Removal and Mechanism of Cadmium, Lead and Copper in Water by Functional Modification of Silkworm Excrement Biochar

Abstract

A new type of biochar, called GBC, was prepared from silkworm excrement, and then modified by chitosan combined with pyromellitic dianhydride. The removal of mono-metal and polymetals (Pb, Cd and Cu) from an aqueous solution by GBC was investigated in this research. Compared to unmodified biochar, the removal rate of Pb and Cd by GBC was about 12% higher, while that of Cu was about 94.6% higher. It also shows the types of functional groups in biochar have a great impact on their adsorption. The removal of Pb is mainly involved in the N-C=O functional group, the removal of Cd is mainly involved in N-containing functional group and C=C bond, and that of Cu is mainly involved in N-containing functional group, carboxyl group, hydroxyl group, and a carbonyl group. Five adsorption–desorption cycles of GBC were carried out, and it was found that the adsorption capacities of GBC for Pb, Cd and Cu decreased by 7.28%, 10.78% and 6.07%, respectively, indicating that GBC had a good renewable performance. The adsorption capacity of GBC for Cu in different water samples is between 89.62 and 93.47 mg·g−1, indicating that GBC has great application potential for the removal of Cu in wastewater.

A Review on Biochar as an Adsorbent for Pb(II) Removal from Water

“…Modification increased the functional groups but decreased the mineral components, so the role of ion exchange and the precipitation mechanism in Pb removal were not significant; therefore, complexation played a dominant role. This counterbalancing effect is the reason adsorption did not significantly increase after modification [114].…”

“…Therefore, both the kinetic and equilibrium behavior of the adsorption process are influenced by the extent of dispersion of magnetic particles on the biochar surface. Several other researchers [103,107,114,116,119] have investigated the comparative adsorption capacity between magnetic biosorbents and nanoparticle modifications and found that nanoparticles are less favorable for adsorption compared to magnetic biosorbents. This is partly due to the fact that magnetization causes a decrease in pHZPC, which reduces the difference between the pH and pHZPC.…”

“…A study was conducted by Bian et al where they used silkworm excrement as the feedstock, which was pyrolyzed at 600 • C for 2 h and was followed by wet impregnation using chitosan combined with pyromellitic dianhydride [114]. Chitosan is a polymer with amino and hydroxyl groups that can be used to functionalize the surface of biochar and enhance its adsorption properties.…”

“…Chitosan is a polymer with amino and hydroxyl groups that can be used to functionalize the surface of biochar and enhance its adsorption properties. When combined with Pyromellitic Dianhydride (PD), the resulting synergistic compound contains functional groups, such as -CONH2-, and carboxyl groups that can interact with heavy metals through mechanisms like ion exchange, electrostatic attraction, and surface complexation [114]. While these compounds were used to modify the silkworm excrement, the resulting biochar showed an increased surface area and pore volume and increased OFG content.…”

“…Ding et al [95] were able to achieve 85% of Pb(II) recovery using HCl. Bian et al demonstrated only a 7.28% reduction in the adsorption capacity of the silkworm excrement biochar, even after the 5th cycle when NaOH was used as an eluent [114]. Ding et al investigated the regeneration of hickory wood biochar using HCl [58].…”