Influence of dissolved inorganic carbon and calcium on gas formation and accumulation in iron permeable reactive barriers

Abstract

Uncertainties in long-term reactivity and gas accumulation in Fe(0) permeable reactive barriers still hinder a broad application of this groundwater remediation technology. In this study long-term column experiments were conducted under varying geochemical conditions. Generation of hydrogen by anaerobic corrosion in Fe(0) reactive filters was mainly influenced by the mass flux of dissolved inorganic carbon. Both increased concentrations and volume flows led to a substantial rise in gas generation but only to slight differences of gas accumulation within the pores of the reactive filter. Comparisons of columns with different lengths showed higher averaged corrosion rates in the shorter and lower corrosion rates in the longer columns. Calcium in conjunction with dissolved inorganic carbon formed compact and localized aragonite minerals, while in the absence of calcium chukanovite dominated, which covered and passivated the reactive surface to a higher extent. Magnetite was the major crystalline corrosion product in the absence of carbonate and no decline in long term corrosion rates was observed within up to 700days of operation. Total gas yields of columns were restricted by passivation and approached a volume of approximately 13.5mL/g granulated cast iron.