Sibanye’s approach to dust management is to have controls at source. Such controls include dust extraction and filtration systems, and dust suppression controls such as water sprays.
A complaint related to the No 1 and No 2 TSFs, located on the northwestern side of East Village of the Driefontein Operation, was recorded in 2013. Higher-than-normal dust levels occur when tailings deposition is reduced or interrupted, resulting in the top surfaces drying out and being liberated by prevailing winds. Investigations are underway to further improve existing dust controls at the No 1 and No 2 TSFs.
Some of the aspects under investigation include options to use sewage sludge to improve the vegetation growth and water sprays.
All operations have submitted applications for atmospheric emissions licences (AELs) in terms of the National Environmental Management (NEM): Air Quality Act, 2004 (Act No 39 of 2004).
The promulgated national dustfall regulations list the American Society for Testing and Materials (ASTM) International D1739 as the reference method. The promulgated reference method is a single bucket in which dustfall is collected and concentrations determined.
A challenge with the promulgated method is that it is not easy to differentiate the dust source or direction from which the collected dust originated. Sibanye uses a four-bucket system, which aids in interpretation of collected dust and relating it to wind direction and potential sources.
During the year, a study was concluded, which included elemental analysis and source apportionment of the dustfall from the multi-directional buckets. Discussions with the authorities on processes to align the current monitoring with legislative changes have begun. See case study: Dust control for a healthier environment.
SANS 1929 provides the basis for ambient air quality standards. These national standards have informed legislation with some already incorporated into regulations under the NEM: Air Quality Act. The Act sets out to reform the law regulating air quality in order to protect the environment by providing reasonable measures for the prevention of pollution and ecological degradation.
Case study: Dust control for a healthier environment
Control of dust from TSFs is a key focus at Sibanye, particularly around the Driefontein Operation, just 75km west of Johannesburg, where the volume of wind-borne dust has reached higher-than-normal levels in the past year.
“It is particularly important for us to know the size of the dust particles, which can be harmful to human health, especially to the respiratory system,” says Danny Ramsuchit, Unit Manager: Sustainable Development for Sibanye.
In August 2013, Ramsuchit conducted and completed a 12-month study, in the residential West Village at Driefontein on the impact particulate matter with an aerodynamic diameter less than 10 micrometres (PM10) can have on health.
He identified the Driefontein No 4 TSF dump as a potential PM10 source but, despite this risk, the average PM10 concentration recorded at West Village (11.2µg/m³) in a year was well below the current South African annual average limit of 50µg/m³, as well as the World Health Organisation guideline of 20µg/m³ in a year. The study involved collection of data from July 2011 to June 2012.
Characterised by different types of material processed at different stages in Driefontein’s operating life, the largest of the five TSFs, No 4, has a large top surface area with a spread of deposition points that make it relatively more difficult to keep the entire surface area wet at any given time. While the side slopes have vegetation for dust control, the top surfaces present a major source of dust. The volume of dust is higher when slurry or tailings deposition abates and the top surface is drier than normal.
As a result, Ramsuchit points out, Sibanye continues to consider effective contingency plans to control wind-borne dust during periods when new tailings deposition on operating tailings dams is reduced, whether planned or unplanned (during strike action, for example), which could potentially lead to adverse health effects. Sibanye is, therefore, investigating the use of sewage sludge to promote vegetation growth on the slopes of TSFs so as to improve existing dust-control measures.
“Dust originating outside the mine boundaries also needs to be considered when assessing exposure of communities to dust,” adds Ramsuchit.
He found that the Driefontein No 11 rock dump was also a source of dust, as well as the gravel road surface, which is now watered down periodically. The rock dump was formed by trucks hauling larger material from the shaft and spreading it in terraces on the dump. This rock dump is currently being loaded and transported to the No 2 and No 3 gold plants for processing to extract any residual gold content; reducing the potential liability.
In addition, the ground surface at West Village and the neighbouring commercial farmland outside the Driefontein lease area have been identified as potential sources of dust that may be liberated by wind. These known sources of dust are considered when interpreting results from the routine monitoring programme. The results are also presented and discussed at meetings of the West Rand District Municipality Environmental Technical Working Group.
Excavation of sand for brick manufacture from a pit located to the northeast of West Village has been identified as another potential source area outside the lease area. Dust from the off-site brick manufacturer is not Sibanye’s responsibility, however.
Ramsuchit used a network of nine multi-directional “Dustwatch” dustfall buckets to determine the sources of the dust. The multi-directional dustfall method differs from the ASTM International method in that four buckets are used to collect dust from different directions (north, east, west and south). The ASTM method results in dustfall from all directions being deposited into a single bucket and, therefore, does not determine the original direction of the dust. Mines and other industries are required to comply with the legislated National Dust Control Regulations of the NEM: Air Quality Act in terms of the ASTM D1739 method.
Ramsuchit’s research was presented at the 16th International Union of Air Pollution Prevention and Environmental Protection Associations World Clean Air Congress in Cape Town from 29 September to 4 October 2013 – where his paper was well received.