General
South Africa currently accounts for about 75% of the world’s identified manganese resources. These mostly occur near Hotazel in the Northern Cape Province. According to the USGS, reserves were estimated at 15 billion tons in 2011. South Africa was the world’s largest producer of manganese in 2011, producing 3.4 million tons.
Production
For the production of ferromanganese, the manganese ore is mixed with iron ore and carbon, and then reduced either in a blast furnace or in an electric arc furnace.The resulting ferromanganese has a manganese content of 30 to 80%.Pure manganese used for the production of iron-free alloys is produced by leaching manganese ore with sulfuric acid and a subsequent electrowinning process.
A more progressive extraction process involves directly reducing manganese ore in a heap leach. This is done by percolating natural gas through the bottom of the heap; the natural gas provides the heat (needs to be at least 850 °C) and the reducing agent (carbon monoxide). This reduces all of the manganese ore to manganese oxide, which is a leachable form. The ore then travels through a grinding circuit to reduce the particle size of the ore to between 150–250 μm, this increases the surface area to aid in the leaching process. The ore is then added to a leach tank, which contains sulfuric acid and ferrous iron.
The iron reacts with the manganese dioxide to form iron hydroxide and elemental manganese. This process yields approximately 92% recovery of the manganese. For further purification, the manganese can then be sent to an electrowinning facility.
Demand
Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties.Steelmaking, including its ironmaking component, has accounted for most manganese demand, presently in the range of 85% to 90% of the total demand. Among a variety of other uses, manganese is a key component of low-cost stainless steel formulations.
Small amounts of manganese improve the workability of steel at high temperatures, because it forms a high-melting sulfide and therefore prevents the formation of a liquid iron sulfide at the grain boundaries. If the manganese content reaches 4%, the embrittlement of the steel becomes a dominant feature. The embrittlement decreases at higher manganese concentrations and reaches an
Acceptable level at 8%. Steel containing 8 to 15% of manganese can have a high tensile strength of up to 863 Mpa. Steel with 12% manganese was used for British steel helmets. This steel composition was discovered in 1882 by Robert Hadfield and is still known as Hadfield steel.
Uses and Role-players
The second large application for manganese is as an alloying agent for aluminium. Aluminium with a manganese content of roughly 1.5% has an increased resistance against corrosion due to the formation of grains absorbing impurities which would lead to galvanic corrosion. The corrosion-resistant aluminium alloys 3004 and 3104 with a manganese content of 0.8 to 1.5% are the alloys used for most of the beverage cans. Before year 2000, more than 1.6 million tonnes have been used of those alloys; with a content of 1% manganese, this amount would need 16,000 tonnes of manganese.
A new shaft complex, Nchwaning No 3 became fully operational in February 2006. This new mining operation has a hoisting capacity of +/- 200000 tons per month.
In 1997, Assmang formed a joint venture company, Cato Ridge Alloys, on its Cato Ridge site to produce medium and low carbon ferro-manganese alloys. In 2005, a metal from slag recovery plant with a capacity of 16000mt per annum of saleable product was commissioned. Improvements at this plant are ongoing
