Formation Of Perchlorate By Ozonation Of Aqueous Oxy-chlorine Anions: An Insight To Natural Perchlorate Formation

Perchlorate (ClO4-) is a natural and anthropogenic contaminant of increasing concern. Natural perchlorate was first identified in Chilean nitrates from the Atacama dessert over 100 years ago. However, only in the last two years has the occurrence of natural perchlorate been seriously considered as a potential exposure source. Although there has been considerable research effort in understanding the occurrence, remediation, and impact of ClO4- in the environment, relatively little information is available regarding the mechanism(s) responsible for ClO4- formation. Perchlorate productions from ozone oxidation of chlorine and oxy- chlorine anions (Cl-, OCl-, ClO2-and ClO3-) were conducted in continuous flow reactors at constant ozone concentrations (approximately 6 mg L-1) and at varying concentrations of chlorine materials (ranging from 10 to 1000 mg L-1). Sub samples from both the main reaction flask and alkaline trapping flasks were taken over varying time intervals and the concentrations of oxy-chlorine anions including ClO4- were measured using various ion chromatographic methods whereas OCl- was determined iodometrically using the spectrophotometer. The experiment time ranged from 6 hrs to 7 days depending on the rate of decomposition of the reactants. Results indicate that ClO4- is readily formed during the ozonation of ClO2- and OCl- solutions (maximum conversion of 2.7 %) whereas the Cl- and ClO3- solutions produced relatively lower quantities of ClO4- ( maximum conversion of 0.02 %) . Further the presence of ClO2- in the initial OCl- solution is suspected to significantly contribute the total ClO4- generated augmenting the role of ClO2- in ClO4- formation as mentioned in recent study on the photochemical reactions of oxy-chlorine anions.