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

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

Synthesis of alumina based on industrial waste material

A hazardous waste generated in slag milling process by the aluminium industry was used as a raw material for the synthesis of alumina, α-Al2O3. This waste is considered as hazardous material in the European legislation due to the release of toxic gases (hydrogen, ammonia, methane and hydrogen sulphide) in the presence of water. The process developed in this work allows to obtaining 1 ton of alumina from 4 tons of hazardous waste and generates an inert solid residue consisting principally of spinel, corundum and quartz with possible uses in cements or glass industry. This process consisted of two steps: in the first one, nearly 90% of aluminium present in the waste is recovered as a nanocrystalline boehmite, γ-AlOOH by hydrothermal treatment of the waste. In the second step, the alumina is obtained by calcination of the boehmite at 1400ºC in air. The chemical composition of the alumina obtained consisted of 95% Al2O3, 3.3% Fe2O3, 0.8% SiO2 and other minor oxides to balance

Synthèse et caractérisation de l'alumine á partir d'un dechet dangereux

La dernière Directive Européenne, 2008/98/CE, relative au traitement des déchets a pour objectif la réduction de l’exploitation des ressources naturelles par la gestion des ressources secondaires. Afin d’atteindre cet objectif, cette étude a été menée pour transformer un déchet dangereux, provenant de l´industrie tertiaire de l´aluminium, à alpha alumine (corindon). Le processus développé peut être résumé en deux phases: 1) la obtention de la boehmite (AlOOH) par traitement hydrothermal à basse température; 2) la calcination de la boehmite obtenue à différentes températures (1300, 1400 et 1500ºC) durant 7h. Les échantillons ont été caractérisés par la diffraction des rayons X, fluorescence des rayons X et le microscope électronique à balayage

Synthèses et characterisation de l’alumine à partir d’un dechet dangereux

E3D 2012, Eau, Dechets et Developpment Durable Congrese . Agadir, Marruecos.La dernière Directive Européenne, 2008/98/CE, relative au traitement des déchets a pour objectif la réduction de l’exploitation des ressources naturelles par la gestion des ressources secondaires. Afin d’atteindre cet objectif, cette étude a été menée pour transformer un déchet dangereux, provenant de l´industrie tertiaire de l´aluminium, à alpha alumine (corindon). Le processus développé peut être résumé en deux phases: 1) la obtention de la boehmite (AlOOH) par traitement hydrothermal à basse température; 2) la calcination de la boehmite obtenue à différentes températures (1300, 1400 et 1500ºC) durant 7h. Les échantillons ont été caractérisés par la diffraction des rayons X, fluorescence des rayons X et le microscope électronique à balayage.N