Fluid Phase Equilibria 436 (2017) 13e19

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Fluid Phase Equilibria

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Phase equilibria in the aqueous ternary systems (LiCl þ LiBO2 þ H2O) and (Li2SO4 þ LiBO2 þ H2O) at 323.15 K and 0.1 MPa * Long Li a, Yafei Guo a, b, , Sisi Zhang a, Mengmeng Shen a, Tianlong Deng a a Tianjin Key Laboratory of Marine Resources and Chemistry, College of Chemical Engineering and Material Sciences at Tianjin University of Science and Technology, Tianjin, 300457, PR China b College of Chemistry and Materials Science, Northwest University, Xi'an, 710127, PR China article info abstract

Article history: Combining the methods of isothermal dissolution equilibrium and the wet-residue solid phase Received 7 October 2016 (Schreinemarkers rule), the phase equilibria of the ternary systems (LiCl þ LiBO2 þ H2O) and (Li2SO4þ Received in revised form LiBO2 þ H2O) at 323.15 K and 0.1 MPa were investigated. On the basis of the experimental data on 11 December 2016 solubilities and the physicochemical properties including density, refractive index and pH value, the Accepted 12 December 2016 phase diagrams and physicochemical properties versus composition diagrams of the two systems were Available online 20 December 2016 plotted. For the two systems, there are both in one invariant point, two univariant curves, and two crystallization regions corresponding to lithium metaborate dehydrate (LiBO2$2H2O, Lb2), lithium Keywords: $ $ Phase equilibria chloride monohydrate (LiCl H2O i.e. Lc1, in the former) and lithium sulfate monohydrate (Li2SO4 H2O i.e. Lithium metaborate Ls1, in the later), and the area of the crystallization region of Lb2 is the largest when compared with those Lithium chloride of Lc1 and Ls1, and those results demonstrate that the solubility of lithium metaborate is the lowest. A Lithium sulfate comparison of the phase diagrams between this work at 323.15 K and the literature at (288.15, 298.15 and 308.15) K in the former system, the crystallization region of LiBO2$8H2O existed at 288.15, 298.15 and 308.15 K is disappeared at 323.15 K. Relationships between solubility and temperature for LiBO2 and LiCl are both in positive correlation obviously. However, a comparison of the phase diagrams between this work at 323.15 K and the literature at (288.15, 298.15) K in the later system, it was found that the mineral LiBO2$8H2O existed at 288.15 and 298.15 K is replaced by LiBO2$2H2O, and the component of Li2SO4 in the solution has a relatively strong salting-out effect to LiBO2, and the concentrations of LiBO2 in the solution are decreased considerably with the increasing of lithium sulfate concentration in the solution. The calculated values of refractive index using empirical equations for the two ternary systems are in good agreement with the experimental values. © 2016 Published by Elsevier B.V.

1. Introduction occurring in salt lakes are evaporation, concentration, crystalliza- tion, precipitation, dissolution and phase transformation. It is Borate function materials have been widely used as important obvious that phase equilibria and phase diagrams can explain strategic materials in the fields of mobile communication tech- above phenomenon and even guide those processes effectively [3]. nology, medicine, astronavigation and so on for their excellent Therefore, it is particularly meaningful to engage the research on characteristics [1]. Salt lakes with high concentrations of lithium phase equilibria and physicochemical properties of borate- and boron resources in the western of China are well known around containing and lithium-containing salt-water systems for the world [2]. The major chemical component of brine belongs to describing the geochemical evolution of containing borate and þ þ þ 2þ 2- the complex salt-water system Li ,Na ,K ,Mg //Cl ,SO4 , borate lithium salt lakes and exploiting valuable borate and lithium re- e H2O. The most important physical and chemical processes sources. Aiming to establish the complex brine systems, some salt- water subsystems have been studied in the literature [4e6].In addition, the system (LiCl þ LiBO2 þ H2O) at (288.15, 298.15, 308.15) * Corresponding author. Tianjin Key Laboratory of Marine Resources and Chem- K [7,8], and the system (Li2SO4 þ LiBO2 þ H2O) at (288.15, 298.15) K istry, College of Chemical Engineering and Material Sciences at Tianjin University of [9] have been reported previously. Science and Technology, Tianjin, 300457, PR China. To exploit the valuable brine resources economically, the phase E-mail address: [email protected] (Y. Guo). http://dx.doi.org/10.1016/j.fluid.2016.12.013 0378-3812/© 2016 Published by Elsevier B.V. 14 L. Li et al. / Fluid Phase Equilibria 436 (2017) 13e19 equilibria of salt-water systems at multi-temperatures is essential. and quantitative weighted into the 50.0 cm3 volumetric flask filled Generally, the climate conditions in the region of salt lakes are with DDW for chemical analysis. And then, the supernatant liquids almost of windy, weather aridity, little rainfall, and great evapo- were also sampled for physicochemical properties measurements rating capacity [10]. In order to economic exploit the brine and salt (density, refractive index and pH). In addition, one part of the solid deposit minerals, it is greatly importance to adopt the natural re- phase was identified occasionally combined with the digital sources adequately of the salt lake regions such as the energy of sun polarizing microscope and the XRD. resource for solar pond technique. Although it is impossible to reach 323.15 K naturally, the temperature at the non-convecting 2.3. Analytical methods zone in the deep solar pond (salt gradient pond) was ranged from 313.15 K to 373.15 K [11]. Therefore, the phase equilibria of the two The Cl concentration both in the liquid phase and wet-residue subsystems (LiCl þ LiBO þ H O) and (Li SO þ LiBO þ H O) at 2 2 2 4 2 2 was determined by titration with the standard uncertainty 0.003 323.15 K were reported for the first time in this paper. (0.68 level of confidence) in mass fraction [12]. The concentrations 2- of SO4 and BO2 were analyzed by the gravimetric methods all with 2. Experimental section standard uncertainty ±0.0005 (0.68 level of confidence)in mass þ fraction [12]. The Li concentration was evaluated using the anion- 2.1. Reagents and apparatus cation balance combined with analytical verification using the inductively coupled plasma optical emission spectrometer (ICP- The chemicals used in this study were shown in Table 1.Itis OES, Prodigy, Leman Co., USA) with standard uncertainty of 0.005 worth mentioning that all chemicals were re-crystallized before (0.68 level of confidence) in mass fraction. use. The water prepared a series of artificially synthesized brines Moreover, the densities (r) were measured by the automatic and for chemical analysis is doubly deionized water (DDW, oscillating U-tube densimeter (DMA 4500, Anton Paar, Austria, k 0.0001 S m 1 and pH ¼ 6.6 at 298.15 K) during the whole precision ± 1.0 10 5 gcm 3) with the standard uncertainty of 3 experiment. 0.5 mg cm (0.68 level of confidence). The refractive indices (nD) The magnetic stirring thermostatic bath (HXC-500-6A, Beijing were determined by the Abbe refractometer (WAY-2S, Shanghai Fortunejoy S&T Co. Ltd, China) was used, and the temperature Precision Scientific Instrument Co. Ltd, China) with standard un- precision was within ±0.1 K. The digital polarizing microscope certainty of 0.0001 (0.68 level of confidence), which connected (BX51, Olympus Co., Japan) and the X-ray powder diffractometer with a thermostat (K20-cc-NR, Huber, Germany) to control the (MSAL XD-3, Beijing Purkinje Instrument Co. Ltd, China) were used temperature within 0.01 K. And the pH values were detected with to identified the solid phase samples. the pH meter (PH-7310, WTW Co. Ltd, Germany) with standard uncertainty of 0.001 at 0.68 level of confidence. All measurements of the above physicochemical properties were maintained in a 2.2. Experimental method supper thermostated water bath that controlled at the desired temperature (323.15 ± 0.01 K). The phase equilibrium of salt-water system was studied with the isothermal dissolution method and the wet-residue solid phase identification method i.e. Schreinemarkers rule [3]. Briefly, the se- 3. Results and discussion ries of complexes were loaded in the bottles and capped tightly. The bottles were placed in the magnetic stirring thermostatic bath, 3.1. For the ternary system LiCl þ LiBO2 þ H2O whose temperature was set at 323.15 ± 0.1 K, and stirred at 130 rpm to accelerate the equilibrium of those complexes. A 5.0 cm3 sample The solubilities, densities, refractive indices and pH values of the of the clarified supernatant was taken from the liquid phase of each ternary system (LiCl þ LiBO2 þ H2O) at 323.15 K present in Table 2. bottle with a pipette at regular intervals for chemical analysis. It On the basis of the experimental solubility data in Table 2, the was worthy saying that the magnetic stirrer was allowed to rest for equilibrium phase diagram of the ternary system 1 h in order to ensure the separation the solid phase from the liquid (LiCl þ LiBO2 þ H2O) at 323.15 K shows in Fig. 1. According to the phase before sampling. If the compositions of the liquid phase in Schreinemarkers rule, connect a series of composition points with the bottle became constant, it indicated that the equilibrium was the relative composition points of wet-residues, and then lengthen achieved. Generally, it takes about 50e60 days to be at equilibrium. to cross the composition points of solid phases either in After equilibrium was achieved, the magnetic stirrer was LiBO2$2H2O or in LiCl$H2O as shown in Fig. 1. stopped to separate the solid phase from the liquid phase. When In Fig. 1, there are two crystallization regions corresponding to the complexes in bottles were clarification, the liquid phases were lithium chloride monohydrate (LiCl$H2O, Lc1) and lithium taken out for quantitative chemical analysis. The wet-residue of metaborate dehydrate (LiBO2$2H2O, Lb2), one invariant co- solid phase with the minor adherent mother liquor was sampled saturation point E1 (Lc1 þ Lb2), and two univariant curves B1E1

Table 1 Chemical samples used in this study.

Code Grade Initial mass Purification Final mass Analysis method fraction purity method fraction purity

Lca A.R. 0.99 Recrystallization 0.995 Titration for Cl Ls1b A.R. 0.99 Recrystallization 0.998 Gravimetric method 2- for SO4 Lb8c A.R. 0.99 Recrystallization 0.998 Gravimetric method for BO2 a Lc, lithium chloride anhydrous (LiCl), from the Xinjiang Nonferrous Metal Industry Co. Ltd. b Ls1, lithium sulfate monohydrate (Li2SO4$H2O), from the Shanghai Lithium Industrial Co. Ltd. c Lb8, lithium metaborate octahydrate (LiBO2$8H2O), from the Sinopharm Chemical Reagent Co. Ltd. Download English Version: https://daneshyari.com/en/article/6473339

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