Sorption of Copper, Zinc, and Cadmium by Some Acid Soils

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Abstract
The sorption of Cu, Zn, and Cd as a function of pH was examined for three acid soils. Sorption occurred at pH levels markedly below the zero point of charge (ZPC). Copper sorption increased with increasing pH, and Cu was preferentially sorbed over Zn and Cd. The presence of Cu interfered with the sorption of Zn and Cd. The sorption at higher pH levels varied with the source of hydroxide used. Sodium hydroxide had a greater ability than calcium hydroxide to disperse organic matter and to reduce the ability of the soils to retain metals. Reduction of heavy metal sorption at high pH levels was attributed to the formation of metal‐organic complexes. The metal sorptive capability of Chehalis (Cumulic Ultic Haploxerolls) soil was greater than that of Puyallup (Fluventic Haploxerolls) and Sultan (Aquic Xerofluvents) soils, perhaps due to its higher organic matter and Fe contents and its higher cation exchange capacity (CEC). Further investigation revealed that the CEC played a more important role than soil organic matter content in the sorption of the metals. The solubility of Al and Mn in the soil solution may also help to regulate sorption of heavy metals by acid soils.