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Hexavalent chromium in aqueous environment may result in severe environmental and public health problems. In this study, short-chain polyaniline/palygorskite composites (PANI/PA) were prepared and developed to remove aqueous Cr(VI). Characterized results showed that short-chain polyaniline was successfully incorporated on the surface of PA. The maximum Cr(VI) adsorption amount was found to be 11.54, 14.34, and 16.22 mg/g at 15, 25, and 35°C, respectively, and polyaniline on the adsorbent surface may account for the enhanced Cr(VI) adsorption. Cr(VI) adsorption was highly dependent on both solution pH and ionic strength, which indicates that electrostatic force and anion exchange may account for the increased Cr(VI) adsorption onto PANI/PA. Cr(VI) saturated PANI/PA can be easily desorbed in alkaline solution and regenerated adsorbents still possess high adsorption amount for aqueous Cr(VI). The current study shows that PANI/PA can be used as an effective and recyclable adsorbent for the removal of Cr(VI) in water and wastewater treatment. [ABSTRACT FROM PUBLISHER]

In this study, the removal potential of vinyl polymer/ZnO nanocomposite (PDM/ZnO) by activated sludge (AS) biomass was investigated. PDM/ZnO was effectively removed by AS adsorption (90.3% of total PDM/ZnO removed). The effects of contact time, temperature, pH of the solution, PDM/ZnO production method, initial adsorbate concentration, and properties of the adsorbent were studied. The experimental results are fitted with the Langmuir and Freundlich equations. The adsorption kinetics closely followed the pseudo-second-order model. Thermodynamic parameters (ΔH°, ΔS°, ΔG°) indicate that the adsorption of PDM/ZnO onto AS was feasible, spontaneous, and endothermic. The effects of PDM/ZnO production method and pH value both indicate that electrostatic force may main mechanism in PDM/ZnO adsorption process. The decrease in the adsorption capacity of inactivated sludge suggests that the increase of adsorbent surface area also plays a significant role in the removal process. [ABSTRACT FROM PUBLISHER]

Precipitate adsorbent was produced from aluminum tanning wastewater by alkali precipitation and characterized by XPF, XRD, and FTIR. The results showed that the main components of the precipitate were Al, Ti, and Zr. The adsorption equilibrium for Cr on the precipitate was reached within 60 min. The precipitate had better removal for Cr from wastewater at pH 7.0. The kinetic process of adsorption can be described by the pseudo-second-order kinetic equation, and the adsorption isotherm fitted to the Langmuir model very well. Co-existed cations (Na, Ca) in aqueous solution restrained Cr adsorption on the precipitate. The adsorption of Cr on the precipitate was mainly through the complexation and ion-exchange mechanisms, and oxide may play a major role in Cr adsorption process. [ABSTRACT FROM AUTHOR]

The aim of this study is to evaluate the removal potential of polyacrylate in aqueous solution by activated sludge. Batch experiments investigated the effects of contact time, pH value, temperature, and concentration of adsorbate on polyacrylate removal by activated sludge to evaluate the isotherms, kinetics, thermodynamics, and mechanisms. The materials were characterized by N 2 adsorption-desorption isotherms, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR). The experimental results indicate that more than 90% of polyacrylate was removed by activated sludge in a short time. The adsorption capacity increase with the increase in initial polyacrylate concentration and temperature. Increasing pH value resulted in a decrease in adsorption capacity. The adsorption process fitted well to Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic parameters indicate that the adsorption of polyacrylate onto activated sludge was feasible, spontaneous, and endothermic. The results of kinetics, thermodynamics, SEM-EDS, and FT-IR showed that surface binding, hydrophobic interaction, and hydrogen bond force may play a major role in the removal process. Microbial community structure analysis by 16S rRNA gene revealed that short-term exposure with polyacrylate had a little negative impact on the activated sludge microorganisms. A better understanding of polyacrylate adsorption onto activated sludge is essential for improving predictions of the fate and transport of polyacrylate in waste water treatment process. [ABSTRACT FROM AUTHOR]

Abstract: Polyaniline/attapulgite composite (ATP–PANI) was prepared by in situ chemical oxidation and characterized by FITR, XRD, and TEM. Characterized results showed that polyaniline (PANI) was successfully encapsulated on the surface of attapulgite (ATP). Humic acid (HA) adsorption onto ATP–PANI was investigated by batch experiments and adsorption kinetic tests. In contrast with the low HA adsorption amount on ATP, substantially enhanced HA adsorption onto ATP–PANI was observed. Adsorption isotherms of HA can be well described by Langmuir model and the maximum adsorption amounts were found to be 43.01, 52.91, 61.35mg/g at 15, 25, and 35°C, respectively. HA adsorption increased with rise in temperature indicating of an endothermic process of HA adsorption onto ATP–PANI. Pseudo-second order kinetic equation can fit HA adsorption very well and the adsorption rate decreased with increasing initial HA concentration. HA adsorption decreased monotonously with increasing solution pH. Co-existed cations (Na+, K+, Ca2+) in aqueous solution improved HA adsorption amount on ATP–PANI, and the augment of HA adsorption amount was order as Ca2+ >K+ >Na+. Results of HA adsorption onto ATP–PANI showed that the electrostatic interaction between amine and imine groups of the adsorbents and HA molecules in solution may account for the enhanced HA adsorption. The HA molecules adsorbed on ATP–PANI can be effectively desorbed in 2M NaOH solution, and regenerated adsorbent can be repeatedly used in the subsequently four adsorption-regeneration cycles with little loss of HA adsorption amount. [Copyright &y& Elsevier]

Abstract: Tannic acid is known as one of the refractory organic pollutants in water. Amino-functionalized magnetic nanoadsorbent (Fe3O4@SiO2-NH2) exhibited high adsorption capacity for aqueous TA with maximum adsorption amount of 136.23mg/g at 25°C. TA adsorption on the adsorbent could be well described by Langmuir adsorption model and the adsorption process was endothermic. Furthermore, pseudo-second adsorption kinetics can fit TA adsorption data very well, and the adsorption rate decreased with increasing initial TA concentration. The presence of Na+, K+, and Ca2+ may result in enhanced TA adsorption. In addition, TA adsorption over the adsorbent was highly dependent on solution pH and the maximum adsorption amount was found to be at pH 6.0. The XPS analysis revealed that TA adsorption over the adsorbent may be attributed to the surface complexation between the amino groups of the adsorbent and TA in solution. The TA loaded adsorbent can be effectively desorbed in a 0.5M HCl solution, and the regenerated adsorbent can be recycled. [Copyright &y& Elsevier]