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The separation of Co(II) and Ni(II) from leaching solution is gaining interest because Co(II) and Ni(II) are increasingly used in emerging strategic areas, such as power batteries. Herein, the surface of silica gel is functionalized with 1,2-ethylenediamine and used for the separation of Co(II) and Ni(II). The Co(II) removal efficiency of the modified silica is 80.2%, with a 4-fold improvement in the separation factor. The geometry, frequency, and electrostatic potential of the ethylenediamine modified silica gel (en/SG) are calculated. The corresponding properties of M2+ (M-Co, Ni) adsorbed on en/SG in an aqueous solution are simulated and analyzed. The results show that ethylenediamine tends to form [Men(H2O)4]2+ after binding to M2+, and the binding ability of Co(II) to ethylenediamine is stronger. Besides, the thermodynamic calculations show that en/SG has a more negative Gibbs free energy when absorbing Co(II) in aqueous solution, so en/SG is more inclined to bind with Co(II) preferentially. It is the difference in complexation ability between Ni, Co, and ethylenediamine that enlarges the difference in the original physical adsorption, thus strengthening the separation performance. This work will provide guidance for a rational design of high-performance nickel-cobalt adsorption materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dominant species of FeCl n 3−n in D201 adsorption were screened. • Superior activities of FeCl 3 and FeCl 4 − species in adsorption are confirmed and evaluated for the first time. • FeCl 3 is an intermediate species in the FeCl 4 − adsorption process. • FeCl 3 species tuning broadened the concentration boundary for HCl reuse. Elucidating the dominant adsorption species of FeCl n 3−n is fundamental for precisely regulating the adsorption process and thus enhancing the management of waste pickling liquor. In this work, anion resin (D201) exhibits great adsorption for FeCl 4 −, also exhibits the unexpectedly high adsorption for neutral species FeCl 3. The contribution of various iron species was quantitatively evaluated via Ion Species Contribution Evaluation (ISCE). The results illustrate that both FeCl 3 and FeCl 4 − were the dominant species adsorbed by D201 resin and exhibited similar adsorption activities. Experimental and computational results indicate that the adsorption of FeCl 4 − is accompanied by the shedding of Cl on FeCl 4 − and FeCl 3 recombines with the Cl on D201, which indicate that FeCl 3 is an intermediate species in the FeCl 4 − adsorption process. Accordingly, FeCl 3 was revealed to be critical species for iron adsorption in hydrochloric pickling liquor. The concentration of HCl (20 % w/w) required for FeCl 3 was sufficient for the removal of iron compared with the higher concentration (25 % w/w) required for FeCl 4 −, which broadened the concentration boundary for HCl reuse. Our strategy serves for industrial iron removal from hydrochloric pickling liquor and results in 86 % reduction in the amount of hydrochloric acid during 100 days pilot-scale test. [ABSTRACT FROM AUTHOR]