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[en] The sulfur species existing in different size aerosol particles were determined based on the 'white line' energy shift and the features of post edge structure of sulfur K-edge XANES (X-ray Absorption Near Edge Structure). The results indicated that sulfates were dominant sulfur species in aerosol particles. However, small amount of reductive sulfur species were also found in the ultrafine aerosol particles(<0.1 μm). Sulfates in aerosols mostly exhibited as (NH4)2SO4 and gypsum. Most (NH4)2SO4 distributed in aerosol particles finer than 0.952 μm, while gypsum was the dominant sulfate in coarse aerosols. (authors)
[en] The phosphate fertilizer industry produces an important amount of Phosphogypsum (PG) as a residue of its activity. It is well known that such wastes contain significant amounts of natural radionuclides from the U, Th and K series. The raw material for the production (phosphate rock) has uranium activity concentrations of around 1 kBq kg-1 from which about 15% passes to the PG. At the Huelva industrial area (SW Spain) the wastes produced per year can reach some 3x106 Mg, but in spite of the recent scientific efforts its accumulation still being a problem of great concern for the area. In the other hand, reclamation of sodic soils for agricultural uses requires a Ca amendment to diminish Na saturation. Then, PG (with a high proportion of CaSO4·2H2O) is an effective amendment that has been widely used in the saline-sodic marsh soils from SW Spain. Using PG as an amendment dilutes the radionuclides down to background levels, becoming this practice a possible way to eliminate these wastes with a considerable additional value for the agricultural process. However, it is necessary to study the amount of radioisotopes that can move to water and plants to ensure the radiological safety of the amendment. PG has relatively high concentrations of 226Ra and other radionuclides, with an special concern due to the 222Rn emissions. These wastes could be used to improve the fertility of agriculture soils in a large former marsh area of the Guadalquivir river. Thus, it is interesting to study the levels and behaviour of natural radionuclides within this system to evaluate the radioactive impact of this amendment. An agronomical test is being conducted by one of the authors in an experimental farm in Lebrija (Seville). The soils are treated with 13 and 26 t ha-1 of PG, 30 t ha-1 of manure. Each treatment was repeated twice and continued for two years with beetroot and cotton plant production. We are measuring 226Ra (by alpha counting and gamma spectrometry) and U isotopes (by alpha spectrometry and ICP-MS analysis) in drainage waters, soils and vegetal-tissues samples. The PG used in the treatment has 620 ± 70 Bq kg-1 of 226Ra. The drainage waters have 226Ra contents similar to those from non-contaminated natural waters, but the uranium concentrations are one order of magnitude higher. No significant levels of radionuclides were found in the vegetal tissues
[en] The intensity of the electron paramagnetic resonance (EPR) line corresponding to the carbonate free radical (CO3-) in gypsum (CaSO4·2H2O) drywall was previously shown to be proportional to absorbed dose. Heating irradiated drywall reduces the radiosensitive signal of the CO3- radical. The response of the CO3- EPR line to heat treatments is being studied in order to determine a background for an arbitrary drywall sample. Ultimately this is expected to improve the precision of dose measurements with drywall and to reduce the detection limit. Controlled heating of irradiated drywall was performed at temperatures between 50oC and 100oC. Although higher temperatures reduce the radiosensitive signal rapidly, the non-radiosensitive EPR signals are affected dramatically as well, presumably due to a phrase change from gypsum to plaster of Paris to anhydrite. (author)
[en] Phosphogypsum (PG) or agricultural gypsum, a solid waste from the phosphate fertilizer industry, is used as soil amendment, especially on soils in the Cerrado region, in Brazil. This material may however contain natural radionuclides and metals which can be transferred to soils, plants and water sources. This paper presents and discusses the results of physical and chemical analyses that characterized samples of PG and compares them to the results found in two typical soils of the Cerrado, a clayey and sandy one. These analyses included: solid waste classification, evaluation of organic matter content and of P, K, Ca, Mg, and Al concentrations and of the mineralogical composition. Natural radionuclides and metal concentrations in PG and soil samples were also measured. Phosphogypsum was classified as Class II A - not dangerous, not inert, not corrosive and not reactive. The organic matter content in the soil samples was low and potential acidity high. In the mean, the specific 226Ra activity in the phosphogypsum samples (252 Bq kg-1) was below the maximum level recommended by USEPA, which is 370 Bq kg-1 for agricultural use. In addition, this study verified that natural radionuclides and metals concentrations in PG were lower than in the clayey Oxisol of Sete Lagoas, Minas Gerais, Brazil. These results indicated that the application of phosphogypsum as soil amendment in agriculture would not cause a significant impact on the environment. (author)
[en] On the basis of the analysis of the electron spin resonance spectrum of the SO3- radical ion, it is established that the transformation of gypsum (CaSO4 . 2H2O) into bassanite (CaSO4 . 0.5H2O) with partial removal of water molecules occurs through the formation of an anhydrous metastable phase. This phenomenon, reflecting the processes of recrystallization of materials of this class, serves as the scientific basis for the production of binders from sulfate mineral associations.
[en] The paper introduces a new type of green building which suits for the construction of rural dwellings in Xinjiang, China. Results of the shaking table test on building model show that the single-layer gypsum-adobe structure has better seismic performance. And it also analyzes the construction features and engineering practice, which means that it is significant to extend this type of building to the drier regions in China.
[en] A partition coefficient (λ) for Ra in gypsum was determined from coprecipitation experiment using oversaturation method. The λ-value derived for Ra was: λRa = 0.32±0.15. Saturation state was estimated with the initial concentration of Ca and SO42- in an experiment of the present study. Saturation index was calculated to be (0.49±0.02). This value was similar to those corresponds to analogous case where slow precipitation rate was kept in coprecipitation experiment for Sr in gypsum. Therefore, derived λ-value is thought to describe partition of Ra and Ca in solid phase and solution under an equilibrium condition without the effect of kinetic of precipitation. Determined λ-value was compared with those of other alkaline elements in sulfate minerals. The derived λ-value is smaller than that of Ra in barite and is similar to those of Sr in gypsum. This trend agrees with mechanical understanding for the size effect against partition coefficient. (author)
[en] The precipitation of barium sulphate from aqueous supersaturated solutions has been widely studied as it consists one of the most well known problems in the oil industry. Formation of barite and other insoluble scale types (metal sulphates, calcium carbonate and silicates) occurs due to the incompatibility of the injected seawater with the formation water during their mixing in the reservoirs. The inorganic salts gradually adhere to production tubing and equipment parts leading to serious flow assurance issues and further to reduction in the performance of the petroleum facilities. Barium sulphate scale is characterized by extremely low solubility. It resists many chemical methods of removal including treatments with strong acids. Inhibition of barium sulphate by chemicals is generally recognized as the most appropriate approach for flow assurance. In this study Synchrotron X-Ray Diffraction was used in-situ to investigate the formation of barium sulphate on a stainless steel surface at high temperatures. For the first time in-situ SXRD measurements of BaSO4 formed in the presence of foreign ions (Sr2+, Ca2+ etc) are presented. The formation kinetics of BaSO4 on the surface has been determined and the crystallographic nature of the barite was investigated. In addition the effect of Diethylenetriamine - penta - methylenephosphonic acid (DETPMP) and Poly phosphinecarboxylic acid (PPCA) on barium sulphate was examined at two temperatures. The barite crystal faces present on the surface after the treatment with inhibitors were detected. The lattice planes recorded with the in-situ SXRD measurements revealed that the presence of Sr2+ in the initial formation water resulted in the co-precipitation of Sr2+ within the barite lattice. The in-situ SXRD measurements allowed the assessment of information on the kinetics and crystallography of the formed scale in the absence and presence of inhibitors. The crystallography of the barite revealed high sensitivity to temperature and inhibition effects. (author)
[en] The preparation of calcium sulfate by flame synthesis resulted in the continuous production of anhydrite nanoparticles of 20-50 nm size. After compaction and hardening by the addition of water, the anhydrite nanoparticles reacted to nano-gypsum which was confirmed by X-ray diffraction, diffuse reflectance IR spectroscopy and thermal analysis. Mechanical properties were investigated in terms of Vickers hardness and revealed an up to three times higher hardness of nano-gypsum if compared to conventional micron-sized construction material. The improved mechanical properties of nano-gypsum could in part be due to the presence of calcium sulfate nano-needles in the nano-gypsum as showed by electron microscopy
[en] Phosphogypsum is a waste generated in phosphoric acid production by the 'wet process'. The immense amount of phosphogypsum yearly produced (around 150 million tons) is receiving attention from environmental protection agencies all over the word, given its potential of contamination. In Brazil, this material has been used for many decades, especially for agricultural application on cropland. Although the phosphogypsum is mainly composed of dehydrated calcium sulfate, it can have high levels of impurities, such as metals (Cd, Cr, Cu, Pb), non-metals (As and Se) and radioactive elements from natural series of 232Th and 238U. Therefore, its continuous application as an agricultural agent can result not just in soil contamination, but also contamination of the surface and groundwater due to the runoff and infiltration process. The concern associated with the contamination of aquatic environments increases; when water is used for human consumption, requiring progressive adoption of more restrictive limits. However, some of the conventional analytical techniques used to determine the maximum limit of contaminants in water have detection limits above the maximum limits established by the environmental legislation. This work was aimed to evaluate the mobility of metals and non-metals in soils and, consequently, the contamination of drainage water through greenhouse-scale leaching and transport of toxic elements from soils fertilized with phosphogypsum. Hence, methods were studied and implemented for determination of metals (Cd, Cr, Cu and Pb) using Furnace Graphite Atomic Absorption Spectrometry (GF AAS), as well as for non-metals (As and Se) using Inductively Coupled Plasma Mass Spectrometry (lCP-MS). Effects of different chemical modifiers on the determination of Cd, Cr, Cu and Pb concentration by GF AAS were also investigated. In general, it was observed that the metal and non-metal concentration were below than the actual detection limit of the equipment for all conditions of interest, indicating the low mobility of the analyzed elements in the soil column. (author)