Magnesium hydroxide-coated pyrolytic biochar composite was prepared by chemical precipitation, and the adsorption behavior of anionic dye (directly frozen yellow) onto magnesium hydroxide-coated pyrolytic biochar was investigated in the batch mode. The Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy and X-ray fluorescence spectroscopy of adsorbents were characterized. Adsorption studies were performed at different pH, salt concentration, contacting time and dye concentration. The pH value of the solution influenced the adsorption capacity significantly, and adsorption is favored of pH 6-8. Salt coexisted in solution increased slightly directly frozen yellow adsorption capacity. The isotherm data were analyzed by Langmuir and Freundlich isotherm model, and Langmuir model was better to predict the equilibrium data. Thermodynamic calculations showed that the adsorption was a spontaneous and endothermic process. Exhausted magnesium hydroxide-coated pyrolytic bio-char was treated by microwave irradiation, and yield of regeneration was 98 % in the case of microwave irradiated time 5 min at 320 W. The magnesium hydroxide-coated pyrolytic bio-char can be reused.

Bio-char, a by-product from fast wheat straw pyrolysis, was investigated as adsorbents for the removal of cationic dye, neutral red (NR) from solution. Adsorption studies were performed at bio-cha dose, NaCl concentration, contact time and dye concentration in the batch mode. Salt coexisted in solution is not favor in adsorption and the adsorption is faster process. The equilibrium data are modeled with Langmuir and Freundlich equations and both models are better fitted. Thermodynamic parameters are calculated and the results show that the process was spontaneous and endothermic in nature. Bio-char can be used to remove cationic dye from solution.