Lead Stabilization Mechanisms of AlPO4 Prepared from Waste Acid Etchant in Municipal Solid Waste Incineration Fly Ash

Abstract

The purpose of this study was to find lead stabilization mechanisms for fly ash with AlPO 4 (WAP) synthesized from a waste-phosphorus solution produced from the etching process in liquid crystal manufacture and an Al(OH) 3 solution. The results of JLT 13 showed that the synthesized WAP had greater lead stabilization ability than commercial Al (OH) 3 (CAH). Two lead stabilization mechanisms were identified. One mechanism is a decrease in pH caused by the formation of Friedelʼs salt, apatite and aluminum hydroxide through the dissolution of WAP. In the presence of NaCl instead of CaCl 2 as a major salt in fly ash, Friedelʼs salt was observed using WAP and CAH. However, a decrease in pH using WAP and an increase in pH using CAH were observed. Neutralizing the alkali generated in Friedelʼs salt formation by phosphoric acid causes WAP to decrease pH in the presence of NaCl. The second mechanism was that dissolved phosphoric acid reacts with lead to form insoluble lead chloroapatite and lead phosphate. In addition, the result of a low pH leaching test suggested that WAP has a high lead stabilization ability in acid conditions.