Nondispersive solvent extraction

Nondispersive solvent extraction is a novel configuration of the conventional solvent extraction process. The term nondispersive solvent extraction arises from the fact that instead of producing a drop dispersion of one phase in the other, the phases are contacted using porous membrane modules. The module membrane separates two of the immiscible phases, one of which impregnates the membrane, thus bringing the liquid-liquid interface to one side of the membrane. This process differs from the supported liquid membrane in that the liquid impregnating the membrane is also the bulk phase at one side of the porous membrane, thus reducing the number of liquid-liquid interfaces between the bulk phases to just one. 

The main benefits of nondispersive solvent extraction over the conventional process are (1) it avoids the need of a settling stage for phase disengagement and the consequent risk of dispersed phase carryover (2) the value of the interfacial area per unit volume can be much higher than in a liquid-liquid dispersion as there is no risk of phase inversion and (3) the interfacial area is easily calculated and scale-up of the process is straightforward. 

All the novel separation techniques discussed in this chapter offer some advantages over conventional solvent extraction for particular types of feed, such as dilute solutions and the separation of biomolecules. Some of them, such as the emulsion liquid membrane and nondispersive solvent extraction, have been investigated at pilot plant scale and have shown good potential for industrial application. However, despite their advantages, many industries are slow to take up novel approaches to solvent extraction unless substantial economic advantages can be gained. Nevertheless, in the future it is probable that some of these techniques will be taken up at full scale in industry. 

Alonso, A.I., Galan, B., Gonzalez, M. and Ortiz, I. (1999) Experimental and theoretical analysis of a nondispersive solvent extraction pilot plant for the removal of Cr(VI) from a galvanic process wastewaters. Industrial Engineering Chemistry Research, 38, 1666. 

Alonso, A.I. and Gruhn, G. (2002) Flexibility analysis of nondispersive solvent extraction plant. Separation Science and Technology, 37, 161. 

Nondispersive Solvent Extraction for the Separation, Removal, and Concentration of Actinides.939... 

As a part of our comprehensive programme on membrane technology, we evaluated nondispersive solvent extraction (NDSX) with a hydrophobic microporous hollow fiber contactor (HFC) for the separation and removal of actinides [1,10-12]. As the separation and recovery of actinides from different sources is paramount to radiotoxicity, there is a constant need for advances in the field. Among recently developed technologies, membrane extraction using microporous hollow fibers is particularly... 

Modeling of Nondispersive Solvent Extraction of Multicomponent Metallic Solutions. 1024... 

MODELING OF NONDISPERSIVE SOLVENT EXTRACTION OF MULTICOMPONENT METALLIC SOLUTIONS... 

As a representative example, the model will be applied to the separation of Ni and Cd by nondispersive solvent extraction with the mentioned assumptions to avoid duplicate equations, the subscript i has been used, where i = 1 represents cadmium and i = 2 represents nickel. 

Let us present some examples. The systems presented by the term membrane-based (or nondispersive) solvent extraction describe, as a rule, dynamic LM processes in which the equilibrium-based solvent extraction (forward and back) are only local processes taking place on the immiscible phases interfaces (on the surface of membrane support). The term pertrac-tion or perstraction [2] spread over the supported and emulsion LMs, which is not accurate, because the SLM and ELM are steady state processes. 

Membrane-based or nondispersive solvent extraction systems... 

Inclusion of this technique to the BOHLM has to be explained. Solvent extraction or partition of the solute between two immiscible phases is an equilibrium-based separation process. So, the membrane-based or nondispersive solvent extraction process has to be equilibrium based also. Liquid membrane separation is a rate process and the separation occurs due to a chemical potential gradient, not by equilibrium between phases [114]. According to these definitions, many authors who refer to their works as membrane-based or nondispersive solvent extraction processes are not correct. 

The authors of very many works on so-caUed membrane-based or nondispersive solvent extraction could not prove that the process reaches equilibrium. Therefore, we cannot confirm the processes, published in these works, as membrane-based solvent extraction, but can confirm them as liquid membrane processes. Liquid membrane separations are dynamic nonequilibrium processes, in which only local equilibrium at immiscible phases interface may be suggested. 

In other advanced SILMs technologies, though not essentially SILMs in themselves, they used a solid microporous barrier to separate the aqueous phase from the organic one. Including in this concept are the nondispersive solvent extraction (NDSX) and pseudo-emulsion-based hollow-fiber strip dispersion (PEHFSD). 

FIGURE 26.4 (a) Schematic of nondispersive solvent extraction technique 1, hollow fiber module 2, aqueous phase (from tube side) ... 

Nondispersive solvent extraction (NDSX) is simply a liquid-liquid extraction involving a hoUow-fiber module for the contact of aqueous and organic phases without their dispersion. 

Patil, C.B., Mohapatra, P.K., Singh, R.R., Gurba, P.B., Janardan, P, Changrani, R.D., and Manchanda, V.K. 2006. Transport of uranium from nitric acid solution by nondispersive solvent extraction using a hollow fiber contactor. Radiochim. Acta 94 331-334. 

In what follows the methodology for the selection of the operating conditions of a nondispersive solvent extraction process will be developed. As an example the removal and recovery of Cr(VI) from an indnstrial effluent of a surface treatment plant will be considered. The kinetic modeling including the extraction reactions. Equation (6.17) and Equation (6.22), and the mass balances of chromium compounds to the three fluid phases and considering the hollow fiber modules and the homoge-neization stirred tanks. Equation (6.30) through Equation (6.50) were described in Sections 6.3 and 6.4. 

Consider microporous membrane-based solvent extraction using a hydrophilic porous membrane whose pores are filled with the organic solvent used to extract a product, species i, from an aqueous feed solution. The aqueous-phase pressure is maintained equal to or higher than the organic-phase pressure to maintain the aqueous-organic interface for nondispersive solvent extraction conditions. 

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