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

11oxides. Because extraction methods suggest the mineral form, dissolution data arecommonly used for soil classification.In this study, dithionite citrate will be used for extracting both crystalline andamorphous Fe oxide, and hydroxylamine will be employed for amorphous Fe oxide. Theamount of crystalline Fe oxide is therefore the difference between the two.2.1.4 Coating FactorsThe amount of coating may be influenced by factors such as coating temperature, particlesize, surface area, roughness, and other characteristics of the supporting media. Wang(1995) applied 0.04 g Fe g -1 GAC and Fan (1996) applied 0.055 g Mn g -1 GAC in theirstudies to achieve higher coating efficiencies. Metal concentrations initially applied bymany researchers (Edwards and Benjamin, 1989; Stahl and James, 1991a, b; Wang, 1995;Fan, 1996; Khaodhiar et al. 2000; Kuan et al. 1998; Joshi and Chaudhuri, 1996;Stenkamp and Benjamin, 1994; Bailey et al. 1992) are usually in the order of 10-3 to 10-2g <strong>metal</strong> g-1 media. A <strong>metal</strong> concentration of 0.05 g Fe g -1 silica will be applied in thisresearch.One important variable affecting the degree of coating is temperature. Fan (1996)obtained more Mn oxide coatings on granular activated carbon (GAC) at 160 °C than 105°C, although the same concentration of Mn was applied. Edwards and Benjamin (1989)found that as Fe dose increased a much greater percentage of the surface was coveredupon heating (110 ± 10 °C) as opposed to precipitation without heating. Also, thecoatings produced with heating were observed to be more resistant to abrasion andexposure to mild acid solutions than those produced through alkaline precipitation (noheating). However, from their study it is not clear whether a difference in detachment