143 research outputs found
Estudio cinético de la deshidratación térmica del fosfoyeso
Phsophogypsum is a by-product from the processing phosphate rock. Before the use of it in cement industry such as setting regulator is necessary a study of dehydration reaction of phosphogypsum to avoid the false setting during the milling.
The aim is to study the thermal behavior of two different phosphogypsum sources (Spain and Tunisia) under non-isothermal conditions in argon atmosphere by using Thermo-Gravimetriy, Differential Thermal Analysis (TG-DTA) and Differential Scanning Calorimetry (DSC).
DSC experiments were carried out at temperatures ranging from ambient to 350 °C at different heating rates. The temperatures of conversion from gypsum to hemihydrate and anhydrite states and heat of dehydration were determined. Various methods were used to analyze the DSC data for reaction kinetics determination. The activation energy and frequency factor were calculated for dehydration of phosphogypsum. Activation energy values of the main dehydration reaction of phosphogypsum were calculated to be approximately 61–118 kJ/mol.El fosfoyeso es un subproducto procedente del procesado de la roca fosfato. Una de las posibles vías de reutilización y revalorización es su uso como regulador del fraguado en la industria cementera. Debido a los posibles problemas de falso fraguado asociado a los procesos de deshidratación que tienen lugar durante la molienda del cemento, esta investigación estudió el comportamiento térmico, bajo condiciones no-isotérmicas en atmósfera de argón, de dos fosfoyesos, mediante TG-DTA y DSC.
Los ensayos de DSC se realizaron hasta los 350 °C a diferentes velocidades de calentamiento. La temperatura de conversión del yeso a las formas de hemihidrato y anhidrita y el calor de hidratación fueron determinados.
Las cinéticas de reacción fueron obtenidas analizando los datos de DSC mediante varios métodos. Se calculó la energía de activación y el factor de frecuencia para las reacciones de deshidratación del subproducto. Los valores de energía de activación de las principales reacciones de deshidratación del fosfoyeso fueron obtenidos, aproximadamente 61-118 kJ/mol
Thermal dehydration kinetics of phosphogypsum
© 2015 CSIC. Phsophogypsum is a by-product from the processing phosphate rock. Before the use of it in cement industry such as setting regulator is necessary a study of dehydration reaction of phosphogypsum to avoid the false setting during the milling. The aim is to study the thermal behavior of two different phosphogypsum sources (Spain and Tunisia) under non-isothermal conditions in argon atmosphere by using Thermo-Gravimetriy, Differential Thermal Analysis (TG-DTA) and Differential Scanning Calorimetry (DSC). DSC experiments were carried out at temperatures ranging from ambient to 350 °C at different heating rates. The temperatures of conversion from gypsum to hemihydrate and anhydrite states and heat of dehydration were determined. Various methods were used to analyze the DSC data for reaction kinetics determination. The activation energy and frequency factor were calculated for dehydration of phosphogypsum. Activation energy values of the main dehydration reaction of phosphogypsum were calculated to be approximately 61-118 kJ/mol.The authors are grateful to the Spanish National R&D&I Plan and FEDER (Project CTQ200802012/PPQ) for the financial support of this study.Peer Reviewe
Study of the transformation of boehmite into alumina by Rietveld method
XXII Congress and General Assembly International Union of Crystallography. IUCr2011. Madrid, 22-30 Agosto, 2011. A publicar en Acta Cryst. (2011) A67, C580The aim of this paper is to study the conversion of boehmite into alumina, by means of the application of Rietveld refinement methodPeer reviewe
Environmental impact and management of phosphogypsum
The production of phosphoric acid from natural phosphate rock by the wet process gives rise to an industrial by-product called phosphogypsum (PG). About 5 tons of PG are generated per ton of phosphoric acid production, and worldwide PG generation is estimated to be around 100–280 Mt per year. This by-product is mostly disposed of without any treatment, usually by dumping in large stockpiles. These are generally located in coastal areas close to phosphoric acid plants, where they occupy large land areas and cause serious environmental damage. PG is mainly composed of gypsum but also contains a high level of impurities such as phosphates, fluorides and sulphates, naturally occurring radionuclides, heavy metals, and other trace elements. All of this adds up to a negative environmental impact and many restrictions on PG applications. Up to 15% of world PG production is used to make building materials, as a soil amendment and as a set controller in the manufacture of Portland cement; uses that have been banned in most countries. The USEPAThe authors are grateful to AECI (project N A/5537/06) and to
the Spanish National R&D&I Plan (Project CTQ2008-02012/PPQ) for the financial support of this study. Hanan Tayibi is grateful to the
CSIC (Spanish National Research Council) for an I3P contract
(I3PDR-6-01).Peer reviewe
Study of the thermal behavior of the aluminium dust stabilized with gypsum
[ES]El polvo de aluminio (pAl) es un residuo peligroso procedente de la metalurgia secundaría
del aluminio. Con objeto de reducir la reactividad del mismo, en el CENIM se ha
desarrollado un proceso de estabilización/solidificación mediante su fraguado con yeso. En
este trabajo se presenta el estudio del comportamiento térmico del pAl estabilizado con el
yeso, con el fin de establecer la influencia del residuo en las reacciones de
hidratación/deshidratación del yeso durante el proceso del fraguado, a saber: deshidratación
parcial del sulfato calcico dihidrato, deshidratación del hemihidrato, deshidratación del
hidróxido de aluminio y transformación de anhidrita soluble en anhidrita insoluble.
Asimismo se ha estudiado la cinética asociada a cada una de las reacciones anteriormente
mencionadas mediante Calorimetría Diferencial de Barrido.[EN]The aluminium dust is a hazardous waste from the secondary aluminium remelting industry.
A stabilization/solidification process was developed at CENIM with the aim of decreasing
its reactivity. Gypsum was used as a binder material. Tliis work summarizes the study of the
thermal behavior of the aluminium dust stabilized with gypsum, in order to establish the
influence of the residue in the reactions of hydration/dehydration of the gypsum during the
hardening process, namely: partial dehydration of calcium sulphate dihydrate, dehydration
of calcium sulphate hemi'hydrate, dehydration of aluminium hydroxide and anhydrite
soluble/anhydrite insoluble transformation. The activation energy associated to all those
reactions was determined by Differential Scanning Calorimetry.Los autores agradecen a la Consejería de Educación
de la Comunidad de Madrid la financiación
del proyecto (07M/0136/2000) y a la empresa Recuperación
y Reciclaje Román por el apoyo a esta
investigación.Peer reviewe
Valorización de fosfoyeso como material de construcción: Aspectos radiológicos
Nowadays, alternative uses of phosphogypsum (PG) in the building industry are being considered in several countries; however, the natural radioactivity level in the PG could be a restriction for those uses. United States Environmental Protection Agency (US-EPA) classified PG as Technologically Enhanced Naturally Occurring Radioactive Material (TENORM). This drawback could be avoided controlling its percentage in the cement preparation and the radionuclides content in the other raw materials used in its production, and calculating the activity concentration index (I) in the final by-products.
The valorization of PG as a building material has been studied, from a radiological point of view, by developing a new stabilisation/solidification process. PG is incorporated within a polymeric sulphur matrix, obtaining a concrete-like material, which presents lower natural radioactive content than the initial PG. The 226Ra content of this material ranged between 26-27 Bq·kg-1 and it is quite similar to that of common Spanish building materials.Actualmente, en muchos países se está contemplando el uso alternativo del fosfoyeso (PG) en la industria de la construcción, aunque su contenido en radionucleidos naturales puede presentar ciertas restricciones para dicha aplicación (material clasificado por la US-EPA como TENORM: “Technologically Enhanced Naturally Occurring Materials). No obstante, estos inconvenientes podrían paliarse controlando el porcentaje del PG y los niveles de radioactividad en las materias primas a incorporar al cemento y calculando el índice de concentración de actividad (I) en los productos finales.
La valorización del PG como material de construcción se ha estudiado en este trabajo desde el punto de vista radiológico, desarrollando un nuevo proceso de estabilización/solidificación, obteniéndose un material de características similares al cemento y que presenta menor contenido de radionucleidos naturales que el PG inicial. Los niveles de 226Ra de este material (26-27 Bq·kg-1) son similares a los de algunos materiales de construcción utilizados comúnmente en España
Performance and bacterial community shifts during phosphogypsum biotransformation
Phosphogypsum (PG) is an industrial waste composed mainly by sulfate, turning it a suitable sulfate source for sulfate-reducing bacteria (SRB). In the present work, the capability of two SRB communities, one enriched from Portuguese PG (culture PG) and the other from sludge from a wastewater treatment plant (culture WWT-1), to use sulfate from PG was compared. In addition, the impact of this sulfate-rich waste in the microbial community was assessed. The highest efficiency in terms of sulfate reduction was observed with culture WWT-1. The bacterial composition of this culture was not significantly affected when sodium sulfate from the nutrient medium was replaced by PG as a sulfate source. Next generation sequencing (NGS) showed that this community was phylogenetically diverse, composed by bacteria affiliated to Clostridium, Arcobacter, and Sulfurospirillum genera and by SRB belonging to Desulfovibrio, Desulfomicrobium, and Desulfobulbus genera. In contrast, the bacterial structure of the community enriched from PG was modified when sodium sulfate was replaced by PG as the sulfate source. This culture, which showed the poorest performance in the use of sulfate from PG, was mainly composed by SRB related to Desulfosporosinus genus. The present work provides new information regarding the phylogenetic characterization of anaerobic bacterial communities with the ability to use PG as sulfate donor, thus, contributing to improve the knowledge of microorganisms suitable to be used in PG bioremediation. Additionally, this paper demonstrates that an alternative to lactate and low-cost carbon source (wine wastes) can be used efficiently for that purpose
The worldwide NORM production and a fully automated gamma-ray spectrometer for their characterization
Materials containing radionuclides of natural origin, which is modified by
human made processes and being subject to regulation because of their
radioactivity are known as NORM. We present a brief review of the main
categories of non-nuclear industries together with the levels of activity
concentration in feed raw materials, products and waste, including mechanisms
of radioisotope enrichments. The global management of NORM shows a high level
of complexity, mainly due to different degrees of radioactivity enhancement and
the huge amount of worldwide waste production. The future tendency of
guidelines concerning environmental protection will require both a systematic
monitoring based on the ever-increasing sampling and high performance of gamma
ray spectroscopy. On the ground of these requirements a new low background
fully automated high-resolution gamma-ray spectrometer MCA_Rad has been
developed. The design of Pb and Cu shielding allowed to reach a background
reduction of two order of magnitude with respect to laboratory radioactivity. A
severe lowering of manpower cost is obtained through a fully automation system,
which enables up to 24 samples to be measured without any human attendance. Two
coupled HPGe detectors increase the detection efficiency, performing accurate
measurements on sample volume (180 cc) with a reduction of sample transport
cost of material. Details of the instrument calibration method are presented.
MCA_Rad system can measure in less than one hour a typical NORM sample enriched
in U and Th with some hundreds of Bq/kg, with an overall uncertainty less than
5%. Quality control of this method has been tested. Measurements of certified
reference materials RGK-1, RGU-2 and RGTh-1 containing concentrations of K, U
and Th comparable to NORM have been performed, resulting an overall relative
discrepancy of 5% among central values within the reported uncertainty.Comment: 21 pages, 4 figures, 6 table
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