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Single-Stage Solvent Extraction
Published in Alan M. Lane, Separation Process Essentials, 2019
In the solvent extraction process, a solute dissolved in a diluent is removed by contacting with solvent. The diluent and solvent must be at least partially immiscible to allow physical separation of the products. Raffinate is the liquid product with most of the diluent, while extract is the liquid product with most of the solvent and solute. The composition and amount of each product is determined by mole balances, phase equilibrium relationships, and various process specifications. These equations can be solved graphically or analytically. Measured compositions are best represented by a ternary phase diagram. The phase equilibrium equations can be purely empirical by fitting measured compositions to polynomial equations, or semi-empirical by fitting measured compositions to a model such as NRTL or UNIQUAC.
Polymer inclusion membranes for the separation of uranium and arsenic from dilute aqueous solutions
Published in Alberto Figoli, Jan Hoinkis, Jochen Bundschuh, Membrane Technologies for Water Treatment: Removal of Toxic Trace Elements with Emphasis on Arsenic, Fluoride and Uranium, 2016
Alexander M. St John, Spas D. Kolev, Clàudia Fontàs
This U-rich phase may then undergo further steps to remove remaining impurities, prior to being back-extracted into a clean aqueous phase, ready for drying and calcining. The most commonly used extractants for U are mixtures of long-chain tertiary amines, such as Alamine 336 used in the AMEX process, and organophosphorous acids such as D2EHPA used in the DAPEX process (Musikas et al., 2004; Ring, 2000; Ritcey, 1996). It should be noted that the aqueous waste from the initial extraction step (also called the raffinate) contains low concentrations of U and other environmental contaminants, making it unsuitable for further use or release. This is often discharged to retention ponds or other storage. This low-concentration raffinate is an ideal target for a low-cost, low-energy and efficient separation technique (such as those involving PIMs) to remove residual U from the aqueous waste prior to its re-use or disposal.
Mass Transfer Applications
Published in Theodore Louis, Behan Kelly, Introduction to Optimization for Environmental and Chemical Engineers, 2018
The solution whose components are to be separated is the feed to the process. The feed is composed of a dilutant and solute. The liquid contacting the feed for purposes of extraction is referred to as the solvent. If the solvent consists primarily of one substance (aside from small amounts of residual feed material that may be present in a recycled or recovered solvent), it is called a single solvent. A solvent consisting of a solution of one or more substances chosen to provide special properties is a mixed solvent. The solvent-lean, residual feed solution, with one or more constituents removed by extraction, is referred to as the raffinate. The solvent-rich solution containing the extracted solute(s) is the extract.
Design and optimization of an acetic acid recovery system via extraction–distillation using an isopropyl acetate + isopropanol mixed solvent
Published in Chemical Engineering Communications, 2020
Peng Fang, Chao Yu, Zuoxiang Zeng, Weilan Xue
During the hybrid extraction–distillation system, the dilute acetic acid and solvent (IPA-01 + IPA-02) is first introduced into the top and bottom of the extraction column, respectively. The density of the solvent is lower than that of the aqueous mixture, this feeding method allows them to undergo countercurrent extraction. Thus, the mixture is separated into an extract phase and a raffinate phase. The amount of solvent and the content of IPA-02 in the solvent are very important, because they directly affect the recovery of acetic acid in the extraction process and the acetic acid content in the final wastewater. Moreover, the energy consumption of the azeotropic distillation column and the solvent recovery column is closely related to the amount of solvent and the IPA-02 content.