NEW METHODS
FOR DETERMINATION OF KEY MINERAL SPECIES IN ACID GENERATION PREDICTION
BY ACID-BASE ACCOUNTING
Mine Environment Neutral Drainage at CANMET-MMSL |
MEND Project 1.16.lc
April 1991
EXECUTIVE
SUMMARY
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.
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