Prediction of Metal Remobilization from Sediments under Various Physical/Chemical Conditions "Design of Experiments Cd, Co and Pb"
The metal partition coefficient Kd (L/kg) is the ratio of sorbed metal concentration on the solid phase m (mg/kg) to the dissolved metal concentration at equilibrium. The behavior of metals in surface water is complex and their partition coefficients can be impacted by many factors. Organic matter (OM) content in sediments, pH and salinity, are factors that may influence speciation and partitioning of metals. In this study, the partitioning coefficient of three metals (Cd, Co and Pb) under different levels of salinity, pH, and OM content were examined. A series of factorial experiments were evaluated in which three levels of OM are tested each time against five levels each of salinity and pH; the design of experiments was generated by the statistical software program, MiniTab16®. All metals tested showed a trend of increasing Kd with an increase of OM from 0.36% to 4.36%. Salinity experiments showed that the lower values of Kd were all recorded in freshwater and the highest Kd values were recorded in saltwater. The metal Pb showed the highest Kd values. The average Kd values under acidic conditions for Cd, Co and Pb are 234, 83 and 5,618 L/kg respectively. The relatively higher value of Kd for Pb compared to that of Cd and Co can be attributed to its lower precipitating pH. Multiple regression equations were generated to predict Kd of each metal when comparing multiple factors at the same time (salinity/OM and pH/OM). The study showed no significant interactions between salinity/OM and pH/ OM for all three metals. This supports that tested factors are all affected Kd but act independently.