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Manganese (Mn) is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties. Steelmaking,including its ironmaking component, accounts for most domestic manganese demand, presently in the range of 85% to 90% of the total. Manganese ferroalloys, consisting of various grades of ferromanganese and silicomanganese, are used to provide most of this key ingredient to steelmaking. Products for construction, machinery, and transportation are leading end uses of manganese. Manganese also is a key component of certain widely used aluminum alloys and, in oxide form, dry cell batteries. As ore, additional quantities of manganese are used for such nonmetallurgical purposes as plant fertilizers, animal feed, and colorants for brick.
The manganese ores of the Kalahari Manganese Field are contained within sediments of the Hotazel Formation of the Griqualand West Sequence, a subdivision of the Proterozoic Transvaal Supergroup. The Nchwaning deposit consists of a gently dipping and regular strata bound body of high-grade ore (+48%Mn), which has undergone a hydrothermal upgrading associated with faulting. The combined high metal content and low impurities make this an exceptional smelting ore.
The mine was originally established in 1972, with the Nchwaning No.2 shaft coming into production in 1981. This shaft is still active and ore is mined, and then crushed underground prior to being hoisted up a 450m vertical shaft. This shaft has a capacity of +/- 120000tpm.
A new shaft complex, Nchwaning No.3 was recently completed in order to provide access to high quality ore for decades to come. Production from this complex commenced in May 2004 and became fully operational in February 2006. This new mining operation is serviced by two shafts; a vertical personnel shaft to a depth of 350m and a decline shaft equipped with conveyors, which is the main hoisting shaft. Hoisting capacity is +/- 200000 tons per month.
Ore Processing:
The existing plant has been upgraded and now treats the ore from both Nchwaning No.2 and No.3 mines. Ore is crushed, washed and screened to various sizes and then is stacked according to size and grade. These stacks have nominal capacities of 280 to 320 tons each and are numbered and sampled. This allows extremely accurate grade control for all shipments made from the mine.
Ore Quality:
Typical analyses of manganese ore grades
Element
47% fines 48% lumpy
Mn % 48.0 49.0
Fe % 11.4 10.5
SiO2 6.0 4.5/6.0
P % 0.05 0.05
S % 0.19 0.17
AI2O3 0.39 0.35
CaO 5.0 4.9
MgO 0.7 0.7
K2O <0.1 <0.1
Na2O <0.1 <0.1
Sizing:
Lumpy minus 75 millimetres plus 9 millimetres
Fines minus 9 millimetres
Rail and port facilities:Railroads
Manganese ore produced at Nchwaning and Gloria mines is transported by private rail to Hotazel where the trucks are transferred to the Hotazel-Port Elizabeth railway line. The railing takes approximately 30 hours for the +/- 1100km distance from the mines to the Port Elizabeth harbour.
At the harbour the train is split up into 25 or 50 trucks and shunted into the ore terminal marshalling yard. Here various truck loads are split up per grade and shunted to the truck tippler where the ore is channelled to the storage bins or directly to the ship by means of conveyor belts.
Port Elizabeth harbour
The port facilities at the Port Elizabeth harbour consist of a two-line interconnecting conveyor belt system. From the tippler, the ore is carried either by one or both lines to the storage bins where it is deposited by means of one or two stacker-reclaimers, or directly to the vessel.
There are four bins with a total capacity of 460 000 tons. When required for loading, the reclaimers are positioned alongside the required grades and extract the ore from the bins back onto the conveyor belts to the outloaders for shipping.
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