Citrate has a strong ability to chelate calcium ions at low temperature, but the chelating ability decreases with the increase of temperature. Its ability to chelate magnesium ions is related to the PH value of the solution. When pH is 7 ~ 9, 20~50℃, and the molar ratio of citric acid to magnesium ion is 1: 1, 116mg magnesium ion can be chelated per gram of citric acid, that is, more than 90% magnesium ion can be chelated. Besides alkaline earth metals, it can effectively chelate most divalent and trivalent metal ions.