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www.ache.org.rs/CICEQ Chemical Industry & Chemical Engineering Quarterly 18 (1) 8388 (2012) CI&CEQ
RADOUANNE FEZEI EXTRACTIVE PROCESS FOR PREPARING HALIM HAMMI HIGH PURITY MAGNESIUM CHLORIDE ADEL M’NIF HEXAHYDRATE Technological pole of Borj Cedria, National Center of Research in This paper reports a method for the preparation of magnesium chloride hexa- Materials Sciences, Valorization hydrate (bischofite) from Sebkha el Melah of Zarzis Tunisian natural brine. It is Laboratory of Useful Materials, a five-stage process based on crystallization by isothermal evaporation and Soliman, Tunisia chemical precipitation. The first two steps were dedicated to the crystallization SCIENTIFIC PAPER of sodium chloride and potassium-magnesium double salts, respectively. Then, the resulting liquor was desulfated using calcium chloride solution. After that, UDC 66.06:543.3(611) another isothermal evaporation stage was implemented in order to eliminate
potassium ions in the form of carnallite, KCl·MgCl2·6H2O. At the end of this DOI 10.2298/CICEQ110815049F step, the recovered solution, primarily composed of magnesium and chloride ions, was treated by dioxan in order to precipitate magnesium chloride as
MgCl2·6H2O·C4H8O2. This compound dried at constant temperature of 100 C gave good quality magnesium chloride hexahydrate. Besides this salt, the va- rious by-products obtained from the different treatment stages are also useful. Keywords: process; extraction; magnesium chloride; natural brine.
Brines are seawater-type solutions often assi- Process description + + 2+ - 2– milated to the quinary system Na , K , Mg /Cl , SO4 Choice of the different treatment stages adopted //H2O [1,2]. These solutions, which represent a nearly in the conceived process was directed by some pre- endless reserve of dissolved salts, are expected to vious work [2, 19-22]. The corresponding flowchart is play an important role in the economic sector of some given by Figure 1. It is a five stage process based countries and especially those in developing such as mainly on isothermal evaporation and salts crystalli- Tunisia. Thus, several works were developed on Tu- zation as well as chemical precipitation. nisian natural brines. The first ones studied geological The first step consists of evaporating the con- aspects as well as solubility diagrams related to the sidered brine at 35 C in order to crystallize sodium previously mentioned system [1,3-6]. Then, investiga- chloride (halite). During the second treatment, the re- tions were extended to the modeling of phase dia- sulting solution is further concentrated by isothermal grams [7-14]. Recent studies are rather directed to- evaporation at the same temperature. The precipi- wards the extraction of interesting salts [6,15-18]. tated salts are expected to be sodium chloride and Among these salts, magnesium chloride is of great substantial amounts of kainite (KCl·MgSO4·3H2O). utility in industry as well as agriculture. The third step of the process is a chemical precipi- The present work is a contribution to the vapo- tation reaction of sulfate ions using calcium chloride rization studies of Tunisian brines. In particular, it deals solution. After removing calcium sulphate precipitate, with the preparation of magnesium chloride hexahyd- the mother liquor is subjected to another 35 C iso- rate salt from the naturally occurring brine of Sebkha thermal evaporation in order to eliminate partially po- el Melah of Zarzis. tassium ions as potassium-magnesium double salt,
carnallite (KCl·MgCl2·6H2O). The resulting brine, com- Correspondening author: R. Fezei, Technological pole of Borj posed essentially of magnesium and chloride ions, is Cedria, National Center of Research in Materials Sciences, Va- lorization Laboratory of Useful Materials, Tourist road of Soli- treated by 1,4-dioxan (C4H8O2), which is expected to man B.P. 73 - Soliman 8027, Tunisia. precipitate the magnesium chloride salt as
E-mail: [email protected] MgCl2·6H2O·C4H8O2 [22-25]. This compound was dried Paper received: 15 August, 2011 Paper revised: 10 October, 2011 at constant temperature (100 °C) to eliminate dioxan Paper accepted: 11 October, 2011
83 R. FEZEI, H. HAMMI, A. M’NIF: EXTRACTIVE PROCESS FOR PREPARING HIGH PURITY… CI&CEQ 18 (1) 8388 (2012)
Figure 1. Flowchart of the process conceived for magnesium chloride hexahydrate extraction from Sebkha el Melah natural brine (the given compounds are expected theoretically). molecules and thus obtain magnesium chloride hexa- used: calcium chloride dehydrate (99%) and 1,4-di- hydrate, MgCl2·6H2O. oxan (99%) supplied by Fluka. Apparatus and analysis methods EXPERIMENTAL All treatments were performed at constant tem- Chemicals perature (35 °C) in a thermostatic bath, except the The principal raw material considered in this third and fifth ones. These two treatment stages were study is natural brine sampled from Sebkha El Melah carried out in a jacketed glass reactor where tempera- of Zarzis. Its chemical composition in major ions is tures (35 and 25 °C, respectively) were controlled by given in Table 1. Besides this highly concentrated water circulation. In both steps agitation was assured aqueous solution, two commercial reagents were also by a mechanic stirrer.
Table 1. Ionic composition of brines (g L-1)
+ + 2+ 2+ - 2- Brine Na K Mg Ca Cl SO4
S0 (initial) 41.32 7.36 53.95 0.40 205.14 30.50
S1 21.62 10.95 77.76 0.00 234.57 43.81
S2 13.14 12.77 90.52 0.00 265.97 51.89
S3 6.64 7.55 70.35 0.00 224.73 6.09
S4 4.02 5.88 100.89 0.00 299.35 8.25
84 R. FEZEI, H. HAMMI, A. M’NIF: EXTRACTIVE PROCESS FOR PREPARING HIGH PURITY… CI&CEQ 18 (1) 8388 (2012)
Brines and solid phases collected from the diffe- of the 35 °C isotherm of the quinary system Na+, K+, 2+ - 2- rent treatment stages of the process were chemically Mg /Cl , SO4 //H2O usually used to describe brines analyzed. The chemical analysis methods applied for equilibrium states. In this diagram, the coordinates of sulphate, chloride, magnesium, and alkaline ions a considered solution are expressed as follows: were respectively gravimetry, potentiometry (Titrino 100nK DMS 716 of mark Ω Metrohm), EDTA complexometry %K 2 , 2 D and flame atomic absorption spectroscopy (SAAF). 100n Furthermore, X-ray diffraction analysis using a %Mg Mg , Philips instrument (PW 3040 generator, 3050/60 θ/2θ) D 100nSO and CoK radiation ( = 1.789 Å) were performed. %SO 4 , 4 D Dn n n , RESULTS AND DISCUSSION KM24g SO
where ni is the mole number of the i entity. Ionic composition of the original brine (S0) and Geometrical positions of the original brine (S0) circulating solutions (Si, i refers to the corresponding treatment) are summarized in Table 1. and the mother liquors resulting from the four consi- As expected, the first four treatment stages gave dered treatment stages (S1, S2, S3 and S4) in the equilibrium diagram show the brine’s evolution to- a magnesium chloride solution (S4) containing smaller amounts of sodium chloride, potassium chloride and wards the crystallization field of magnesium chloride magnesium sulphate. Thus, such solution may be suit- hexahydrate (MgCl2.6H2O). able for magnesium chloride salt precipitation by di- Regarding the recovered solid phases (Sdi), their ionic compositions are given in Table 2. Besides oxan as MgCl2·6H2O·C4H8O2. Chemical composition evolution of the treated chemical analysis, they were also characterized by X- brine is well seen in Figure 2. It represents a section -ray diffraction. Results of this characterization are represented by Figures 3 and 4.
+ + 2+ - 2- Figure 2. 35 °C Isotherm of the quinary system Na , K , Mg /Cl , SO4 //H2O (NaCl saturated).
Table 2. Ionic compositions of solid phases (mass%)
+ + 2+ 2+ - 2- Brine Na K Mg Ca Cl SO4
Sd1 35.90 0.26 1.02 0.00 56.25 2.55
Sd2 35.10 0.37 1.27 0.00 55.29 2.42
Sd3 1.92 2.32 1.53 21.06 2.15 50.46
Sd4 0.62 14.02 8.13 0.00 38.32 0.89
Sd5 0.06 0.05 7.94 0.00 23.10 0.00
Sd6 0.11 0.09 11.61 0.00 34.05 0.00
85 R. FEZEI, H. HAMMI, A. M’NIF: EXTRACTIVE PROCESS FOR PREPARING HIGH PURITY… CI&CEQ 17 (X) XXXXXX (2012)
Figure 3. Diffractograms of the solid phases Sd1 (a), Sd2 (b), Sd3 (c) and Sd4 (d).
86 R. FEZEI, H. HAMMI, A. M’NIF: EXTRACTIVE PROCESS FOR PREPARING HIGH PURITY… CI&CEQ 18 (1) 8388 (2012)
Figure 4. XRD Patterns of the solid phase precipitated by dioxane a) before drying and b) after drying.
Solids resulting from the first two treatment vered, only one difference was noted in comparison stages (Sd1, Sd2) are sodium chloride salts containing with our predictions. It is the absence of double salt less than 5% impurities (mainly ions from coating so- KCl·MgSO4·3H2O (Kaïnite) in Sd2 solid phase. Lack of lution). The chemically precipitated compound, Sd3, is this salt could be explained by its low crystallization almost pure gypsum. Salt Sd4 is basically carnallite rate. In fact, magnesium ions exist in aqueous solu- 2+ (KCl·MgCl2·6H2O) containing little quantities of halite tions predominantly as [Mg(H2O)6] which promote the
(NaCl). Solid Sd5 precipitated by dioxan corresponds formation of salts having six water molecules in their to the compound MgCl2·6H2O·C4H8O2 including sub- structures. stantial amounts of sodium, potassium and sulphate To show the importance of prepared salt, we ions. Finally, the end-product obtained by drying Sd5 studied its industrial application in Sorel cement ma- solid phase is an extremely pure magnesium chloride nufacture. The compressive strength and setting time hexahydrate salt. Its purity is more than 99.5%. When of the obtained cement paste were determined and treating one liter of brine, 155 grams of this salt were were 86 MPa and 62 min, respectively. These values recovered, i.e., an overall process yield of 40%. are comparable to those found when using com- Considering the information provided by the ex- mercial magnesium chloride hexahydrate. perimental results regarding the solid phases reco-
87 R. FEZEI, H. HAMMI, A. M’NIF: EXTRACTIVE PROCESS FOR PREPARING HIGH PURITY… CI&CEQ 18 (1) 8388 (2012)
CONCLUSIONS [9] L. Zayani, R. Rokbani, M. Trabelsi-Ayadi, J. Therm. Anal. Calorim. 57 (1999) 575–585 This work is a contribution to the vaporization [10] H. Hammi, A. M’nif, R. Rokbani, J. de physique IV 11 studies of Tunisian natural resources dealing with the (2001) 157-163 extraction of magnesium chloride hexahydrate salt [11] H. Hammi, J. Musso, A. M’nif, R. Rokbani, J. Calphad 27 from Sebkha el melah natural brine. To perform this (2003) 71-77 task, a five stage process based on isothermal eva- [12] H. Hammi, J. Musso, A. M’nif, R. Rokbani, Desalination poration and chemical precipitation was performed. 158 (2003) 215-220 The conceived process gave good quality magnesium [13] H. Hammi, J. Musso, A. M’nif, R. Rokbani, J. de physique chloride hexahydrate (purity higher than 99.5%) which IV 113 (2004) 119-123 was successfully checked in Sorel cement manufac- [14] H. Hammi, J. Musso, A. M’nif, R. Rokbani, Desalination ture. Besides this chloride, all the collected by pro- 166 (2004) 205-208 ducts are also useful. [15] C. Djebali, L. Zayani, A. M’nif, R. Rokbani, J. Société Chi- mique Tunisie 4 (1998) 233–244. REFERENCES [16] L. Zayani, R. Rokbani, J. Therm. Anal. Calorim. 59 (2000) 885–892 [1] A. M’nif, Contribution to the study of equilibrium diagram [17] A. M’nif, R. Rokbani, Asian J. Chem. 12 (2000) 58–68 for the valorization of natural brines, Ph.D. Thesis, Fa- [18] R. Fezei, H. Hammi, A. M’nif, Lat. Am. Appl. Res. 39 culty of Sciences of Tunis, Tunisia, 1984 (2009) 375-380 [2] R. Cohen-Adad, Chr. Balarew, S. Tepavitcharova, D. Ra- [19] Berthon, R., Représentation des équilibres de solubilité et badjieva, Pure Appl. Chem. 74 (2002) 1811-1821 utilisation des diagrammes, Gauthier-Villars, Paris, 1962 [3] A. Chaabouni, Extraction of KCl from Chott el Jerid, DEA, [20] H. Hammi, Contribution to the study of salts crystalli- Faculty of Sciences of Tunis, Tunisia, 1980 zation from Sebkha El Melah natural brine and their + + – 2– [4] N. K. Guerfal, System: K , Na / Cl , SO4 / H2O at 10 °C, transformation, Ph.D. Thesis, Faculty of Sciences of Sfax, Ph.D. Thesis, Faculty of Sciences of Tunis, Tunisia, 1981 Tunisia, 2004 [5] N. Kalai, Contribution to the study of the Tunisian south [21] A. M’nif, R. Rokbani, Cryst. Res. Technol. 39 (2004) 40-49 chotts brines, Ph.D. Thesis, Faculty of Sciences of Tunis, [22] R. Fezei, H. Hammi, A. M’nif, Chem. Eng. Res. Des. 89 Tunisia, 1986 (2011) 367-372 [6] A. M’nif, R. Rokbani, J. Société Chimique Tunisie 4 [23] J.C. Barnes, T.J.R. Weakley, J. Chem. Soc. Dalton (1998) 221-231 Trans. (1976) 1786–1790 [7] L. Zayani, Study of a Tunisian south brine, crystallization [24] M. Bester Rogac, D. Dolar, Acta Chim. Slov. 46 (1999) sequence and modelling, Ph.D. Thesis, Faculty of Sci- 463–470 ences of Tunis, Tunisia, 1999 [25] J.A. Weicksel, C.C. Lynch, J. Am. Chem. Soc. 72 (1950) [8] D.B.H. Chehimi, Contribution to the study and the model- 2632–2636. ling of salts systems, Ph.D. Thesis, Faculty of Sciences of Tunis, Tunisia, 1997
RADOUANNE FEZEI DOBIJANJE MAGNEZIJUM HLORID HALIM HAMMI HEKSAHIDRATA VISOKE ČISTOĆE POMOĆU ADEL M’NIF PROCESA EKSTRAKCIJE Technological pole of Borj Cedria, National Center of Research in Materials Sciences, Valorization U ovom radu je predstavljena metoda za pripremu magnezijum-hlorid heksahidrata (bi- Laboratory of Useful Materials, Soliman, schofite) iz prirodne slane vode Sebkha el Melah u Zarzisu, Tunis. Proces se sastoji iz Tunisia pet faza, koji je u suštini zasnovan na kristalizaciji pomoću izotermnog isparavanja i he- NAUČNI RAD mijske precipitacije. Prve dve faze su kristalizacije natrijum hlorida i dvogube soli kali- juma i magnezijum. Zatim je dobijena smeša tretirana rastvorom kalcijum-hlorida radi desulfatizacije. Nakon toga, izvršena je još jedna faza izotermnog isparavanja u cilju eli-
minisanja jona kalijuma u obliku karnalita, KClMgCl26H2O. Na kraju ove faze, dobijen rastvor, primarno sastavljen od jona magnezijuma i hlorida, tretiran je dioksanom radi
precipitacije magnezijum-hlorida u obliku MgCl26H2OC4H8O2. Dobijeno jedinjenje je su- šeno na konstantnoj temperaturi od 100 C, pri čemu je dobijen je kvalitetan magnezijum -hlorid heksahidrat. Pored ove soli, iz različitih faza procesa dobijeni su sporedni proiz- vodi, koji su, takođe, korisni.
Ključne reči: proces; ekstrakcija, magnezijum hlorid, prirodna slana voda.
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