A long-term study of mine site rehabilitation in Australia

This paper presents a three-part treatment and revegetation program conducted at a derelict metaliferous mine site in Australia from 2000-2013. Program #1 examined the treatment of acidity and leachable metals and the impact of revegetation in a control and three treated areas of contaminated waste rock at one part of the site; Program #2 examined the treatment of acidity, plant uptake of metals and trace elements, and tree growth in a control and four treated areas of contaminated waste rock at a second section of the site; and Program #3 examined the treatment of acidity and leachable metals and revegetation of submerged mine tailings and an exposed tailings beach. Program #1, which assessed lime and biosolids amended waste rock, a standard clay-topsoil capping of waste rock, and the addition of Terra B reagent to waste rock compared to a control, showed soil pH in the control remained unchanged from years 1-14 at around 4.0, while soil pH in the limed and capped areas was initially increased but fell back to starting levels of around 4.0 within 12 months and remained low for 14 years. In contrast, soil pH in the Terra B treated area was 6.8 immediately after treatment and increased to 7.2 in year 6 and 8.7 by year 14 without further treatment; these findings were consistent for data on total actual acidity and total potential acidity. Similarly, leachable metals were generally lower in the Terra B area than either the control or other treatment areas. Tree height and density were also measured in 2005 and again in 2013 indicating acidity in the control, limed and capped areas suppressed tree height and density, however by 2013 in the Terra B area revegetation was comparable to undisturbed, remnant forest. In Program #2, outcomes over the 14-year period were consistent with those observed in Program #1 for the control, biosolids and Terra B treatment areas. Program #3 showed the submerged and exposed tailings had low pH of 3.5 and high concentrations of total and leachable metals before treatment, but heavy metals became non-leachable immediately after treatment with Terra B reagent and pH rose to 8.0, remaining steady for 14 years. Revegetation was achieved on the tailings beach, with almost uniform colonization of bulrush and common reed, along with bottlebrush and golden wattle; a variety of reptiles have also been observed on the revegetated tailings beach, along with migrating ducks, spoonbills and grebes. In each case, what was highly contaminated waste rock or tailings before treatment effectively became a neutralised, stable growth medium after treatment with Terra B reagent