Carbon and iron additions to stimulate in-pit sulfate reduction and removal

Document
Description
Large volumes of water containing elevated concentrations of sulfate and other dissolved solids are present in abandoned mine pits on the Mesabi Iron Range. The release of water with elevated sulfate and, to a lesser extent hardness, is an environmental concern owing to its potential effects on wild rice, mercury, and phosphorus. Using conventional technology for treatment of mine pit waters is a challenge owing to the large volumes of water present and discharge patterns which can be driven by natural hydrologic processes. Biological sulfate reduction is used in both engineered and natural sulfate treatment systems in a process whereby carbon provides the fuel to drive the transformation of sulfate to sulfide, and iron or another metal provides a means to remove sulfide from water. The primary objective of this study was to determine whether the artificial addition of iron and carbon could be used to stimulate biological sulfate reduction and remove high sulfate and hardness from mine pit waters on the Mesabi Iron Range. Towards this end, short term, batch laboratory studies tested the effectiveness of different carbon and iron sources at both room temperature and 4?C under mixed and unmixed conditions. The effectiveness of carbon and iron sources was evaluated based on the rate at which sulfate was removed and the ability of added iron to keep hydrogen sulfide, a toxin to the sulfate reduction process, concentrations low. The ability to simultaneously remove hardness through precipitation with carbonate was also evaluated. Of the carbon sources tested, ethanol was the most effective in driving biological sulfate reduction. While >90% sulfate reduction was observed after only 3 weeks in well-mixed ethanol-amended waters at room temperature, the reaction occurred 10-20 times slower at 4?C. Iron materials were not added in great excess; however, of the two iron sources tested, iron carbonate was most effective at keeping hydrogen sulfide concentrations low. No combinations of iron and carbon amendments were able to remove hardness effectively. Due to the high cost and non-local source of commercial iron carbonate, future investigations should further consider the ability of locally available minerals to effectively provide iron for in-situ sulfate reduction and removal processes.
Date Issued
2012
Number of Pages
35
Decade
Rights Holder
Minnesota Water Research Digital Library
Rights Management
Public Domain