Phosphorus is obtained by reducing

Options

A. phophatic fertilizers with boron and alumina in an electric furnance
B. phosphate rock with silica and iron oxide in an electric furnace
C. phosphate rock with coke at a high temperature in the presence of silica in an electric furnance
D. phosphate rock with sulphur and alumina.

Answer

3

Explanation

phosphorus is such a reactive element that quite extreme methods have to be used to extract it from its compounds, The raw material is calcium phosphate. This compound is found in large deposits whose origin is not well understood, althoughbthey may have been the result of the interaction of the calcium carbonate of coral reefs with the phosphate dropping of seabrids over a period of hundreds of thousands of years.
Processing of phosphate rock is highly dependent on electric energy. As a result, the ore is usually shipped to countries where electric power is abundant and inexpensive, such as North America and Europe. The conversion of phosphate rock to the element is accomplished in a very large electric furnace containing`60`-tonne carbon electrodes. In this electrothermal process, the furnace is filled with a mixture of ore, sand and coke and a current of about `1,80,000 A(at 500V)` is applied across the electrodes.
At `1500^(@)C` operating temperature of the furnace, the calcium phosphate react with carbon monoxide and gaseous tetraphosphorus:
`2Ca_(3)(PO_(4))_(2)(s)+10CO(g)overset(Delta)rarr6CaO(s)+10CO_(2)(g)+P_(4)(g)`
The carbon dioxide is then reduced back to carbon monoxide by the coke,
`CO_(2)(g)+C(s)rarr2CO(g)`
Some of the gas is reused, but the remainder escapes from the furnace. The calcium oxide react with silicon dioxide (sand) to give calcium silicate (slag) :
`CaO(s)+SIO_(2)(s)rarrCaSiO_(3)(l)`
The escaping carbon monoxide is burned and the heat is used to dry the three raw materials:
`2CO(g)+O_(2)(g)rarr2CO_(2)(g)`
To condense the gaseous tetraphosphours, it is plumed into a tower and sprayed with water. The liquefied phosphorus collects at the bottom of the tower and is drained into holding tanks. The average furnace produces about `5` tonnes of tetraphosphorurs per hour.
Another version Sand `("silica "SiO_(2))` is added to remove the calcium as a fluid slag (calcium silicate) and to drive off the phosphorus as `P_(4)O_(10)`. The `P_(4)O_(10)` is reduced to phosphorus by`C`. At this temperature gaseous phosphours distills off, mainly as `P_(4)` but with some `P_(2)`. This is condensed to white phosphorus `P_(4)` by passing the gas through water.