title: Effects of gas generation and precipitates on performance of Fe0 PRBs.
abstract: Long-term reactivity and permeability are critical factors in the performance of granular iron permeable reactive barriers (PRBs). Thus it is a topic of great practical importance, as well as scientific interest. In this study, four types of source solutions (distilled H2O, 10 mg/L TCE, 300 mg/L CaCO3, and 10 mg/L TCE + 300 mg/L CaCO3) were supplied to four columns containing a commercial granular iron material. In all four columns, gases accumulated to approximately 10% of the initial porosity and resulted in declines in permeability of approximately 50% to 80%. In the columns receiving CaCO3, carbonate precipitates accumulated to approximately 7% of the initial porosity, with no apparent decline in permeability. The data indicate that precipitates formed initially at the influent ends of the columns, reducing the reactivity of the iron in this region. As a consequence of the reduced reactivity, calcium and bicarbonate migrated further into the column, to precipitate in a region where the reactivity remained high. Thus precipitation occurred as a moving front through the columns. The results suggest improved methods for PRB design and rehabilitation, and also suggest improvements that are needed in the mathematical models developed for predicting long-term performance.
authors.affiliation: SEACOR Environmental Inc., 201-6200 Dixie Rd., Mississauga, Ontario, L5T 2E1, Canada.
authors.forename: Yousheng
authors.initials: Y
authors.lastname: Zhang
authors.forename: Robert W
authors.initials: RW
authors.lastname: Gillham
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry; D011232:Chemical Precipitation; D005618:Fresh Water / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D016062:Porosity; D014241:Trichloroethylene / Q000737:chemistry*; D014874:Water Pollutants, Chemical; D018508:Water Purification / Q000379:methods
chemical_list: D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D006859:Hydrogen; D007501:Iron; D002119:Calcium Carbonate