Method of removing rust from ironcontaining materials, particularly for the cleaning of boiler plants

Claim 1

IN A PROCESS OF DE-RUSTING THE SURFACE OF AN IRONCONTAINING MATERIAL IN WHICH A HOT ACIDIC AQUEOUS ETCHING SOLUTION IS CONTACTED WITH SAID SURFACE, THE ACID BEING TAKEN FROM THE GROUP CONSISTING OF HYDROCHLORIC AND SULFURIC ACID, THE IMPROVEMENT COMPRISING CARRYING OUT SAID PROCESS IN THE PRESENCE OF A SUBSTANCE WHICH CAN FORM A SALT WITH THE ACID BY ADDITION COMPOUND FORMATION, THE SALT BEING DISSOCIATED IN THE HOT SOLUTION, THE PROCESS BEING CARRIED OUT AT A TEMPERATURE ABOVE ABBOUT 90* C. AT AN ACID PH OF NOT BELOW ABOUT 3, THE ACID BEING IN A CONCENTRATION OF LESS THAN A HUNDREDTH OF A PERCENT, SAID SUBSTANCE BEING TAKEN FROM THE GROUP CONSIST: ING OF INORGANIC AND ORGANIC NITROGEN CONTAINING BASIC SUBSTANCES, THE CONCENTRATION OF SAID SUBSTANCE BEING NOT GREATER THAN THAT WHICH WOULD GIVE A PH OF ABOUT 9 IN WATER ALONE.