Laboratory Investigations of Processing Highly Mineralized Alkali Solutions by Means of Electromembrane Technology

Abstract

An analysis of water utilization systems at thermal power plants (TPPs) shows that highly mineralized effluent waters are mainly generated at these facilities by their water-treatment plants. Highly mineralized alkali liquid waste is presented by the products from continuous and periodic blowdowns of thermal demineralization systems and drum boilers, by spent anion exchange filter regeneration solutions, and by alkali concentrates from reverse osmosis plants. In view of the fact that the alkali used in technological processes has quite a high cost, it is economically expedient to subject alkali effluents to processing with the extraction of alkali for repeatedly using it in the production cycle. The article presents the results obtained at a TPP from experimental investigations into processing of highly mineralized alkali–salt solutions by means of electromembrane technology. The experimental investigations were carried out using the EMA-100 laboratory electromembrane apparatus and included two series of tests: a sequential diffusion–dialysis extraction with concentration by electrodialysis and a single-stage concentration by electrodialysis. As a result, a concentrated alkali solution and partially demineralized softened water were obtained. An analysis of the qualitative and quantitative compositions of the obtained products has shown the effectiveness of the proposed electromembrane processing arrangements, because an alkali solution suitable for its repeated use in the TPP water-treatment cycle was obtained in both series of tests. However, it should be borne in mind that single-stage concentration by electrodialysis is a more economically efficient and simple method, which provides high throughput and yields solutions containing satisfactorily separated alkali and salt components.