Abstract
M.Sc.
Atmospheric emissions of dust and chemicals from gold mine tailings are ongoing
environmental management issues on the Witwatersrand, where residential areas have
developed in proximity to dumps. Residual amounts of cyanide, used as a chemical in the
gold extraction process, are deposited with the mineral tailings. This study deals with the
evaluation of population exposure to cyanide vapour emitted from gold mine tailings dams,
an issue of environmental impact and public health concern.
The first part of this study deals with the determination of the emission factors of cyanide
vapour from three selected gold mine tailings dams: one under reclamation; one no longer
operational; and one fully operational as a slimes deposition site. These three sites are
located in the Boksburg area of the Ekurhuleni Metropolitan Municipality. Twelve samples
were collected in all: six from the Cason (2628AAL91) mine dump (under reclamation in
2006); four from the ERPM tailings complex [comprising the dormant deposits 4/L/47,
4/L/48, 4/L/49 and 4/L/50, which are north of the N17 national highway; and the
2628ACL1 deposit, which is south of the N17]; and two from the Rooikraal (active)
deposition site. All samples were collected in the year 2006. In the second part of the
study, the obtained emission factors were used in an Industrial Source Complex dispersion
model to measure the degree of population exposure to cyanide vapour for communities
that are in proximity to the operational gold mine tailings dams in the Johannesburg
Metropolitan Municipality. In the third part, a health risk assessment was carried out for
communities in proximity to the selected gold mine tailings dams.
The study revealed the average flux (± std. dev.) of Cason to be (4.7 ± 0.8) x 10-7 g m-2 s-1,
the average flux of ERPM (3.9 ± 0.6) x 10-7 g m-2 s-1, the average flux of Rooikraal
(1.7 ± 0.2) x 10-5 g m-2 s-1. The concentrations of cyanide vapour emitted from the older
tailings deposits (sand) that are under reclamation and the dormant slimes dams are very
low (and pose little health risk to occupants of adjacent land). However, HCN emission
factors from operational tailings dams, which are receiving continuous depositions, are 3 to
80 times higher than the emission factors from dormant mine tailings. Ambient cyanide
concentrations near the active tailings deposits may sometimes exceed selected
international health standards. The average hourly, daily and annual dispersion model
calculations for the Nasrec tailings deposition sites in Johannesburg revealed that 117 938,
18 722 and 8 130 people respectively were exposed to hydrogen cyanide concentrations
that were above international (Ontario, Canada) standards. This raises environmental
concerns that require institution of cyanide monitoring and setting of emission limits
applicable to South African legal and environmental circumstances. These conclusions are
based on a small number of emission factor determinations and hence these findings
should be regarded as provisional. Further testing and verification are required for
emission factors from a larger number of dormant, reworked and active tailings dams.