Current situation in Chile
Chile is, with 27 % of the global production, the largest producer of copper before Indonesia and the world´s largest exporter of copper. In addition, Chile has the world´s largest economically available deposits of copper ores. More than 50 % of Chilean export revenue is attributable to copper mining. However, mining has significant downsides. In the Chuquicamata mine alone, about 45 million tons of ores are mined annually. The concentration of copper in the ore is only 0.5-2 %.
Where the challenge begins
During the following process of increasing the concentration to a copper content of 30-35 %, large amounts of the introduced material ends up as waste that must be deposited accordingly. In Addition an enormous demand of water - a scarce resource especially in northern Chile – is needed and contaminated with chemicals and heavy metals in the course of copper production. Unclear is also the handling with the steadily increasing arsenic content in the remaining ores. In Chile copper is mostly found in sulfide ores. The continual mining of metallic reserves leads to the necessity of exploring lower positioned ores with increasing mineralogical complexity. Arsenic in particular is a highly toxic inorganic pollutant that not only poses a threat to the human health, but also to the entire ecosystem.
This led to the introduction of arsenic limits for imported copper concentrates (e.g. Japan and China). The simplest way to meet this Problem is to dilute arsenic-rich with arsenic-poor concentrates. However, this strategy will not be practicable in the long term due to rising arsenic levels. Real alternatives are already developed and in operation. For example, the roasting process is a technology that was recently installed at Codelco DMH and developed as well as built by Outotec GmbH & Co.KG (here partner). But since there are only a few plants (roasters) of this kind worldwide installed and because the process has so far only been used for a few concentrates, it is necessary to improve the understanding of the chemical reaction mechanism, the process engineering and the plant optimization.
In addition to the removal of arsenic from the various intermediates and residues of copper smelters (e.g. fly dust), the best possible fixation of arsenic is also a field of research interest. In Chile, arsenic is currently mostly bound as calcium arsenate. However landfilling in this form is only conceivable in very dry areas such as the Atacama Desert. Due to the climate change more and more precipitation is observed there (like on the excursion during the definition project), which of course raises the question of sustainability.
More stable arsenic compounds exist in the form of iron arsenates, in particular scorodite, or arsenic sulfide. Scorodite is an iron arsenate phase, which is considered to be one of the most stable forms to deposit arsenic under aerobic conditions, with a very high long-term stability. Although the Chilean company Ecometales has developed an industrial scaled process to bind arsenic as scorodite, unfortunately the conversion of the arsenic into this compound is more than twice as expensive as the binding as calcium arsenate. The primary rice drivers in this process, which are relevant for a cost reduction, are hydrogen peroxide (H2O2) and iron. For environmental reasons, Chile however wants to introduce this high standard and hence stabilize arsenic in the form of scorodite in the future. Therefore more efficient and above all more cost-effective processes for the production of scorodite have to be developed. Finally, it is important to find the best possible barrier system for the landfilling of the corresponding arsenic compounds so that any possible entry into the environment is kept as low as possible.