Effective Pb2+ adsorption by calcium alginate/modified cotton stalk biochar aerogel spheres: With application in actual wastewater

A spherical composite aerogel adsorbent (CA/KCB aerogel) with excellent Pb2+ adsorption performance was prepared by sol-gel method using calcium alginate (CA) and KMnO4 modified cotton stalk biochar (KCB). The preparation parameters of CA/KCB aerogel were optimized by response surface methodology. The physicochemical properties and Pb2+ adsorption characteristics of CA/KCB aerogel were systematically investigated. The CA/KCB aerogel before and after Pb2+ adsorption was characterized by SEM, EDS, FTIR and XRD, and the adsorption mechanism was discussed. The optimal preparation parameters of CA/KCB aerogel are: the dosage of KCB was 6 g/L, the mass concentration of sodium alginate and CaCl2 was 3% and 1% respectively. CA/KCB aerogel was rich in oxygen-containing functional groups, exchangeable cations and interconnected pores, and can exist stably in aqueous solutions with a wide pH range (2−12). The data of adsorption kinetics and adsorption isotherms can be well fitted by the pseudo-second-order model and Langmuir model, respectively. The maximum adsorption capacity of Pb2+ was 664.6 mg/g. The adsorption process was an endothermic reaction dominated by monolayer chemisorption. The binding of CA and KCB in aerogel can promote the adsorption of Pb2+ synergistically. Finally, CA/KCB aerogel was directly applied to the treatment of electroplating wastewater. The coexisting heavy metals (Pb, Cu and Zn) in the wastewater can be effectively removed when the adsorbent dose was 35 g/L. The conclusion is that CA/KCB aerogel has a promising application prospect as adsorbent for heavy metal removal.