Kinetic analysis of anionic surfactant adsorption from aqueous solution onto activated carbon and layered double hydroxide with the zero length column method

Low cost adsorption technology offers high potential to clean-up laundry rinsing water. From an earlier selection of adsorbents, layered double hydroxide (LDH) and granular activated carbon (GAC) proved to be interesting materials for the removal of anionic surfactant, linear alkyl benzene sulfonate (LAS), which is the main contaminant in rinsing water. The main research question is to identify adsorption kinetics of LAS onto GAC-1240 and LDH. The influence of pre-treatment of the adsorbent, flow rate, particle size and initial LAS concentration on the adsorption rate is investigated in a zero length column (ZLC) set-up. The rate determining step is obtained by fitting an adsorption model and an ion exchange model describing intraparticle diffusion to the experimental data. GAC-1240 is well described with the adsorption model following Fick's second law. The effective diffusion coefficient of GAC-1240 is 1.3 × 10-10 ± 0.2 × 10-10 m2/s and is not influenced by particle sizes or initial LAS concentrations. The ion exchange of LAS onto LDH is not well described by the ion exchange model. The rate determining step is obtained by comparing several models to different experimental data. A double layer model resulted in a good description of the experimental data. At the outer surface of LDH a stagnant film resistance originating from an electric double layer is assumed. The double layer mass transfer coefficient is 7 × 10-5 ± 2 × 10-5 m/s.