Verfahren zur Herstellung von reinen Metalloxyden bzw. Metallen und reiner Salpetersaeure durch thermische Zersetzung von Metallnitraten

Liquid nitric acid is obtained by the thermal decomposition of nitrates of metals other than aluminium, bismuth and iron and those which give rise to nitric oxide when decomposed, by decomposing the metal nitrate whilst spread over a metal or mineral surface, in the presence of steam in excess of that required to obtain nitric acid from the nitrogen oxides liberated, thereby obtaining a solid decomposition product and nitric acid vapours which are removed from the reaction zone and condensed. Thus the invention may be applied to the nitrates of Be, Ca, Cd, Ce, Cr, Co, Ga, Hg, In, Pb, Mn, Ni, Sn, Te, U and Zn to form oxides and nitrates of Ag, Au and Pt to form metals. The nitrite to be decomposed may be applied as a coating on a granulated material or alternatively the molten nitrate may be spread out on a heated metal surface. According to examples: (1) a manganese nitrate solution was fed to an internallyheated rotatable drum maintained at 190 DEG C.; simultaneously air was sucked through the system for the removal of gases from the hot reaction zone and the gases containing nitric acid vapours were cooled down to room temperature in a condenser to obtain liquid nitric acid. The manganese dioxide product was taken off from the drum by a knife. The nitrates of zinc, cobalt, nickel and chromium may be similarly decomposed; (2) lead nitrate was decomposed in a tube heated externally to 370 DEG to 400 DEG C. whilst blowing steam thereover. The steam and nitric acid vapours were condensed to liquid nitric acid and a yellow red oxide powder was recovered. Mercuric and cadmium nitrates may be similarly decomposed. (3) Calcium nitrate solution coated on sand was decomposed at 600 DEG C. Further granulated materials capable of acting as carriers are alumina, clay, infusorial earth or a recycled solid decomposition product. The coating of the carrier with the salt to be decomposed may be effected outside or inside the decomposition apparatus. (4) A manganese ore was reduced at 400 DEG to 500 DEG C. to Mn2O3 and the reduced ore was treated with nitric acid at 60 DEG C. to convert it to manganese dioxide solid and manganese nitrate solution. The suspension was filtered and the solid precipitate was thoroughly washed and dried. The manganese nitrate solution was concentrated and introduced into a decomposition equipment as in (1) above which was supplied with heated air. Further manganese dioxide was obtained and nitric acid was recovered in liquid form and could be