralogical composition of both, concentrate (sample 13) and residue (sample14), shows a reasonable efficiency of the calcination step. Over 92% of concentrate is the desired β-spodumene phase with minor amounts of anorthite and quartz. The corresponding tailing mainly consists of analcime, however, there are over 7% remaining β-spodumene.
The mineralogical analyses showed that the conversion of α- to β-spodumene during calcination was effective, however, the separation process should be further optimized to increase the yield of β-spodumene in the final concentrate.
Additional XRD-tools for process monitoring
In the above section we analyzed the mineralogy of 14 lithium ore samples, concentrates and tailings and residues. The results identified the weak spot in the process, which can be further improved. However, accurate full mineralogical analysis is not the only process monitoring tool, which XRD can offer.
Any deviation from a normal data spread within a cluster immediately a signals possible issues in the production process.
To summarize, hard-rock lithium recovery is a complex process, heavily dependent on the ore mineralogy. A flexible, fast and accurate mineralogical probe, like X-ray diffraction, greatly improves the efficiency throughout the whole process, provides tools for quick and easy monitoring of the process stability and gives necessary insights for counteractive measures when production issues arise.
Written by: Dr. Olga Narygina, Posted by: Malvern Panaltyical (www.materials-talks.com)