Wastewater Treatment in the Production of Purified Sodium Bicarbonate to Produce Sodium Hydroxide

Abstract

The production of purified sodium bicarbonate is accompanied by the formation of wastewater containing sodium carbonate and bicarbonate. Up to 1.5 m3 of sewage is formed per 1 ton of filtered sodium bicarbonate. Wastewater contains about 23.5 g/l sodium carbonate and about 40.4 g/l sodium bicarbonate. The article presents the results of studies related to the processing of wastewater generated in the production of purified sodium bicarbonate in a membrane electrolyzer with a cation exchange membrane. The wastewater treatment process was carried out at a membrane current density of 30 mA/cm2 to 60 mA/cm2. The research shows that in the process of electrochemical processing of wastewater, sodium carbonate is obtained first, and only then sodium bicarbonate is extracted. At the same time, during the electrolysis, sodium hydroxide is formed. The maximum achieved concentration of sodium hydroxide was 362 g/l. The current efficiency of electrolysis process calculated by changing sodium hydroxide concentration depends on the membrane current density. The maximum current efficiency is observed at a current density of 30 mA/cm2 and equals 64.3%. The specific energy costs of sodium hydroxide producing increases with increasing current density. The minimum energy consumption was 2.2 kWh/kg.