Swelling and consolidation behaviour of polymerised bentonites with cation solutions

The objective of this study is to develop a novel method for producing polymerised bentonite (PB) that will have a high swelling capacity and low permeability when treated with aggressive cation solutions. PBs with polymer-to-bentonite ratios of 0.1 (0.1PB) and 0.2 (0.2PB) were produced using natural sodium bentonite (UB) and two monomers (acrylic acid (M ₁) and acrylamide (M ₂)) by a free-radical polymerisation method. The optimum conditions for polymerisation were an M ₁/M ₂ ratio of 0.5, initiator (I) to monomer I/(M ₁ + M ₂) ratio of 0.5% and a pH of 6. Instead of using nitrogen gas, a vacuum pressure was used to remove oxygen during the polymerisation process. The results of X-ray diffraction test showed that 0.2PB is an intercalated composite. The results of free swelling index (FSI) and swelling pressure tests indicated that the PBs have higher swelling capacities than UB (e.g. in 0.6 M sodium chloride (NaCl) solution, the FSIs of PBs were more than 24 ml/2 g). In terms of consolidation behaviours, the compression indexes of PBs were higher than those of UBs. For given void ratios, the permeabilities of PBs calculated from the results of consolidation tests were smaller than 10⁻¹⁰ m/s for 0.6 M sodium chloride solution.