SOUTH AFRICA'S MINERAL WEALTH

1. South Africa's mineral resources

A selection of some South African minerals (Source: M E R Delpierre)

A MINERAL ORE is a mineral that has enough of a particular element in it to make exploitation of that mineral commercially viable. Africa is exceptionally rich in minerals, and South Africa has extensive deposits of important mineral ores. One distinguishes between PRECIOUS METALS, whic are rare metals with a high monetary value, such as gold , silver and the platinum metals, and the BASE METALS, such as copper, lead, zinc, iron and tin. Both types are extensively mined in South Africa.

South Africa has numerous important mineral resources, notably gold, iron, and phosphates. Apart from this, diamonds, manganese and platinum (to name only three!) are of major importance to the South African economy.

2. Gold

In South Africa gold is mined on the Witwatersrand and in the Northern Free State. Gold mining was the mainstay of South Africa's economy, but dwindling reserves and high production costs have diminished South Africa's reliance on gold. Nevertheless, South Africa holds 35% of the world's gold reserves, and produces around 350 t of pure gold per year, most of which is exported. The gold is found as finely dispersed particles of the free element in sediments known as "auriferous conglomerates" () (known to miners as "reef").

These sediments were laid down about 2.8x109 years ago. At present, the grade of ore that is being mined produces about 4-6 grams of gold for every tonne of ore. South Africa operates the deepest mines in the world ().

The recovery of pure gold from the solid rock involves a variety of engineering, mining, chemical and metallurgical processes.

3. Phosphates

Rocks containing the phosphate anion () are sources for the element phosphorus. This element is indispensible for plants, and thus phosphates are important constituents of fertilisers. Large phosphate deposits are exploited at Phalaborwa, in Mpumalanga. The mineral is "rock phosphate", which is basically a mixture of calcium phosphate and calcium fluoride, Ca3(PO4)2.CaF2, which is converted to superphosphate, a fertilizer, and phosphoric acid, which is converted to ammonium phosphate, another fertilizer. Large quantities of phosphoric acid are exported from Richards Bay.

Phosphorus promotes flowering and seed production in plants. It is made available to plants in the form of the phosphate ions (H2PO4-, HPO42- and PO43-. Commonly, these are supplied as fertilisers made up of SUPERPHOSPHATE (a mixture of calcium phosphate, Ca(H2PO4)2 and calcium sulphate, CaSO4), or TRIPLE SUPERPHOSPHATE (a mixture of calcium phosphate, Ca(H2PO4)2, and calcium fluoride, CaF2).

Superphosphate is produced by the action of sulphuric acid on phosphate rock, Ca3(PO4)2.CaF2. Rock phosphate is unsuitable as a source of phosphate ions to plants as it is very insoluble. Superphosphate is more soluble and thus makes phosphate ions more readily available to plants.

4. Iron

South Africa is the largest producer of iron ore in Africa, which is not only used locally in the steel-making industry, but exported on a large scale (20 Mt in 2003). The mineral is haematite, Fe2O3, which is mined in several places, notably Sishen, in the Northern Cape, and Thabazimbi in the Northern Province.

The extraction of iron from its ore, and its subsequent conversion to steel is carried out as follows:

  • The iron ore is mixed with coke (which is derived from coal and is an impure form of carbon) and limestone (largely calcium carbonate, CaCO3), and fed into the top of a tower called a BLAST FURNACE, shown on the right.

  • The hot air reacts with coke to form carbon monoxide:

  • The carbon monoxide reduces the iron ore, to form molten iron (which collects at the bottom of the furnace, and is tapped off through an outlet pipe) and carbon dioxide:

  • The heat converts the lime to calcium oxide and carbon dioxide:

  • The calcium oxide reacts with the sand originally present in the iron ore (mainly silica, SiO2) to form a slag consisting largely of calcium silicate, CaSiO3, which is a liquid at the operating temperatures, and floats on top of the iron, to be drawn off through a pipe:

The iron obtained from a blast furnace is known as "pig iron", and contains 4%-5% carbon, as well as other elements. It is not suitable for most uses, and is converted into other forms:

5. Additional questions














Diamonds

About half of the world's output of diamonds comes from central and southern Africa. Diamond, an allotrope of carbon, is highly prized as a gem, and when polished, high-quality diamonds find their way into jewelry. Lower quality diamonds, the so-called "industrial diamonds", are used in tool-making and other applications that require materials of exceptional hardness.

Diamonds are formed deep in the earth's crust, under conditions of very high pressures and temperatures. They come to the surface through volcanic action, where they may be found in "pipes". Such pipes may be mined directly, but the erosion of ancient pipes cause diamonds to be scattered about and deposited by rivers. These are called "alluvial diamonds". Large operations to harvest alluvial diamonds are under way in Namaqualand and Namibia. Such diamonds are also recovered from the sea-bed.














Manganese

Manganese, Mn, is used as an alloy with iron in order to make ferro-manganese steels, which are very hard and particularly resistant to abrasion. South Africa has the world's largest known reserves of manganese ore, and produces about 15% of the world's total manganese annually (3.5 Mt)














Platinum

The so-called PLATINUM GROUP ELEMENTS () are mined near Rustenburg, in the so-called Bushveld Igneous Complex, in the Northern province. Platinum is used in jewelry and as a catalyst for a variety of chemical reactions. In this role, it is used to reduce the emission of carbon monoxide from car exhausts. South Africa has the world's largest known resources of platinum group elements, of which rhodium is the most expensive (ten times more than gold).