Process engineering principles are used to analyse the features of leaching
processes for large masses of low grade, unprocessed ore. Different
performance characteristics are related to the numerous variants of these
processes. The variant for which reagent enters a heap only via the input
solution is further subdivided into three modes of operation. The three
modes may occur in testwork and full-scale operations; the effects of
process variables on the rate of the process are completely different in
each mode. The mode can be identified by the time at which reagent first
appears in the pregnant solution. It is related to the ratio of the height of
the heap and the thickness of a band of ore in which the reactions are
localised. Synthesis of the phenomena occurring within a heap via a
computer program has produced a quantitative relation for the reaction
band thickness. The program has been validated for several different
systems. The overall achievement is that the mode of operation and the
rate of the process can be forecast before column testwork is commenced.
Some applications of the outcomes to testwork, process design and
operational tactics are described.