Rate-control quotient of mineral dissolution from waste rock dumps Liu, Zhong-Sheng (Simon); Huang, Cheng; Ma, Liang; Dy, Eben; Xie, Zhong; Tufa, Kidus; Fisher, Elizabeth; Zhou, James; Morin, Kevin; Aziz, Mike; Meints, Cody; O’Kane, Mike; Tallon, Lindsay
Rain-water and/or snow-melt water infiltrate into or through waste rock dumps at mine sites and dissolve minerals (salts) from rock surfaces. Collecting and treating the drainage is required to meet mine-water-discharge regulations. Generally speaking, less solute loadings in the collected drainage would mean lower cost (e.g., less lime consumption). Thus it is important to identify the rate-control mechanisms of mineral dissolution under different storage configurations of waste rock dumps. In this paper, the authors present an analysis of rate-control mechanisms. The main point is the rate of water-infiltration Q relative to the rate of solute production (kβλ), i.e., (kβλ)/Q. Here k represents the effective kinetic constant of a mineral species’ dissolution from a rock surface, β represents rock dump depth, and λ represents the sum of rock surface areas that are flushed by infiltrated water within a unit volume of rocks. One significance of the quotient (kβλ)/Q is its quantitative indication of the rate-control mechanisms. When (kβλ)/Q becomes smaller, say (kβλ)/Q <0.5, the rate of solute production becomes in control because the solute loading is nearly independent of water-infiltration rate Q; when (kβλ)/Q becomes larger, say (kβλ)/Q > 2.5, infiltration rate Q is in control, that is, the solute concentration would become close to the saturation concentration of the mineral species and the solute loading would become proportional to infiltration rate Q; when 0.5 < (kβλ)/Q < 2.5, both water-infiltration rate Q and the rate of solute production (kβλ) are in control, a mixed control mechanism.
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