Effect of different sulfides on cadmium distribution during sludge combustion based on experimental and thermodynamic calculation approaches

Abstract

The effects of sulfur compounds on the migration of a semi-volatile heavy metal (cadmium) during sludge incineration were investigated with two methods, i.e., experiments in a tubular furnace reactor and thermodynamic equilibrium calculations. The representative typical sludge with and without the addition of sulfur compounds was incinerated at 850 °C. The partitioning of Cd among the solid phase (bottom ash) and gas phase (fly ash and flue gas) was quantified. The results indicate that sulfur compounds in the elemental form and a reduced state could stabilize Cd in the form of CdS, aluminosilicate minerals, and polymetallic sulfides, whereas sulfur in the oxidized forms slightly increases Cd volatilization during incineration. For Cd solidification points, the inhibition effect on the volatilization of Cd is as follows: S > Na2SO4 > Na2S. Chemical equilibrium calculations indicate that sulfur binds with Cd and alters Cd speciation at low temperatures (<950 K). Furthermore, SiO2- and Al2O3-containing minerals can function as sorbents stabilizing Cd as condensed phase solids (CdSiO4 and CdAl2O4) according to the results of equilibrium calculations. These findings provide useful information for understanding the partitioning of Cd and thus facilitate the development of strategies to control Cd volatilization during sludge incineration.

Thermal Behavior of Cd During Sludge Incineration: Experiments and Thermodynamic Equilibrium Model

“…The homogenized sludge samples were passed through a sieve with a mesh size of , 150 lm and stored in jars at room temperature. Table 1 shows the properties of dried sewage sludge employed (Liu et al, 2015).…”

“…This entire set is an effective experimental approach to simulate the migration and distribution of heavy metals in a real incinerator (Chiang et al, 1999). The detailed descriptions were presented in the literature of Liu et al, (2013Liu et al, ( , 2014Liu et al, ( , 2015. A quartz tube burner was placed in a glass-fiber-lined insulated steel shell, and a quartz boat moved by a quartz rod was used to feed the dry sludge into the combustion chamber.…”

“…However, the number of reaction products is limited in the FACTsage software, which results in some deviation from the actual situation. On the other hand, the chemical thermodynamic equilibrium calculations can predict the heavy metal transformations under ideal conditions in the diverse and complex incineration system, but these calculations are not validated by experimental means (Liu et al, 2015).…”

Experimental investigation on co-combustion kinetics and gas emission law of sewage sludge-bituminous coal

“…From Wang et al, low temperature (800°C) and low oxygen concentration (10%) can be concluded to achieve reasonable control of heavy metal elements, but at the expense of reducing the combustion efficiency and destroying the integrity of the whole combustion process. Jing‐Yong Liu et al reported that sulphur can promote cadmium fixation in slag in the form of CdS and aluminosilicates among others in a local‐reducing atmosphere. The control of pollutants in the exhaust gas has also gained attention.…”

Thermodynamic Equilibrium Calculations on Cd Transformation during Sewage Sludge Incineration

“…Alternately, Cadmium (Cd) is one of the most heavily regulated heavy metals in the standard for pollution control of MSW incineration, in which the Cd emission concentration limit is 0.1 mg/m 3 in China under the standard state of a concentration of 11% (v/v)O 2. To understand the transfer of Cd during the sludge incineration, it is necessary to study the influence of combustion conditions, such as temperature, gas composition, residence time and the presence of reactive compounds (chlorine, sulfur, or aluminosilicates), on the final Cd speciation in the residues (Han et al, 2006;Liu et al, 2013;Liu et al, 2015).…”