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Table 2 Forms of existing cations of transition metals as a function of the medium acidity and chemical composition of buffer solution

From: Natural Minerals Coated by Biopolymer Chitosan: Synthesis, Physicochemical, and Adsorption Properties

Ion pH
pH 1.0 HCl pH 2.5 acetic acid pH 5.0 acetate buffer Distilled water pH 8.0 ammonium acetate buffer
Zn(II) [Zn(H2O)6]2+ [ZnCl4]2− [Zn(CH3COO)2(H2O)2]2− [Zn(H2O)6]2+ [Zn(CH3COO)2(H2O)2]2− [Zn(H2O)6]2+ [Zn(H2O)6]2+ [Zn(CH3COO)2(H2O)2]2− [Zn(NH3)4]2+ [Zn(NH3)2(CH3COO)2]
Cu(II) [Cu(H2O)6]2+ [CuCl4]2− [Cu2(CH3COO)2(H2O)2]2+ [Cu(H2O)6]2+ [Cu2(CH3COO)2(H2O)2]2+ [Cu(H2O)6]2+ [Cu(H2O)6]2+ [Cu2(CH3COO)2(H2O)2]2+ [Cu(NH3)2(H2O)4]2+ [Cu(NH3)4(H2O)2]2+
Cd(II) [Cd(H2O)4]2+ [CdCl4]2− [CdCl3] [Cd(CH3COO)4]2− [Cd(H2O)4]2+ [Cd(CH3COO)4]2− [Cd(H2O)4]2+ [Cd(H2O)4]2+ [Cd(NH3)4]2+ [Cd(CH3COO)4]2− [Cd(NH3)(CH3COO)3]
Pb(II) [PbCl4]2− [PbCl3] [Pb(H2O)6]2+ [Pb(OH)(H2O)2(CH3COO)] 2- [Pb(H2O)6]2+ [Pb(OH)(H2O)2(CH3COO)] 2- [Pb(H2O)6]2+ [Pb(OH)(H2O)3]+ [Pb(OH)(H2O)2(CH3COO)] 2-
Fe(III) [Fe(H2O)6]3+ [FeCl2]+ [FeCl4] [Fe(H2O)6]3+ [Fe3O(CH3COO)6](CH3COO)2 [Fe(H2O)6]3+ [Fe3O(CH3COO)6](CH3COO)2 [Fe(H2O)6]3+ [Fe(H2O)5(OH)]2+ [Fe(H2O)4(OH)2]+ [Fe3O(CH3COO)6](CH3COO)2 [Fe(NH3)6]3+