New method for the direct determination of dissolved Fe(III) concentration in acid mine waters

Environmental Science & Technology
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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 method requires inexpensive commercial reagents and simple procedures that can be used in the field. Calcium(II), Ni(II), Pb(II), Al(III), Zn(II), and Cd(II) cause insignificant colorimetric interferences for most acid mine waters. Waters containing >20 mg of Cu/L could cause a colorimetric interference and should be measured by GFAAS. Cobalt(II) and Cr(III) interfere if their molar ratios to Fe(III) exceed 24 and 5, respectively. Iron(II) interferes when its concentration exceeds the capacity of the complexing ligand (14 mg/L). Because of the GFAAS elemental specificity, only Fe(II) is a potential interferent in the GFAAS technique. The method detection limit is 2 μg/L (40 nM) using GFAAS and 20 μg/L (0.4 μM) by colorimetry.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title New method for the direct determination of dissolved Fe(III) concentration in acid mine waters
Series title Environmental Science & Technology
DOI 10.1021/es980684z
Volume 33
Issue 5
Year Published 1999
Language English
Publisher ACS
Contributing office(s) Toxic Substances Hydrology Program
Description 7 p.
First page 807
Last page 813
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