Does mining waste have an impact on aquatic ecosystems?

In a mining operation, the mineral of interest is processed, but in the procedure of obtaining it, there are other residues and secondary minerals that are obtained. Generally, these are left near the mining site, and this has environmental consequences such as water pollution and loss of biodiversity. On the other hand, these mining residues may still contain traces of minerals of commercial and strategic interest for energy transition and industrial development, and therefore of value to industry. BETA TC participates in RAWMINA, a European project coordinated by Leitat, that aims to develop a pilot system to establish a sustainable and efficient recovery process of strategic metals from mining waste.

Sustainable metal recovery

In this pilot plant, bioleaching technology is first applied, which is the extraction of metals through bacteria that lower the pH and dissolve them in an aqueous medium. The result of this process goes through a battery of technologies that retain strategic metals in solution, such as cobalt, gold, antimony or tungsten. These materials are used in the manufacture of mobile phones, motors, windmills or lithium car batteries for the ecological transition.

Although the process is highly efficient to maximise the recovery of strategic material and minimise water use, it also has stages where there may be releases to the environment in the form of liquid waste. Within the RAWMINA project, the BETA TC is carrying out different experiments to ensure the absence of environmental impact of the waste generated in this pilot plant.

The research at the BETA TC

Releasing this effluent waste into the river will have a greater or lesser environmental impact depending on the river flow. If it is released into a river with a high flow rate, the environmental impact will be less than if it is released into a river with a low flow rate. In this experiment, the flow and dilution conditions of different peninsular rivers that could receive these effluents are simulated. To this end, work is carried out in the laboratory with several channels that imitate real rivers, where parameters such as water speed, temperature and light are controlled. These channels allow the water to circulate and dilute the effluent. The dilution varies depending on the flow rate to be simulated. As in any experiment, it is necessary to have a control, to which no effluent waste is added.

To determine that the effluent from the pilot plant does not have a significant effect on the aquatic ecosystems, two types of food webs (food relationships between organisms) are used. One food web is based on biofilm (photosynthetic micro-organisms) and freshwater snails, and the other is based on decomposition with alder leaves simulating leaves that have fallen into the river, and river shrimps eating the leaf litter.

With all this, different parameters are observed: how much chlorophyll is in the channels, what is the biomass of the biofilm, the survival of the animals, the enzymatic activity, the rate of decomposition of the leaves, the algal community. The number of parameters affected and the magnitude of the change with respect to the control will give us information on the degree to which the effluent is affecting the aquatic ecosystem.

The research carried out at the BETA TC within the framework of the RAWMINA project aims to ensure that the liquid waste generated does not affect aquatic ecosystems, thus contributing to a more respectful mining industry aligned with the ecological transition.