Perchlorate removal by quaternary amine modified reed

We report a kinetic and equilibrium study of perchlorate adsorption onto giant reed modified by quaternary amine (QA) functional groups in batch reactors. The effect of pH, contact time, and initial perchlorate concentration on removal was investigated. The adsorption capacity for perchlorate was 169 mg/g on the modified reed (MR) particles ranging in size from 100 to 250 μm. The isotherm results were best described by the combined Langmuir-Freundlich equation. Optimum removal occurred in the pH range 3.5-7.0 and was reduced at pH > 8.5. The maximum adsorption rate occurred within the first minute of contact and equilibrium was achieved within 7 min. A three-stage adsorption occurred. In stage 1, adsorption was rapid and was controlled by boundary layer diffusion. In stage 2, adsorption was gradual and was controlled by both boundary layer and intraparticle diffusion. In stage 3, adsorption reached a plateau. The kinetic results fit well with a pseudo second-order equation. The adsorption mechanism was explored using Zeta potential analysis and Raman spectroscopy. Zeta potential measurements showed that reed modification enhanced perchlorate removal by increasing the surface potential. Electrostatic attraction between perchlorate anion and positively charged quaternary amine groups on the MR was the primary mechanism responsible for perchlorate removal.