A lot of concern has been raised by individuals and organizations regarding the menace associated with heavy metal contamination of marine sediments in Norway. This has necessitated the remediation of heavy metal contaminated areas. Stabilization and solidification is one of the techniques used to immobilize heavy metals in marine sediments. Laboratory leaching tests are generally used to assess the effectiveness of stabilization and solidification. Results of laboratory leaching tests are, however, used only on short term basis. Geochemical models have evolved into invaluable tools that can be used as a substitute for laboratory leaching experiments. Results from geochemical modelling can be used for future predictions and also help in management options. Previous studies have revealed that several leaching experiments have been successfully simulated with geochemical models. This study, which is in connection with a larger project being carried out by NGI, has been designed with the intent of using geochemical modelling code, PHREEQC to simulate the binding and release of Pb and Cu and their long-term behaviour in cement-stabilized polluted sediments from three Norwegian harbours namely: Hammerfest, Grenland and Bergen.
The Freundlich empirical adsorption isotherm was utilized in this study to describe the behaviour of the heavy metals in the three stabilized sediments. Results showed that the Freundlich empirical isotherm could be used to describe the adsorption characteristics of the stabilized sediments for Cu and Pb as the isotherm fitted rather well to experimental data from the three sediments. The sorption capacities of the stabilized sediments for the heavy metals were determined using the nonlinear Freundlich equation. Stabilized sediments from Hammerfest demonstrated the least sorption capacity for both metals with stabilized sediments from Bergen showing the highest capacity to sorb the two heavy metals. The sorption capacity of the stabilized sediment from Grenland was between that of Bergen and Hammerfest. In general, results indicated that the sorption capacities of the sediments were higher for Pb than for Cu. A 1-dimensional transport based on PHREEQC using diffusion and a non-linear sorption was employed to simulate heavy metal releases from the cement-stabilized sediment into sea water and to predict their long-term behaviour using time spans of 2, 10 and 20 years. It followed thus from the results of the fluxes calculated that stabilized sediment from Bergen was effective in retaining the heavy metals and consequently reduced their diffusive transport for all the time spans studied. The fluxes of both metals from Hammerfest stabilized sediment for all the time spans were relatively high due to the inability of the sediment to retain the metals. Fluxes of both metals from Grenland sediments were between those of Bergen and Hammerfest sediments.