Simultaneous Removal of Cu²⁺, Cd²⁺ and Pb²⁺ by Modified Wheat Straw Biochar from Aqueous Solution: Preparation,...

As an eco-friendly and efficient adsorbent for removal of potential toxic metals from aqueous solution, biochar has received widespread attention. In the present study, wheat straw biochar (BC) and corresponding modified biochar (HNC) were used to remove Cu²⁺, Cd²⁺ and Pb²⁺ from an aqueous solution. The influence of the environment factors on metals adsorption and adsorption mechanism were discussed in detail. The results showed that the HNC had porous structures and owned ample functional groups (-OH, -COOH and C-N groups) compared with the BC. In the single system, the adsorption capacities of HNC for Cu²⁺, Cd²⁺ and Pb²⁺ at a pH of 5.5 were 18.36, 22.83 and 49.38 mg/g, which were 76.89%, 164.36% and 22.75% higher than that of the BC, respectively. In addition, the adsorption process of Cu²⁺ and Cd²⁺ on BC and HNC fitted to the Langmuir isotherm model and pseudo-second-order kinetics, but the adsorption of Pb²⁺ on BC and HNC fitted to the Langmuir isotherm model and pseudo-first-order kinetics. Adsorption isotherms indicated that the adsorption of Cu²⁺, Cd²⁺ and Pb²⁺ by BC and HNC was a spontaneous endothermic process. The competitive adsorption of mixed metal ions (Cu²⁺, Cd²⁺ and Pb²⁺) revealed that HNC was more preferential to adsorb Cu²⁺ compared with Cd²⁺ and Pb²⁺. Furthermore, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that the main adsorption mechanisms were surface complexation and precipitation, and the adsorbed Cu²⁺, Cd²⁺ and Pb²⁺ on HNC mainly exist as CuO, Cd(OH)₂, Pb₃O₄ and Pb(OH)₂.