Modified red clays as adsorbents in the removal of cationic dyes from aqueous solutions

Thermal and thermo-chemical modification methods were applied to a red clay mineral and the resulted products were comparatively studied. The modified clays were characterized by XRD, XRF, UV-vis and FTIR spectroscopy. The adsorption properties towards two cationic dyes, namely methylene blue and crystal violet, were investigated and the effect of initial concentration and contact time was analyzed, revealing superior adsorption properties for the thermo-chemical modified clay. The values of dye removal rate are very high, over 85%, with better adsorption of methylene blue and a competition between dyes as demonstrated by using binary solutions. The best match with the experimental results was obtained for the pseudo-second-order kinetic model.