Process for the production of acicular gamma-iron (iii) oxide

Claim 1

A PROCESS FOR THE PRODUCTION OF ACICULAR GAMMAIRON (III) OXIDE WHICH COMPRISES PRECIPITATING IRON (III) HYDROXIDE FROM A SOLUTION OF AN IRON (III) SALT SELECTED FROM THE GROUP CONSISTING OF IRON (III) CHLORIDE, IRON (111) NITRATE AND IRON (III) SULFATE WITH A SOLUTION OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF SODIUM HYDROXIDE, POTASSIUM HYDROXIDE, SODIUM CARBONATE, POTASSIUM CARBONATE AND AMMONIA, SAID COMPOUND BEING APPLIED IN AN EXCESS OF AT LEAST 100% OVER THE STOICHIOMETRIC AMOUNT, WHILE STIRRING VIGOROUSLY, AT TEMPERATURES BETWEEN 10*C. AND 50*C., SEPARATING THE IRON (III) HYDROXIDE THUS OBTAINED, TREATING IT FOR SEVERAL HOURS WITH A CAUSTIC SOLUTION HAVING A CONCENTRATION OF ABOUT 3 TO 20% OF ALKALI METAL HYDROXIDE AT TEMPERATURE OF 20 TO 90*C. AND THEN HEATING TO TEMPERATURE HIGHER THAN 90* C. UP TO TEMPERATURES NEAR THE BOILING POINT OF SAID CAUSTIC SOLUTION, FILTERING, WASHING AND DRYING IT, HEATING THE DRIED IRON (III) OXIDE IN A STREAM OF A REDUCING GAS A T TEMPERATURES BELOW 400*C. TO REDUCE THE IRON (III) OXIDE TO MAGNETITE, AND OXIDIZING SAID MAGNETITE TO GAMMA-IRON (III) OXIDE WITH A GAS CONTAINING FREE OXYGEN AT TEMPERATURES UP TO ABOUT 400*C.