Adsorption characteristics of Direct Red 23 azo dye onto powdered tourmaline

The high electric field on the surface of tourmaline particles has a potential of enhancing electrostatic reactions during adsorption. However, information concerning the adsorption characteristics of dyes onto tourmaline is currently unavailable. In the present study, the behavior and efficiency of powdered tourmaline (PT) in removing the diazo Direct Red 23 (DR23) dye from aqueous solution were investigated. The observations from batch adsorption experiments indicated that the adsorption was more favorable under low adsorbate surface loading, low pH, high temperature, and low ionic strength conditions. A homogeneous particle diffusion model (HPDM) was used to characterize the process, and the rate of adsorption was found to be controlled by intra-particle diffusion. An activation energy of 4.54 kcal/mol was calculated, suggesting that the adsorption proceeded with a low energy barrier and that a physisorption was involved. The functional groups binding anionic DR23 on the PT particles were also identified. A maximum adsorption capacity of 153 mg/g was determined according to the Langmuir isotherm. The PT was subjected to a total of 5 regeneration runs without losing much of its dye-adsorption capacities. Due to its low price, abundant availability, and superb adsorption capacity, PT has a great potential for use as an effective adsorbent in removing DR23 from aqueous solutions. (C) 2016 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.