Biodiversity: Friend or foe of invasive species?

Wetland-based passive treatment systems for gold ore processing effluents containing residual cyanide, metals and nitrogen species

“…The most important mechanism effecting cyanide removal has been found to be the acidification of the solution by means of the action of the atmospheric CO 2 25,28,29,30 . In accordance with [eq 1], as the pH of the solution 60 drops, the predominant form of free cyanide becomes HCN, which is easily volatilized (boiling point in aqueous solution is 24ºC) 31 . Important auxiliary processes include hydrolysis (yielding the formate ion and ammonium), bio-degradation 32,33 , adsorption onto mineral surfaces 34,35 , and photolytic degradation 65 (to which SAD cyanides are especially sensitive) 36 .…”

“…Both lines displayed noticeable removal of metalcyanide complexes (WAD and SAD cyanide) and copper, though rates were clearly greater in the treatment line. More significant 60 are the differences in removal rates between dissolved cyanide (21.6% in the treatment line, compared with 14.1% in the blank line), and nitrate/nitrite ions (80% in the treatment line, 0% for the sum of nitrate and nitrite in the blank line). The organic substrate mixed with gravel that was used in the anaerobic cell of 65 the treatment line, showed a capacity to retain an average of 6.7 mg of TCN kg -1 .…”

“…In the search for a more appropriate technology for the abatement of cyanide seeping from closed tailings ponds 18,59,60 , experimental investigations into the laboratory-and field-scale passive treatment of cyanide-bearing 35 leachates are reported here.…”

“…Cattails were analysed before and after the experiment. 15 A pilot-scale passive system was constructed between the cyanidation plant and the tailings disposal facility of a gold mine, within the perimeter of the latter, which is fenced and screened to prevent access by local wildlife (a potential handicap for engineered wetlands treating ecotoxic substances) 60 . The in-situ 20 pilot-scale system was designed in the light of the laboratory findings, and consisted of four units in series:…”

“…Although modern cyanidation plants are designed to minimise the concentrations of cyanide in slurries dispatched to tailings dams for long-term storage, even the modest residual concentrations of cyanide present in tailings dam pore waters can render the leachate 55 potentially toxic to freshwater organisms (and sometimes also to birds and terrestrial animals 13 ; ecotoxic effects may also arise from other contaminants (metals, sulphate, ammonium, nitrate) present in these pore waters, as cyanide complexation has been proved to enhance the release of lots of heavy metals such as Co, Fe, Hg, Ni, 60 Zn, Cu and Ag 14,15,16,17 .…”