Hoechst Aktiengesellschaft

Raban Von Schenck

Renate Adrian

Peter Wirtz

Bernardus J Damman

Bernd Cox

Wouter Roos

Gero Heymer

Alexander Maurer

Horst-Dieter Wasel-Nielen

Dieter Steidl

Hermann Weber

Herbert Panter

Klaus Somme

Johannes-Wilhelmus Kinneging

Andries Jelsma

Arie Lagendijk

Metal ions are reduced from a higher to a lower oxidation stage using ferrophosphorus as the reductant.

Process for reducing metal ions in aqueous solutions

Alkali metal phosphate solutions containing little vanadium are made from phosphoric acid containing vanadium. To this end, a negative redox potential is established in the phosphoric acid by addition of a reductant, the acid is partially neutralized and an alkali metal-phosphorus-molar ratio between 0.85 and 1.0 is established, the partial neutralization being continued over a period of at least 10 minutes. The partially neutralized acid is not filtered intermediarily and the alkali metal/phosphorus-molar ratio is increased to 1.9 to 2.1 in a second neutralization stage, collected precipitate is separated and processed, if desired.

Process for making alkali metal phosphate solutions containing little

The invention relates to a process for making phosphorus-containing anticorrosive pigments having a size of at most 20 microns by reacting one or more compounds of magnesium, calcium, strontium, barium, zinc, aluminum, iron, chromium or manganese with an oxygen acid of phosphorus or its alkali metal or ammonium salts at temperatures within the range 10.degree. to 100.degree. C. More particularly pigments consisting to an extent of at least 90% of particles with a size between 0.05 and 8 microns are produced by introducing an aqueous suspension or solution of the reactants into a dispersing means rotating at a speed of 3000 to 10,000 rpm, reacting the reactants by intimately mixing them, and separating and drying precipitated pigment.

Production of anticorrosive pigments containing phosphorus

Pure Maddrell salt is produced by heating sodium phosphate to temperatures of 250.degree. to 420.degree. C. The sodium phospate used as starting material is sodium trimetaphosphate or a mixture of sodium trimetaphosphate with Maddrell salt, monosodium orthophosphate or disodium pyrophosphate, the mixture containing Na and P in a molar ratio of 1:1. Prior to heating the starting material, it is admixed with 0.5 to 5 weight% of orthophosphoric acid, polyphosphoric acid, phosphorus pentoxide or at least one salt of a volatile base forming polyphosphoric acid at the temperatures specified. The resulting mixture is calcined over the period necessary to transform the starting material to Maddrell salt.

Production of Maddrell salt

Aluminum polyphosphate is made. To this end, solid aluminum hydroxide and polyphosphoric acid which are used in proportions corresponding to an Al:P molar ratio of 1:2.5 to 1:3.5, are introduced separately from, but concurrently with, one another into a reaction zone kept at 150.degree. to 200.degree. C. A moist friable consistency of the starting materials is maintained in the reaction zone by continuously mixing, kneading and comminuting them over substantially the entire period during which they are introduced into the reaction zone. The reaction is continued until a dry sandy powder is formed; and the powder is annealed at 400.degree. to 600.degree. C. over a period sufficient to yield a product undergoing a 0.5 to 1% weight loss on ignition.

Production of aluminum polyphosphate

Hardeners of condensed aluminum phosphates for use in water-glass cementing compositions and process for making them. The hardeners consist substantially of a short chain aluminum polyphosphate with a chain length of 3 to 6 and a long chain aluminum polyphosphate with a chain length or more than 40. Quick-setting hardeners contain a high proportion of the short chain component and slow-setting hardeners contain a high porportion of the long chain component.

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Hurth, Germany

Raban Von Schenck