Metal ion source
Experimental concentration, mg/dm3
Fe3+: FeCl3·6H2O
20, 40, 60, 80,
Cu2+: Cu(NO3)2·6H2O
10, 20, 40, 60, 80
Zn2+: ZnSO4·7H2O
10, 20, 50
Cr3+: Cr2(SO4)3·6H2O
10, 20, 35, 50