ISEC The 21st International Solvent Extraction Conference

Transcription

1 Lithium Sovent Extraction (LiSX ) Process Evauation using Tenova Pused Coumns (TPC) Jonathan LIPP 1, * 1 Tenova Advanced Technoogies Ltd., Yokneam, Israe Conventiona ithium recovery reies amost soey on soar evaporation technoogy. As ithium prices have expoded in the ast coupe of years and as this od technoogy suffers from severa drawbacks, the search for a new technoogy is on. Sovent extraction (SX) bears high promise to be a superior aternative. Athough SX is widey used in minera processing, SX for ithium was not avaiabe unti recenty. This new process was evauated in recent years over ab scae tests and its appicabiity was demonstrated. However, a arger scae evauation has to be performed if this technoogy is to be adopted as the chosen aternative for ithium recovery. It was therefore, the objective of this work, to evauate the performance of the ithium sovent extraction (LiSX ) process on a arger scae, using Tenova Pused Coumns (TPC) with a cross section diameter of 40 mm and 100 mm. The resuts showed that athough high ph is required to faciitate the extraction stage, compete ithium recovery is achievabe even for neutra raffinate ph. Scrubbing indicated that practicay a akai meta impurity is removed from the oaded sovent, and the striping stage demonstrated the abiity of the process to produce saturate ithium sat soution. Overa the LiSX process demonstrated its abiity to extract, purify and saturate ithium, showing its attractiveness as the new generation ithium recovery process. 1. Introduction Eectric cars are expected to become ever more popuar in the coming years [1]. As the key component in its battery is ithium, ithium production is gaining ever increasing interest. Od-schoo production is based on a series of evaporation ponds with residence time of roughy 18 month [2]. In addition to that, ow ithium recovery is but another drawback that this conventiona technoogy has [3]. These drawbacks have initiated a wordwide search for an aternative technoogy. Athough sovent extraction is commony used in hydrometaurgica processes, it was not considered as an aternative unti recenty. This new emerging sovent extraction process for the recovery of ithium, LiSX, was tested on a aboratory scae [4]. The resuts of the aboratory scae showed that the proprietary Tenova Advanced Technoogies (TAT) sovent has a maximum oading capacity of 1.75 g/l ithium (0.25 M). It was aso indicated that, the process shoud be executed in aqueous continuity and that practicay 100% of the ithium is recovered when extraction is carried out at ph=12. Stripping was indicated to remove a ithium from the oaded sovent (LS) even at ph=7. Athough promising, these test resuts required to be vaidated on a arger scae testing if this technoogy is to be impemented on a commercia scae. It is therefore the objective of this paper to

2 further the evauation of this process, and to eucidate the performance of the LiSX using sma scae industria equipment Tenova Pused Coumns (TPC), in the production of a saturated and pure Li₂SO₄ soution. 2. Experimenta 2.1 Reagents A chemica used in the ine of the current work (reagent grade) were used as received. Both aqueous and organic soutions used were syntheticay prepared. The aqueous feed soution was synthesized to imitate the expected composition fed to the LiSX process when operating with a typica South American ithium soution. As these brines normay contain akaine earth eements, which are preferaby extracted, the synthesized soution was prepared without these eements. In the commercia process this eimination is achieved by an upstream TAT process (LiP ). Feed composition is dispayed in Tabe 1 beow. Tabe 1 Aqueous Feed Stream composition Eement Li Na K B C S.G. Units mg/l g/l g/l mg/l g/l Vaue Anaysis Anayses of Li, Na, K and B were performed using ICP or Atomic Absorption (AA), whie titration was used for C determination. As a rue, high concentrations of a meta interfere with the determination of other metas that are present in very ow concentrations. Therefore, standard soutions were used. These soutions contained a background of the ion present in high concentration in order to determine the ions present in ow concentrations. For exampe, in the case of ow ithium concentrations in the presence of high sodium concentrations (mainy for the determination of Li in the aqueous phase) anayses were performed by using standard soutions of Li containing simiar Na concentrations to the concentrations in the diuted sampes. The owest concentration of Li that can be determined in this manner is 3 mg/l. In a simiar way, ow concentrations of other eements were quantified. It shoud be noted that the anaytica accuracy of this method is ±10%. Organic soutions were stripped quantitativey using nitric acid soutions and the resuting aqueous soutions were anayzed. The concentrations in the organic soutions were cacuated using the phase ratio in the stripping. 2.3 Hydrauic Test Hydrauic tests, for a stages of the process, were conducted in counter current using a TPC with 100 mm cross-section diameter having a tota active section height of 7 m (PVDF disk-and-doughnut internas 7 X 90 cm PVDF sections separated by 10 cm gass sections), gass decanters with a diameter of 150 mm (top) and 110 mm (bottom). A mechanica pusator (piston from PTFE) 120 mm in diameter, pusating in a frequency of 1 Hz, was used to deiver pusation to the coumn. A streams were pumped to the coumn using VFD controed FMI (metering) or Peristatic pumps. Pusation intensity (PI the product of the frequency and puse ampitude) and fux were

3 changed in order to determine the optima operating parameters. Hodup (the fraction of dispersed phase in the tota voume) vaues were monitored by periodicay samping in order to ascertain the optima fux and pusation intensity. For each of the sovent extraction stages (Extraction, Scrubbing and stripping) the test focused on the more chaenging side of the coumn. Hence, for the extraction stage LS was tested with the feed brine (expected conditions at the upper part of the extraction coumn); for the scrubbing stage LS versus spent scrub soution (expected conditions at the ower part of the scrubbing coumn) were evauated and for the stripping stage the purified sovent was tested with the Li₂SO₄ product stream (expected conditions at the ower part of the stripping coumn). 2.4 Mass Transfer Test Mass transfer tests, for a stages of the process, were conducted in counter current using a TPC having a 40 mm cross-section diameter and a tota active section height of 7 m (PVDF disk-and-doughnut internas, gass sections), and top and bottom gass decanters having 80 mm in cross-section diameter. A mechanica pusator (piston of PTFE) with a cross-section diameter of 69 mm, pusating in a frequency of 1 Hz, was used to deiver pusation to the coumn. A streams were pumped to the coumn using VFD controed FMI (metering) or Peristatic pumps. For a tests organic and aqueous sampes were periodicay coected and anayzed. For the extraction stage, the ithium feed concentration is 720 mg/l, which sets the extraction organic to aqueous ratio (O:A) at 0.41 (cacuated as ithium feed concentration divided by maximum ithium eve in the LS). This ratio was maintained throughout the test work. As was previousy reported [4] basic ph is required in order to faciitate the extraction process. Therefore, NaOH was added to the feed soution, resuting in feed brine ph of In the scrubbing stage 0.73% H₂SO₄ soution was used to scrub the LS. Tests were conducted at O:A=10. Whie in the stripping stage, the purified sovent (PS) was stripped using a soution containing g/l of H₂SO₄ and 246 g/l of Li₂SO₄ at O:A=5. 3. Resuts and Discussion 3.1 Hydrauic Tests Extraction hydrauic test were conducted for fuxes raging m³/m²/h. At a fux of 40 m³/m²/h, or grater, coumn operation proved to be unstabe and fooding was observed regardess of the pusation intensity (PI) used. The maxima fux which permitted continuous operation without fooding was 35 m³/m²/h with a pusation ampitude of 4mm, which corresponds to coumn PI=350 mm/min. At these conditions hodup vaues aong the coumn were between 15-20%. Scrubbing hydrauics was tested for fux vaues of 5-20 m³/m²/h. Fooding was observed at fux of 15 m³/m²/h and above at any PI. Maxima fux that enabed continuous operation was 12.5 m³/m²/h with an ampitude of 3mm, which corresponds to PI=260 mm/min. At these conditions hodup vaues aong the coumn were between 25-30%. Stripping hydrauics was tested for fux vaues of 5-30 m³/m²/h. At fuxes above 25 m³/m²/h, the coumn was fooded, indicating that the maxima fux that enabes continuous operation is 25 m³/m²/h with a pusation ampitude of 3mm, which corresponds to coumn PI=260 mm/min. At these conditions hodup vaues aong the coumn were between 25-30%

4 3.2 Mass Transfer Tests Simiary to other meta extraction process, ithium extraction is a chemica process. Thus, sovent deprotonation, achieved by basic ph at the feed brine, faciitates ithium extraction. This process, eiminate proton from the extracting agent and creates an active area on the sovent capabe of chemicay bonding with the ithium ions from the brine. The extraction profie is dispay in Tabe 2 and in Figure 1. As can be seen, near the organic entrance (at the ower section) to the coumn, the ithium content of the aqueous phase is minima. In this area the sovent is being oaded with a other impurities, especiay sodium. As the sovent fows up the coumn, ithium repaces those impurities, thus oading the sovent with ithium and removing co-extracted impurities at the same time. The sovent eaving the coumn is at maximum oading eve regarding ithium and minima oading with regards to other impurities. Those impurities wi need, in any case, to be scrubbed out if purified ithium is to be produced. Figure 1 Extraction Coumn Profie Due to the extraction mechanism, a ph profie deveops in the coumn. As protons are reeased from the organic into the aqueous phase the ph is reduced aong the coumn unti the raffinate

5 eaves the coumn at practicay neutra ph. This coumn ph profie is achieved by an optima addition of NaOH. Excessive addition woud resut in higher ph eve in the raffinate, whereas the outcome of inadequate addition wi be incompete ithium extraction due to insufficient active extraction sites on the sovent, and subsequenty ithium oses to the raffinate. As ithium concentration in the raffinate is driven beow the detection imit, these resuts indicate that ithium was competey extracted from the feed. Moreover, the ithium purity, from feed brine to oaded sovent, was increase from roughy 0.6% to 92% on meta base, or from ca. 1.4% to 92% on either LiC or Li₂SO₄ basis, which further highights the advantages the sovent extraction process bears for ithium production. Tabe 2 Extraction Coumn Profie Height Stream Li Na K B C ph m mg/l mg/l mg/l mg/l mg/l LS <3 <3 Feed Org <3 Aqu Org Aqu Org Aqu BS <3 <3 <3 <3 <3 Raff < The scrubbing process is aimed at removing the co-extracted impurities and producing highy pure ithium soution. This is achieved by partia stripping of the sovent. As the objective is to maximize the impurity eves in the spent scrub soution whie minimizing its ithium content the exact acid concentration in the scrub soution is determined to aow ph=12 in the spent scrub. In this ph the ithium eves at the spent scrub soution are assumed to be minima and as, in the industria pant, this soution wi be fed back to the extraction stage, this eve woud not increase the caustic demand. As sodium is the major impurity, acid consumption is based soey on its concentration. In this process, each proton triggers the scrubbing of one sodium ion. ph=12 wi be reached if sodium ions are in excess of 0.01 M over H + ions, which wi induce proton eimination from the water resuting in a soution with OH concentration of 0.01 M. The acid used in this stage wi be the same acid used in the stripping stage in order to minimize the fina product contamination. Therefore, H₂SO₄ was used as scrubbing acid. As the scrub soution is expected to be weak acidic one a specific gravity of 1 is assumed and O:A=10 is being taken into account in cacuating the required acid concentration: g mo O: A 0.01 mo gr [%H 2 SO 4 ] = M w H 2SO4 ( [Na org] g g ) M wna mo Where [%H₂SO₄] is the acid concentration in the scrub soution, M wh is the moecuar 2SO

6 weight of the sufuric acid, [Na org ] is the sodium concentration in the LS, and M wna is the moecuar weight of sodium. Cacuating the required acid concentration for this case gives: [%H 2 SO 4 ] = 98 g mo ( g g mo ) = 0.73% 100gr mo The resuts of the scrubbing test is dispayed in Tabe 3, as can easiy been seen a the impurities were successfuy scrubbed out of the sovent resuting in PS containing practicay ony ithium. Additionay, ithium concentration in the spent scrub was indeed minima. Nevertheess, there wi be no ithium osses in the industria scae, as this soution wi be fed back to the extraction stage. The PS purity is adequate to aow for sovent stripping and production of the purified ithium soution. Tabe 3 Scrubbing resuts Stream Li Na K B C ph mg/l mg/l mg/l mg/l mg/l LS <3 <3 PS 1730 <3 <3 <3 <3 Spent Scrub Simiary to scrubbing the stripping is a chemica neutraization reaction, where one proton is required to strip one ithium ion. The concentration of the strip soution is then derived from the designed O:A ratio, which is set on 5. This ratio is set in order to faciitate better phase dispersion in the coumn, and minimize axia mixing that woud otherwise (in higher ratios) dominate coumn operation and may hinder ithium stripping. Thus, the required H₂SO₄ concentration is cacuate as the product of O:A and ithium concentration in the PS (taken as 0.25 M), resuting in acid concentration of 1.25 N (0.625 M). In order to imit the demand for process water consumption, in the industria pant, and to produce 40 g/l ithium soution (Li₂SO₄ soubiity imit), part of the product stream is cyced back to the stripping and mixed with 98% H₂SO₄. Therefore the strip soution concentration is g/l of H₂SO₄ and 246 g/l of Li₂SO₄. As the stripping process requires ony one stage this mixing procedure bares no impact on the overa process. The resuts of the stripping stage are shown in Tabe 4. As can be seen the target ithium concentration was achieved, and the product soution has a neutra ph which indicates compete proton consumption by the sovent from the aqueous soution. Impurity eves are minute and indicate ithium purity of 99.97% on meta base and 99.99% on Li₂SO₄ basis. This purity eve significanty exceeds the 99.5% that is considered battery grade, and serves as an additiona indication of the abiity of the LiSX process to become the next generation technoogy for the production and recovery of ithium. Tabe 4 LiSX product composition Li Na K B C ph g/l mg/l mg/l mg/l mg/l <3 <

7 4. Concusion Lithium recovery via sovent extraction using TPC was evauated. The sovent was shown to seectivey extract the ithium where ithium purity of 0.6 (on meta basis) in the feed brine was eevated to 92% in the oaded sovent, with essentiay obtaining 100% ithium recovery. Coumn ph profie reveaed that athough the feed brine entering the extraction stage is extremey basic (12.5) raffinate ph is practicay neutra. As some co-extraction takes pace, scrubbing of akai metas and other non-metaic impurities is required. 0.73% H₂SO₄ soution was used to scrub the oaded sovent. Virtuay a impurities where scrubbed out were minima ithium concentration was detected in the spent scrub soution. As this soution wi be cyced to the extraction stage these ithium eves wi not contribute to any ithium oses. The stripping of the purified sovent has produced saturated (40 g/l) and pure (99.97% on meta base) ithium sufate soution. The resuts presented in this paper indicate that the sovent extraction process outperforms the traditiona soar evaporation technoogy. The current study continues to underine the vaidity of the LiSX process as an attractive aternative to the existing ithium production technoogy. References 1) R. Bayis, 9 th Lithium Suppy & Markets Conference (2017). 2) L. T. Peiro, G. V. Mendez, R. U. Ayres, JOM, 65(8) 8, (2013). 3) W. Tahi, Meridian Internationa Research, 1-22 (2007) 4) J. Lipp, proceedings of the Internationa Sovent Extraction Conference ISEC2014, (2014)