Pb Stabilization by a New Chemically Durable Orthophosphate Phase: Insights into the Molecular Mechanism with X-ray Structural Analysis

Environ Sci Technol. 2020 Jun 2;54(11):6937-6946. doi: 10.1021/acs.est.0c00643. Epub 2020 May 14.

Abstract

The rapid progression of piezoelectric technology and the upgradation of electronic devices have resulted in a global increase in Pb-based piezoelectric ceramic materials. In this study, the feasibility of incorporating Pb into a PbZr(PO4)2 double orthophosphate structure was evaluated by investigating the interaction mechanism of the perovskite with phosphate. The unique combination of X-ray absorption spectroscopy, selected area electronic diffraction, and Pawley refinement revealed that Pb was incorporated into a hexagonal structure and tetra-coordinated with oxygen in the phosphate-treated product. The chemical durability was enhanced through the structural alterations via Zr-O-P and Pb-O-P bond linkages. The stable phase encapsulating both Pb and phosphate showed effectiveness not only in stabilizing Pb but also in inhibiting P release as a secondary pollution risk within a wide pH range (1 ≤ pH ≤ 13). Despite the excellent chemical durability of the robust PbZr(PO4)2 crystalline phase, the increased Ti doping amounts at the Zr site resulted in a slight decrease in the lattice parameters and further enhanced the Pb stabilization effect through the formation of PbZrxTi(1-x)(PO4)2 solid solutions. This study demonstrates that the newly robust crystalline structure, developed through a well-designed thermal treatment scheme, provides an effective strategy for the treatment of Pb frequently encountered in electronic wastes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ceramics
  • Lead*
  • Phosphates*
  • X-Ray Absorption Spectroscopy
  • X-Rays

Substances

  • Phosphates
  • Lead