No abstract

This study was conducted to investigate the effect of dissolved organic matter (DOM) extracted from common soil amendments and citric acid on the P sorption of an acidic soil. Hairy vetch (Vivia billosa L.) and crimson clover (Trifolium incarnatum L.) were used as sources for green manure‐derived DOM. Cattle manure (Bos taurus) and poultry manure (Gallus domesticus) were used as sources for animal manure‐derived DOM. The negative charge density of the water‐soluble DOM ranged from 4.6 to 13.4 mmolc g−1 C. Estimated molecular weight ranges were 710 to 850 for the green manure DOM and 2000 to 2800 for the animal manure DOM. Phosphorus sorption experiments were conducted at 40 mmol P kg−1 soil and 0, 5, 10, 15, and 20 mM total soluble carbon (Crs) for each green and animal manure source. The DOM extracted from vetch and clover, as well as citric acid, inhibited P sorption in the order citric acid > clover > vetch. The DOM extracted from the animal manures did not affect P sorption. The ability of the green manure DOM to inhibit P sorption was related to its ability to react with soil Al through ligand exchange reactions at lower DOM concentrations and through complexation reactions at higher DOM concentrations. The average ratio of Al solubilization to P sorption inhibition on a molar basis was 1.76 ± 0.44. Ultraviolet absorbance and fluorescence data suggested that the higher molecular weight of the animal manure derived‐DOM was a factor in its inability to react with soil Al. The results of this study suggest that management systems that use green manures may increase the availability of P by decreasing the sorption of added P to soils.

The mechanisms of heavy metal stabilization of calcium-based dry scrubber residue using soluble PO4 3- were investigated. This stabilization technology is presently used in the U.S. and Japan to reduce metals leaching from municipal solid waste combustion residues. At an experimental dose of 1.2 mol of H3PO4/kg of residue and using a relatively dry mixing system, the reduction in the operationally defined fraction available for leaching (using the Dutch Total Availability Test) is 38% for Cd, 58% for Cu, 99% for Pb, and 28% for Zn. pH-dependent leaching (pH 4, 6, 8) showed that the treatment was able to reduce equilibrium concentrations by 0.5−2 log units for many of these metals, particularly Pb and Zn. Depth profiling of particles using secondary ion mass spectroscopy suggests that stabilization is by precipitation of metal phosphate reaction products rather than by adsorption of metals to phosphate particle surfaces. Bulk and surface spectroscopies show that the insoluble reaction products are nanometer-sized, crystalline and amorphous calcium phosphates, tertiary metal phosphates, and apatite family minerals. The geochemical thermodynamic equilibrium model MINTEQA2 was modified to include both extensive phosphate minerals and simple ideal solid solutions for modeling pH-dependent solid phase control of leaching. Both apatite family and tertiary metal phosphate end members and ideal solid solutions act as controlling solids for Ca2+, Zn2+, Pb2+, Cu2+, and Cd2+. The prevalence of small, nanometer-sized reaction products suggest that Ostwald ripening and precipitate maturation has not completely occurred during initial mixing. Nevertheless, soluble phosphate is an effective stabilization agent for divalent heavy metals in waste materials such as scrubber residues.