As-RICH APATITE FROM MT. CALVARIO: CHARACTERIZATION BY ΜICRO-RAMAN SPECTROSCOPY

Abstract

In order to investigate content and localization of arsenic in natural fluorapatite, a micro-Raman spectroscopic study was carried out on As-rich fluorapatite crystals from the volcanic region of Mt. Calvario (Mount Etna, Italy). The crystals, from both the unaltered lavas and the metasomatized rocks, show a pure fluorapatite composition in the core, but an arsenic content of up to 15 wt.% As 2 O 5 in the rim of the crystals from the altered lavas. [AsO 4 ] 3− ⇔ [PO 4 ] 3− substitutions are proposed on the basis of chemical analysis performed with Electron Microprobe (EMP), Scanning Electron Microscopy (SEM-EDS), and Raman spectroscopy. Micro-Raman investigations carried out on the same crystals studied by EMP show a large band, anomalous for fluorapatite, near 860 cm −1 , where chemical microanalyses revealed high contents of As 2 O 5. The Raman broad band near 860 cm −1 is produced by the vibrational modes of [AsO 4 ] 3− tetrahedra. No evidence of arsenate phase crystallization was found, therefore it is proposed that [AsO 4 ] 3− groups substitute for [PO 4 ] 3− groups in the apatite structure. Through μ-Raman spectroscopy, it has been possible to relate the iron content revealed by chemical analysis to magnetite in the fluorapatite from the unaltered lava, and to hematite inclusions in the inner core of the fluorapatite from metasomatized areas.

Analytical Capabilities of the Community Bureau of Reference Protocol to Estimate the Mobility of Nutrients and Toxic Elements from Mineral Fertilizer

“…−3 can naturally occur because of its structural and electronic similarities. 35 This information justifies the similarity between the As and P fractionation profiles (Figure 2A) and their high mobility. In addition, it can be confirmed that As comes from phosphate rocks.…”

“…Apatite, mainly fluorapatite (Ca 5 (PO 4 ) 3 F), is the predominant mineral in phosphate rocks, which are used in the production of phosphate fertilizers. These minerals are treated with H 2 SO 4 to increase the solubility of phosphate, a primary nutrient. , In these minerals, the substitution of PO 4 –3 for AsO 4 –3 can naturally occur because of its structural and electronic similarities . This information justifies the similarity between the As and P fractionation profiles (Figure A) and their high mobility.…”

Arsenic Apatite From the Calcareous Skarns of the Kanakay Fe-Deposit (Southern Urals)

“…Апатит кристаллизуется в широком интервале физико-химических условий, однако его состав часто позволяет интерпретировать эти условия [1,2]. Мышьяковистый апатит, судя по доступной опубликованной литературе, является очень редким [3] и условия его формирования изучены слабо. В изученных породах стабильные концентрации Cl в As-апатите являются свидетельством образования в гипогенных условиях, а не гипергенных.…”

Avaliação da mobilidade e biocessibilidade de As, Cd, Cr e Pb em fertilizantes minerais

“…Na produção de fertilizante, esses minerais são tratados com H2SO4 para aumentar a solubilidade do fosfato, um nutriente primário (Perez-Lopez et al, 2007;Pérez-López et al, 2010). Nesses minerais pode ocorrer, naturalmente, a substituição de PO4 -3 por AsO4 -3 , devido às suas similaridades estruturais e eletrônicas (Gianfagna et al, 2014). Figura 13.…”