Implementation of a procedure for buffering acid mine drainage waters from pyrite-rich tailings at Fushë Arrëz copper enrichment flotation plant

The extraction process from metal deposits has the inevitable consequence to generate enormous amounts of waste (close to mines and enrichment plants) mainly solid and in the form or accumulation of sterile minerals or tailings deriving from the processes of concentration and refinement. These waste materials, if not properly treated, constitute a considerable environmental risk. Some of them can be very rich in sulfides, hence the capacity of inducing the formation of high acidic waters rich in Potentially Toxic Elements (PTE). The present work is focused on the copper enrichment plant of Fushë Arrëz (Northern Albania copper mining district) where a change in tailings environmental impact, due to the transition from double flotation, with separation of pyrite as a by-product, and single flotation, without pyrite separation has been documented. Pyrite, due to its abundance, high reactivity and high S to metal ratio is the main responsible of Acid Mine Drainage (AMD). The aim here was to define the most suitable procedures for the buffering of leached samples and natural waters from sulfur-enriched mining tailings, through the evaluation of samples chemical parameters and assessment of major, minor and trace elements distribution. The buffering of the leached products and natural waters was carried out by adding to the solutions fine-grained calcium carbonate supplied by UNICALCE company. The results show an important reduction in the concentrations of the metals in solution. The metal removal efficiency obtained through this procedure turned out to be excellent and even higher than 90% for most of the PTE considered. In terms of absolute amounts, moreover, almost all the concentrations detected after the buffered remain below the legal limits envisaged for Albanian industrial water discharges. The precipitate produced takes over all the PTE in high concentrations and therefore will require a specific purification or storage treatment. In order to better understand the buffering process of acid solutions rich in heavy metals and improve their application, two insights are suggested for next steps: • perform MP-AES analyses at each buffering step allowing, in addition to validating the buffering model created, to yield buffering curves for each ion considered as a function of pH • perform tests with different buffering materials and subsequently compare the costs and the buffering performance