Innovations in Sustainable Mining: Balancing Environment, Ecology and Economy

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021

K. Randive et al. (eds.)Innovations in Sustainable MiningEarth and Environmental Sciences Libraryhttps://doi.org/10.1007/978-3-030-73796-2_1

A Sustainable Approach to Transforming Mining Waste into Value-Added Products

Sanjeevani Jawadand¹ and Kirtikumar Randive¹  

(1)

Department of Geology, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur, (MH), India

Kirtikumar Randive (Corresponding author)

Email: randive101@yahoo.co.in

Abstract

Mine waste is usually considered worthless in the subsequent stages of mineral production; but it will become valuable in the future and will be needed for the ever-increasing demand of society. Over several decades, large-scale extraction of minerals to cater ever-increasing demand for the growing global population has generated enormous mining wastes, polluted water bodies and air thereby leaving a deleterious effect on the environment. Each year, several billion tons of solid waste is generated worldwide by mining industries as mine byproducts during all types of mining activities, particularly drilling, blasting, and transportation for the extraction of the desired products. The mining wastes are generated at every step of activity, depending on the type of mining method, type of ore, the geological set-up and processing techniques adopted. It is estimated that about a million ton of ore and waste is generated from the large-scale mines per day, and a couple of thousand tons generates from small-scale mines per day. As per an estimate, mining of 1 ton of coal generates approximately 0.4 tons of waste and tailings. Similarly, the production of 1 ton of copper generates approximately 110 tons of waste and 200 tons removal of overburden. Besides, over 500 million tons of mill tailings is generated per year from various ore concentration processes (e.g., lead-zinc, copper, iron). Therefore, the adoption of optimal waste management strategies is sorely needed for the efficient recycling of large quantities of mining waste products generated each year from hundreds of mining operations across the country (or worldwide). In this study, we present a critical overview of solid wastes in mining and the optimal waste management strategy including legal remedies and economic constraints. A holistic approach to end-to-end mining processes to understand and frame the waste management strategy is needed for reducing the risk and maximizing the resource potential.

Keywords

Mining wasteResource efficiencySustainable management

1 Introduction

Mining waste is the result of complex mining processes, which involves steps from exploration to mine closure and the current economic paradigm based on unlimited growth. In each of these steps, a large amount of waste is generated which contain significant levels of toxic substances. So, these mining wastes needs to be tackled effectively to lessen its negative impact on environment. Furthermore, the over-exploitation of mineral resources to meet the burgeoning demands by increasing population result in increased generation of mining waste. The mining waste involves materials that need to be discarded to get access to the mineral resources (such as topsoil, overburden and waste rocks), and materials remaining after selection/processing/treatment (operating residues, as well as tailings); indeed, the desired mineral may be present in the ore in minute amount (less than 1%). It indirectly poses challenge of disposing of such large quantities of waste. Large amounts of overburden and tailings are of growing concern in the mining sector, specifically due to the presence of heavy metals. The storage of the mine wastes is commonly identified as one of the most important causes of environmental impact. The total amount of tailings which would need storage will also surpass the in situ volume of the ore being mined and processed. The global production of solid wastes from primary extraction of minerals and metals is on rise (over 110 billion tons per year) and may range from few times the mass of the valuable element (e.g., iron and aluminium), up to millions of times for scarce elements (e.g., gold) [1].

With the development of mining sector, mining activities have generated more solid waste and caused increasingly serious problems for the environment. An optimal strategy is needed to pursue solid waste management, particularly in the present-day mine waste approach. The mining and processing wastes are considered as a potential resource and have many potential applications because of their low-grade metal content. The waste management system for transforming mining waste into resources creates a complex cluster of inter-related aspects (socio-economic, environmental, and technological) and have many stakeholders including local communities, NGO’s, mining and related industries, etc. Inadequate data on mine waste materials impede the identification of most suitable waste management approaches, the optimization of treatment processes, the evaluation of environmental impacts of reuse or landfilling, and the assessment of the release of chemical substances from products or materials. In addition, extracting ores below cut-off grade, recycling mine waste in commercial products and recovering value-based products require advanced processing technologies. Certain mine waste materials contain elements which could be useful to the industry and can be obtained from other sources at a nominal environmental cost. Recycling of the mine wastes extracts valuable resources from the waste stream or transform the entire waste material into a new value-added product [2]. The recycling basically refers to the versatility of waste materials to be processed and transformed into a new product or re-used in almost the same capacity [3].

The diverse forms of mining wastes are of global concern but the present study is limited to solid wastes in mining. Now worldwide, the countries are attempting to adopt the sustainable management strategies for mining waste which further transitions from throwaway society to a zero-waste economy, in which mine waste materials are reused, recycled or reclaimed, and are only disposed of when there is no other alternative. The present study highlights the solid wastes in mining and the holistic approach of end-to-end mining to curb waste and the best use of resources.

2 Mineral Wastes: Nomenclature and Classification

Mineral waste can be defined as a material leftover from exploration, mining and quarrying operation that cannot find a productive use. It is the high-volume material that originates from the excavation and physical and chemical processing of a wide range of metalliferous and non-metalliferous minerals by opencast and deep shaft methods [4]. The mine waste is the geological material below the cut-off grade that is generated during mining operations [5]. Waste rock, tailings, overburden and other solid waste are the largest solid industrial waste produced in the mineral resource exploration process. Much of this waste is used to backfill old pits, create haul roads or bunds, but a lot remains in waste tips or tailings lagoons This increase in mining and mineral waste has serious consequences for humankind, biodiversity and the environment. Different exploitation phases and related solid wastes generated in mining can be classified as follows (Fig. 1).

Fig. 1

Solid wastes generated in different stages from exploitation to final product

Waste rock: Waste rock is a bedrock that has been mined and moved out of the pit, but has no commercial metal concentrations [6]. The mine waste rock can further be categorized as clean waste or special waste based on its mineral content and its ability to produce acid [7]. The composition of the waste rock controls the element’s behaviour released in the atmosphere.

Tailings: Tailings normally consist of various mixtures of quartz, feldspars, carbonates, oxides, ferromagnesian minerals, and minor amounts of other minerals. Because tailings are essentially finely crushed rocks, their mineralogical composition generally corresponds to that of the parent rock, from which the ore was derived [8]. These are of great concern in the mining sector due to the presence of toxic heavy metals in them. For several mining activities, the storage of tailings is commonly identified as one of the most significant sources of environmental concern. Most probably, the quantity of tailings exceeds the total in situ volume of the mined and processed ore and causes storage issues [9]. For e.g., if the grade of ore were 1% copper, 99% of the total ore would be deposited as tailings. Iron ores generally have higher grades than sulphide or gold ores, often going over 50% or more. Less tailings are therefore produced in the iron ore mines.

Coal Refuse: During the preparation and cleaning of coal, the raw coal is put through a series of shakers to separate rock material from the coal and the resulting solid waste commonly called as coal refuse. Coal refuse contains heavy metals and also a certain amount of sulfur-bearing minerals, especially pyrite and marcasite, that when exposed to water, result in acidic discharge [8]. The processing of 1 ton of hard coal produces 0.4 tons of waste material, much of which is deposited on the ground (about 1300 hectares) and below ground (about 1500 hectares) as waste piles [10, 11]. In India, the opencast mines being a major source of coal production, the ratio of waste generated is much higher than the underground operation due to stripping nature of extraction [12]. In China, about 95% of the total coal output comes from underground coal mines that generate 727.5 million tons of coal mining waste (CMW) annually [13].

Mine dust, aerosols, suspended particles (which settles down to form solid waste): Mining operations such as grinding, milling and management of mine tailings result in coarse particles (about 1 μm diameter) by mechanical action while smelting and refining may result in ultrafine particles (about 0.1 μm) and accumulation mode (0.1–1.0 μm) by condensing high-temperature vapors and subsequent diffusion and coagulation [14–18]. The transport efficiency and deposition of dust particles depend on the particle diameter. The mine dust, aerosols and suspended particles affect the ecosystem health and biogeochemical cycles. It covers leaves and therefore inhibits its capacity to photosynthesis and transpiration, leading to the deterioration of biomass. Secondly increased toxicity in the crops in nearby fields through intake via contaminated soils as well as groundwater. Several effects of mine dust and aerosols from mining operations worldwide are well documented [18].

3 Global Scenario of Solid Wastes in Mining

Owing to the large volume of waste material disposed of from the mines, the problems of mining waste and its management are significant worldwide. In general, an open-pit mine has a higher stripping ratio than an underground mine; which means that generation of waste through open-pit mining is higher. Surface mining operations (open-pit, open-cast or open-cut mining) produce high volume of waste, such as open-pit copper, iron, uranium and taconite mines. For example, the production of 1tonne of copper generates 110 tons of waste and 200 tons of overburden [9].

The global mining sector generates millions of tons of overburden, waste rocks and mineral processing wastes. More than 70% of this global mining waste is generated by UK, Germany, Sweden, Poland and Romania [4]. However, most of these materials end-up being disposed of in landfills either due to their low market value or remote locations of most mining activities [2, 3, 19–21]. At present, almost 100 billion tons of solid waste are generated annually by 3500 mine waste facilities operating worldwide [22, 23]. Mineral processing wastes in the United States accounts for about half of all solid waste produced per year. From 2008 to 2019, Brazil have produced 3.6 billion tons of solid mining waste in dump piles [24]. In India, the Sukinda mining area has produced approximately 7.6 metric tons of solid waste in the form of waste rock and overburden [25, 26]. EU-27 (27 European Union) countries produced about 697 million tons of mining and mineral processing waste in 2016 [27]. In 2018, over two-thirds of the total amount of waste have been generated in EU-27 is major mineral waste [28].

4 Disposal Methods for Solid Wastes from Mines

The proper method of mine waste disposal can circumvent its impacts to some extent. There also needs to build operational flexibility within waste disposal so that waste (material below cut-off grade) will be accessible in the future if commodity prices rise. The concerns related to the disposal of solid waste from metal mines are to choose suitable methods for the systematic use of mining waste and for the management of waste rock and tailing contamination. Some of the solid waste disposal methods are as follows [9].

4.1 Pond Storage

The problems associated with the management of tailings becomes critical with its increasing volume. In pond storage method, the exhausted open pit mines are refilled with the tailings. Technological developments make it possible to mine lower grade ores generating higher volumes of waste that require proper handling. Recently, tailings are stored in mined-out open pits with special designs, especially with uranium mining in Saskatchewan, Canada, so that the transport of pollutants is largely regulated [29]. However, this surface storage may render them vulnerable to potential, sometimes unavoidable disruptions and/or dispersion indefinitely [30]. It can also facilitate percolation of toxic elements into the ground and intoxicate the water table.

4.2 Dry Stacking

In this process, the dewatering of tailings is done using vacuums or pressure filters so the tailings can be stacked [31]. It reduces the potential seepage rates and thereby the impact on the environment. Dry tailing can be transmitted to the tailings storage facility (TSF). However, the construction of TSF is often cost-prohibitive.

4.3 Disposal into Underground Workings

In this process, the disposal of the tailings is done in the exhausted underground mines. It is a somewhat more complex operation than disposal into an exhausted open pit. It involves consideration for stabilization of ground and some type of fill for roof support. So, the tailings need to be combined with additives to bind the water forming a self-hardening fill [32].

4.4 Disposal into the Oceans/Submarine Tailings Disposal (Std)

Tailings can be conveyed using a pipeline and then discharged in such a manner that they can ultimately descend into the depths. In 2015, there were sixteen mining operations around the world using STD [33] as an alternative to land-based tailings storage [29]. Practically, it is not a viable method of reducing the amount of waste as it caused poorly defined environmental impacts.

4.5 Co-disposal of Tailings and Waste Rock

Currently, the methods for the co-disposal of tailings and waste rock to create more stable products and eliminate traditional subaerially discharged slurry tailings are being developed in the mining industry [34]. Thus, depending on the strength and rapid stabilization of the waste co-disposal, the risk and implications of static and dynamic loading have been minimized and allow adequate access to the tailings for rehabilitation [35].

5 Optimal Waste Management Strategy

The mining process generates a significant quantity of waste materials that must be operated strategically to balance economic productivity with environmental sustainability. It will require a holistic approach which integrates all the geological, economic, technical, environmental and social factors. Systematic utilization of solid waste from mines would have considerable social and economic benefits to mitigate resource shortages and for environmental sustainability [36]. Zero waste requires transforming infrastructures and policies, but also education, training, and research. Optimal waste management strategy involves specific approaches as depicted in Fig. 2.

Fig. 2

Waste management strategy

5.1 Technological Innovations

Several technologies are available for management and treatment of mining waste, however, choosing the appropriate one depends on the nature and extent of waste. Characterization and classification play an important role when we need to make a decision on mining waste management. Nevertheless, a regular study in accordance with the application of state-of-the-art technologies is needed to mitigate the severe effects of mining waste and sustain this earth. Some innovative uses of technologies can be explained by the following examples.

The mapping of wastes such as solid waste dumps, tailing ponds, overburden, ore stakes, etc. can help to determine its extent.

The use of hyperspectral imaging in mine waste management and recycling sector provides high performance in terms of material identification. For example, to study the mobility of sediments containing toxic residues [37], the mitigation of toxic metals spread in redox areas [38], the use of biochemical and mineral dissolution processes in sulfurous tailings [39], the dilution of tailings products, the geochemical and mineral elimination of submarine tailings [40], reduction of the discharge of solid waste by recovering sand from ore dressing flow for the construction industry and backfilling approaches [36].

Other remediation systems include the use of heat to volatilize toxic components, and the use of microorganisms to reduce the reactivity and toxicity [41]. There are many instances of successful implementation of microorganisms for the treatment of metal waste in published studies, as well as in ongoing technological applications. For example, Mint Innovation, a start-up in New Zealand, uses micro-organisms to extract metal from waste streams [42]. In this way, we can not only focus on waste treatment but also avoid waste generation altogether by turning potential waste into a resource.

Also, the geochemical characterization establishes the most appropriate form of containment for the post-processing waste materials and improved waste management. Usually some low -grade ore due to lack of advanced technologies considered as a waste and not used in the industry. Technological up-gradation helps effective re-mining the staked low-grade dumps in the mining fields. Some of the success stories are given below.

a. Chromite: Chromite ore having concentrate of >50% Cr2O3 with <2.0% SiO2 which has got a good market potential was earlier considered as a waste. Using advanced technologies, it has become possible to reduce the loss of chromite values in tailings and recover values from previous stacked waste. For example, concentrates with 46–55% Cr2O3 can be produced from the low-grade ores with 18–33% Cr2O3 by recovering 60–80% of chromite values [43]. In Sukinda, Orissa, the chrome beneficiation plant has been installed to utilize the low-grade chromite ores. Nafziger [44] also describes the major low-grade chromite deposits in the world and gives a review of the recovery methods used.

b. Tungsten: Repositories of historical tungsten mining tailings (e.g., Yxjöberg tungsten mine) are potential resources for valuable metals [45]. Considering the technical viability of reprocessing the tailings, extraction of low-grade tungsten deposits is possible e.g., tungsten from low-grade wolframite deposit.

c. Cryolite: Synthetic cryolite can be recovered as a by-product in phosphate rock processing and alumina manufacture.

d. Nickel: The technology so developed pave the way for the extraction of nickel from lateritic nickel ore and chromite overburden or its utilization in the manufacture of nickel-based chemicals. The secondaries/wastes like catalysts are utilized for the production of high-value metals like nickel, cobalt etc. (e.g., in Institute of Mineral and Materials Technology, Bhubaneswar, National Metallurgical Laboratory NML, Jamshedpur).

e. Iron Ore: Iron-bearing materials are processed for alloy production using different advanced techniques such as smelting reduction, production of advanced materials by adopting chemical/electrochemical/biotechnological routes under different conditions (e.g., in National Institute for Interdisciplinary Science and Technology, NIIST, Thiruvanthapuram).

f. Furthermore, usable minerals could be recycled using advanced mineral processing technologies. The Sivas-Divrigi processing plant in America achieved cobalt recovery ratio of 94.7%, the nickel recovery ratio of 84.6% and copper recovery ratio of 76.8% by recycling of iron tailings using floatation method [36, 46].

5.2 Phytostabilization

Phytostabilization is a type of phytoremediation which, by sequestering pollutants in the soil near the roots, uses plants for long-term stabilization and remediation of tailings. Through adsorption or precipitation, plants can immobilize contaminants and provide a zone around the roots wherein the contaminants can accumulate and stabilize. Worldwide, nearly 6.5 million tons of tailings is produced in a single year. So, one of the most common methods of stabilization is by plantation. A phytostabilization approach can be particularly useful in dry environments that are vulnerable to wind and water dispersion. As plantation improves soil moisture content, bulk density, pH and overall soil nutrient content, overburden dumps are typically reclaimed by tree species. The tree species such as Acacia mangium, Eucalyptus camaldulensis, Dalbergiasissoo, Cassia seamea, and Peltophorum pterocarpum are suitable for bioreclamation of overburden dumps (Fig. 3). By this approach, the contaminants become less bioavailable and the exposure to animals, ecosystems, and human beings is significantly restricted.

Fig. 3

Phytostabilization of mine wastes and ideal plant species

5.3 Towards the Circular Economy

As far as the mining sector is concerned, it has been a linear economy model that was in vogue since the 19th century. However, more recently another model called circular economy has been considered seriously by various nations [47]. It is an alternative to a conventional linear economy (make, use and dispose) in which resources are kept for a long-term to extract optimum value from them while in use, and then recover and recycle the products and materials in a synchronised way. Promotion of the 4Rs (Reduce, Reuse, Recycle, Recover) and adoption of the framework of the circular economy (produce-use-return) has created a vibrant new economy in which waste can re-enter the economy in modified form. The introduction of a circular economy model to mining waste presents a huge opportunity to alleviate risk and increase the benefits in terms of value-added products (see Fig. 4). In this transition to sustainability, the material cycle would need to be gradually closed in ways that minimize demand for new minerals and reduce the volume of waste [1]. The espousal of this model for recovering materials as well as energy from waste is not just an environmental obligation but a real economic opportunity. It ensures a resource-efficient pathway to sustainable development. It encourages cradle-to-cradle thinking which emphasizes productive alteration of waste and retrieving it in the system. It supports the concept of upcycling i.e., producing products of greater environmental value than their material inputs over downcycling-based recycling practices which leads to quality loss.

Fig. 4

Towards circular economy—transformation of mineral waste

5.3.1 Some Initiatives and Innovation-Centred Approach

A range of initiatives is taking place throughout the mining industry to improve resource recovery and shift the sector towards a truly circular economy. Several firms are making investments in modern processing technologies to extract and reuse some of the beneficial materials that are often discarded from tons of less usable mining waste, rather than that waste itself [42]. In order to recover as much waste as possible, implementation is done at the mining field and enterprise level itself, in mineral value chain and the system as described by Zhao et al. [48] (Table 1). This circular economy approach in the mining industry in broad scope solves the problems of mineral resource scarcity, growing resource waste and environmental pollution and thus leads to sustainable economic development.

Table 1

Waste management implementation strategy [48]

The mining sector has some of the greatest opportunities to reinvent itself in terms of managing waste and converting it into a resource. As the environmental risks associated with extractive waste, both during operation and post-closure are extensive, good planning around these risks requires consideration of climate-related data and information. Through the years, solid waste has evolved in line with technological progress, from multi-centimetre grain size with a still high content of the desired element to micron grain size with very low chemical contents [49]. Research and innovative approach are significant considering the reactivity of specific mining waste. This could be advanced in different ways such as leaching tests, long-term column tests and stabilized tests as being developed in the context of the Landfill Directive. It is advantageous to check the behaviour of metallic molecules (originating from mining waste) in the subjacent geologic layers and within the waste deposit (adsorption and other attenuation processes) and prediction of their fate using tools such as geochemical and solute-transport modelling. Mitsubishi materials with its recycling-oriented business model recycle and recovers metals and also rare metals. JX Nippon Mining & Metals reuses 83% of its total volume of waste materials produced in 2015, while its copper recycling system recovers about 26% of its total scrap production [50]. Sumitomo Metal Mining almost doubles the recovery rates of copper scrap in the five years following 2010. Recently, Canada-based Mineworx announced an agreement with Tennessee’s Davis Recycling Inc. in April to construct a pilot plant which is a crucial move in demonstrating the effectiveness of the technology; the project will recycle platinum group metals from used catalytic converters [42]. Another firm Comstock Mining, a Nevada-based miner works on improving recovery of mercury from mine tailings and produce over 1,000 tonnes of mercury in the artisanal gold mining sector, owing to the use of mercury in separating gold from non-precious ores [51]. Some firms outside the mining sector (for example, Lafarge, Apple and Tiffany) are focusing on industrial symbiosis and closed-loop production, helping to encourage or drive circularity within it. The L-Max hydrometallurgical method has been developed by the Lepidico company to extract lithium carbonate from lithium mica and phosphate minerals, which is often overlooked by mainstream producers [52]. VTT’s collaborative project¹ not only focused on supply chain optimization but the optimal use of residual material from which metals have already been recovered. The innovation-centred approach gives a better understanding of the barrier and opportunities in the context of mine waste avoidance and resource recovery e.g., MetGrow Calculator.²

5.3.2 Enhanced Landfill Mining (ELFM)

Another approach for the productive use of mining waste is Enhanced Landfill Mining (ELFM). Landfill mining is the method by which waste from active or closed landfills is excavated to reduce its environmental effects. It involves extracting the hazardous material from the ground and preparing it for recovery after a predefined time. Waste valorization emphasises the use of any leftover material or by-product to produce other valuable goods and remain as long as possible in production and consumption systems. ELFM includes the valorization of landfill waste, namely waste-to-energy (WtE) and waste-to-material (WtM) in combination with the ecofriendly approach in preventing CO2 and other pollutants emissions during the valorization processes [53]. It envisages an important major shift in both the waste management vision as well as waste management technology. Its better implementation mostly depends on technological improvements and innovations and surmounting different socioeconomic constraints like social acceptance, protocols,