Adsorption Of Cadmium Ions By Cadmium-tolerant Fungus-biochar Composite And Mechanism

As an important part of the material cycle in ecosystems,water bodies are highly susceptible to the effects of industrial pollutants.As one of the heavy metal ions with high biological toxicity,cadmium in water bodies has become a subject of intense research.Physical adsorption has been promoted in heavy metal wastewater treatment processes due to the advantages of easy manipulation and good adsorption properties,and plant biochar is a commonly used adsorbent,but problems with biochar alone limit its application;Microbial adsorption is applied due to low treatment costs and the absence of secondary contamination,but it is also limited by environmental factors and microbial survival rates.It was found that synergistic treatment of heavy metal wastewater with microorganisms and biochar can solve the above problems.This study focused on screening and tolerance gradient acclimation of indigenous microorganisms,and mixed them with agricultural waste biochar in equal ratio through freeze-drying physical modification to explore the optimal adsorption conditions and adsorption capacity of the synthesized adsorbent.Biological scanning electron microscopy（SEM）,Fourier infrared spectrometer（FTIR）,X-ray photoelectron spectroscopy（XPS）,X-ray powder diffractometer（XRD）and other characterization methods,adsorption kinetics and adsorption isotherm were used to describe the physicochemical properties and adsorption mechanism.This research will provide theoretical and technical support for the search for efficient reusable agricultural and forestry waste materials,the development of environmentally friendly composite microbial adsorbents,and the treatment of heavy metal pollution in water bodies.In addition,this study could also provide high-quality strain resources for microbial adsorption processes.The main results of the study are as follows:An indigenous fungal strain,H1,identified as Epicoccum sorghinum,was preferentially selected by concentration gradient domestication from the soil of the Cangshan World Geopark in Dali.The FTIR and XPS characterization shows that the elemental composition of the strain is C,N,O,S,P,Na,and its surface functional groups such as-OH/-NH,C-N,C=O,PO₄^3-participate in the adsorption reaction.The logarithmic growth period of the strain is 5 d,the optimal growth and adsorption time is12 d,and the optimal adsorption pH is 8.0.The best adsorption effect of corn stover biochar（CSC）was prepared by firing at500℃for 6 h.The surface of CSC was characterized by SEM-EDS and XPS,and the main elements were C,N,O,K and Si.FTIR shows that the-OH,C=C,C=O,and C-O-C bonds are involved in the adsorption reaction,and XRD results indicate that no new phase emerges after the adsorption of Cd²⁺.The adsorption efficiency of the Epicoccum sorghinum-corn straw biochar composite adsorbent（HC）reached 96.6%for 30 m L of Cd²⁺-containing solution at a concentration of 50 mg/L at a temperature of 25℃,pH of 8.0 and a dosing rate of 0.05 g.Its optimal initial Cd²⁺concentration and reaction time are 20 mg/L and 1 h,respectively.In this study,the influence of common cations on the adsorption of HC was investigated for later engineering applications,and the degree of influence was Ca²⁺>Mg²⁺>Na⁺>K⁺.The process of Cd²⁺adsorption by HC is consistent with the quasi-quadratic and quasi-first-order kinetic models and is fitted with the Freundlich model.The C=O bond and the C-N bond in the amide III band are jointly involved in the adsorption of Cd²⁺,which mainly undergoes coordinated complexation reactions to form Cd ammoniated and Cd hydroxide,and XRD characterization demonstrates the formation of CdS on the HC surface.