Abstract: Process for the preparation of high purity alumina containing less than 0.1 weight percent of residual chlorine starting from impure aluminum chloride solutions, which process comprises a crystallization step to provide aluminum chloride hexahydrate crystals having a diameter of from about 400 to about 4000 micrometers in the presence of hydrochloric acid; washing the aluminum chloride hexahydrate crystals so obtained with pure hydrochloric acid; and pyrohydrolyzing the washed crystals of aluminum chloride hexahydrate at a temperature of from about 700.degree. to about 1300.degree. C., in which pyrohydrolysis a gas is forced through a layer of the washed aluminum chloride hexahydrate so as to remove the gaseous reaction products while obviating any possible movement of the solid by the gas, the process particularly producing transition aluminas simultaneously having a specific surface area greater than 100 m.sup.2 /g and a chlorine content less than 0.1 weight percent.

Abstract: Process for preparing high purity aluminas from ammonium alum, the process comprising separately dehydrating the alum and thereafter thermally decomposing the dehydrate, wherein the thermal decomposition is carried out by forcing a gas through a layer of the dehydrated alum so as to continuously remove the gaseous reaction products formed without removal of solids by the carrier gas, and providing improved productivity of high purity transition aluminas having specific surfaces above 125 m.sup.2 /g and/or bulk densities above 0.2 g/cm.sup.3, the transition aluminas so obtained being characterized by their greater reactivity for the preparation of corundum so that corundum having a bulk density greater than 0.4 g/cm.sup.3 can be economically prepared.

Abstract: The present invention relates to an anhydrite binder and to the method of making the same from the gypsum by-product (phosphogypsum) resulting from the production of phosphoric acid by the wet method, said binder comprising particulate anhydrous CaSO.sub.4 with an insoluble CaSO.sub.4 content of at least 93%, an average particle size diameter of 5 to 30, with 15% by weight or more of the particles having a diameter smaller than 10.mu. and 20% by weight or more of the particles having a diameter larger than 20.mu., and a pore volume of less than 0.29cc/g in the case of pores having a radius less than about 6.6.mu..