Abstract
Water contamination with harmful arsenic compounds represents one of the most serious calamities of the last two centuries. Natural occurrence of the toxic metal has been revealed recently for 21 countries worldwide; the risk of arsenic intoxication is particularly high in Bangladesh and India but recently also Europe is facing similar problem. Liquid membranes (LMs) look like a promising alternative to the existing removal processes, showing numerous advantages in terms of energy consumption, efficiency, selectivity, and operational costs. The development of different LM configurations has been a matter of investigation by several researching groups, especially for the removal of As(III) and As(V) from aqueous solutions. Most of these LM systems are based on the use of phosphine oxides as carriers, when the metal removal is from sulfuric acid media. Particularly promising for water treatment is the hollow fiber supported liquid membrane (HFSLM) configuration, which offers high selectivity, easy transport of the targeted metal ions, large surface area, and non-stop flow process. The choice of organic extractant(s) plays an essential role in the efficiency of the arsenic removal. Emulsion liquid membrane (ELM) systems have not been extensively investigated so far, although encouraging results have started to appear in the literature. For such LM configuration, the most relevant step toward efficiency is the choice of the surfactant type and its concentration.
Highlights
Arsenic (As) is a toxic metal that derives its name from the Greek word “arsenikon” meaning “yellow orpiment” [1]
To improve the Liquid membranes (LMs) stability, Molinari et al [73] and Chiarizia et al [74] proposed a nonstop support reimpregnation with LM phase, but the drawback of contaminated feed and/or strip solution(s) still persists in the system. Another feasible operation consists of plasma polymerization surface coating, which could stabilize the supported or immobilized liquid membrane (SLM) [75] but at the same time could reduce the pore size in the membrane surface and decrease the membrane permeability
The use of LMs is one of the most promising solutions. As they combine extraction with subsequent stripping in a single step, SLM and Emulsion liquid membrane (ELM) represent the two most attractive. The efficiency of these processes has been investigated by several authors, who showed that the choice of extractant/surfactant is crucial in the optimization process
Summary
Arsenic (As) is a toxic metal that derives its name from the Greek word “arsenikon” meaning “yellow orpiment” [1]. The adsorption procedure [19,20,21], mainly based on the use of activated carbons, is efficient for the removal of both As(III) and As(V) species and offers the possibility to use a simple apparatus It presents high costs, which impedes its use on a large scale, as well as high toxic solid waste production and the need for periodic replacement of the specific As resin. Membrane processes represent a promising alternative for arsenic removal, offering the possibility to carry out the separation continuously in one step, under mild operational conditions and with sustainable costs [22,23,24,25,26] They offer highly efficient As removal without producing toxic solid waste. LMs systems allow us to obtain high permeability, especially compared to solid membranes, due to higher diffusion coefficients in liquids, low operating costs, and easy feasibility [36,37,38]
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