Selective removal of organochlorine pesticides (OCPs) from aqueous solution by triolein-embedded composite adsorbent

The influence of the surface chemical groups of an activated carbon on the removal of different classes of dyes is evaluated. Starting from the same material (NORIT GAC 1240 PLUS), the following treatments were carried out in order to produce a series of samples with different surface chemical properties but with no major differences in their textural properties: oxidation in the liquid phase with 6M HNO(3) and 10 M H(2)O(2) (acid materials) and heat treatment at 700 degrees C in H(2) or N(2) flow (basic materials). The specific micropores volume and mesopores surface area of the materials were obtained from N(2) adsorption equilibrium isotherms at 77K. The surface chemistry was characterised by temperature programmed desorption, by the determination of the point of zero charge (pH(pzc)) and by the evaluation of the acidity/basicity of the samples. Elemental and proximate analyses were also carried out. Equilibrium isotherms of selected dyes (an acid, a basic and a reactive dye) on the mentioned samples were obtained and the results discussed in relation to their surface chemistry. In general, the Langmuir model provided the best fit for the adsorption data. It is shown that the surface chemistry of the activated carbon plays a key role in dye adsorption performance. The basic sample obtained by thermal treatment under H(2) flow at 700 degrees C is the best material for the adsorption of all the tested dyes.

Adsorption is one important technique in fluoride removal from aqueous solutions. The viability of adsorption techniques is greatly dependent on the development of adsorptive materials. A large number of materials have been tested at a fluoride concentration greater than 2 mg/l, and the lowest limit for fluoride reduction by them is about 2 mg/l. Decreasing the fluoride concentration to less than 2 mg/l, most of the tested materials displayed a very low capacity of fluoride removal. This paper has concentrated on investigating the adsorption kinetics and adsorption capacity of low cost materials at a low initial fluoride concentration. The experiments were carried out at a natural pH, and radioisotope 18F rather than 19F was used since 18F can be rapidly measured by measuring the radioactivity with a resolution of 1 x 10(-13)mg or 0.01 microCi. The tested materials are hydroxyapatite, fluorspar, calcite, quartz and quartz activated by ferric ions. Their adsorption capacities follow the order: Hydroxyapatite>Fluorspar>Quartz activated using ferric ions>Calcite>Quartz. The uptake of fluoride on hydroxyapatite is an ion-exchange procedure and follows the pseudo-first- and second-order equations, while the uptake of fluoride on the others is a surface adsorption and follows the pseudo-second-order equation. Calcite has been seen as a good adsorbent in fluoride removal and has been patented. However, our data suggested that its adsorption capacity is only better than quartz. The external mass transfer is a very slow and rate-determining step during fluoride removal from the aqueous solution. Under static conditions, there was no relative movement between adsorbents and solutions, the fluoride uptake was at a very slow rate and the adsorbent properties did not significantly affect the fluoride uptake. Under shaken conditions, the adsorption of fluoride was controlled by the adsorbent structure and chemical properties.