Removal of Congo red, methylene blue and Cr(VI) ions from water using natural serpentine

Natural layered magnesium silicate mineral (serpentine) was investigated as an adsorbent material for three common water pollutants (methylene blue dye, Congo red dye, and Cr(VI) metal ions). The adsorption properties of serpentine were explored as a function of contact time, serpentine dosage, initial concentrations and the initial pH value. The kinetic studies uncovered that the equilibrium time for the adsorption of Congo dye, methylene blue dye, and Cr(VI) ions was acquired after 180 min, 240 min, and 480 min, respectively. The uptake process of all the examined pollutants is chemical adsorption and represented by pseudo-second-order kinetic model instead of by Intra-particle diffusion and Elovich kinetic models. The adsorption equilibrium modeling of methylene blue and Cr(VI) was described as a monolayer adsorption and fitted well with Langmuir model rather than with Freundlich or Temkin isotherm models. The adsorption of Congo red dye occurred in a multilayer form and fitted well with Freundlich isotherm than the other studied models. The adsorption of the three pollutants controlled for the most part by the pH value. The basic media is promising for the removal of methylene blue, while the acidic conditions are favored for the adsorption of Congo red dye and Cr(VI) metal ions. The thermodynamic parameters revealed that the adsorption of methylene blue dye is endothermic reaction while the adsorption of Congo red dye and Cr(VI) metal ions is an exothermic reaction. Modifying the serpentine surface through acid and thermal activation improve the removal of the contemplated pollutants to a high degree. Acid leached serpentine utilizing HCl acid of 15%concentration and thermally activated serpentine at 200 degrees C are the best-modified products for maximum removal of Congo red dye, methylene blue dye, and Cr(VI) metal ions. Fixed bed Colum study gives the best results at bed thickness 3 cm, flow rate 5 mL/min and initial concentration 25 mg/L. (C) 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.