Release Behavior of Zinc and Lead from Molten Fly Ash

摘要

In order to obtain fundamental data for developing the recovery process of heavy metals from molten fly ash,the release of zinc and lead from the fly ash was followed under the conditions of a heating rate of 30 K/min,terminal temperatures from 873 to 1073 K and a holding time of 60min in a nitrogen stream with the use of a fixed bed.Polyvinyl chloride or carbon powders were mixed with the ash in an attempt to accelerate the release of zinc and lead.When a molten fly ash sample was heated at 1073 K without the additives,over 60% of the lead volatilized,but zinc did not volatilize at all.On the other hand,all of zinc and lead were released from the solid phase at the same temperature when polyvinyl chloride was added to the fly ash.XRD analysis showed that lead existed as oxides,while zinc was combined as a carbonate and an aluminosilicate in the raw fly ash.Lead and zinc were volatilized as chlorides via oxychlorides during heat treatment with addition of polyvinyl chloride.Both zinc and lead were released into the gas phase from the fly ash by heat treatment at 1073 K with addition of carbon powder.These results suggest that the addition of polyvinyl chloride and carbon powders is very effective for volatilization of zinc and lead from molten fly ash.