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

545.2.4 Environmental Scanning Electron Microscopy (ESEM)The ESEM micrographs of US and Alfa Aesar silica are taken at similar magnification.Considering that Alfa Aesar silica has an average particle size of 220 p.m, while that ofUS silica is 900 1.1,m, Figure 5.5 and Figure 5.6 were collected at lower magnification toshow the relative roughness of these two particles at larger scale. Both have relativelysmooth and rough areas on the surface. Figure 5.7 and Figure 5.8 show the surface ofAlfa Aesar and US silica particles at 1500x, respectively; similarly, both rough andsmooth parts of the surfaces. The surface roughness of Alfa Aesar and US silica particlesare comparable.Trivedi (2001) found that the goethite crystals are needle-shaped or acicular,approximately 0.5 to 1 pm in length, and goethite crystals aggregate into somewhatspherical particles. At a lower ionic strength of 10 -3, the largest particles wereapproximately 10 to 20 μm. The upper two figures in Figure 5.9 show the size and shapeof the goethite particles that will be used in this research, and the lower two figures revealthe 0.5-1.0 1.1m, needle-shaped goethite crystals at higher magnification. The ESEMresults are in agreement with Trivedi's (2001).From the ESEM analysis of the surface roughness of silica particles and the sizeof goethite particles, both Alfa Aesar and US silica are suitable for goethite coating.