Analysis of latex, gold and smectite colloid transport and retention in artificial fractures in crystalline rock

The transport behavior of artificial (gold and latex) and natural (smectite) colloids within artificial fractures in natural crystalline rock was analyzed. The selected colloids presented different size, shape, density and surface charge: the effects of these parameters on their transport and retention in the fractures were evaluated in conjunction with the effects of the hydrodynamic characteristics of the system (water velocity/residence time in the fracture and fracture width). that, in crystalline rock fractures, all the analyzed colloids travel as fast as or faster than water (retardation factors, Rf ≤ 1). Different parameters were identified to simultaneously control the velocity of colloids in the fracture, and an efficient analysis of Rf values could be performed relating them to the Taylor dispersion. This parameter accounts for the Brownian diffusion (colloid size), the mean water velocity and the fracture width. e experiments were carried out under unfavorable electrostatic conditions (rock and colloids both negatively charged) and, in spite of clear exclusion effects observed, colloids were retained on the fracture surface. Under similar water velocities, the recovery of smectite colloids was always higher than that of latex and gold colloids, most probably due to the different morphology of the particles. d retention was observed mainly in zone of the rock with defects, micro-fractures and grain boundaries and increased significantly as the water flow rate decreased. The retention behavior observed could not be totally explained considering only sedimentation and Brownian motion effects.