Prediction of acid rock drainage in waste rock piles part 2: Water flow patterns and leaching process.

In waste rock piles, the leaching process involved in acid rock drainage is mainly controlled by water flow. This paper (Part 2) investigates the effects of heterogeneities on the water flow patterns by applying probability density functions to hydrogeological properties. In this study, a piecewise constant distribution is proposed to describe the permeability inside waste rock piles, which reflects the effect of both finer and coarser pores. Compared with uniform water flow obtained from traditional homogeneous modeling, various water flow patterns and their pathways inside waste rock piles can be simulated by the proposed model. In addition, the leaching process is also investigated by coupling the calculated water flow with the geochemical reaction based on the water film model proposed in part 1. For demonstration, these models are integrated and applied to the full-scale waste rock pile at Equity Silver mine in British Columbia, Canada. Because the iron loading is highly correlated to the acidity at this site, it is found that the fluctuation of annual lime consumption for neutralization at this site can be well predicted by the integrated model. In addition, the results indicate that waste rock piles with different spatial patterns of permeability distribution, but with the same probability density function, may have different water flow patterns and spatial distributions of iron concentrations inside the pile. However, the total water flow discharge rate and iron loading profiles from the pile are almost the same on the temporal scale.

The correlation between drainage chemistry and weather for full-scale waste rock piles based on artificial neural network.

In this paper, a machine learning algorithm based on artificial neural network architecture investigates the correlation between drainage chemistries in seepage water and ambient weather conditions around waste rock piles. The proposed neural network consists of a long short-term memory unit and a fully connected neural network which uses sequenced input to consider current and previous weather impact on the drainage chemistries. A 20-year (1998-2017) monitoring database obtained from the full-scale waste rock pile of the Equity Silver mine in BC, Canada is used for validating the proposed approach. The neural network is trained based on total precipitation and mean temperature as input and the acidity as output. The results indicate that the calculated acidity from the trained neural network matches with that measured in the field well. In addition, the accuracy of calculated acidity can be further increased by adding a time tag of acidity measurement date into the input layer. This refined approach can capture the long-term evolution and dynamics of hydrogeochemical and biochemical properties inside the waste rock piles.

Uncarboxylated osteocalcin ameliorates hepatic glucose and lipid metabolism in KKAy mice via activating insulin signaling pathway.

Osteocalcin, expressed in osteoblasts of the bone marrow, undergoes post-translational carboxylation and deposits in mineralized bone matrix. A portion of osteocalcin remains uncarboxylated (uncarboxylated osteocalcin, GluOC) that is released into blood where it functions as a hormone to regulate insulin secretion and insulin sensitivity. As insulin resistance is closely associated with metabolic syndrome, this study is aimed to elucidate how GluOC regulates glucose and lipid metabolism in KKAy mice, an animal model displaying obese, hyperglycemia, hyperinsulinemia, insulin resistance, and hepatic steatosis. GluOC (3, 30 ng/g per day, ig) was orally administered to female KKAy mice for 4 weeks. Whole-body insulin sensitivity, glucose metabolism, hepatic steatosis, dyslipidemia were examined using routine laboratory assays. We found that GluOC administration significantly enhanced insulin sensitivity in KKAy mice by activating hepatic IRß/PI3K/Akt pathway and elevated the whole-body insulin sensitivity with decreased FPI and HOMA-IR index. Furthermore, GluOC administration alleviated hyperglycemia through suppressing gluconeogenesis and promoting glycogen synthesis in KKAy mice and in cultured hepatocytes in vitro. Moreover, GluOC administration dose-dependently ameliorated dyslipidemia and attenuated hepatic steatosis in KKAy mice by inhibiting hepatic de novo lipogenesis and promoting fatty-acid ß-oxidation. These results demonstrate that GluOC effectively enhances hepatic insulin sensitivity, improves hyperglycemia and ameliorates hepatic steatosis in KKAy mice, suggesting that GluOC could be a promising drug candidate for treating metabolic syndrome.

The characteristic properties of waste rock piles in terms of metal leaching.

Surface/ground waters could be polluted when rain-water and/or snow-melt water infiltrate through waste rock piles at mine sites and dissolve secondary minerals (salts) from rock surfaces. It is important to reduce solute loading by the optimal configuration of waste rock piles. This requires the proper definition and determination of the characteristic properties of waste rock piles in terms of metal leaching and, in particular, rate control mechanisms and scaling laws, and their dependence upon configuration variables. For revealing these characteristic properties this paper proposes a pile-scale C-Q relation: C = Cs(1 - e-P/Q), (P ≡ kλßψ), where C and Cs are respectively solute concentration and particle's saturation concentration, Q is the flow rate of the water through a waste rock pile, k represents the effective or average dissolution coefficient of a mineral specie from rock surfaces, ß represents rock pile depth, λ represents the ratio of the sum of the surface areas of rocks to the volume that the rocks occupy, and ψ is the sum of the cross-sections of water-flow channels in a waste rock pile. The two characteristic properties revealed by the C-Q relation are: (1) P, the product of k, λ, ß, and ψ (P ≡ kλßψ), which is the characteristic property of a waste rock pile in terms of metal leaching, named here the solute production potential; and (2) the ratio of P to Q, P/Q, a non-dimensional number, designated as α (α ≡ P/Q), named here the rate control quotient, which is the scaling law and the rate control mechanism indicator. The value of α quantitatively indicates what controls the rate of mineral dissolution, and it also relates smaller-scale metal-leaching testing results to their corresponding full scales. When α becomes small, say α < 0.5, the rate of solute production potential P becomes in control, and the solute loading is nearly independent of Q; when α becomes larger, say α > 2.5, solute concentration would become close to its saturation concentration Cs, and Q determines solute loading (that is, the solute loading is proportional to Q). When 0.5 < α < 2.5, both Q and P are in control, a mixed control mechanism. The 20 years of measurements of mine drainage chemistry from the main waste rock piles at the Equity Silver mine, BC, Canada, are used to illustrate how to determine the two characteristic properties P and α, and how well they are able to describe the waste rock piles in terms of metal leaching.

Prediction of acid rock drainage in waste rock piles Part 1: Water film model for geochemical reactions and application to a full-scale case study.

Geochemical reactions taking place at the rock surface and pore water interface, and rapid preferential water flow through waste rock piles are identified as two primary steps for acid rock drainage (ARD) and metal leaching (ML) processes. This paper (Part I) develops a water film model to describe the interactions among sulphide minerals, pore water and oxygen, which considers the reactive surface areas as the primary sites to capture geochemical reactions including sulphide oxidation and neutralization reactions, and also considers acid and metal ion storage in pore water. In addition, the proposed water film model is further coupled with a pile-scale mass transport model to investigate a specific case of the main waste rock pile at the Equity Silver mine, Canada. Overall, the simulated profile of oxygen concentration matches the historical monitoring data. The modeling results revealed potential controlling mechanisms for ARD generation inside the waste rock pile and provided insights into the impact of an engineered cover on the waste rock pile.

The effect of relative humidity on binary gas diffusion.

The dependence of diffusion coefficient of O2-N2 mixture in the presence of water vapor was experimentally determined as a function of relative humidity (RH) with different temperatures using an in-house made Loschmidt diffusion cell. The experimental results showed that O2-N2 diffusion coefficient increased more than 17% when RH increased from 0% to 80% at 79 degrees C. In the experiments, the RH in both top and bottom chambers of the diffusion cell were the same, and the pressure inside the diffusion cell was kept as ambient pressure (1 atm.). Maxwell-Stefan theory was employed to analyze the mass transport in the diffusion cell, and found that there was no effective water vapor diffusion taking place, indicating that the gas diffusion in this ternary (O2-N2-water vapor) system could be considered binary gas (O2-N2) diffusion. The Fuller, Schettler, and Giddings (FSG) empirical equation of the kinetic theory of gases was generalized to accommodate the dependence of the binary diffusion coefficient on the RH. The prediction of the generalized equation was found to be consistent with experimental results with the difference of less than 1.5%, showing that the generalized equation could be applied to calculate the diffusion coefficients of the binary gaseous mixture with different temperature and RH values. The effect of water vapor on the increase of O2-N2 diffusion coefficient was discussed using molecule theory.