Synergistic effect of polyvinyl chloride and coal ash on thermal separation of heavy metals from MSWI fly ash through molten salt process

Municipal solid waste incineration fly ash (FA) contains high contents of salts and high concentrations of heavy metals, which makes FA disposal extremely difficult. However, heavy metal elements could potentially be separated from FA during thermal treatment process to make it possible to be recycled. This work aims to study the volatilization of heavy metals in FA treated by molten salt method. The influence of polyvinyl chloride (PVC) and coal ash (CA) on volatilization of heavy metals was investigated. Within the scope of this study, the highest heavy metal removal rate can be under the condition: the calcium chloride/sodium chloride weight ratio 1:1, the FA/molten salt weight ratio 1:10, treatment temperature 1000°C for 2 hours in reducing atmosphere. The volatilization rates of lead, zinc, copper, chromium and manganese were 86.20, 67.53, 65.24, 50.07 and 39.45%, respectively. On the basis of molten salt treatment, adding PVC could promote the volatilization of heavy metals. The volatilization rate of lead was 96.71%, and the volatilization rates of chromium and manganese were higher than 60% when the content of PVC was 5 wt%. When adding 10 wt% CA and 1 wt% polyvinyl chloride, the volatilization rate of lead could reach 100%. The experiments and thermodynamic calculations showed that silicon dioxide and aluminium oxide in CA and hydrochloric acid decomposed from PVC could promote the chlorination and volatilization of heavy metals. The volatilized heavy metal chlorides provided the possibility of recovery and utilization of heavy metals in FA.