Correlation between mercury content and leaching characteristics in waste phosphor powder from spent UV curing lamp after thermal treatment

This study evaluated the correlation between the amount of mercury (Hg) compounds in waste phosphor powder from spent UV curing lamps and their leaching characteristics. The appropriate thermal treatment conditions and Hg content in the residue necessary to satisfy the leaching criteria for classification as non-hazardous waste were identified. The decomposition of Hg compounds by thermal treatment was also evaluated by comparing sequential extraction results based on thermal stability and leaching potential of Hg compounds. Before the thermal treatment, the Hg content in waste phosphor powder and concentration in the leaching extract were 108.7 mg-Hg/kg and 0.56 mg-Hg/L, respectively. Hg compounds with low thermal stability were removed rapidly during the initial stage of thermal treatment at temperatures between 400 °C and 600 °C. After thermal treatment, Hg in the form of an intermetallic compound, such as Sr-Hg, was expected to be remained mainly, and the Hg content was reduced to 13 mg-Hg/kg in the waste phosphor powder, at that point the residue satisfied the leaching standard limit (5 μg-Hg/L) for non-hazardous waste stipulated in the legislation of Republic of Korea.