Quench-Layer-Based Model for Leaching Prediction of MSWI Bottom Ash

The water-based cooldown process (quenching) of Municipal Solid Waste Incineration Bottom Ash (MSWI BA) after incineration may adversely affect its leaching by forming a highly contaminated quench layer on BA particles. A model is proposed to rapidly estimate the leaching of potentially toxic elements from this MSWI BA quench layer.

The semi-empirical model is based on calculating the quench-layer-to-core ratio for size fractions for the particle size range from < 63 µm to > 22.4 mm and building leaching profiles for each element. A particle core and quench layer get assigned contribution values based on only two experimental points: leaching data for the largest (the minimum role of the quench layer) and smallest (quench layer domination) fractions of the test sample.

The calculated leaching profiles for major anions, alkali and alkaline-earth metals, and copper for a set of 18 narrow fractions demonstrate good leaching prediction, the underestimation error is –(10–20)%. For Ba, Sr, and Sb, the model provides a satisfactory error of 30% mainly due to contribution of core leaching; for Ni, Mn, and Zn, > 50%.

Adequate modelling for most elements shows that, despite MSWI BA complexity, a simple semi-empirical model can predict the leaching behavior using a limited experimental dataset and supports the assumption of quench layer contribution to the total MSWI BA leaching.