Adsorption of Copper on Particulates along a Salinity Gradient

Abstract

<p>The scavenging or Cu was studied along a salinity gradient using a reference clay mineral (SiIver HiII Illite. 1Mt-1) and sediments from La Have estuary (Nova Scotia). Experiments were conducted in progressive (Sal inograd) and batch mixing systems. The adsorption of Cu in the Salinograd is not significantly different from that in the batch system. The higher values in the Salinograd probably reflect experimental artifacts resulting from the inclusion or dialysis membrane to retain suspended particles in each mixing tank or the Salinograd.</p> <p>The measured adsorption (distribution coefficient, Kd) of Cu in the laboratory experiments decreased drastically in the low salinity regime. This suggests a dilution phenomena of Cu along an estuarine profile. Field measurements or particulate Cu and other trace metals support this hypothesis.</p> <p>The distribution coefficient varies inversely with sediment concentrations (100-1000 mg/L). The experimental data fit the O'Connor & ConnolIy (1980) Power law function: Kd = β/mc at salinities of 2.9-11.0°/oo, where α, and β are empirical coefficients and m is the sediment concentration. It appears however, that this inverse relations is strongIy dependent on salinity ( i.e. α and β are the salinity parameters in the Power law function).</p> <p>The explanation to this inverse relationship can be related partIy to "radiocolloid" formation which tends to increase the metal concentration in the particulate phase. The effects of these colloids are more important at the lower solid concentrations than at the higher concentration. An additional or possibly more important contributor to the decrease in Kd as particle concentration increases is inter-particle association. This particle-particle interaction tends to block adsorption sites as particle come closer, colIide and aggregate at large sediment concentration and higher ionic strength.</p> <p>The adsorption or Cu prior to and after chemical extractions or the particulates, indicates that the organic phase is the most important "sink" for Cu. The order of importance or the different phases in iIlite (IMt-1) and La Have sediments is:</p> <p>Organic > Fe-Mn oxide >>>> Clay mineraI (Illite)</p>