Abstract
The characteristics of arsenic adsorption onto Fe-XAD8-DEHPA resin were studied on the laboratory scale using aqueous solutions and natural underground waters. Amberlite XAD8 resin was impregnated with di(2-ethylhexyl) phosphoric acid (DEHPA) via the dry method of impregnation. Fe(III) ions were loaded onto the impregnated resin by exploiting the high affinity of arsenic towards iron. The studies were conducted by both in contact and continuous modes. Kinetics data revealed that the removal of arsenic by Fe-XAD8-DEHPA resin is a pseudo-second-order reaction. The equilibrium data were modelled with Freundlich Langmuir and Dubinin Radushkevich (D-R) isotherms and it was found that the Freundlich model give the poorest correlation coefficient. The maximum adsorption capacity obtained from the Langmuir isotherm is 22.6 µg As(V)/g of Fe-XAD8-DEHPA resin. The mean free energy of adsorption was found in this study to be 7.2 kJ/mol and the ΔG° value negative (−9.2 kJ/mol). This indicates that the sorption process is exothermal, spontaneous and physical in nature. The studied Fe-XAD8-DEHPA resin showed excellent arsenic removal performance by sorption, both from synthetic solution and the natural water sample, and could be regenerated simply by using aqueous NaOH or HCl solutions.
Highlights
Because in developing countries underground waters represent the main source of drinking water, their contamination with arsenic is a problem which must be solved [1,2,3]
It was considered that for the loading of the XAD8-di(2-ethylhexyl) phosphoric acid (DEHPA) resin, using a S:L ratio of 0.1:25, the concentration of the Fe(III) ions in the aqueous solutions should not exceed 100 mg/L. In this way the loading of the highest quantity of iron ions onto the impregnated resin is obtained, which will lead to a higher adsorption of As(V) ions from the aqueous solution, due to the fact that the Fe(III) ions are responsible for the arsenic removal because of its affinity for this pollutant [3,4,7,8,9,10,11,24,32]
Environmental Sustainability Assessment compared with the adsorption process [48], the research from this paper showed that the use of Fe-XAD8-DEHPA as adsorbent material in the As(V) removal process presents good efficiency both in batch and fixed-bed column tests, and especially in the treatment process of real underground drinking water, without the applying any extra pre-treatment processes
Summary
Because in developing countries underground waters represent the main source of drinking water, their contamination with arsenic is a problem which must be solved [1,2,3]. In order to reduce its adverse health effects it is necessary to minimize the pollution of underground water with arsenic content or to find some effective methods for their remediation [3]. In an aqueous solution of As(V) there are four species: H3AsO4, H2AsO4−, HAsO42−, AsO43− that predominate at pH values between 6 and 9. In the same mode in aqueous solutions at pH values below 9 they exist the As(III) species: H3AsO3, H2AsO3−, HAsO32−, AsO3 [4,5,6,9,10]. The conventional methods used for the arsenic removal from aqueous solutions are precipitation, coagulation and filtration, reverse osmosis, ion exchange and adsorption. In order to improve the adsorption properties of the SIRs four method of impregnation with an organic extractant of the polymeric support were developed
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