Impact of Black Carbon Amendments on the Retention Capacity of Cadmium in Soil

The aim of this research was to study the changes of available cadmium (Cd) with associated factors in Cd-contaminated soil, following addition of black carbon (BC). Black carbon produced from rice straw under temperatures of 300, 500, and 700°C was tagged as R-300, R-500, and R-700, while black carbon produced from camphorwood under temperatures of 500, 700, and 900°C was tagged as C-500, C-700, and C-900. BC was incubated in Cd-polluted soil, to detect changes of heavy metal form and cation exchange capacity (CEC) of soils. The results showed that the content of bioavailable Cd in the soil was decreased by 59.68% when the added amount of R-700 was 6%, while it was reduced by 60.56% when the added amount of C-900 was 6%. The soil stabilization to Cd was strengthened with the increase of BC pyrolysis temperature and added amount of BC. The average CEC of the soil increased 4.77, 6.16, and 5.80 cmol kg⁻¹ when the added amount of rice-BC varies as 2, 4, and 6%; with respect to camphorwood-BC, the average CEC increased 4.71, 9.31, and 5.50 cmol kg⁻¹. The results indicated that the soil characteristics changed after adding biomass BC, the soil immobilization to Cd was improved, and the Cd mobility in the soil medium was reduced; hence, its ecological risks were also decreased.