Heavy metal adsorption on iron oxide and iron oxide-coated silica ...

83to silica was deducted from that sorbed on the goethite-coated one and normalized to thetheoretical surface area of the coating. Comparing <strong>adsorption</strong> to discrete goethite, Nisorbed on coatings was approximately one order of magnitude greater (Figure 6.11insert), suggesting a larger specific <strong>adsorption</strong> capacity. Uygur and Rimmer (2000)reached similar conclusions for Zn <strong>adsorption</strong> on iron oxide-coated calcite. Theseobservations may suggest that the surface properties of discrete oxides may not beapplicable when modeling the oxide-coated system. In summary, the complementarysuite of analyses used in this research demonstrates that the presence of sub-micrometeriron oxide coatings at the mineral-water interface increased the <strong>adsorption</strong> capacity ascompared to the discrete oxide.6.3 SummaryIn summary, a model system — iron oxide-coated silica was synthesized andcharacterized. Adsorption and precipitation methods were used for producing goethitecoatings, which ranged between 0.59 and 21.36 mg Fe g -1 solid. A more crystalline formof iron oxide was achieved in <strong>adsorption</strong> than in precipitation potentially due to the effectof the substrate inhibiting crystallization. The degree of coating was highly sensitive tothe particle size of silica. Abrasion studies were found to be necessary in removing theloosely attached goethite particles and the interaction between goethite and silicapotentially involves chemical forces. The iron oxide coatings on the silica surface arenon-uniform increasing surface area and introducing small pores. The pHpzc of coatedsilica is between that of pure silica and iron oxide suggesting both silica and goethitesurfaces are important for <strong>adsorption</strong>. Ni <strong>adsorption</strong> on the coated silica is greater than