Phosphorus Adsorption by an Aluminum-Peat Complex
1981
Bloom, P. R.
Phosphorus adsorption by an organic matter Al complex in acid soils was studied using Al-peat containing 0.8 equivalents of Al per equivalent of peat carboxyl groups. Phosphate adsorption isotherms were determined with suspensions in 0.005M CaCl₂ to which either HCl or Ca(OH)₂ was added. The pH ranged from 3.2 to 6.0. Phosphate is strongly adsorbed by Al-peat. The data suggest that phosphate removal from solution is due both to adsorption of complex Al-phosphate cations by the peat and to the precipitation of amorphous Al-hydroxy-phosphate, likely AlH₂PO₄(OH)₂. For suspensions with similar pH, the strength of phosphate adsorption in Al-peat is less than that for an Al-permanent charge resin and greater than that, per gram of organic matter, of an andept soil. As in acid soil and Al-resin, phosphate adsorption in Al-peat increased with increasing pH in the pH range studied. It was concluded that the Al-organic matter complex in acid surface soils is an important source of phosphate adsorption, especially in mineral soils of high organic matter content.
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