Quantification of Au nanoparticles retention on a heterogeneous rock surface

Colloid-mediated contaminant transport within geological media is still not fully understood, mainly because the mechanisms that lead to colloid retention onto the rock walls are not clear and are difficult to quantify. tudy presents an experimental methodology to quantify at a mineral scale colloid surface distribution coefficients (Ka) in a heterogeneous rock surface (granite). The retention of negatively charged Au nanoparticles of different size (2, 40 and 100 nm) was analyzed in static (batch) experiments. Two different pHs were used to account for different rock–colloid electrostatic interactions: the first one when the rock has some positively charged minerals and the nanoparticles are negatively charged (favorable electrostatic attraction) and the second case where all granite minerals and the Au nanoparticles are negatively charged (unfavorable electrostatic attraction). cro-Particle Induced X-Ray Emission (μPIXE) technique was used to visualize and quantify the colloid retention on the granite surface. Colloid surface distribution coefficients were measured on the main minerals composing the rock. favorable case, higher Ka values were observed on the minerals bearing positive charge and a Ka dependence on the colloid size was observed. However, non-negligible Ka values were measured also on negatively charged minerals, without clear size dependence effects. The main mechanisms responsible for colloid retention in these unfavorable areas were analyzed. They were mostly related to higher porosity of certain minerals or to physical defects of the granite surface (roughness, grain boundaries). stribution coefficients obtained in this study can be used as input data for theoretical description of colloid transport in fractures.