Improvement of chemical and biological properties of gossan mine wastes following application of amendments and growth of Cistus ladanifer L.

• Higher amendment application rates improve the fertility and nutrient availability.
• Amended materials had high enzymatic activities and lead to high C. ladanifer growth.
• Cistus ladanifer did not increase the available concentrations of hazardous elements.
• C. ladanifer shoots in amended treatments had lower contents of hazardous elements.
• Combined use of amendments and C. ladanifer is promising for gossan rehabilitation.

Gossan wastes represent one of the most hazardous mine wastes in several mining areas from the Iberian Pyrite Belt. Phytostabilisation of mine wastes with Cistus ladanifer L. could be a good option, but its growth and germination are impaired by substrata conditions. To overcome these limitations, application of organic and inorganic amendments may speed up the growth of C. ladanifer while improving the mine wastes. This study evaluated the simultaneous influence of different application rates of amendments and growth of C. ladanifer on chemical and biological properties of gossan wastes.Amendments used were mixtures (30, 75, 150 Mg/ha, 1:1:1) of rockwool, agriculture wastes and wastes from liquor distillation of Arbutus unedo L. fruits. A microcosm assay with four treatments was carried out (control and three amended treatments) under controlled conditions in a greenhouse during 505 days. Cistus ladanifer was sown in half of the pots from each treatment while the remainder was left bare.Gossan wastes had large total concentrations of several elements (g/kg; Al: 24.8, As: 3.03, Cu: 0.23, Pb; 9.21) whereas the available concentrations of these elements were small (< 5.7 % of total). The amendments applied (in particular at 75 and 150 Mg/ha) improved the structure and increased the water-holding capacity, pH and nutrient concentrations in the available fraction of the gossan materials. They also led to increases in dehydrogenase and β-glucosidase activities and in plant growth (plant cover, plant height, length of young leaves, fresh biomass). In addition, plants from amended treatments presented lower concentrations of hazardous elements in shoots than plants from unamended control. The presence of the plant did not increase the available concentrations of hazardous elements in wastes, except for As when 150 Mg/ha of amendments was applied.Phytostabilisation with C. ladanifer using a Technosol, resulting from the application of the studied amendments at 75 and 150 Mg/ha to gossan materials, seems a promising solution for rehabilitation of this type of mine wastes.