Problem Statement:

A zinc sulfide concentrate containing 35% ZnS by mass is to be leached with dilute sulfuric acid containing 50 g/L of H2SO4. The reaction is as follows:

ZnS + H2SO4 ZnSO4 + H2S

The leaching process is carried out in three stages:

a) In the first stage, 80% of the zinc is to be leached out in 2 hours at 60C.

b) In the second stage, the remaining 20% of the zinc is to be leached out in 4 hours at 70C.

c) In the third stage, the leach solution from the second stage is treated with hydrogen sulfide to precipitate all the zinc as ZnS.

Determine:

The amount of hydrogen sulfide required to precipitate all the zinc in the leach solution.