Industrial process of preparing magnesia of high purity
AssigneeVeitscher Magnesitwerke-Aktiengesellschaft
InventorsMichael Grill, Georg Bouvier
Life of this patent
Estimating the term…
Abstract
Magnesia of very high purity is produced industrially from a magnesite waste material wherein impurities are present in such amounts that the weight ratio of the precipitable hydroxide ions, calculated as the sum of Fe.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + Cr.sub.2 O.sub.3 + Mn.sub.3 O.sub.4 to the sum of SiO.sub.2 + TiO.sub.2 + B.sub.2 O.sub.3, is at least 1 : 3. The starting material is dissolved in hydrochloric acid of 15-32% concentration, the impurities are precipitated by adjusting the pH of the acidic solution to 4 - 9, and the purified magnesium chloride solution is thermally decomposed into magnesia and hydrochloric acid gas, the latter being recycled to form the hydrochloric acid of the stated concentration for dissolving the starting material.
Claims12
An industrial process of preparing magnesia containing more than 98% MgO and less than 0.1% each of the oxides of Fe, Al, Cr, Mn, Si, Ti, Na, K, and B, all percentage values being by weight, which comprises:
- 1. dissolving a starting material at a first temperature of more than 70.degree. in an amount of aqueous hydrochloric acid sufficient to produce an acidic solution,
- a. said starting material essentially consisting of magnesium carbonate, magnesium oxide, magnesium hydroxide, or mixtures thereof, and containing, as impurities, at least one compound of members of a first group consisting of iron, aluminum, chromium, and manganese, and at least one compound of members of a second group consisting of silicon, titanium, and boron,
- b. the starting material being treated until the ratio in said solution of the combined weight of the compounds of said first group, calculated as Fe.sub.2 O.sub.3+ Al.sub.2 O.sub.3+ Cr.sub.2 O.sub.3+ Mn.sub.3 O+.sub.4 to the combined weight of the compounds of said second group, calculated as SiO.sub.2+ TiO.sub.2+ B.sub.2 O.sub.3, is changed to at least 1 :
- 3, and
- c. the concentration of said hydrochloric acid being 15% to 32% by weight,
- 2. adding to said acidic solution a magnesium or calcium compound sufficiently alkaline to raise the pH of said solution to the range of 4 to 9 and to substantially completely precipitate the compounds of members of said first group as hydroxides, the compounds of members of said second group being coprecipitated therewith;
- 3. separating the precipitate from the residual purified magnesium chloride solution;
- 4. heating said solution to a second temperature between about 400.degree.C and 900.degree.C, whereby the magnesium chloride therein is decomposed in the presence of water to magnesia and gaseous hydrochloric acid;
- 5. recovering said magnesia;
- 6. converting said gaseous hydrochloric acid to aqueous hydrochloric acid having said concentration of 15% to 32% by weight, and
- 7. dissolving an additional amount of said starting material in said last mentioned aqueous hydrochloric acid.
Dependencies are inferred from the claim text.