Continuous Process for Photodegradation of Industrial Bayer Liquor

Photodegradation of spent Bayer liquor has been carried out in an 18-L pilot-scale continuous annular photoreactor. The performance of the reactor was studied with respect to various process parameters such as the gas flow rate, liquid flow rate, initial solution pH, initial substrate concentration, light intensity, and catalyst loading. The average reaction rate and overall conversion of Bayer liquor, in terms of total organic carbon, have been found to be strongly dependent on all of these parameters. Despite the very dark color and high initial pH (ca. 12) of the reaction mixture, significant conversion (25−35%) was achieved within about 2 h of operation, showing a considerable improvement over the existing industrial oxalate removal methods. Notwithstanding the complex composition of the spent Bayer liquor, the rate data could adequately be analyzed in terms of simple linear or hyperbolic-type kinetic expressions.