What Determines Lag Times in Humidity Cell Tests?

Kelly Sexsmith and Dylan MacGregor
Monday, February 24, 2014
First presented: 
SME Annual Meeting and Exhibit 2014

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.

Feature Author

Dylan MacGregor

Dylan MacGregor has worked in mining-related earth sciences and engineering for over 17 years, including the past twelve with SRK’s GeoEnvironmental Group. At SRK, Dylan’s experience has included evaluating mine waste geochemistry at both operating and closed mines, developing and refining water quality predictions for mines at all stages (from pre-production to post-closure), guiding the design of tailings and waste rock storage facilities to allow the implementation of appropriate end-of-life closure measures, evaluation of closure options for abandoned mines, and oversight of multi-disciplinary technical teams for mine development, mine expansion, and mine closure projects.

Principal Geochemist
M.A.Sc., PGeo
SRK Vancouver
SRK Latin America