Process for removing copper-containing iron oxide scale from metal surfaces

Claim 1

A PROCESS FOR THE REMOVAL OF COPPER-CONTAINING IRON OXIDE SCALE FROM METAL SURFACES WHICH COMPRISES CONTACTING SAID SURFACE WITH AN AQUEOUS SOLUTION CONTAINING AT LEAST ABOUT 1% W./V. CITRIC ACID TOGETHER WITH SUFFICIENT BASE TO PROVIDE A PH BETWEEN ABOUT 2.5 AND ABOUT 5, SAID BASE BEING SELECTED FROM THE GROUP CONSITING OF AMMONIA, AN UUNSUBSTITUTED ETHANOLAMINE AND A WATER-SOLUBLE ALIPHATIC HYDROCARBON AMIN, CONTINUING SAID CONTACT UNTIL THE IRON CONTENT OF SAID SOLUTION BECOMES SUBSTANTIALLY CONSTANT, SUBSEQUENTLY ADJUSTING THE PH OF SAID SOLUTION WITH ONE OF SID BASES TO A VALUE BETWEEN ABOUT 8 AND ABOUT 10, AND MAINTAINING THE PH WITHIN SAID ALKALINE RANGE WHILE CONTINUING SAID CONTACT UNTIL THE COPPER CONTENT OF SAID SOLUTION BECOMES SUBSTANTIALLY CONSTANT.