Coagulation/flocculation process is regarded as an important environmental protection technology. finding wide application in water/wastewater treatment facilities. The continuous need for more efficient coagulation process has lead to the development of new modified coagulation reagents, such as polyferric silicate sulphate (PFSiS). The aim of the present study is to discuss the possible structure and investigate the surface morphology of PFSiS and, additionally, to evaluate the coagulation efficiency of the reagents by treating a typical ("model") kaolin-humic acid suspension, as well as a biologically pre-treated landfill leachate, in comparison with the relevant iron based, but non-modified coagulant (ferric sulphate, FS). The effect of preparation method, Fe/Si molar ratio, coagulant dosage and pH of test suspension on the destabilisation ability and coagulation behaviour of PFSiS was also discussed. Overall, it is suggested that PFSiS is an efficient coagulation reagent and it can be possibly considered as a promising option for tertiary treatment of wastewaters, especially for the removal of phosphate ions. Finally, it is emphatically shown that PFSiS exhibit a markedly better coagulation performance, than the non-modified iron-based coagulant (FS). (C) 2008 Elsevier B.V. All rights reserved.