Treatment of waste incinerator air-pollution-control residues with FeSO4: Concept and product characterisation

Abstract

This paper describes a new concept for treatment of air pollution-control (APC) residues from waste incineration and characterises the wastewater and stabilised residues generated by the process. The process involves mixing of APC-residues with a ferrous sulphate solution and subsequent oxidation of the suspension (Ferrox-process 1996). The process results in a significant reduction in the leaching of salts and heavy metals from the residue, by washing out most of the salts and by binding the heavy metals in the iron oxides formed. In the laboratory, a semidry gas-cleaning residue and a fly ash were treated by the process. The generated wastewater contained low concentrations of heavy metals (e.g. Pb: 27-39 microg l(-1) and Cd: 2.6-4.6 microg l(-1)), but high concentrations of salts (e.g. Cl, Na, K, and Ca). The treatment process redUced the leaching of Pb from the residues by more than two orders of magnitude at fixed pH as determined by pH-static leaching tests. Likewise, the leaching of Cd, Zn and Cu was significantly reduced. The effect on elements that form oxyanions (e.g. Cr) is marginal and in the current process there is no reduction in the release of Hg.

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

“…The results for S were expected, because S was added as FeSO 4 as a part of the treatment and in highest quantities in the case of SD (see Table 1). A comparison of the achieved results with the laboratory studies reported in Jensen et al 8 and Lundtorp et al 9,10 shows that the leaching properties are the same even though the process has been developed with changes in both the process and the scale. This indicates that the leaching properties of treated residues are very robust and only slightly affected by variations in the process.…”

“…[8][9][10] The process is based on the established facts that many trace metals in natural environments, such as those in soils and sediments, are bound to iron oxides 11 and that engineered iron oxides are able to bind substantial amounts of trace metals. 12 In the Ferrox process, the alkaline APC residue is mixed with an FeSO 4 solution.…”

“…The pilot plant studies build on the results from the laboratory-scale studies [8][9][10] but provide much better insight into scale-dependent issues such as process control, aeration of the suspension, filtration, and washing of the treated residues and provide much more reliable data on wastewater composition, leaching characteristics of treated APC residues, and mass balances. The primary objective of the Ferrox process is to treat the APC residues so they can be landfilled in a safe way with a minimum of emissions to the environment.…”

Fly Ash Pollutants, Treatment and Recycling

“…Aeration oxidised the precipitated ferrohydroxide to ferrihydrite and the suspension was then separated into treated residue and wastewater. This process was reported to leach out large amounts of salts (Cl, Na, K and Ca) but low concentrations of trace metals (Pb and Cd) from FA residues (Lundtorp et al 2002). Hu (2005) studied the effectiveness of mixing FeSO 4 and Fe 2 (SO 4 ) 3 solutions with FA residues in order to stabilize heavy metals and they concluded that the solution reacted with the FA to form Ca 4 Fe 9 O 17 , which coated the surface of ash particles, and for that reason the heavy metal releasing was decreased.…”

“…The Ferrox ® -process was developed in Denmark as an on-site treatment for FA residues prior to landfill disposal (Lundtorp et al 2002;Jensen et al 2002). The process consisted in mixing of three mayor units that were ferrous sulphate solution, recycled water and FA residues; suddenly the oxidation of ferrous iron took place followed by pH adjustment with either additional FeSO 4 or H 2 SO 4 and finally, in a plate-and-frame filter press, the treated residue was dewatered.…”