Characterization and comparison of aeolian dust collected by horizontal flux gauges and vertical deposit gauges.

Abstract

Windblown dust is often a major nuisance problem faced in South African urban and near urban areas due to the prevailing dry climatic conditions, extensive surface mining and mineral processing. Dust deposit gauges single and double bucket are widely used in South Africa to monitor fugitive dust. The use of bucket deposit gauges in areas where predominant wind speeds are greater than 2 m.s-1, has yielded very poor collection efficiency (typical recoveries being < 20%). A wedge dust flux gauge has been designed and manufactured. The collection efficiency of the Modified Wedge Dust Flux Gauge (MWDFG) is tested against a Single Bucket gauge and, modified Wilson and Cooke (flux gauge) at Landau Colliery in Mpumalanga. Scanning Electron Microscopy analysis of dust particles obtained from the four samplers, exhibited six clusters of particulate morphology; irregular square, agglomerate, sphere, floccule and column or stick. Based on their shape characteristics most of the samples of the particles under investigation were probably soil and coal particles. The particle size distribution analysis carried out on the dust samples had the MWDFG collecting the largest fraction of particulate matter with 10μm diameter at 23 percent. The MWDFG in this study recorded more dustfall rates than the other samplers at the sampling site. The Modified Wedge Dust Flux Gauge recorded dustfall rates that were within the INDUSTRIAL range while the other samplers recorded dustfall levels that were within RESIDENTIAL range. The Single Bucket was commissioned at Landau Colliery site RAMP 6 in August 2006, and has been recording dustfall rates in the RESIDENTIAL range. The MWDFG during this study recorded dustfall rates in the INDUSTRIAL range indicating that there are other dust sources from other wind directions which the Single Bucket has been unable to collect over the years. The predominant winds in the Witbank region are from the east and the Single Bucket was installed in such a way that it records dust from the east. The Modified Wedge Dust Flux Gauge should be used in combination with the bucket in Landau Colliery site RAMP 6 to v account for dust generated from others sources other than those located in the east. Further dust collection efficient tests to the MWDFG at different locations and times within Landau Colliery are required.