Sachin Pandey
PhD Student
Hydrology, Water Resources, and Env. Fluid Mechanics
Civil, Environmental, and Architectural Engineering
University of Colorado at Boulder
sach@colorado.edu

Abstract

Study of microbial activity in acid mine drainage (AMD) has focused on transformations of 
iron and sulfur. However, carbon cycling, including formation of soluble microbial products 
(SMP) from cell growth and lysis, is an important component of the biogeochemistry in the 
AMD environment. Experiments were conducted to study the interaction of SMP with soluble 
ferric iron in acidic conditions, particularly the formation of complexes that inhibit its 
effectiveness as the primary oxidant of pyrite during AMD generation. The presence of 0.3 mg 
lysis SMP-DOC per mg-total soluble ferric iron reduced pyrite oxidation rate by 87% in 
sterile suspensions at pH 1.8. A first order pyrite oxidation model coupled to a chemical 
speciation model allowed us to approximate a set of equilibrium constants for SMP using an 
optimization scheme in conjunction with experimental data. This helps substantiate the 
assumption that free ferric iron is the active oxidation species, and that complexation of 
Fe3+ with SMP can account for the observed inhibition of pyrite oxidation. The results 
improve the current understanding of the role of heterotrophic microorganisms in AMD 
remediation and can be used in a rigorous reactive transport model investigating the complex 
interactions of hydrogeology and biochemistry occurring at the waste rock pile scale.