Boric oxide in seawater derived magnesia

Abstract

The study has examined the possibility of application of the combined rinsing method used to rinse the precipitate of magnesium hydroxide obtained from seawater by substoichiometric precipitation with the addition of 80% of the stoichiometric quantity of the dolomite lime as the precipitation agent. The rinsing agent was distilled water with pH = 6.26 and alkalised distilled water with pH = 12.50. The product quality was established by determining the concentrations of MgO, CaO and B₂O₃ in the calcined magnesium oxide. The purpose of the study was to determine the operating conditions that might be used for production of good quality caustic magnesia from seawater, i.e. caustic MgO with a low B₂O₃ and CaO content. It has been noted that the contents of B₂O₃ and CaO in caustic magnesia from seawater are significantly reduced by this rinsing method, which is of considerable importance as the substoichiometric precipitation is much more economical than the overstoichiometric one in the so-called “wet phase”.