State of the art of the passive treatment of Acid Mine Drainage in the Iberian Pyrite Belt (Spain)
Nieto, Jose Miguel (1); Macías, Francisco (1); Ayora, Carlos (2); Orden, Salud (1); Olias, Manuel (1); Canovas, Carlos R. (1); Basallote, M. Dolores (1); Perez-Lopez, Rafael (1)
1: Department of Earth Sciences, University of Huelva, Spain; 2: Institute of Environmental Assessment and Water Research, CSIC, Barcelona, Spain
The Tinto and Odiel rivers drain the central and eastern part of the Iberian Pyrite Belt (IPB) in SW Spain. Both rivers are highly polluted by Acid Mine Drainage (AMD). Conventional passive treatment systems were tested in the region, showing serious problems of clogging and loss of reactivity. After more than 10 years of laboratory and pilot field experiments, DAS treatment system has been tuned up to overcome most of the typical operational problems faced by conventional passive treatments at the IPB (Ayora et al., 2013).
Two full-scale DAS treatment plants have been installed in the IPB, located at Mina Esperanza and Mina Concepción, in the upper part of the Odiel watershed. Both plants consist on two DAS reactive tanks based on limestone dissolution, and serially connected with two decantation ponds. The DAS plant at Mina Esperanza started operating in December 2014, treating a mean water flow of 0,8 L/s (with peaks up to 2 L/s in the rainy season) of AMD with mean pH values of 2,7 and high metal contents (683, 117, 16, 15 mg/L of Fe, Al, Cu, Zn, and 0.1-3 mg/L of As, Cr, Cd, Co, Ni). All metals at plant outflow are below detections limits but Fe, with a retention ranging 90-97%. The outflow discharge is net alkaline, with a mean pH of 6,6. After 3 years of continuous operation, in December 2017, alkalinity started to decrease in the first reactive tank.
The DAS plant at Mina Concepción started operating in April 2016, treating a mean water flow of 1 L/s (with peaks up to 3 L/s in the rainy season) of AMD with mean pH values of 2,66 and high metal contents (446, 85, 11, 26 mg/L of Fe, Al, Cu, Zn, and 0.1-3 mg/L of As, Cr, Cd, Co, Ni). All metals at plant outflow are below detections limits but Co and Ni, with a retention of 95%. The outflow discharge is net alkaline, with a mean pH of 7. In December 2017, after 3 years of continuous operation, alkalinity started to decrease in the first reactive tank. Permeability reduction and/or alkalinity generation decrease at the outflow has not been observed up to now.
A Life Cycle Assessment (LCA) has been performed for the plant at Mina Concepción. Results show that although the construction of the plant initially creates some environmental impacts, these become negligible within a few years of operation.