왕겨 biochar를 이용한 중금속 오염토양의 안정화

Abstract

The sample soil used in this study was obtained from contaminated soils at Jang-gun mine site located at Kyeong-buk Bong-hwa-gun, Korea. The obtained sample was air dried, followed by sieving #10 mesh (2 mm) and then analyzed. The sample was stabilized with rice husk derived-biochar and then cured for 28 days. The total content of lead, zinc, and copper were 3,441 mg/kg, 16,466 mg/kg, 780 mg/kg, respectively. The rice husk derived-biochars were produced under temperature at 500℃(RH-500) and 700℃(RH-700). To evaluate heavy metal stabilization efficiency, the sample was separated into two groups: the first group treated with RH-500, and the second group treated with RH-700. Each group was then separated into three different biochar/soil weight percentages: 10.0, 15.0, and 20.0 wt%. The Toxicity Characteristic Leaching Procedure(TCLP) was used to evaluate the effectiveness of stabilization process using rice husk derived-biochar. The pH values for the 20.0 wt% treated sample for the RH-500 and RH-700 groups were 8.08 and 8.22, respectively. An increase was observed in the pH values for the biochar treated samples as compared to that of non-treated sample (6.58). This phenomenon was concluded to be an effect of alkalinity of the rice husk derived-biochar. EC values for 20.0 wt% biochar treated samples from both groups (RH-500 and RH-700) increased by 57% and 76%, while the CEC values for the samples from both groups increased by 114% and 140%, respectively. The TCLP heavy metal concentrations for the 20.0 wt% biochar(RH-700) treated sample suggested that the leached concentration for lead, zinc, and copper were significantly decreased and the soil was successfully stabilized. The concentrations of lead, zinc, and copper were reduced as compared to original analytical results by 96.17~98.16%, 75.49~78.14%, and 99.92~99.95%, respectively. The TCLP lead concentration reduction was significant, and there are two theories that were explored to elucidate the mechanism responsible for effective lead stabilization. The first theory was that the phosphate from rice husk-derived biochar reacted with lead in the contaminated sample, which resulted in the formation of sparingly insoluble chloropyromorphite and hydroxypyromorphite or other insoluble compound. The second theory was that the stabilization of the sample was accomplished through the formation of pozzolanic reaction products caused by increasing pH levels.