Recycling feldspar wastes as buffer for AMD remediation: preliminary tests on sulfide-rich materials from Sardinia abandoned mines

Acid mine drainage and release of potentially toxic elements are the main source of pollution in sulfiderich mining sites. In Italy, several regions are affected by environmental pollution caused by the extraction and processing of sulfide minerals. Several studies have assessed the acidification potential of sulfide mine wastes, and suggested some procedures to neutralize the acidity and reduce the high metal content of the waters produced by these materials. Adding carbonate-based materials, such as lime (Grieco et al., 2021), can neutralize acid mine drainage by raising pH of water and triggering precipitation of metals as hydroxides at the same time, but the treatment processes are often expensive in terms of capital and operating costs. The aim of this research is to test the neutralizing capacity of a carbonate-bearing buffering material derived from feldspar quarrying in Sardinia. The Sardinia region has one of the longest mining histories in Italy, and mining dumps are currently causing environmental pollution (Da Pelo et al., 2009). Selected samples were collected from Campo Pisano and Furtei abandoned mines. Campo Pisano is part of a giant and high-grade MVT and SEDEX Zn-Pb-Fe district with variable proportions of Cd-rich sphalerite, Ag-rich galena and pyrite. The abandoned mine at Furtei exploited an epithermal deposit comprising Cu, Au and Ag sulfides and sulfosalts + base metal minerals (e.g., pyrite, sphalerite). Grain size, XRD and XRF were used to characterize the samples. The acidification potential was determined through ABA tests. Leaching tests simulated the contaminant release from tailings following the Synthetic Precipitation Leaching Procedure. Leachates were analyzed for major and trace elements through ICP-MS and were then buffered with waste materials from feldspar quarrying, provided by Minerali Industriali. The Potential Toxic Element contents of buffered materials was also determined through ICP-MS. All samples show positive Net Acid Potential Production, with higher values at Campo Pisano. Leaching tests show very different behavior between the two mines in terms of both acidification and metal contents, with Furtei showing much lower pH and higher metal contents. Buffering with feldspar waste was very efficient on highly acidic Furtei samples, even though the amount of buffered material required is high. At Campo Pisano were leached solutions are near neutral the addition of buffer has limited impact.