Comparative study on adsorption and immobilization of Cd(II) by rape component biomass.

Agricultural wastes have promising potential for the production of low-cost and sustainable adsorbents for heavy metals, while the characteristics of those biosorbents and the stability of the passivated heavy metals under natural conditions need to be studied further. In this paper, the oilseed rape plant after seed harvesting was divided into three parts: root (RT), stem (ST), and pod (PD). The isotherm adsorption of cadmium (Cd(II)) on the biomass was conducted. In practice, the biomass was aged in the Cd(II)-contaminated soil, and the concentration of Cd(II) in the leachate was measured after the continuous eluent of typical acid rain. The components and elements of the biomass were determined for the analysis of the differences between the immobilization abilities of the biomass. Results showed the CC (corn cob, as a comparison), ST, RT, and PD had the adsorption capacities of 6.34, 7.58, 9.22, and 9.87 mg/g for Cd(II) through the Langmuir fitting of the isothermal adsorption experiments, respectively. The leached Cd(II) were reduced 1063, 2073, 2824, and 3621 μg by CC, ST, RT, and PD biomass aging, respectively. Compared that by CC, the immobilization differences between the biomass in soil were much greater than that in isotherm adsorption, indicating the biosorption ability of rape biomass was enlarged during the 30 days of aging. Nitrogen, phosphorus, and sulfur contents showed sequences as pod>root>stem and had high correlations with the reduced amount of leached Cd(II), which indicated protein might be beneficial for the enhancement of adsorption/immobilization in the soil.