PROJECT DESCRIPTION
BACKGROUND
Social and economic development in the south-west of the Iberian Peninsula - mainly Huelva, Spain - has been strongly associated with intensive mining in the Iberian Pyrite Belt (IPB). This belt of land - approximately 250 km long and 30-50 km wide – is a notable source of volcanic and sediment-hosted deposits of sulphide. Its original reserves were estimated at 1700 Mt (Sáez et al., 1999).
However, at present, mining has ceased and the only legacy for the population of the region is the existence of more than 100 abandoned mines and over 2x108 m3 of waste, which is scattered across the area in the form of mine tailings, tailing dams, open pits, etc. These remnants of the area’s mining past have a very severe impact on the landscape and present a significant environmental risk, especially from the leaching of minerals into the natural environment.
The superficial oxidation of pyrite – an iron sulphide and the most common of the sulphide minerals - results in a mine-water discharge characterised by its elevated acidity and high concentrations of sulphates, metals and metalloids. In a phenomenon known as Acid Mine Drainage (AMD), these acid leachates with high contents of metals flow into the local Tinto and Odiel rivers, through the Marismas del Odiel Nature Reserve and into an important coastal wetland - the Ría of Huelva Estuary. The effluents from the Odiel River Basin are some of the most contaminated in the world.
The EU Water Framework Directive (2000/60/CE) fixed 2015 as the deadline for achieving the good ecologic and chemical status of European waters – although this was extended to 2027 for highly contaminated waters. However, traditional treatments of waters contaminated by acid leachate from mining waste are very expensive. This is one of the reasons why many such mining activities in Spain and elsewhere in Europe are no longer economically feasible.
OBJECTIVES
The LIFE ETAD project aimed to remediate waters contaminated by mining activities through passive treatment that relies on natural water flow and biogeochemical reactions. It hoped to demonstrate a pilot full-scale application of passive treatment technology to clean acid waters from mining leachate to the standards required for irrigation water.
The project would use dispersed alkaline substrate (DAS) as the passive treatment. This would consists of an inert, coarse, high-surface matrix, such as wood chips, mixed with a fine-grained alkaline material, such as limestone sand. Passing the water through this treatment would remove metals such as iron, zinc, nickel, cadmium, cobalt and aluminium. Only natural energy sources would be needed to power the system - gravity, microbial metabolic energy and photosynthesis.
The project expected to show the technical and economic feasibility of this process as a means of cleaning water contaminated with acid leachate from mines. The project thus hoped to contribute to the faster achievement of the objectives of the National Hydrological Plan for the Tinto, Odiel and Piedras Rivers and the EU Water Framework Directive. It also hoped to enable the development of vineyards and citrus plantations as alternative economic activities in the affected areas.
Through the validation of this water treatment process at these highly polluted sites in southern Spain, the project also expected to demonstrate its potential use in other locations and possibly the renewed economic feasibility of mining activities to meet growing demand for minerals from countries such as China.
RESULTS
The LIFE-ETAD project team designed, constructed and demonstrated the feasibility, on a large scale, of a novel process for the passive treatment of water of high metallic concentrations and high acidity that is seeping from abandoned mines.
This novel passive treatment process was shown to be capable of eliminating 90% -100% of toxic metals and acidity present in waters of this type, as well as reaching pH values close to neutral.
Regarding the policy impact, the treatment plant provides a feasible solution to pursue the aims of the EU Water Framework Directive, and to a more rapid achievement of the national objectives included in the Hydrological Plan for the Tinto, Odiel and Piedras Rivers in this region of Spain, which has a large number of abandoned mines.
The LIFE-ETAD consortium aimed to become a point of reference for the future restoration plan of these river basins, as well as for other basins with similar water pollution problems due to mining activity, at the regional, national and international levels.
