Experimental Verification of Consumer Information on Calcium Stain Removal with Citric Acid

Abstract

  Consumer information on acid cleaning of water stain containing calcium was investigated and the chemical reaction was experimentally verified. The results show that most related consumer information recommended the use of citric acid for water stain removal, but no information referred to precipitation caused by the reaction between citric acid and calcium. Removability of calcium soil with citric acid solution showed the same effectiveness as hydrochloric acid solution and acetic acid solution, but a great amount of precipitation was observed after a long period of mixing citric acid solution with calcium salt. Measurement of pH, Ca concentration (using XRF) and citric acid concentration (using HPLC) indicated that the precipitation is formed by calcium carbonate recrystallization followed by citric ion exchange. This fact indicates invalidity of the so-called “neutralization theory” which is often referred to in consumer information.