Harmless treatment and resource utilization of incineration fly ash via integrated water washing and low-temperature thermal decomposition: a full-scale study

Incineration fly ash, a hazardous waste from municipal solid and hazardous waste incineration, contains heavy metals, soluble chlorides, and dioxins. A full-scale 'water washing + low-temperature thermal decomposition (LTD)' process for the treatment of incineration fly ash was evaluated in this study, which was conducted in a 20,000-ton/year project in Yancheng, China. Bench-scale tests were used to optimize washing parameters (30 min, 1:3 solid-to-liquid ratio, pH 6, 50-70°C) and LTD conditions (400°C, 45 min), achieving 99.5% dioxin removal - from 440.26 ng TEQ/kg in raw ash to 2.02 ng TEQ/kg. A significant reduction in heavy metal leaching was confirmed during full-scale operation. The treated fly ash was utilized in hollow brick production by mixing with cement, aggregates, and water in a mass ratio of 5:1:4:1, followed by moulding and curing. Additionally, crystalline salt was generated that met industrial standards, while hollow bricks were manufactured in compliance with GB/T 15229-2011 (compressive strength MU 10.0). This integrated technology facilitates the harmless treatment (via detoxification) of hazardous fly ash and the resource recovery of byproducts, thereby addressing the shortcomings of conventional landfilling and high-energy consumption processes. The approach establishes a scalable technical framework for the management of incineration fly ash, thereby contributing to the advancement of circular economy and environmental sustainability objectives.