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Forms of Solid Phase Copper in Copper-enriched Swine Manure¹

ABSTRACT

Manure from swine fed high levels of copper (Cu) was extracted sequentially and nonsequentially with reagents designed to selectively solubilize specific Cu forms from the manure. Fresh (slurry), freeze-dried, and oven-dried samples were used. Water-soluble Cu increased from 2% to 30% with increasing severity of drying. Salt solutions [calcium (Ca) and lead (Pb)] were no more effective than H₂O in extracting Cu, suggesting both a lack of Cu adsorbed on inorganic mineral surfaces (which were composed largely of quartz, calcite, and gypsum), and a strong binding of the Cu against Pb-exchange, presumably with organic material. Dilute acetic acid (pH 2.5) removed 67% of the Cu from oven-dried samples, but only 7 to 11% from the slurry or freeze-dried samples. This suggests that Cu oxide and hydroxide minerals, which are soluble in this reagent, were not present in the fresh, slurried manure, but that oven-drying of the manure affects chemical forms of Cu in a significant fashion. Most of the Cu in all the manure samples was extractable with sodium hydroxide (NaOH) or potassium pyrophosphate (K₄P₂O₇), suggesting association with organics. Little Cu remained after sequential K₄P₂O₇ extraction, at which point CuS minerals would be expected to remain in the residue. It was concluded that Cu minerals are probably not found in this waste, but that most, if not all, of the Cu is associated with the organic fraction.

Key Words: copper fractionation • sequential extraction • copper minerals • organically-bound copper

¹ Contribution of Dep. of Agronomy, Univ. of Georgia, Athens, GA 30602, and Dep. of Agronomy and Dep. of Animal Science, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061. This research was partially funded by the International Copper Research Association, Inc., New York 10017.

² Assistant Professor, Dep. of Agronomy, Univ. of Georgia, Athens; Professors of Agronomy, and Professor of Animal Science, Virginia Polytechnic Inst. and State Univ., Blacksburg, respectively.

Received for publication April 12, 1985.