Sludge-incinerated ash based shape-stable phase change composites for heavy metal fixation and building thermal energy storage

Incineration is a harmless way to treat municipal sludge. However, it is difficult to fix heavy metals in the sludge-incinerated ash (SIA). To fix the heavy metals and recycle the SIA effectively, this work innovatively proposed the SIA as skeleton material, and five shape-stable phase change composites (SSPCCs) with different mass ratios of SIA to NaNO3 (phase change material, PCM) were fabricated via the cold-compression & hot-sintering (CCHS) method. Then, key thermal performance, mechanical strength, and micromorphology were investigated while the chemical compatibility between the SIA components and NaNO3 was analyzed. Results showed that the SSPCCs could fix the heavy metals properly, and the SIA was suitable for skeleton material; The SSPCC with the mass ratio 5:5 of SIA to NaNO3 reached a maximal thermal energy storage (TES) density of 409.25 kJ/kg in the range of 100–400 °C, which had high mechanical strength of 139.65 MPa and good thermal stability; The SIA components demonstrated excellent chemical compatibility with NaNO3.