The Spontaneous Combustion of Chemically Activated Carbons from South African Coal Waste

ABSTRACT

A spontaneous combustion test termed the Wits-Ehac test was used to examine the spontaneous combustion liability of activated carbons prepared using KOH activation from three coal waste samples obtained in South African Coalfield. The effect of KOH addition on the activated carbon textural characteristics, physicochemical properties, and self-heating characteristics was investigated. The textural properties such as pore volume and surface area were evaluated using the nitrogen gas adsorption method. The morphological effect of the activated carbons on their liability toward spontaneous combustion was studied. The results showed that, with increased KOH weight ratio, the pore volume, and surface area of the activated carbon increased. The influence of KOH addition decreases the volatile matter, while the influence either increases/decreases the moisture, ash, or fixed carbon contents of the activated carbons. In addition, an increase in the KOH weight ratio increases the liability values of the activated carbons. The liability of activated carbon depends not only on the origin of the coal material but also on the volume of pore and surface area, which also depends on the quantity of KOH used during the preparation process. This study provides a scientific basis for a simple test to establish whether pore volume and surface area of activated carbon can promote its propensity to self-heating.

KEYWORDS:

• Activated carbon
• spontaneous combustion
• KOH
• liability index
• surface area
• pore volume

Acknowledgments

The Goldfields laboratory, School of Mining Engineering, University of the Witwatersrand Johannesburg. This work is based on the research supported by the National Research Foundation (NRF) of South Africa, SARChI Clean Coal Technology Grant (Grant Number: 86421). Opinions, findings, and conclusions stated are those of the authors and are not necessarily to be attributed to the NRF.

Additional information

Funding

This work was supported by the National Research Foundation, South Africa [86421].