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Mining Waste Reduction Methods Veiko Karu, Ingo Valgma, Tiit Rahe

Tallinn University of Technology (Estonia)

veiko.karu@ttu.ee, ingo.valgma@ttu.ee, tiit.rahe@ttu.ee

Abstract — Mining waste reduction methods include all

mining processes beginning from resource distribution until final yield in the plant. For comparing and testing possibilities of mine waste reduction cooperation project has been set up aiming to create a transnational network with regional networks. The activities carried out on the regional and transnational level will secure better access to knowledge, state-of-the-art technologies and good practice to Small and Medium Enterprises active in the mineral waste management & prevention sector. The project addresses all the waste management challenges and opportunities, which face the Baltic Sea Region mining industry, which should be understood as extending to all forms of extraction of natural non-renewable resources. The project activities will be facilitated by the commitment to participate by an additional 15 associated organizations representing mining industry stakeholder associations and/or national government bodies.

I. INTRODUCTION

Knowledge and technology transfer to Small and Medium Enterprises (hereinafter SME) in the Baltic Sea Region (hereinafter BSR) will demonstrate promising technologies/processes that have already been substantially researched and tested, but not demonstrated in situ. These demonstration investments will represent added value for the BSR as a whole. Follow-up activities will ensure that these examples of good practice are transferable or at least adaptable to multiple regions represented in the BSR [1].

The regions participating in follow-up activities to the given investment will specify the waste streams they want tested. Based on this feedback, the investing organization will identify key process parameters essential for obtaining a product with the required properties for selected types of waste.

Each of the investments proposed is justified by the current state of waste management and the commonalities shared by different regions in the BSR.

A. Waste Rock Dumps Are Located in Huge Amounts Near the Area of Abandoned Mines

As an example, the total volume of waste rock from oil shale mining is more than 76 million m3 and covers about 790 ha in Estonia itself. Similar problems are found in Sweden and Finland. In Sweden there are several old deposits from oil-shale mining, the largest one (Kvarntorp) contains some 40 million m3 of crushed processed black shales and contains several metals of potential value. The Estonian solution will help bring down the scale of unused waste rock by offering up a technological process for the production of aggregate for structural concrete and for other types of construction material.

II. UNIT ESTONIA: WASTE TO PRODUCT MOBILE UNIT

Investment objective: Production of material from mining wastes appropriate for construction industries (aggregate for

structural concrete). Therefore construction of a mobile unit for sieving, crushing, screening of material has been chosen. The mobile unit can be transported to different locations where waste dumps are situated. Alternatives to Portland cement and other standard aggregates are being sought.

Oil shale utilisation losses reach 70% in some cases [3][5][6]. These are closely related to legislation, backfilling and waste rock usage. Much smaller sections include production of oil, electricity and chemicals in which most of the research and development is performed today. Current urgent topics for investigating, testing and developing of oil shale mining related questions are backfilling, mechanical extracting of shale, fine separation, selective separation and optimised drilling and blasting.

Mining related waste is mainly solid waste from separation and processing, operating solid waste from overburden removal and drifting, liquid waste from dewatering, processing and washing processes. Origin of mining waste is separation waste form HMS, processing waste, crushing and screening waste [2][4][7].

The main usage of solid mining waste is filling material, construction material, cementing material [12]. The principal direction of developing mining technology is filling the mined area. This provides control over majority of environmental effects. Filling the workings decreases the loss of resources and land subsidence, and at the same time provides usage for stockpiling. Filling the spoils of surface mine decreases dewatering; harmless waste can be used for filling surface mines and in this manner offer new building land [8] [9][10][11] [13][14][15].

Fig. 1. Crushing bucket and wheel loader.

Tests with dry crushing have been carried out on several sites with oil shale, run of mine (Fig. 2) and waste rock in addition to sand and gravel crushing. The material has been evaluated and initial results received.

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Fig. 2 Oil shale selective crushing test results with ALLU crushing buckets.

B. Mining Waste Very Often Contains Metal Elements, Including a Mix of Rare Earth Metals

They are as follows: Zn, Pb, Cu, Cd, As, Ag, Au, Ni and Co, which are both valuable and pose an environmental threat when dispersed in nature. In Sweden 61 800 000 tonnes of mining waste was produced in 2006, which accounts for 51% of all waste produced in this country.

Of this almost nothing was reused or recycled and in the few cases when mining waste was reused. There are no statistics for the amounts of historical mining waste produced since medieval times in the more than 8500 deposits that have been in production in Sweden. The level of recovering or reuse of waste from metal mining is low, especially in copper mine located in Lower Silesia, where all amount of waste is storied on the tailing dump, which is the biggest in Europe. Wastes from metal mining (some valuable and other toxic) which poses a dual challenge for the waste management community - how to recover metals elements, which are used in a variety of advanced and emerging technologies, AND how to contain compounds with toxic properties (or remove them for separate storage).

The challenge is made even greater by environmental regulations, both on the national level and on the EU-level. The Sweden pilot investment will address both of these issues, by introducing a novel process for recovery of rare earth metals and in parallel a range of remediation methods using alkaline waste materials will be developed. In this investment, the emphasis will be on waste from the extractive industry (waste rock & tailings) and the metal processing industry (slags etc.). In the Finnish pilot investment, the emphasis will be on a different mix of waste (magnesite, calcite-bearing waste material), and the product-like output would be used as an adsorbent in the waste water purification processes.

III. UNIT SWEDEN: POST M INING VALUABLE METAL

RECOVERY

Pilot plant to develop business opportunities for SMEs by extracting valuable and/or hazardous metals etc. from mining and metal processing waste. Pilot unit involve: (1) Crushing and milling (2) Leaching (3) Recovery of elements from solution. Possible innovation related to treating old tailings and slags through leaching with different aqueous media,

which hasn't been done before. Transnational relevance as metal recovery from waste is not usual in BSR.

Fig. 3. Mobile unit for recovery of metals from various categories of mining waste and metal-rich process residues: 1) a combination of a jaw crusher and another type of mill crushing the waste down to roughly 0.1 mm; 2) a leaching apparatus designed to leach (using manipulated water solutions) solid waste using high pressure and temperature; 3) a mixer-settler unit for recovery of metals by using liquid/liquid extraction (photo by Bert Allard).

C. Total Amount Mining and Mineral Processing Wastes Stored on the Waste Facilities

Most of it has ended up as tailings in tailings ponds or earthen structures. A similar situation can be observed in Germany, Finland, and Estonia. The Polish pilot investment will develop the aggregate, which will rely on the hard coal treatment and possibly other wastes streams. These waste streams will be different than those proposed in the Estonian investment, which will rely on mining waste mix based on oil shale waste rock, and will include oil shale combustion by-products such as ash. The aggregate developed will be beneficial because they reflect the different waste streams which are prevalent in the BSR.

IV. UNIT FINLAND : MOBILE RESEARCH ENVIRONMENT

SUPPORTING M INING AND PROCESS WASTE RESEARCH

Objective: to test the recycling of mine waste with view to future commercial potential. A mobile module will be constructed, transportable to site where the waste is processed. The main element is dry grinding and classification of the material according to the grain size. Simultaneous analysis is required to control the promotion of classification procedure. Novelty: produced material combined with other components can be used as an adsorbent in waste water purification.

Fig. 4. XRF MiniPal4 for chemical characterization of the samples (photo by Hanna Repo).

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V. UNIT POLAND: NOVEL ARTIFICIAL AGGREGATE FOR

CONSTRUCTION INDUSTRY

Investment objective: to prepare an aggregate for wastes from mineral treatment plant and useful minerals enrichment plant. Aggregate from fine-grained wastes will be produced using agglomeration process. Installation will include screamer, crusher, mixer, and measurement devices (to control physical & chemical properties). The installation will allow to test various coal processing wastes, and other mineral processing wastes (sandstone/mudstone/claystone mixed wastes from gravity washers in heavy liquids). The product: crushed aggregates mix 4(5)-31.5 mm, useful in mining, building and road construction.

Fig. 5. Polish pilot installation (scheme by Krzysztof Galos).

ACKNOWLEDGMENT

The research is supported by project MIN-NOVATION – http://www.min-novation.eu; ETF8123 “Backfilling and waste management in Estonian oil shale industry” – http://mi.ttu.ee/ETF8123 and AR12007 “Sustainable and environmentally acceptable Oil shale mining” – http://mi.ttu.ee/etp. This research work has been supported by European Social Fund (project “Doctoral School of Energy and Geotechnology II”), interdisciplinary research group “Sustainable mining” – http://egdk.ttu.ee

Part-financed by the European Union (European Regional Development Fund and European Neighbourhood and Partnership Instrument)

Scientific work financed from science funds in 2011-2013 allocated for co-financing implement international project.

REFERENCES

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