Evaluation of heterogeneous sulfide – rich mine tailings as secondary raw materials: a case study in the Mirdita District (Northern Albania)

Sulphide-rich tailings constitute a major environmental concern due to the acid drainage (AD) production and release of potentially toxic elements (PTE). Therefore, the management of active mine dumps and the reclamation of inactive ones require to reduce the exposure of the possible environmental receptors to contamination. A common, critical feature of mine dumps is the heterogeneity of the tailing materials that may complicate the quantitative prediction of potential contamination. On the other hand, heterogeneity can be a key for a more rational and cost-effective remediation, given a good characterization of the dump materials. Moreover, mine wastes often contain valuable components and therefore a suitable solution is to make positive use of them. In fact, as mining and processing (comminution and concentration) constitute a major cost of the ore mineral cycle, the availability of partly-processed, although low-grade resources may represent an interesting opportunity of exploitation. The present work is a case-study for a quantitative flow-sheet-related approach to the aim of heterogeneous sulphide-rich tailing dumps management. We selected the former processing site of Reps, in the Mirdita District (northern Albania), where we characterized two tailing dumps and assessed the contamination. Moreover, we evaluated the concentration potential of commodities, namely pyrite and gold, from the tailing materials. We analysed the Reps tailing samples in order to evaluate mineralogy, grain size and bulk chemical composition, concentration of PTE, the presence and persistence of AD. The data set splits in two classes, based on the sulphide content. The reconstruction of the former processing flow-sheet allowed us to recognize this pattern as resulting from two distinct processing stages and to quantitatively improve the AD prediction results. We selected a shaking table concentration method for testing separation of pyrite and gold, by taking into consideration the need of reducing both costs and volumes. The effectiveness of the method was verified by monitoring both the feed and the output materials for grain size, geochemical and mineralogical parameters. The optimal grain size of the input samples was obtained through a closed-circuit regrinding and milling method. The concentrate output shows an enrichment in pyrite in all the samples. The concentrates constitute 16-37.4 wt% of the shaking table output, depending on the initial sulphide content of the sample. Au concentration data were gained by Activation Analysis on selected grain size classes, in order to verify the correlation of Au concentration and the particle size distribution. Preliminary data show that in our samples a valuable recovery can be achieved by sieving in order to separate the Au- rich (up to 580 ppb) fine fraction (<38μm), followed by tabling of the coarser fraction. Thus the Metal Recovery reaches 49.6%. Our results show that information about former processing can provide a useful insight for remediation planning. Moreover, this quantitative approach can lead to a rationale recycling of tailings and thus to a reduction of their volumes and environmental impact.