Metal mobility assessment for the application of biochar amendments in acidic and neutral pH mine tailing soils under variable moisture conditions

Abstract

At the Technical University of Cartagena, the research group of Environmental Soil Science, Chemistry and Agricultural Technology focusses on environmental pollution caused by toxic metals in mine tailings in the Cartagena-La Union mining district (SE Spain). Metals are mobilised due to changes in pH and humidity regimes. However, organic amendments are of potential use to immobilise metals, reducing their environmental risk. Therefore, this master's thesis investigates the influence of organic amendments on metal mobility under natural conditions. Previous to this master's thesis, biochar and municipal solid waste (MSW) were added to samples of acidic and basic pH mine tailings. Next, these samples were periodically irrigated or flooded. After a year of treatment, this master's thesis assessed the change in metal (Cu, Mn, Zn, Pb and Cd) fractionation employing a single extraction (H2O, CaCl2, NaNO3, EDTA and HCl) and a four-steps sequential extraction. Then, metal concentrations were measured using ICP-MS and AAS. Eventually, MSW immobilised all metals, except Mn, in the irrigated basic mine tailing soils after one year. Biochar only immobilised Pb and Zn when irrigated, but was never successful under flooding conditions. Furthermore, single extractions indicated changes in the most mobile fraction which were not viewed in the sequential extraction. Therefore, a more elaborate extraction is required to analyse changes in metal mobility, i.e. seven-steps sequential extraction and to confirm immobilisation by MSW.