Characteristics of a Novel Decomposed Corn Straw-Sludge Biochar and Its Mechanism of Removing Cadmium from Water.

The utilization of high-efficiency adsorption materials to reduce cadmium pollution in aquatic environments is the focus of current environmental remediation research. Straw waste and sludge, which are available in huge amounts, can be best utilized in the preparation of environmental remediation materials. In this study, six types of biochar (SBC, CBC, DBC, SDBC, SDBC, and SDBC) were prepared from straw and sludge by co-pyrolysis, and their cadmium adsorption mechanisms were explored. Cd(II) adsorption isotherms and kinetics on the biochar were determined and fitted to different models. Kinetic modeling was used to characterize the Cd(II) adsorption of biochar, and findings revealed the process of sorption followed pseudo-second-order kinetics ( > 0.96). The Langmuir model accurately represented the isotherms of adsorption, indicating that the process was monolayer and controlled by chemical adsorption. SDBC had the highest capacity for Cd(II) adsorption (72.2 mg g), 1.5 times greater than that of sludge biochar, and 3 times greater than that of corn straw biochar. As the pH level rose within the range of pH 5.0 to 7.0 and the ionic strength decreased, the adsorption capacity experienced an increase. SDBC contained CaCO mineral crystals before Cd(II) adsorption, and CdCO was found in SDBC after adsorbing Cd(II) via X-ray diffraction analysis; the peak of Cd could be observed by Fourier transform infrared spectroscopy after the adsorption of Cd(II). The possible adsorption of Cd(II) by SDBC occurred primarily via surface complexation with active sorption sites, precipitation with inorganic anions, and coordination with π electrons. Collectively, the study suggested that the six types of biochar, particularly SDBC, could be used as highly efficient adsorbents for Cd(II) removal from aquatic environments.