It is common practice to run kinetic tests on potentially acid generating rock or tailings samples to determine the amount of time it will take for acidic conditions to develop—often called “lag time”. Defining lag time is important for understanding when management plans need to be in place for preventing or mitigating acid rock drainage. However, it is relatively rare for acidic conditions to develop over the course of a laboratory test. More often, acidic conditions are present from the start of testing or they never develop at all. For this latter group of tests, lag times can be calculated, but are considered to have a wide range of uncertainty. This paper presents the results for a number of exceptional tests where there was a distinct delay to the onset of acidic conditions. It also explores the relationships between the lag time in these tests and corresponding data on oxidation rates, neutralization potential, total inorganic carbon content, and mineralogy. The results emphasize the value of running some tests for an extended period of time.
