Laboratory Studies of Electric Current Generated during Fracture of Coal and Rock in Rock Burst Coal Mine

Experiments show that electric current would be produced in uniaxial compression of coal and roof rock. The electric current of coal shows a rapid increasing tendency when the loading stress is greater than or equal to 0.75σmax which can be regarded as an omen for coal failure. The current of roof rock shows reversal tendency while loading stress is greater than or equal to 0.91σmax and revised from negative to positive at the main fracture and the reversal of current can be regarded as the omen of rock fracture. There are obvious differences in physical and mechanical properties, composition, and failure process between coal and rock. The dominant mechanism of electric current generated by coal is triboelectrification of coal particles and charge separation during crack propagation. The mechanism of electric current of roof rock is piezoelectric effect of quartz materials in the early stage and charge separation during crack propagation in the later stage of loading. It can be found that the rapid increasing and reversal characteristic of electric current can reflect the failure process of coal and roof rock, respectively. Thus, it can be considered the omen of coal and rock failure.

Nexus between Artisanal and Small-Scale Gold Mining and Livelihood in Prestea Mining Region, Ghana

Drawing on the DFID’s sustainable livelihood framework, this paper explores the nexus between artisanal and small-scale mining (ASM) and livelihood in Prestea mining region, Ghana. A cross-sectional mixed method survey involving simple random and purposively sampled participants (N=151) was carried out. The results suggest both positive and negative relationships between ASM and livelihoods of the people. The study found various livelihood assets associated with ASM and how critical assets are adversely affected by ASM activities. Limited employment opportunities in rural areas (82%), economic hardships/poverty situations of people (59%), and “quick” income earnings from ASM (90%) were the major factors that influenced people to combine and use their personal assets to enable them to engage in ASM. ASM contributes to the livelihood enhancement through income generation, increased well-being and asset acquisition (50.7%), reduced vulnerabilities (31.1%), and empowerment of people (19.2%) to establish other economic activities. However, the small-scale miners and farmers as well as farmlands, forest, and water resources are most vulnerable to adverse effects of ASM activities. Accidents of various degrees, diseases, and death were the shocks in ASM. Regarding the massive impact of ASM on employment creation and poverty reduction in rural communities, it is recommended that stakeholders recast Ghana’s mineral policy to ensure concurrent environmental sustainability and socioeconomic development.

Reduction of Hexavalent Chromium by Viable Cells of Chromium Resistant Bacteria Isolated from Chromite Mining Environment

Environmental contamination of hexavalent chromium [Cr(VI)] is of serious concern for its toxicity as well as mutagenic and carcinogenic effects. Bacterial chromate reduction is a cost-effective technology for detoxification as well as removal of Cr(VI) from polluted environment. Chromium resistant and reducing bacteria, belonging to Arthrobacter, Pseudomonas, and Corynebacterium isolated from chromite mine overburden and seepage samples of Orissa, India, were found to tolerate 12–18 mM Cr(VI) during growth. Viable cells of these isolates were also capable of growing and reducing 100 μM Cr(VI) quite efficiently in Vogel Bonner (V.B.) broth under batch cultivation. Freshly grown cells of the most potent isolate, Arthrobacter SUK 1201, reduced 100 μM Cr(VI) in 48 h. Reduction potential of SUK 1201 cells decreased with increase in Cr(VI) concentration but increased with increase in cell density and attained its maximum at 1010 cells/mL. Chromate reducing efficiency of SUK 1201 was promoted in the presence of glucose and glycerol while the highest reduction was at pH 7.0 and 25°C. The reduction process was inhibited by divalent cations Ni, Co, and Cd, but not by Cu. Similarly, carbonyl cyanide m-chlorophenylhydrazone, N,N,-Di cyclohexyl carbodiimide, sodium azide, and sodium fluoride were inhibitory to chromate reduction, while 2,4 dinitrophenol promoted the process. Cells permeabilized by toluene increased the efficiency of Cr(VI) reduction and, thereby, indicate that Arthrobacter sp. SUK 1201, indigenous to chromite mining environment, could be used as an ideal tool for chromium bioremediation.

Alteration in Material Properties of an Intact Rock due to Drilling and Bolting Operations

Rock material properties play an important role in assessing rock mass behaviour. Passive rock bolts stabilize a rock mass by restricting relative displacements; however, they may reduce rock material properties. While assessing properties of rock mass reinforced by rock bolts, the alteration caused in rock material properties due to drilling and bolting operation should be well understood. The present work makes an attempt to study the alteration in rock material properties due to drilling and bolting operations. The study has been conducted through physical tests on natural rock specimens in the laboratory. Virgin cylindrical specimens of intact rock were tested under uniaxial compression. Drilling was done through specimens and fully grouted bolts were installed. These specimens were also tested under uniaxial compression. It is observed that the drilling has substantial effect on the uniaxial compressive strength and modulus. A simple problem of tunnel is analysed which demonstrates the effect of alteration in material properties on the strength of rock mass around the tunnel in the field condition.

Biochemical Engineering Parameters for Hydrometallurgical Processes: Steps towards a Deeper Understanding

Increasing interest in biomining process and the demand for better performance of the process has led to a new insight toward the mining technologies. From an engineering point of view, the complex network of biochemical reactions encompassed in biomining would best be performed in reactors which allow a good control of the significant variables, resulting in a better performance. The subprocesses are in equilibrium when the rate of particular metal ion; for example, iron turnover between the mineral and the bacteria, is balanced. The primary focus is directed towards improved bioprocess kinetics of the first two subprocesses of chemical reaction of the metal ion with the mineral and later bacterial oxidation. These subprocesses are linked by the redox potential and controlled by maintenance of an adequate solids suspension, dilution rate, and uniform mixing which are optimised in bioreactors during mining operations. Rate equations based on redox potential such as ferric/ferrous-iron ratio have been used to describe the kinetics of these subprocesses. This paper reviews the basis of process design for biomining process with emphasis on engineering parameters. It is concluded that the better understanding of these engineering parameters will make biomining processes more robust and further help in establishing it as a promising and economically feasible option over other hydrometallurgical processes worldwide.

Rock Load Estimation in Development Galleries and Junctions for Underground Coal Mines: A CMRI-ISM Rock Mass Rating Approach

Rock mass rating (RMR) plays important role in design and selection of support system (Ghosh, 2000). For stability assessment of rock mass it is very important to know the amount of rock load mobilized around the development gallery which is estimated using RMR (Singh et al., 2003, Barton et al., 1974, Bieniawski, 1984, and Ghosh et al., 1992). In Indian coal mines, Central Mining Research Institute-Indian School of Mines rock mass rating (herein after referred to as CMRI-ISM RMR) is mostly used for formulating design guidelines for supports. In this paper an attempt has been made to correlate CMRI-ISM RMR values and rock load of galleries and junctions for different gallery widths, ranging from 3.6 m to 4.8 m, at different densities of roof rocks. The proposed empirical expression can help in quick design of support system for underground coal mines working in the same regime.

Maintainability Analysis of Underground Mining Equipment Using Genetic Algorithms: Case Studies with an LHD Vehicle

While increased mine mechanization and automation make considerable contributions to mine productivity, unexpected equipment failures and planned or routine maintenance prohibit the maximum possible utilization of sophisticated mining equipment and require a significant amount of extra capital investment. This paper deals with aspects of maintainability prediction for mining machinery. A PC software called GenRel was developed for this purpose. In GenRel, it is assumed that failures of mining equipment caused by an array of factors follow the biological evolution theory. GenRel then simulates the failure occurrences during a time period of interest using genetic algorithms (GAs) coupled with a number of statistical techniques. A group of case studies focuses on maintainability analysis of a Load Haul Dump (LHD) vehicle with two different time intervals, three months and six months. The data was collected from an underground mine in the Sudbury area in Ontario, Canada. In each prediction case study, a statistical test is carried out to examine the similarity between the predicted data set with the real-life data set in the same time period. The objectives of case studies include an assessment of the applicability of GenRel using real-life data and an investigation of the impacts of data size and chronological sequence on prediction results.

Exploitation of Bacterial Activities in Mineral Industry and Environmental Preservation: An Overview

Since the identification and characterization of iron and sulfur oxidizing bacteria in the 1940s, a rapid progress is being made in minerals engineering based on biological activities. Microorganisms can play a beneficial role in all facets of minerals processing, from mining to waste disposal and management. Some of the applications, such as biologically assisted leaching of copper sulfide ores, uranium ores, and biooxidation of refractory sulfide gold ores, are now established on the scale of commercial processes. A variety of other bioleaching opportunities exist for nickel, cobalt, cadmium, and zinc sulfide leaching. Recently, other uses of microorganisms are potentially possible. These include the bioleaching of nonsulfide ores, bioflotation, and bioflocculation of minerals, and bioremediation of toxic chemicals discharged from mineral engineering operations. These activities acquire considerable opportunities for further research and development in these areas. This paper is an attempt to provide a critical summary on the most important efforts in the area of bacterial activities in the mineral and mining industry.

Nickel and Zinc Removal from Acid Mine Drainage: Roles of Sludge Surface Area and Neutralising Agents

During acid mine drainage (AMD) treatment by alkaline reagent neutralisation, Ni and Zn are partially removed via sorption to Fe and Al hydroxide precipitates. This research evaluated the effect of surface area of precipitates, formed by neutralisation of AMD using three alkalinity reagents (NaOH, Ca(OH)2, and CaCO3), on the sorption of Ni and Zn. The BET surface area of the precipitates formed by neutralisation of AMD with NaOH (173.7 m2 g−1) and Ca(OH)2 (168.2 m2 g−1) was an order of magnitude greater than that produced by CaCO3 neutralisation (16.7 m2 g−1). At pH 6.5, the residual Ni concentration was 0.32 and 0.41 mg L−1 for NaOH and Ca(OH)2 neutralised AMD, respectively, resulting in up to 60% lower Ni concentrations than achieved by CaCO3 neutralisation which had no effect on Ni removal. The residual Zn concentration was even more dependent on precipitate surface area for NaOH and Ca(OH)2 neutralised AMD (0.33 and 1.02 mg L−1), which was up to 85% lower than the CaCO3 neutralised AMD (2.20 mg L−1). These results suggest that the surface area of precipitated flocs and the selection of neutralising reagent critically affect the sorption of Ni and Zn during AMD neutralisation.

Magnetic Behavior of Natural Fe2O3 from Lhoong Iron Ore Mining Area, Aceh Province, Indonesia

The mineral composition and magnetic behavior of nano-Fe2O3 of iron ore from Lhoong mining area, Aceh province, were studied. The iron ore was prepared by mechanical milling method. The mineral and chemical compositions of samples were investigated by XRD and XRF analysis tests. The XRF test showed that the Lhoong iron ore contains Fe2O3 (93.88%) in association with other isomorphous impurities, such as SiO2, MnO, and Al2O3, in varying proportions. Compared to XRD results, it was consistent with XRF; the phase compositions of iron ore were mainly hematite (Fe2O3). The XRD revealed that hematite was the major mineral component in the Lhoong iron ores. SEM observation showed fine crystalline structure of Lhoong iron ore after the milling process. The main mineral morphology was microcrystalline in agglomerate forms. The magnetic properties of the samples after milling showed the increasing in the remanent (Br) and coercivity (Hc). This increasing can be explained that nano-Fe2O3 phase after milling for 20 hours plays an important role in the magnetic behavior of Lhoong iron ore. It is understood that the longer milling time is sufficient to complete the transformation of hematite (Fe2O3) to magnetite (Fe3O4).