Modeling heavy metals transport in an arctic fjord system polluted from mine tailings

Abstract

A computerized mathematical model has been used to describe the dissolution and transport of lead, zinc, and cadmium in the Agfardlikavsa Fjord, Marmorilik, West Greenland, where tailings from the Greenex A/S lead/zinc mine and concentrator are being deposited. The hydraulic model basis is a quasi-stationary box model representation which has been calibrated using salinity profiles. The superimposed metals model assumes equilibrium between dissolved and particulate metal forms using Langmuir adsorption isotherms to calculate particulate concentrations from concentrations of dissolved metals and suspended solids, respectively. Calibration of the model parameters (sedimentation rates and dissolution rates) has been made observing quite narrow constraints established by field observations and laboratory experiments. In the course of the time period being modeled, 1978–1980, the pollution with heavy metals has been mitigated significantly. The abatement measures undertaken include: (1) alteration of the lead flotation process and lime addition to tailings by June/July 1978; (2) alum coagulation of the effluent by January 1979; and (3) establishment of a new tailings discharge system in December 1979. The model has been used to estimate the reductions brought about in inputs of dissolved metals as well as to quantify the dynamics of the heavy metals transport in the fjord system. A particular important objective was to estimate the net outflow of metals to the adjacent Quamarujuk Fjord and to predict how the outflow responded to a decreased pollution load. A further result from the model study was the finding that routine monitoring of soluble metals in the discharged tailings as assayed by a specific method did in fact approximate model estimates of metals discharge rates if pH in the test was changed from pH 7.0 to pH 8.0.