engleski

The effect of the pH of the rinsing solution on the properties of magnesium oxide from seawater

The effect of the pH of the rinsing agent on the B2O3, CaO and MgO content in magnesium oxide obtained from seawater by substoichiometric precipitation (where precipitation of magnesium hydroxide took place with 80 percentage of the stoichiometric quantity of doplomite lime as the precipitation agent) has been investigated. In such a case, i.e. when this precipitation method is employed, the content of boron adsorbed onto magnesium hydroxide during precipitation is somewhat higher than at stoichiometric precipitation, and should therefore be reduced. The purpose of this study has been to ensure high purity magnesium oxide, particularly as regards the B2O3 content, because boron causes problems in refractory magnesia for specialized refractory applications where high hot-strength is required. The rinsing agent was alkalized distilled water with pH = 11.0 and 12.5 which was alkalized by the addition of concentrated NaOH prior to each use, as well as non-alkalized distilled water with pH = 5.95. It has been established that the content of B2O3 in magnesium oxide samples is significantly lower when the pH value of the agent used for rinsing of the magnesium hydroxide precipitate increases. The magnesium oxide samples obtained were then sintered with addition of TiO2 (1, 2 and 5 mass percentage) in order to determine the properties of sintered samples (density, porosity, the B2O3 content) relative to the method used for rinsing the magnesium hydroxide precipitate and to the quantity of TiO2 added. The results indicate that all samples sintered at 1650 oC with duration of isothermal sintering of 3 hour have very low porosity and the density achieved amounts to 95 percentage of the theoretical density. Also, B2O3 content in the products is much lower (by up to 90 percentage) than it was in the sample prior to sintering.

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