Experimental study on thermal runaway of sodium nitrate-containing hazardous waste during thermal treatment

Abstract

Sodium nitrate-containing organic solid waste (NaNO3-OSW) has been classified as hazardous waste because it engendered severe fire and explosion risk, while large amounts of NaNO3-OSWs were generated during the metal recovery process from e-waste recently. This study aims to characterize thermal runaway behavior and reaction mechanism of NaNO3-OSW via theoretical and experimental analysis. Component characterization results show that this waste contains 23.3% wt. NaNO3, mixed with 11.8% wt. ascorbic acid, 47.2% wt. dehydroascorbic acid, and 17.7% wt. polyvinylpyrrolidone. Thermal risk assessment could provide guidance on the kind of safety measurements. Results present that this waste is thermal sensitive with high deflagration potential while its minimum ignition temperature is 290 ℃, and the maximum explosion pressure is 0.51 MPa. The predicted self-accelerating decomposition temperature is 148.3 ℃ for a standard 50 kg package. Combustion behavior characterization could offer insights into the realization of essential safety during disposal. Results reveal that the self-redox reaction between organic compounds and NaNO3 has occurred in the temperature range of 276–405 ℃. The reaction mechanism suggests that the catalytic decomposition of ascorbic acid by melting NaNO3 is the crucial factor that results in intense combustion. The findings of this study provide practical insights into the in-situ disposal of this waste by removing organic compounds at low temperatures.