Acid water as irrigation resource for citrus production

The province of Huelva is not only responsible for some of the most suggestive and even enigmatic worldwide landscapes. It is also an authentic gruyère. The mining activity performed for more than 2.000 years in the Iberian Pyrite Belt (FPI) that crosses it, is the responsible for what is presently considered an authentic jigsaw. The result of that mining industry – there is presently an estimated 100 abandoned mines – is a countless number of slag heaps and pits, which are a serious environmental problem that reaches even Atlantic waters. The phenomenon, which took place for centuries, consists of acid mine drainage – AMD – which have never stopped being produced in those areas. This drainage consists of water that undergoes an alteration of its PH to acid levels which nullifies its potability. This AMD produces acidity, sulphates, metals and toxic metalloids which are to be found in those slag heaps and are subject to a natural oxidation process.

The basins of the main rivers in the Huelva region have all been affected by that phenomenon, although the Odiel river undergone the most detrimental effects. The Andévalo district, located in the west side of the province, counts on the greater number of abandoned mine explorations.  

The teacher responsible for the Geology subject at the University of Huelva (UHU), José Miguel Nieto Liñán, is in charge of setting up the Life-Etad project, financed by the European Union with more than 2.5 million Euros and an completion time till 2017. The teacher explains that “the cleaning process of water deriving from the mining activity is not something new; the Aguas Teñidas mine, a quarry presently operating, owned by the company Matsa does it already”. Nevertheless, the project goes much further than that. It aims at providing an integral response to AMD at affordable costs. This is translated by the system that the Life-Etad project pursues: a passive treatment with a strong ecological inspiration, which aims at using that water as an irrigation resource for vineyards and citrus production and positions it at levels that establish the pre-potability requirements. Nieto stresses the innovation of the project: “Japan counts on an area of 80 mines that pour acid waters, actively treated, a totally different level from our proposal.”

The process that allows such purity level of water consists of a decantation system in which the reactive reservoir acquires special relevance and has the goal of rising the PH with which the metals precipitate to the bottom of that reservoir. This contains an under soil container with a reactive inside, filled with wood chips and calcareous sand or magnesia. When the water flows through the reactive inside, the limestone dissolves generating thus alkalinity and the consequent rise of the PH. In that moment, the precipitation of the iron and aluminium hydrosulphates is induced, with which, by means of absorption or co-precipitation, a great part of the remaining metals is retained: arsenic, copper, lead, that is to say, the most present metals in the Iberian Pyrite Belt. The decantation process, in which metals will go on being retained, will continue in the subsequent settling tanks.

This is not the first time that a passive treatment is used, but the goal is to achieve more efficient results than the ones that have been reached so far. This is, in the end, the follow up of research previously conducted: Anoxic Limestone Drains (ALD), the Alkalinity Producing Systems or the Sulphate Reducing Bioreactors, which would require a relatively low maintenance cost but are not adequate to drainage with high metal load as the ones to be found at the Iberian Pyrite Belt.

One of the objectives that remains unclear is the location for the development of the project. Although experts have not still come to an understanding, most probable the choice will be Mina Concepción, on the edge of Almonaster la Real, county of Huelva.

The Life projects are purely environmental and deal with other topics as the protection of the lynx. The Junta de Andalucía and the company Sacyr also participate in the project that presently draws our attention.


Source: Saber Universidad

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