CLEAN ION-EXCHANGE TECHNOLOGIES - 2 - RECOVERY OF HIGH-PURITY MAGNESIUM COMPOUNDS FROM SEAWATER BY AN ION-EXCHANGE ISOTHERMAL SUPERSATURATION TECHNIQUE

This paper reports the results obtained by studying the ion-exchange i sothermal supersaturation (IXISS) of magnesium carbonate solutions whi ch is observed during elution of Mg2+ from carboxylic resin equilibrat ed with decalcinated seawater (artificial or natural) with either 2 M NH4HCO3 or with the mixture of 1.5 M Na2CO3 and 0.6 M NaHCO3. Crystall ization of supersaturated solution in the first case has been shown to lead to the formation of previously unknown complex ammonium-magnesiu m carbonate. The results of X-ray, chemical, and differential thermal analyses have allowed the proposal of the following formula for the ne w magnesium compound: (NH4)(2)Mg(CO3)(2) . 5H(2)O. In the second case, crystallization of magnesium carbonate leads to the formation of a pu re phase of nesquegonite: MgCO3 . 3H(2)O of 99.9% purity. Samples of M gO obtained after annealing ammonium-magnesium precipitates at 773 K c ontain less than 10(-3)% of impurities.