M. Streat

Sorption of phenol and para-chlorophenol from water using conventional and novel activated carbons

A comparative study of the sorption of phenol and p-chlorophenol from water has been performed using novel samples prepared by carbonisation and subsequent activation of straw and used rubber typres as well as conventional activated carbons based on coal, coconut shell and wood. Pseudo-equilibrium sorption of phenol and p-chlorophenol obeys a Freundlich type adsorption isotherm of the form; q = k cn in the adsorbate concentration range 0–6 mmol 1−1. Measured values of k and n indicate that the sorption of phenol and p-chlorophenol onto active carbons derived from straw and used rubber tyres is almost identical to that for conventional activated carbons. The rate of adsorbate uptake has been measured and the sorption half-times lie in the range 1.4–15 min for phenol. The sorption kinetics of the straw and rubber tyre based carbons are likewise identical to conventional carbons based on coal and wood but appreciably faster than the coconut shell sample selected for comparison.

Adsorption of cadmium by activated carbon cloth: influence of surface oxidation and solution pH.

The surface of activated carbon cloth (ACC), based on polyacrylonitrile fibre as a precursor, was oxidised using nitric acid, ozone and electrochemical oxidation to enhance cadmium ion exchange capacity. Modified adsorbents were physically and chemically characterised by pH titration, direct titration, X-ray photoelectron spectroscopy, elemental analysis, surface area and porosimetry, and scanning electron microscopy. BET surface area decreased after oxidation, however, the total ion exchange capacity increased by a factor of approximately 3.5 compared to the commercial as-received ACC. A very significant increase in cadmium uptake, by a factor of 13, was observed for the electrochemically oxidised ACC. Equilibrium sorption isotherms were determined at pH 4, 5 and 6 and these showed that cadmium uptake increased with increasing pH. There was clear evidence of physical damage to ozone-oxidised fibre, however, acid and electrochemically oxidised samples were completely stable.

Characterisation of the surface of oxidised carbon adsorbents

The surface reactivity and functional group content of a series of oxidised active carbons has been assessed by elemental analysis, electrophoretic mobility measurements and potentiometric titrations. Oxidation of carbons with hot air resulted in a greater proportion of relatively weak acidic surface functional groups (i.e., phenolic), whereas nitric acid modification produced a greater amount of carboxylic groups. Electrophoretic mobility measurements suggest that the carbon surface is negatively charged within the range of the pH values studied. pH titration results indicate that the surface acidity of active carbons is stronger than that of a commercial polymeric carboxylic acid ion exchange resin. Possible mechanisms of carbon surface oxidation are discussed.

Characterisation of novel modified active carbons and marine algal biomass for the selective adsorption of lead

This paper discusses the sorption performance of novel materials for the removal of lead(II) and copper(II) from near-neutral aqueous solutions. Active carbons with surface heteroatoms of oxygen and phosphorus have been prepared. The surface functional groups display weakly acidic ion exchange characteristics. The optimum solution pH for maximum metal sorption is related to the pK values of the surface functional groups. In oxygenated active carbons, pK values are not distinct but can be obtained by describing proton binding to the heterogeneous adsorbent surface as a continuous proton affinity distribution. Information derived from zeta-potential measurements combined with knowledge of the pK distribution function and concentration of surface functional groups has been used to explain the selectivity of oxidised active carbons towards lead(lI) in the presence of copper(II) from multi-metal bearing solutions. Marine algal-based biosorbents have been challenged with lead(II) and copper(II)-bearing wastewater. The weakly acidic carboxyl groups of structural polysaccharides present within the algal matrix display high sorption capacity for both metals. The negative surface charge of algal particles results in electrostatic interactions as well as coordination between metal species and the adsorbent surface. Proton affinity for the algal surface lowers the negative surface potential at pH values around 2. The surface functional groups in algae unlike those in oxidised active carbons may be represented by discrete acid-dissociation constant values. The influence of conformational differences in uronic-acid segments upon metal ion selectivity is discussed.

Removal of Cr(VI) by solvent impregnated resins (SIR) containing aliquat 336

Abstract Solvent impregnated resins (SIR) have been prepared by a wet-impregnation technique using two different polymer matrices, Diaion HP-20 and HP-2MG. Diaion HP-20 possesses a hydrophobic styrene–divinylbenzene polymeric structure whereas HP-2MG is a hydrophilic methacrylic based polymer. Aliquat 336 was employed as the extractant and acetone as the solvent for impregnation. Batch sorption studies have shown that solvent impregnated resins containing Aliquat 336 can be effectively used for the removal of hexavalent chromium from aqueous solutions. The Langmuir adsorption isotherm gave a satisfactory fit of the equilibrium data. A kinetic study has been performed for SIR at two different concentrations of Cr(VI) (2×10 −4 and 4×10 −4 M). A finite-bath diffusion-control model with changing bulk concentration was used for sorption of Cr(VI) by SIR. Increasing the impregnation ratio from 0.5 to 1.0 (g Aliquat 336/g polymer adsorbent) increased the breakthrough capacity in a column-mode sorption study. The Cr(VI) bound by the SIR has been quantitatively desorbed using 0.1 M NaOH–0.1 M NaCl mixture.

ADSORPTION OF URANIUM FROM AQUEOUS SOLUTIONS USING ACTIVATED CARBON

Abstract The adsorption of uranium from aqueous solution has been investigated using conventional commercially available activated carbons. It was found that treatment with hot nitric acid oxidized the surface of activated carbon and significantly increased the adsorption capacity for uranium in near-neutral and slightly acidic nitrate solutions. Equilibrium data were fitted to a simplified Freundlich isotherm for the purpose of comparison of oxidized and as-received samples. The decontamination of aqueous solutions was investigated in small column experiments. An ionexchange mechanism of uranium sorption from aqueous solution is discussed.

Extraction of Cd(II) and Cu(II) from phosphoric acid solutions by solvent-impregnated resins (SIR) containing cyanex 302

Solvent-impregnated resins (SIR) containing Cyanex 302 (bis [2,4,4-trimethylpentyl] monothiophosphinic acid) have been prepared using Amberlite XAD-2, XAD-4, XAD-7 and XAD-8 as polymeric support. These prepared SIR have been used for the extraction of Cd(II) and Cu(II) from phosphoric acid solutions. The effect of phosphoric acid concentration on Cd(II) uptake has been investigated by batch extraction method. Columnar extractions of Cd(II) and Cu(II) from 40% H3PO4 have been performed using XAD-7 resin impregnated with Cyanex 302. The resin exhibited similar column sorption behaviour for both Cd(II) and Cu(II). The elution of both Cd(II) and Cu(II) from SIR has been achieved with 4 M HCl solution. The elution of Cd(II) occurred sharply but with a long tail-off and furthermore the elution of Cu(II) was slow.

Highly polar polymeric sorbents: Characterization and sorptive properties towards phenol and its derivatives

Abstract Six porous copolymers of acrylonitrile (AN)/divinylbenzene (DVB) and methacrylonitrile (MAN)/DVB have been synthesised by suspension polymerization in the presence of inert diluents. They have different specific surface area (460–720 m 2 /g for AN/DVB and 560–730 m 2 /g for MAN/DVB) and contain various amounts of the strongly polar nitrile groups. Their sorptive properties have been studied using dilute (0.5 mmol) solutions of phenol and its derivatives ( o -chlorophenol, o -, m - and p -nitrophenol, 2,3- and 2,6-dimethylphenol, p -hydroxyphenol). It has been found that sorption of the most hydrophobic compounds and compounds capable of forming strong intramolecular hydrogen bonds does not depend on the polarity of the polymer surface. Sorption of phenol and m - and p -nitrophenol is stronger on sorbents having more polar groups. The influence of these groups on the sorption process is highly significant in the case of hydrophilic, water soluble sorbates such as p -hydroxyphenol. Polymeric sorbents were characterized using elemental analysis, inverse gas chromatography and their porous structure was characterized by nitrogen adsorption at 77 K.

Physical and adsorptive properties of Hypersol-MacronetTM polymers

Hypersonal-MacronetTM polymers are a new series of hypercrosslinked polymeric ion-exchange sorbents under investigation for the removal of organic pollutants from potable water. Adsorption isotherms are presented for three polymers, MN-100, MN-150 and MN-200 sorbing phenol, 2-chlorophenol, 3-chlorophenol and 4-chlorophenol. Surface area and pore size distribution data are given for the polymers. The surface functionality of the Macronets determined by diffuse reflectance IR and X-ray photoelectron spectroscopy is presented.

Removal of Pesticides from Water Using Hypercrosslinked Polymer Phases: Part 1 — Physical and Chemical Characterization of Adsorbents

The physical and chemical properties of hypercross linked polymers have been compared with a commercial grade activated carbon for the sorption of organic micropollutants from water. Surface area and pore size distribution were measured by nitrogen sorption and the data analysed using a modified form of the Horvath and Kawazoe method. Surface reactivity and functionality of polymers was measured by diffuse reflectance infrared spectroscopy, X-ray photoelectron spectroscopy, solid state nuclear magnetic resonance, direct titration, elemental and zeta potential analysis. Chemviron F-400 activated carbon has a large surface area and is microporous but contains a significant proportion of mesopores. The hypercrosslinked polymer phases identified in this work have high surface areas (800−1000m2 g−1) and contain predominantly micro and macropores but virtually no mesopores. Chemical analysis of the surface of the polymers has identified oxygen and nitrogen functionalities which will have an advantageous influence on the binding of polar and non-polar organic micropollutants.