Researchers at Chile’s Pontifical Catholic University are working on a project called Tailings to Construction Materials (T2CM), which aims to transform copper tailings into high-quality geopolymers and cementitious materials.
The proposal is part of BHP’s Tailings Challenge and it is backed by DITUC, a research center; Melon, a leading cement company; Eral, an engineering firm; the Paris Geopolymer Institute; and Noracid, a manufacturer of sulphuric acid.
T2CM’s goal is to transform all tailings produced at a given operation into usable components for buildings by employing an approach that merges cleaning/extractive processes to recover Cu/Mo and sulfuric acid with conversion/recycling processes.
Besides limiting the accumulation of tailings in the environment, the process drastically cuts the almost one tonne of CO2 that is released into the atmosphere per tonne of cement produced under conventional mechanisms.
The new technique involves transporting fresh tailings to a near or on-site treatment facility, fine grinding and particle size classification of the tailings for surface activation and early sand and pozzolanic material production, as well as rougher sulphide flotation to obtain a desulphurized material and a sulphur polymetallic concentrate.
The sulphur-enriched material is then separated into copper sulphide and pyrite fraction by flotation, and the pyrite-enriched concentrate goes to a roasting step for sulphur removal and H2SO4 production. Finally, the iron oxide desulphurized material is used to develop construction materials.
Such tailings-based construction materials are then further converted into non-treated materials, which can be used as fillers; geopolymeric aggregations of non-treated materials; geopolymeric aggregations of treated materials for high-performance materials; tailings-based cementitious materials, and bio-cemented materials.
The tailings used to test the process were retrieved from eight sites located near the cities of Copiapó, Salamanca y Til Til.
When it came to the manufacturing of cementitious materials, grinding time and temperature were optimized so that it was possible to obtain solid residues whose microstructure and size allowed for the replacement of 40% of cement for tailings.
According to project lead Mauricio López, the use of tailings to produce cement is not a new idea. However, previous proponents used untreated tailings and were able to replace only 15% of the cement in construction materials.