oxidation process and to identify the mineral weathering products. The process was ... products from the bacterial oxidation of pyrrhotite under laboratory ...
APPLIED AND ENVIRONMENTAL MICROBIOLOGY, June 1993, p. 1984-1990
Mineral Products of Pyrrhotite Oxidation by Thiobacillus ferrooxidanst TARIQ M. BHATTI,1t JERRY M. BIGHAM,2 LIISA CARLSON,2§ AND OLLI H. TUOVINENl* Department of Microbiology' and Department of Agronomy, 2 Ohio State University, Columbus, Ohio 43210 Received 6 January 1993/Accepted 15 March 1993
The biological leaching of pyrrhotite (Fel.xS) by Thiobacilus ferrooxidans was studied to characterize the oxidation process and to identify the mineral weathering products. The process was biphasic in that an initial phase of acid consumption and decrease in redox potential was followed by an acid-producing phase and an increase in redox potential. Elemental S was one of the first products of pyrrhotite degradation detected by X-ray diffraction. Pyrrhotite oxidation also yielded K-jarosite [KFe3(SO4)2(OH)6], goethite (ot-FeOOH), and schwertmannite [Fe808(0H)6S04j as solid-phase products. Pyrrhotite was mostly depleted after 14 days, whereas impurities in the form of pyrite (cubic FeS2) and marcasite (orthorhombic FeS2) accumulated in the leach residue. purpose of this study was to characterize the solid-phase products from the bacterial oxidation of pyrrhotite under laboratory conditions. A research-grade pyrrhotite sample from Santa Eulalia, Mexico (no. 49E5885) was obtained from Ward's Natural Science Establishment, Inc. (Rochester, N.Y.), and ground to a -200-mesh (
s042-
+ 2H+
(3)
Bacterial and chemical oxidation of ferrous iron:
4Fe2+ + 02 + 4H+ Oxyhydroxide formation:
Fe3+
+
--
(228)
(2)
4Fe3+ + 2H20
2H20 -O FeOOH + 3H+
(4)
(5)
(1228)
A
10
20
30
40
50
60
70
Degrees 2E CuKa XRD FIG. 2. Powder patterns from untreated pyrrhotite (A) and from pyrrhotite leach residue after 30 days of contact with chemical control solution (B) and with inoculated leach solution (C). Miller indices and d values are given for lines not subject to major interference from associated minerals. 1 A = 0.1 nm.
FIG. 3. Plot of normalized XRD peak intensities for pyrrhotite and elemental sulfur (A), ratio of peak intensities shown in panel A (B), and normalized XRD peak intensities for K-jarosite and goethite (C). Maximum intensities of the specified peaks were assigned a value of 100.
