Bayer Aktiengesellschaft

Werner Fuhr

Jakob Rademachers

Horst Brunn

Gerhard Franz

Gerhard Winter

Karl Brandle

Gerd-Hermann Schulten

Bernd Holle

Klemens Jaschinski

Karlheinz Turban

A process for the production of black iron oxide pigments having a magnetite structure from iron ion-containing acidic waste water which comprises precipitating the iron ions with alkaline substances in a first stage at ambient temperature to produce a raw slurry and in a second stage, concentrating the raw slurry adjusted to a pH of from 5.0 to 8.0 with acidic substances and then ripening the concentrated slurry at temperatures above 70.degree. C.

Process for the production of black pigments based on iron

A process for the production of an anisometric yellow-brown zinc ferrite pigment comprising homogeneously mixing zinc oxide having a specific BET surface of more than 2 m.sup.2 /g with needle-shaped .alpha.-FeOOH obtained from an iron salt solution by mixing with alkali and subsequently oxidizing in a nucleation and pigment growth stage, the FeOOH having a specific BET surface of about 15 to 25 m.sup.2 /g, an average needle width of about 0.025 to 0.125 .mu.m and an average needle length of about 0.2 to 0.6 .mu.m, annealing the mixture at a temperature of about 700.degree. to 1000.degree. C., cooling and grinding.

Process for the production of yellow-brown zinc ferrite pigments

A process for indirect heat-exchange between a solids-containing gas and the inner wall of a heat-exchanger through which the solids-containing gas to be cooled or heated flows, comprising introducing a flushing medium separately from the solids-containing gas into the heat exchanger, the flushing medium being directed angularly at the wall and sweeping about said wall whereby said wall is kept substantially free from solid deposits. Advantageously the heat exchanger is circular in cross-section, the gas/solids mixture is introduced tangentially, and the flushing medium is discharged toward said inner wall through openings in an arm which rotates within the heat exchanger, means being provided to remove gases and solids from the heat exchanger.

Heat exchange with gas/solids mixtures

A white composite pigment, containing isometric rutile pigment particles and acicular modified potassium hexatitanate, is produced by reacting titanium dioxide or a titanium compound which can be converted into titanium dioxide under the reaction conditions in the presence of rutile seeds with a potassium compound which reacts basically under the reaction conditions, a mineralizer and a polyvalent metal fluoride at a temperature of about 700.degree. to 1100.degree.C.

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Krefeld-Uerdingen, Germany

Werner Fuhr