Relationship between Surface Hydroxyl Complexation and Equi-Acidity Point pH of MnO₂ and Its Adsorption for Co²⁺ and Ni²⁺

Abstract

MnO 2 has shown great potential in the field of adsorption and has a good adsorption effect on heavy metal ions in aqueous solution, but there have been problems in the adsorption of heavy metal ions in high-concentration metal salt solutions. In this paper, different crystal forms of MnO 2 (α-MnO 2 , β-MnO 2 , γ-MnO 2 , δ 1 -MnO 2 , δ 2 -MnO 2 , and ε-MnO 2 ) were prepared and characterized by XRD, SEM, EDS, XPS, ZETA, and FT-IR. The reasons for the equi-acidity point pH change of MnO 2 and the complex mechanism of surface hydroxylation on metal ions were discussed. The results showed that the equi-acidity point pHs of different crystalline MnO 2 were different. The equi-acidity point pH decreased with the increase of reaction temperature and electrolyte concentration, but the reaction time had no effect on it. The equi-acidity point pHs of MnO 2 were essentially equal to the equilibrium pH values of adsorption and desorption between surface hydroxyl and metal ions on them. The change of equi-acidity points was mainly due to the complexation of surface hydroxyl, and the equi-acidity point pHs depended on the content of surface hydroxyl and the size of the complexation ability. According to the equi-acidity point pH characteristics of MnO 2 , more hydroxyl groups could participate in the complexation reaction by repeatedly controlling the pH, so that MnO 2 could adsorb heavy metals Co 2+ and Ni 2+ in high-concentration MnSO 4 solution, and the adsorption rates of Co 2+ and Ni 2+ could reach 96.55 and 79.73%, respectively. The effects of MnO 2 dosage and Mn 2+ concentration on the adsorption performance were further investigated, and the products after MnO 2 adsorption were analyzed by EDS and FT-IR. A new process for MnO 2 to adsorb heavy metals Co 2+ and Ni 2+ in high-concentration MnSO 4 solution was explored, which provided a reference for the deep purification of manganese sulfate solutions.

Study on the Adsorption Mechanism of Cobalt and Nickel in Manganese Sulfate by δ-MnO2

“…The affinity and adsorption capacity of manganese dioxide for different metal ions are different. The adsorption order is generally Pb 2+ > Cu 2+ > Co 2+ > Ni 2+ > Zn 2+ > Mn 2+ > Ca 2+ > Mg 2+ > Na + , which is basically consistent with the order of ionic hydrolysis constants . This is also the reason why Co 2+ is preferentially adsorbed and Co 2+ and Ni 2+ could be adsorbed in the manganese sulfate solution.…”

“…It can also be found from the study of Li et al that the adsorption efficiency of δ 2 -MnO 2 on cobalt and nickel is higher than that of δ 1 -MnO 2 . In this paper, based on the two δ-MnO 2 adsorption conditions of Li et al, 20 g/L Mn 2+ concentration and 10 g/L MnO 2 addition were obtained as the better conditions. The optimal reaction time, reaction temperature, reaction pH, Co 2+ concentration, and Ni 2+ concentration were further explored; the adsorption efficiency of MnO 2 for Co 2+ and Ni 2+ was determined; and the influence of process conditions on the adsorption performance of MnO 2 was analyzed.…”

“…According to the above research, the mechanism of manganese dioxide adsorbing Co and Ni ions is as follows. The protonation and deprotonation of surface hydroxyl (SOH) occurred first when MnO 2 was in contact with solution. , The reaction formulas are shown in formula 1 and formula 2. …”

“…Therefore, Li Mingdong, of our research group, did the determination of different crystal MnO 2 acid point pH, and he compared different crystal manganese dioxide adsorption of cobalt and nickel in manganese sulfate solution. He did the analysis of its influencing factors and explored the interaction between manganese dioxide and manganese sulfate solution . On this basis, this paper explored the process conditions of manganese dioxide adsorption of metal ions in heavy metal salt solutions, analyzed the surface hydroxyl complexation mechanism, and further studied the adsorption characteristics of MnO 2 surface hydroxylation on heavy metal ions.…”

“…He did the analysis of its influencing factors and explored the interaction between manganese dioxide and manganese sulfate solution. 53 On this basis, this paper explored the process conditions of manganese dioxide adsorption of metal ions in heavy metal salt solutions, analyzed the surface hydroxyl complexation mechanism, and further studied the adsorption characteristics of MnO 2 surface hydroxylation on heavy metal ions. The adsorption mechanism of impurity ions in high-salt solutions was theoretically clarified to solve the difficult removal of heavy metal ions in the manganese sulfate solution, the raw material of manganese battery.…”