Paste and thickened tailings — friend against acid and metalliferous drainage?

Abstract

Tailings management has been a rapidly growing and demanding challenge across the global mining industry over the past century, primarily due to growing metals demand (and consequently production), declining ore grades (including refractory mineralogy issues), and increasingly stringent environmental and technical requirements. The typical approach historically has been to build engineered storage structures, involving valley fill walls or ring dykes, with the tailings delivered to the tailings storage facility (TSF) via a slurry pipeline. Conventional embankments, however, can fail under a variety of mechanisms and cause catastrophic environmental and public health impacts - the most recent event being the red mud dam failure in Hungary. Another major environmental issue associated with tailings (and waste rock) is the generation of acid and metalliferous drainage or AMD (also commonly known as acid mine drainage). The cause of AMD is the exposure of sulphidic minerals, such as pyrite and pyrrhotite, in mine wastes to water and oxygen, leading to oxidation and the release of sulphuric acid. This in turn dissolves a strong cocktail of heavy metals and if allowed to reach the environment, AMD can cause extreme impacts on biodiversity, water quality, ecosystem health and public amenity. If left unaddressed, AMD pollution can continue for hundreds or potentially even thousands of years. Over recent decades, major advances in thickening technology have enabled the development of paste and thickened tailings (P&TT) to be adopted as a realistic and economic alternative to conventional tailings dams. The primary driver of P&TT technology is the non-Newtonian fluid behaviour of the solid suspension of water and tailings. Given that one of the primary drivers of AMD is excess water flowing through the mine waste - can the relatively low moisture content and rheological characteristics of P&TT provide a natural defence against AMD generation?