Method for the risk assesment related to the possible collapse of tailings dams

Kurzfassung

An Andalusian research group has developed a methodology to assess the polluting capacity of roasted pyrite ashes through physical, chemical and mineralogical studies. This methodology creates a dynamic model to simulate and predict the outflow, the pathways and spatio-temporal dispersion of waste into the environment. This process has been developed with the aim of determine the potential environmental impact in case of dam collapse. They are looking for technical cooperation agreement.

Details

Mining is one of the main industrial activities occurring in almost every part of the world. Through ore extraction and processing, large amounts of waste material are produced and stored, much of it being of a highly toxic nature. Of waste storage sites, mine tailing dams are more vulnerable than other retention structures and constitute the greatest threat because of their: (1) unstable nature (principally of earth construction), (2) location (often situated near sensitive aquatic ecosystems), (3) large number (in the tens of thousands world-wide), and (4) generally poor to non-existent maintenance (especially after closure of mining activities)

The main environmental problem deriving from mining wastes is a direct consequence of the high content in sulphide minerals, mostly pyrite.
Sulphides react readily with oxygen and water, and their weathering implies a series of chained geochemical and microbiological reactions whose result is the production of extremely acid drainages containing high concentrations of sulphate, metals and metalloids, known as Acid Mine Drainage (AMD).

As a result of this problem, a research group has developed a methodology to assess the environmental impact of roasted pyrite ashes in case of dam collapse. This methodology is divided into the following stages:

- Description of the place under study with their main mining characteristics
- Sample collection and preparation for the analysis
- Analytical methods for the characterization of the chemical and mineral composition of the roasted pyrite ashes from the oxide dam.
- Sequential extraction method and quality control: the sequential extraction procedure is the most common technique used to calculate the different forms of metals in e.g. sediments, soils, wastes whereby several reagents are utilized consecutively to extract operationally defined phases in a sequence.

For the application of this methodology, a mathematical model has been developed for the flow numerical simulation that computes the resultant outflow hydrograph and simulates the dam break flood wave formation and subsequent downstream progression. The modelling has been developed for water containing high sediment concentration, such as those observed in debris and mud flows resulting from landslides mainly in mountain regions.

Overall, the present process illustrates the potential of applying a simple assessment methodology based on combining chemical sequential extraction with dam break flood simulation as a more comprehensive and holistic approach to risk evaluation related to collapse of tailings dams.

The group has applied this process to the roasted pyrite wastes from Almagrera mine (Huelva) placed in the IPB (Iberian Pyrite Belt) district for three reasons: (1) residues produced and stored in dams in this type of complex display a little-known chemical nature, with little information on the threat posed by them to the environment; (2) dam stability requires a continuous monitoring and control during emplacement, construction and operation; and (3) in case of dam failures, the zone that may be affected potentially has a huge ecological value.

Innovative Aspects:
- This method enables the prediction of a few hydrodynamic and chemical characteristics that can be used for damage evaluation.

- The total amount of mobile contaminants that would be released in different environmental conditions could be easily estimated.

- Given the simplicity of the integrated tool, this methodology could be extremely promising and useful for researchers and managers to use in identifying, characterising, and assessing systems globally threatened by mine tailings dams.

- The information presented in this paper may be used to design possible remediation strategies at roasted pyrite ashes storage systems distributed around the world.