SO2 is used as a fruit preserving agent and as a food preservative or additive.
SO2 can be emitted from fossil fuel power plants, wood pulping and paper manufacturing processes, decaying vegetation and volcanic activity
It is used in the fermentation stage of wine making, for bleaching textile fibres, in the manufacture of paper, as a disinfectant in breweries and food factories, and as a fumigant for grains, grapes and citrus fruits.
SO2 is a common substance to which we are exposed at very low levels every day by breathing air in cities, with vehicle exhaust being a significant source of SO2
History of roasting in Kalgoorlie-Boulder
Mining and the town have always existed in close proximity to one another and roasting has been occurring in Kalgoorlie-Boulder since 1898.
Miners working along the Golden Mile had very few transport options available to them so they lived and worked on their leases. The obvious lack of transport meant that they had to find an efficient and economical means of processing their gold, so the majority of them established their own mineral processing and roasting facilities on their individual leases. By the early 1900’s there were a total of 88 roasting facilities in operation along the Golden Mile.
A large proportion of gold ore in the Golden Mile is refractory in nature. This means that the gold is intricately bound in various sulphide minerals, such as pyrite and tellurides, making the gold difficult to extract. For this ore type, roasting although producing sulphur dioxide (SO2) as a by-product, has proven to be the most effective method to maximise gold recovery.
In 1989 a number of operations on the Golden Mile were consolidated to form Kalgoorlie Consolidated Gold Mines Pty Ltd (KCGM). With the formation of KCGM came the development of large scale open cut mining and an expansion of milling (Fimiston Mill) and additional roasting capacity.
Part of the advantage of bringing all the operations along the Golden Mile together under KCGM was the opportunity for a phased reduction of in town roasting through the decommissioning of the remaining three roasters and the establishment of a central roasting facility, Gidji, located 20kms north of the City.
Roasting at the Gidji Roaster
The Gidji Roaster is designed for the roasting of refractory sulphide concentrate produced by the Fimiston Mill. The sulphide concentrate is treated in either of two re-circulating fluid bed roasters that can be operated separately and run at 650°C. The off-gases from each combine and exit through a single stack. During roaster operation the temperature is maintained by the heat generated from the exothermic reaction of the concentrate.
Roasting oxidises the sulphide particles (pyrite) to iron oxide(s), making them porous so that the gold can be removed. The iron oxide product (referred to as calcine) from roasting is then treated by a carbon-in-pulp circuit which leaches the gold from the calcine via conventional leaching methods. At this stage the gold is dissolved into the solution, coarse granulated carbon is then added which absorbs the gold. The carbon with the gold attached is then captured for further processing.
How does KCGM manage Gidji air emissions?
Air quality in the Goldfields residential areas is subject to the Environmental Protection (Goldfields Residential Areas) (Sulphur Dioxide [SO2]) Policy 2003 (EPP). The purpose of this policy is to specify the maximum SO2 concentration permitted in the ambient air of the protected area and also to control and progressively reduce the SO2 concentration of ambient air in those protected areas. Local SO2 emitters are required to monitor and manage the SO2 emissions in accordance with this policy and their licence conditions. In order to manage Gidji SO2 emissions in the EPP area, KCGM has developed an Air Quality Control Strategy (AQCS). The AQCS uses prevailing and predicted weather conditions and an extensive SO2 monitoring system to ensure roasting operations adhere to the air quality requirements of the EPP.
Together with data from the Bureau of Meteorology the AQCS uses data collected from KCGM’s sophisticated weather monitoring network to determine wind and atmospheric conditions at various heights in the atmosphere. This data in combination with data from the extensive SO2 monitoring network, located within the protection areas, ensures the Gidji Roaster operates in accordance with the strategy. The strategy will limit or even stop production as determined by the prevailing conditions.
The SO2 comprises ten continuous ambient SO2 monitoring stations, seven of which are located in Kalgoorlie-Boulder. The other stations are located at Coolgardie, Kurrawang and Kambalda. KCGM’s Environment Department has a team of trained On Call Advisors, who are readily available to provide assistance to the Gidji Roaster personnel on AQCS management.
KCGM is dedicated to protecting the local air quality through the appropriate operation and management of the Gidji Roaster. We are also committed to meeting stricter targets on our emissions to ensure that Kalgoorlie-Boulder continues to enjoy a safe environment.
What is KAMN?
KAMN stands for the Kalgoorlie Air Monitoring Network and it is co-operative arrangement between local SO2 emitters. The current members are BHP Kalgoorlie Nickel Smelter, Barrick Kanowna and KCGM. Members of the Environmental Departments from each of these companies meet quarterly to discuss air quality matters. The KAMN is committed to protecting the air quality of Kalgoorlie-Boulder and surrounding areas.
What is the Environmental Protection (Goldfields Residential Areas) (Sulphur Dioxide) Policy 2003?
The Environmental Protection (Goldfields Residential Areas) (Sulphur Dioxide) Policy 2003 (EPP), was first introduced in 1987. It specifies the areas which the EPP protects and states the maximum ambient SO2 concentrations allowed in those areas. The maximum limit is 0.25ppm over one hour, which is never to be exceeded.
The EPP also specifies a "desirable” ambient air quality standard for SO2 of 0.2ppm over one hour, which is not to be exceeded more than one day a year at any monitoring site. The EPP concentration standard in place aligns with the National Environmental Protection Measure Standard (NEPM) of 0.20ppm. The EPP has been reviewed numerous times over the past several years, most recently in 2003, with a continuous progressive tightening of the limit and standard (See graph below).
The EPP is regulated via environmental licence conditions, issued under the Environmental Protection Act (1986). KCGM adheres to stringent regulatory licence conditions for its operations, this involves monitoring and reporting quarterly emissions from the Gidji Roaster. While also reporting on ambient air data in the EPP area on a monthly basis.
Is there an impact on vegetation?
The ambient SO2 concentration is also monitored in the vicinity of the roaster to assist with the monitoring of potential impacts of SO2 to vegetation with results from monitoring reported to government annually. To date monitoring has indicated that SO2 has no adverse effect on local vegetation.
Why does the Gidji plume sometimes appear brown?
The typical composition of the Gidji plume does not change however it can appear darker under particular atmospheric conditions. Wind strength, plume dispersion, atmospheric temperature and the presence of cloud can all contribute to colour perception. Sun angle is also an important variable. Particles and gases in the plume scatter, reflect and absorb light, resulting in an apparent brown colour.
Why can the Gidji plume sometimes come toward town?
The AQCS allows for restricted roasting to occur when the winds are in a northerly arc. At all times the operations of the Roaster are carefully monitored and managed.
Sulphur dioxide facts: Did you know?
Gidji Operation facts: Did you know?
The Gidji stack is approximately 180m tall.
The roaster is operated at 650°C, so much heat is generated that this temperature has to be controlled by the addition of cooling water.
Approximately 4,000 hours of roasting are lost each year due to AQCS restrictions for certain atmospheric conditions.
The concentrate is self combusting, once the right temperature is reached the concentrate ignites and continues to burn due to a heat generating chemical reaction inside the roaster.
Gidji employs 33 local people as well as additional contractors.