U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 1 of 3--Contamination From Hard-Rock Mining, Water-Resources Investigation Report 99-4018A

A New Method for the Direct Determination of Dissolved Fe(III) Concentration in Acid Mine Waters

By James W. Ball, D. Kirk Nordstrom, R. Blaine McCleskey, and Tanya Bangthanh To

This report is available in pdf format: Ball.pdf 66KB

ABSTRACT

A new method for direct determination of dissolved Fe(III) in acid mine water has been developed. In most present methods, Fe(III) is determined by computing the difference between total dissolved Fe and dissolved Fe(II). For acid mine waters, frequently Fe(II) > > Fe(III); thus, accuracy and precision are considerably improved by determining Fe(III) concentration directly. The new method utilizes two selective ligands to stabilize Fe(III) and Fe(II), thereby preventing changes in Fe reduction-oxidation distribution. Complexed Fe(II) is cleanly removed using a silica-based, reversed-phase adsorbent, yielding excellent isolation of the Fe(III) complex. Iron(III) concentration is measured colorimetrically or by graphite furnace atomic absorption spectrometry (GFAAS). The colorimetric method requires inexpensive commercial reagents and simple procedures that can be used in the field. The method detection limit is 0.002 mg/L (40 nM) using GFAAS, and 0.02 mg/L (0.4 µM) by colorimetry.