Bayer Aktiengesellschaft

Lanxess Deutschland Gmbh

Bernd Rosenow

Hans-Dieter Block

Rainer Weber

Norbert Lonhoff

Jan-Gerd Hansel

Bernhard Spreckelmeyer

Uwe Brekau

Jost Halstenberg

Rolf-Michael Jansen

The present invention relates to a process for continuous purification of yellow phosphorus by adsorption onto activated carbon.

Method for the purification of yellow phosphor

The present invention relates to a process for producing low-salt silica sol dispersions in low-boiling alcohols and to the use of the organosols obtained by this process for the production of coatings on metallic and nonmetallic substrates.

Process for producing low-salt silica sol dispersions in low-boiling

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. and filtration, and the residual monochromate ions which remain in the solution are converted into dichromate ions by electrolysis and/or by reaction with carbon dioxide and/or with chromic acid.

Process for the preparation of sodium dichromate

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. and filtration, any monochromate ions still present in the remaining solution are converted into dichromate ions by addition of an acid and the sodium monochromate filtered off is added to the sodium monochromate solution before conversion with carbon dioxide into a sodium dichromate solution.

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Leverkusen, Germany

Bernd Rosenow