AN ANALYSIS OF MANGANESE AS AN INDICATOR FOR REA VY METAL REMOVAL IN PASSIVE TREATMENT USING LABORATORY SPENT MUSHROOM COMPOST COLUMNS
B. A. Jacobson, R. F. Unz, Brian A. Dempsey · Journal American Society of Mining and Reclamation · 1999
The National Pollution Discharge Elimination System (NPDES) dictates removal of manganese in mine drainage to less than 4 mg/I daily or less than 2 mg/I on a monthly average.Owing to its high solubility at low and circumneutral pH, removal of manganese is often the most difficult of the NPDES discharge standards.This has lead to the use of Mn (II) as a surrogate for metal removal.However, recent studies concluded that zinc or nickel may be more appropriate indicators for removal of other metals.Our previous field studies showed zinc removal to be highly correlated to the removal of copper, cobalt, and nickel in a sulfate reducing subsurface loaded wetland, whereas manganese removal was poorly correlated.The objective of this study was to evaluate zinc and manganese retention under sulfate reducing conditions in bench scale columns containing fresh spent mushroom compost.Column effluent data were analyzed using an EPA geochemical computer model (MINTEQ) over the pH range of 6.0 to 6.8.Under these conditions, zinc and manganese displayed distinctly reactivities.Zn(II) was supersaturated with respect to ZnSc,i and the Zn(HS), 0 and Zn(HS),-complexes dominated solubility.Soluble zinc concentrations were inversely correlated to sulfide.Mn(II) remained as soluble Mn• 2• During early column operation at pH>7, MnC0 3 c,i was supersaturated.Manganese concentrations did not correlate with pH or sulfide.Given these fundamental differences in removal mechanisms between Zn and Mn under sulfate reducing conditions, the use of manganese removal as a surrogate for heavy metal removal in passive treatment of mine drainage seems unjustified.