DEVELOPMENT OF BORON RECOVERY SYSTEM FROM DESULFIRIZATION WASTEWATER OF COAL THERMAL POWER PLANT

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The process for the recovery of boron in the wastewater from desulfurization unit of coal thermal power plant was investigated. The solvent extraction was selected as a most suitable method to recover boron from aqueous solution. Based on the extraction equilibrium study of various extractants, 2-buty, -2-ethyl-1,3-propandiol as an extractant and 2-ethylhexanol as a diluent were selected as the best extraction system of boric acid. The effects of various operating parameters such as extractant concentration, borate concentration and temperature were investigated to establish the optimum conditions. As a result, 1kmol/m^3 of extractant was found to be optimum from the viewpoints of extractability and easiness of phase separation after extraction. Boric acid extracted in the solvent could be stripped completely into aqueous alkaline solution. The effects of boric and concentration in solvent and the alkaline concentration was examined to determine the stripping conditions. A series of alkali well functioned as a stripping reagent. The continuous operation was also achieved using mixer-settlers. Various types of operation were investigated to find the optimum way that guaranteed a high concentration ratio of boron after recovery. The dissolution of extractant and solvent to aqueous phase during the contact between two phases causes another pollution problem if the effuluent after extraction and stripping is discharged without any treatments. We proposed to use the dissolved organic components as an organic carbon source of biological denitrification and obtained a satisfactory result.