Coal Preparation » Environmental Improvement
Dust samples collected in coastal locations using High Volume Air Samplers (HVAS) can contain significant amounts of water soluble “salt” particles. HVAS, which draw precise volumes of air through the sampler and particulates are deposited on a pre-weighed filter paper, were used for sample collection. This meant that for these samples, unless the contribution from the water soluble particulates are considered, all of the water insoluble particles in these samples, including coal, would have been significantly over estimated. Obtaining quantitative information about the amount of water soluble and water insoluble components and composition and size distribution of the different constituents in a dust sample is critical.
A sampling program was conducted in the Newcastle area over a 12 month period over which time two TSP (Total Suspended Particulates) samples and a PM10 (particulates <10 microns) were collected at the same location on two different sampling days each month. In total 14 sets of samples were collected. For selected TSP and PM10 samples, the proportion of coal and other particulates in the water insoluble fraction was determined using the Coal Grain Analysis (CGA) method.
Depending on weather conditions and season, between 10% and 90% of the sample mass collected with HiVol TSP and PM10 air samplers consisted of water soluble particulates. Prior to the start of the project, it was considered that the water soluble fraction would consist predominately of sea salt (NaCl) so it was somewhat unexpected to establish that nitrates and other anions make up a significant amount of this fraction. Furthermore, the amount and composition of this fraction varied. Less NaCl and indeed total salts were present in the samples collected in winter and more NaCl and total salts were present in the samples collected in summer.
This project also investigated whether the CGA method could determine whether dust particulates generated during open cut mining operations at a Hunter Valley coal mine could be distinguished from dust particulates generated off the mining lease.
The CGA method was also used successfully to differentiate between coal and non-coal particulates in samples collected in the Wollongong area. To date the particle size information generated from the CGA images has not been compared to size information obtained by other analytical methods such as physical sizing using screens, a laser sizing method, or Scanning Electron Microscopy.
This study demonstrated that a significant amount of the particulate mass collected with HiVol PM10 samplers were particles greater in diameter than 10 μm.
We believe that this combined method of collecting all particles using a HiVol TSP sampler and then separately using wet chemistry methods to analyse the water-soluble fraction and using the CGA dust method to analyse the water insoluble fraction is the best method for not only determining the total amount of coal but also the amount of coal in the 10 - 1 micron fraction.