Comparison of rate laws for the oxidation of five pyrites by dissolved oxygen in acidic solution

Abstract

Pyrites from five localities were oxidized with dissolved oxygen (DO) in acidic solution at 298 K. The objective of this study was to compare the oxidation rates of pyrite samples with different impurity contents. Initial conditions were a solution pH adjusted to approximately 4 and air saturation. DO, Fe 2+ , Fe(III) (as Fe 3+ and Fe(III) OH complexes), and SO 4 2− concentrations in the experimental solutions were periodically measured along with pH and redox potential (Eh). On the basis of the relationship between DO concentration and reaction duration, the rate laws for the oxidation of the pyrites were obtained. The rate laws differed for the various pyrites and can be expressed as follows:where the unit of oxidation rate is mol m ), t is time (s), k is a rate constant at pH ~ 4, and n is the reaction order (0.5 1). The differences in the rate laws were due to differences in the oxidation rates of Fe 2+ during the oxidation of the pyrites, and the differences in the oxidation rates of Fe 2+ were related to the occurrence of impurities in the pyrites. Oxidation of Fe 2+ was accelerated by increases in the total amount of impurities in the pyrite. Precipitation of the Fe 3+ produced during the reaction was promoted by increased amounts of arsenic in the pyrites.

The effect of As, Co, and Ni impurities on pyrite oxidation kinetics: Batch and flow-through reactor experiments with synthetic pyrite

“…They provide some trace element concentrations, though they were unable to determine if the trace elements were in the pyrite or secondary phases; arsenic was not reported. Manaka (2007) reported that pyrite oxidation rate was positively correlated with impurity concentrations for five pyrites from different locations in experiments using dissolved oxygen as a reaction progress variable at pH 4. Impurities distributed in secondary sulfide phases were treated analytically in the same way as those in solid solution.…”

Mobilization and natural attenuation of arsenic in acid mine drainage ( AMD )

“…2.10). The obtained values in this study are in the same order as the values reported by Smith and Schumate (1970) who found a value of 0.7 for a mixture of pyrite and marcasite, or Kamei and Ohmoto (2000), Manaka et al (2000), and Manaka (2007) with values from 0.5 to 1 for pyrite, or McKibben (1984), Williamson and Rimstidt (1994) and Domènech et al (2002) for pyrite (0.4-0.5±0.04) at pH 2-10. In the case of arsenopyrite, the obtained value is higher than those reported by Yu et al (2007)…”

Modeling of Thermal-Hydrological-Chemical (THC) Processes During Waste Rock Weathering Under Permafrost Conditions

“…Two additional cases were considered to investigate WRPs with lower and higher reactivity for the same temperature scenarios, which was achieved by decreasing or increasing the reference pyrite reaction rate constant by one order of magnitude, respectively. These modifications to the rate constant were selected based on literature values reported by Lefebvre et al (2001) and Manaka (2007). All cases were simulated with for well-aerated conditions (assuming a fixed pO 2 at atmospheric levels).…”

“…The porous medium properties of waste rock based on theNoel and Ritchie (2012) andPantelis et al (2002); the heat transport parameters are chosen at the midpoints of literature values fromPantelis et al (2002); the chemical parameters as well as gaseous diffusion coefficient are constrained by literature values reported inLefebvre et al (2001) andManaka (2007). Optimal temperature for microbial activity was obtained fromXie et al (2007).…”