Hygienic Chemical Studies of Water Supply : Disappearance of Residual Chlorine and Presence of Ferrous Compounds in the Water during Contact with Model Iron Material

Abstract

Changes in th quality of domestic tap water during contact with model iron materials were investigated by chemical and instrumental analyses. When neutral chlorinated water was placed in contact with pure iron pieces at 20°, the concentration of residual chlorine (free and combined) and solved oxygen in the water decreased rapidly with time, and pH of the water was lowered in the presence of free chlorine, but rose in the presence of combined chlorine. Dissolution of Fe²⁺ from iron pieces into the water was accelerated by residual chlorine suddenly followed by oxidation of Fe²⁺ to Fe³⁺ precipitate. After disappearance of free Cl, however, presence of Fe²⁺ compounds in the water was found in a higher concentration. The rate of disappearance of free Cl, combined Cl, and dissolved oxygen in the water showed a linear relation with logarithm of each concentration. Rate constants for the disappearance of free Cl, combined Cl, and dissolved oxygen in the neutral water at 20° were about 3.2×10^-2, 2.7×10^-2, and 1.5×10^-2M/dm² (Fe)/min, respectively, when the concentration of these substances and SO₄^2- was less than 10 ppm.