新生成 Ti(OH)₄ 沉淀物对水中Mn²⁺ 的吸附机理研究

The adsorption efficiency of Mn²⁺ in water by newly generated Ti (OH)₄ flocs as adsorbent which was prepared by Ti³⁺ oxidation was studied. The thermodynamics and dynamics aspect of adsorption, the zeta potential changes of Ti(OH)₄ flocs after adsorption, and the effects of pH value and several common ions on the adsorption were studied. The results show that the adsorption of Mn²⁺ ions by Ti(OH)₄ flocs fit the pseudo-second-order kinetic model well. The thermodynamic results show that the change value of Gibbs free energy ΔG^Θ is negative, and the adsorption reaction can be spontaneous at different temperatures. The adsorption can be well described by Langmuir isotherm, and the calculated q_m values are 58.8 mg/g and 92.6 mg/g at pH 7.0 and 8.5, respectively. However, when pH is 8.5, the removal of Mn²⁺ ions by precipitation cannot be excluded. Under the experimental conditions, the adsorption reaction proceeded rapidly and the adsorption reached quasi-equilibrium soon. In addition, the equilibrium adsorption capacity is close to the maximum adsorption capacity. The adsorption property belongs to monolayer chemisorption. There is a certain correlation between the adsorption capacity and zeta potential value on the surface of Ti(OH)₄ flocs, that is, the lower the zeta potential is, the greater the adsorption capacity of Ti(OH)₄ for Mn²⁺, and the change of pH before and after adsorption (⃤pH) and Mn² + removal rate (%) are positively correlated. The common anions such as SO²₄^-, NO₃^-, H₂PO₄^- and HCO₃^- can promote the adsorption of Mn²⁺ by Ti(OH)₄ flocs, while cation Ca²⁺ has a strong inhibition effect, while K ⁺, Na ⁺, Mg²⁺ and Cl ^- have little effect on the absorption. The adsorption mechanism of Mn²⁺ is the combined action of electro static attraction, surface coordination reaction, and chemical co-precipitation (at high pH).