Activities of Cu2+ and Cd2+ in Soil Solutions as Affected by pH

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Abstract
The concentrations of free copper and cadmium ions in soil suspensions were measured by an ion‐selective electrode as a function of pH after equilibrating metal salt solutions with the soils. Similar experiments were done with water‐extractable organic matter. Free (uncomplexed) Cu2+ concentrations were strongly pH‐dependent in the soil systems, but well below the level where precipitation could have occurred. Free Cd2+ concentrations were much less affected by pH adjustment, and the nonacid soil systems approached saturation or oversaturation with respect to CdCO3 precipitation at high pH. Similiar dependence of the free metal ion concentration on pH was found in water extracted organic matter solutions. Precipitation of CdCO3 in oversaturated solutions containing the extracted organic matter was slow, while none of the copper‐organic matter solutions attained oversaturation with respect to Cu(OH)2 or Cu2(OH)2CO3.
Funding Information
  • Regional Research Project (NE-96)