TREATMENT OF MINERAL-METALLURGICAL RESIDUES FOR THE RECOVERY OF USEFUL SPECIES AND THE REUSE OF PROCESS WASTE

Millions of tons of mining waste now represent a huge ecological challenge, perhaps also an economic opportunity. This paper illustrates and discusses an innovative approach in the reclamation of old mining areas, which is inspired by the principle of circular economy and considers the waste from old mining and mineral processing activities as potential secondary raw materials.The research proposes to apply the technique of flotation to extract from solid mining residues fractions of useful but polluting species, obtaining the double result of downgrading the material below the CSC (Contamination Threshold Concentration) and extracting a concentrate with commercial characteristics. The materials of potential interest are those of which the dumps from the cultivation and processing of the ores of Pb and Zn are composed. The establishment of the Centre of Excellence for Environmental Sustainability (CESA) has enabled an experimental activity based on the treatment of various mining residues in the Sulcis Iglesiente Guspinese area. The results obtained appear to be important in terms of both technological feasibility and costs compared to those of a Permanent Safety Deposit [1] [2]. The project has been developed, with reference to a pilot basin; the studies carried out so far have concerned samples taken from the Montevecchio Levante mud basin on which batch flotation tests were carried out for the reconstruction of a two-section plant flowsheet, one for the recovery of Zn sulphide and the second for the separation of the oxidized fraction from the final waste. Starting from feed concentrations around 2% Zinc, three products were obtained: a commercial Zn sulphide concentrate with 50% content; a final waste with heavy metal concentrations (Zn and Pb) lower than the CSC for industrial sites; and an intermediate concentrate (not marketable) whose residual Pb and Zn content requires inerting or disposal in a collection site. The collaboration with the Geological Survey of Finland (GTK), Europe's leading competence center for the evaluation and sustainable use of geological resources, has allowed the realization of a project aimed at the implementation of high quality data that have highlighted important characteristics of mineralogical composition of the treated material

Trace Elements in Soils of the South Texas Uranium District: Concentrations, Origin, and Environmental Significance

UT Librarie

Towards a Sustainable Management of Mine Wastes: Reprocessing, Reuse, Revalorization and Repository

The need for efficient and sustainable management methods of mine waste is continuously growing all around the world. These waste products often present serious management problems due to their more or less significant amounts and possible environmental threats. This Special Issue highlights the recent and new trends in sustainable mine waste management techniques. Currently, it is essential to sustainably manage mine waste, considering social, economic, environmental and technical aspects. In this Special Issue, insights related to the following issues are highlighted: the problems around mine waste, the fine characterization of mine waste, the latest available technical and environmental solutions to efficiently manage mine waste, including treatment and processing before disposal and high value element recovery, with the view of moving towards defining effective, low-cost and ecofriendly methods, the recycling of mine waste products as alternative resources in different sectors, and finally laboratory, pilot and/or industrial-scale studies related to these topics of research. Scientists and industry and governance stakeholders have to face these new challenges to find the best management practices for the future

Strength assessment of mining soil treated with steel slag as liner material for retention pond

Clay soil has always been associated with low shear strength and high compression behavior due to the high content of organic matter. The limited amounts of clay available onsite and acid mine drainage (AMD) problems have necessitated the continuous search for the treatment technology potentials. Mining soils, obtained from Selinsing Gold Mine in Raub, Pahang were evaluated to determine their suitability for use as mining soil and steel slag mixtures as compacted retention pond liners for AMD treatment. The studied samples were subjected to classification, compaction, permeability and strength tests. The results indicated that the index properties of the samples met the minimum requirements for use as liners. The compaction test showed that the maximum dry density (MDD) and optimum moisture content (OMC) decreased and increased, respectively, for all studied samples. At OMC, hydraulic conductivities of the compacted soil-steel slag were in the order of ≤ 10-9 m/s. The results from unconfined compression strength (UCS) tests gave values of 204 kN/m2 and 61° for soil cohesion and soil internal friction angle, respectively. Furthermore, the influence of steel slag treatment on strength properties has generally shown an improvement of up to 15% steel slag which gives the acceptable results of stress-strain in respect of its usability as liner material

Design of hydrometallurgical stages for reprocessing artisanal mine tailings from Madre de Dios

The objective of this work was to design hydrometallurgical stages to reprocess artisanal gravimetric table concentration tailings from Madre de Dios. These tailings are currently considered waste, even though they still contain gold and rare earths. The scope is limited to the design and technical-economic assessment of leaching stages of gold and rare earths, as well as their subsequent recovery and the neutralization of effluents. Leaching stages were experimentally evaluated in a laboratory scale through a three-step experimental design. Each stage evaluated one independent variable on two levels and its effect on reagent consumption and gold or rare earths extraction. The first step considered gold extraction through thiourea leaching with ferric sulfate as oxidizing agent in an equivalent molar proportion to thiourea. The second step evaluated the inclusion of a hydrochloric acid leaching stage at 80°C before gold leaching. Finally, the third experimental step included a pretreatment at 80°C with potassium hydroxide before the other two stages. According to experimental results, rare earth extraction was too low to consider it further, while thiourea leaching achieved 86.8% of gold extraction after 1 hour, using a thiourea concentration of 8 g/L on a 40% solids slurry. Based on these results, the designed batch process included the following stages: thiourea leaching, sedimentation of solids, cementation of gold using zinc powder, effluent neutralization, and zinc dissolution with sulfuric acid to recover zinc-free, high purity solid gold. Reagent and energy requirements were estimated for 40 kg batches of tailings. Approximately 0.5 g of gold are obtained per batch. An economic assessment indicated that for a five-year projection on which 500 batches are processed yearly, the net present value of the project is $2555.37, and the internal rate of return is 27.2%. A sensitivity analysis revealed that the project can remain profitable if the capital expenditure and the cost of reagents are modified within a ±20% range, while the price of gold and the number of yearly batches can only be reduced by 7.5% and 11.4%, respectively

Slope Stability Enhancement of an Upstream Tailings Dam: Laboratory Testing and Numerical Modelling

Mine tailings are the byproduct of mining activities, which need to be disposed of once the ore is extracted. They can be disposed of in either dry or wet forms. The latter is most common with the tailings being disposed of in the form of slurry inside retention structures. The retention structure may be a natural, manmade, or built dam, which is the case in most of nowadays mining locations. In this thesis, improving the stability of an upstream tailings dam using soil additives is investigated. The experimental phase of this study involved laboratory tests conducted to characterize mine tailings and to investigate any change in their properties upon stabilization with traditional and non-traditional additives; namely, emulsified polymer and a mixture composed of Cement Kiln Dust, CKD, and re-cycled Gypsum. Afterwards, the soil modified parameters are used to establish finite element model employing the commercial code PLAXIS 2D to simulate the behavior of the improved soil when a tailings dam is formed. The numerical model demonstrated that utilizing CKD: B mix increased the overall stability tailings’ impoundment and indicated it is very useful to construct robust dams yet being environmentally friendly

Novel and Emerging Strategies for Sustainable Mine Tailings and Acid Mine Drainage Management

Renewable energy and clean storage technologies are at the forefront of the world’s fight against climate change, including the UN-led move towards a carbon-neutral society. Because these complex technologies require more ‘critical’ metals and elements than fossil fuel-based technologies, the demands for raw materials in their manufacturing are skyrocketing and are projected to continue to increase into the foreseeable future.With ore grades on a steep decline, huge amounts of low-grade ores will have to be mined and processed to satisfy the world’s current and future demands for ‘critical’ metals and elements. Expansion of mining and mineral processing operations would mean more mining-related wastes—tailings, waste rocks and acid mine drainage (AMD)—notorious for their devastating and long-term destructive impacts on the environment. This Special Issue explored repurposing/reprocessing of tailings and AMD treatment cost reduction as promising alternatives to manage mine wastes more sustainably. It also includes articles on the critical roles of redox conditions and galvanic interactions on mine waste stability, hydrogeochemical controls on waste rock weathering, and climate change impacts on AMD formation in closed mines

Potential toxic elements in the soil of a closed Metalliferous Ore Mine

Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2019Potential Toxic Elements (PTEs) contamination is a serious environmental concern in soils and sediments. In many ways, mining activities contribute negatively to the environment and its ecosystems with PTE pollution extending far beyond the seizure of mining activity. Some of the negative impact of mining industry includes formation of sinkholes, contamination of groundwater, surface water and as for the scope of this research study, PTE contamination of soils. Understanding PTE bioavailability and mobility in the contaminated soil near mining activity has become a public concern, and research towards the minimization of the PTEs ecological impact is required, thus the aim of this study, i.e. to evaluate the bioavailability and mobility of PTEs from a closed metalliferous ore mine, deemed to be a potential polluter. The three-stage BCR sequential extraction procedure along with multivariate analysis techniques such as XRF and FTIR were employed to evaluate metal chemical fractions and total concentrations of selected PTEs, such as Aluminium (Al), Chromium (Cr), Copper (Cu), Iron (Fe), Manganese (Mn) and Zinc (Zn) in the analysed soil samples. The total organic matter and distribution of particle size were investigated and the affinity of organic matter to grain size was highlighted. The results indicated that higher susceptibility and bioavailability of Cu, Zn and Mn with a strong affinity to the exchangeable fraction – carbonate bounded. Substantial amount of Fe was observed in the reducible fraction which may be due to the stable complexes formed and bound to the Fe-Mn oxides. In the oxidizable fractions, Al showed dominance with Fe and Cu also showing the strong affinity to be embedded in organic matter. Cr was generally the least mobile metal as indicated by the lowest concentration in all fractions. Generally, the mobility of PTEs in the sediments was as follows: exchangeable>reducible and oxidizable. The strong affinity of organic matter to attach to fine grain sized soil was observed with a high fine fraction being observed in samples obtained from the source of pollution. Furthermore, downstream from the source of pollution, there was an indication that the soil had lower organic matter content with coarser particle sized soil. The FITR and XRF results showed a strong association of silicates and quartz minerals, with the soil being constituted predominantly by SiO2, Fe2O3, Al2O3 and traces of MgO, Cr2O3 and MnO. A Risk Assessment Code (RAC) was also used as a criterion to quantitatively evaluate the risks associated with the soil samples and PTEs risk to the environment decreased as follows Cu>Al>Fe>Mn>Zn> with the least risk posed by Cr

A Comparative Study of Natural Rehabilitation at a Former Mine Waste Site in the Carnon Valley, Cornwall

This study was carried out in the Carnon valley, which is located in Cornwall, south-west England. A river runs through the Carnon valley while former settlement ponds for processing tin and copper ore from the Wheal Jane mine are found on the floodplain. Tailings and waste rocks have accumulated on the floodplain to a height of about 6 meters. The valley is physically divided by a country road into the Middle valley and the Lower valley. Plant growth on tailings in the Middle valley, where tailings heaps were bulldozed, is visibly different from plant growth in the tailings and coarse waste rock observed in the Lower valley. The Lower valley, which features hummocks and hollows, appears to be less rehabilitated than the Middle valley. However, flora diversity in the Lower valley is considerably higher compared to the Middle valley, where a relatively homogeneous vegetation coverage is dominated by a few species. Other noticeable differences between the Lower and Middle valleys are a relative consistent soil compaction and the absence of visible ponds in the Middle valley. This research aims to identify the main drivers and limiting factors in the natural rehabilitation process and local biodiversity development in the middle and lower sections of the Carnon Valley. Through close year-round recording of natural plant species and colonies and habitat survey in the evolving terrain, it was attempted to correlate biota to progressive structural amelioration of the site. Species success was observed in relation to habitat evolution, restrictions imposed by residual toxicity of the former metal-mining terrain, advantages gained by artificial topographic diversity present on abandonment, and the stages reached in the dynamic progression of the combination of all of these features. By observing and recording the outcome of natural revegetation and identifying the impacts of abiotic factors, recommendations are made about the significance of such abandoned mine-sites in relation to ecological conservation value of such former disturbed land, and derive proposals for its onward management. We conclude that, on the site, complex interwoven processes occur of which we observe the state at one moment in time. The volume of data collected in the Carnon Valley is probably greater than available for any other known mine site of comparable history and size. While the data enabled inference of important biotic progressions, this study suggests that the 9 approaches may be applied to other abandoned mine sites, especially for assessment of natural attenuation of residual toxic legacies and ways to engineer future biotic rehabilitation patterns. The potential development of abandoned mine sites to re-establish natural biodiversity is thus recommended, together with a strategy for monitoring of future rehabilitation progression. The study consists of a field survey to record the present vegetation assemblage pattern, laboratory experiments to investigate soil features, data interpretation with statistical software, and evaluation of the interrelationship between emerging vegetation patterns and soil features. Extensive field work was undertaken within a one-year period, observing the highly heterogeneous vegetation community in a state of succession towards natural rehabilitation. The study generated up-to-date, detailed insight into year-round biodiversity development, notably of species diversity and seasonal stages of its development. Both transect surveys and quadrat surveys were carried out to capture general and spatial vegetation distribution variances. Fifty-seven quadrats, deemed to be representative, are surveyed in terms of plant species present and physical and chemical properties of the soil. While the natural vegetation of areas surrounding the valley has already been mapped, it is possible to build a factually-based picture of the progression of on-site species-assembly in relation to taxa that are, or are not, present in the surrounding landscape’s natural vegetation. This revealed that, out of a total of 87 species found in the valley, 9 are classified as very rare species in Cornwall. The presence of local rare species suggests the Carnon valley and other post-mining sites potentially have a significant ecological conservation value. This diversity and biotic taxonomic content of the former mine site highlights the importance of allowing natural biotic colonisation to continue in the wider interest of biodiversity conservation and utilisation of such sites as future biotic reserves. Vegetation survey revealed a host of unusual species assemblage settling on the contaminated soil, which is especially true in the community around ditches. The significantly high species richness and presence of rare species in the ditch community indicates the potential of an edge effect, which has a benefit for biodiversity and may be applied in mine site rehabilitation. The prominent high species richness in the core area (excluding the ditch community) of the Lower valley (75 species compared to 18 10 species in the Middle valley) emphasizes the value of heterogeneity. Bulldozing and human disturbance proved to be effective to improve vegetation coverage, but failed to promote biodiversity recovery. To investigate the effect of chemical contaminants on vegetation development, data is interpreted with ordination techniques such as redundancy analysis (RA) and principal component analysis (PCA). Both techniques indicate that arsenic and copper have a negative impact on vegetation development. Absorbed arsenic or phosphate exchangeable arsenic were found to be the most influential fractions of total arsenic in the soil which affect local species richness and biodiversity. Controlling arsenic fractionation is therefore an important strategy towards supporting vegetation recovery. The thesis postulates that sites with mine waste have special conservation value and that an edge effect may exist -from observing relatively high species diversity in zones along ditches. Water availability has great influence in ditch community development, but is remains unclear how it interacts with other factors to contribute to biodiversity development. The study shows the potential of natural rehabilitation, which should be considered as an option when planning for rehabilitation of former mine sites

Hydraulic Conductivity of Mine Waste Treated Using Enzyme-Induced Calcite Precipitation Method Under Various Curing Conditions

The hydraulic conductivity of mine waste soil is considered moderately high attributed to the high percentage of pore spaces. One of the risks associated with this poor property is possible intrusion of contaminated acid drainage into the groundwater or river. Biocementation using enzyme-induced calcite precipitation is relatively new, more inventive, and environmentally sustainable method compared to the other techniques in improving soil properties. However, limited available data on how this method can be applied in improving heavy-metal contaminated mining wastes. This paper summarizes the effect of this treatment include different cementation concentrations, degree of compactions, curing temperatures and curing durations in reducing the hydraulic conductivity of mining waste. Results obtained indicate greater effect of 1.0M compared to 0.5M concentration, degree of compaction of 80% compared to 70%, curing temperature of 25 °C compared to 15 °C and 5 °C, and immediate reaction effect after 1-day then slowed down after 3 and 7-day curing. When compared to control sample, the reduction in hydraulic conductivity is ranging 75.66 to 97.14%. The positive result is attained due to the production of calcite, CaCO3 that biocemented the soil particles together and reduced the pore spaces, indicated by their content obtained ranging 2.0-5.15 % in the treated soil. Visual images through SEM and spectra of x-ray diffraction confirmed the presence of CaCO3 in soil particles. This work contributes significantly to the study of the properties of copper mine tailings in Ranau, Sabah, including the first study on biocementation of copper mine tailings. The method could be used to reduce the hydraulic conductivity of mining waste soils contaminated with heavy metals. Various scenarios such as curing temperature, duration, cementation concentration and degree of compaction have been proposed to optimize the effectiveness of the treatmen