Excel calculation of extraction separation in a full countercurrent cascade with decreasing distribution coefficients in the washing part

Abstract

Liquid-liquid extraction is widely used in the hydrometallurgy of non-ferrous, rare and radioactive metals. The most difficult of the tasks solved using this method is the separation of elements with similar properties, in which, as a rule, it is necessary to obtain one or even both elements in pure form and with a high recovery. In most cases, this is achieved only in the complete countercurrent process, which is realized in a cascade consisting of two parts — extraction, which ensures the production of a worse extractable component (or a group of components) in a pure form in the aqueous phase (raffinate), and washing, which ensures additional extraction of a worse extractable component (or a group of components) into a raffinate or obtaining a better extractable component (or a group of components) in pure form in the organic phase (extract). However, the washing solution dilutes the original solution, which leads to a decrease in the concentrations of the components in the products. To reduce this negative effect, it is possible to reduce the volume of the washing solution by lowering the distribution coefficients of the separated components in the washing part of the cascade and again increasing them in the extraction part. This type of separation is called a full countercurrent process with decreasing distribution coefficients in the washing part. Since the organic phase from the extraction part of the cascade enters the washing part, and the aqueous phase from the washing part together with the initial solution enters the extraction one, when determining the required conditions for extraction separation (i.e., the necessary ratios of the extractant and washing solution flows to the flow of the initial solution, the number of stages extraction and washing parts of the cascade, the compositions of the products obtained – raffinate and extract), the full countercurrent cascade can be calculated only as a whole. As a result, the execution of the calculation is associated with a large amount of computation and takes a lot of time even when using modern computing means. An effective way to automate calculations is to create templates in the Excel© spreadsheet processor environment that allow, when switching to another extraction system, not to program the calculation again, but only to enter new initial data into the corresponding cells of the template. This article is devoted to the development of such a template for a complete countercurrent process with constant but different distribution coefficients of the components in the extraction and washing parts of the cascade.