Gas quantity and composition from the hydrolysis of salt cake from secondary aluminum processing.

Abstract

A systematic approach to understanding the hydrolysis of salt cake from secondary aluminum production in municipal solid waste landfill environment was conducted. Thirty-nine (39) samples from 10 Aluminum recycling facilities throughout the USA were collected. A laboratory procedure to assess the gas productivity of SC from SAP under anaerobic conditions at 50 °C to simulate a landfill environment was developed. Gas quantity and composition data indicate that on average 1400 µmol g-1 (35 mL g-1) of gas resulted from the hydrolysis of SC. Hydrogen was the dominant gas generated (79% by volume) followed by methane with an average of 190 µmol g-1 (21% by volume). N2O was detected at a much lower concentration (1.2 ppmv). The total ammonia released was 680 µmol g-1, and because of the closed system nature of the experimental setup, the vast majority of ammonia was present in the liquid phase (570 mg L-1). In general, the productivity of both hydrogen and total ammonia (the sum of gas and liquid forms ammonia) was a fraction of that expected by stoichiometry indicating an incomplete hydrolysis and a potential for re-hydrolysis when conditions are more favorable. The result provides substantial evidence that SC can be hydrolyzed to generate a gas with relative long-lasting implications for municipal solid waste landfill operations.