Spectroscopic study of aluminium speciation in removing humic substances by Al coagulation

Removal of humic substances (HS) isolated from swamp water. surface soil. p eat and brown coal by aluminium (Ai) coagulation under different conditions was studied using the jar test method and spectroscopic techniques. At low er pHs < 4.5, humic substances formed soluble complexes with Al3+ and the a mounts of these HS-Al complexes increased with increasing concentration of the humic substances. Maximum removal of the humic substances was found to occur in the pH range from 5.0 to. 7.0, due to the adsorption of humic subs tances on the surface of Al(OH)(3(s)) crystal. Sequential extraction of the humic substances adsorbed on Al(OH)(3(s)) using the Soxhlet technique with different solvents showed that the adsorption forces involved were great. The effects of humic substances on the Al speciation are discussed and a mo del is proposed-to explain the mechanism for the removal of humic substance s during the Al coagulation process. (C) 1999 Elsevier Science Ltd. Ail rig hts reserved.