Effects of Selected Good’s pH Buffers on Nitrate Reduction by Iron Powder

The effects of three selected Good’s pH buffers on the performance of an ${\mathrm{Fe}}^0∕\text{nitrate}∕{\mathrm{H}}_2\mathrm{O}$ system were evaluated. The Good’s 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 ${\mathrm{Fe}}^{2+}$ (or ${\mathrm{Fe}}^{3+}$ ) was released after adding the Good’s pH buffer into the ${\mathrm{Fe}}^0∕{\mathrm{H}}_2\mathrm{O}$ system with or without nitrate. In general, the pH of the buffered solution increased from the initial pH ( $=\sim 4.6–5.3$ , depending on buffer’s ${\mathrm{pK}}_{\mathrm{a}}$ ) to near-neutral pH. After the initial pH hiking, the pH in the system was more or less stable for a period of time ( $\sim 5–10\mathrm{h}$ , usually concurrent with a fairly stable aqueous ${\mathrm{Fe}}^{2+}$ ). The pH then drifted to $\sim 7.1$ to 8.6, depending on the buffer’s initial concentration, the buffer’s ${\mathrm{pK}}_{\mathrm{a}}$ , and the consumption of ${\mathrm{Fe}}^{2+}$ concurrent with nitrate reduction. While a common assumption made by researchers is that Good’s pH buffers do not directly participate in reaction processes involved in contaminant remediation, this study shows that as side effects, the Good’s pH buffer may react with iron powder.