Phosphate speleothems in caves developed in iron ores and laterites of the Carajás Mineral Province (Brazil) and a new occurrence of spheniscidite

Abstract

Abstract:The Carajás Mineral Province has one of the largest concentrations of caves in Brazil, and its iron ore is among the country's main exports. As a result of iron ore intense extraction, new environmental policies have been implemented. In an attempt to balance economic activity and environmental conservation, an inventory and a relevance-based classification of caves were implemented in 2008 as criteria for environmental licensing of mining ventures. This implementation motivated the present study of phosphate speleothems in Carajás' caves developed in ferriferous rocks. The objectives of this study are to describe the phosphate minerals and their formation processes based on geochemical and petrographic analysis, X-ray powder diffraction (XRD), differential scanning calorimetry coupled with thermogravimetry (DSC-TG), Fourier-transform infrared (FTIR) and scanning electron microscopy (SEM). Eight caves were selected for this study, along the slopes of the plateaus from Carajás. The phosphate speleothems usually present compositional zoning, with strengite-phosphosiderite in the core and leucophosphite-spheniscidite on the edges. This zoning cannot be related to leucophosphite-spheniscidite decomposition, since the DSC-TG curves show that dehydroxylation and loss of NH 3 from leucophosphite-spheniscidite require temperatures higher than 250°C. FTIR results allowed us to identify the NH 4 functional group, based on absorbance bands at 1,430 and 3,040 cm -1 , which associated to other data confirm the presence of spheniscidite. Refined values of the unit cell parameters for spheniscidite (a = 9.803 Å, b = 9.722 Å, c = 9.858 Å, β = 102.78°) obtained using the Rietveld refinement, were slightly lower than those of the ICSD-39654 file. These smaller values are attributed to increasing substitutions of K + for NH 4 + , and Al 3+ for Fe 3+ . Based on the geochemical analysis, significant enrichment in P 2 O 5 , Zn, Ni, and Rb was detected in phosphate speleothems, and phosphatized laterite, suggesting that bat guano was a potential source of these elements.cave, iron ore, phosphate speleothems, spheniscidite, Carajás

Nature-inspired compositional control of transition-metal-doped ammoniotinsleyite and spheniscidite particles for design of color hue

“…Spheniscidite [(NH 4 )Fe 2 (PO 4 ) 2 (OH)·2H 2 O] also belongs to the leucophosphite group of minerals, and is the iron analog of ammoniotinsleyite. 4,10,11 Similarly to ammoniotinsleyite, this iron phosphate phase can be obtained by using aqueous solution techniques. Trobajo et al synthesized iron( iii ) phosphate materials from aqueous solutions containing FeCl 3 ·9H 2 O and H 3 PO 4 under hydrothermal conditions.…”

“…21,22 Natural ammoniotinsleyite and spheniscidite minerals often contain impurity ions such as K + , Na + , Ca 2+ , and Mg 2+ ; these impurities substitute for cations, namely NH 4 + , Al 3+ , and Fe 3+ , in the leucophosphite lattice. 4–7,10,11 Therefore, nature-inspired compositional changes of ammoniotinsleyite and spheniscidite might enable us to control the color for their use as pigment and jewelry materials. In this work, we prepared transition-metal (Mn 2+ , Co 2+ , Ni 2+ , and Cu 2+ )-doped ammoniotinsleyite and spheniscidite particles via a hydrothermal route.…”

Atividade enzimática e antimicrobiana de microrganismos isolados de uma caverna da região Amazônica

“…The Carajás region is located in southeastern Pará, and has the largest number of natural underground cavities known in Brazil, with more than 2,800 recorded cavities and hundreds still to be inventoried in iron lithology with biospeleogenesis, minerals and unique speleothems [10]. The Parque Nacional dos Campos Ferruginosos, study area, has a high number of endemic species adapted to extreme conditions, such as soil poor in nutrients [11], high concentrations of heavy metals (e.g.…”