Effects of Preparation Conditions and Environmental Conditions on Rice-straw-biochar Adsorption of Urea

To investigate the feasibility of using biochars to adsorb urea in aqueous solution, we extracted biochar which was generated at pyrolysis temperature of 400℃, 600℃ and 800℃ respectively from rice-straw combustion residues. In this study we evaluated the effect of adsorption time, the pH of environment, the contents of urea and biochar yield on the ability of adsorption for urea using a solution adsorption method. The results showed that all biochars could sorb the higher amounts of urea at pyrolysis temperature of 800℃, which was larger than 600℃ and 400℃ successively with prolonging adsorption time, increasing environmental pH, larger amounts of urea and greater the addition of biochars. However, biochars particle size of 1.91mm and 0.38mm had no significant effect. We conclude that rice-straw derived biochars can be used for adsorbing urea under the conditions where the pyrolysis temperature of 800℃, adsorption time of 3 hours, environmental pH of 7, biochar particle size of 2.0mm, initial urea concentration of 3mol/L and lesser usage of biochars.