Question

The simplest method of removing iron from sulphuric acid leach solutions (iron is a common impurity element in all hydrometallurgical processes that needs to be removed and disposed in specially designed tailings ponds) is by neutralization with lime (CaO) to cause its precipitation in the form of ferric hydroxide (Fe(OH)3) at ambient temperature or in the form of goethite (FeOOH) at elevated temperatures (near the boiling point of water). [Of course iron may be precipitated/removed also in the form of jarosite (a complex salt NaFe3(SO4)2(OH)6 ) or hematite (Fe2O3) but these processes are not considered in this problem]. Lime (CaO) plays two roles: first it acts as base by its quick conversion to Ca(OH)2 upon mixing with water (this is called slaking)

CaO (s) + H2O = Ca(OH)2
hence helps to raise the pH by neutralizing the acid; and second by forming gypsum
(CaSO4 ..2H2O (s) ) which is an insoluble compound thus helping to remove excess sulphate from the solution.

You are asked
(a) to write all reactions involved in the neutralization with lime of a 9.8 g/L H2SO4 solution

containing 5.6 g/L Fe3+ (as Fe2(SO4)3);
(b) to calculate the moles of gypsum and Fe(OH)3 will be produced if 100% of the acid and

iron contained in 100 m3 solution are made to react with lime.