The Use of Wetlands to Remove Nickel From Mine Drainage - Is Perpetual Treatment Really Possible?

Abstract

Although wetland treatment systems have been shown to be effective for treating both coal and metal mine drainage, the longevity of the treatment has always been a question. Data collected from a wetland in northeastern Minnesota suggests it may be possible to build a wetland that will provide long term treatment. A 7000 square meter overland flow wetland was built in 1992 to treat a mine drainage with an av798798erage pH of 7.2 and an average nickel concentration of 5.1 mg/L. Nickel removal exceeded 90% for the first three years of operation. In 1995, the stockpile which contributed the major input to the wetland was capped, and both flow and concentrations in the drainage were reduced. An intensive study was conducted on one section of the wetland where a large percentage of the overall removal was occurring. Nickel concentrations in the substrate reached 1.5% by weight and the calculated nickel mass in the substrate was about the same as the overall mass removal calculated from the water quality and flow data. Based on a model of substrate accumulation in wetlands, the wetland generates 7 kg of nickel removal capacity each year. Since the annual input of nickel has been reduced to around 10 kg, the projected lifetime of the wetland is about 300 years.

Effect of Mass Ratio on Phytoremediation of Nickel Contaminated Water

“…The reduction of Ni concentration were due to several reasons including phytoremediation mechanisms (phytodegradation, phytoextraction, phytostabilization) [21] and physical mechanisms (adsorption, precipitating) [22]. Ni removal percentages were calculated for each week within different mass ratios (0, 2,800, 34,000) and three concentrations throughout 21 days.…”

Controlling Mine Drainage Problems in Minnesota - Are All the Wetland Treatment Systems Really Above Average?

“…By revegetating the stockpile and reducing the total flow, the estimated lifetime of the system has doubled. Using a model developed for the W1D wetland, this wetland should generate enough metal removal sites each year to balance about ½ of the estimated annual metal load to the wetland and as a result the lifetime can be calculated to be on the order of 400 years (Eger et al, 2002).…”

“…Since the wetland was built to treat the volume and quality of drainage flow from the stockpile prior to reclamation, the decrease in flow and concentration has dramatically increased the projected lifetime of the system. Currently there appears to be an approximate balance between the annual production of new removal sites and the annual input of nickel, which suggests that the wetland should be capable of treating the drainage in perpetuity (Eger et al, 2002) Seep X Seep X originates from the 8013 stockpile that was reclaimed in 1991. Since the wetland was constructed in 1995, the flow into the wetland has averaged about 100 L/min.…”