Influence Of Acid Treatment Research Articles

Adsorption of Pb 2+, Cd 2+ and Sr 2+ ions onto natural and acid-activated sepiolites

The adsorption mechanisms of Pb 2+, Cd 2+ and Sr 2+ ions on natural sepiolite and the influence of acid treatment on the adsorption capacity of sepiolite were investigated. The point of zero charge, pH pzc, is 7.4 ± 0.1 for natural sepiolite and 6.9 ± 0.1 for partially acid-activated sepiolite. The shift of the pH pzc of sepiolites toward lower pH values in solutions of Pb 2+ and Cd 2+ ions indicates that specific adsorption of these cations on natural and acid-activated sepiolites occurred, which was more pronounced for Pb 2+ ions than for Cd 2+ ions. There was no shift of the pH pzc in solution containing Sr 2+ ions, suggesting that specific adsorption of this cation did not occur. The affinity for ion exchange with the Mg 2+ ions from the sepiolite structure was the highest for Pb 2+ ions, then Cd 2+, whereas the affinity for Sr 2+ ions was negligible. The adsorption isotherms suggest that the sequence of the efficiency of the sepiolites adsorption is Pb 2+ > Cd 2+ > Sr 2+. The retention of Pb 2+ and Cd 2+ ions by sepiolite occurs dominantly by specific adsorption and exchange of Mg 2+ ions from the sepiolite structure. The concentration in the external outer sphere of the Stern layer by electrostatic forces is the dominant mechanism for the retention of Sr 2+ ions on the surface of sepiolites. Despite increases in the surface areas upon acid activation, improvements in the adsorption were not observed, as a result of the decreasing number of Mg–OH groups, as main centers for specific adsorption, and the number of Mg 2+ ions available for ion exchange with Pb 2+, Cd 2+ and Sr 2+ ions. The removal of Mg–OH groups from the sepiolite also resulted in a decrease in the point of zero charge and an increase of the relative surface acidity, from 2.6 ± 0.1 for the natural to 6.4 ± 0.1 for the acid-activated sepiolite.

The Influence of Acid Treatment on the Composition of Bentonite

AbstractBentonite from the ‘Bogovina’ coal mine in Serbia, was characterized. The influence of acid treatment on its composition, as well as mathematical descriptions of this influence are reported. The purpose of this work was to correlate the concentration of the acid used for the treatment with the resulting bentonite composition. X-ray diffraction (XRD), infrared spectroscopy and quantitative chemical analysis were employed to define the changes caused by acid treatment.The contents of all the cations, except Si, decreased exponentially with increasing concentration of the HCl used for the treatment of the bentonite. This approach was tested on previously published data and was shown to be valid.The basal reflections of smectite decreased gradually and eventually disappeared after intense treatment, while the other reflections remained in the XRD patterns of all the samples, but decreased slightly with increasing acid strength. In addition, the amount of X-ray amorphous matter formed increased rapidly with increasing acid concentration up to 4.5 M. With further increase in the acid strength, the amount of X-ray amorphous matter remained virtually constant.

Influence of Acid Treatment on Dispersion of Carbon Nanotubes in PBO Matrix

Dispersion of carbon nanotubes (CNTs) in polymeric matrix has been a key factor on forming CNTs/polymer composites. In this paper, the O-MWNTs were first derived from raw multi-walled carbon nanotubes (MWNTs) which were purified with a mixed solution of concentrated H2SO4 and concentrated HNO3, then the O-MWNTs were dispersed with sonication in H3PO4 and the resultants were denoted as U-MWNTs. After processed with poly (p-phenylene–2, 6–benzoxazole)(PBO) by in-situ polymerisation successfully, the O-MWNTs and the U-MWNTs were finally formed into O-MWNTs/PBO composites and U-MWNTs/PBO composites, respectively. The SEM and AFM morphological analysis showed that a perfect dispersion of U-MWNTs in U-MWNTs/PBO composites was obtained. These composites can be widely used in photoelectric devices and engineering applications, etc.

Influence of acid treatment on the surface activity and mass transfer inhibition of a splittable surfactant

AbstractA splittable surfactant, Triton SP‐190, was used to evaluate the effects of acid treatment on the mass transfer rate of an extraction process and on the interfacial tension‐lowering activity of a system containing this surfactant. Equilibrium and dynamic interfacial tensions at the interface of CCl4 and the aqueous phase containing surfactant were measured by using pendent drop tensiometry enhanced by video digitization. A single‐drop extraction apparatus was used to obtain the extraction percentage of acetic acid from the dispersed CCl4 droplets to the aqueous phase. The results indicate that the inorganic acid treatment can inhibit the dynamic and equilibrium interfacial tension‐lowering activity of Triton SP‐190. The mass transfer resistance induced by the addition of Triton SP‐190 can also be reduced by the pre‐treatment of acid. The effectiveness of acid treatment on both properties was greater at low pH values, lower surfactant concentrations, and longer treatment times. With HCl treatment, the equilibrium interfacial tension was not able to increase to the value of a surfactant‐free system, but approached a maximum value which was independent of the pH value, but dependent on surfactant concentration. On the contrary, the extraction percentage, which has decreased due to the presence of surfactant, can be recovered completely to that of a surfactant‐free system by acid treatment. The acid‐treatment time required to achieve a significant recovery of mass transfer rate was much longer than that required to recover the interfacial tension. The present results also demonstrate that the constituents contained in an acid‐treatment system had different effectiveness in affecting the interfacial tension and mass transfer rate due to the different mechanisms involved. Copyright © 2004 Society of Chemical Industry

Influence of acid treatments on the activity of carbon nanotube-supported catalysts

Influence of acid treatments on the activity of carbon nanotube-supported catalysts

Influence of in vivo Formed Salivary Pellicle on Enamel Erosion

This study assessed the protective effect of the salivary pellicle formed in vivo during 24 h or 7 days against demineralization of bovine enamel caused by citric acid. In addition, the influence of acid treatment on the behavior of the pellicle was investigated. Enamel specimens with and without in vivo pellicles were immersed in citric acid (0.1, 1.0%) over 30, 60, and 300 s, and processed for scanning (SEM) and transmission electron microscopy (TEM), as well as for measurement of surface microhardness (SMH). Specimens coated with the in vivo formed pellicles revealed less extensive erosive demineralization of the enamel surface compared to uncovered enamel specimens. SEM analysis and SMH results did not indicate distinct differences between erosive surface alterations on enamel slabs covered with 24–hour pellicles and on those covered with 7–day pellicles. TEM analysis showed that the pellicle layer was dissolved in part from the enamel surface due to acid exposure. However, pellicle residues could be detected by TEM in all specimens, even after 5–min exposure to 1.0% citric acid. It is concluded that the in vivo salivary pellicle can resist the acidic action to some extent and provides protection to the underlying enamel surface against erosive destruction caused by short–term action of citric acid.

The Influence of Acid Treatment on the Sorption Properties of Latvian Clays

n-Hexane and carbon tetrachloride vapour sorption isotherms at 20°C are reported for two series (A and U) of Latvian clays. Samples of the A series were prepared from triassic montmorillonite clays by sulphuric or hydrochloric acid treatment at 100°C. Samples of the U series were prepared from quaternary hydromica clays in the same way. It was found that the vapour sorption isotherms exhibit a reproducible closed hysteresis loop at P/P0 = 0.3–0.99. For samples of series A, both the shape and the location of the hysteresis loop change as the acid concentrations increase. The BET specific surface area of both series samples increases at first and then decreases as the concentration of acid increases. Kelvin pore radii distribution curves have been calculated. It was found that the pore radius increases when the concentration of acid increases. The total pore volume of the samples was estimated as the amount of adsorbed vapour at P/P0=0.99. The pore volume at first increases and then decreases when the concentration of acid increases.