Overburden Removal

Bucketwheel excavators are used for overburden removal at phosphate mines in eastern North Carolina, Senegal, and Togo. One mine in central Florida has used cutter head dredges for both overburden removal and ore excavation. 

Using a new planarization monitor, the planarization efficiency and planarization distance were computed for a copper CMP process. The influence of polish pad, slurry and process conditions was demonstrated. Results indicate that harder, stiffer pads can extend planarization performance to wider structures given a suitable choice of slurry. Process conditions play a relatively minor role. The planarization of copper during the as-plated copper overburden removal was found to exhibit similar behavior to the planarization of oxide topography in oxide CMP, with a planarization distance of approximately 2mm for a typical stiff-pad copper CMP process. 

The quarrying process can be divided into five operations - overburden removal, drilling, blasting, loading and hauling to the processing plant. 

The thickness of overburden can vary from less than Im to tens of metres. Indeed, if the thickness is considerable, the costs of overburden removal can make the development of an open-cast quarry uneconomic and may force the developer to consider mining (see section 4.3.7). The overburden generally consists of top-soil and sub-soil, but may also include rock overlying the limestone. 

FIGURE 5.12 A dragline engaged in overburden removal. Weight 7,000,000 lb, boom length 425 ft, boom vertical height 210 ft, and bucket capacity 60 yd. ... 

Similar types of equipment are nsed for coal removal as are used for overburden removal, although it is very rare that the same dragline or bucket system would be used for both tasks. 

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