Search

In this study, two new epoxy-modified oilwell cement slurries were synthesized. All characterization measurements were performed and compared in relation to a standard cement slurry, which was synthesized using only cement and water. The XRD patterns, as well as TG/DTG and DSC analyses have suggested that portlandite (Ca(OH)2) and carbonate phases were not present in detectable amounts in the new cement slurries. The isothermal kinetic data of the interaction of HCl with the epoxy-modified cement were obtained using the batch mode from 25 to 55 degrees C. The kinetic data were best fitted to the second-order and the Avrami kinetic models, since differences between experimental and calculated values were lower for these models. The intraparticle diffusion model has pointed out that the new slurries present positive values for the parameter "C," which is related to higher boundary layer resistance to HCl diffusion into the internal parts of the slurries, in relation to the standard slurry. The characterization and the HCl interaction kinetic studies have suggested that the new cement slurries present good potential, from the chemical viewpoint, to be used in oilwell operations.

Isothermal calorimetry was used to determine enthalpy changes for interaction of divalent cobalt, nickel, copper, and zinc chlorides with silica gel functionalized with vanillin, Sil Van. The thermal effect, Q int , and the corresponding amount of cation that interacts, n int , were obtained in the same experiment. Langmuir expressions for adsorption isotherms were applied to determine the maximum adsorption capacity to form a monolayer, N mon , and the energy of interaction for a saturated monolayer per gram of Sil Van, Q mon . From knowledge of N mon and Q mon , the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of Sil Van, Δ mon H m , was determined. Interactions between the Lewis-acidic cations and the donor atom attached to silica are reflected by Δ mon H m values in the order Ni2+ > Cu2+ > Zn2+ ≅ Co2+.

In this work silica–aminopropyl (Sil–NH2) was synthesized and employed to evaluate the quantitative roles of temperature, pH, dye concentration, and Hg(II) or anionic surfactant SDB interferents in the adsorptions of blue and red remazol dyes in aqueous medium using four distinct 24 factorial designs. The results were analyzed statistically using multiple regressions, Student's t-test, analysis of variance, and F-test. Polynomial modelings were used to define the most important factors affecting dye adsorption. The results indicate that the principal effects of dye concentration and pH, as well as most of the interactions of all factors, are statistically very important in relation to the equilibrium adsorption quantities. However, the adsorption Gibbs free energies are influenced, in general, only by pH, dye concentration, and some binary interactions. Temperature changes do not affect the ΔG values significantly.

In this work, a hybrid silica/chitosan was synthesized and characterized by nitrogen elemental analysis and thermal analysis (TG, DTG, DTA, and DSC) and BET surface area. The hybrid was used in adsorption studies of two anionic dyes from aqueous solutions. A rise of temperature accelerates mass transfer of dyes into the hybrid. However, the maximum adsorption capacities reach similar values from 25 to 55 °C. The kinetic data were first evaluated in relation to the decrease of the time-related residual concentration of the dyes in solution, where the second-order model has presented the best fitting. The solid-phase interaction of dye data presents a rough fitting to the traditional first-order Lagergren kinetic model. However, a modified Avrami kinetic equation was successfully fitted to the kinetic quantities, where from five to seven kinetic regions were found. A pore-diffusion model has also demonstrated that the diffusion is the rate-controlling interaction mechanism. However, the experimental–calculated comparative values are the best way to evaluate a specific aqueous- or solid-phase kinetic model.

Sílica-dithizone (Sil-dtz) was synthesized and used to adsorb Hg(II) in solution at pH 6.0. Increasing the temperature accelerates the mass transfer of Hg(II) to the silica surface. The kinetic data were evaluated using the traditional pseudo-first-order Lagergren equation and an alternative Avrami kinetic equation. From the latter equation, two regions presenting distinct kinetic parameters were found, at 25 and 35 degrees C, and the use of the parameter n was also related to the determination of distinct kinetic orders. Variations of the adsorption kinetic rate in relation to the time and the temperature were also calculated and are discussed. The adsorption isotherms data were well fitted to the Freundlich model. Interestingly, good adsorption data correlation of the Langmuir model and experimental values was observed only at 45 and 50 degrees C, suggesting, for this temperature range, the formation of complexes with the proportion Hg:dithizone 1:1 on the silica surface.

A 2(4-1) fractional factorial design is employed to study Cu(II) desorption on organofunctionalized silicas. Two types of silicas, at amounts of 100 and 200 mg and two acidic levels, and contact times were employed. Our study indicates that the effects of HCl and contact time on the percentage number of moles of copper are 13.23 and 18.53, respectively. However, the binary interaction of these factors is very small. Three important antagonistic and synergistic binary effects involving the silica type, acidic quantity, and contact time factors are found. The silica mass showed an insignificant principal effect. The desorption data are compared with those previously published concerning adsorption processes on both functionalized silicas. Copyright 2000 Academic Press.

The silylating agent 3-trimethoxysilyl-1-propanethiol was immobilized on silica gel. Sulphur analysis showed 0.98 mmol of thiol groups per gram of support. These groups chemisorbed divalent cations: nickel, cobalt, copper, and mercury in the pH range from 1 to 6. The adsorption is more significant for mercury in relation to the other cations in the pH range studied. The primary amines, methylamine, ethylamine, n-butylamine, and benzylamine, were adsorbed on silica-thiol surface and on silica-thiol surface with mercury adsorbed. The values of adsorption constants were calculated using Langmuir isotherms data. Using these values, equilibrium constants and DeltaG values for each adsorption system were also obtained. When mercury is present on the silica surface, the adsorption of n-butylamine and benzylamine is significatively enhanced in relation to the other amines. This behavior suggests that the degree of adsorption of the studied amines is intimately related to their dissociation constants. Copyright 1997 Academic Press. Copyright 1997Academic Press

Interaction parameters at epichlorohydrin-crosslinked chitosan beads/Cr(VI) interfaces from aqueous solutions was obtained by using immersion heat-conduction microcalorimetry. This technique permits simultaneous determinations of adsorbed amounts and interaction energies. The experimental variables evaluated were pH of the Cr(VI) solutions of 4.0 and 6.0, initial Cr(VI) concentration in solution of 0.50 and 5.00 × 10 −3 mol L −1 and temperature of 25 and 45 °C. The calorimetric results were evaluated using a 2 3 full factorial design. The responses were the adsorption amounts ( n int ), the adsorption energies ( Q int ) and the adsorption enthalpies ( Δ int H ). The results indicated that all thermodynamic responses (adsorption energies and adsorption enthalpies) are all exothermic in nature. The initial Cr(VI) concentration in solution was the most important parameter in all responses evaluated in this study. Polynomial fits have pointed out that almost all interactive effects are statistically important on the values of n int , Q int and Δ int H . It is concluded that the thermodynamical aspects of the Cr(VI) adsorption parameters are greatly influenced by the interactive factors and not by temperature changes alone.

A surface tension technique was used to determine the critical aggregation concentration (cac) of a yellow and a red dye in relation to the presence of the anionic surfactant sodium dodecylbenzene sulfonate (DBS) and to temperature changes in buffered aqueous solutions. The cac values of the yellow dye increase from 25 to 45 °C (from 41.37 to 50.32 mg L−1) and decrease from 45 to 55 °C (from 50.32 to 38.72 mg L−1). The cac values for the red dye/DBS aggregates decrease (from 124.52 to 88.50 mg L−1) from 25 to 55 °C. Adsorption of the two dyes onto a mesoporous aminopropyl silica (Sil–NH2) was also studied. The adsorption of the yellow dye increases with an increase in temperature from 25 to 55 °C. In the presence of DBS the adsorption on Sil–NH2 for the yellow dye decreases, and for the red dye increases from 25 to 55 °C. Adsorptions occurred below and above the cac of the anionic dyes/DBS aggregates. Adsorption of the dyes onto Sil–NH2 fitted well to the Langmuir, Freundlich, and Redlich–Peterson adsorption models. However, in the presence of DBS, only the Freundlich model fit the experimental adsorption data at low dye concentrations (less than 400 mg L−1). In this case, the Redlich–Peterson model was only fitted to the red dye adsorption data. The magnitude of the Dubinin–Radushkevich energetic parameters (E, from 7.00 to 15.00 kJ mol−1) indicates that the adsorption of the dyes onto Sil–NH2, in the absence and in the presence of DBS, is controlled by water adsorbed/dye in solution ion-exchange interactions. It is observed that the values of Δ ads H are positive for both dyes and the values are quite similar to each other. The exception is the adsorption of the yellow dye in the presence of DBS, which is slightly exothermic. The Δ ads G values are all negative. However, the interactions of the dyes with Sil–NH2 silica are more spontaneous in the presence of the surfactant. The positive adsorption entropy values ( Δ ads S ) for the interaction of the dyes suggest that entropy is a driving force of the dye adsorptions. However, the entropic contribution is higher for the adsorptions in the presence of DBS. It was suggested that the chemical structures of the dyes play an important role in the formation of the dye/DBS aggregates and in dye adsorption onto the aminopropyl silica.

Mesoporous activated carbon has been prepared from coconut coir dust as support for adsorption of some model dye molecules from aqueous solutions. The methylene blue (MB) and remazol yellow (RY) molecules were chosen for study of the adsorption capacity of cationic and anionic dyes onto prepared activated carbon. The adsorption kinetics was studied with the Lagergren first- and pseudo-second-order kinetic models as well as the intraparticle diffusion model. The results for both dyes suggested a multimechanism sorption process. The adsorption mechanisms in the systems dyes/AC follow pseudo-second-order kinetics with a significant contribution of intraparticle diffusion. The samples simultaneously present acidic and basic sites able to act as anchoring sites for basic and acidic dyes, respectively. Calorimetric studies reveal that dyes/AC interaction forces are correlated with the pH of the solution, which can be related to the charge distribution on the AC surface. These AC samples also exhibited very short equilibrium times for the adsorption of both dyes, which is an economically favorable requisite for the activated carbon described in this work, in addition to the local abundance of the raw material.

In this work silica-aminopropyl (Sil-NH2) was synthesized and employed to evaluate the quantitative roles of temperature, pH, dye concentration, and Hg(II) or anionic surfactant SDB interferents in the adsorptions of blue and red remazol dyes in aqueous medium using four distinct 2(4) factorial designs. The results were analyzed statistically using multiple regressions, Student's t-test, analysis of variance, and F-test. Polynomial modelings were used to define the most important factors affecting dye adsorption. The results indicate that the principal effects of dye concentration and pH, as well as most of the interactions of all factors, are statistically very important in relation to the equilibrium adsorption quantities. However, the adsorption Gibbs free energies are influenced, in general, only by pH, dye concentration, and some binary interactions. Temperature changes do not affect the deltaG values significantly.

In this work, a hybrid silica/chitosan was synthesized and characterized by nitrogen elemental analysis and thermal analysis (TG, DTG, DTA, and DSC) and BET surface area. The hybrid was used in adsorption studies of two anionic dyes from aqueous solutions. A rise of temperature accelerates mass transfer of dyes into the hybrid. However, the maximum adsorption capacities reach similar values from 25 to 55 degrees C. The kinetic data were first evaluated in relation to the decrease of the time-related residual concentration of the dyes in solution, where the second-order model has presented the best fitting. The solid-phase interaction of dye data presents a rough fitting to the traditional first-order Lagergren kinetic model. However, a modified Avrami kinetic equation was successfully fitted to the kinetic quantities, where from five to seven kinetic regions were found. A pore-diffusion model has also demonstrated that the diffusion is the rate-controlling interaction mechanism. However, the experimental-calculated comparative values are the best way to evaluate a specific aqueous- or solid-phase kinetic model.

The nature of interactions between metal ions Ag(I), Hg(II), Cu(II) and chitosan derivative of 1,2-ethanedithiol, QTDT, was investigated by isothermal calorimetry using the membrane breaking technique. Simultaneous determination of thermal effects, Q(int), and amount of cation that interacts, n(int), are described. The experimental data have been interpreted in terms of the Langmuir equation to determine the maximum adsorption capacity to form a monolayer, N(mon), and the energy of interaction for a saturated monolayer per gram of QTDT, Q(mon). With N(mon) and Q(mon), the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of QTDT, Delta(mon)H(m), was determined. The Delta(mon)H(m) values for Ag(I), Hg(II), and Cu(II) were -60.56, -58.05, and -84.36 kJ mol(-1), respectively. Negative values of DeltaG show the spontaneity of the interaction processes. The least entropically favourable processes, i.e., those which present more negative DeltaS values, seem to be compensated by the more favourable enthalpic parameter.

In this work, chitosan beads were synthesized in acidic medium and cross-linked in 1% glutaraldehyde solution. The characterization of the materials using TG/DTG, XRD, and BET surface areas showed that the beads did not modify their characteristics after the cross-linking reaction. The cross-linked beads were utilized as adsorbents for the removal of the yellow-, blue-, and red-anionic reactive dyes from aqueous solutions at pH 2.0. Adsorption of the yellow-dye increased from 25 to 50 degrees C. However, adsorption of the blue-dye decreased from 25 to 50 degrees C. Interestingly, the adsorption of the red-dye decreased from 25 to 35 degrees C and increased from 45 to 50 degrees C. The kinetic data were evaluated using an Avrami kinetic model, where the parameter n was related to the determination of changes in the adsorption mechanisms. Adsorption data of the dyes in relation to the contact time, the chemical structures of the dyes, and temperature were presented and were discussed.

In this work, thin chitosan membranes were utilized as an adsorbent for the removal of Hg(II) from aqueous solutions. A rise of temperature accelerates the mass transfer of Hg(II) to the membranes, surfaces. The kinetic data did not present a good fitting to the traditional Lagergren adsorption kinetic equations. An alternative Avrami kinetic equation was employed and successfully fitted to the kinetic adsorption quantities. From this new equation, two regions presenting distinct kinectic parameters were found, and the use of the parameter n was also relationed to the determination of the kinetic order. Variations of the adsorption kinetic rate in relation to the time, the initial Hg(II) concentration, and the temperature were also calculated and are discussed.

Chitosan can use its protonated amine groups to adsorb strongly anionic species from diluted solutions. In this work, adsorption and thermochemical data on the interaction of the dye indigo carmine with chitosan in aqueous medium were found, in order to obtain new adsorption data on this relatively unexplored chitosan field. The studies were carried out by the batch method from 35 to 50 degrees C. The adsorption results were well fitted to both Langmuir and Freundlich adsorption models. The increase in the temperature decreased the adsorption of the dye. The enthalpy of interaction, when a monolayer of the dye was formed on the chitosan surface, delta(int)H, of -23.2 kJ mol(-1) was encountered for all temperature ranges studied. The spontaneity of the interaction is indicated by the delta(int)G values from -9.1 to -8.2 kJ mol(-1). Other thermodynamic quantities were also calculated and are discussed.

Adsorption processes of Cu(II), Co(II), and Hg(II) on two aminated silica gel surfaces with immobilized ethylenediamine and diethylenediamine groups were studied by a new 2(3) full factorial design. Two metal quantity levels, temperatures of 25 and 50 degrees C, and silica amounts of 100 and 200 mg were employed. Our study indicates that higher factorial design levels increase adsorption for all metals evaluated, with the exception of the mass parameter. Adsorption is also significantly affected by important antagonistic and synergistic effects involving all factors. Both functionalized silica gel surfaces present higher interactions and good perspectives in preconcentration studies for mercury. The factorial design results are also discussed in terms of some solvation properties for each of the metals studied. Copyright 2001 Academic Press.