Ligy Philip

This paper describes the fluoride removal potential of a novel sorbent, magnesia-amended activated alumina (MAAA) from drinking water. MAAA, prepared by calcining magnesium hydroxide impregnated alumina at 450 °C has shown high fluoride sorption potential than activated alumina from drinking water. Batch sorption studies were performed as a function of contact time, pH, initial fluoride concentration, and adsorbent dose. Studies were also performed to understand the effect of various other co-existing ions present in real ground water samples. X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDAX) and a gas adsorption porosimetry analyses were used to characterize the physicochemical properties of MAAA. More than 95% removal of fluoride (10 mg l-1) was achieved within 3 h of contact time at neutral pH. Sorption of fluoride onto MAAA was found to be pH dependant and a decrease in sorption was observed at higher pHs. Among the kinetic models tested, pseudo-second-order model fitted the kinetic data well, suggesting the chemisorption mechanism. Among the various isotherm model tested, Sips model predicted the data well. The maximum sorption capacity of fluoride deduced from Sips equation was 10.12 mg g-1. Most of the co-existing ions studied have negligible effect on fluoride sorption by MAAA. However, higher concentrations of bicarbonate and sulfate have reduced the fluoride sorption capacity. © 2007 Elsevier B.V. All rights reserved.

Sorption of three surfactants and personal care products in four types of commonly occurring Indian soils was extensively studied. The soils used in the study were red soil, clay soil, compost soil and sandy soil as classified by American Society for Testing and Materials (ASTM). The three surfactants used in the study were representative of cationic, non-ionic and anionic surfactant groups. The sorption of surfactants followed the descending order: sodium dodecyl sulphate (SDS) > trimethyl amine (TMA) > propylene glycol (PG). The maximum adsorption capacity (Qmax) was obtained in compost soil (28.6 mg/g for SDS; 9.4 mg/g for TMA and 4 mg/g for PG). The rate of adsorption was the maximum in compost soil followed by clay and red soils, and minimum for sandy soils. It is found that the Freundlich model fits the isotherm data better than the Langmuir model. Freundlich coefficient (Kf) increased as the organic content of soils increased. Desorption of target pollutants in tap water was 20–50% whereas acid desorbs 40–90% of target pollutants from soil matrix. It was also found that the adsorption and desorption were significantly affected by the presence of clay and organic matter. The results also indicate that surfactants and personal care products, especially TMA and PG, are highly mobile in sandy soil followed by red soil. Therefore, immobilization of target pollutants is most economical and effective in compost and clayey soils whereas for other type of soils the combination of physiochemical and biological process will be effective option for remediation.

In order to investigate the possible options to improve the pore properties of metal-organic frameworks (MOFs), the sorptive capacity of MOF-199 was assessed based on the two contrasting activation approaches (i.e., ‘chemical (C)’ and ‘thermal (T)’ activation) against four reduced sulfur (S) compounds (RSCs: H2S, CH3SH, (CH3)2S (DMS), and CH3SSCH3 (DMDS)). In order to represent the pristine (C1) and chemically activated forms of MOF-199 (C2), the pores were filled by N,N′-dimethylformamide (DMF) (i.e., as synthesized) and dichloromethane (CH2Cl2), respectively. For comparative purpose, these samples were further subject to thermal treatment (150 °C under 100 mL min−1) and named as T1 and T2, respectively. The combined effects of chemical/thermal activation were found to be most effective to enhance the sorption capacity of MOF-199. (Note that such advantage was not evident when treated by chemical activation only.) Overall, the relative ordering of sorption capacities between four different types of MOF-199, when tested against diverse S compounds, was found to be DMDS > CH3SH > H2S > DMS. The mechanism for such sorption patterns was ascribed to two major competing interactions: a) S-Cu for lighter S and b) –CH3 group (in S compound) and aromatic ring (in MOF ligand) for heavier S. This synergetic effect was also confirmed by both theoretically (density functional theory (DFT)) and experimentally (Fourier Transform Infrared (FTIR) spectroscopy analysis). As such, MOF-199 prepared through both chemical and thermal treatments was identified as an efficient sorbent to capture S compounds even in ambient conditions.

Adsorption and desorption characteristics of endosulfan in four Indian soils were studied extensively. The soils used were clayey soil (CL-lean clay with sand), red soil (GM-silty gravel with sand), sandy soil (SM-silty sand with gravel) and composted soil (PT-peat) as per ASTM (American Society for Testing and Materials) standards. Adsorption and desorption rates were calculated from kinetic studies. These values varied for alpha and beta endosulfan depending on the soil type. Maximum specific adsorption capacities (qmax) for different soils were calculated by Langmuir model. The values varied from 0.1 to 0.45 mg g-1 for alpha endosulfan and 0.0942-0.2722 mg g-1 for beta endosulfan. Maximum adsorption took place in clay soil followed by composted soil and red soil. Adsorptions of alpha and beta endosulfan were negligible in sand. The binding characteristics of various functional groups were calculated using Scatchard plot. Effect of functional groups was more predominant in clayey soil. Organic matter also played a significant role in adsorption and desorption of endosulfan. Endosulfan adsorption decreased drastically in clay soil when the pH was reduced. Desorption was higher at both acidic and alkaline pH ranges compared to neutral pH. Results indicated that alpha endosulfan is more mobile compared to beta endosulfan and mobility of endosulfan is maximum in sandy soil followed by red soil. It can be inferred that crystal lattice of the clay soil plays a significant role in endosulfan adsorption and desorption. Immobilization of endosulfan is more advisable in clay soil whereas biological and or chemical process can be applied effectively for the remediation of other soil types. © 2005 Elsevier Ltd. All rights reserved.

Adsorption and desorption characteristics of three insecticides on four Indian soils were studied. Insecticides used were representative of organochlorine, organophosphate, and carbomate groups. The order of adsorption of pesticides on soils was: lindane > methyl parathion > carbofuran. Compost soil had shown the maximum adsorption capacity. The order of adsorption capacity of various soils were: compost soil > clayey soil > red soil > sandy soil. Adsorption isotherms were better fitted to Freundlich model and Kf values increased with increase in organic matter content of the soils. Thermodynamic parameters indicated favorable adsorption of all the three pesticides in four different soils. Adsorption was exothermic in nature. Distilled water desorbed 30-60% of adsorbed pesticides whereas; organic solvents were able to affect 50-80% of sorbed pesticides. Clay content and organic matter played a significant role in pesticide adsorption and desorption processes. Hysteresis effect was observed in red, clayey and compost soils. Hysteresis effect increased with increase in organic matter and clay content of the soils. © 2008.

In this study, the potential of eight low cost and readily available materials as adsorbents for the removal of pharmaceutically active compounds (carbamazepine (CBZ), diclofenac (DCF) and ibuprofen (IBU)) and nutrients was evaluated through batch studies under various environmental conditions. Results showed that wood charcoal, light-weight expanded clay aggregate (LECA), natural zeolites and waste AAC blocks has a potential as promising adsorbents for the elimination of micro-pollutants with the sorption capacity of 0.57-2.83 mg/g for the selected compounds due to their superior properties including higher surface area, pore volume and organic content. Studies revealed that hydrogen bonding, electrostatic and ligand interaction and Vander Waals force are the predominant mechanisms responsible for the sorption process. The selected materials exhibited better removal of phosphate (70-90%) than ammonia (20-81%) and nitrate (14.1-61.8%). Surface area, pore volume, organic content, cation exchange capacity and elemental content (CaO, Al2O3, K2O and Fe2O3) significantly influenced the pollutant removal by the substrates. Being hydrophobic and anionic in nature, DCF exhibited higher removal than IBU and CBZ. Based on the results, the order of preference of material as adsorbent is: wood charcoal > natural zeolite > waste AAC blocks > LECA > blast furnace slag > natural pyrite > brickbats > sand. The results of this batch study will be helpful for selecting appropriate substrate material for the low-cost natural treatment systems where the bio-enhanced sorption/degradation processes help to eliminate the toxic emerging contaminants (ECs) from wastewater.