Classification and utilization of different types of mine tailings: An environmental perspective

Concerns about the availability and sufficiency of raw materials for the green transition, as well as the need to operate within the limits of the Earth’s capacity, have created increasing interest in utilizing secondary raw materials instead of extracting primary ones. Utilizing mine tailings produced by the mining industry offers a way to utilize already extracted material suitable for many applications, with a smaller carbon footprint compared to primary materials. However, practical examples of mine tailings utilization outside the mining area remain rare due to economic viability and the complexity of the productization process. This issue is continuously evolving and is actively being pursued by the Finnish Ministry of Economic Affairs and Employment. This thesis seeks to enhance the use of secondary raw materials by identifying the differences and potential uses of various types of mine tailings, preliminarily classified into four groups based on their chemical and mineralogical properties. The groups are felsic mine tailings (FMT), mafic mine tailings (MMT), carbonate mineral-rich mine tailings (CMT) and hazardous mine tailings (HMT). Mine tailings classified as hazardous are challenging to utilize outside the mining area but are frequently used as cemented paste backfill (CPB) materials to fill mining cavities. The stabilization of HMT requires large amounts of cement, the production of which is known to result in carbon dioxide emissions. Hence, there is a need to replace cement with secondary binders. In this study, cement in gold mine tailings-based CPB was partially and completely replaced with blast furnace slag. According to the results, the partial replacement of cement yielded the highest compressive strength values for CPB materials. However, exposure of CPB materials to mine water revealed that replacing cement with blast furnace slag increased the dissolution of calcium-bearing phases, resulting in a reduction in the concentration of As, Sb and Ni in the mine water and unwanted deterioration of the CPB material. Further research with different cement-to-slag ratios is nevertheless needed to confirm the findings. These findings highlight the advantages and challenges of replacing cement with high proportions of blast furnace slag in the stabilization of gold mine tailings. The characterization and classification of mine tailings, as well as investigation of the properties of tailings-based materials, is crucial for facilitating mine tailings utilization. This helps in identifying suitable materials for various applications, thereby reducing the reliance on primary raw materials and minimizing the environmental footprint of mining.