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摘要
Extraneous humic substances could alter the dynamics of Cd in soils. An insoluble humic acid, produced from a leonardite, was used in laboratory experiment as an adsorbent to immobilize Cd in a silt-loam soil near a smelting plant and a Cd-spiked and aged sandy-loam soil, whereas a soluble peat-derived potassium humate was employed as a washing agent to mobilize Cd in, and remove it out of, the contaminated soils. Addition of 2% humic acid could reduce CaCl2 extractable Cd in a soil (0.103 mg?L-1) by 19.7%. This immobilization effect was greater in sandy-loam soil than in silt-loam soil. Similarly, Cd removed from the contaminated soils increased with washing agent dosage. A single washing at 10 g?L-1 of potassium humate removed up to 38.1% of the total Cd in soils. Fourier transform infrared spectroscopic analysis indicated the formation of Cd-carboxyl complex. This study suggests that Cd-contaminated soils can be remediated by humic substances through either an immobilization or mobilization process. The key to the success is to select humic substances with a suitable solubility: water insoluble humic acid for Cd immobilization and water soluble potassium humate for effective removal of Cd out of soils.
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