Effect of production temperature and particle size of rice husk biochar on mercury immobilization and erosion prevention of a mercury contaminated soil

Mercury (Hg) contaminated soil is a potential hazardous material especially under soil erosion and surface runoff. This work aims to use rice husk biochar to immobilize Hg and prevent erosion, and find the optimal production temperature and particle size of the biochar. The biochars were produced at 300, 500, and 700. C and sieved to three particle sizes similar to 20, < 2, and < 0.15 mm. They were applied to a Hg contaminated loamy sand (20.2 mg/kg) and undergone simulated rainfall erosion representing 7 years of heavy rain events in Beijing. All biochar amendments reduced the runoff volume by 5.1-15.4%. Hg amount in runoff were significantly reduced by 36.7-48.8% after the amendments of biochar. The Hg concentration of infiltration was reduced by biochar treatments except that produced at 300 degrees C, while its amount was increased due to larger infiltration volume. All biochar amendments significantly reduced soil loss in runoff by 43.5-77.2%. Hg was enriched in the sediments (39.7-46.8 mg/kg) compared with the parent soil (20.2 mg/kg) regardless of biochar treatment, but its bioavailability was low. Higher pyrolysis temperature of the rice husk biochars resulted in less runoff, more infiltration, and better erosion prevention, while the effect of biochar particle size is less significant.

Automated summary

The use of rice husk biochar at different production temperatures and particle sizes can effectively reduce runoff and soil erosion on mercury-contaminated soil, decreasing the concentration of mercury in runoff and soil. Higher pyrolysis temperature of the biochar results in less runoff, more infiltration, and better erosion prevention, while the effect of biochar particle size is less significant.