Dissolution kinetics of zinc silicate (hemimorphite) in ammoniacal solution

The influence of ammonia–ammonium ratio, specific surface area of particles, associated anions, temperature and total ammonia concentration on the dissolution kinetics of zinc silicate (hemimorphite) has been investigated in ammoniacal solutions. The results show that the initial dissolution rate increases with the specific surface area, temperature and total ammonia concentration. The associated anions have a significant influence on the zinc extraction from hemimorphite due to their different complexing affinity with zinc ion. SEM analysis shows that cleavage of hemimorphite appears during dissolution. The silica formed in the dissolution process is absorbed back and covers some active sites of the particles. The Elovich equation typifies the dissolution behavior of hemimorphite in ammoniacal solution with an activation energy of 57.6 kJ/mol which is characteristic for a chemically controlled process.