Mixed biochar obtained by the co-pyrolysis of shrimp shell with corn straw: Co-pyrolysis characteristics and its adsorption capability

Abstract

The co-pyrolysis characteristics of shrimp shell (SS) with corn straw (CS) were investigated by comprehensive characterization to reveal the synergistic effects and further discuss the adsorption capability. TGA results showed that pyrolysis behavior and reactivity were improved with the increase of heating rate and doping ratio of CS. Flynn-Wall-Ozawa (FWO) and distributed activation energy model (DAEM) indicated that co-pyrolysis can effectively reduce energy consumption and promote the decomposition of CaCO3. TG-FTIR and Py-GC/MS analysis indicated that the release of CH4, CO2, CO and NH3 at the doping ratio of 25% CS (75SS+25CS) was higher than that at other doping ratios, and the relative proportions of N-heterocyclics and oxygenates were lower, which was conducive to the development of pore structure for mixed biochar and effectively alleviated the pollution during co-pyrolysis process. The structure of mixed biochar was improved, confirmed by the characterizations of BET, SEM, FTIR and XRD. The mixed biochar prepared at 800 °C (75SS+25CS800) exhibited optimal porosity, aromatization and the most thorough CaCO3 decomposition. Batch adsorption experiment showed that the removal rate of 50 mg/L Cu(II) by 75SS+25CS800 was close to 100% under the dosage of 1 g/L and pH = 3–6. The adsorption process was well described by Langmuir, pseudo-second-order and Webber-Morris model, illustrating diffusion monolayer chemisorption was the main adsorption mechanism of Cu(II) on 75SS+25CS800. The maximum adsorption capacity of 75SS+25CS800 for Cu(II) was 79.77 mg/g at 35 °C. In short, this study provided a reference in optimizing the preparation process and improving the adsorption performance of mixed biochar.