Adsorption of Ni(II) and Cd(II) in Compacted Peat and the Utilization of the Adsorption Properties in Hydraulic-Barrier Layers in Tailing Impoundments

Landfills and tailing impoundments contain barrier layers that prevent the migration of contaminants into groundwater by slowing down the water flow through the structures. Many materials used in hydraulic barrier layers also have sorption properties, which could be utilized to reduce environmental risks. The adsorption of Ni(II) and Cd(II) on peat was studied using a single metal column test. Two samples with different dry unit weights, low-density (LD) and high-density (HD) peat, were tested. A batch test was made for comparison. Both samples in the column test adsorbed the metals well; peat adsorbed 9,500 mg/kg of nickel and 11,200 mg/kg of cadmium. The adsorption was twice as high in the column test as in the batch test. Cadmium adsorbed strongly on the top layers of the sample, whereas the adsorption profile of nickel was more even through the sample. The density of the peat did not affect the maximum adsorption capacity. In HD peat, the heavy metals adsorbed more on the top layers of the sample, and in LD peat, the metals migrated deeper. In a hypothetical field impoundment, the liquid/solid ratio of the column experiment would represent a time period of 38–59 years and the structure would adsorb 99% of both metals. A 50-cm layer of HD peat would have the capacity to adsorb 1.96 kg of cadmium and 1.66 kg of nickel per square meter.