Fabric effect on hydraulic conductivity of kaolin under different chemical and biochemical conditions

A reasonably less permeable compacted clay liner (CCL) is critical to the long-term safety of waste containment facilities. This study experimentally investigates a variety of factors, including salinity, pH, fluctuation in permeant, permeation duration and presence of microorganisms, that are found to influence the hydraulic conductivity (k) of consolidated kaolin and the fabrics of suspended kaolin. Amongst these factors, a reduction in hydraulic conductivity of up to 4 orders of magnitude is obtained from the modification of the microfabrics of kaolin; a reduction of 2 orders of magnitude is brought about by bioclogging; a reduction of 1 order of magnitude is related to the concentrated Ca solution (>10 mM). The hydraulic conductivity of consolidated kaolin can obviously be changed by adjusting the fabrics of the kaolin particles, e.g., clogging the pore spaces with bioslurry, permeating them with alkaline solution, or transforming the kaolin into metakaolin. An effluent pH larger than the isoelectric point (pHIEP) leads to a rapid reduction in k until 1×10–11 m/s. A 3-dimensional fabric map was established for kaolin suspension in contact with a wide range of Ca concentrations and pH levels. The fabrics of kaolin suspension are predominated by a salt concentration (C>2.0 mM) and a pH solution (C<2.0 mM), respectively.