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Effect of TiO2 on the Sintering Process of Magnesium Oxide from Seawater

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Author(s): Martinac, V. | Labor, M. | Jakić, J. | Petric, N.

Journal: Kemija u Industriji
ISSN 0022-9830

Volume: 59;
Issue: 11;
Start page: 533;
Date: 2010;
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Keywords: Seawater

ABSTRACT
This study examines the effect of the addition of TiO2 on the properties of magnesium oxide obtained from seawater by substoichiometrical precipitation with 80 % of the stoichiometrically required quantity of dolomite lime as the precipitation agent. Magnesium oxide obtained from seawater by substoichiometrical precipitation contains boron(III) oxide as an impurity. During the precipitation of magnesium hydroxide, the boron present in seawater (in the form of non-dissociated orthoboric acid H3BO3, and partly as borate ion H2BO3 –) adsorbs onto the magnesium hydroxide precipitate, and therefore has to be reduced as much as possible using the appropriate method of rinsing the magnesium hydroxide precipitate. B2O3 is an undesirable admixture in seawater magnesium oxide. Specifically, the properties of special purpose magnesium oxide, i. e. high strength magnesium oxide, are affected significantly by the content of boron in the product. Good quality sintered magnesium oxide contains a very small amount ofB2O3. The impurity should not exceed w(B2O3) = 0.005 % in refractory magnesium oxide.The combined method of rinsing the magnesium hydroxide precipitate (3+2) was used in sample preparation, i. e. rinsing by decanting was done three times with alkalized distilled water of pH = 12.50 and twice with distilled water of pH = 6.74. Multiple rinsing on filter paper (five times) was done using the same rinsing agent (fresh distilled water of pH = 6.74). The MgO (80 % precipitation) samples were then subjected to isothermal and activated sintering without TiO2addition, as well as with the addition of TiO2, w(TiO2) =5 and 8 %, at the temperature of 1700 oC for 1 hour, with the aim of determining the properties of these samples primarily with regard to the B2O3content in the samples after sintering. The results indicate that the addition of TiO2strongly affects the reduction of the B2O3content during activated sintering of seawater magnesium oxide, and that the samples can be characterized as refractory material with very low B2O3 content. The addition of TiO2, w(TiO2)=5 %, is sufficient to bind the present CaO and thereby lead to greater evaporation of B2O3 in the process of activated sintering of seawater magnesium oxide. The samples thickened significantly during sintering, i. e. all the samples examined had a very smallamount of open pores.

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Tangokurs Rapperswil-Jona

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