engleski

B2O3 and CaO in magnesium from seawater

The effect of alkalized distilled water with pH of 12.50 has been examined in rinsing the precipitate of magnesium hydroxide obtained from seawater by substoichiometrical precipitation with 80% of the stoichiometrical quantity of dolomite lime as precipitation reagent. The substoichiometrical method of precipitation of magnesium hydroxide from seawater is much more economical in the so-called « wet phase» than the stoichiometrical precipitation method, primarily due to the increase in the sedimentation rate of the precipitate formed, and consequently of the thickener capacity. However, with the 80% precipitation method the content of B2O3 increases in the product, i.e. magnesium oxide obtained from seawater. The purpose of this study was not only to reduce the B2O3 quantity as much as possible, but also to determine the minimum number of rinses needed to attain calcined magnesium oxide of satisfactory quality. Specifically, boron causes significant disturbances in electrolysis of magnesium chloride aimed at obtaining metal magnesium, if magnesium chloride obtained from seawater is used as the cell charge, and it also adversely affects the quality of refractory material produced from sintered magnesium oxide obtained from seawater. The results indicate that if this method of rinsing the magnesium hydroxide precipitate is used, the B2O3 content in MgO samples (80% precipitation) is 0.069 mass %, which is by 66% less than the B2O3 content in samples prepared without rinsing the magnesium hydroxide by alkalized distilled water (B2O3 = 0.200 mass %). It is sufficient to carry out rinsing by decantation three times, as further rinsing does not provoke further reduction of B2O3 in the sample. This rinsing method does not change the CaO content in calcined magnesium oxide, which indicates that further rinsing should be done with not-alkalized distilled water.

substoichiometric precipitation; B2O3 content; rinsing agent; magnesium oxide from seawater

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