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

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 silicabased, 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.

Major and trace element composition of copiapite-group minerals and coexisting water from the Richmond mine, Iron Mountain, California

“…The cations Na, K, and Li were analyzed by flame atomic absorption spectrometry (FAAS). Iron redox species were determined using a modification of the FerroZine colorimetric method (Stookey, 1970;To et al, 1999).…”

Hydrogen Peroxide Cycling in High-Temperature Acidic Geothermal Springs and Potential Implications for Oxidative Stress Response

“…Briefly, a 60-mL syringe filled with geothermal spring water was capped immediately with a septum (zero headspace) to avoid ingassing of atmospheric O 2 , then treated with appropriate reagents and titrated against Na 2 S 2 O 3 . Ferrous and ferric iron were measured on site using a modified version of the Ferrozine method (To et al, 1999) employing a 5 mL filtered (0.2 µm) sample. Briefly, Ferrozine solution (1 g L −1 ) was added to replicate subsamples in the absence (Fe(II) only) and presence (total Fe) of excess hydroxylamine (0.25 M stock), which reduces all Fe(III) to Fe(II) prior to complexation with ferrozine.…”

Niche specialization of novel Thaumarchaeota to oxic and hypoxic acidic geothermal springs of Yellowstone National Park

“…Total dissolved sulfide was measured using the amine sulfuric acid method (APHA, 1998a). Aqueous Fe(II) and Fe(III) were measured using the ferrozine method (To et al, 1999). Anions were measured using ion chromatography (Dionex, Sunnyvale, CA).…”