Calcite precipitation induced by clay-bleach cation exchange in andesitic reservoir rocks

Experiments were carried out on the sodium hypochlorite bleach sensitivity of a deep subsurface andesitic reservoir in order to predict possible deleterious mineral transformations during a downhole clean-up job. Experiments involved examination of core samples from the reservoir using an Environmental Scanning Electron Microscope (ESEM) with an attached Energy Dispersive Spectrometer (EDS) before and after the samples were immersed in bleach. Bleach immersion of whole-rock samples resulted in rapid (less than 1 min) precipitation of abundant 3.0-10.0-μm-wide calcite rhombs within clay-associated micropores and on clay and feldspar grain surfaces. Abundant microporefilling calcite rhombs also formed in pure separates of constituent chlorite/corrensite, whereas no calcite formed in a pure separate of constituent zeolite. These experiments indicate that corrensite is the likely calcium source in this experimental fluid-rock system. Formation of calcite occurs via a cation exchange reaction in which calcium in the smectitic interlayers of corrensite exchanges for sodium in the bleach. Serious formation damage due to calcite precipitation would have occurred in the andesite reservoir had it been exposed to bleach. This finding gives credence to earlier suggestions that cation exchange reactions have the potential to cause calcite precipitation in some sandstone reservoirs when exposed to drilling, completion or stimulation fluids. © 1993.

Hydraulic conductivity increases in a sodic clay soil in response to gypsum applications impacts of bulk density and cation exchange

Amelioration of sodic soils is commonly achieved by applying gypsum, which increases soil hydraulic conductivity by altering soil chemistry. The magnitude of hydraulic conductivity increases expected in response to gypsum applications depends on soil properties including clay content, clay mineralogy, and bulk density. The soil analyzed in this study was a kaolinite rich sodic clay soil from an irrigated area of the Lower Burdekin coastal floodplain in tropical North Queensland, Australia. The impact of gypsum amelioration was investigated by continuously leaching soil columns with a saturated gypsum solution, until the hydraulic conductivity and leachate chemistry stabilized. Extended leaching enabled the full impacts of electrolyte effects and cation exchange to be determined. For the columns packed to 1.4 g/cm3, exchangeable sodium concentrations were reduced from 5.0 ± 0.5 mEq/100 g to 0.41 ± 0.06 mEq/100 g, exchangeable magnesium concentrations were reduced from 13.9 ± 0.3 mEq/100 g to 4.3 ± 2.12 mEq/100 g, and hydraulic conductivity increased to 0.15 ± 0.04 cm/d. For the columns packed to 1.3 g/cm3, exchangeable sodium concentrations were reduced from 5.0 ± 0.5 mEq/100 g to 0.51 ± 0.03 mEq/100 g, exchangeable magnesium concentrations were reduced from 13.9 ± 0.3 mEq/100 g to 0.55 ± 0.36 mEq/100 g, and hydraulic conductivity increased to 0.96 ± 0.53 cm/d. The results of this study highlight that both sodium and magnesium need to be taken into account when determining the suitability of water quality for irrigation of sodic soils and that soil bulk density plays a major role in controlling the extent of reclamation that can be achieved using gypsum applications.

Pressurized capillary electrochromatography separation of peptides with strong cation exchange and hydrophilic interaction

A pressurized capillary electrochromatography (pCEC) instrument with solvent gradient capability has been used for the separation of a peptide mixture. Retention mechanism and selectivity of the peptides were studied by pCEC using a strong cation exchange (SCX) column. The effects of applied voltage, supplementary pressure, organic modifier concentration, ionic strength,, and pH value on pCEC separation were investigated. It was found that the retention mechanism of the peptides in this system is based on a mixed mode of hydrophilic interaction, strong cation exchange, and electrophoresis. Compared with the separation results obtained by reverse phase pCEC and capillary electrophoresis (CE), this mixed-mode pCEC is more powerful for the separation of hydrophilic peptides with similar charge-to-mass ratio.

Separation of peptides by strong cation-exchange capillary electrochromatography

Separation of small peptides on ion-exchange capillary electrochromatography (IE-CEC) with strong cation-exchange packing (SCX) as stationary phase was investigated. It was observed that the number of theoretical plates for small peptides varied from 240 000 to 460 000/m, and the relative standard deviation for t(0) and the migration time of peptides were less than 0.57% and 0.27%, respectively for ten consecutive runs. Unusually high column efficiency has been explained by the capillary electrophoretic stacking and chromatofocusing phenomena during the injection and separation of positively charged peptides. The sample buffer concentration had a marked effect on the column efficiency and peak area of the retained peptides. The influences of the buffer concentration and pH value as well as the applied voltage on the separation were investigated. It has been shown that the electrostatic interaction between the positively charged peptides and the SCX stationary phase played a very important role in IE-CEC, which provided the different separation selectivity from those in the capillary electrophoresis and reversed-phase liquid chromatography. A fast separation of ten peptides in less than 3.5 min on IE-CEC by adoption of the highly applied voltage was demonstrated. (C) 2000 Elsevier Science B.V. All rights reserved.

Capillary electrochromatography using a strong cation-exchange column with a dynamically modified cationic surfactant

A novel mode of capillary electrochromatography (CEC), called dynamically modified strong cation-exchange CEC (DMSCX-CEC), is described in this paper. A column packed with a strong cation-exchange (SCX) packing material was dynamically modified with a long-chain quaternary ammonium salt, cetyltrimethylammonium bromide (CTAB), which was added to the mobile phase. CTAB ions were adsorbed onto the surface of the SCX packing material, and the resulting hydrophobic layer on this packing was used as the stationary phase. Using the dynamically modified SCX column, neutral solutes were separated with the CEC mode. The highest number of theoretical plates obtained was about 190 000/m, and the relative standard deviations (RSD's) for migration times and capacity factors of alkylbenzenes were less than 1.0% and 2.0% for five consecutive runs, respectively. The effects of CTAB and methanol concentrations and the pH value of the mobile phase on the electroosmotic flow and the separation mechanism were investigated. Excellent simultaneous separation of the basic and neutral solutes in DMSCX-CEC with a high-pH mobile phase was obtained, A mixture containing the acidic, basic, and neutral compounds was well separated in this mode with a low-pH mobile phase; however, peak tailing for basic compounds was observed in this mobile phase.

Preparation of monolithic silica column with strong cation-exchange stationary phase for capillary electrochromatography

A monolithic silica based strong cation-exchange stationary phase was successfully prepared for capillary electrochromatography. The monolithic silica matrix from a sol-gel process was chemically modified by treatment with 3-mercaptopropyltrimethoxysilane followed by a chemical oxidation procedure to produce the desired function. The strong cation-exchange stationary phase was characterized by its substantial and stable electroosmotic flow (EOF), and it was observed that the EOF value of the prepared column remained almost unchanged at different buffer pH values and slowly decreased with increasing phosphate concentration in the mobile phase. The monolithic silica column with strong cation-exchange stationary phase has been successfully employed in the electrochromatographic separation of beta-blockers and alkaloids extracted from traditional Chinese medicines (TCMs). The column efficiencies for the tested beta-blockers varied from 210,000 to 340,000 plates/m. A peak compression effect was observed for atenolol with the mobile phase having a low phosphate concentration.

The relationship between diffuse spectral reflectance of the soil and its cation exchange capacity is scale-dependent

Diffuse reflectance spectroscopy (DRS) is increasingly being used to predict numerous soil physical, chemical and biochemical properties. However, soil properties and processes vary at different scales and, as a result, relationships between soil properties often depend on scale. In this paper we report on how the relationship between one such property, cation exchange capacity (CEC), and the DRS of the soil depends on spatial scale. We show this by means of a nested analysis of covariance of soils sampled on a balanced nested design in a 16 km × 16 km area in eastern England. We used principal components analysis on the DRS to obtain a reduced number of variables while retaining key variation. The first principal component accounted for 99.8% of the total variance, the second for 0.14%. Nested analysis of the variation in the CEC and the two principal components showed that the substantial variance components are at the > 2000-m scale. This is probably the result of differences in soil composition due to parent material. We then developed a model to predict CEC from the DRS and used partial least squares (PLS) regression do to so. Leave-one-out cross-validation results suggested a reasonable predictive capability (R2 = 0.71 and RMSE = 0.048 molc kg− 1). However, the results from the independent validation were not as good, with R2 = 0.27, RMSE = 0.056 molc kg− 1 and an overall correlation of 0.52. This would indicate that DRS may not be useful for predictions of CEC. When we applied the analysis of covariance between predicted and observed we found significant scale-dependent correlations at scales of 50 and 500 m (0.82 and 0.73 respectively). DRS measurements can therefore be useful to predict CEC if predictions are required, for example, at the field scale (50 m). This study illustrates that the relationship between DRS and soil properties is scale-dependent and that this scale dependency has important consequences for prediction of soil properties from DRS data

Isolation of lactoperoxidase using different cation exchange resins by batch and column procedures

Lactoperoxidase (LP) was isolated from whey protein by cation-exchange using Carboxymethyl resin (CM-25C) and Sulphopropyl Toyopearl resin (SP-650C). Both batch and column procedures were employed and the adsorption capacities and extraction efficiencies were compared. The resin bed volume to whey volume ratios were 0.96:1.0 for CM-25C and ≤ 0.64:1.0 for SP-650 indicating higher adsorption capacity of SP-650 compared to CM-25C. The effluent LP activity depended on both the enzyme activity in the whey and the amount of whey loaded on the column within the saturation limits of the resin. The percentage recovery was high below the saturation point and fell off rapidly with over-saturation. While effective recovery was achieved with column extraction procedures, the recovery was poor in batch procedures. The whey-resin contact time had little impact on the enzyme adsorption. SDS PAGE and HPLC analyses were also carried out, the purity was examined and the proteins characterised in terms of molecular weights. Reversed phase HPLC provided clear distinction of the LP and lactoferrin (LF) peaks. The enzyme purity was higher in column effluents compared to batch effluents, judged on the basis of the clarity of the gel bands and the resolved peaks in HPLC chromatograms.

Electrochemical investigation of the dimeric oxo-bridged ruthenium complex in aqueous solution and its incorporation within a cation-exchange polymeric film on the electrode surface for electrocatalytic activity of hydrogen peroxide oxidation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

(Table 1) Cation exchange capacity and other characteristics of soils common in Lower Saxony, Germany

The chemical and biochemical processes associated with the filtration of rainwater through soils, a step in groundwater recharge, were investigated. Under simulated climatic conditions in the laboratory, undisturbed soil columns of partly loamy sands, sandy soils and loess were run as lysimeters. A series of extraction procedures was carried out to determine solid matter in unaltered rock materials and in soil horizons. Drainage water and moisture movement in the columns were analysed and traced respectively. The behaviour of soluble humic substance was investigated by percolation and suspension experiments. The development of seepage-water in the unsaturated zone is closely associated with the soil genetic processes. Determining autonomous chemical and physical parameters are mineral composition and grain size distribution in the original unconsolidated host rock and prevailing climatic conditions. They influence biological activity and transport of solids, dissolved matter and gases in the unsaturated zone. Humic substances, either as amorphous solid matter or as soluble humic acids play a part in diverse sorption, solution and precipitation processes.

Cation exchange capacity and water content of ODP sites from Nankai

Pore fluid chlorinity lower than seawater is often observed in accretionary wedges and one of the possible causes of pore water freshening is the smectite to illite reaction. This reaction occurs during diagenesis in the 80-150°C temperature range. Low chlorinity anomalies observed at the toe of accretionary wedges have thus been interpreted as evidence for lateral fluid migration from inner parts of the wedge and the seismogenic zone. However, temperature conditions in Nankai Trough are locally high enough for the smectite to illite transition to occur in situ. Cation exchange capacity is here used as a proxy for smectite content in the sediment and the amount of interlayer water released during the smectite to illite reaction represents in average 12 water molecules per cation charge. Water and chloride budget calculations show that there is enough smectite to explain the chlorinity anomalies by in situ reactions. The shape of the pore fluid chlorinity profiles can be explained if compaction is also taken into account in the model. Lateral flow is not needed. This argument, based solely on chloride concentration, does not imply that lateral flow is absent. However, previous estimations of lateral fluid fluxes, and of the duration of transient flow events along the de.collement, should be reconsidered.