Rust Removal using Citric Acid Many different acids can be used to remove rust from iron and steel. The advantage that citric acid has over some other acids, is that it is less caustic, not as hazardous environmentally, while remaining quite effective. Mixing acid with water can be treacherous, and one of the rules for remembering which way to do so goes something like this: "May her rest be long and placid, she poured the water in the acid. The other girl did as she oughter…..she poured the acid in the water." So, when diluting acid, pour the acid in the cold water "slowly". And follow your safety rules by wearing goggles and apron. (This is primarily a reminder to those who insist on using concentrated hydrochloric, sulphuric or nitric acid) If, after mixing several minutes, you see citric acid crystals forming on the bottom of the mixing vessel, don’t add any more crystals. The solution is at or beyond the saturation point. Citric acid + rust yields iron oxide, carbon monoxide, water and hydrogen. C6H8O7 + Fe2O3 -----------‡ 2 FeO + 6 CO + 2 H2O + 2 H2 The balanced equation shows that 1 mole of citric acid will react with 1 mole of iron(III) oxide to produce 2 moles of Iron(II) oxide, 6 moles of carbon monoxide, 2 moles of water and 2 moles of hydrogen. This is what happens…..in theory. And like my old college prof used to say: "Theory guides…..experiment decides." You can alter the reaction rate in 3 ways. 1. Concentration: Adding acid (before saturation) increases the number of hydrogen citrate ions that collide with rust particles. 2. Stirring: Mixes the solution, diffusing away reacted particles and exposing the rust surface to additional ions. 3. Increase solution temperature: Increases velocity of the ions, resulting in a more violent collision with the rust particles. As the reaction time increases, concentration decreases as ions are used up and products formed. This is simply a basic explanation for those wishing to know what happens. Good luck, and hope it helps. Larry Holland 11/20/05