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Ca-Al layered double hydroxides (LDHs) with different Ca/Al molar ratios were composited at pH ranges, using a co-precipitation method, and were experimented to remove fluoride from wastewater and studied in terms of isotherm models such as Langmuir and Freundlich reactions. The composite LDHs were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). The results showed that different synthesis conditions of Ca-Al LDHs had an influence on their morphology, layered structure, and particle size distribution, which substantially affected the uptake capacity for aqueous fluoride. LDHs with the Ca/Al molar ratio of 2 and synthesized at the pH of 12 had the highest capacity for the fluoride removal (e.g., 146.6 mg/g) and such reaction reached an equilibrium within 1 h. The Freundlich model was a better fit for this study. The high adsorption method of Ca-Al LDHs can be favorable to removing fluoride from wastewater streams. [ABSTRACT FROM AUTHOR]

In this study, thermo-sensitive magnetic cationic hydrogel (TSMCH) based on (3-acrylamidopropyl) trimethyl ammonium chloride (APTMACl) and N-isopropylacrylamide (NIPAm) was synthesized by free radical copolymerization. The TSMCH was characterized with Fourier transform infrared spectroscopy, thermal gravimetric analysis, x-ray diffraction, scanning electron microscope with energy dispersive x-ray, vibrating sample magnetometer, and zeta potential, and employed as adsorbent for adsorbing reactive red (RR) dye. Effects of molar ratios of APTMACl to NIPAm on the adsorption capacity of TSMCH were studied, and the results showed that a maximum adsorption capacity (1428.57 mg RR g−1TSMCH) had been achieved when the molar ratio of APTMACl to NIPAm was 1:1. The adsorption isotherm of RR was well fitted by the Langmuir isotherm equation. TSMCH had good selectivity for adsorbing RR. Solution pH hardly affected the adsorption of RR on the TSMCH. The adsorption amount of RR increased with the increase of temperature. The adsorption–desorption of TSMCH was evaluated in three circles and a high regeneration rate was demonstrated. [ABSTRACT FROM AUTHOR]

Magnetic cationic hydrogel (MCH) was synthesized, and its removal efficiency and mechanisms in regard to natural organic matter (NOM, represented by humic acid and fulvic acid) from the aqueous environment were studied. The effects of time, adsorbent dosage, initial pH, ionic strength, background ions, and NOM types were also investigated. MCH was characterized and found to have a strong magnetic character, yielding an extra advantage for recycling and reuse. Batch studies showed that the removal of Aldrich humic acid (AHA) by MCH was effective. The main mechanism for the removal of NOM is believed to be due to electrostatic interaction. NOM with larger molecular weight tended to be preferentially removed. Solutions with low pH, high ionic strength, and background electrolytes containing calcium, sulfate and bicarbonate were unfavorable for AHA removal. The adsorption–desorption of MCH was evaluated in three cycles, and demonstrated high regeneration rates. [Copyright &y& Elsevier]

The effects of humic acid (HA) on As(V) removal by zero-valent iron (Fe0) from groundwater, associated with corrosion products analyses, were investigated using batch experiments. It was found that arsenic was rapidly removed from groundwater possibly due to its adsorption and co-precipitation with the corrosion products of Fe0. The removal rate of arsenic by Fe0 was inhibited in the presence of HA probably because of the formation of soluble Fe-humate in groundwater which hindered the production of iron precipitates. A longer reaction time was then required for arsenic removal. Such an influence of HA on arsenic removal increased with increasing HA concentration from 5 to 25mgL−1. The binding capacity of HA for dissolved Fe was estimated to be about 0.75mg Femg−1 HA. When the complexation of HA with dissolved Fe was saturated, further corrosion of Fe0 would produce precipitates, which significantly accelerated the removal of arsenic from groundwater via adsorption and co-precipitation with the corrosion products. Iron (hydr)oxides such as maghemite, lepidocrocite, and magnetite were characterized by XRD analyses as the corrosion products, while As(V) was found on the surface of these corrosion products as detected by fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. [Copyright &y& Elsevier]

Abstract: Adsorption of anionic surfactant (sodium dodecylbenzenesulfonate, SDBS) and nonionic surfactant (an alcohol ethoxylates with 12 carbons and 9 oxyethyl groups, A12E9) mixtures, widely used as the major constituents of synthetic detergents in China and become the most common pollutants in the environment, on soils was conducted to investigate the behavior of mixed surfactants in soils. The effects of addition order and mixing ratios of two surfactants, associated with pH and ion strength in solutions, on adsorptions were considered. The results show that saturated adsorption amount of SDBS and A12E9 on soils decreased respectively when A12E9 was added into soils firstly compared with that secondly, possibly resulting from the screening of A12E9 to part adsorption sites on soils and the hydrocarbon chain–chain interactions between SDBS and A12E9. The adsorption of SDBS and A12E9 on soils was enhanced each other at pre-plateau region of isotherms. At plateau region of isotherms, the adsorption of SDBS on soils decreased with the increase of molar fraction of A12E9 in mixed surfactant solutions, while that of A12E9 increased except the molar ratio of SDBS to A12E9 0.0:1.0. With the increase of pH in mixed surfactant solutions, adsorption amount of SDBS and A12E9 on soils decreased, respectively. The reduction of ion strength in soils resulted in the decrease of adsorption amount of SDBS and A12E9 on soils, respectively. [Copyright &y& Elsevier]