Abstract:
This study focused on the recovery value of zinc from both boiler ash (BA) and fly ash (FA) in medical waste incineration systems and put forward a chemical leaching procedure for recovering zinc oxide (ZnO). The procedure included sequential steps of pretreatment, citric acid leaching, precipitation separation, drying, and calcination. The element contents at each stage and the effect of pH value on ZnO yield and content were analyzed, and the feasibility was evaluated from the technical and economic viewpoints. The result showed that with the increase of pH, ZnO yield and content decreased gradually. The optimal parameters were identified as follows: pH value 2, pickling temperature 25 ℃, pickling duration 12 h, calcination temperature 400 ℃, and calcination duration 2 h. Under these conditions, the extraction efficiency was relatively high while the cost remained low, yielding 0.077 kg ZnO per kg BA and 0.036 kg ZnO per kg FA, with a recovery efficiency reaching 70% or higher. Economic analysis indicated that the recovering cost of 12.33 CNY/kg ZnO from BA and 10.78 CNY/kg ZnO from FA. The total profit could reach up to 2 400 CNY per ton, with an investment payback period of approximately 3.63 years, demonstrating significant economic benefits. These findings provide critical references for the resource utilization of medical waste incineration residues.