Is the use of a geotextile a necessary rehabilitation strategy to mitigate tailings contamination in soil cover materials? A 7-year field study

The potential pollution risk associated with poor management of mine tailings includes metal pollution of the surrounding environment from dusting and runoff. Thus, the establishment of a vegetation cover (rehabilitation) is viewed as an effective management strategy. Mine tailings can be inhibitory to plant growth due to their physico-chemical characteristics such as extreme pH, high salinity and potential high metal(loid) content, and the provision of a cover soil (≥ 30 cm) is usually recommended. This requires significant volumes of topsoil, which are often in limited supply at mine sites. An alternative may be the use of engineered soil (using organic and/or inorganic additives to improve physico-chemical properties) and placement of a barrier layer to prevent migration of tailings water or fines into the soil cover medium. Metal(loid)s content in soil cover treatments and vegetation uptake were evaluated after 7 years of rehabilitation in 1 m3 plots on a Pb/ Zn TSF. Final 30 cm covers included unamended tailings, subsoil material and subsoil amended with organic wastes (Spent Mushroom Compost (SMC) and Compost like output (CLO)). Treatments were divided into with/without geotextile inclusion. Soil samples were taken at 0–10 cm and 10–20 cm and analysed for pH, salinity (EC), and metal(loid)s/elements (As, Pb, Zn, Ca, Mg, Mn and, K) content. Vegetation was sampled after 1 yrs. growth (2015) and again after 7 years (2021) and analysed for their metal (loid)s/element content. Unamended tailings showed high metal(loid)s content at both depths, but concentrations were much lower in soil treatments. Herbage samples analysed in 2015 showed a higher concentration of metals than for 2021, highlighting the effectiveness and sustainability of amendments over a long period. Vegetation grown in unamended tailings showed the highest content of metal(loid)s, with significantly lower content in soil treatments. No significant difference was found for soil or vegetation metal(loid) content between geotextile inclusion/ exclusion. Results, highlight the relatively shallow soil covers without geotextile provide long term success with no evidence of metal(loid) contamination from underlying tailings.