A review of chemical literature has been completed to find new methods for determining important mineral phases in the generation of acidic water from waste rock. Methods were ranked and four procedures selected for preliminary testing. Recommendations are made for improvement to the acid-base accounting procedure that may reduce the effects of atypical mineral associations in metal deposits.
A number of different methods are available for estimation of the concentrations of total sulphur and sulphur forms in mineral waste and ore samples. Techniques to discriminate between sulphur as different types of sulphates, and sulphur as pyrrhotite, pyrite and base metal sulphides are available.
A key concern in the measurement of neutralization potential is that the presence of silicates and ferrous iron-bearing minerals may lead to anomalously high results. Methods to directly and quantitatively determine calcium and magnesium carbonates are not commercially available. Modification of the current neutralization potential procedure by adding hydrogen peroxide, and analysis of hydrochloric acid leachate for calcium, magnesium, and iron are recommended to address this problem.
Methods were ranked using weighting schemes which emphasized phase analysis, rapid inexpensive analysis, or suitability for mine site laboratories. Four methods were selected for limited testing using
mixtures prepared from samples of known mineralogical composition. These methods were:
(a) determination of sulphur as pyrrhotite and pyrite
(b) field determination of sulphur as pyrite
(c) modification of conventional U.S. EPA neutralization potential procedure by filtration of leachate and addition of hydrogen peroxide and
(d) determination of carbonates by metal analysis.
Procedure (a) performed well for each mineral matrix tested. Further development of the other procedures is required, particularly those dealing with carbonate analysis. Standard reference materials for this type of project are required to refine the methods.
It is recommended that routine acid-base accounting include a supporting mineralogical description to provide confidence in the chemical results. A number of mineral phase-specific procedures are available for testing and these should be selected on a project-by-project basis, depending on the complexity of the mineralogy and the Phase of the project.
