Evaluating evaporite minerals sedimentation potential and the origin of brine chemical composition

Abstract

Mighan playa is a closed intracontinental watershed and located 15 kilometers northeast of Arak city. The playa water level is affected by the sodium sulfate company's effluent, the purified wastewater plant, underground water, precipitation and evaporation. Mighan playa consists of two parts of island in the center and a lake in the periphery and is the most important pole of sodium sulfate extraction in Iran. In order to study brine and its evolution, 25 samples were taken from the playa, and it determined EC, TH, pH, Ca, Mg, K, Na, Cl, SO4, Br, I, Li, HCO3, NO3 and PO4. The inlet water shows the molar ratio of HCO3 < < Ca + Mg and the diagram of the geochemical evolution of Mighan brine follows the geochemical path (II), so the type of Mighan brine is Na-Cl-SO4, which authorized with Piper diagram. Also, according to the results of saturation indexes, Mighan brine has the possibility of forming evaporite deposits such as glauberite, mirablite, thenardite, halite, gypsum, calcite and small extent dolomite, anhydrite. The most important and effective mineralization factors were identified by factor analysis and factorial fuzzy maps. The salinity of Mighan playa brines is related to anions and cations that originate from the gypsum and salt layers in the northern part. Alkalinity and bicarbonate resulting from the dissolution of limestone rocks in the southern layers of the Mighan watershed.