The removal of organic impurities from industrial waste salt by pyrolysis

The presence of organic impurities hinders the resource utilization of industrial waste salt (IWS). In this study, pyrolysis treatment was chosen to remove these organic impurities. The optimal process parameters for the pyrolysis of organic impurities were as follows: a temperature of 500 °C and a holding time of 20 min. Under these optimal conditions, the total organic carbon (TOC) removal rate was 96.32%, inducing a decrease in the TOC mass fraction from 1.88 to 0.08%. Fourier transform infrared spectroscopy (FTIR) results obtained during this process showed that prolonging the pyrolysis time (10-70 min) for IWS resulted in a gradual decrease in the relative content of characteristic functional group, such as C-O in ether groups, and the disappearance of functional group, such as benzophenone carbonyl group and ester carbonyl. Organic impurities can release gas-containing compounds that destroy the initially smooth IWS surface, and the resulting particles with rough and irregular shapes fuse into large or lumpy particles during the pyrolysis process. GC‒MS results clearly showed that the number of different semivolatile organic compounds in the IWS was reduced from 35 to 19 as a result of the pyrolysis process. Correspondingly, organic impurities with molecular formulas containing 5-10 carbon atoms converted into compounds containing 6-20 carbon atoms. These findings provide theoretical support for IWS resource utilization.