[Preparation and Characterization of a Calcium Alginate/Biochar Microsphere and Its Adsorption Characteristics and Mechanisms for Pb(Ⅱ)].

A microsphere (CA/BC) was prepared using biochar (BC) encapsulated with calcium alginate (CA) as a green adsorbent for Pb(Ⅱ) removal from aqueous solution. The effects of the initial Pb(Ⅱ) concentration, initial pH value of the Pb(Ⅱ) solution, and equilibrium contact time were investigated. The isothermal thermodynamic data of the BC and CA/BC conformed to the Langmuir model. The maximum adsorption capacities of the BC and CA/BC from the Langmuir equation were 93.20 mg·g and 155.04 mg·g respectively, at pH=5. The adsorption of Pb(Ⅱ) by the BC was in good agreement with the pseudo-second-order equation, indicating that chemisorption was the rate-controlling step. The adsorption of Pb(Ⅱ) by the CA/BC was in good agreement with the pseudo-first-order model, which suggested that the rate-limiting step was governed by diffusion. Mechanism studies for Pb(Ⅱ) removal by the CA/BC showed that the nature of Pb(Ⅱ) abstraction took place through ion exchange between Ca(Ⅱ) and Pb(Ⅱ) as well as via the formation of a coordination complex.