Sodium alginate/graphene oxide (SA/GO) gel balls for Pb(II)-containing mine wastewater treatment: Molecular design and Pb(II) adsorption characteristics

In view of the difficulty in treating Pb(II)-containing mine wastewater and the low adsorption efficiency of adsorbents, a sodium alginate/graphene oxide (SA/GO) gel ball was designed via molecular simulation using graphene oxide (GO) and sodium alginate (SA) as raw materials and Ca2+ as a crosslinking agent. The morphology and structure of the prepared SA/GO gel spheres were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their Pb(II) adsorption properties were studied. Molecular simulation studies showed that strong hydrogen bonding occurs between SA/GO and Ca2+. At a CaCl2 concentration of 5 wt%, the shear modulus reached 2.4199, indicating that the SA/GO gel balls had good mechanical strength. An SA/GO gel ball was prepared based on the optimal formula. The adsorption exploration experiment showed that when the temperature was 35 °C, the dosage of the gel ball was 0.02 g, and the adsorption time was 24 h, it had good adsorption performance. Isothermal adsorption analysis showed that at 25,35, and 45 °C, the equilibrium adsorption capacities are 418.41 mg/g, 366.30 mg/g, and 400.00 mg/g, respectively and Pb(II) adsorption using the SA/GO gel balls followed the Langmuir isothermal model, and the adsorption kinetics were quasi-second-order. XPS and EDS studies shown that Pb(II) was successfully adsorbed through complexation, ion exchange and hydroxy-carboxyl functional group reaction. The recovery experiment showed that after four adsorption cycles, the adsorption capacity of SA/GO decreased from 202.56 mg/g to 188.65 mg/g, indicating that SA/GO has a certain degree of recyclability.