8.1 Mining and mineral processing  (Page 6/7)

• About 40 million tons of iron ore is mined annually in South Africa. Approximately 15 million tons are consumed locally, and the remaining 25 million tons are exported.
• South Africa is ranked about 20th in the world in terms of its crude steel production.
• South Africa is the largest steel producer in Africa.
• South Africa exports crude steel and finished steel products, and a lot is also used locally.
• Some of the products that are manufactured in South Africa include reinforcing bars, railway track material, wire rod, plates and steel coils and sheets.

Iron

Iron is usually extracted from heamatite (iron(III)oxide). Iron ore is mixed with limestone and coke in a blast furnace to produce the metal. The following incomplete word equations describe the extraction process:

• A coke + oxygen $\to$ gasX
• B gasX + coke $\to$ gasY
• C iron(III)oxide + gasY $\to$ iron + gasX

1. Name the gases X and Y.
2. Write a balanced chemical equation for reaction C.
3. What is the function of gas Y in reaction C?
4. Why is limestone added to the reaction mixture?
5. Briefly describe the impact that the mining of iron has on the economy and the environment in our country.

(DoE Exemplar Paper, Grade 11, 2007)

Mining and mineral processing: phosphates

A phosphate is a salt of phosphoric acid (H ${}_3$ PO ${}_4$ ). Phosphates are the naturally occurring form of the element phosphorus. Phosphorus is seldom found in its pure elemental form, and phosphate therefore refers to a rock or ore that contains phosphate ions. The chemical formula for the phosphate ion is PO ${}_4^{3-}$ .

Mining phosphates

Phosphate is found in beds in sedimentary rock, and has to be quarried to access the ore. A quarry is a type of open pit mine that is used to extract ore. In South Africa, the main phosphate producer is at the Palaborwa alkaline igneous complex, which produces about 3 million tons of ore per year. The ore is crushed into a powder and is then treated with sulfuric acid to form a superphosphate (Ca(H ${}_2$ PO ${}_4$ ) ${}_2$ ), which is then used as a fertilizer. In the equation below, the phosphate mineral is calcium phosphate (Ca ${}_3$ (PO ${}_4$ ) ${}_2$ .

$C{a}_{10}{\left(P{O}_4\right)}_6{F}_2+7H_{2}S{O}_4+3H_{2}O\to 3Ca{\left(H_{2}P{O}_4\right)}_2{H}_{2}O+7CaS{O}_4$

Alternatively, the ore can be treated with concentrated phosphoric acid (which forms a triple superphosphate), in which case the reaction looks like this:

$C{a}_{10}{\left(P{O}_4\right)}_6{F}_2+14H_{3}P{O}_4+10H_{2}O\to 10Ca{\left(H_{2}P{O}_4\right)}_2{H}_{2}O+2HF$

Uses of phosphates

Phosphates are mostly used in agriculture . Phosphates are one of the three main nutrients needed by plants, and they are therefore an important component of fertilisers to stimulate plant growth.