Academic literature on the topic 'Citric acid; calcite'

The floatability of scheelite and calcite in the presence of single depressant (SHMP or H3Cit) and mixed depressant (SHMP/H3Cit) was studied by microflotation experiments and artificial mixed mineral experiments. Solution chemical calculation, zeta potential tests, thermodynamic analysis and XPS analysis were used to explain the relevant depressive mechanism. Mixed depressant (SHMP/H3Cit) exhibited excellent selective depressive effect on calcite. The optimal molar ratio of SHMP to H3Cit was 1:4. The depressant SHMP and H3Cit can be chemically bonded with Ca2+ to form CaHPO4 and Ca3(Cit)2 at pH 8. The CaHPO4 was more easily formed than Ca3(Cit)2 on the mineral surface, which indicated that the depressive effect of SHMP was stronger than H3Cit. The SHMP and H3Cit of the mixed depressant were co-adsorbed on the calcite surface, while the H3Cit of the mixed depressant was weakly adsorbed on the scheelite surface. The mixed depressant can significantly improve the separation efficiency of scheelite from calcite.

Chemical interactions between the injected fluids and the minerals during the fracturing process can affect fluid flow and production. However, there is still a need to understand the impact of geochemistry on the interactions at the rock-fluid interface and how these interactions affect the wettability of the rock and fluid flow in organic-rich mudrocks. In this paper, we quantify the mineral-fluid affinity by performing adsorption calculations. Molecular dynamics simulations (MDS) are carried out to (i) quantify the adsorption of fracturing fluids on the surface of minerals, (ii) perform sensitivity analysis on the composition of fracturing fluid and reservoir temperature on adsorption and mobility, and (iii) analyze the spatial distribution of water and chemicals on mineral surfaces. The minerals evaluated include illite and calcite, and the fracturing-fluid components are methanol, citric acid, sodium chloride, and water. We evaluate the effect of each chemical separately. First, systems composed of mineral surfaces in contact with brine are generated. Then, we analyze the mineral in contact with a solution containing brine and methanol and with a solution composed of brine and citric acid. MDS are carried out in the canonical (NVT) ensemble at the temperature of 330 K to evaluate the adsorption of the fracturing fluid. To quantify the impacts of reservoir temperature, we carry out MDS at a temperature of 360 K. Results suggest that methanol does not have a strong effect on water adsorption and the ion spatial distribution on the mineral’s surface. We found that citric acid tends to form aggregates and that some cations present in the solution might participate in these aggregates. When methanol or citric acid is added to the brine solution, the mobility of both sodium and water on the illite surface decreases. The effects of each additive on the affinity between the mineral and fracturing fluids were also investigated. We found that the number of hydrogen bonds between illite and the fluid did not change when additives were added. However, the number of hydrogen bonds between calcite and the fluid was affected when methanol was added to the system. The quantification of adsorption in the molecular scale provides a fundamental understanding of the electrochemical interactions between the rock surface and the fracturing/reservoir fluids at reservoir conditions, which enables the enhanced design of fracturing-fluid composition for different reservoir types. This information can also be used to quantify the impacts of injected and reservoir fluids on the wettability of the rocks.

Increased amounts of available biomass residues from agricultural food production are present widely around the globe. These biomass residues can find essential applications as bioenergy feedstock and precursors to produce value-added materials. This study assessed the production of biogenic silica (SiO2) from different biomass residues in Africa, including cornhusk, corncob, yam peelings, cassava peelings and coconut husks. Two processes were performed to synthesize the biogenic silica. First, the biomass fuels were chemically pre-treated with 1 and 5% w/v citric acid solutions. In the second stage, combustion at 600 °C for 2 h in a muffle oven was applied. The characterization of the untreated biomasses was conducted using Inductively coupled plasma—optical emission spectrometry (ICP-OES), thermal analysis (TG-DTA) and Fourier-transform infrared spectroscopy (FTIR). The resulting ashes from the combustion step were subjected to ICP, nitrogen physisorption, Energy dispersive X-ray spectroscopy (EDX) as well as X-ray diffraction (XRD). ICP results revealed that the SiO2 content in the ashes varies between 42.2 to 81.5 wt.% db and 53.4 to 90.8 wt.% db after acidic pre-treatment with 1 and 5 w/v% acid, respectively. The relative reductions of K2O by the citric acid in yam peel was the lowest (79 wt.% db) in comparison to 92, 97, 98 and 97 wt.% db calculated for corncob, cassava peel, coconut husk and cornhusk, respectively. XRD analysis revealed dominant crystalline phases of arcanite (K2SO4), sylvite (KCl) and calcite (CaCO3) in ashes of the biomass fuels pre-treated with 1 w/v% citric acid due to potassium and calcium ions present. In comparison, the 5 w/v% citric acid pre-treatment produced amorphous, biogenic silica with specific surface areas of up to 91 m2/g and pore volumes up to 0.21 cm3/g. The examined biomass residues are common wastes from food production in Africa without competition in usage with focus application. Our studies have highlighted a significant end-value to these wastes by the extraction of high quality, amorphous silica, which can be considered in applications such as catalyst support, construction material, concrete and backing material.

During the past decades, emission of greenhouse gases has accelerated to unsustainable levels. This is a serious issue that can have a devastating impact on everything from global economy to the terrestrial or marine ecosystem. A method for reducing the emission is named carbon capture and storage, which this project is based on. In this study, different concentrations of citric acid (CA) is used (as an additive) for the enhancement and optimization of carbon dioxid sorption properties of amorphous calcium carbonate (ACC), mesoporous magnesium carbonate (MMC) and calcium magnesium carbonate composite (CMC). These materials were heat treated in a calcination and an alternating carbonation process in order to study the carbon dioxid sorption performance. During the calcination process, CA undergoes a pyrolysis reaction in order to increase the specific surface area of the individual nanoparticles, which is an important factor for the sorption capacity. In the case of CMC, different molar ratios of magnesium oxide and calcium oxide were used in order to alter the concentration of the resulting magnesium oxide prior to heating. All three materials consisted of aggregations of nanometer-sized particles. Thermogravimetric analysis, scanning electron microscopy, surface area and porosimetry and infrared spectroscopy analysis suggest that the carbon dioxid sorption properties and the sintering stability of ACC and MMC do not improve since CA evaporates due to pyrolysis. Sintering was a greater problem for the evaluated CA treated ACC sample. However, in the case of CMC, the sorption and sintering properties were enhanced due to the higher Tamman-temperature of magnesium oxide, specifically for the lower concentration of magnesium oxide. After 19 carbonation cycles, CMC-1:1-25% CA showed signs of improved sintering stability and sorption capacity, compared to ACC-75% CA.

Presentationen genomfördes på distans.

Five experiments were conducted, utilizing 512 crossbred weanling pigs to determine the P (Exp. 1) and Ca (Exp. 2 and 3) equivalency values of microbial phytase based on performance, rib mineralization and P and Ca digestibility estimates, and to investigate the possible interactions of phytase and citric acid (Exp. 4 and 5). In Exp. 1, adding phytase to low P diets linearly increased ADG (P < .001), rib shear force (P < .01), shear energy (P < .02), ash weight (P < .001) and ash percent (P < .001), Ca (P < .001) and P (P < .001) digestibility and digestible Ca (P < .001) and P (P <.001). Added P linearly increased ADG (P < .003), rib shear force (P < .003) shear energy (P < .001), ash weight (P < .001) and ash percent (P < .01), Ca (P < .02) and P (P < .001) digestibility and digestible Ca (P < .02) and P (P <.001). Based on phytase and P linear or nonlinear response equations for ADG, rib shear force, shear energy, and ash weight, P digestibility, and digestible P, the average equivalency of 500 U/kg of phytase was .78 g of P per kg of diet. In Exp. 2, dietary addition of phytase linearly increased rib ash % (P < .03), Ca (P < .001) and P (P < .001) digestibilities, and digested Ca (P < .001) and P (P < .001), but had no effect (P > .10) on ADG and rib shear force and ash weight. Added Ca linearly increased ADG (wk 3-4, P < .04), and rib shear force (P < .001), ash percentage (P < .001) and ash weight (P < .01), and digested Ca (P < .001), but P digestibility (P = .07) and digested P (P = .08) were numerically decreased. In Exp. 3, added phytase linearly increased ADG (wk 3-4, P < .002), feed efficiency (wk 3-4, P < .02), rib ash weight (P < .001), Ca total tract digestibility (P < .001), and Ca (P < .001) and P (P < .001) ileal digestibilities. Added Ca linearly increased ADG (wk 3-4, P < .02), feed efficiency (wk 3-4, P < .01), rib ash percentage (P < .001) and ash weight ( P < .001), shear force (P < .03) and energy (P < .008), and total tract (P < .001) and ileal (P < .001) digestible Ca. Based on phytase and Ca linear or nonlinear response equations for ADG in wk 3-4, measurements of rib mineralization, and digestible Ca, 500 U of microbial phytase was estimated to be equivalent to 1.08 g and .78 g of Ca in Exp. 2 and 3, respectively. In Exp. 4 and 5, dietary phytase addition linearly increased rib shear force (P < .004 and P < .02), shear energy (P < .001), dry bone weight (P < .001), ash weight (P < .001) and ash percent (P < .001). Calcium (P < .001) and P (P < .001) digestibilities were also improved in both experiments when phytase was added. Addition of citric acid in both experiments, reduced dietary pH and stomach digesta pH (P < .05). The addition of citric acid improved ADG (P < .05), feed efficiency (P < .04) and Ca digestibility (P < .05) in Exp. 4, but decreased Ca digestibility in Exp. 5 and had no effect on performance. In Exp. 5, the addition of 2.0% citric acid to the diet supplemented with 500 U/kg of phytase caused a decrease (P < .04) in the phytase activity recovered in the stomach digesta resulting in a phytase by citric acid interaction (P < .02). In summary, the addition of 500 U/kg microbial phytase to weanling pig diets, causes the release of approximately .78 g of P and .93 g of Ca, thus decreasing the need for supplemental P and Ca. The addition of citric acid to phytase supplemented diets does not appear to enhance the efficacy of microbial phytase based on the results of these studies.
Master of Science

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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

[EN] Persimmon (Diospyros kaki L.) 'Rojo Brillante' is an astringent variety characterised by good growing conditions, excellent colour, size, sensory characteristics and good nutritional properties. In the last decade, its production has grown substantially in Spain given the application of high levels of CO2 to remove astringency while firmness is preserved. This technology has also increased its potential as a fresh-cut commodity. However, physical damage during processing result in degradation of the colour and firmness of the product and a higher susceptibility to microbial spoilage that significantly reduces the fruit's shelf life. The objective of the present thesis was to develop optimum procedures for processing and marketing 'Rojo Brillante' persimmon into a fresh-cut product with the maximum shelf life and best physicochemical, nutritional, sensory and microbiological quality. Firstly, the objective was to evaluate the effect of the maturity stage (MS) at harvest, storage time at 15 ºC before processing, and the application of different antioxidant treatments on enzymatic browning, sensory and nutritional quality of fresh-cut 'Rojo Brillante' persimmon during storage at 5 ºC. Concentrations of 10 g L-1 ascorbic acid (AA) or 10 g L-1 citric acid (CA) controlled tissue browning and maintained the visual quality of fresh-cut persimmon above the limit of marketability for 6-8 storage days at 5 ºC, depending on the MS. However, these acidic solutions reduced fruit firmness as compared to control samples. Further studies showed that the combination of these antioxidants with 10 g L-1 CaCl2 maintained firmness of the persimmon slices within the same range as the control samples. In another work, the application of 1-methylcyclopropene (1-MCP) allowed to process fruits after 45 days of storage at 1 ºC with commercial firmness and the antioxidant solution (10 g L-1 CA + 10 g L-1 CaCl2) extended the limit of marketability up to 9 days of storage at 5 ºC. Different controlled atmosphere conditions in combination with AA or CA dips were also evaluated as a first step to select optimum O2 and CO2 concentrations for modified atmosphere packaging (MAP) of fresh-cut 'Rojo Brillante' persimmons. Overall, the combination of antioxidant dips and a controlled atmosphere composed of 5 kPa O2 (balance N2) was proved to be the most effective combination to control enzymatic browning. This atmosphere maintained the visual quality of persimmon slices within the limit of marketability during 7- 9 days at 5 ºC. On the contrary, high CO2 concentrations (10 or 20 kPa) induced darkening in some tissue areas, associated with a flesh disorder known as 'internal flesh browning'. Later studies confirmed the beneficial effect of an active MAP in 5 kPa O2 compared to passive MAP to improve the visual quality of fresh-cut 'Rojo Brillante' persimmon, showing a synergic effect with the antioxidant dip (10 g L-1 CA + 10 g L-1 CaCl2). Antioxidant edible coatings were prepared from whey protein isolate (WPI), soy protein isolate (SPI), hydroxylpropyl methylcellulose (HPMC) and apple pectin as the polymeric matrix. All edible coatings were amended with the antioxidant combination selected (10 g L-1 CA + 10 g L-1 CaCl2). All the edible coatings tested proved effective to control enzymatic browning of persimmon slices. However, the samples treated with the HPMC- and pectin- based coatings were scored with a better visual quality that the rest of the treatments. In general, free radical scavenging activity and total carotenoid content increased in late-season persimmons; whereas, processing (cutting and storage at 5 ºC), antioxidant dips, controlled atmosphere storage or edible coatings had no clear effect on nutritional quality (vitamin C, free radical scavenging activity, total phenolic content, and carotenoids) of fresh-cut persimmons.
[ES] El caqui persimmon (Diospyros kaki L.) 'Rojo Brillante' es un cultivar astringente que presenta unas propiedades organolépticas y nutricionales excelentes. En la última década, su cultivo en el área mediterránea de España se ha incrementado de manera exponencial con el desarrollo de la tecnología que permite eliminar la astringencia, manteniendo la firmeza del mismo. Esta nueva forma de presentación, aporta numerosas ventajas, entre la que se incluye la posibilidad de ser comercializado como fruta fresca cortada. Sin embargo, el éxito comercial del producto está limitado por el pardeamiento enzimático, la pérdida de firmeza y al crecimiento microbiano. En este contexto, el objetivo de la Tesis ha sido el desarrollo de caqui 'Rojo Brillante' fresco cortado mediante un enfoque que integra el estudio de las características del producto en el momento del procesado y de distintas tecnologías que mantengan la calidad físico-química, sensorial, nutricional y microbiológica del producto durante un periodo que permita su comercialización. En primer lugar, se evaluó el efecto del estado de madurez (MS) en el momento de recolección, el tiempo de almacenamiento a 15 ºC antes del procesado y la aplicación de diferentes antioxidantes en el pardeamiento enzimático y la calidad sensorial y nutricional del caqui 'Rojo Brillante' cortado y almacenado a 5 ºC. La aplicación de 10 g L-1 de ácido ascórbico (AA) ó 10 g L-1 ácido cítrico (CA) controló el pardeamiento enzimático y mantuvo la calidad visual del caqui por encima del límite de comercialización entre 6 y 8 días de almacenamiento a 5 ºC, dependiendo del MS. Sin embrago, la aplicación de estos antioxidantes redujo de manera significativa la firmeza del fruto respecto al control. La combinación de estos antioxidantes con 10 g L-1 de CaCl2 permitió mantener la firmeza en el mismo rango que las muestras control. En un trabajo posterior, la aplicación de 1-metilciclopropeno (1-MCP) permitió procesar caqui almacenado 45 días a 1 ºC con una buena firmeza comercial y el tratamiento antioxidante (10 g L-1 CA + 10 g L-1 CaCl2) consiguió alcanzar un límite de comercialización del producto de 9 días a 5 ºC. La evaluación de distintas atmósferas controladas en combinación con tratamientos antioxidantes (AA o CA), como paso previo al envasado en atmósfera modificada (MAP) del caqui, mostró como más efectiva en el control del pardeamiento enzimático la atmósfera compuesta por 5 kPa O2 (balance N2). Esta atmósfera mantuvo la calidad visual del caqui cortado dentro del límite de comercialización durante 7-9 días a 5 ºC. Por el contrario, la aplicación de altas concentraciones de CO2 (10 ó 20 kPa) dio lugar a un pardeamiento en ciertas zonas de la pulpa que se conoce como 'internal flesh browning'. Estudios posteriores confirmaron el efecto beneficioso del envasado de caqui cortado y tratado con solución antioxidante (CA-CaCl2) en una MAP activa de 5 kPa O2 en la calidad visual del fruto frente a la aplicación de una MAP pasiva. El desarrollo de recubrimientos comestibles con capacidad antioxidante se realizó mediante la incorporación de antioxidantes (10 g L-1 CA + 10 g L-1 CaCl2) a formulaciones a base de proteína de suero lácteo (WPI), proteína de soja (SPI), hidroxipropilmetilcelulosa (HPMC) y pectina. Todos los recubrimientos fueron efectivos controlando el pardeamiento enzimático del caqui cortado, siendo las muestras recubiertas con HPMC y pectina las mejor evaluadas visualmente. En general, el procesado, la aplicación de antioxidantes, el envasado en atmósferas controladas y los distintos recubrimientos comestibles estudiados, si bien no mostraron un efecto claro en los parámetros de calidad nutricional evaluados, no tuvieron un efecto negativo en los mismos. Por otra parte, los frutos cosechados a final de campaña tuvieron mayor actividad antioxidante y contenido en carotenoides.
[CAT] El caqui persimmon (Diospyros kaki L.) 'Rojo Brillante' és un cultiu astringent que presenta unes propietats organolèptiques i nutricionals excel¿lents. En la última dècada, el seu cultiu en l'àrea mediterrània d'Espanya s'ha incrementat de manera exponencial amb el desenvolupament de la tecnologia que permet eliminar l'astringència, mantenint la fermesa del mateix. Esta nova forma de presentació, aporta un gran nombre d'avantatges, entre els quals s'inclou la possibilitat de comercialitzar-lo com fruita fresca processada. No obstant, l'èxit comercial del producte està limitat per pardetjament enzimàtic, la pèrdua de fermesa i el creixement microbià. L'objectiu de la Tesis ha estat en el desenvolupament de caqui 'Rojo Brillante' tallat en fresc mitjançant un enfocament que integra l'estudi de les característiques del producte en el moment del processat i de diferents tecnologies en el manteniment de la qualitat físico-química, sensorial, nutricional i microbiològica del producte durant un període que permeta la seua comercialització. En primer lloc, es va avaluar l'efecte de l'estat de maduresa (MS) en el moment de recol¿lecció, el temps d'emmagatzemament a 15ºC abans del processat i l'aplicació de diferents tractaments antioxidants en el pardetjament enzimàtic i la qualitat sensorial i nutricional del caqui 'Rojo Brillante' tallat i emmagatzemat a 5 ºC. L'aplicació de 10 g L-1 d'àcid ascòrbic (AA) o 10 g L-1 d'àcid cítric (CA) va controlar el pardetjament enzimàtic i va mantenir la qualitat visual del caqui per damunt del límit de comercialització entre 6-8 dies d'emmagatzemament a 5 ºC, depenent del MS. No obstant, l'aplicació d'antioxidants va reduir de manera significativa la fermesa del fruit comparat amb el control. La combinació d'aquestos antioxidants amb 10 g L-1 de CaCl2 va permetre mantenir la fermesa en el mateix rang que les mostres control. En un treball posterior, l'aplicació de 1-metilciclopropeno (1-MCP) va permetre processar caqui emmagatzemat 45 dies a 1 ºC amb una bona fermesa comercial i a més, el tractament antioxidant (10 g L-1 CA + 10 g L-1 CaCl2) va aconseguir un límit de comercialització del producte tallat de 9 dies a 5 ºC. L'avaluació de diferents atmosferes controlades en combinació amb tractaments antioxidants (AA o CA), com a pas previ a l'envasament en atmosfera modificada (MAP) del caqui 'Rojo Brillante, va mostrar com a més efectiva en el control del pardetjament enzimàtic l'atmosfera composta per 5 kPa O2 (balanç N2). Aquesta atmosfera va mantenir la qualitat visual del caqui tallat dins del límit de comercialització durant 7-9 dies a 5 ºC. Per contra, l'aplicació d'altes concentracions de CO2 (10 ó 20 kPa) va donar lloc a un pardetjament en certes zones de la polpa, el qual és conegut com 'internal flesh browning'. Estudis posteriors van confirmar l'efecte beneficiós de l'envasament de caqui tallat i tractat amb solució antioxidant (CA-CaCl2) en una MAP activa de 5 kPa O2 millorant la qualitat visual de la fruita front a l'aplicació de una MAP passiva. El desenvolupament de recobriments comestibles amb capacitat antioxidant es va realitzar mitjançant la incorporació d'antioxidants (CA-CaCl2) en formulacions a base de proteïna de sèrum làctic (WPI), proteïna de soia (SPI), hidroxipropilmetilcel-lulosa (HPMC) i pectina. Tots els recobriments van ser efectius controlant el pardetjament enzimàtic del caqui tallat. No obstant, les mostres recobertes amb HPMC i pectina van ser millor avaluades visualment que la resta de tractaments. En general, el processat, l'aplicació d'antioxidants, l'envasament en atmosferes controlades i els distints recobriments comestibles estudiats, si bé no van mostrar un efecte clar en els paràmetres de la qualitat nutricional avaluats, no van tindre un efecte negatiu en els mateixos. Per altra banda, els fruits recol¿lectats a final de temporada van tenir major activitat antioxidant i contingut en
Sanchís Soler, E. (2016). Effect of processing on the physicochemical, sensory, nutritional and microbiological quality of fresh-cut 'Rojo Brillante' persimmon [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/62588
TESIS

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library.
This study is the first one to examine the reaction of citric acid with calcite over a wide range of parameters. Its main focus is to study the effects of different parameters such as initial citric acid concentration and temperature on the citric-calcite reaction. A rotating disk apparatus was used to study the reaction of calcite (CaC0₃) with citric acid. Using the rotating disk theory, the calcite dissolution rates in citric acid solutions were evaluated as a function of rotating speed, initial concentration of citric acid, concentration of magnesium (Mg²⁺) & Iron (Fe³⁺) ions, temperature, and pressure. In addition, Scanning Electron Microscopy (SEM) technique was used to explore the precipitation mechanism of calcium citrate during the reaction of citric acid with calcite. Using this technique, several factors affecting the precipitation of calcium citrate were identified. In this research, citric acid was found to be an effective stimulation fluid at pH values < 4, rotational speeds of (100-1,000 rpm), initial citric acid concentration of 1-7.5 wt%, pressure values of 1,000-1,500 psi, and temperatures of 25-50oC. However, SEM analysis has shown that calcium citrate precipitation occurred during the reaction at the calcite disk. The precipitation of calcium citrate was found be function of disk rotational speed, initial citric acid concentration, and the concentration of both Mg²⁺ and Fe³⁺ ions. More calcium citrate precipitated at high rotational speeds and high initial citric acid concentration. The presence of both Mg²⁺ and Fe³⁺ ions minimized the precipitation of calcium citrate. The rate of calcite dissolution in citric acid was found to be mainly dependent on the rotational speed. In general, at low rotational speeds, below 500 rpm, the calcite dissolution is mainly governed by the mass-transfer rate, while at high rotational speed, above 500 rpm, it is controlled by the surface-reaction rate. The mass-transfer and the surface-reaction mechanism were investigated thoroughly. Using the rotating disk theory, the overall mass transfer coefficient was determined at various rotational speeds, initial citric acid concentrations, and temperature values. The effective diffusion coefficient of citric as was determined at various citric acid concentrations and various temperature values. In addition, the apparent activation energy of calcite dissolution in mass-transfer regime was found to be 37.9 kJ/mol. Finally, a simplified expression was developed to model the reaction kinetics of citric acid with calcite. The model parameters: reaction order, and activation energy were found to be 0.833 and 63.1 kJ/mol, respectively. This study highlights the importance of the initial acid concentration, temperature, and calcium citrate precipitation on the citric acid reaction with calcite. Another important outcome is the effect of various key parameters on the performance of citric acid as a stand-alone stimulation fluid at conditions similar to those present in a typical field case. Findings based on this work provide new insights into the applications, usage, and potential limitations of citric acid. Factors controlling downhole reaction of citric acid with calcite are also disclosed.
Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2010

碩士
國立成功大學
材料科學及工程學系碩博士班
96
In order to increase the emission intensity and gain the white light phosphor, strontium-calcium aluminate phosphors were synthesized by citric acid method in this study. Influence factors of synthesis & luminescence for phosphors were discussed : as (a) Citrate complex method (ratio of citric acid/metal ions vs. pH value), (b) Citrate gel method (ratio of citric acid/metal ions vs. ratio of ethylene glycol/citric acid), (c) Amount of Eu3+ ions, (d) Amount of Mn2+ ions The precursors were amorphous when the ratio of citric acid/metal ion≧2, pH=2 or the ratio of citric acid/metal ion≧2, the ratio of ethylene glycol/ citric acid≧1. Strontium-calcium aluminate phosphors were obtained and composed of monoclinic CaAl2O4 and hexagonal SrAl2O4 after calcining ar 1000℃/8h for most precursors. It means citrate complex method and citrate gel method can lower the synthesis temperature about 300~400℃. When Eu2+ ions doped into these two host lattices, phosphors showed blue (λp=440nm) and green (λp=520nm) emission bands in PL spectra. The 440nm emission intensity increased with pH value increased in citrate complex method during 1300℃~1400℃ calcination temperature. The PL integral intensity decreased with the amount of ethylene glycol increased in citrate gel method at 1400℃ calcination temperature.. Phosphors synthesized by citrate gel method showed higher PL integral intensity than those synthesized by citrate complex method. In experimental of synthesizing strontium-calcium aluminate phosphors with Eu3+, phosphors were composed of monoclinic CaAl2O4, hexagonal SrAl2O4, and EuCaAl3O7. These phosphors emitted 616nm, 598nm and 587nm red light, and and the PL emission intensity increased with amount of Eu3+ increased during Eu3+ = 1~16 mol%. Them, because of concentration quehching, PL emission intensity decreased with amount of Eu3+ increased when Eu3+>16 mol%. By mixing red phosphors with blue-greed phosphors, color rendering index were increased. In experimental of synthesizing strontium-calcium aluminate phosphors with Mn2+, Mn2+-doped powder didn’t emit, and Eu2+ & Mn2+-doped phosphors showed 440nm、520nm emission band from Eu2+ and 480nm emission band from Mn2+. For all the Eu2+, Mn2+-doped phosphors, PL integral intensity were large then phosphors only doped Eu2+.When increasing the amount of Mn2+, PL integral intensity, 440nm and 520nm emission intensity decreased, but 480nm emission intensity increased. For all these phosphors calcinated during 1300℃~1400℃, 1 mol% Eu2+ & 0.5 mol% Mn2+-doped phosphor showed the maximum PL integral intensity, and mixing powder of twice 18 mol% Eu3+-doped phosphor and 1 mol% Eu2+-doped phosphor showed the best color rendering and closest to white light center.

Objetivos: O objetivo do presente trabalho foi comparar a eficácia de diferentes soluções de irrigante – Hipoclorito de sódio 3%, Ácido etilenodiaminatetraacético 17% e Ácido cítrico 10% - na remoção de pó hidróxido de cálcio misturado com gel de clorhexidina 2%, previamente aplicado em dois sulcos longitudinais realizados no canal radicular. Materiais e Métodos: Foram selecionados 45 dentes humanos monocanalares, moldados em cubos de silicone de forma a criar uma base; seguidamente, foram instrumentados com limas Pro-Taper® até F3 e divididos longitudinalmente, com o uso de um micrótomo. Realizaram-se, então, dois sulcos, que foram preenchidos com a medicação intracanalar. Os dentes foram divididos aleatoriamente em 3 grupos (n=15) e a medicação intracanalar previamente aplicada foi removida usando diferentes soluções de irrigante: Hipoclorito de sódio 3%, Ácido etilenodiaminatetraacético 17% e Ácido cítrico 10%. A irrigação ultrassónica foi utilizada como técnica de agitação do irrigante para todos os grupos experimentais e todos os sulcos foram fotografados, após aplicação da medicação intracanalar e após a remoção da mesma. Resultados: As solução de Ácido cítrico 10% foi superior às soluções de Hipoclorito de sódio 3% e Ácido etilenodiaminatetraacético 17% na remoção da medicação intracanalar (P<0,05). Não houve diferenças significativas entre os outros grupos (P>0,05). Em todos os dentes do grupo experimental do Hipoclorito de sódio 3% observou-se um precipitado laranja-acastanhado, mas em nenhum dos outros grupos. Conclusão: A solução de Ácido cítrico 10% demonstrou maior eficácia do que Hipoclorito de sódio 3% e do que Ácido etilenodiaminatetraacético 17%. O precipitado laranja-acastanhado foi apenas encontrado no grupo irrigado com Hipoclorito de sódio 3%.
Introduction: The objective of the present study was to compare the efficacy of different irrigant solutions - sodium hypochlorite 3%, ethylenediaminetetraacetic acid 17% and citric acid 10% - in removal of calcium hydroxide powder mixed with 2% chlorhexidine gel, previously applied in two longitudinal grooves made in the root canal. Materials and Methods: 45 monocanal human teeth were selected, molded in silicone cubes in order to create a base; after, they were instrumented with Pro-Taper® files till F3 and divided lengthwise with the use of a microtome. Two grooves were, then, made which were filled with intracanal medication. The teeth were randomly divided into 3 groups (n = 15) and the intracanal medication previously applied was removed using different irrigant solutions: sodium hypochlorite 3%, ethylenediaminetetraacetic acid 17% and citric acid 10%. Ultrasonic irrigation was used as the irrigant solution stirrer technique for all experimental groups and all furrows were photographed after intracanal dressing application and after its removal. Results: The 10% citric acid solution was superior to 3% sodium hypochlorite and 17% ethylenediaminetetraacetic acid in the removal of intracanal dressing (P <0.05). There were no significant differences between the other groups (P> 0.05). An orange-brown precipitate was observed in all teeth of the 3% sodium hypochlorite experimental group but in none of the other groups. Conclusions: The 10% citric acid solution demonstrated greater efficacy than 3% sodium hypochlorite and 17% ethylenediaminetetraacetic acid. The orange-brown precipitate was only found in the group irrigated with 3% sodium hypochlorite.

Dissolution rate of limestone for wet flue gas desulfurization in the presence of citric acid was measured by pH-stat method. It was found that limestone dissolution rate in the presence of citric acid was controlled by mass transfer. As can be seen from the experimental results, in the presence of citric acid, limestone dissolution rate increased with increasing stirring speed and reaction temperature. When pH value was greater than or equal to 5.5, due to the formation of calcium citrate, citric acid would inhibit the dissolution process of limestone. And the inhibition effect was more obvious at higher pH value.

Surfactin is an anionic bio-surfactant produced by Bacillus subtilis. Although it has high capacity to decrease interfacial tension between oil and water and improve oil recovery, it has not been used for enhanced oil recovery because it forms precipitation by binding with divalent cations such as calcium ions which are contained in formation water. This study examined the countermeasure to prevent surfactin from forming the precipitation for applying it to enhanced oil recovery. Alcohols, chelating agents, a cationic surfactant and an ion capturing substance were selected as the candidates for inhibiting surfactin from forming the precipitation. Citric acid and trisodium citrate were selected as promising candidates through the measurements of turbidity of the mixture of the candidate, surfactin and calcium ions. Those chemicals also had a function as a co-surfactant for surfactin. The interfacial tension between crude oil and the mixture of citric acid or trisodium citrate (0.6 %) and surfactin (0.3 %) was decreased to 0.1 mN/m, whereas that between crude oil and 0.3 % of surfactin was 3.5 mN/m (see Figure 1). The permeability of a sandstone core into which the solution containing surfactin and trisodium citrate was injected was decreased significantly, whereas citric acid could be injected into the core without significant permeability reduction. Citric acid was therefore selected as the best inhibitor and subjected to the core flooding experiments. 25 % of oil remaining after the primary oil recovery was additionally recovered by the injection of the mixture of surfactin and citric acid after the primary oil recovery (see Figure 2). Moreover, the pressure drop was not increased during the injection of the mixture of surfactin and citric acid. Those results suggest that citric acid has a dual role as the binding inhibitor and co-surfactant for surfactin.

Abstract Calcium sulfate scale is one of the challenges that face production stability in the oilfield industry as it is one of the most challenging scales to manage. Sulfate-scales are very hard to dissolve because of their low solubility-product. This work studies the dissolution capacity of different chemical additives and recipes on calcium sulfate scales. In this work, the maximum dissolution capacity (gram of scale/mole of chelating agent) of various chemical additives and recipes will be studied to evaluate the efficiency in the dissolution of Calcium Sulfate scales. Several experiments were conducted at multiple doses, pH, and in-presence of a catalyst. Potassium Carbonate was used as a catalyst in the dissolution of Calcium Sulfate scales. The performance of each additive was studied in a catalyzed and non-catalyzed pathway and with various. A Series of experiments conducted showed that parameters such as the additive-dose, pH, and a catalyst affect the dissolution efficiency. The dissolution performance efficiency of each additive (Lactic Acid, Citric Acid, N,N-Dicarboxymethyl Glutamic Acid (GLDA), and Gluconic Acid) was compared to the additive performance efficiency under a catalyzed pathway in a formulated recipe. The outcome of this work will contribute to the economic value added by finding the most efficient and cheap recipe to remove Calcium Sulfate scales from the wellbore.

The fast precipitation of ettringite in conventional Calcium Sulfo Aluminate (CSA) cement causes rapid stiffening of the cement paste and is directly associated with short setting times and self-desiccation. To extend the time during which those types of cement remain workable, retarding admixtures can be used. However, retarders may affect the amounts and types of hydration products formed and as a consequence the ability of hydrated cement to chemically bind water. This work investigates the influence of two natural-based admixtures on the self-desiccation ability of a vernacular CSA ternary binder used as earth stabilization. Vicat measurements were used to study the efficiency of citric acid and sucrose as retarding admixtures on the setting time of stabilized earth. A quantitative study of the self-desiccation ability of the binder was performed on dried binder pastes using thermogravimetric analysis (TGA). Results show that both admixtures have a significant impact on the setting time of the binder. Furthermore, TGA showed that the self-desiccation ability of this vernacular CSA binder is significantly reduced when citric acid at high dosages is used, both at early hydration and after 14 days. On the contrary, the use of sucrose does not affect the water chemically bound at an early age but can maximize bound water after 14 days of hydration.

The U.S. team studied the role of cations and pH on thermolabile (TL-PE) and thermostable (TS-PE), permeation in ultrafiltration (UF) membranes, affinity to ion exchange membranes, mechanism of cation and pH activation, and effect on PE stability. An optimum pH and cation concentration exists for activity and UF permeation, which is specific for each cation type. Incomplete release of PE from a pectin complex resulted in low PE binding to cationic and anionic membranes. Incubation of PE at low pH increases the surface hydrophobicity, especially TL-PE, but the secondary structure of TL-PE is not greatly affected. The Israeli team showed that stable cloud colloidal constituents flocculate following the conversion of soluble to insoluble biopolymers. First, formation of pectic acid by pectinesterase activity is followed by the formation of calcium pectate gel. This process initiates a myriad of poorly defined reactions that result in juice clarification. Second, protein coagulation by heat resulted in flocculation of proteinacous bound cloud constituents, particularly after enzymatic pectin degradation. Pectinesterase activity is proposed to be an indirect cause for clarification; whereas binding of cloud constituents is the primary event in clarification by pectate gel and coagulated proteins. Understanding the mechanism of interaction of protein and pectic polymers is key to understanding cloud instability. Based on the above, it was hypothesized that the structure of pectin-protein coagulates plays a key role in cloud instability.