A Micro-CT Approach for 3D In-Situ Visualizing the Cu (II) Adsorption in Corn Cob Biochar

This study aims to visualize the in-situ dynamic change process of Cu (II) adsorption in biochar. First, this study used corn cob biochar as the characterization object, CuCl 2 solution with an initial Cu (II) concentration of 200 mg/L as the adsorption solution, and 5 min, 10 min, 30 min, 1 h, 2 h, 5 h, 8 h, 12 h, 24 h, and 48 h as the adsorption time to obtain the adsorption kinetics samples of corn cob biochar. Then, Bruker Skyscan 1275 micro-CT was used for in-situ three-dimensional visualization of Cu (II) adsorbed biochar samples, and Fourier infrared spectroscopy was used to explore the Cu (II) adsorption mechanism of corn cob biochar. It was found that the characterization results of raw biochar samples and Cu (II) adsorbed samples has group difference, which may be related to the heterogeneity of sample composition and microstructure; 80% of Cu (II) adsorption of biochar occurred in the early stage of adsorption, and the surface adsorption was preferential adsorption; Cu (II) biochar particles showed internal diffusion with the extension of adsorption time. The micro-CT characterization results agree with the physicochemical test results, which show that micro-CT is feasible for the three-dimensional in-situ visual characterization of Cu (II) adsorption in biochar and the exploration of the adsorption mechanism. The findings may provide advanced methodological support for an in-depth dissection of the adsorption mechanism of heavy metals in biochar.