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Article Purification of from Sulphate Solutions through Hydrogenation Using the Dowex G26 Resin

Wei-Sheng Chen 1, Cheng-Han Lee 1,* and Hsing-Jung Ho 2,*

1 Department of Resources Engineering, National Cheng Kung University, No. 1, Daxue Road, Tainan City 70101, Taiwan; [email protected] 2 Graduate School of Environmental Studies, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan * Correspondence: [email protected] (C.-H.L.); [email protected] (H.-J.H.)

 Received: 11 October 2018; Accepted: 12 November 2018; Published: 15 November 2018 

Abstract: Purification of , in the battery industry, is an important step in the future. In this experiment, the waste lithium- batteries were crushed, sieved, leached with sulfuric acid, eluted with an extractant, and finally sulphate solutions were extracted, through selective precipitation. Next, carbonate was first added to the sulphate solutions, to precipitate lithium carbonate (Li2CO3). After that, lithium carbonate was put into the to create lithium carbonate slurry and CO2 was added to it. The aeration of CO2 and the hydrogenation temperature were controlled, in this experiment. Subsequently, Dowex G26 resin was used to remove impurities, such as the calcium and sodium in lithium carbonate. Moreover, the adsorption isotherms, described by means of the Langmuir and Freundlich isotherms, were used to investigate the ion-exchange behaviors of impurities. After removing the impurities, the different heating rate was controlled to obtain lithium carbonate. In a nutshell, this study showed the optimum condition of CO2 aeration, hydrogenation temperature, ion-exchange resin and the heating rate to get high yields and purity of lithium carbonate.

Keywords: lithium carbonate; sulphate solutions; hydrogenation; ion-exchange; purification

1. Introduction In the early industrial development, lithium (Li) was used in many industries. For example, lithium acted as a fluxing agent in the ceramic industry and as a deoxidizer and dechlorination agent in the metallurgical industry. In addition, lithium has attracted more and more attention, worldwide, in the recent years, because of its application in the battery industry [1,2]. Lithium is mainly supplied to electronic industrial products, especially the power battery market. Lithium-ion batteries (LIBs) are widely used in electric vehicles and hybrid vehicles, due to their high energy density and high tolerance of a wide range of temperatures [3,4]. According to the report of the US Geological Survey [5–9], the market for lithium is mainly 39% for the battery industry, 30% for the ceramics and glass industry, and 8% for the lubrication industry. Lithium is usually extracted from [10–12] and [13] and the world’s annual crude lithium production is about 35,000 tons. Among all countries, and Chile are the largest and second largest crude lithium exporters, respectively. In order to meet the needs of the battery industry, lithium production increased by, approximately, 12% in 2016. It is expected that the lithium-ion battery industry will flourish in the future and the demand for lithium metal will become more and more urgent. The refore, it is important to recycle lithium metal or its compounds from LIBs.

Appl. Sci. 2018, 8, 2252; doi:10.3390/app8112252 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 2252 2 of 10

It not only achieves the goal of waste reduction but also improves the secondary resource utilization of waste LIBs. In the LIBs, lithium, cobalt (Co), nickel (Ni), and manganese (Mn) are the main materials that are needed to recycle. Among them, Lithium is usually obtained in the form of lithium carbonate. Lithium carbonate has become a very important material in recent years. The global demand for lithium carbonate has gradually increased, due to its versatility, and the price will rise significantly in the future [14]. According to the report of Sociedad Quimica y Minera de Chile, the demand for lithium carbonate will increase six hundred thousand tons to eight hundred thousand tones. For industrial activities, lithium carbonate is not only used as cathode materials in the LIBs but is also used to create other compounds, such as (LiCl), lithium (LiBr) and lithium oxide (Li2O). LiCl, LiBr, and Li2O all can be raw materials for other industries. For example, LiBr can be used as an absorbent and a refrigerant. On the other hand, in the medical industry, lithium carbonate can also be used as a treatment for [15,16]. Due to the unlimited development of lithium carbonate, a lot of countries try various methods to purify lithium carbonate to apply in different industries. In the purification process, the methods used mainly are the causticization method, electrolysis, recrystallization, hydrogenation–decomposition, and the hydrogenation–precipitation method [17]. As the hydrogenation–decomposition method generates little waste of materials and solutions and can achieve a higher purification of lithium carbonate, it was chosen for this experiment. During the decomposed process, calcium and lithium, both, separate out in the form of , due to their common properties of precipitation with an increase in temperature. In addition, sodium is also a critical problem in the purification process. To deal with these problems, the ion-exchange resin was chosen to remove the impurities. Comparing the literature, it could be observed that as a resin, IRC-748 has a great adsorption efficiency on Ca2+, but insufficient efficiency on Na+; Dowex G26 has the better effect on both Ca2+ and Na+. In order to reduce the impurities, efficiently, Dowex G26 was used in this experiment. To sum up, the hydrogenation–decomposition method and the Dowex G26 resin were used to get a high purity of the lithium carbonate.

2. Materials and Methods

2.1. Materials The sulphate solutions came from a recycling LIBs waste cathode materials, which were done by previous research; their content is shown in Table1[ 18]. (Na2CO3) was purchased from Nihon Shiyaku Reagent, Tokyo, Japan (NaCO3, 99.8%), for the chemical precipitation. CO2 was purchased from Air Product and Chemical, Taipei, Taiwan (CO2 ≥ 99%), to carry out the hydrogenation–decomposition method. Dowex G26 was obtained from Sigma-Aldrich (St. Louis, MO, USA) and was used as a strong acidic cation exchange resin, to remove impurities. Multi-elements ICP standard solutions were acquired from AccuStandard, New Haven, Connecticut State, USA. The nitric acid (HNO3) and sulfuric acid (H2SO4) were acquired from Sigma-Aldrich (St. Louis, MO, USA) (HNO3 ≥ 65%) (H2SO4 ≥ 98%).

Table 1. The metal composition of leach liquor.

Element Ni Li Concentration (ppm) 130 ppm 8000 ppm

2.2. Equipment The materials were analyzed by energy-dispersive X-ray spectroscopy (EDS; XFlash6110, Bruker, Billerica, MA, USA), X-ray diffraction (XRD; DX-2700, Dangdong City, Liaoning, China), scanning electron microscopy (SEM; S-3000N, Hitachi, Tokyo, Japan), and inductively coupled plasma optical emission spectrometry (ICP-OES; Varian, Vista-MPX, PerkinElmer, Waltham, MA, USA). In order to Appl. Sci. 2018, 8, 2252 3 of 10 control the hydrogenation temperature and heating rate, a thermostatic bath (XMtd-204; BaltaLab, Vidzemes priekšpilseta,¯ R¯ıga, Latvia) was used to heat the lithium carbonate slurry and the lithium solutions. On the other hand, a stainless-steel machine which was a closed, eight hundred milliliters cylinder, was designed, in which CO2 could be added from the top. Moreover, an electric blender was appended to make the CO2 dissolve into the lithium carbonate slurry. To calculate the amount of CO2 aeration, Flowmeter (GP5700; SIARGO, Lexington, MA, USA) was used in this experiment.

2.3. Experimental Procedures

2.3.1. Chemical Precipitation The metal which was dissolved in the liquid phase was selectively precipitated, in the solid phase, by the chemical reaction in this process. The lithium was precipitated by carbonate sodium as shown in Equation (1). + + 2Li + Na2CO3 → Li2CO3 + 2Na (1) The lithium carbonate was recovered after filtration and washed with hot water, to remove the residual impurities. In this procedure, lithium carbonate would precipitate when the temperature increased. However, the content of nickel ion would decrease intensely. Due to the different characteristics of , the composition of lithium carbonate would change, as well. Table2 shows the metal composition of the lithium carbonate obtained, after the chemical precipitation by inductively-coupled plasma optical emission spectrometry (ICP-OES; Varian, Vista-MPX, PerkinElmer, Waltham, MA, USA).

Table 2. The composition of lithium carbonate.

2+ + 2− Element Lithium Carbonate Ca Na SO4 Content (%) 98% 0.15% 1.5% 0.35%

2.3.2. Lithium Carbonate Slurry Enough lithium carbonate was obtained in order to make lithium carbonate slurry, in the first process. However, the amount of the water would affect the hydrogenation and decomposition processing. If the amount of water was low, it would not be possible to add enough CO2 to the slurry. If there was too much water, it would cause more energy consumption in the decomposition procedure. On account of these conditions, 10 g lithium carbonate with 400 milliliters of deionized water were mixed to make our lithium carbonate slurry.

2.3.3. Hydrogenation Processing After making the lithium carbonate slurry, it was first put into the thermostatic bath to maintain its temperature. Subsequently, it was poured into the aeration and stirring device and the CO2 was added into it. Equation (2) shows the reaction for the dissolution of the CO2 into the slurry.

Li2CO3 + CO2 + H2O 2LiHCO3 (2)

In this procedure, the CO2 aeration and hydrogenation temperature were controlled and the pressure was kept at 0.2 MPa. The parameters for the CO2 aeration (1 L–2.5 L) and hydrogenation temperature (26.5 ◦C–30 ◦C) were set up. The initial weight of lithium carbonate and deionized water was 410 g. On adding the CO2 into the slurry, it turned into the solution. However, it still had some lithium carbonate, which did not change into lithium bicarbonate. By filtering the remain lithium carbonate solid, we could weigh the lithium bicarbonate solutions. At last, the value we got the yields of the lithium bicarbonate solutions and this has been shown in this study. Appl. Sci. 2018, 8, 2252 4 of 10

2.3.4. Ion-Exchange Dowex G26 is a strongly acidic resin which was used to exchange cations efficiently. Dowex G26 was used to remove the Ca2+ and Na+ which were the two most abundant impurities in the Appl. Sci. 2018, 8, x FOR PEER REVIEW 4 of 10 lithium bicarbonate solutions, in this process. The adsorption isotherms, described by means of the 2+ Langmuir2.3.4. and Ion-Exchange Freundlich isotherms, were used to investigate the ion-exchange behaviors of Ca . 2+ + With the parametersDowex G26 of pHis a strongly value, theacidic Ca resin, which and Na was usedadsorption to exchange efficiencies cations ions wereefficiently. compared, Dowex without − high pH values,G26 was because used to theremove Ca2+ thewould Ca2+ and precipitate Na+ which whenwere the it combinedtwo most abundant with OH impurities. On thein the other hand, the effect oflithium the reaction bicarbonate time solutions, was also in this compared. process. The The adsorption parameters isotherms, of described the ion-exchange by means of experiments,the Langmuir and Freundlich isotherms, were used to investigate the ion-exchange behaviors of Ca2+. the pH values (1–8) and reaction times (2 min–1024 min), were set. After removing the impurities, With the parameters of pH value, the Ca2+, and Na+ adsorption efficiencies were compared, without the contenthigh of thepH values, lithium because bicarbonate the Ca2+ would solutions precipitate was when investigated it combined in with this OH study.-. On the other hand, the effect of the reaction time was also compared. The parameters of the ion-exchange experiments, 2.3.5. Decompositionthe pH values Processing (1–8) and reaction times (2 min–1024 min), were set. After removing the impurities, the content of the lithium bicarbonate solutions was investigated in this study. After removing the impurities in the lithium bicarbonate solutions by Dowex G26, lithium carbonate was needed2.3.5. to precipitate Decomposition from Processing the lithium bicarbonate solutions. Equation (3) shows the reaction through which the lithiumAfter carbonate removing wasthe impurities acquired, in by the heating lithium thebicarbonate lithium solutions bicarbonate by Dowex solutions. G26, lithium carbonate was needed to precipitate from the lithium bicarbonate solutions. Equation (3) shows the reaction through which the lithium carbonate was acquired, by heating the lithium bicarbonate 2LiHCO3 + heat Li2CO3 + CO2 + H2O (3) solutions.

The heating rate was an important2LiHCO factor to3 + heat control ⇌ Li2CO the3 + impurities CO2 + H2O in this procedure. If (3) the heating rate was too high,The heating the lithium rate was carbonate an important crystal factor wouldto control contain the impurities other in ions. this procedure. If the heating If the rate was too low, theheating energy rate consumptionwas too high, the would lithium carbonate increase. crys Intal order would to contain compare other theions. effect If the heating of the rate heating rate, the solutionswas weretoo low, put the into energy a thermostatic consumption would bath, increase. the parameters In order to compare (0.5 ◦C/min–1 the effect ◦ofC/min) the heating were set up and the solutionsrate, the solutions were heated were put to 90into◦ aC. thermostatic The whole bath, process the parameters of experiment (0.5 °C/min–1 is shown °C/min) in were Figure set 1. up and the solutions were heated to 90 °C. The whole process of experiment is shown in Figure 1.

Figure 1. TheFigure outline 1. The outline of the of purification the purification process process forfor lithium lithium carbonate carbonate from fromsulphate sulphate solutions. solutions.

3. Results and Discussion

3.1. Hydrogenation Processing

3.1.1. Effect of CO2 Aeration

The effect of CO2 aeration was investigated with a range of 1 L–2.5 L. The result of Figure2 shows that 1 L, 2 L, 2.25 L, and 2.5 L of aeration had the lower yields and the 1.75 L had the highest Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 of 10

3. Results and Discussion 3. Results and Discussion

3.1. Hydrogenation Processing 3.1. Hydrogenation Processing Appl. Sci. 2018, 8, 2252 5 of 10 3.1.1. Effect of CO2 Aeration 3.1.1. Effect of CO2 Aeration The effect of CO2 aeration was investigated with a range of 1 L–2.5 L. The result of Figure 2 The effect of CO2 aeration was investigated with a range of− 1 L–2.5 L. The result of Figure 2 yield.shows By that Equations 1 L, 2 L, (4)2.25 and L, and (5), if2.5 CO L2 ofwas aeration insufficient, had the the lower HCO yields3 was and insufficient the 1.75 L as had well. the However, highest showsif the CO that was1 L, 2 excessive, L, 2.25 L, theand HCO 2.5 L −ofturned aeration back had into the COlower− yieldsand caused and the the 1.75 yields L had of the lithiumhighest yield. By 2Equations (4) and (5), if CO3 2 was insufficient, the HCO3 3− was insufficient as well. However, yield. By Equations (4) and (5), if CO2 was insufficient, the HCO3− was insufficient as well. However, bicarbonate solutions to decrease. The− optimum aeration of the− CO2, in the condition of 10 g lithium if the CO2 was excessive, the HCO3− turned back into CO3− and caused the yields of the lithium ifcarbonate the CO2 withwas 400excessive, mL H O,the was HCO 1.753 L,turned due to back these into conditions. CO3 and caused the yields of the lithium bicarbonate solutions to decrease2 . The optimum aeration of the CO2, in the condition of 10 g lithium bicarbonate solutions to decrease. The optimum aeration of the CO2, in the condition of 10 g lithium carbonate with 400 mL H2−2O, was 1.75 L, due −to these conditions.− − carbonate with 400 mLCO 3H2O,+ was 2H2 O1.75 L,HCO due3 to+ these H2O conditions. + OH H2CO3 + 2OH (4) 2− ⇋ − − ⇋ − CO32− + 2H2O HCO3− + H2O + OH− H2CO3 + 2OH− (4) CO3 + 2H2O ⇋ HCO−3 + H2O+ + OH ⇋ H2CO3 2+− 2OH + (4) H2CO3 + 2H2O HCO3 + H3O + H2O CO3 + 2H3O (5) H2CO3 + 2H2O ⇋ HCO3− + H3O+ + H2O ⇋ CO32− + 2H3O+ (5) H2CO3 + 2H2O ⇋ HCO3− + H3O+ + H2O ⇋ CO32− + 2H3O+ (5)

Figure 2. The yields of lithium bicarbonate solutions with different CO2 aeration. Figure 2. The yields of lithium bicarbonate solutions with different CO2 aeration.

3.1.2. Effect of Hydrogenation Temperature 3.1.2. Effect of Hydrogenation Temperature The hydrogenation temperature was investigated from 26.5 ◦°C–30C–30 ◦°C.C. As the hydrogenationhydrogenation The hydrogenation temperature was investigated from 26.5 °C–30 °C. As the hydrogenation process was a a reversible reversible reaction, reaction, the the slurry slurry temperat temperatureure played played an animportant important role, role, even even if it only if it onlyhad process was a reversible reaction, the slurry temperature played an important role, even if it only had hada little a littlechange. change. Figure Figure 3 shows3 shows the theyields yields of the of theparameter. parameter. As seen As seen in the in thefigure, figure, 27.5 27.5 °C was◦C wasthe a little change. Figure 3 shows the yields of the parameter. As seen in the figure, 27.5 °C was the theoptimum optimum parameter parameter with with the thehighest highest yield. yield. In Inth thee lower lower temperature, temperature, the the solubility solubility of of lithium optimum parameter with the highest yield. In the lower temperature, the solubility of lithium carbonate was high but the reaction was too difficult difficult to be in in progress. progress. If If the the temperature temperature was was higher, higher, carbonate was high but the reaction was too difficult to be in progress. If the temperature was higher, the solubility of lithium carbonate was low and the reverse reaction became faster to make lithium the solubility of lithium carbonate was low and the reverse reaction became faster to make lithium bicarbonate turn back into lithium carbonate. Howe However,ver, the effect of hydrogenation temperature on bicarbonate turn back into lithium carbonate. However, the effect of hydrogenation temperature on purity was only a little because it was irrelevantirrelevant toto thethe precipitationprecipitation ofof impurities.impurities. purity was only a little because it was irrelevant to the precipitation of impurities.

Figure 3. The yields of lithium bicarbonate solutions with different hydrogenation temperatures. Appl. Sci. 2018, 8, 2252 6 of 10

Appl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 10 3.2. Ion-ExchangeAppl. Sci. 2018, 8, x FOR PEER REVIEW 6 of 10

FigureFigure 3.3. TheThe yieldsyields ofof lithiumlithium bicarbonatebicarbonate solutionssolutions withwith differentdifferent hydrogenationhydrogenation temperatures.temperatures. 3.2.1. Isothermal Adsorption Models In3.2.3.2. this Ion-ExchangeIon-Exchange study, the different initial concentrations of Ca2+ (10, 20, 50, 100, 200 and 400 ppm) and the relationship between Ce (concentration of adsorbate in the liquid when adsorption is in 3.2.1.3.2.1. IsothermalIsothermal AdsorptionAdsorption ModelsModels equilibrium) and qe (equilibrium adsorption capacity of the adsorbent), were used to create the 2+ isothermalInIn this adsorptionthis study,study, thethe curve differentdifferent (Figure initialinitial4). concentrationsconcentrations From the results, ofof CaCa2+ the(10,(10, 20, saturated20, 50,50, 100,100, 200 adsorption200 andand 400400 ppm)ppm) amount andand was 80 mg/g.thethe relationshiprelationship betweenbetween CCee (concentration(concentration ofof adsorbateadsorbate inin thethe liquidliquid whenwhen adsorptionadsorption isis inin equilibrium)equilibrium) andand qqee (equilibrium(equilibrium adsorptionadsorption capacitycapacity ofof thethe adsorbent),adsorbent), werewere usedused toto createcreate thethe In order to get a high accuracy of the adsorption model, Langmuir and Freundlich equations were isothermalisothermal adsorptionadsorption curvecurve (Figure(Figure 4).4). FromFrom thethe results,results, thethe saturatedsaturated adsorptionadsorption amountamount waswas 8080 used to create the figures. Equation (6) and Figure5 show the Langmuir equation [ 19] and indicate mg/g.mg/g. that theyInIn use orderorder the toto relationship getget aa highhigh accuracyaccuracy between ofof C thethee and adsorptionadsorption Ce/qe, model, tomodel, get theLangmuirLangmuir maximum andand FreundlichFreundlich adsorption equationsequations capacity qm and adsorptionwerewere usedused toto equilibrium createcreate thethe figures.figures. constant EquationEquation KL. On (6)(6) theanandd otherFigureFigure hand, 55 showshow Equation thethe LangmuirLangmuir (7) and equationequation Figure [19][19]6 show andand the Freundlichindicateindicate equation thatthat theythey useuse [20 ]thethe and relationshiprelationship indicate between thatbetween they CCee use andand the CCee/q/q relationshipee,, toto getget thethe maximummaximum between adsorptionadsorption lnCe and capacitycapacity lnqe, to get 2 the empiricalqqmm andand adsorptionadsorption constant equilibriumequilibrium n and the constantconstant adsorption KKLL.. OnOn equilibrium thethe otherother hand,hand, constant EquationEquation KF (7).(7)By andand R FigureFigurein Figures 66 showshow5 the theand 6, the adsorptionFreundlichFreundlich equation behaviorequation [20][20] of Dowexandand indicateindicate G26 thatthat fits they withthey useuse the thethe Langmuir relationshiprelationship model. betweenbetween It showed lnClnCee andand that lnqlnqee, the, toto getget resin thethe has a 2 uniformempiricalempirical adsorption constantconstant position, nn andand thethe on theadsoadso surface.rptionrption equilibriumequilibrium constantconstant KKFF.. ByBy RR2 inin FiguresFigures 55 andand 6,6, thethe adsorptionadsorption behaviorbehavior ofof DowexDowex G26G26 fitsfits withwith thethe LangmuirLangmuir model.model. ItIt showedshowed thatthat thethe resinresin hashas aa uniformuniform adsorptionadsorption position,position, onon thethe surface.surface.C C 1 e = e + (6) qe CCee =qCmCee + q11mK L = + (6)(6) qqee qqmm qqmmKKLL 1 ln q = ln K + ln C (7) e = F +11 e lnlnqqee = lnlnKKFF + nlnlnCCee (7)(7) nn

FigureFigureFigure 4. 4.4.Isothermal IsothermalIsothermal adsorption adsorpadsorptiontion curvecurve curve ofof of CaCa Ca2+2+.. 2+ .

FigureFigureFigure 5. 5.5.Langmuir LangmuirLangmuir isothermalisothermal adsorptionadsorption adsorption curve.curve. curve. Appl. Sci. 2018, 8, 2252 7 of 10 Appl. Sci. 2018,, 8,, xx FORFOR PEERPEER REVIEWREVIEW 7 of 10

Figure 6. Freundlich isothermal adsorption curve.curve.

3.2.2. Effect of the pH Value 3.2.2. Effect of the pH Value 2+ + In order to test the parameters (pH 1–8), the concentration ratio of Ca 2+ and Na + were set 1 and In order to test the parameters (pH 1–8), the concentration ratio of Ca2+ andand NaNa+ werewere setset 11 andand 10 mg/L, which were based on the concentration of lithium bicarbonate solutions. Figure7 shows that 10 mg/L, which were based on the concentration of lithiumlithium bicarbonatebicarbonate solutions.solutions. FigureFigure 77 showsshows 2+ + the relationship between the pH value and the adsorption efficiency of Ca 2+and Na +. In the figure, thatthat thethe relationshiprelationship betweenbetween thethe pHpH vavaluelue andand thethe adsorptionadsorption efficiencyefficiency ofof CaCa2+ andand NaNa+.. InIn thethe figure,figure, pH 6 and pH 7 had the optimum adsorption efficiency. As the pH value of the lithium bicarbonate pH 6 and pH 7 had the optimum adsorption efficiency. As the pH value of the lithium bicarbonate solution was near 7 (7.32–7.38), pH 7 was chosen to be the parameters in this experiment. solution was near 7 (7.32–7.38), pH 7 was chosen toto bebe thethe parametersparameters inin thisthis experiment.experiment.

2+ + Figure 7. 2+ + Figure 7. AdsorptionAdsorption efficiencyefficiency onon Ca Ca2+ and Na+ withwithwith pHpH pH value.value. 3.2.3. Effect of Reaction Time 3.2.3. Effect of Reaction Time The influence of reaction time was investigated to see that the longer the reaction time, fewer was The influence of reaction time was investigated to see that the longer the reaction time, fewer the adsorptionThe influence efficiency of reaction of the time resin. was Figure investigated8 shows thatto see the that adsorption the longer efficiencies the reaction were time, similar fewer at was the adsorption efficiency of the resin. Figure 8 shows that the adsorption efficiencies were similar 2 min to 16 min of reaction time. However, after 16 min, the values got lower drastically. The reason at 2 min to 16 min of reaction time. However, after 16 min, the values got lower drastically. The reason was that some Li+ was adsorbed by resin and caused the precipitation of Ca2+ and Na+. In order to was that some Li++ waswas adsorbedadsorbed byby resinresin andand causedcaused thethe precipitationprecipitation ofof CaCa2+2+ andand NaNa++.. InIn orderorder toto minimize the adsorption of Li+, 4 min was chosen to be our reaction time. minimize the adsorption of Li++,, 44 minmin waswas chosenchosen toto bebe ourour reactionreaction time.time. After getting the optimum parameters of the Dowex G26, the lithium bicarbonate solutions were After getting the optimum parameters of the Dowex G26, the lithium bicarbonate solutions were purified, and the data are shown in Table3. purified, and the data are shown in Table 3. Table 3. The composition of lithium bicarbonate solutions.

+ 2+ + 2− Element Li Ca Na SO4 Content (%) 99.475% 0.015% 0.5% 0.01% Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 10

Appl. Sci. 2018, 8, 2252 8 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 10

Figure 8. Adsorption efficiency on Ca2+ and Na+ with reaction time.

Table 3. The composition of lithium bicarbonate solutions.

Element Li+ Ca2+ Na+ SO42− Content (%) 99.475% 0.015% 0.5% 0.01% FigureFigure 8.8.Adsorption Adsorption efficiencyefficiency onon CaCa2+2+ and Na+ withwith reaction reaction time.

3.3. Decomposition Processing 3.3. Decomposition ProcessingTable 3. The composition of lithium bicarbonate solutions.

TheThe Effect Effect of of Heating Heating Rate Rate Element Li+ Ca2+ Na+ SO42− Content (%) 99.475% 0.015% 0.5% 0.01% TheThe heating heating rate rate was was the the most most important important parameter paramete ofrthe of yieldsthe yields and and impurity. impurity. If the If heating the heating rate + wasrate high, was ithigh, would it causewould impurities cause impurities such as Nasuchto as be Na wrapped+ to be bywrapped lithium carbonate.by lithium The carbonate. impurities The 3.3. Decomposition Processing precipitatedimpurities precipitated would have would an increase have an in increase yields and in yi aelds decrease and a in decrease purities. in In purities. Figure 9In it Figure can be 9 seen it can thatbe seen the experiment that the experiment with resin with had resin only had a small only change a small of change purity of because purity thebecause impurities the impurities were already were The Effect of Heating Rate ◦ eliminatedalready eliminated by the Dowex by the G26, Dowex at theG26, beginning. at the beginning. The highest The highest yield wasyield at was 1 C at of 1 the°C of heating the heating rate ◦ becauserate Thebecause the heating impurities the impuritiesrate was precipitated, the precipitated, most andimportant the and highest the paramete highest purityr purityof was the at wasyields 0.5 atC. 0.5and °C. impurity. If the heating rate AfterwasAfter high, the the ion-exchange ition-exchange would cause and and theimpurities hydrogenation-decomposition,the hydrogenation-decomposition such as Na+ to be wrapped the lithium, theby lithium carbonatelithium carbonate.carbonate was enriched Thewas andimpuritiesenriched separated andprecipitated from separated the calcium would from have andthe sodium calciuman increase (as and seen in sodium yi inelds Table and(as4). aseen By decrease concentrating in Table in purities. 4). andBy concentrating heating,In Figure the 9 it XRD canand andbeheating, seen SEM that analysisthe the XRD experiment of and the SEM metal withanalysis oxides resin wereof had the shownonly metal a small inoxides Figures change were 10 shown andof purity 11 .in The Figuresbecause re was 10 the no and impurities impurity 11. There phase were was detectedalreadyno impurity eliminated and thephase ICP by detected analysis the Dowex and also G26,the showed ICP at the analysis that beginning. the purityalso showedThe of lithiumhighest that carbonateyield the purity was wasat of 1 almostlithium°C of the99.9%. carbonate heating ratewas because almost 99.9%.the impurities precipitated, and the highest purity was at 0.5 °C. TableAfter 4.theThe ion-exchange element content and of thethe lithium hydrogenation-decomposition carbonate after the hydrogenation–decomposition, the lithium carbonate and was enrichedtheTable ion-exchange. and 4. Theseparated element from content the of calcium the lithium and carbonate sodium after(as seenthe hydrogenation–decomposition in Table 4). By concentrating and and heating,the theion-exchange. XRD and SEM analysis of the+ metal oxides2+ were shown+ in Figures2− 10 and 11. There was Element Li Ca Na SO4 no impurity phase detected and the ICP analysis also showed that the purity of lithium carbonate Content (%)Element 99.9% Li+ 0.005%Ca2+ 0.095%Na+ SO N.D.42− was almost 99.9%. Content (%) N.D.:99.9% Not-detected. 0.005% 0.095% N.D. Table 4. The element content of the lithiumN.D.: carbonate Not-detected. after the hydrogenation–decomposition and the ion-exchange.

Element Li+ Ca2+ Na+ SO42− Content (%) 99.9% 0.005% 0.095% N.D. N.D.: Not-detected.

Figure 9. The yields and purities of the heating rate with resin.

Appl. Sci. 2018, 8, x FOR PEER REVIEW 9 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 9 of 10 Appl. Sci. 2018, 8, 2252 9 of 10 Figure 9. The yields and purities of the heating rate with resin. Figure 9. The yields and purities of the heating rate with resin.

Figure 10. XRD analysis. Figure 10. XRD analysis.

Figure 11. SEM analysis. Figure 11. SEM analysis. 4. Conclusions 4. Conclusions This study proposed a hydrometallurgical way to recover lithium carbonate, effectively, from This study proposed a hydrometallurgical way to recover lithium carbonate, effectively, from the sulphate solutions. Calcium and sodium could be separated, effectively, with pH 7 and a 4 min the sulphate solutions. Calcium and sodium could be separated, effectively, with pH 7 and a 4 min reaction time in the ion-exchange step. In the hydrogenation–decomposition procedure, yields were reaction time in the ion-exchange step. In the hydrogenation–decomposition procedure, yields were the highest with 1.75 L of CO aeration, 27.5 ◦C of hydrogenation temperature, and 1 ◦C of the heating the highest with 1.75 L of CO2 aeration, 27.5 °C of hydrogenation temperature, and 1 °C of the heating the highest with 1.75 L of CO2 aeration, 27.5 °C of hydrogenation temperature, and 1 °C of the heating rate; purity was highest with a 0.5 ◦C heating rate, with the Dowex G26 resin. With these conditions, rate; purity was highest with a 0.5 °C heating rate, with the Dowex G26 resin. With these conditions, the lithium carbonate product could be acquired by the drying treatment, at 90 ◦C and its purity and the lithium carbonate product could be acquired by the drying treatment, at 90 °C and its purity and recovery rate were almost 99.9% and 87.6%. In comparison with other methods, this method produced recovery rate were almost 99.9% and 87.6%. In comparison with other methods, this method less waste and energy consumption, less use of chemicals, and could efficiently purify the lithium produced less waste and energy consumption, less use of chemicals, and could efficiently purify the carbonate from the sulphate solutions. lithium carbonate from the sulphate solutions. Author Contributions: Supervision, W.-S.C. and H.-J.H.; Writing–original draft, C.-H.L.; Writing–review & Author Contributions: Supervision, W.-S.C. and H.-J.H.; Writing–or Writing–originaliginal draft, C.-H.L.; Writing–review Writing–review & editing, C.-H.L. and H.-J.H. editing, C.-H.L. and H.-J.H. Funding: This research was funded by NCKU ResearchResearch & Development FoundationFoundation (106S281).(106S281). Funding: This research was funded by NCKU Research & Development Foundation (106S281). Acknowledgments: We are pleased to acknowledge the support of the Laboratory of Resources Circulation (LRC) Acknowledgments: We are pleased to acknowledge the support of the Laboratory of Resources Circulation Acknowledgments:at National Cheng Kung We University.are pleased to acknowledge the support of the Laboratory of Resources Circulation (LRC) at National Cheng Kung University. (LRC)Conflicts at National of Interest: ChengThe Kung authors University. declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. References 1. Alias, N.; Mohamad, A. Advances of aqueous rechargeable lithium-ion battery: A review. J. Power Sources 2015, 274, 237–251. [CrossRef] Appl. Sci. 2018, 8, 2252 10 of 10

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