The metal mining activity has been the source of large volumes of tailings that must be stored in tailings storage facilities (TSFs). Since tailings might contain residual valuable metals, these are often subject of assessment studies aimed to find a feasible way to reprocessing. One of these TSFs was built and operated during the 1930’s for the exploitation of a giant porphyry copper deposit in Chile, a deposit that is still under exploitation today. For these old tailings a historical assessment was varied out about the copper recovery potential in a reprocessing scenario by flotation. Based on theoretical concepts and available historical operational data, it can be shown that the main reason for the relatively high copper grades found in these tailings are the corresponding high grades of the processed ores, instead of being the result of an inefficient past technology of flotation with consequential low recoveries. Conversely, the former flotation circuit was optimal concerning the recovery of copper sulphides favoured by the less restrictive high copper content of these sulphides. Consistently, it is argued for the study case that the main advances in flotation circuits have focused on improving selectivity without sacrificing recovery, due to the changes in the mineralogy of the exploited ores. These are relevant facts for a reprocessing scenario, indicating a low copper recovery potential if the current conventional flotation technology is considered; thus other and/or newer processing technologies could be more efficient for recovery of the remaining copper. There are hydrometallurgical potential alternatives for reprocessing but limitations are expected in relation to milling size of the tailings material. The present findings may apply elsewhere, due to the high representativeness of the present study case.

Introduction

The mining activity is and has been vital for the economy of many countries, e.g. Chile, especially since the beginning of the 20th century. It has resulted not only in the production of metals but also in the generation of waste products, particularly when processing sulphides ores from porphyry copper deposits. This leads to large amounts of tailings that must be stored in tailings storage facilities (TSFs) (Hansen et al., 2005). These mine tailings are the remaining fine grained (1–۶۰۰ µm) ground-up rock after the minerals of economic importance have been extracted, mixed with the associated process water which includes dissolved metals and processing reagents (Edraki et al., 2014). Since the solid phase from tailings might contain remaining valuable metals that were not recovered in the past, they represent potential resources and therefore they are objects of assessment studies and eventually of reprocessing. Reprocessing implies that the tailings material is used as a feedstock for producing valuable products such as recovered minerals and metals (Edraki et al., 2014). According to Gordon (2002), mine tailings can be observed as the single largest source of copper in waste deposits in the US copper cycle and Johansson et al. (2013) categorized tailings as valuable stocks of metals in the “technosphere”, indicating that reprocessing could also be an innovative reclamation technology. The reprocessing of tailings for recovery of metals like gold (Bugnosen, 2001), copper (EPA, 1993) or iron (Karlberg, 2010) is a past and current practice. Rampacek (1982) provides an overview of mining and mineral processing waste as a resource; in 1994 for example, 2% of the total worldwide copper production came from reworked tailings (Graedel et al., 2004). In Chile since the early nineties mining companies have been established and exclusively dedicated to reprocess old as well as fresh porphyry copper tailings to recover copper and molybdenum.