Chemical stabilization of cadmium in acidic soil using alkaline agronomic and industrial by-products

Abstract

In situ immobilization of heavy metals using reactive or stabilizing materials is a promising solution for soil remediation. Therefore, four agronomic and industrial by-products [wood biochar (WB), crushed oyster shell (OS), blast furnace slag (BFS), and fluidized-bed crystallized calcium (FBCC)] and CaCO₃ were added to acidic soil (Cd = 8.71 mg kg⁻¹) at the rates of 1%, 2%, and 4% and incubated for 90 d. Chinese cabbage (Brassica chinensis L.) was then planted in the soil to test the Cd uptake. The elevation in soil pH caused by adding the by-products produced a negative charge on the soil surface, which enhanced Cd adsorption. Consequently, the diethylenetriamine pentaacetic acid (DTPA)-extractable Cd content decreased significantly (P < 0.05) in the incubated soil. These results from the sequential extraction procedure indicated that Cd converted from the exchangeable fraction to the carbonate or Fe-Mn oxide fraction. The long-term effectiveness of Cd immobilization caused by applying the 4 by-products was much greater than that caused by applying CaCO₃. Plant shoot biomass clearly increased because of the by-product soil amendment. Cd concentration in the shoots was < 10.0 mg kg⁻¹ following by-product application, as compared to 24 mg kg⁻¹ for plants growing in unamended soil.

Keywords:

• Amendment
• bioavailability
• biochar
• cadmium
• Chinese cabbage
• soil remediation

Acknowledgments

We thank the National Science Council of the Republic of China, Taiwan, for financially supporting this study under Contract No. NSC 101-2622-E-020-011-CC3.