1. Field of the Invention This invention relates to a composition and method for removing metal oxides such as rust and mill scale from ferrous metals such as steel. More particularly, the invention relates to metal oxide removal from ferrous metals while avoiding corrosion and discoloration of the metal. 2. Description of the Prior Art It is known to use citric acid and citrates for the removal of rust from ferrous metals, see for example US. Pat. No. 3,510,432. The disadvantage of such mate rials is that they leave a discoloration or black ?lm on the rust-free metal. Another reference teaching the use of citric acid is US. Pat. No. 3,492,238 which employs citric acid in combination with EDTA (ethylene diamine tetracetic acid). This reference employs the solution at a pH of about 6.0-7.0. ' Triethanolamine has been employed in metal cleaning formulations as an inhibitor for acid attack on the metal substate. It has been employed to avoid the blackening or discoloration of the cleaned metal. In this connec tion, reference is made to US Pat. No. 1,723,923 which teaches the combination of triethanolamine in highly corrosive pickling baths such as cold concentrated sul phuric form or a heated more dilute form. Such pickling baths are corrosive to the plant in which they are used and present an ecologically unacceptable disposal prob lem. US. Pat. No. 3,095,379 describes a metal cleaning composition which is the high temperature reaction product of citric acid and monoethanolamine. Such a formulation has been found to also leave an undesirable black coating on the cleaned metal surfaces. Other references considered include the following: US. Pat. Nos. 2,006,216; 2,505,785; 2,994,664; 3,056,746; 3,282,848; 3,510,432; 3,589,895; and 3,779,935. Attention is invited to the parent of this application referenced above for the citation of additional prior art.
