Patent GB-498510-A (GB)
Title: Improvements in and relating to the production of alumina and its derivatives
IPC: C01F7/28
Filed: 1937-04-02
Abstract: For the production of alumina and its compounds, alumina-containing materials are decomposed by sulphurous acid with heat and if desired increased pressure, in the presence of water insufficient for the solution of the alumina compounds formed (although the reaction mixture may be pulpy), the solid first reaction product thus obtained being then heated to split off the combined acid.  This second reaction product, which may be used as a regenerative adsorbent for liquids, vapours, and gases, readily reacts with aqueous acids or lyes to produce alumina solutions, or with halogen-containing gases in the presence of reducing agents to produce volatile alumina compounds.  Nephelin and leucite, roasted clay and kaolin, and bauxite and feldspar decomposed by lime may be used as raw materials. The following are examples of the production of the first and second reaction masses: (a) anhydrous SO2 was introduced under pressure (20-22 atmospheres) into an autoclave containing roasted clay, the temperature raised to 80-90 DEG  C., water pumped in intermittently in small quantities over a period of 9 hours, excess SO2 led off, and the first reaction product dried. This was then heated in a rotating drum to 250-280 DEG  C. for 16 hours, with removal by suction of the evolved moist SO2 gases; (b) the water was pumped in in one quantity, so that prior to the reaction the contents were liquid; (c) to nephelin and SO2 in an autoclave, water was added over a period of 4 hours and the first product then heated 15 hours at 250 DEG  C., yielding a second product from which sodium salt content was removed by washing.  The following are examples of the treatment of the second reaction product: (i) SO2 in excess and water were introduced into a rotating autoclave containing the second product, the temperature rising to 80 DEG  C. when the autoclave is not cooled. After blowing off excess SO2, the viscous content was diluted with water or washing lye, and filtered contained only a small amount of SiO2 relative to the dissolved alumina.  (ii) The product mixed with milled charcoal, after drying in an air-current, was heated to 300 DEG  C. in a current of chlorine which may contain CCl4 vapour, the reaction thereafter proceeding spontaneously forming vapours of anhydrous Al2Cl6, yielding a product which is substantially free from silicon compounds and may be purified from iron by fractional sublimation.  (iii) The product was stirred for 15 hours with excess of acetic acid, self-heating raising the temperature to 40 DEG  C. The basic acetate was separated by boiling and neutralizing.  (iv) The difficulty volatile mineral acids, as sulphuric and hydrochloric, may be used on the second product. Titanic acid, as well as silicic acid, content is reduced by the invention.  Salts of alkalis, alkaline earths, and heavy metals may be washed out of the first product by acids or water, but only salts of the alkalis can be washed out of the second product with water.  The Specification as open to inspection under Sect. 91 refers to the use of volatile acids in general, and of oxalic, formic, and trichloracetic acids in particular, for decomposing the alumina-containing materials, with the following two further examples of the production of the first and second reaction masses.  (d) Clay and formic acid, covered with paraffin oil, were stirred at 90 DEG  C. in an open container and the water introduced. After 15 hours the excess formic acid was removed by a pump, and the first reaction product dried.  This product was then heated 20 hours at 275 DEG  C.  (e) To clay mixed with crystallized oxalic acid the water was introduced in small quantities during heating in an open dish, the temperature rising to 106 DEG  C. The first product was dried, and then heated for 16 hours at 350 DEG C.  The following example of the treatment of the second reaction product is also given.  (v) To a stirred mixture of the second product with water, hydrofluoric acid was added over a period.  To the filtered lye Na2SO4 was added, after reduction of trivalent iron by SO2 in the hot, to obtain cryolite with but low contamination by Fe2O3 and SiO2.  This subject-matter does not appear in the Specification as accepted.