Treatment of Acid Mine Drainage Using Bauxsol and Zero Valent Iron

The Bureau of Land Management (BLM) conducted a treatability study of acid mine drainage at the Eveline Mine near Silverton Colorado during 2007.  The reagents evaluated were zero-valent iron (ZVI) and bauxsol, a by-product of aluminum refining.  The chemistry of the drainage featured aluminum, iron, manganese and zinc at 12.1, 20.7, 3.1, 1.1 mg/L, respectively.  Cadmium and copper were present at 12 and 77 ug/L. The flow is approximately 8 gpm and the pH is 3.4.  The site is poorly accessible at 10,600 feet near an avalanche chute.  For these reasons, conventional methods of treatment were not feasible.

 

The AMD was directed through five 3”x8’ PVC reaction chambers.  The chambers were filled with 1%, 10% and 20% ZVI mixed with sand.  Two additional chambers were filled with bauxsol pellets and 30% bauxsol and 70% sand.  AMD flow was reduced to 100 ml/min and split among the five chambers.  Six sets of samples were collected weekly during August and September.

 Results show similar performance among the materials. Results indicate that for cadmium, copper and zinc, the principal heavy metals of concern, that 10% ZVI or bauxsol pellets meet water quality standards.  Cement Creek water quality standards are: 10 ug/L, 200 ug/L and 2000 ug/L for cadmium, copper and zinc, respectively. Animas River table value standards are: 0.7 ug/L, 16.2 ug/L and 224 ug/L for the same metals.  Although 10% ZVI did not attain the Animas River cadmium standard, it exceeded the Cement Creek standard by a large margin. Copper and zinc standards were attained by 10% ZVI. Aluminum and zinc were removed from 67-98 percent.  Removal rates for iron were poor by ZVI and ranged from 20-87 percent for bauxsol. A full scale pilot is currently being designed.