Abstract: The cement of the invention comprises chemically combined oxides, percent by mass: CaO, 50 to 60; Al.sub.2 O.sub.3, 28 to 37; Fe.sub.2 O.sub.3, 0.01 to 1; SiO.sub.2, 0.1 to 8; Na.sub.2 O, 0.1 to 1; K.sub.2 O, 0.1 to 0.5; H.sub.2 O, 3 to 12; and incorporates 85 to 99% by mass of a fraction with a particle size of below 80 .mu.m and 1 to 15% by mass of a fraction with a particle size of from 80 to 200 .mu.m. The cement can also contain one or more additives: calcium oxide or calcium hydroxide, calcium carbonate, calcium carboaluminate.The method according to the invention for preparing said cement comprises a heat-treatment of calcium hydroalumosilicate containing SiO.sub.2 in an amount of not more than 8% by mass at a temperature of from 250.degree. to 600.degree. C. The heat-treated product is disintegrated to produce 85 to 99% by mass of a fraction with a particle size of below 80 .mu.m and 1 to 15% of a fraction with a particle size of from 80 to 200 .mu.m.

Abstract: The process consists of two desilication stages. In the first stage the aluminate liquor resulting from digestion of the sinter is subjected to an autoclave treatment to remove the major portion of impurities of SiO.sub.2 and Fe.sub.2 O.sub.3. In the second stage the aluminate liquor is treated with a desilication agent comprising a lime pulp containing oxides CaO, Al.sub.2 O.sub.3, SiO.sub.2, Fe.sub.2 O.sub.3, Na.sub.2 O in a mass ratio of CaO:(SiO.sub.2 +Fe.sub.2 O.sub.3)=1,000 to 5,000:1 and Na.sub.2 Al.sub.2 O.sub.3 =0.25-0.60:1, wherein CaO is active, Na.sub.2 O--in the carbonate form. This lime pulp is employed in such an amount as to ensure the content of active CaO in the aluminate liquor within the range of from 5 to 10 g/l . The impurities of SiO.sub.2 and Fe.sub.2 O.sub.3 present in the liquor pass into the solid phase with the formation of calcium hydrogarnets of the formula 3 CaO(Al,Fe).sub.2 O.sub.3 mSiO.sub.2 (6-2m)H.sub.2 O, wherein m=0.01-0.5 which are separated as a mud.

Abstract: The present invention relates to the production of alumina and, more specifically, to a process for desilication of aluminate solutions.The process of desilication according to the present invention comprises treatment of the aluminate solution first with a calcium-containing reagent "a" which is a product of the reaction of desilication of the aluminate solution; reagent "a" contains mainly calcium hydrogarnet of the formula:3CaO.Al.sub.2 O.sub.3.nSiO.sub.2 (6-2n)H.sub.2 Owherein n.ltoreq.1, and then with a reagent "b" of the formula:4CaO.Al.sub.2 O.sub.3 (0.1-0.6)X.mH.sub.2 Owherein X is CO.sub.2 and/or SO.sub.3 ; m=8 to 15. The treatment of the aluminate solution with reagent "a" is carried out for 0.5 to 2 hours at a temperature ranging from 40.degree. to 105.degree. C. Weight ratio of reagents "a" and "b" is maintained within the range of from 1:1 to 3:1.The process according to the present invention is useful in the manufacture of alumina.

Abstract: An improved method for recovering aluminum values from alkaline aluminosilicate raw material by sintering a comminuted aqueous mixture of the alkaline aluminosilicate material, limestone and soda solution wherein the alumino-silicate material is first comminuted with the soda solution to form a mixture with a fraction of particles larger than 0.08 mm greater than 20 percent by weight, mixing limestone with the mixture and comminuting until the fraction of particles larger than 0.08 mm is between 2 and 15 percent by weight.