A simplified approach to assess seismic stability of tailings dams

In the zones of high seismic activity, tailings dam should be assessed for the stability against earthquake forces. In the present paper, a simplified method is proposed to compute the factor of safety of tailings dams. The strain-dependent dynamic properties are used to assess the stability of tailings dams under seismic conditions. The effect of foundation soil properties on the seismic stability of tailings dams is studied using the proposed method. For the given input parameters, the factor of safety for lowfrequency input motions is nearly 26% lower than that for high-frequency input excitations. The impedance ratio and the depth of foundation have significant effect on the seismic factor of safety of tailings dams. The results from the proposed method are well compared with the existing pseudo-static method of analysis. Tailings dams are vulnerable to damage for low-frequency input motions.

A virtual geographic environment for dynamic simulation and analysis of tailings dam failure

It is of great significance for disaster prevention and mitigation to carry out disaster simulations for dam failure accidents in advance,but at present,there are few professional systems for disaster simulations of tailings dams.In this paper,we focused on the construction of a virtual geographic environment(VGE)system that provides an effective tool for visualizing the dam-break process of a tailings pond.The dam-break numerical model of the tailings dam based on computational fluid dynamics(CFD)was integrated into the VGE system.The infrastructure of the VGE was supported by a 3-D geographic information system(GIS)with a user-friendly interface for the initiation,visualization,and analysis of the dynamic process of tailings dam failure.Key technologies,including the integration of numerical models,rendering of large-scale scenes,and optimizations of disaster simulation and visualization,were discussed in detail.In the prototype system,information on the run-out path,travel distance,etc.can be obtained to visually describe the flow motion released by two dam failure cases.The simulation results showed that the VGE can be used for the multidimensional,dynamic and interactive visualization of dam-break disasters,and can also be useful for assessing the risk associated with tailings dams.

Using Piezocone Tests for Analysis of Phreatic Water Conditions and Prediction of Soil Behavior in Tailing Dams

In this work the possibility of identifying two important aspects in the process of adopting soil parameters for calculating stability analysis models in tailing dams is discussed. The use of commercial computer programs for stability calculations allows obtaining numerically exact results. Its representativeness, however, will be linked to the correct definition of the phreatic regime and to the prediction of volumetric soil behavior during shearing (contractile vs. dilating materials). The theoretical principles for the selection of soils parameters for different failure models are briefly presented. Also, how the incorrect assumptions regarding material behavior can significantly affect the estimation of tailing dams’ stability. The results of CPTu tests for the diagnosis of the phreatic and mechanical condition of the materials are discussed and two examples are presented to remark on the care that should be taken to avoid incorrect soils parameters adoption.

Identification and Selection of Regional Plants withPotential for Phytoremediation in Abandoned Open PitTailing Dams

The degree of adaptability and phytoremediation potential of the plant species, Zacate Garrapata, Zacate Banderita, Chivatillo, Oregano, Chamizo and Sotol were evaluated on different substrates (S) composed of tailing (JM) and agricultural land (TA) in different proportions in mass: S1 = 100% TA, S2 = 100% JM, S3 = 50% TA and 50 % JM, S4 = 25% JM and 75% TA, S5 = 75% JM and 25% TA. With the combination of species and substrates, 30 treatments were generated. The heavy metals evaluated were Pb, As, Cu. Fe, Cr and Zn, in root, leaf and stem. The results showed significant statistical differences (p < 0.05), with the Sotol and Zacate Garrapata species being the ones with the highest degree of adaptability and accumulation of heavy metals in interaction with S3. These two species can be used in the remediation of open pit tailing dam.

Physico-chemical characteristics and heavy metal concentrations of copper mine wastes in Zambia:implications for pollution risk and restoration

Soil characterization is a vital activity to develop appropriate and effective restoration protocols for mine wastelands while insights into the total content of heavy metals in the soil is an important step in estimating the hazards that the metals may pose to the vital roles of soil in the ecosystem.This study addressed the following research questions:(1)To what extent do the physico-chemical characteristics vary between mine waste sediments and the nearby forest soil?(2)Are the concentrations of heavy metals high enough to be considered as toxic?and(3)Are heavy metals present in mine waste sediments potential sources of pollution?We hypothesized that the physicochemical characteristics of mine waste sediments are less favorably for plant establishment and growth while the concentrations of heavy metals are very high,thus restricting the success of revegetation of mine waste lands.Mine waste sediments were sampled following a diagonal transect across tailings dams,overburden dump sites and the local forest soil from the top layer(0-20 cm)using a closed auger.Samples were analyzed for arsenic,barium,lead,cadmium,cobalt,copper,chromium,nickel,vanadium,and zinc as well as for soil physico-chemical properties.The mine waste sediments were dominated by silt whilst the forest soil by sand particles,with significantly high bulk density in the former.Both the forest soil and overburden sediments were acidic than the alkaline tailings dam sediment.Total organic carbon and nitrogen contents were significantly low in mine wasteland substrates but the concentration of Ca and Mg were significantly higher in tailings dam substrate than the forest soil.The concentrations of available P,K and Na were similar across sites.The mean concentrations of heavy metals were significantly(p<0.01)higher in mine waste sediments than the forest soil;except for cadmium(p=0.213).The order of contamination by heavy metals on the tailings was Cu>Co>Ba>Ni>As>Zn>Pb>Cr>V>Cd,and that on the overburdens was Cu>Co>Ba>Ni>Zn>Cr>Pb>V>As>Cd.The pollution load index(PLI)was nearly twice higher for the tailings dam(8.97)than the overburden(5.84).The findings show that the copper mine wastes(the tailings dams and overburden waste rock sites)are highly contaminated by heavy metals;which,in turn,might pose serious hazards to human health and agricultural productivity.In addition,poor macro-nutrient availability,substrate compaction and soil acidity(particularly on overburden sites)coupled with toxic level of heavy metals would be the main challenges for successful phytostabilization of copper mine wastelands.

Progresses in restoration of post-mining landscape in Africa

Mining alters the natural landscape and discharges large volumes of wastes that pose serious pollution hazards to the environment, to human health and to agriculture. As a result, the recent 2 decades have witnessed a global surge in research on post-mining landscape restoration, yielding a suite of techniques including physical, chemical, biological(also known as phytoremediation) and combinations. Despite the long history of mining in Africa, no systematic review has summarized advances in restoration research and practices after mining disturbance. Thus, the aim of this review was to document the state-of-knowledge and identify gaps in restoration of postmining landscape in Africa through literature review. We found that:(1) there has been substantial progress in identifying species suitable for phytoremediation;(2) few studies evaluated the feasibility of organic amendments to promote autochthonous colonization of mine wastelands or growth of planted species; and(3) restoration of limestone quarries in Kenya, sand mining tailings in South Africa,and gold mine wasteland in Ghana are successful cases of large-scale post-mining restoration practices in Africa.However, the pace of post-mining landscape restoration research and practice in Africa is sluggish compared to other parts of the global south. We recommend:(1)mainstreaming the restoration of mine wastelands in national research strategies and increased development planning to make the mining sector ‘‘Green'';(2) inventory of the number, area, and current status of abandoned mine lands;(3) expanding the pool of candidate species for phytostabilization;(4) further evaluating the phytostabilization potential of organic amendments, e.g., biochar;(5)assessing the impacts of mining on regional biodiversity.

Determination of mercury and its fractionation products in samples from legacy use of mercury amalgam in gold processing in Randfontein,South Africa

This study aimed at determining the levels of total mercury(THg)in tailings dams,soil,sediments and water samples collected in the vicinity of legacy mercury amalgam gold mines.Acid digestion was employed in sample digestion followed by analysis using CVAAS.Tailings dams,community and garden soil,and stream sediments were further investigated for mercury fractions using a five step sequential extraction procedure.The concentrations of THg in tailings dams,community and gardens soil were 0.890e6.755 mg/g,0.431e0.968 mg/g and 0.471e1.019 mg/g,respectively and the concentrations of THg in the sediments obtained from tailings dams,streams and wetlands were 0.649e1.998 mg/g,0.604 e1.356 mg/g and 0.681e1.356 mg/g,respectively.The concentrations of THg,in aqueous samples obtained from tailings,streams and wetlands were 0.032e0.070 mg/l,0.004e0.068 mg/l and 0.007e0.012 mg/l,respectively.The sequential extraction procedure showed that most Hg in the tailings dams was largely elemental Hg and Hg bound to sulphur.Soil and sediments were largely dominated by organic bound Hg.Moderate seasonal correlation was observed in tailings dams soil,but weak seasonal correlation in soils collected in the vicinity of tailings.However,a strong seasonal correlationwas observed in sediments and water samples.The concentrations of Hg obtained largely existed in organic and sulphate bound Hg and there is elevated potential to methylate Hg.