Modelling SO2 emissions from Anglogold Ashanti's East Acid Plant: detemining impacts on ambient air quality
Date
2010-03-29T07:11:13Z
Authors
Buthelezi, Malusi Hlakaniphani
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Since the promulgation of the new air quality legislation in South Africa, sulphur dioxide
(SO2) has been a pollutant of concern especially in the heavily industrial South African
regions. AngloGold Ashanti’s sulphuric acid (H2SO4) plant located in Klerksdorp, North
West province is an important local source of SO2. Other important sources in the North
West province include the platinum mine smelters which are responsible for elevated
SO2 concentrations in the Rustenburg area. The impacts of these emissions are
exacerbated by the poor atmospheric dispersion potential for a substantial portion of the
year. An air dispersion modelling study undertaken by Scorgie and Venter (2004a)
indicated that the AngloGold Ashanti’s East Acid Plant was likely not to comply with its
Air Pollution Prevention Act (APPA) registration certificate (RC) conditions and the
proposed South African ambient air quality standards. AngloGold Ashanti subsequently
implemented emission reduction measures to minimise elevated SO2 levels and for the
first time initiated continuous emission monitoring in the stack and the nearby village.
This study aimed at determining the impacts from implementing emission control
measures in 2007 whilst establishing the relationship between quantified stack emissions,
modelled and monitored ambient air quality data. Other AngloGold Ashanti SO2 sources
i.e. South Uranium Plant and Great Noligwa No. 8 Gold Plant were included in the
model runs to assess their contribution to the cumulative SO2 concentrations. AERMOD
was applied to examine the dispersion potential of stack and fugitive emissions.
Modelled SO2 stack concentrations were within the current South African ambient air
quality standards for all averaging periods prior and post East Acid Plant shutdown1.
However, exceedances were noted for 1-hour and 24-hour averaging periods for
modelled stack and volume sources combined i.e. East Acid Plant, South Uranium Plant
and Great Noligwa No. 8 Gold Plant. The stack emissions and ambient data compared
well with an exception of the fugitive emissions. The model demonstrated a satisfactory
performance to calculate stack emissions from the East Acid Plant. However, the model
compared poorly with the monitored ambient air quality data partly due to the lack of
comprehensive emission factors for fugitive sources. Based on these results it can be
concluded that the Acid Plant stack concentrations solely, do not pose significant health
risk to the nearby receptors and that the implemented air pollution abatement measures
are mostly effective. However, it is important to note that the model may have
underestimated fugitive emissions which contribute to low-lying emissions thus
impacting on sensitive receptors.