The flow of solutions of sodium alkybenzene sulphonate through porous media
Abstract The hydraulic conductivity of columns of coarse sand, silica gel or soil aggregates has been found to be greatly reduced when water is followed by solutions of a commercial detergent containing a range of homologues of sodium alkylbenzene sulphonate (ABS c ). There was no reduction when either pure C 12 homologues of ABS were used, or pure quartz and ABS c , and the reduction was temporary in the case of sand and silica gel. The concentration of ABS c required to reduce flow through sand was 120–250 ppm. The upper limit corresponded approximately to the measured critical micelle concentration. ABS c was precipitated at lower calcium concentrations than some C 12 homologues and was also more strongly absorbed. Gel filtration indicated that about 20% of ABS c consisted of homologues higher than C 12 . It is suggested that the reduction in flow rate was due to partial blockage of the porous medium by a gel of calcium ABS c , the calcium being derived from the matrix by ion exchange. With continued flow, the exchangeable calcium was depleted and the gel started to dissolve. Simultaneously the flow rate increased, unless ion exchange in itself had caused irreversible swelling of the matrix.