In order to accurately simulate the fluidity and bioavailability of metals in soil and sediments, systematic adsorption studies are needed to consider the minerals that are characterized by heterogeneity.

　　The two important surfaces are iron oxide and silica, which are ubiquitous and interrelated in the environment and play an important role in the distribution of metals. This study focuses on the synthesis and characterization of such systems as iron oxide coated silica. The optimum conditions for producing SiO2 coated goethite are determined by using the three stage fractional factor study. The amount of coating achieved is 0.59 to 21.36mg Fe g (-1) solid. The most important factor in the use of adsorbed or precipitated coatings is the particle size of silica, which increases from an average of 0.85 to a 9.6mg Fe g (-1) solid as the size of silica decreases from 1.5mm to 0.2mm.

　　Other factors, including coating temperature, initial iron concentration and contact time, are not important. It was observed that the iron oxide coating was uneven and concentrated in the rough concave area. FTIR found band displacements and new bands indicating changes in the chemical environment of the FeO and SiO bonds; these results and wear studies show that the interaction between the oxide coating and the silica surface may involve chemical forces. Because the nanoscale iron oxide coating increased the surface area, introduced small pores and changed the surface charge distribution of silicon dioxide. Compared with the uncoated silica, the coating system showed a greater affinity for Ni.