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Tomasz Bajda, Tomasz Marchlewski and Maciej Manecki

Pyromorphite formation from montmorillonite adsorbed lead

The reaction of Pb-adsorbed montmorillonite with aqueous solutions of PO4 and Cl ions results in the decrease in phosphate concentration associated with the formation of a new phase - pyromorphite Pb5(PO4)3Cl. Pyromorphite crystals range in size from hundreds of nm to several tens of μm, depending on the PO4, K, and Ca concentrations in the reacting system. A strong ion-exchange effect of K+ and Ca2+ cations on desorption of Pb2+ from Pb-adsorbed montmorillonite was observed. Also, a high concentration of cations leads to a rapid desorption of Pb and the formation of fine pyromorphite crystals. In contrast, low PO4, K and Ca concentrations result in the formation of relatively large euhedral crystals. Final Pb concentrations are much lower in experimental sets than in control experiments with no phosphate present.

Open access

Piotr Turek, Tomasz Bajda and Maciej Manecki

Abstract

Mimetite Pb5(AsO4)3Cl is the most insoluble lead arsenate mineral and could be used in remediation techniques to reduce As(V) mobility in soils. However, low-molecular-weight organic acids such as malic acid increase its solubility. The effect of malic acid on the dissolution of mimetite strongly depends on the pH of the equilibrium solution. At low pH, mimetite is decomposed mostly by the mechanism of protonation. With increasing pH, the solubility of mimetite decreases and a greater influence in its dissolution is ascribed to complexation of Pb(II) by organic ligands. During dissolution experiments, the amount of arsenic released to solution was > 26% higher in organic solutions than in inorganic solutions, and the amount of lead was > 8% greater. The solubility product of mimetite (KSP) was calculated in order to quantify the thermodynamic stability of the investigated mineral. The value obtained, i.e., -24.52 ± 0.49 fluctuates between the values of -21.69 ± 1.05 and -27.87 ± 0.42 reported in the literature.

Open access

Urszula Janicka, Tomasz Bajda and Maciej Manecki

Abstract

The bromide analogue of pyromorphite Pb5(PO4)3Br was synthesized and characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. The solubility of the brompyromorphite was measured at 25°C and pH values of 2.0, 2.6 and 3.2. For the 3 pH measurements, the average solubility product, log KSP, for the reaction Pb5(PO4)3Br ⇔ 5Pb2+ + 3PO- 3- + Br- at 25ºC is -77.38 ± 0.70. The free energy of formation, ΔG°f,298, calculated from this measured solubility product is -3724.7 ± 4.3 kJ mol−1. These results confirm that brompyromorphite is more soluble than pyromorphite.

Open access

Karolina Gołuchowska, Abigail K. Barker, Jarosław Majka, Maciej Manecki, Jerzy Czerny and Jakub Bazarnik

Abstract

The purpose of this study is to determine the role of metamorphism and thereby identify the preserved magmatic signature in metavolcanics from Wedel Jarlsberg Land in southwestern Svalbard. Samples have been collected from late Precambrian metavolcanics occurring within metasedimentary rocks of the Sofiebogen Group, as well as dikes cutting older metasedimentary rocks of the Deilegga Group. The volcanic rocks were metamorphosed under greenschist facies conditions during the Caledonian Orogeny. To investigate the role of metamorphism, we present petrography, major and trace element geochemistry, and use factor analysis as a tool to identify correlations that correspond to primary magmatic signals.

The metavolcanics are classified as subalkaline basalt to basaltic andesite and they contain relicts of primary clinopyroxene and plagioclase. The metamorphic minerals are actinolite, secondary plagioclase, chlorite and minerals belonging to the epidote group. Major element variations are highly scattered with no obvious trends observed. The HFSE and REE show strong trends attributed to fractional crystallization. The LILE, Th and La show elevated contents in some samples.

Factor analysis shows that the HFSE and REE are well correlated. The LILE form a separate well correlated group, while the major elements are not correlated, except for Na2O, Fe2O3 and CaO. The lack of correlation for major elements, as well as the lack of observed fractional crystallization trends between these elements suggests that they were modified by metamorphism. The strong correlation of HFSE and REE reflects the original geochemical signal generated by magmatic processes. The correlation of the LILE is consistent with their elevated composition implying the influence of crustal contamination processes, and though some variability is likely superimposed due to metamorphism, the primary magmatic record is not completely destroyed. We conclude that the HFSE and REE are not influenced by metamorphic processes and therefore provide robust records of magmatic processes.