Removal of Heavy Metals from Mine Wastewater Using Cementation/ Reductive Precipitation

Principal Investigator: Dr. Larry Twidwell
ltwidwell@mtech.edu

The main objective of this study was to assess cementation/reductive precipitation as a relatively simple and cost effective means of treating heavy metal bearing wastewater streams. Cementation refers to the direct electrochemical reduction of aqueous species to their elemental form. Reductive precipitation consists of using elemental iron (Fe) to control the solution potential at a level that is favorable for the removal of toxic and heavy metals by their precipitation as metal sulfides. Five heavy metals were targeted in this project, and those were cadmium, copper, lead, nickel, and zinc. Project goal levels were 1 μg/L (Cd), 30 μg/L (Cu), 15 μg/L (Pb), 100 μg/L (Ni), and 388 μg/L (Zn). These goals were based on Montana aquatic life standards (at a hardness of 400 mg/L CaCO3) and MCLs. Exploratory studies investigated the influence of pH, the presence and absence of an Fe slurry to fix the solution electrochemical potential, the presence and absence of sulfide, sulfide concentration, and type of reagent supplying the sulfide. Work was conducted first with synthetic water, and given satisfactory results, moved on to “real” mine waters. It was found that with waters containing high concentrations of heavy metals, the target metals can be removed to the project goal levels with stated conditions of pH, time, and sulfide addition rate.
MWTP Activity IV, Project 25
Final Report

Susie Anderson • 406-496-4311