Tuz Gölü), Turkey

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 Yavİan) 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 Yavİan, 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 Yavİan 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 ğ. Koçhisar

C B 0 200km Kaldırım 0 2 4 km D A

ğereflikoçhisar

Main Zone

D SALT LAKE 2 A D1 B Kayacık C Gölbaİı Yavİan 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 ğen (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 Ğnsuyu, 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. Geological map of the Tuz Gölü Basin (Çemen et al., 1999).

GEOLOGICAL SETTING Cretaceous) time. This basin is currently bounded by the northwest-to southeast-trending Aksaray–Koçhisar faults The Tuz Gölü Basin, located in the dry central plateau of (Cemen et al., 1999; Ayyildiz, 2001), (Figure 3). In this Turkey, was formed during the Maastrichtian (Late basin, an ophiolitic complex known as the Ankara Kilic and Kilic 1321

Figure 4. Generalized stratigraphic columnar section of the Tuz Gölü Basin. Abbreviations; PL-Q: Pliocene– Quaternary, AM: Akbogaz Member, CM: Cavuskalesi Member, KM: Karamollausagi Member, ABM: Asmayaylasi Member, KCC: Kirsehir Crystalline Complex, BP: Baranadag Pluton (Aydemir, 2008).

below the salt crust were analyzed in the determination of the chemical composition of the salt and participated evaporates in the Salt Lake. The samples of water and salt crust were gathered; striped solar ponds of evaporation to the various sectors (Kaldırım Saltpan, Kayacık Saltpan and Yavİan Saltpan), and those were analyzed by using the liquid meter of chromatography (LCA10A). The salt crust and unconsolidated muddy sediment below the salt crust were analyzed to determine mineralogical composition of salt by analysis of XRD. The analysis was performed with a Shimadzu XRD-6000 and Cu X-ray tube (λ=1.5405 Å). The diffraction interval was between 2θ - 20° - 60° with a step of 0.02°. The microscopic observation of salt sample and unconsolidated muddy sediment below the salt crust was carried out to determine the salt crystals of occurrence by means of electronic microscopy of sweeping (SEM) (JEOL/JSM-6335F). In this study, the salt of Kaldırım saltpan was employed in SEM analyses.

RESULTS AND DISCUSSION

Figure 5. Cubic halite crystalls on the Tuz Gölü. In the field observation, cubic chevron type halite minerals in the upper levels of the salt crust was seemed to have dimensions of 0.5 mm-1 cm, and they were easily Melange (nappes) constitutes the basement, which is recognized and distinguished from the underlying halites unconformably overlain by a thick sedimentary cover by their clean colors in the Salt Lake (Figure 5). accumulated between the Late Cretaceous and the The lake water and salt crust were analyzed in the Pliocene (Uygun, 1981; Görür et al., 1984). A number of determination of the chemical composition of the Salt evaporite units of various ages (Upper Cretaceous, Lake, and the analysis results are listed in Tables 3 - 4. Paleocene, Middle Eocene, and Oligo-Miocene) are The Salt Lake water is determined to dominate by Na+ interlayered in this sedimentary cover (Figure 4) - 2- 2+ 2+ + and Cl , with lesser amounts of SO4 , Mg , Ca and K (Aydemir, 2008). (Table 3). Table 4 shows that halite present in the brine is Recent (Holocene) sediments of the Tuz Gölü Basin precipitated with little contamination by other salts; occupy a depression. Sediments in this depression are sodium salts, potassium salts, sulphate salts, Mg-bearing mainly composed of gypsum, dolomite, magnesite, salt etc. It is clear that participated salts are mainly huntite, and polyhalite (Irion and Müller, 1968; Ergun, consisting of halite mineral. 1988; Gündo₣an and Helvacı, 1996; Camur and Mutlu, The Salt Lake water is determined to dominate by Na+ 1996). - 2- 2+ 2+ + and Cl , with lesser amounts of SO4 , Mg , Ca , K , 2- - CO3 and HCO3 . The chemical analysis data of participated salts at the experiments indicated that the EXPERIMENTAL chemical compositions of brines vary significantly

The lake water, the salt crust and unconsolidated muddy sediment, between the Na-K-Mg-Ca-Cl type and the Na-K-Mg-Cl- 1322 Sci. Res. Essays

Table 3. The chemical composition of the Salt Lake brine (mg/l).

Sample Place Cl SO4 Ca Mg Na K Kaldırım Saltpan 192115 8016 1353 47002 71583 38316 Kayacık Saltpan 201338 4055 958 21441 71071 7394 Yavİan Saltpan 201200 5008 976 29950 70050 8010

Table 4. The composition of the salt crust.

Components, % Kaldırım salt Kayacık salt Yavİan salt

CaSO4 0.477 0.579 0.613

MgSO4 0.022 0.009 0.013

MgCl2 0.143 0.136 0.181

K2SO4 0.247 0.4623 0.437 NaCl, dry 99.10 98.04 98.28 Moisture 2.500 2.083 2.929

Table 5. XRD data for crystalline phases of the salt crust and chemical industry. 60 - 70% of the amount of salt unconsolidated muddy sediments below the salt crust. consumed in industrialized countries is on the account of chemical sector. Therefore, the major importance of salt Samples Composition 2θ degrees (°) for us as a developing country should never be Halite 27.33 45.49 56.53 neglected. Salt crust Gypsum 20.80 29.19 47.93 Salt Lake has the capability to meet the salt need of Kieserite 21.75 29.66 - Turkey providing that its three saltpan are improved on the basis of production, transportation and storage Gypsum 20.80 29.19 47.93 features. Magnesite 32.66 43.03 53.93 Current salt formation and production at the lake are Sediments Thenardite 28.27 32.12 48.78 directly related with amount of water entering the lake area and evaporation. The settlement media of Salt Lake Polyhalite 28.10 30.70 31.43 is the brine saturated with NaCl as composition. Aragonite 26.24 27.25 45.90 The Salt Lake (Tuz Gölü) water has been classified as Montmorillonite 26.69 30.62 36.07 Na-Cl type brine whose NaCl rate is over 98%. The salt

obtained from this lake accounts for 70 -80% of Turkey’s need. It also has considerable salt (NaCl) and salt co- SO4 type according to Eugster and Hardie (1978) product potential (Kilic and Kilic, 2005) for industries and classification. It could be classified as a Na-Cl-type brine human activities. (Kilic and Kilic, 2005). The chemical analysis data of participated salts at the XRD analysis result show that the salt crust is experiments indicated that the chemical compositions of composed of halite, gypsum and kieserite (Table 5). The brines vary significantly between the Na-K-Mg-Ca-Cl type mineralogy of muddy sediments, below the salt crust was and the Na-KMg-Cl-SO4 type according to Eugster and determined; gypsum, magnesite, thenardite, polyhalite, Hardie (1978). The water of salt lake was to dominate by aragonite and montmorillonite (Table 5). SEM Na and Cl, with few quantities of SO4, magnesium, Ca observation results were emphased on XRD analysis and K. It is clear that taken part salts are composed results (Figures 6 - 7). The cubic halite crystals were mainly of the halite. given to dominate all the salt samples (Figure 6). The salt During the progressive evaporation of water in a saline crust was determined in the composition of halite lake, the sequence of minerals precipitated follows the (98.50%) and kieserite. chemical divides proposed by Eugster and Hardie (1978). During evaporation, saturation with respect to alkaline earth carbonates is reached quickly. Therefore, calcite Conclusion and high Mg-calcite precipitate during early stages of salinity increased. Subsequent precipitation of a mineral Salt, consumed as a nutrient since the early ages of sequence of sulfates, silicates and chlorides is controlled 2+ 2+ - 2- mankind, has later been one of the most significant by the relative concentration of Ca , Mg , HCO3 , SO4 reagents utilized for exceedingly growing needs of the and Cl. Carbonate precipitation may also occur at higher Kilic and Kilic 1323

Figure 6. SEM images of the salt crust.

reaction with Na-rich brines (Hardie, 1991). It is generally not expected in closed basin evaporate deposits as it would also re-dissolve to form glauberite and halite. The salt crust is composed of halite (98.50%), gypsum and kieserite. The cubic halite crystals were given to dominate all the salt samples. Cubic chevron type halite minerals in the upper levels of the salt crust was seemed to have dimensions of 0.5 mm-1 cm, and they were easily recognized and distinguished from the underlying halites by their clean colors in the Salt Lake.

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