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1 INTRODUCTION Environmental considerations have become one of the primary factors in the economic feasibil-

Environmental considerations have become one of the primary factors in the economic feasibil-
ity of any mining project especially those with sulfide rich ores. Acid mine drainage is the main
problem caused by the mining of sulfide ore. Under certain conditions (the presence of oxygen
and water and the possible presence of bacteria like Thiobacillus), oxidation of sulphide miner-
als within the tailings (mainly pyrite and pyrrhotite but also ore sulfides lost in the milling proc-
ess) can occur and generate toxic elements and acid when the neutralization potential of the
waste is either absent or exhausted.
The predictive tests used to evaluate the acid generation potential of mine waste are critical
for determining the environmental impact of a mine site and for choosing a waste management
method to minimize that impact. Static tests, kinetic tests, and geochemical models have been de-
veloped and are used on a regular basis, primarily to establish if and when a given material would
generate acid. Static tests have been so named because they are usually conducted at a given
point in time, and do not account for the rate and evolution of the observed reactions. They gen-
erally rely on measuring the sulphur content to predict the Acidic Potential (AP) of the waste
and a titration to estimate the Neutralization Potential (NP). When the results of static tests are
inconclusive (the test results are in a relatively large uncertainty zone), or when one is interested
by the evolution of drainage quality in time, kinetic tests are desirable.
There are different types of kinetic tests to estimate the reaction rates and depletion time for
various minerals; the most common tests are column and humidity cell. The main advantage of


Source: Aubertin, Michel - Département des génies civil, géologique et des mines, École Polytechnique de Montréal


Collections: Engineering; Environmental Management and Restoration Technologies