In Situ XRD Study of the Thermal Decomposition of Natural Arsenian Plumbojarosite

Abstract

The thermal decomposition of arsenian plumbojarosite, Pb 0.59 Fe 3 (AsO 4 ) 0.18 (SO 4 ) 1.82 (OH) 6 , from the Lomo Deltoro mine, Mexico, has been studied using in situ X-ray powder diffraction, combined with thermogravimetric and chemical analyses. The minor arsenic becomes enriched in the crystalline products of decomposition as SO 3 is evolved during heating, and it eventually controls the phases that form. Dehydroxylation at 400°C produces an initially amorphous product from which metastable nanocrystalline b-PbSO 4 and b-Fe 2 O 3 crystallize. With an increasing size of crystallites, these transform to the stable anglesite (incorporating As) and hematite phases. Above 620°C, the arsenian anglesite incorporates Na and Fe from the amorphous component and transforms to a cubic eulytine-type phase, Pb 5 Na 2 Fe(AsO 4 ) 3 (SO 4 ) 3 , plus PbO (litharge). At temperatures in the range 720 to 760°C, the eulytine phase and PbO react to form an apatite-type phase, Pb 5 (AsO 4 ) 2 (SO 4 )O, via an intermediate partially amorphous phase region. The phase assemblage of Pb 5 (AsO 4 ) 2 (SO 4 )O plus hematite is stable to about 860°C, where partial melting occurs. Above 860°C, hematite coexists with an amorphous phase and poorly crystalline lanarkite, Pb 2 O(SO 4 ).Keywords: arsenian plumbojarosite, Lomo Deltoro mine, Mexico, thermogravimetric analysis, in situ powder X-ray diffraction, Rietveld quantitative phase-analysis, amorphous phases, metastable phases. SoMMaIreNous avons documenté la décomposition thermique de la plumbojarosite arsenifère, Pb 0.59 Fe 3 (AsO 4 ) 0.18 (SO 4 ) 1.82 (OH) 6 , provenant de la mine Lomo Deltoro, au Mexique, en employant la diffraction X in situ sur poudre et les résultats d'analyses thermogravimétriques et chimiques. L'arsenic, composant mineur au départ, devient progressivement concentré dans les produits cristallins de décomposition à mesure que le SO 3 produit par chauffage s'échappe, et il régit éventuellement les phases qui apparaissent. La déshydroxylation à 400°C produit au départ une phase amorphe à partir de laquelle se forment de façon métastable des nanocristaux de b-PbSO 4 et b-Fe 2 O 3 . A mesure que la taille de ces cristallites augmente, ceux-ci se transforment en anglésite (avec incorporation de l'arsenic) et hématite stables. Au delà de 620°C, l'anglésite arsenifère incorpore le Na et le Fe provenant du composant amorphe et se transforme en une phase cubique de type eulytine, Pb 5 Na 2 Fe(AsO 4 ) 3 (SO 4 ) 3 , avec PbO (litharge). A températures dans l'intervalle de 720 à 760°C, la phase de type eulytine réagit avec le PbO pour former une phase du groupe de l'apatite, Pb 5 (AsO 4 ) 2 (SO 4 )O, via une phase intermédiaire partiellement amorphe. L'assemblage Pb 5 (AsO 4 ) 2 (SO 4 )O + hématite est stable jusqu'à environ 860°C, le point de fusion du mélange. Au-delà de 860°C, l'hématite coexiste avec une phase amorphe et la lanarkite, Pb 2 O(SO 4 ), à faible cristallinité. (Traduit par la Rédaction)Mots-clés: plumbojarosite arsenifère, mine Lomo Deltoro, Mexique, analyse the...

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Assessment of Solid Wastes and By‐Products as Solid Particle Materials for Concentrated Solar Power Plants

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