Effect of inorganic potassium compounds on the hydrothermal carbonization of Cd-contaminated rice straw for experimental-scale hydrochar
2019
Xu, Zhi | Guo, Zhaohui | Xiao, Xiyuan | Zeng, Peng | Xue, Qinghua
Nowadays, it is extremely important to reuse the harvested biomass from contaminated soils. In this study, the effect of inorganic potassium compounds, such as K₂SO₄, KCl, KOH, and K₂CO₃, on the hydrothermal carbonization of heavy metal-contaminated rice straw as well as the distribution of heavy metals in the corresponding hydrochars were examined. In the presence of K₂SO₄, the higher heating value, carbon recovery, and energy recovery of the resulting hydrochar significantly increased from 23.34 MJ kg⁻¹, 42.74%, and 42.99% to 24.46 MJ kg⁻¹, 44.20%, and 45.03%, respectively. Concomitantly, the enhanced decarboxylation and dehydration process led to a decrease in the oxygen content of the resulting hydrochar. In the presence of KOH, the Cd and Cu content of the corresponding hydrochar significantly increased (p < 0.05) from 70.72% to 79.09%–89.96% and 93.73%, respectively, while only slightly changing upon the addition of K₂SO₄ or KCl, which was attributed to the morphology and microstructure of the different hydrochars. These results suggest that hydrothermal carbonization is a viable method to reuse contaminated biomass for solid fuel, while K₂SO₄ is a suitable additive to improve the energy recovery of hydrochars.
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