Diatomite and manganese oxide modified-diatomite (Mn-diatomite) were tested for heavy metal removal from wastewater. Impregnating the diatomite surface with 0.38g g(-1) of manganese oxide gave a 2.4-fold increase in the adsorbent surface area. Equilibrium studies demonstrated that diatomite has a higher removal capacity for pb(2+), Cu2+ and Cd2+ from water than untreated diatomite. Furthermore, the adsorption capacity of Mn-diatomite increased by decreasing the quantity of manganese oxides deposited on the surface. Electronic microscopy was carried out to study the effect of heterogeneity, modification and diatomite frustule type on adsorption. Both centric and pennate types of diatomite were present. The scanning micrographs also indicated the birnessite structure of manganese oxides, which is characterised by a platy-like-crystal structure. Adsorption kinetics confirmed the effectiveness of the manganese chemical treatment, which also significantly improved the diatomite filtration properties. (C) 2004 Elsevier B.V. All rights reserved.