Abstract: A method for the decomposition of chromium ore in a directly heated revolving tube is described, in which oxygen-containing gases are introduced into the revolving tube by means of below-bed nozzles.

Abstract: A method for manufacturing alkali chromates by the reacting of chromium ore with alkali compounds and oxidation in an atmosphere containing at least 50% oxygen is described, in which the mixture consisting of chromium ore, alkali compound and optionally leaning materials is heated in a first stage in an atmosphere containing not more than 5 vol. % oxygen to a temperature between 1000.degree. and 1 400.degree. C., and in a second stage is oxidized at a lower temperature of 900.degree. to 1 070.degree. C. with supply of an atmosphere containing at least 50% oxygen.

Abstract: A process for the preparation of sodium dichromate and sodium dichromate solutions by alkaline oxidizing roasting of chromium ores, leaching resulting roast with water, adjustment of the pH to 7 to 9.5, removal of the insoluble constituents by filtration, a sodium monochromate solution containing 300 to 400 g/l of Na.sub.2 CrO.sub.4 being obtained, conversion of the monochromate ions of this solution into dichromate ions by addition of an acid and/or by electrolysis and/or by reaction with carbon dioxide under pressure and crystallization of sodium dichromate by concentration of this solution. The improvement wherein before the conversion into a sodium dichromate solution, the sodium monochromate solution is concentrated to contents of 700 to 1000 g/l of Na.sub.2 CrO.sub.4, the monochromatic ions, the solution is subsequently freed as far as possible from sodium sulphate by cooling to a temperature of below 0.degree. C.

Abstract: The invention relates to a process for the production of sodium dichromate and sodium dichromate solutions by oxidative roasting of chrome ores under alkaline conditions, leaching of the furnace clinker obtained with water or an aqueous chromate-containing solution, adjustment of the pH to from 7 to 9.5, removal of the insoluble constituents by filtration, a sodium monochromate solution being obtained, conversion of the monochromate ions of this solution into dichromate ions by acidification and crystallization of sodium dichromate by concentration of this solution, characterized in that the acidification is carried out with carbon dioxide under pressure with removal of sodium hydrogen carbonate, the remaining solution is then very largely freed from sodium monochromate by cooling to a temperature below 10.degree. C.

Abstract: A process for the production of chromic acid, comprisinga) dissolving ferrochrome in sulphuric acid, optionally with the addition of catholyte and/or anolyte overflow from the electrolysis,b) removing undissolved constituents by filtration,c) adding a reducing agent in a quantity more than equivalent to the quantity of iron(III) and chromium(IV) in the solution,d) precipitating chromium(III) hydroxide by raising the pH to about 4-6 by the addition of a base while maintaining the reducing conditions in the solution,e) separating the precipitated chromium hydroxide while maintaining the reducing conditions,f) working up the aqueous solution containing iron by oxidation; precipitating iron(III) hydroxide or iron(III) oxide and optionally isolating the sulphate in the solution as sodium sulphate, ammonium sulphate or calcium sulphate,g) dissolving the separated chromium hydroxide in chromic acid and optionally sulphuric acid where either a single solution in chromic acid is produced or two solutions are produced,

Abstract: A process for the preparation of alkali metal dichromates and/or chromic acid by electrolysis of alkali metal monochromate and/or alkali metal dichromate solution in electrolysis cells, the anode and cathode compartments of which are separated by cation exchange membranes, wherein the cation exchange membranes are single-layer membranes based on perfluorinated polymers having sulfonic acid groups as cation exchange groups, and an aqueous solution having a pH of 4 to 14 is produced in the cathode compartment of the cells.

Abstract: A dimensionally stable anode comprised ofa) an electrically conductive valve metalb) a conductive intermediate layer andc) an electrode coating of an electrocatalytically active substance, wherein the intermediate layer comprises one or more noble metals or their alloys which have been applied to the valve metal by deposition by electroplating from melts containing noble metal salts. This anode can be used in the production alkali metal dichromates and chromic acid by electrolysis of alkali metal monochromate and/or alkali metal dichromate solutions.

Abstract: A process for the production of chromic acid, comprising(a) dissolving ferrochrome in sulphuric acid and mother liquor from the subsequent crystallization of ammonium chrome alum, optionally with the addition of at least one of catholyte and anolyte overflow from the subsequent electrolysis,(b) removing undissolved constituents by filtration,(c) removing dissolved iron by the addition of at least one of ammonia and ammonium sulphate to the filtrate obtained, crystallizing iron ammonium sulphate and filtering,(d) crystallizing and filtering ammonium chrome alum from the remaining solution and returning the filtrate for dissolving ferrochrome in step (a),(e) dissolving the ammonium chrome alum in water,(f) precipitating and separating chromium-(III) hydroxide from the resulting solution by adding a base, optionally under reducing conditions,(g) dissolving the separated chromium hydroxide in chromic acid and optionally sulphuric acid so that either a single solution in chromic acid is obtained or two solutions a

Abstract: A process for the preparation of alkali metal dichromates and chromic acid by the electrolysis of monochromate and/or dichromate solutions in an electrolytic cell in which the anode and cathode chamber are separated by a cation exchanger membrane anolyte fluid containing dichromate and/or chromic acid being formed in the anode chamber and alkaline catholyte fluid containing alkali metal ions being formed in the cathode chamber, the improvement wherein the catholyte fluids are periodically replaced by a solution which is at a pH below 6.

Abstract: A process for the preparation of chromic acid by the electrolysis of dichromate and/or monochromate solutions in electrolytic cells in which the anode chamber and the cathode chamber are separated by a cation exchanger membrane, the improvement wherein the chromic acid content of the solution in the anode chamber is periodically increased above that of a continuous operating state.

Abstract: A process for the production of chromic acid by the multistage electrolysis of dichromate and/or monochromate solutions in two-compartment electrolysis cells, of which the anode and cathode compartments are separated by cation exchanger membranes, at temperatures in the range from 50.degree. to 90.degree. C., the dichromate and/or monochromate solutions being obtained by the digestion of chrome ores and leaching, the improvement wherein, optionally after the removal of aluminum, vanadium and other impurities, the monochromate solution obtained after leaching is adjusted at 20.degree. to 110.degree. C. to a pH value of from 8 to 12 by the addition and/or in situ formation of carbonate in a quantity of from 0.01 to 0.18 mol/l (for 300 to 500 g/l Na.sub.2 CrO.sub.4, converted with CO.sub.

Abstract: A process for the preparation of alkali metal dichromates and chromic acid by the electrolysis of monochromate and/or dichromate solutions in an electrolytic cell in which the anode and cathode chambers are separated by cation exchange member, the improvement wherein the formation of deposits on the membrane is prevented comprising continuously introducing a solution containing chromate at a pH of about 3 to 10 into the cathode chamber during the electrolysis.

Abstract: A process for the production of alkali dichromates and chromic acid by electrolysis of alkali monochromate or alkali dichromate solutions wherein the anodes used in the electrolysis are dimensionally stable anodes of valve metals activated by electrodeposition of noble metals and/or noble compounds from melts containing noble metal salts.