Chemical Species of Phosphorus and Zinc in Water-Dispersible Colloids from Swine Manure Compost.

The release of phosphorus (P) and zinc (Zn) from swine manure compost and from soils applied with swine manure compost can be accelerated by colloidal particles. This study investigated the concentrations and chemical species of P and Zn in water-dispersible colloids (WDCs) collected from swine manure compost by using X-ray absorption fine structure (XAFS) spectroscopy. A filtration and ultracentrifugation process was used to separate and collect WDCs (20-1000 nm) from the bulk swine manure compost (<2 mm). The swine manure compost contained 2.7 g kg WDC, in which P (140 g kg) was highly concentrated and Zn concentrations were greater than in the bulk compost (1.45 g kg). Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy determined the presence of struvite (NHMgPO·6HO) as a major P species (74%), followed by tricalcium phosphate as a secondary component (26%). In the WDC fraction, struvite was not found, but tricalcium phosphate (56%) occurred as a primary component. Zinc K-edge XAFS spectroscopy determined hopeite [Zn(PO)·4HO, 59%] and to a lesser extent smithsonite (ZnCO, 24%) and Zn adsorbed on ferrihydrite (17%). In the WDC fraction, hopeite (44%) and organically bound Zn (35%) were predominant. Our results demonstrate the notable difference in the concentration and chemical species of P and Zn between the WDC and bulk fractions of swine manure compost.