Multiscale Investigation of Acid Mine Drainage: the Effect of Organic Carbon Cycling on Microbial Activity and Pyrite Oxidation

Yacob, Tesfayohanes W.

Graduate Thesis Or Dissertation

Multiscale Investigation of Acid Mine Drainage: the Effect of Organic Carbon Cycling on Microbial Activity and Pyrite Oxidation Público Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/g445cd342

Abstract

Acid mine drainage (AMD) generation from abandoned waste rock piles is a serious environmental problem. One proposed solution is the use of organic carbon to bring about biogeochemical changes that can slow down AMD. The growth of mine waste rock enrichments on a glucose substrate was studied in batch cultures and a monod kinetic model was developed. Various concentrations of soluble microbial products (SMPs) of these enrichments were studied for their interaction with ferric iron and the resulting effect on pyrite oxidation. Four Waste rock packed columns were run in series and the chemical and biological indicators of interest measured for the rock pore liquid and column bulk liquid effluent. The growth experiment results gave a maximum specific growth rate of 0.13 ± 0.01 (1/hr). The enrichments were able to grow from pH 1.6 to 6.0 and had a pH optimum between 2.5 and 3.0. A dissolved oxygen half saturation constant of 0.11 ± 0.05 mg/l was obtained indicating the high sensitivity of the organisms to oxygen. SMPs were able to reduce the pyrite oxidation rate by up to 90% with lysis derived SMPs having a much higher impact than growth derived SMPs for an equivalent SMP-DOC (dissolved organic carbon). A mathematical relationship was developed to predict the rate of pyrite oxidation given an SMP-DOC concentration. The column experiments showed that rock pores contain up to 16 times higher iron and sulfate concentrations compared to column bulk liquid effluents. These and other microbial evidence suggest high pyrite oxidation rate is maintained at rock pores and that bulk liquid effluent concentrations are controlled by diffusional exchange with rock pores as indicated by a tracer test. Results of the growth and SMP-ferric iron interaction study can be incorporated to AMD models and used to predict remediation effects of carbon addition. Waste rock AMD generation results can be used as preliminary guides to design efficient carbon delivery schemes to reactive sites of waste rock piles.

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