Removal of Heavy Metals from Mine Tailings in Central Chile Using Solidago chilensis Meyen, Haplopappus foliosus DC, and Lycium chilense Miers ex Bertero.

Mining activities have been a part of the history of Chile since time immemorial, generating pollution and environmental liabilities. Due to the lack of regulation, many tailings are deposited close to rivers or/and on unstable ground, near which towns have been built, generally in locations with no budget for their treatment. This study tested three plant species from Northern and Central Chile to remove total chromium, nickel, and zinc from tailings: Solidago chilensis, Haplopappus foliosus, and Lycium chilense, which complements the few existing studies on heavy metals removal with native or endemic Chilean shrubs. The experiments were conducted ex situ, and the initial and final concentrations of metals were determined in tailings and plants to obtain the removal efficiency, translocation and bioconcentration factors. Among these species, the best performance was obtained using Solidago chilensis, achieving removal efficiencies of 24% for Cr, 19% for Ni, and 17% for Zn, showing the ability to phytostabilize chromium and the higher resistance concerning the toxicity threshold. Haplopappus foliosus and Lycium chilense presented a slight tendency to stabilize chromium. Only Solidago chilensis showed little ability to extract Zn.

Evaluation of mine tailings' potential as supplementary cementitious materials based on chemical, mineralogical and physical characteristics.

In order to reduce emissions of CO2 from cement production and avoid severe environmental pollution from the deposition of mine waste, this study investigated the possibility of utilizing mine tailings as supplementary cementitious materials (SCM) for partially replacement of cement in concrete. This study provides a characterization study of mine tailings to evaluate their potential for contributing chemically or physically as SCM. 13 mine tailing samples were characterized in regards to chemical composition (XRF, Loss on Ignition, CaCO3 and pH), mineralogical content (XRD) and physical characteristics (Grain size distribution, Specific Surface Area, SEM-analysis). The characterization study showed five mine tailings to possess potential chemical contribution as SCM based on their chemical composition (SiO2, Al2O3, Fe2O3 and CaO) and amorphous content. Three mine tailings showed potential physical contribution as SCM based on grain size and grain morphology. The remainder mine tailing characteristics suggest that their potential as SCM may be improved by pretreatment such as milling and/or thermal treatment.

Electrokinetic treatment of an agricultural soil contaminated with heavy metals.

The high organic matter content in agricultural soils tends to complex and retain contaminants such as heavy metals. Electrokinetic remediation was tested in an agricultural soil contaminated with Co(+2), Zn(+2), Cd(+2), Cu(+2), Cr(VI), Pb(+2) and Hg(+2). The unenhanced electrokinetic treatment was not able to remove heavy metals from the soil due to the formation of precipitates in the alkaline environment in the soil section close to the cathode. Moreover, the interaction between metals and organic matter probably limited metal transportation under the effect of the electric field. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used in the catholyte as complexing agents in order to enhance the extractability and removal of heavy metals from soil. These complexing agents formed negatively charged complexes that migrated towards the anode. The acid front electrogenerated at the anode favored the dissolution of heavy metals that were transported towards the cathode. The combined effect of the soil pH and the complexing agents resulted in the accumulation of heavy metals in the center of the soil specimen.