Our task for iGEM is to address something in the world we see as a problem. We’ve chosen to look at the very serious problems caused by mining waste. We are studying the case in Bahía de Portman in Spain. Read on to learn a little more about the problem…
Portman Bay is an area in South-east Spain. It is about 10 x 5 km and contains one of the highest densities of galena concentrations
in Spain. Open pit mining for galena (Pb-Zn) and sphalerite (ZnS) began in the 1960s. Pyrate (FeS2) also taken as a product for industrial production of sulphuric acid. The mining carried out was open-pit. This meant that the minerals were blasted from the ground using explosives. The rock collected was then crushed, milled, and processed in a plant. The processing involved separating the useful minerals (concentrates) from the rest (tailings) through a process called froth flotation. The concentrates could then be sent to the smelter while the tailings were disposed of. The tailings can make up 95% of the original material. Usually the tailings will be disposed of in a specially designed impoundment plant. However, in Portman Bay, there was no room for an impoundment plant to be built. At the time, this problem was got around, simply by pumping the waste from the plant straight into the bay. Between the years 1957 and 1990 when it was finally shut down, 50 million tons of tailings were pumped into the bay.
The separation processes at the Portman Bay plant were not 100% efficient and though some pyrite was removed for industrial use, the content of pyrite in the tailings exceeded 10%. Small but significant quantities of the other minerals being mined also ended up in the tailings. The tailings themselves also contain high concentrations of metals known to be toxic including zinc, lead and arsenic. The combination of pyrate with the other sulphates causes serious problems as they react to produce environmentally hazardous products. The layers of rock underneath Portman bay are rich in carbonate and this reacts to consume some but not all of the sulphuric acid produced.
Studies in the area show the serious impacts this is having on the local wildlife. The main problems are caused by the leaching of metals from the soil. Fish in the area accumulate the highest lead, mercury and arsenic levels, and mussels, the highest lead, cadmium and mercury levels on the Mediterranean coast of Spain. Biodiversity is suffering as many larval species cannot develop properly in the environment. Marine communities are becoming overwhelmed by the few species able to survive and the future ecological impacts are unknown.
What’s being done?
In 2011, it was agreed that 2,700,000 m3 of tailings would be dredged, moving the shoreline 250m inland. Simply the volume of tailings present means that the whole area cannot be cleared and once this is complete, 30% of treated tailings will remain in the area and covered with gravel and compost. If this were not bad enough, the 70% of tailings removed will be moved to a specially built impoundment plant in the San José pit in the surrounding hills. The capacity would be 3500 m3 which is, in fact, not that large and overflows would be likely.
This process, though seemingly the only option, is not a good one. Even under the most controlled conditions, dredging tends to lead to an uncontrollable mess. One study warned that the greatest danger to marine organisms would be from toxic metals trapped in the tailings being resuspended in the water. With dredging, this would be an inevitability.
What are we doing?
The York iGEM team is looking at an alternative to solving the problem. We are interested in the dangerous chemical reactions occurring due to the mix of materials making up the tailings. Our project involves the genetic engineering of a bacteria to produce one which may be able to process some of the chemical present and turn them in to less hazardous waste.