TA10 Microbial Remediation of Acid Mine Drainage Wastes
D135-136
8:00 AM - 12:00 PM, Tuesday
() Removal of heavy metals through limestone precipitation: Biotic or abiotic?
Wildeman, T1, Ranville, J1, 1 Colorado School of MInes, Golden, CO, USA
ABSTRACT- In neutral waters associated with mining heavy metals such as Mn, Ni, Zn, and Cd can still persist at levels significantly above the limits of aquatic toxicity. In particular, Mn in coal mine drainage and Zn in metal mine drainage are ubiquitous problems. Two situations have been encountered where calcium carbonate is involved in the removal of these heavy metals. If this mechanism could be easily duplicated, it would be an effective method for treatment of these waters. In the Pinal Creek in Arizona, a bench scale treatment system was built that used a 60 cm deep limestone bed to treat an impacted stream that contained 55 mg/L of Mn and 2.2 mg/L of Zn. Algae were added to the system because it appeared to be associated with formation of MnO2 in the natural stream. In the system, there were no diurnal changes, which suggest that photosynthesis is not involved, and when the system was spiked with sodium azide bacteriacide, removal did not change. Nevertheless, Mn was removed to 3 mg/L and Zn to 0.04 mg/L even though the pH remained 7, a chemical condition where it is difficult to form MnO2. In another situation in Rico, Colorado, a drainage has the following chemistry: pH 7.05, Ca 424 mg/L, alkalinity 595 mg CaCO3, Zn 11.4 mg/L, and Mn 0.66 mg/L. The water is super saturated with CaCO3. As the drainage flows for 200 m in a trench, calcite precipitates and Zn drops to 0.019 mg/L and Mn to 0.04 mg/L. The Rico situation appears to be abiotic, however, the Pinal Creek system appears to have a biotic component that is difficult to determine. Developing these systems in a manner to where the processes were understood and could be duplicated would result in the development of inexpensive treatment systems that would remove important metal contaminants from mining influenced waters
Key words: manganese, mine water, zinc, limestone