Examination of the United Nations self-heating test for sulphides

Some materials when exposed to various conditions can exhibit a rise in temperature without requiring an external heat source. Generally referred to as pyrophoric or self-heating substances, they challenge the safety of materials handling, storage and transportation. Reliably assessing the self-heating potential of materials is thus essential. Over the years several test protocols have been developed. A widely accepted method is that recommended by the United Nations (UN) to certify the safety of shipping pyrophoric goods. Our test work on sulphide materials has shown that the UN test can give false negatives if the sample oxidation history is not considered. Depending on the degree of oxidation (‘weathering’), the same sulphide material can exhibit self-heating ranging from safe to hazardous. To make the UN test, and other single-stage self-heating procedures, more reliable in assessing self-heating potential of sulphide materials, it is recommended that a weathering step be incorporated in the test protocol. Our test work on two sulphide samples, an ore and a concentrate, demonstrates the impact of incorporating a weathering stage in the test protocol.