Identification of pyromorphite in mine‐waste contaminated soils by ATEM and EXAFS

Abstract

Calcium-rich pyromorphite [Pb5(P04)3Cl] has been positively identified as the major lead-bearing phase in mine-waste soils from the South Pennine Orefield, UK, by a combination of EXAFS spectroscopy, ATEM and XRD. Evidence for a pyromorphite-like structure was provided by electron diffraction of individual Ca-rich, lead chlorophosphate grains in the soil using ATEM. Approximate unit-cell parameters derived from electron diffraction were used to identify peaks on the powder XRD trace obtained from the soil sample, allowing the cell parameters to be refined. The unit-cell parameters derived for the Ca-rich pyromorphite [a = 0.9789 (7), c = 0.726( 1) nm] are smaller than those reported for pure end-member pyromorphite (a = 0.998, c = 0.733 nm; Baker, 1966) and are sufficiently different to prevent positive identification by conventional XRD analysis. Lead absorption spectra and interatomic distances obtained from EXAFS performed on bulk soils confirmed the predominance of pyromorphite-like structure. EXAFS is shown to be a useful tool in the identification of soil minerals. It gives information about the local environment of one specific element in solids, be they crystalline or amorphous, and is unaffected by the limited chemical substitution of Ca for Pb.The identification of impure Pb minerals in soil by techniques other than XRD suggests that previous studies, based on XRD, may have underestimated the amount of soil Pb present as discrete Pb compounds.

Measuring the solid-phase fractionation of lead in urban and rural soils using a combination of geochemical survey data and chemical extractions

“…A possible explanation for component 3 comes from literature studies in which a number of research groups show that Pb derived from anthropogenic sources where significant concentrations of P also exist results in a relatively stable form in soils as chloropyromorphite (Pb 5 (PO 4 ) 3 Cl) or similar pyromorphite minerals (Hettiarachchi and Pierzynski 2004;Cotter-Howells et al 1994;Scheckel et al 2005 -Howells et al 1994). This is in agreement with the composition of component 3 which clearly contains Pb, P and possibly Ca (Fig.…”

Characterization and speciation of mercury-bearing mine wastes using X-ray absorption spectroscopy

“…Synchrotron radiation-based XAS has been shown to provide direct, in situ information on heavy metal speciation, and has been used successfully for such elements as arsenic, lead, and Ž zinc Cotter-Howells et al, 1994;Manceau et al, 1996;Hesterberg et al, 1997;Foster et al, 1998;. Morin et al, 1999;Ostergren et al, 1999 .…”

Factors influencing metal bioavailability in soils: preliminary investigations for the development of a critical loads approach for metals

“…Furthermore, Nriagu (1984) showed that Pb phosphate minerals such as pyromorphite and plumbogummite could precipitate in a wide variety of soils and sediments. Cotter-Howells et al (1994) found pyromorphite to be the major Pb bearing phase in a study of mine waste soils. Precipitation of Cd in the carbonate, phosphate, sulphate and chloride forms has also been reported, generally in non-acidic conditions (Street et al, 1977;Jones and Jarvis, 1981;Moir, 1992).…”