Hydrothermal treatment of incineration fly ash for PCDD/Fs decomposition: the effect of iron addition

Abstract

The catalytic effect of Fe addition on the decomposition of polychlorinated dibenzo-dioxins and polychlorinated dibenzofurans (PCDD/Fs) contained in municipal solid waste incineration (MSWI) fly ash during the hydrothermal process was investigated. Influencing factors, such as Fe addition mode, reaction time and cooling procedure after reaction, were tested to evaluate their effects. Experimental results indicated that Fe addition in the form of a mixture of ferrous sulphate and ferric sulphate enhanced decomposition of PCDD/Fs contained in the MSWI fly ash, particularly for the decomposition of 2,3,7,8-tetrachlorodibenzo-dioxin and 2,3,7,8-tetrachlorodibenzo-furan under the reaction temperature of 563 K. The decomposition rate of PCDD/Fs reached 90.33% by international toxicity equivalent (I-TEQ) when Fe was added as a mixture of ferrous and ferric sulphates by 5% (wt/wt) with the Fe (III)/Fe (II) ratio being 2; without Fe addition, the decomposition rate of PCDD/Fs was only 46.17% by I-TEQ in the same process. Fe addition in the form of ferrous sulphate alone also showed an enhancing effect on PCDD/Fs decomposition, but the associated decomposition rates were relatively lower, suggesting iron oxides formed from the mixture of ferric and ferrous sulphates are more favourable catalysts. At the same time, the cooling procedure after the hydrothermal reaction became more flexible if Fe was added in the form of a mixture of ferric and ferrous sulphates. Although a longer reaction time was helpful to increase decomposition rates of PCDD/Fs, 1 h was proved to be a reasonable time under this condition.

Stabilization and separation of heavy metals in incineration fly ash during the hydrothermal treatment process

“…Pre-treatment + HT process + Phosphate addition afterwards Water wash as pre-treatment Very slightly Good Acid wash as pre-treatment Good Good but not necessarily None pre-treatment + HT process + subsequent phosphate addition None Moderate to good None pre-treatment + HT process + subsequent acid washing Moderate to good helpful Water-washing pre-treatment + HT process + acid wash afterwards Moderate helpful Acid wash pre-treatment + HT process Good Good a Ferric/ferrous salts addition during HT process is always needed for the purpose of PCDD/F decomposition [24].…”

“…Moreover, the HT processes were reported to have destruct on effect on dioxins contained in the MSWI fly ash [23][24]. However, when the HT products of MSWI fly ash were subjected to the subsequently issued leaching standard, namely the Acetic Acid Buffer Solution Method (HJ/T 300-2007) [25], sometimes the leaching concentration of Pb exceeded the limitations of the sanitary landfill entrance standard [26], indicating that further stabilization or pre-treatment was required for environmentally sound management of MSWI fly ash with respect to heavy metal issue.…”

Effects of Microwave-Assisted Hydrothermal Treatment on the Major Heavy Metals of Municipal Solid Waste Incineration Fly Ash in a Circulating Fluidized Bed

“…15,16 Furthermore, it has been successfully applied to fly ash in alkali solutions, both coal fly ash 17 and MSWI fly ash. 7,18,19 Hydrothermal process has been successfully applied for the reason that it can convert fly ash or other hazardous materials into more stable forms by stabilization 20 or extraction. 21 Aluminum silicate was found after hydrothermal treatment in alkaline solution, which contributed to the stabilization of fly ash and an increase of the residual form.…”

“…Moreover, thermal treatment is too costly to be practiced on a large scale in developing countries. It is a growing trend that hydrothermal processes will become a promising technology for fly ash disposal because it offers considerable merits in terms of economic, technical, and environmental effectiveness. , Furthermore, it has been successfully applied to fly ash in alkali solutions, both coal fly ash and MSWI fly ash. ,, Hydrothermal process has been successfully applied for the reason that it can convert fly ash or other hazardous materials into more stable forms by stabilization or extraction . Aluminum silicate was found after hydrothermal treatment in alkaline solution, which contributed to the stabilization of fly ash and an increase of the residual form .…”

Stabilization of Heavy Metals in Municipal Solid Waste Incineration Fly Ash in Circulating Fluidized Bed by Microwave-Assisted Hydrothermal Treatment with Additives

“…Recent studies have shown that additives can be used to improve the hydrothermal process. Alkali metals are popular additives in the hydrothermal process, as reported by Jin et al, Chen et al, and Hu et al Hu et al found that the leaching of Cu, Pb, and Cr from fly ash was controlled during the hydrothermal process with ferric/ferrous salt with acid washing pretreatment. Li et al indicated the leaching of toxic heavy metals could be effectively reduced with silica fume additions, because of the formation of C–S–H.…”