DEVELOPMENT OF CHALCOPYRITE DISSOLUTION RATE LAWS THROUGH META-ANALYSIS

Chalcopyrite is the most abundant Cu-bearing sulfide mineral. Its dissolution has the potential to contribute to acid rock drainage and Cu toxicity in vulnerable habitats. A better understanding of the kinetics of chalcopyrite dissolution will aid in efforts to predict Cu release to the environment from current and future mining excavations. For this purpose, meta-analysis of 173 rate measurements from 21 publications was used to develop rate laws for chalcopyrite dissolution under environmentally relevant conditions.

Multiple linear regression analysis of 28 rate measurements for chalcopyrite dissolution involving reaction with protons in the presence of O₂ and Cl^- produced the following rate law:

r = 10^-1.52e^-28200/RT[H⁺]^1.68

For this and the following rate law, r is the rate of chalcopyrite dissolution in units of mol m^-2 s^-1 and surface area is expressed on a geometric basis. Multiple linear regression analysis of 36 rate measurements for chalcopyrite dissolution caused by reaction with Fe(III) in the presence and absence of O₂ and Cl^- produced the following rate law:

r = 10^1.88e^-48100/RT[H⁺]^0.8[Fe(III)]^0.42

Certain rate measurements were excluded from these rate law models because they were considered to be inconsistent with the overall dataset or were relatively unconstrained.

No rate data could be clearly identified as representing chalcopyrite dissolution caused by O₂ oxidation alone. Although there are numerous reports that suggest that chalcopyrite dissolution rates are increased by the presence of Cl^- in solution, the regression models presented here document that the effect of Cl^- on dissolution of chalcopyrite under environmental conditions is insignificant. Given that most rate measurements were generated at low pH, these empirical rate laws are most appropriate for characterizing chalcopyrite dissolution at low pH (≤ 3). This study has provided further insights into the mechanisms by which chalcopyrite dissolves in the environment and the developed rate laws will ultimately allow better modeling of acid rock drainage and Cu release to the environment.