New approaches in recovery of potassium-magnesium salts from the sea bitterns, coast of Sarbandar city, North Persian Gulf, Iran

The need of humans to magnesium, potassium, and lithium compounds has increased considerably and the production of these compounds is important for each country. These compounds are used as the raw materials of chemical, agricultural, medicine and other industrial sectors. The current research has been carried out on the bittern solutions obtained in industrial salt production lakes in southern Khuzestan in the Persian Gulf coast of Bandar Imam Khomeini (city Sarbandar) with the purpose of the recovery of magnesium and potassium compounds. The bittern under study has been produced via the gradual evaporation of sea water in salt production lakes. The chemical analysis showed that the concentrations of magnesium and sulfate have increased from 0.139% and 0.26% in sea water to 5.1% and 6.7% in the bittern solution respectively. Pilot plant trials have also performed in 5000 liter reactors for the production of magnesium hydroxide precipitate using the reaction of sodium hydride and the bittern solution. The purification of the magnesium hydroxide precipitate was also studied using different washing techniques. The effects of the addition of 12.5 Molar NaOH solutions into the bittern were examined in laboratory experiments. Different volume ratio of NaOH solution including 5, 7, 9, 11 and 13% were evaluated and the most suitable weight of the precipitate has been produced using 9% volume ratio. The volumes of sea water and potable water that have been used in washing stages were 9 times and 3 times of the volume of the precipitate respectively. The purity of the magnesium hydroxide precipitate was increased from 46% to 99% after washing. More technical issues should be considered for using the calcined lime or calcined dolomite for the precipitation of magnesium, due to the high concentration of sulfate in the bittern solution. The mechanical screw classifier and washing screens were used and the results were compared. On the basis of the results of experiments, the consumptions of chemicals and the value of the products were calculated. Fractional crystallization was also used to separate different compounds from the bittern solution. The results of investigations showed that about all of NaCl was removed from the bittern before 35o Beume and the crystallization of magnesium sulfate was started at this concentration. The composition of the precipitate produced in 36o Beume was 10% K, 30% SO42-, 30% Cl and 12% Mg and Shoenite was defined as the major phase in this precipitate using the XRD analysis. The results of this research indicate that the bitterns of salt production lakes are a good economic source for the production of magnesium sulfate and potassium sulfate.