Dependence of reaction rate of pyrite oxidation on temperature, pH and oxidant concentration

Pyrite is a common sulfide mineral, particularly abundant in mining waste. It is a focus of mine envi-ronmental concern because the oxidation of exposed pyrite may lead to acid drainage and poisonous mate-rials (like As and heavy metals) release. In the United States, approximately $1000000 per day is spent in alleviating acid mine drainage[1], while the Canadian mining community has environmental liabilities that exceed $2 billion for disposal, management, and rec-lamation of mine waste[2]. …

Dependence of reaction rate of pyrite oxidation on temperature, pH and oxidant concentration

The kinetic sstudy of pyrite oxidation was performed in a series of experiments by a mixed flow reactor. The release rates of Fe(II) are in the order of 3.22×10-9-5.51×10-7 mol·m-2·s-1 at temperature (T ) 25 to 44℃, initial pH (pH )1.4 to 2.7, and initial Fe(III) concentration ([Fe(III)]I) 10-5 to 5×10-3 mol·kg-1. The release rate of Fe(II) increased with increasing T or/and pH or/and [Fe(III)]I in the above range. The rate law and activation energy of pyrite oxidation were derived by statistical analyses of Rfe(II) vs. [Fe(III)]I, Rfe(II) vs. pH and Rfe(II) vs. T, and are given as (1) Rate law: Rfe(II)=104.65e-64.54×103/8.31T[Fe(III)]i0.6./[H+]0.45 ; (2) activation energy: 64.54 ( 8.07 kJ·mol-1. The expression can be applied to more cases (e.g., quantifying the pollutant released from sulfide-rich mining waste and assessing reliable performance of underground repository sites where pyrite acts as an engineered barrier material). Using the rate law derived from this study, the magnitude of the pollutants transferred to secondary phases, soil and water from oxidized pyrite during Jiguanshan mine waste weathering was preliminarily estimated. The estimated magnitude is very high, suggesting that the pile has possibly posed significant impact on the water quality in this region.