Pyromorphites

Braun, n. brown, -bleisrz, n. pyromorphite. Brkune,/. qmnsy angina brownness (Min.) — Braunerz,... 

Phosphor-athcr, m. phosphoric ether (ester of phosphoric acid, specif, ethyl phosphate), -basis, phosphorus base, -bestimmung, /. determination of phosphorus, -blei, n. lead phosphide Min.) pyromorphite. -bombe, f. phosphorus bomb. -brandgranate, /. phosphorus incendiary shell, -brei, m. phosphorus paste, -bromid, n. phosphorus bromide, specif, phosphorus pentabromide, phos-phorus(V) bromide, -bromijr, n. phosphorus tribromide, phosphorus(III) bromide, -bronze, /. phosphor bronze, -calcium, n. calcium phosphide, -chlorid, n. phosphorus chloride, specif, phosphorus pcntachloride, phosphorus(V) chloride, -chloriir, n. phosphorous chloride (phosphorus trichloride, phosphorus(III) chloride), -dampf, tn. phosphorus vapor or fume, -eisen, n. ferrophos-phorus iron phosphide, -eisensinter, m. diadochite. 

In sediments of the Mezica mining and smelting area, mineral phases such as cerussite (PbC03), galena (PbS) (Fig. 2), pyromorphite (Pb5(P04)3CI), descloizite (PbZn(V04)(0H)), bindheimite... 

The principal lead oxide minerals include pyromorphite, wulfenite, mimetite and plum-bojerusite. Some galena is also present in this ore type. The principal gangue minerals include silicate, dolomite, siderite, ferohydrooxides and clay minerals. About 20% of the ore is represented by ultra-fine slime with an average size of K%0 = 12 pm. These slimes are composed of Fe-hydroxides, kaolin and slimes of plumbojerusite, rich in silver. 

Pyromorphite belongs to the apatite group. This group is divided into two series, the apatite series and pyromorphite series. These minerals are isostruc-tural, however the unit cell volume of pyromorphite is about one-fifth larger... 

Fig. 4.26. a-d Laser-induced time-resolved luminescence spectra of pyromorphite demonstrating Ce, Sm and possibly Pb centers... 

Caldte, Feldspars, Hardystonite, Pyromorphite, Scheelite, Zircon, Baddeleyite... 

Figure 4.26 demonstrates the time-resolved liuninescence of pyromorphite under 355 and 266 nm laser excitations. Luminescence lines of Eu + are clearly seen in both cases. 

As was described earlier, evidently Ce " emission in pyromorphite is characterized by a very long decay component, which is not typical for this luminescence center. The possilile reason may be energy migration from Pb ions, which are the major elements in these minerals. It is well known that Pb is a very effective sensitizer for many luminescence centers in minerals, including Mn " and REE (Marfunin 1979). The excitation spectrum of Ce luminescence in esperite revealed a UV band at 280 nm, which is not typical for Ce luminescence and is possibly connected with Pb excitation with energy migration. 

For example, narrow bands in pyromorphite luminescence spectra at 380 and 439 nm (Fig. 4.26) maybe connected with Pb emission. Two structurally... 

Pyromorphite usually has an orange to yellow UV excited liuninescence characterized by a broadband peaking at 580 nm (Fig. 4.26). It was earlier supposed... 

G3j2- H9j2 fluorite, anhydrite, titanite, zircon, hardystonite, pyromorphite... 

In anthropogenically impacted systems, Cotter-Howells Thornton (1991) used SEM-EDS to characterize soil grains from a Derbyshire, UK, mining village where Pb mining historically occurred. Many of the soil grains were chloro-pyromorphite. EXAFS was used to identify pyro-morphite in mine-waste-contaminated soils in follow-on studies (Cotter-Howells et al. 1994). 

The presence of the metal cation and an appropriate anion (OH-, Cl-, F-, etc.) in contact with the surface of the apatite is sufficient to cause partial/complete dissolution of the apatite and precipitation of the more stable pyromorphite. A typical set of stoichiometric dissolution and precipitation reactions would be (Lower et al. 1998b) ... 

At some distance close to the mineral surface, the saturation index (SI, IAP/Xsp) of pyromorphite must be greater than zero to allow local super saturation and precipitation. The question is whether this is a heterogeneous nucleation/ surface precipitation reaction or a dissolution homogeneous nucleation reaction. 

Laperche Traina (1998) studied Pb uptake on hydroxyapatite at low initial solution concentration of Pb (103 mg/L). For this, EXAFS was used to characterize the local coordination environment of Pb on the apatite. The baseline corrected, Fourier-transformed EXAFS spectra revealed fc-values at >3 A, suggesting that Pb was not randomly sorbed. Radial structure functions (RSF) showed three intense peaks, characteristic of pyromorphite. 

In systems where all components are initially soluble, it is simple to form pyromorphites (Nriagu 1974, 1984 Ma 1996) or ternary metal apatites where Pb21, Cd2+, Cu2+, and Zn2+ iso-morphically substitute for Ca2+ and form solid... 

Ryan et al. (2001) studied the effects of hydroxyapatite addition to soils impacted by Pb from smelter operations. Dialysis experiment were conducted where the soil and hydroxyapatite solids were placed in separate dialysis bags suspended in 0.01 M NaN03. Chloropyromor-phite formed on the dialysis membrane containing the soil. The dissolution of solid-phase soil Pb was the rate-limiting step for pyromorphite formation. EXAFS showed that after the 240 day incubation the hydroxyapatite treatment caused a change in the average, local molecular bonding environment of soil Pb. 

Cotter-Howells, J. D., Champness, P. E., Charnock, J. M. Pattrick, R. A. D. 1994. Identification of pyromorphite in mine-waste contaminated soils by ATEM and EXAFS. European Journal of Soil Science, 45, 393-402. 

Zhang, P., Ryan, J. A. Bryndzia, L. T. 1997. Pyromorphite formation from goethite adsorbed lead. Environmental Science Technology, 31, 2673-2678. 

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