Effects of Thermal Treatment on Mineralogy and Heavy Metal Behavior in Iron Oxide Stabilized Air Pollution Control Residues

Abstract

Stabilization of air pollution control residues by coprecipitation with ferrous iron and subsequent thermal treatment (at 600 and 900 °C) has been examined as a means to reduce heavy metal leaching and to improve product stability. Changes in mineralogy and metal binding were analyzed using various analytical and environmental techniques. Ferrihydrite was formed initially but transformed upon thermal treatment to more stable and crystalline iron oxides (maghemite and hematite). For some metals leaching studies showed more substantial binding after thermal treatment, while other metals either volatilized or destabilized with respect to leaching. Pb, in particular, exhibited increased reactivity following the formation of an ordered iron oxide structure at 900 °C. The thermal treatment had a positive effect on Cr release, which was reduced significantly at 900 °C in the presence of organic matter. Thermal treatment of the stabilized residues produced structures with an inherently better iron oxide stability. However, the concentration of metals in the leachate generally increased as a consequence of the decreased solubility of metals in the more stable iron oxide structure.

Stabilization of APC Residues from Waste Incineration with Ferrous Sulfate on a Semi-Industrial Scale

“…If Pb was confined inside an iron oxide structure, it presumably would only be released as the iron is released. This is consistent with the study performed by Sørensen et al, 13 who found Pb to be associated with the particle surface of an SD APC residue and an FA treated with the Ferrox process. Furthermore, Sørensen et al 13 mention that, in general, Pb 2+ cannot be incorporated in crystalline iron oxides because of the larger radius of the Pb 2+ ion.…”

“…This is consistent with the study performed by Sørensen et al, 13 who found Pb to be associated with the particle surface of an SD APC residue and an FA treated with the Ferrox process. Furthermore, Sørensen et al 13 mention that, in general, Pb 2+ cannot be incorporated in crystalline iron oxides because of the larger radius of the Pb 2+ ion. However, it is possible that Pb is associated with another phase formed during the treatment process.…”

“…Furthermore, gypsum and ferrihydrite previously had been identified in Ferrox-treated SD and FA. 13 A calculation of the total weight based on these minerals showed that the assumptions made (e.g., full oxidation) fit within 5-11% of the weight of untreated residues and within 2-5% of the weight of the treated residues. The greater difference for the untreated residues is probably caused by the presence of elements such as Al, which is not fully oxidized.…”

“…Subsequently, the suspension is aerated, thereby oxidizing Fe(OH) 2 to Fe(III) oxides in the form of ferrihydrite. 13 The trace metals are bound to the Fe(III) oxides during the process, resulting in low concentrations of trace metals in the wastewater. Easily soluble elements (e.g., Cl, Na, and K) dissolve during the process and are removed from the residue with the wastewater.…”

Treatment and use of air pollution control residues from MSW incineration: An overview

“…6 and 7 were prepared on the basis of their work, and we can conclude that S/S technology Ferrihydrite was formed initially but converted upon thermal treatment into more stable and crystalline compounds (maghemite and hematite). However, the overall effect of the Ferrox process followed by thermal treatment is an initially more contaminated leachate but the product obtained is more stable in the long term Sorensen et al (2000) ESP is at present in the maturing phase (Fig. 6), with a number of research projects aiming at optimizing the process.…”