Effects of Selected Goods pH Buffers on Nitrate Reduction by Iron Powder

The effects of three selected Goodʹs pH buffers on the performance of an Fe0/nitrate/H2O system were evaluated. The Goodʹs pH buffer itself did not reduce nitrate directly. Nitrate reduction by iron powder at near-neutral pH was negligible in an unbuffered system, but it was greatly enhanced with the presence of the buffer. A significant amount of aqueous Fe^2+ (or Fe^3+) was released after adding the Goodʹs pH buffer into the Fe^0/H2O system with or without nitrate. In general, the pH of the buffered solution increased from the initial pH (= ~4.6-5.3, depending on bufferʹs pKa) to near-neutral pH. After the initial pH hiking, the pH in the system was more or less stable for a period of time (~5-10  h, usually concurrent with a fairly stable aqueous Fe^2+). The pH then drifted to ~7.1 to 8.6, depending on the bufferʹs initial concentration, the bufferʹs pKa, and the consumption of Fe^2+ concurrent with nitrate reduction. While a common assumption made by researchers is that Goodʹs pH buffers do not directly participate in reaction processes involved in contaminant remediation, this study shows that as side effects, the Goodʹs pH buffer may react with iron powder.