Synchronous attenuation of metal ions and colour in aqua stream using tannin–alum synergy Original Research Article

The need to ameliorate the discolouration of the aqua system by soluble phenolics, in the use of tannin and tannin rich materials as a metal ion scavenger, without reducing the efficiency of the process necessitated this study. Tannin–alum synergy was used to remove metal ions (Cu, Zn, Cd and Pb) and the imparted colour from the aqua system. At lower alum dose, higher amounts of metal ions, in addition to the imparted colour by tannin was removed by the tannin–alum combination, when compared with the use of alum alone. The removal effieciency reduced, though minimally, as the pH of the solution increased from 3 to 6 and the percentage metal ion removal, for each metal ion, reduced when all metal ions were all present in a single solution but the colour removal efficiency was not affected. The metal–tannin interactions, studied using FTIR spectrophotometer, revealed an interaction between the –OH group and the metal ions.