Tuz Gölü), Turkey
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Scientific Research and Essays Vol. 5 (11), pp. 1317-1324, 4 June, 2010 Available online at http://www.academicjournals.org/SRE ISSN 1992-2248 © 2010 Academic Journals Full Length Research Paper Salt crust mineralogy and geochemical evolution of the Salt Lake (Tuz Gölü), Turkey O. Kilic and A. M. Kilic* Mining Engineering Department, Engineering and Architecture Faculty, Cukurova University, Adana, Turkey. Accepted 19 May, 2010 The Salt Lake (Tuz Gölü) is the second largest lake in Turkey and also is one of the greatest salty lakes in the world. Salt Lake has a great salt potential. The salt was produced in large quantities on saltpans in the Salt Lake. In this study, a detailed mineralogical investigation was carried out with salt crust samples and unconsolidated muddy sediments, below the salt crust collected from the Kaldırım Saltpan in the Salt Lake. The salt crust and below the salt crust (1 - 20 cm) evaporate mineralogy were determined by X-ray diffraction method. The analysis results show that the salt crust was in composition of halite, gypsum and kieserite; muddy sediments and below the salt crust which was in the composition of gypsum, magnesite, thenardite, polyhalite, aragonite and montmorillonite. The mineralogical variations of the participated salts indicated that, the chemical compositions of brines vary significantly between the Na-K-Mg-Ca-Cl type and the Na-K-Mg-Cl-SO4 type. Key words: Salt Lake, solar evaporation, evaporates, salt crust, XRD, SEM. INTRODUCTION Sodium chloride, NaCl (halite), the most common only poorly modeled by studying brine evolution in man- evaporite salt, is used in several forms by virtually every made sea water ponds. In such salt works (Eugster and person in the world. There are more than 14000 reported Hardie, 1978; Dean, 1978; Harvie et al. 1980; Harvie and usages of halite and it, along with other salts, has long Weare, 1980; Mccaffrey et al., 1987; Spencer and played a very important role in human affairs (Lefond, Hardie, 1990), the evolved seawater brines are separated 1983; Harben and Bates, 1990; Hardie, 1991; Harben from earlier precipitated mineral species and evaporation and Kuzvart, 1996; Warren, 1999). conditions. Salt exists as a solution in seas, lakes and salty water In Turkey, salt needs are mostly met by lakes. Brine sources; whereas, it is found as solid in the form of rock- extraction for sodium chloride with subsequent lined and salt. It is not only mined, it is also produced more unlined solar evaporation saltpans (Kaldırım, Kayacık economically by solar concentration of brines for and Yavan) concentration also takes place on the edge centuries. The salts formed at the more saline end of a of Salt Lake (Tuz Gölü) in central Anatolia, Turkey. It is phreatic precipitation sequence is made up of normally 80 km long and 50 km wide at an elevation of progressively more soluble evaporitic minerals; silicates 905 m above sea level. On the east, west and north (zeolites), calcite, Ca-, Na-, (K) and Mg-sulphates, shores of Salt Lake near Kaldırım, Kayacık and Yavan, chromates, borates and perchlorates (Warren, 1999). respectively, brines are concentrated in more than 38.86 Salts can back react with the parent brine as they km2 solar ponds within a total area ~1600 km2 of the Salt crystallize both at the surface and in the sub surface. Lake (Figure 1). The salt production is four lined ponds (1 Hence bittern chemistry and associated brine evolution is × 3 km) and unlined solar evaporation pan (~4 km2) in Kaldırım saltpan, five lined ponds, A, B, C, D1, D2, (10.86 2 km ) in Kayacık saltpan and lined ponds, A, B, C1, C2, D, (10.86 km2) in Yavan saltpan in the Salt Lake (Figure 2). *Corresponding author. E-mail: [email protected]. Fax: +90 322 The salt crust (97 - 99% NaCl) was precipitated by the 338 61 26. solar evaporation on the lake basin during the May and September. Every year, between August and November, Symbol: ~, Approximately. solar salt is harvested by mechanical harvesting equip- 1318 Sci. Res. Essays Figure 1. The map of the Salt Lake (Tuz Gölü) and landslide view. Ankara N . Koçhisar C B 0 200km Kaldırım 0 2 4 km D A ereflikoçhisar Main Zone D SALT LAKE 2 A D1 B Kayacık C Gölbaı Yavan A B D C Figure 2. The solar evaporation pond of the Salt Lake (Tuz Gölü). Kilic and Kilic 1319 Table 1. Mean ion concentrations (mg/l) of the Salt Lake brine in a yearly cycle (Çamur and Mutlu, 1996). Month K Na Ca Mg SO4 Cl pH Jan 1610 115625 617 4445 9675 188812 7.42 Feb. 800 107500 870 2100 6100 161100 7.50 Apr. 800 106300 1000 2200 6600 173100 7.10 May 944 101980 925 2860 7371 167438 7.34 Jun. 1458 114717 772 3963 8838 185454 7.30 Jul. 3358 106667 429 10591 19097 172710 7.33 Aug. 6300 113000 380 10932 20809 184104 7.45 Sep. 9400 89625 273 20686 37018 196448 7.15 Oct. 9900 69750 192 36667 67785 171159 6.95 Nov. 9950 105417 621 61194 13646 176527 7.33 Dec. 10000 102083 600 5095 10885 168018 7.55 ment. The harvesting pond is flooded again with new brines with low Na/Cl (<1), Br/Cl, Li/Cl and B/Cl ratios. brine from the lime pond to repeat the cycle. The lake was divided into two zones by Erol (1969): a The annual halite surface reserve of the Salt Lake is main zone to the west and a deep zone to the east approximately 211.2 106 ton. The thickness and density (Uygun, 1981; Koday, 1999). The main zone water level of the salt crust and salt production area are 0.08 m, 2.2 averages 70 cm in spring but dries in summer or early ton/m3 and 1200 106 m2, respectively. In the Salt Lake, fall. The deep zone maintains its water content through- the overall salt production is about 2500000 tons/year out the year and the water level reaches >1 m in spring. (Uyanık, 2004). As suggested by Irion and Muller (1968) and Uygun and During normal summer conditions, 90% of the halite en (1978), these two zones exhibit different chemical present in the brine is precipitated with little contamina- and mineralogical characteristics as well. Mean ion tion by other salts; sodium salts, potassium salts, concentrations of the Salt Lake brine in a yearly cycle are sulphate salts, Mg-bearing salt etc. This was observed in given in Table 1 (Çamur and Mutlu, 1996). Çamur and previous study; during the evaporation of lake water, Na+ Mutlu (1996) determine thermodynamic evaluation of and Cl- are removed to crystallize as halite; Mg2+ and K+ mineral precipitates in the Salt Lake (Tuz Gölü). The exhibit conservative behaviour until later precipitation of water composition of the Tuz Gölü also shows large sulphate salts (kieserite and langbeinite) and chlorides seasonal variations. In the summer period, when evapo- (carnalite and bischofite). As amount of Na+ is decreased ration is most intense, the ionic concentration reaches during the evaporation process in the brine, K+, Mg2+ and values close to halite saturation before becoming Cl- are increased continuously. During the evaporation of oversaturated in this mineral. In the winter period, the water of Salt Lake, the first Mg-bearing salt is found to be concentration decreases to a minimum value due to rain in the form of carnalite and langbeinite (Kilic and Kilic, (Table 1). 2005). The main zone evaporite mineralogy in the salt crust of The lake is fed by three major rivers; Peçeneközü, the northern limb consists of halite, gypsum, aragonite Uluırmak and nsuyu, with mean annual discharge rates and calcite. The mineralogy of the unconsolidated muddy of 37.106, 41.106 and 10.106 m3, respectively. Several sediment, below the salt crust (1 - 30 cm), starts with ephemeral stream and one man-made agricultural dis- gypsum, huntite and magnesite (Table 2 Minerals for charge canal with a mean annual discharge rate of 87.106 Formulas) bearing levels reaching ~25 cm in thickness m3 also feed the lake (DSI, 2003). Mean annual precipita- and continues in the central parts with polyhalite occur- tion averages 353 ± 36 mm and the potential monthly rences. evaporation ranges from 1175 - 1390 mm (MTA, 1982). This level is ~35 cm thick and is underlain by gypsum, Rivers and ground waters are the source of most of the huntite, magnesite, illite and montmorillonite bearing ions that are ultimately deposited as evaporite salts in sediments (Ergün, 1988; Tekin et al., 2007). Cubic halite nonmarine settings. In a closed hydrological system, the minerals in the upper levels of the salt crust have composition of nonmarine brines depend on lithologies dimensions of < 0.5 mm and are distinguished from the that are leached in the drainage basin surrounding a salt underlying halites by their clean with colors. lake (Eugster and Hardie, 1978; Eugster, 1980). In the This study, aimed to determine the chemical com- Salt Lake, inflow surface river waters, are modified by position of the lake water and the change that occurred in preferential dissolution of halite and potassium and the components of the precipitated salt on the lake magnesium salts. Evaporation of such waters Na-(Mg)-Cl surface and sediments, below the salt crust (1 - 20 cm). 1320 Sci. Res. Essays Table 2. Minerals discussed in the paper and their formulas. Mineral Formula Calcite CaCO3 Magnesite MgCO3 Gypsum CaSO4.2H2O Anhydrite CaSO4 Huntite CaMg3(CO3)4 Illite (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,H2O] Montmorillonite (1/2Ca,Na)0.7(Al,Mg,Fe)4(Si,Al)8O20(OH)47nH2O Halite NaCl Thenardite Na2SO4 Bloedite Na2 SO4.MgSO4.4H2O Mirabilite Na2SO4.10H2O Carnalite KMgCl3.6H2O Sylvite KCl Bischofite MgCl2.6H2O Langbeinite 2MgSO4.K2SO4 Kieserite MgSO4.H2O Polyhalite K2SO4.MgSO4.2CaSO4.2H2O Figure 3.