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Phytostabilisation with native plant species has been advocated as a cost-effective approach to rehabilitate mine tailings containing phytotoxic metal-bearing minerals. For this purpose, five Acacia species (natural colonisers) native to north-west Queensland region of Australia were investigated for metal uptake and root exudation characteristics in response to growth for 3 weeks in three different mine tailings (Cu and Cu-Pb-Zn) differing in their degree of weathering. Root tissues of the plant species grown in the three types of tailings accumulated up to 0.9 mg Cd kg–1, 10 mg Co kg–1, 177 mg Cu kg–1, 38 mg Pb kg–1 and 4800 mg Zn kg–1 (DW basis) – being suitable for phytostabilisation purposes. However, elevated levels of root exudates in rhizosphere tailings enhanced the bioavailability of metals, leading to the accumulation of high levels of some metals in Acacia shoots (e.g. shoot concentrations of 140 mg Zn kg–1 in Acacia acradenia F.Muell. and 230 mg Zn kg–1 in Acacia hilliana Maiden). Positive correlations (P < 0.05) between citric acid levels and metal root uptakes suggested that citric acid production in these plant species may be the main driver for metal mobilisation. The results suggest that the native acacia species have the potential to mobilise metals (albeit in mineral forms) in the tailings, when used for phytostabilisation.

Poor soil fertility is often the biggest challenge to the establishment of vegetation in mine wastes deposits. We conducted field trials in the El Gorguel and El Lirio sites in SE Spain, two representative tailing ponds of similar properties except for pH, to understand the environmental and plant-relevant benefits of marble waste (MW) and pig slurry (PS) applications to mine tailings. Low pH (5.4) tailings (El Lirio) exhibit reduction of up to fourfold in bio-availability of metals as shown by the DTPA-Zn, Pb, water-soluble Zn, Pb and up to 3× for water-soluble Cd. Tailings in El Gorguel have high pH (7.4) and did not exhibit significant trends in the reductions of water-extractable Zn, Pb, Cd and Cu. Improvements to the edaphic (plant-relevant) properties of tailings after the amendments are not as sensitive to pH compared to the environmental characteristics. The two sites had increases in aggregate stability, organic matter (total N and organic C) although total N is higher in the El Gorguel (up to 212 μg N kg(-1)) than the El Lirio (up to 26 μg N kg(-1)). However, cation exchange capacities are similar in both sites at 15.2 cmol(+) kg(-1). We conclude that the characteristics, especially pH, of tailing materials significantly influence the fate of metals but not improvements to plant-relevant properties such as cation exchange capacity and aggregate stability 1 year after the application of MW and PS amendments.

Tesis DoctoralTrabajo presentado por SEBLA KABAS para aspirar al grado de Doctora por la Universidad Politécnica de Cartagena Dirigida por DR. ÁNGEL FAZ CANO DR. JOSÉ ALBERTO ACOSTA ÁVILES Cartagena, 2013. To my parents and my brother ACKNOWLEDGMENTS Working on the Ph.D. has been a great, but at the same time generally an overwhelming experience. Even it is hard to grapple with the topic itself which has been the real experience of learning. Grappling with how to write papers and proposals, give talks, work in a group, stay up until the sunrise, and still stay focus... In any case, I am indebted to many people for making the time working on my Ph.D. First of all, to the Project IRIS (no: CP-IP 213968-2) funded by the European Union FP7 for its throughout support which enabled the realization of this work. I am deeply grateful to my advisor Ángel Faz Cano. To work with you has been a pleasure to me. Thank you for your confidence to give me the opportunity to perform this study, for all your professional and moral support. Furthermore, I am also very grateful to my co-director José Alberto Acosta Áviles, for his insightful comments both in my work and in this thesis, for his support, and for his positive energy. In addition I would like to thank to Dr. Arocena and Dr. Mermut, for their professional supports, innovative approaches and helpful comments and advises. I have been very privileged to get to know and to collaborate with my colleges in GARSA-UPCT who became real friends over the last several years. I have learned a lot from you about life, research, how to tackle new problems and how to develop techniques to solve them. Thank you very much for all your company José,