digital divide network - article database

The use of semi-continuous mining technology does not dictate any particular form of excavation machine. Applicable units for feeding a mobile crushing system might include:

(1) hydraulic shovels,

(2) large front end loaders,

(3) medium-sized rope shovels,

(4) large rope shovels.

All of these styles of equipment are used to load mobile in-pit crushing systems at varying rates. Typically front end loaders are used for rates up to 2000 t/h (Caterpillar Handbook). In those instances where greater capacity than this is required either a hydraulic shovel or a rope shovel may be used.

Currently the largest mobile crushing machines in service are fed directly by large rope shovels (P&H 4100XPB). Large electric rope shovels offer significant economies of scale. A single machine, capable of a continuous capacity of up to 10 000 t/h, operating without replacement for the life of the mine, offers an attractive option for large-scale operations. At the limits of current standard machine operations, the 100 tonne rope shovels are able to mine an 18 m face (P&H 4100XPB). At 10 000 t/h, a mobile crushing machine of this size is readily able to mine up to 44 Mtpa (without a belt wagon) and possibly as much as 50 Mtpa with one.

Possibly more appropriate for operation in an iron ore operation, mid-sized electric rope shovels (approximately 60 tonnes/pass of the P&H 2800XPB variety (P&H 2800XPB)) offer some economies of scale. A single such machine is capable of up to 5000 t/h. At the limits of current machine operations, the 60 tonne rope shovels are able to mine an 18 m face, but might be more appropriately employed on a 9 or 10 m bench. Remote mining operations frequently utilise hydraulic shovels in lieu of electric rope shovels. Their selection often reflects a need for their greater mobility and, since diesel powered machines are readily available, the absence of any requirement for electrical reticulation into the mine. Diesel hydraulic units do not have the capacity to shift 100 tonnes of waste per dipper pass and as such are not directly comparable to large electric rope shovels, but they are an attractive alternative to the smaller rope shovels. The maximum extraction rate anticipated for this style of machine would be of the order of 4000 t/h.

Having considered styles of loading equipment, it is important to note that both the electric rope shovels and hydraulic shovels exhibit similar life of mine capital cost profiles. The hydraulic shovels are cheaper to purchase, but do not have the same operational life and require more frequent refurbishment or replacement.

For smaller operations, large front end loaders could load a mobile crusher hopper without difficulty. An interesting possibility would be two units operating simultaneously; although this offers possible production rate improvements over a single hydraulic shovel it does not offer any significant operational cost advantage. Sand and gravel deposits above the water table are excavated with bulldozers, front-end loaders, tractor scrapers, and draglines. Deposits below the water table, including stream and lake bed deposits may be excavated with draglines or from barges using hydraulic or ladder dredges. Mining and quarrying stone generally require drilling and blasting, after which the rock is then transported to a processing facility such as impact crusher on trucks and conveyors.