Potential for reuse of gold mine tailings as secondary construction materials and Phytoremediation

The potential for re-use of gold mine tailings as secondary construction materials and in phytoremediation was investigated using tailings from Geita and Bulyanhulu gold mines in Tanzania. Properties investigated include particle size, permeability, pH, electrical conductivity, cation exchange capacity, organic matter content, soil/plant nutrient content and heavy metal content. Through laboratory tests, tailings have been classified as alkaline silt materials of low plasticity with low organic and nitrogen contents (1.99–2.45) % and (0.9 1.0) mg/kg respectively. The cation exchange capacity of these materials varies from 6.0 to7.5 meq/100g and is dependent on clay content. The pH varies from 7.2 to 7.5, typical for soils with large amounts of Ca²⁺ and Mg²⁺. The major tailings oxides are SiO₂, which form more than 50% w/w, Al₂O₃ (9.61 to 14.60), Fe₂O₃ (10.4 to 17.47), and SO₃ (11.40 to 12.10). Cd²⁺ concentration in samples from both sites and Cu²⁺ and Pb²⁺ in sample from Bulyanhulu are above permissible toxicity levels for soil and plants. Zn²⁺ and Cd²⁺ concentrations exceed their respective predicted No Observable Adverse Effect Levels (NOAEL) for plants and soil organisms. In general, tailings sample from Bulyanhulu is more contaminated, and has less potential for phytoremediation compared to the one from Geita. Based on these findings, it is concluded that physical and chemical properties support the potential of tailings for use as a construction materials, supported by the abundance of quarts which enhances resistance to extreme weather conditions and durability. Nevertheless, low mineral nutrient levels and associated physical properties hinders the potential of these materials for use in phytoremediation. Enhancement of phytoremediation potential for gold mine tailings can be achieved through amendments with Terminal Electron Acceptors (TEA) in order to improve cation exchange properties.