A study of pyrite reactivity and the chemical stability of cemented paste backfill

Valérie J. Bertrand
A two-fold study was carried out to 1) characterize the evolution of the reactivity of pyrite in the early cycles of kinetic test leaching, using cyclic voltamperometry, and 2) document the weathering characteristics of various paste backfill mixtures that contain pyritic tailings, when exposed to leaching environments similar to those encountered in mine settings. Pyrite leaching experiments were carried out on 6 different pyrite samples from existing mines. Cyclic voltamperometry was
more » ... ometry was performed on carbon paste electrodes (CPE) containing fine grained pyrite samples on the unleached samples and after leaching periods of 4, 10 and 20 weeks. Pyrite reactivity profiles, supported by scanning electron microscope (SEM) observations and leachate chemistry data showed that minor phases of sphalerite and galena present in the pyrite samples were the most important parameters affecting pyrite reactivity in the initial leaching cycles. Sphalerite and galena were found to effectively retard the oxidation of pyrite in the early leaching cycles. As sphalerite and galena were leached out, an increase in the reactivity of pyrite was observed, followed by a gradual loss of reactivity from precipitate coatings. At a fundamental level, mineral surface characterization by cyclic voltamperometry was found useful in the interpretation of kinetic test data for the prediction of acid rock drainage (ARD) generation. For the backfill weathering study, paste backfill samples of 4 different mines were leached in deionized water (pH 5.5) in flooded and alternating air-flooded environments and in a simulated ARD solution (Fe=500 mg/1, SO4=1.5 g/1 and pH 2.5) for 20 weeks. SEM, solid phase chemistry, paste pH, acid-base accounting measurements and leachate chemistry were also used to document the weathering characteristics of cemented paste backfill (CPB). This study revealed that hydrated portland cement minerals are pH sensitive and highly soluble. Short-term exposures of portland-CPB to circum-neutral water or to AR [...]
doi:10.14288/1.0081119 fatcat:3p75ayefwzbtvneugfz4yj7rhy