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

The utilization ofhigh-efficiency adsorption materials to reducecadmium pollution in aquatic environments is the focus of currentenvironmental remediation research. Straw waste and sludge, whichare available in huge amounts, can be best utilized in the preparationof environmental remediation materials. In this study, six types ofbiochar (SBC, CBC, DBC, SD1BC, SRDBC, and SCDBC) were prepared from straw and sludge by co-pyrolysis,and their cadmium adsorption mechanisms were explored. Cd(II) adsorptionisotherms and kinetics on the biochar were determined and fitted todifferent models. Kinetic modeling was used to characterize the Cd(II)adsorption of biochar, and findings revealed the process of sorptionfollowed pseudo-second-order kinetics (R (2) > 0.96). The Langmuir model accurately represented the isothermsof adsorption, indicating that the process was monolayer and controlledby chemical adsorption. SCDBC had the highest capacityfor Cd(II) adsorption (72.2 mg g(-1)), 1.5 times greaterthan that of sludge biochar, and 3 times greater than that of cornstraw biochar. As the pH level rose within the range of pH 5.0 to7.0 and the ionic strength decreased, the adsorption capacity experiencedan increase. SCDBC contained CaCO3 mineral crystalsbefore Cd(II) adsorption, and CdCO3 was found in SCDBC after adsorbing Cd(II) via X-ray diffraction analysis;the peak of Cd could be observed by Fourier transform infrared spectroscopyafter the adsorption of Cd(II). The possible adsorption of Cd(II)by SCDBC occurred primarily via surface complexation withactive sorption sites, precipitation with inorganic anions, and coordinationwith & pi; electrons. Collectively, the study suggested that thesix types of biochar, particularly SCDBC, could be usedas highly efficient adsorbents for Cd(II) removal from aquatic environments.