Dissertations / Theses on the topic 'Sodium dithionite'

Deux approches sont envisagees : la catalyse par transfert de phase et la fixation de l'anion dithionite sur polymere. L'etude comparative des proprietes extractantes de differents agents de transfert a montre la superiorite du cation methyl trioctylammonium. Reduction d'aldehydes et de cetones par le dithionite de na dans les conditions de transfert de phase. Reduction par l'anion dithionite fixe sur resines echangeuses d'ions

Sodium dithionite (Na2S2O4) is a powerful reducing agent. It has therefore been suggested to be used as an additive in kraft pulping to improve the yield. However, sodium dithionite easily decomposes and it is thus important to determine the effect of different conditions. The aim of this thesis has been to investigate the thermal stability of sodium dithionite under anaerobic conditions using ATR-FTIR spectroscopy under different conditions, such as heating temperature, concentration of the solution, heating time and pH. The stability of sodium dithionite was found to decrease with increasing heating temperature, concentration of sodium dithionite, heating time and pH. Sodium dithionite was found to be relatively stable at moderate alkaline pH:s 11.5 and 12.5, while a rapid decrease in stability with time was noted at higher heating temperatures and concentrations of sodium dithionite. Based on this study on the thermal stability of sodium dithionite, the following conditions are suggested as the most promising, when adding sodium dithionite to the kraft cooking as an additive; pH 12.5, with 0.4 M concentration of the solution, at a heating temperature of 100 °C.

The three main components of wood, namely, cellulose, hemicellulose, and lignin, can be used in various areas. However, since lignin covalently crosslinks with wood polysaccharides creating networks that is an obstacle for extraction, direct extraction of different wood components in high yield is not an easy matter. One potential approach to overcome such obstacles is to treat the wood with specific enzymes that degrade the networks by specific catalysis. However, the structure of wood is so compact that the penetration of the wood fibers by large enzyme molecules is hindered. Thus, the pretreatment of wood prior to the application of enzymes is necessary, for “opening” the structure. One pretreatment method that was performed in this thesis is based on kraft pulping, which is a well-established and industrialized technique. For untreated wood, the wood fibers cannot be attacked by the enzymes. A relatively mild pretreatment was sufficient for wood polysaccharides hydrolyzed by a culture filtrate. A methanol-alkali mixture extraction was subsequently applied to the samples that were pretreated with two types of hemicellulases, Gamanase and Pulpzyme HC, respectively. The extraction yield increased after enzymatic treatment, and the polymers that were extracted from monocomponent enzyme-treated wood had a higher degree of polymerization. Experiments with in vitro prepared lignin polysaccharide networks suggested that the increased extraction was due to the enzymatic untying. However, the relatively large loss of hemicellulose, particularly including (galacto)glucomannan (GGM), represents a problem with this technique. To improve the carbohydrate yield, sodium borohydride (NaBH4), polysulfide and anthraquinone were used, which increased the yields from 76.6% to 89.6%, 81.3% and 80.0%, respectively, after extended impregnation (EI). The additives also increased the extraction yield from approximately 9 to 12% w/w wood. Gamanase treatment prior to the extraction increased the extraction yield to 14% w/w wood. Sodium dithionite (Na2S2O4) is an alternative reducing agent for the preservation of hemicelluloses because it is less expensive than metal hydrides and only contains sodium and sulfur, which will not introduce new elements to the recovery system. Moreover, Na2S2O4has the potential to be generated from black liquor. Na2S2O4 has some preservation effect on hemicelluloses, and the presence of Na2S2O4 also contributed to delignification. The extraction yield increased to approximately 15% w/w wood. Furthermore, Na2S2O4 has been applied in the kraft pulping process of spruce. The yield and viscosity increased, while the Klason lignin content and kappa number decreased, which represents a beneficial characteristic for kraft pulp. The brightness and tensile strength of the resulting sheets also improved. However, the direct addition of Na2S2O4 to white liquor led to greater reject content. This problem was solved by pre-impregnation with Na2S2O4 and/or mild steam explosion (STEX) prior to the kraft pulping process. Following Na2S2O4 pre-impregnation and mild STEX, the obtained kraft pulp had substantially better properties compared with the properties exhibited after direct addition of Na2S2O4 to the white liquor. The wood structure opening efficiency of mild STEX alone was also tested. The accessibility of the wood structure to enzymes was obtained even at very modest STEX conditions, according to a reducing sugar analysis, and was not observed in untreated wood chips, which were used as a reference. The mechanical effect of STEX appears to be of great importance at lower temperatures, and both chemical and mechanical effects occur at higher STEX temperatures.

QC 20140903

Par la technique du stopped-flow nous avons mené une étude systématique de l'effet du microenvironnement, apporte par des polyélectrolytes, des cyclodextrines, des micelles et des microémulsions, sur la cinétique de transfert d'électron entre un donneur, le dithionite de sodium et différents accepteurs, une série de dialkyl viologénes d'hydrophobie variable. Ceci nous a permis d'avoir une meilleure compréhension des contributions respectives des interactions électrostatiques et hydrophobes, qui jouent un rôle primordial dans le phénomène de séparation de charges directement lié au problème de conversion et de stockage de l'énergie solaire. Les constantes de vitesse apparentes pour la réduction des viologénes ont été déterminées dans les différents milieux. L'effet de retard le plus important (environ 50 fois) a été obtenu avec un copolymère de l'acide maléique et du cetyl vinyl éther. Des modèles théoriques ont été développés pour rendre compte de l'effet des polyélectrolytes. Les différents milieux considérés peuvent avoir un effet de stabilisation sur les viologénes réduits à caractère fortement hydrophobe, en empêchant leur dimerisation. Les constantes de vitesse apparentes pour la dimerisation ont été déterminées à partir de modèles théoriques et l'effet de stabilisation confirme par RPE

Dans le domaine pharmaceutique, la séparation des énantiomères est souvent effectuée par des méthodes de cristallisation. L’avantage de la déracémisation est la possibilité d’obtenir un rendement théorique de 100% grâce à la conversion du contre énantiomère en l’énantiomère désiré en solution. Le mécanisme de la déracémisation par cycles de température (TCID), a été étudié dans ce manuscrit. Les recherches se sont concentrées sur le développement d’un procédé de TCID pour NaClO3. Ce composé modèle pour la déracémisation est achiral à l’état solvate, ce qui permet de se focaliser sur les mécanismes de cristallisation impliqués dans le procédé de déracémisation. Après la caractérisation complète de l’état solide de Na2S2O6, ce composé a été utilisé comme une impureté nonchirale dans le procédé de TCID du NaClO3 et a permis de mettre en évidence le rôle important de la nucléation secondaire dans le procédé. Ainsi, le succès du TCID dépend d’un bon équilibre entre la croissance des cristaux et la nucléation secondaire. A des fins industrielles, les réacteurs du type Couette Taylor sont des appareils prometteurs pour le développement de procédés de déracémisation en continu. Les premiers tests de déracémisation réalisés dans ce type de réacteur ont montré que la brisure de symétrie et la déracémisation du NaClO3 ont été réalisés avec succès. Néanmoins, le ≪ recyclage de cristaux ≫, soit par attrition soit par la nucléation secondaire, doit être amélioré pour obtenir un procédé de déracémisation plus performant avant de considérer l’implémentation d’un procédé en continu
In the field of pharmaceutical chemistry, crystallization based methods are used to obtain pure enantiomers. The advantage of deracemization is the conversion of the unwanted enantiomer into the desired enantiomer by means of racemization in liquid phase, giving rise to a theoretical yield of 100%. The mechanism of Temperature Cycling Induced Deracemization (TCID) process, still matter of debate, has been investigated in this thesis. Research was focused on the development of the TCID process for sodium chlorate (NaClO3). This model compound is achiral at the solvated state which enables to focus investigation on crystallization mechanisms involved during deracemization. After the full solid state characterization of sodium dithionate (Na2S2O6), this compound has been used as a nonchiral impurity in the TCID process of NaClO3 and highlighted the key role of secondary nucleation in the process. Thus, the success of the TCID process depends on the right balance between growth and secondary nucleation. From an industrial perspective, the Couette Taylor reactor has been considered as a promising device for the development of continuous deracemization process. Attempts to deracemize NaClO3 in this kind of reactor showed that symmetry breaking and deracemization of NaClO3 were successful. Nonetheless, crystal recycling, via either attrition or secondary nucleation, has to be improved to enhance deracemization process before considering the execution of continuous process

A detailed study into the crystal habit modification of the NaClO3 / Na2S2O6 (host / impurity) system is presented. Ordinary morphology of NaClO3 present faces of {001}, {110} and {111} types. The presence of impurity Na2S2O6 has led to rapid development of new faces of {111} type on the NaClO3 crystals grown from solution. Above 70ppm doping concentration, the morphology of NaClO3 crystal is dominated by {111} faces. Crystal twinning occurred under 800ppm doping concentration and above. X-ray topography was used to investigate the growth history and defect configuration of the pure and doped crystals. Lattice distortions at various lattice planes within the pure and doped crystals were determined using X-ray multiple-wave diffraction (XRMD). The local structure of S2O6 2- in NaClO3 crystal was determined using X-ray absorption fine structure (XAFS). Molecular modelling was applied to investigate the molecular similarity between the impurity and the host. Strong impurity incorporation in the {111} sectors was revealed by X-ray topography. The growth history of doped crystal was reconstructed and interpreted with respect to the inhibiting effect of S2O6 2-. Disturbance in lattice planes of doped crystals was investigated, which was attributed to the incorporation of S2O6 2- on { 111} faces. It also revealed different types of local strain on the { 111 } faces along two different directions. The three-dimensional orientation and the actual structure of S2O6 2- impurity on the {111} faces of NaClO3 crystal were obtained. A structural model for the impurity incorporation was established, showing good consistency with the experimental results. In addition, the segregation coefficient of the impurity was determined by elemental mapping, indicating strong impurity incorporation on the {111} faces rather than others. The incorporated S2O6 2- was concluded to be capable of disrupting the proper packing structure of the {111} faces, obstructing the generation and propagation of growth steps, and decreasing of driving force for crystal growth.

The potential of using acid hydrogen peroxide under Fenton conditions to lower the electrical energy consumed during the production of Black spruce (Picea mariana) thermomechanical pulp (TMP) was investigated. The chemical system, which consisted of ferrous sulphate, hydrogen peroxide and optionally an enhancer (3,4-dimethoxybenzyl alcohol, ethylenediaminetetraacetic acid or oxalic acid/sodium oxalate), was evaluated as an inter-stage treatment where the primary refiner was used as a mixer. The produced TMPs were thoroughly characterised in order to explain the effect of the chemical system on fibre development and to be able to propose a mechanism for the impact on refining energy reduction. The possibility to improve the optical properties by washing, chelating and sodium dithionite or hydrogen peroxide bleaching the treated pulps was evaluated.

 

The results obtained in a pilot plant trial show that it is possible to significantly reduce the comparative specific energy consumption by approximately 20% and 35% at a freeness value of 100 ml CSF or a tensile index of 45 Nm/g by using 1% and 2% hydrogen peroxide respectively. The energy reduction is obtained without any substantial change in the fractional composition of the pulp, though tear strength is slightly reduced, as are brightness and pulp yield. No major differences between the reference pulp and the chemically treated pulps were found with respect to fibre length, width or cross-sectional dimensions. However, the acid hydrogen peroxide-treated pulps tend to have more collapsed fibres, higher flexibility, a larger specific surface area and a lower coarseness value. The yield loss accompanying the treatment is mainly a consequence of degraded hemicelluloses. It was also found that the total charge of the chemically treated pulps is higher compared to the reference pulps, something that may have influenced the softening behaviour of the fibre wall.

 

A washing or chelating procedure can reduce the metal ion content of the chemically treated TMPs considerably. The amount of iron can be further reduced to a level similar to that of untreated pulps by performing a reducing agent-assisted chelating stage (QY) with dithionite. The discoloration cannot, however, be completely eliminated. The brightness decrease of the treated pulps is thus not only caused by higher iron content in the pulp, but is also dependent on the type of iron compound and/or other coloured compounds connected with the acid hydrogen peroxide treatment. Oxidative bleaching with hydrogen peroxide (P) is more effective than reductive bleaching with sodium dithionite in regaining the brightness lost during the energy reductive treatment. Using a QY P sequence, a hydrogen peroxide charge of 3.8% was needed to reach an ISO brightness of 75% for the chemically treated pulps. The corresponding hydrogen peroxide charge for the untreated TMP reference was 2.5%.

 

The radicals generated in the Fenton reaction will probably attack and weaken/soften the available outer fibre wall layers. This could facilitate fibre development and consequently lower the electrical energy demand for a certain degree of refinement.

碩士
文化大學
應用化學系
85
Abstract The Sodium Dithionite manufactured process is made from Sodium Formate reacting with Sulfur Dioxide and Sodium Hydroxide. Based on the test datum, try to find the optimum condition ex. SO2 feed concentration, SO2/HCOONa Feed ratio, HCOOCH3 content in Methanol, reaction temperature, enable to increase the purity of Na2S2O4 product, meanwhile to develop the whole production process.

This study consisted of three parts, an investigation of potential reducing agents, an investigation of conventional dithionite brightening at 1% pulp consistency and an investigation of in-situ electrochemically generated dithiomte brightening. Preliminary brightening experiments by four reducing agents, hydrazine sulfate, hydroquinone, hydroxylamine sulfate and sodium hypophosphite were conducted. At 60 °C, with 1 hour brightening period, 4 to 16 wt% brightening agent charge and 0.5 wt% chelating agent charge on od pulp under nitrogen purge, these agents could only achieve a brightness gain of up to 4 % ISO. They were less effective than sodium dithionite in mechanical pulp brightening. Sodium dithionite brightening of softwood TMP at 60 °C and 1% pulp consistency was done with a single addition of dithionite, multiple addition of dithionite and addition of dithionite in multiple stages with interstage washing. With a single addition of the same dithionite charge, the brightness gain at 1 % pulp consistency was equal to that in conventional brightening at 3 to 4% pulp consistency. For a given total sodium dithionite charge on od pulp, addition of clithionite in multiple stages with interstage washing could achieve about 1 % ISO higher brightness gain than multiple addition of dithionite in a single run, while multiple addition of dithionite in a single run could achieve about 1 % ISO higher brightness gain than a single addition of dithionite. The time and amount of each charge did not seem to affect the brightness gain for multiple additions of dithiomte. In dithionite brightening with a large amount of (bi)sufflte (13 to 131 wt% sodium sulfite on od pulp), the brightness gain was about 3 % ISO lower than that with only dithionite, but about 4 % ISO higher than that with only sulfite. Sodium bisulfite and dithionite reaction products seemed to decrease dithionite brightening capability. The addition of 2-propanol or methanol could alleviate this negative effect of sodium bisuffite on dithionite brightening by about 1% Iso. The electrochemical synthesis of sodium dithionite (without pulp) was conducted in a 1 L mixed tank batch reactor evenly divided by a cation exchange membrane with cathode area of 5500 to 13000 mm². Runs were carried out at 40 °C and 60 °C. High time average dithionite concentration (5 to 10 g/l) and fairly good current efficiency (35 - 80 %) were obtained at high current ( ≥2.3 A) together with high sodium sulfite dose (≥25.3 g). Dithionite concentration became very low ( 0 to 1 g/l) at low sulfite dose (4.6 g). Cathode area, current and sodium sulfite dose were very significant variables in this process. Increases in these variables raised the time average dithionite concentration. Increases in cathode area as well as increases in sulfite dose raised the final current efficiency for dithionite generation. Decreases in current raised final current efficiency with the cathode of 5500 mm² area, but did not have significant effect with cathode of 13000 mm² area. In-situ electrochemically generated sodium dithionite brightening at ambient temperature was briefly investigated in Plexiglas reactor of the same dimensions as the reactor given above, but with a cathode of 1000 mm² area. These runs gave a maximum brightness gain of about 5 % ISO. In-situ electrochemically generated sodium dithionite brightening at elevated temperature was extensively investigated with the same reactor and cathodes used in the electrosynthesis of dithionite. When electrochemical dithionite brightening was carried out at 0.8 % consistency in the following ranges: pH (4.0 to 5.5), sodium sulfite dose (4.6 to 46.0 g), current (0.5 to 4.0 A) and temperature (40 to 60 °C), the highest range of brightness gain was 8 to 9 % ISO with time average dithionite concentration equivalent to a charge of 10 to 103 wt% on od pulp. This highest range of brightness gain was obtained at any pH with a combination of high sulfite dose (46.0 g), high temperature (60 °C) and high current (4 A). At pH 5.5, this highest range of brightness gain was also obtained with a combination of high sulfite dose (46.0 g), high temperature (60 °C) and low current (0.5 A). Temperature had the most significant effect on brightness gain in this process, increases in temperature raised brightness gain but lowered the final net current efficiency for dithionite generation. Increases in cathode area, addition of 2-propanol and chromium did not raise this highest range of brightness gain in the ranges of operating variable studied. In the subsequent optimization of brightness gain for in-situ electrochemically generated dithionite brightening at 2% consistency, the highest range of brightness gain obtained was 11 to 12 % ISO, which was only obtained at the highest range of temperature (74 to 83 °C), with time average dithionite concentration equivalent to a charge of 7 to 10 wt% on od pulp along with a very poor final current efficiency for dithionite (0 to 13 %). Yellowness decreased in electrochemical dithionite brightening in the same way as in conventional dithionite brightening. Comparing the brightness gain of the blank experiment (no current) to the highest brightness gain obtained from the electrochemical dithionite brightening at the same sodium suffite dose, temperature, pH and pulp consistency, the maximum further brightness gain contributed by the brightening species generated by current was only about 4 % ISO. For a brightness gain of 11.4 % ISO, the fraction of the brightness gain contributed by the brightening species generated by current was about 26 % of the total brightness gain.

Three different treatments were applied on several specimens of dolomitic and calcitic marble, properly stained with rust to mimic real situations (the stone specimens were exposed to the natural environment for about six months in contact with rusted iron). Thirty six marble specimens, eighteen calcitic and eighteen dolomitic, were characterized before and after treatment and monitored throughout the cleaning tests. The specimens were characterized by SEM-EDS (Scanning Electron Microscopy coupled with Energy Dispersion System), XRD (XRay Diffraction), XRF (X-Ray Fluorescence), FTIR (Fourier Transform Infrared Spectroscopy) and color measurements. It was also made a microscopic and macroscopic analysis of the stone surface along with the tests of short and long term capillary absorption. A series of test trials were conducted in order to understand which concentrations and contact times best suits to this purpose, to confirm what had been written to date in the literature. We sought to develop new methods of treatment application, skipping the usual methods of applying chemical treatments on stone substrates, with the use of cellulose poultice, resorting to the agar, a gel already used in many other areas, being something new in this area, which possesses great applicability in the field of conservation of stone materials. After the application of the best methodology for cleaning, specimens were characterized again in order to understand which treatment was more effective and less harmful, both for the operator and the stone material. Very briefly conclusions were that for a very intense and deep penetration into the stone, a solution of 3.5% of SDT buffered with ammonium carbonate to pH around 7 applied with agar support would be indicated. For rust stains in its initial state, the use of Ammonium citrate at a concentration of 5% buffered with ammonium to pH 7 could be applied more than once until satisfactory results appear.

碩士
淡江大學
水資源及環境工程學系碩士班
102
Printed Circuit Board is one of the three major electronic parts manufacturing industries. The manufacturing of PCB consumes a lot of water and produces enormous heavy metal-containing wastewater. Without appropriate treatment wastewater will cause great damage to human health. The literature shows that Cu ion could be reduced to Cu atom by sodium dithionite and removed from water with removal rate of 99% at pH>9.25. According to these authors, NH3 played a key role in the reduction process by chelating with Cu ion to form [(Cu(NH3)4)]2+ . In this research, we use MINEQL+ (chemical equilibrium software) to simulate the chelation between Cu ion and NH3. The simulation indicates that Cu ion doesn’t chelate NH3 at low pH value and most of Cu ions are in the form of Cu(OH)2 at pH6-10. Fraction of [(Cu(NH3)4)]2+ species is very tiny at pH>9.25, therefore, the significance of NH3 in Cu reduction needs to be verified. Meanwhile, if chelation of copper is important in copper reduction, EDTA which is ubiquitous in PCB wastewater might play the same role as NH3, and the effect of EDTA on copper reduction is also investigated. Experimental results show that at high pH value NH3 molecules vaporize into gas phase, Cu ion doesn’t chelate NH3 and cause lower removal rate. After a long time, the removal rate recovered due to formation and precipitation of Cu(OH)2. Nitrogen purging can effectively prevent formation of Cu(OH)2. At low pH value without ammonium ligand, Cu ion could be reduced to Cu atom by sodium dithionite, which indicated NH3 is not essential in reduction. The reduction of Cu ion to metallic Cu in EDTA-Cu water by sodium dithionite could happen efficiently at pH3-11 at reaction time of 30 min.

This study explores alternative alkaline agents other than sodium carbonate for ASP process on reactive and non-reactive crude oil recovery at 55oC and 100oC. The alkalis studied were sodium metaborate, pH of 10-10.5, and a sodium silicate/borax mixture, pH of 11. Sodium metaborate showed very optimistic results similar to sodium carbonate studies. Sodium metaborate ASP floods recovered 97-99% of residual oil after waterflood in Berea sandstone at 55oC. The oil saturation in the core after the chemical flood was between 0.5-2%. Sodium metaborate ASP floods recovered 96% of the tertiary oil with a residual oil saturation of 2.6% in Bentheimer sandstone at 100oC. More importantly, the retention of surfactant was very low with the use of metaborate in Berea, Bentheimer and high clay content reservoir cores. 0.18 mg/g rock (68%) and 0.07 mg/g rock (30%) of surfactant was retained in Berea and Bentheimer respectively with the use of sodium metaborate. Sodium metaborate ASP floods recovered 96% and 98% of residual oil with a final oil saturation of 4.8% and 0.56% at 100oC and 55oC respectively in reservoir rock. The retention in reservoir core was 0.13 mg/g (48%) and 0.29 mg/g (80%) at 100oC and 55oC respectively. Sodium borax/metasilicate had a lower tertiary oil recovery due to higher surfactant retention in Berea sandstone. The ASP flood recovered 81% and 86% of tertiary oil at 100oC and 55oC respectively. The retention was 0.326 mg/g (97%) and 0.267 mg/g (98%). The last section involves treatment and reduction of reservoir cores containing clays and iron minerals. Reservoirs exist as anaerobic and reduced environments and these conditions must be emulated in laboratory experiments. Exposure of reservoir cores to aerobic conditions causes an oxidizing environment in the core leading to higher surfactant retention in the laboratory than the field. Dithionite was used to reduce reservoir cores and produce lower surfactant retention closer to field tests. Proper reduced conditions also improved oil recovery. Dithionite must be buffered with sodium bicarbonate to maintain the reducing power of dithionite. Dithionite oxidation by ferric iron and water causes hydroxyl ion consumption and pH decrease. The EH and iron concentration of the effluents must be monitored to determine the success of the core reduction. Effluent EH matching injected values and iron concentration close to the mineral solubility in brine should be used as benchmark for the success of core reduction
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碩士
國立臺灣大學
農業化學研究所
95
There are two oxidation states of chromium in the environment, Cr(III) and Cr(VI). Chromium(III) is easily precipitated and adsorbed by soils, contrarily, Cr(VI) that exists as Cr2O72- or CrO42- is more mobile and soluble than Cr(III). Since the toxicity and mobility of Cr(VI) are higher than that of Cr(III), the reduction of Cr(VI) to Cr(III) by applied composts could be a feasible method to reduce available Cr(VI) in soils. However, in alkaline soils, the efficiency of compost amendments to reduce the Cr(VI) availability is lower than that in acid soils. In this study, Fe(II) and sodium dithionite solutions were added into Cr(VI)-spiked soils and their effects on the decrease of availability of Cr(VI) were investigated. Two representative alkaline soils of Taiwan, Chingchung (Cf) and Taikang (Tk), were treated with K2Cr2O7 solution to reach the level of 0, 250, 500, and 1000 mg Cr kg-1 soil respectively. The soils then underwent three wetting-drying cycles at room temperature to mimic field conditions. Reductants, as electron donors, FeSO4, Na2S2O4, Fe(NH4)2(SO¬4)2, mixture of FeSO4 and Na2S2O4 (4:1 mol/ mol), or mixture of Fe(NH4)2(SO4)2 and Na2S2O4 (4:1 mol/ mol) were applied to Cr(VI) spiked soils. The application rates (number of equivalents) of reductants were 0.5, 1 and 5 folds of number of equivalents of Cr presented in soils. Distilled water were added into soil samples to reach water holding capacity, then soil samples were air-dried at room temperature. The Cr(VI)-spiked soil samples, with and without reductant amendments, were evaluated for the availability of Cr(VI) in soils with DOWEX M4195 selective ion exchange resin extraction method, and the Cr(VI) on solid the X-ray absorption near edge structure spectroscopy (XANES) was used to identify the species of Cr in soils. The results showed that the level of resin-extractable Cr(VI) in reductant-treated soils was lower than the level in the control of Cr(VI)-spiked soils, and the decrease of available Cr(VI) content in soil depended on the amounts of reductants added. Previous studies proposed that the S2O42- of Na2S2O4 with K2CO3 buffer solution was more stable than that without the buffered solution. In order to create an optimal pH condition to reduce Fe(III) of soils into Fe(II), the Na2S2O4 was prepared with 0.05 M K2CO3. The available Cr(VI) content decreased while the soil pH（about 8）decreased slightly after adding the buffered Na2S2O4 solution. The Fe(II) solutions were adjusted to pH < 1 to be more effective in reducing Cr(VI) into Cr(III). Although this reductant was most effective in reducing Cr(VI) into Cr(III), the pH of Cr(VI)-spiked soils decreased the soil pH to 3.5. In order to increase the efficiency of Cr(VI) reduction and alter the soil pH to neutral, the two solutions were mixed to a 4:1 (mol/ mol) ratio at pH between 1-6. The addition of the mixed reductants decreased by 67 %-72 % of the available Cr(VI) content in alkaline soils and only decreased the pH to 7.0-7.8. The addition of the Fe(II) reductants at pH 1.4 decreased the soil pH to 6.7. The mixed Fe(II) and Na2S2O4 at pH 1.4 decreased the soil pH to 7.0-7.2 and reduced more availale-Cr(VI) content than the Fe(II) reductants. The XANES spectra of reductant-treated soils indicated that the intensity of Cr(VI) peak was smaller than that of the control of the Cr(VI)-spiked soil. This observation suggested most of the spiked Cr(VI) was reduced into Cr(III).

The purpose of this work was to study polymer degradation mechanisms as well as ways to mitigate it. In the area of chemical stability, defined as divalent cation tolerance of acrylic polymers as hydrolysis increases, use of the n-vinyl pyrrolidone (NVP) monomer helps to preserve viscosity and tolerate higher calcium concentrations over those polymers without NVP. Also, ethylenediaminetetraacetate tetrasodium salt (EDTA-Na+4) is shown to sequester calcium ions at alkaline conditions (pH>10) and, in the case of lab-aged post-hydrolyzed poly(AM-co-AMPS), helps to retain full viscosity at all calcium concentrations when EDTA is present at a stoichiometric equivalence of calcium. Many discrepancies exist in the literature concerning the presence or absence of degradation under various field or laboratory conditions. Carbonate and bicarbonate, which are typically present in natural waters but often neglected in lab-prepared brines, prove to be a hidden variable in resolving why Shupe (1981) saw no loss in viscosity when sodium dithionite was added to polymer in the presence of oxygen (with bicarbonates) but others (Knight, 1973 and Levitt and Pope, 2008) observed severe degradation under similar conditions (but without bicarbonates). A commercial HPAM polymer (Flopaam 3630S) has been shown to be stable in the presence of ferrous iron in the absence of oxygen, clarifying an apparent discrepancy in the literature between the results of Yang and Treiber (1985) and Kheradmand (1987). Dissolved oxygen (DO) levels, and not redox potential (ORP) measurements, are often reported in polymer stability research on oxidative degradation. ORP is shown to be a better measure of the onset of degradation because oxygen is initially being consumed and may not appear until substantial degradation has occurred. Although generally believed to be a detriment to polymer stability in the field, aeration of iron-laden source water prior to hydration of polymer may be beneficial in certain cases where exposure to air in unavoidable. Also, a novel process of safely producing sodium dithionite in the field proves to perform better in terms of long-term polymer stability in anaerobic conditions than the traditional method of using a solution made from powder dithionite. Finally, a pre-sheared 5 million Dalton HPAM is successfully injected into a 3 mD carbonate reservoir core plug. Remarkably, permeability reduction factors remain at values close to unity. However, pressure data from ASP tertiary corefloods suggest that polymer is not feasible for field injections.
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