المحاضرة 5

(b) from the gaseous state as in the reduction of titanium tetrachloride vapour with molten magnesium – the well-known Kroll process.
Refined rutile (or ilmenite) from the ore is reduced with petroleum-derived coke in a fluidized bed reactor at 1000 °C. The mixture is then treated with chlorine gas, affording titanium tetrachloride TiCl4 and other volatile chlorides, which are subsequently separated by continuous fractional distillation. In a separate reactor, the TiCl4 is reduced by liquid magnesium or sodium (15–20% excess) at 800–850 °C in a stainless steel retort to ensure complete reduction:[2]
2Mg(l) + TiCl4(g) ? 2MgCl2(l) + Ti(s) [T = 800–850 °C]
(c) from the aqueous solution as in the precipitation of 1. cement copper from copper sulphate solution with iron or in the reduction of an ammoniacal nickel salt solution with hydrogen under pressure (hydrometallurgical method). Low cost copper powder is produced from solution obtained by leaching copper ores or copper scrap. Large quantities of this ‘cement copper’ are produced which are a by-product of the copper refinery industry. Most of this cement copper is eventually melted and cast rather than used as powder for two reasons: (i) the cement copper produced as a by-product is rather impure unless special precautions are taken and (ii) the powder is quite fluffy, i.e. it has a low apparent density, which is not satisfactory for many copper powder applications. To make the powder suitable, a furnace treatment which would increase the cost would be necessary.