Preparation of immobilized crab shell biochar and its adsorption of Pb2+

The crab shell biochar（BC） was prepared from waste crab shells，and the composite gel ball was prepared by sodium alginate fixation. Combined with the shape of the ball and the removal rate of Pb2+，it was found that the performance of the crab shell biochar sodium alginate gel ball（BC-SA） was the best when the mass ratio of crab shell biochar to sodium alginate was 1∶2. The factors affecting the adsorption of Pb2+ by BC-SA and its regeneration ability were investigated. The blank rubber ball and BC-SA before and after adsorption of Pb2+ was characterized by scanning electron microscopy and Fourier infrared spectroscopy. The results showed that the initial pH of the Pb2+ solution，the amount of BC-SA dosage，the initial concentration of Pb2+，and the reaction time had significant effects on the adsorption of Pb2+ by BC-SA. The adsorption process conformed to the pseudo-second-order kinetic model，indicating that the adsorption was mainly chemical adsorption. Langmuir isotherm could better fit the experimental data，and the maximum removal rate was 91.06%. The regeneration results showed that after five desorption adsorption cycles，the removal rate of Pb2+ by BC-SA was 82%，showing good reusability. BC was successfully immobilized and the carboxyl group of hydroxyl group on the surface of BC-SA complexed with Pb2+.