Effect of Cl Removal in MSWI Bottom Ash via Carbonation with CO₂ and Decomposition Kinetics of Friedel’s Salt

Abstract

In this study, the effect of Cl removal in bottom ash via a carbonation treatment with CO₂ was investigated by comparing it with a water washing treatment. First, this was also focused on examining the existence of Cl contained in the bottom ash. The overall (soluble and insoluble) Cl content was close to that of bottom ash with fine particle. Next, the washing with water was confirmed and it was not effective in decreasing the Cl content because of the existence of insoluble Cl. Whereas, the removal effect of Cl via carbonation with CO₂ was very high compared to the washing treatment because of the decomposition of Friedel’s salt (main insoluble Cl).

In addition, the kinetics data pertaining to the decomposed Friedel’s salt as the carbonation process proceeds was confirmed. The theoretical was well fitted to the kinetics data. The variation of the rate is constant upon decomposition with the reaction temperature followed the Arrhenius equation (19.676 kJ/mol of activation energy) and the orders with respect to water-to-solution and particle size were also obtained. The decomposition rate of Friedel’s salt based on diffusion through the product layer of shrinking core model could be expressed by the equation.

Fig. 10 Effect of particle size on the decomposition kinetics of Friedel’s salt (a) and effect of particle size on the decomposition rate constants (b) (30% CO₂ concentration, 10 mL/g water-to-solid, and 20°C temperature). d₀ indicates the mean diameter of bottom ash; 75 µm, mean of under 0.15 mm; 225 µm, mean of 0.15–0.3 mm; and 450 µm, mean of 0.3–0.6 mm.