Urmia Lake, with total area of 5200 km2 (before drought) , is located between 44°14' to 47°53'E and 35°40' to 38°30'N. It is the largest and saltiest permanent lake of Iran as well as one of the largest ultra-saturated lakes of the world that is compared with the Great Salt Lake of the United States These lakes, due to their exclusive characteristics, enjoy high economic value from aquatic ecosystems and strategic minerals points of view. In spite of several diverse investigations, the trend of elements deposition in relation with the evaporation has not been studied up to now. Therefore, in this study, the trend of changes and elements deposition has been studied under laboratory conditions based on the lake salinity (450g/l).
Materials and Methods
Solar evaporation method and evaporation pond used and were established to study sedimentation trend and exploitation of economic elements of the brines. At first, samples were taken from 10 aquatic regions of the lake highest water density was measured to be about 1.320 gr/ml. approximately 2025 lit brines pumped and evaporated in pre-constructed evaporation pond. The dimensions of evaporate pond are water density was measured in sampling site making use of densitometer. Evaporation lasted 3 months and 3 days. In the first two months, 3-4 samples and in the last month 2 samples, were taken daily form the evaporation pond that their volume was 120 ml. Some parameters recorded during sampling include. Date and time of sampling, air and brine temperatures, wind speed, air humidity, brine height and density. Samples were sent to the chemistry laboratory to be analyzed by Flame Photometer Corning and Titration in order to measure exact amount of Li, K, Mg and Na elements. All analyses were carried out at the first hour before salt depositions in sampling container. Sampling continued where brine height was readable and maximum mixing of brine with the deposited salts observed. In diagram 1, changes of the elements have been drawn based on Reduce the height (Elevation) of the brine in pond.
Results and discussion
According to figure 4, correlation of magnesium and potassium is the lowest. It means that when epsomite or loweit minerals are composed, potassium is higher relative to the magnesium, otherwise potassium has more than Concentration in Brine remain and when kainite is composed, all of the magnesium doesn't react with the potassium. The amount of the magnesium consumption is equivalent to the amount of the remained potassium and sulfate. Therefore, Potassium compounds excluded, but magnesium remains in the solution. At the next step, namely formation of magnesium-potassium chloride and magnesium chloride, the amount of magnesium that enters to the composition is proportional to the remained potassium and chlorine. After bonding Potassium, chlorine, and deposition of sylvite in Brine, potassium and magnesium remain combined with the chlorine to form Bischofite. At the end, due to Bischofite solubility, magnesium chloride is concentrated at the maximum amount, destructed and finally deposited. maximum Correlation of the lithium and magnesium indicates that these elements are excluded synchronously and accompanied with the remained chloride. Considering that both elements indicate high correlation with the chlorine, while chlorine is existed in the brine, magnesium and lithium illustrate ascending trend. It must been noted that the amount of Lithium is negligible in the Urmia Lake, but it could be considered that in this project, evaporation pond has not been changed in the failure point of each element. Therefore, there is a high possibility for composition change and re-sedimentation in the pond. As a result, elements with the Maximum concentration aren’t completely excluded from the environment however, with the change of brine composition these elements participate in the next reactions and chemical bonds as a chain and re-deposited in the environment again.
We were monitoring the brine evaporation ponds for 96 days. During this days the volume of brine showed reduction from2025 liters to881.25 (reduced by2.3 times), Increase of magnesium concentration from 56grams per liter to104 grams per liter (1.85-fold increase). Increase of potassium concentration from 10 grams per liter to 23 grams per liter (2.3-fold increase).Decrease of sodium concentration from37 grams per liter to 4 grams per liter (9.25-fold decrease) decreased and reduction of the lithium concentration from 21 ppm 34 ppm (increased 1.61-fold).Magnesium sulfate compounds (such Pntahdryt) simultaneously precipitate with mineral halite and Sylvite. In next step the amount of sulfate in brine gradually decrease, affinity of magnesium and chlorine increase and if there is potassium in the brine environment, precipitation of magnesium chloride (Carnallite) starts. At the final stage, there is the least amount of potassium in the brine and the magnesium chloride compounds (Bischofite) can been see independently.