Application of X-ray diffraction to identify the phases formed during lead stabilization and resource recovery

Abstract

X-ray diffraction (XRD) has become one of the most powerful techniques for crystal structure studies and phase composition identifications. In this thesis, using the quantitative XRD (QXRD) technique to assist the development of reliable engineering strategies of stabilizing hazardous lead pollutants into ceramic matrix and resource recovery will be introduced. Metal stabilization strategies have been sought to replace the traditional disposal methods for the management of waste metal sludge. To demonstrate the unique capability of QXRD in monitoring the lead incorporation behavior, different ceramic precursors was used to react with lead oxide to investigating metal transformation mechanisms during the sintering process. When heating with alumina, influences of Pb/Al molar ratio, temperature, and treatment time on lead incorporation efficiency on the formation of PbAl2O4and PbAl12O19phasesweresuccessfully revealed by QXRD. Moreover, the influence of silica on lead stabilization effect was analyzed by blending amorphous SiO2 and quartz with -Al2O3 as the precursors. The results suggest that both silica precursors could crystallochemically incorporate lead into the lead feldspar (PbAl2Si2O8) structure in significant quantities. In addition, by sintering clay-based precursors with lead oxide, a complete lead incorporation into lead feldspar occurred above 950℃. Lead glass-ceramics were produced by thermally treating waterworks sludge with lead oxide, and amorphous contents in the products were quantified using QXRD. When hematite was used as a Fe-rich precursor to treat lead oxide, three types of lead ferrite crystals were observed and quantitatively determined. Furthermore, the mechanism of incorporating lead-zinc tailing with P-rich municipal waste sludge ash was investigated under different thermal conditions. By detailed X-ray diffraction analysis, Pb was crystallochemically incorporated into the Ca5.5Pb4.5(PO4)6(OH)2 crystalline structure and Zn was stabilized into Zn(Al0.5Fe1.5)O4 spinel phase. The stability of lead in all the product phases was evaluated byprolonged acid leaching, and the results indicated the lower intrinsic lead leachability of the product phases.

The progress in optimizing experimental parameters in resource recovery suggest an opportunity of using QXRD technique to investigate the feasibility of extracting Pb from CRT and recycling P by struvite precipitation. A novel process of thermal reduction treatment with the addition of metallic iron (Fe(0)) to recover lead from cathode ray tube (CRT) funnel glass was introduced. The optimal operational parameters for the thermal extraction of lead from CRT glass were determined by QXRD technique as 50 wt.% Fe addition, heating at 700 °C for 30 min. Struvite crystallization for phosphorus recovery from wastewaters has gained strong attention. While the aspects of application and modeling have been widely studied, the phase composition of recovered phosphorus products was rarely reported. The obtained high degree of accuracy supports the validity of Rietveld method for the quantification of both amorphous and crystal phases in the products. QXRD results suggest the amount of increase of struvite in the products with the elevated N/P molar ratio from 0.2/1 to 1.2/1. All the results have demonstrated the capability of QXRD in contributing to the advancements of both material and environmental technologies.