Phosphates in soils treated with sewage water IV

The reaction of phosphate (P) with Al(OH)₃ can be distinguished by adsorption and a process designated here as long-term reaction. The long-term reaction may remove several times the amount of P removed initially. No long-term reaction of P (0.5 mmol/liter) and Xray amourphous Al(OH)₃ was detected at pH 8. To columns of quartz sand mixed with Al(OH)₃ domestic sewage water (pH ≅ 8) was added during 10 mo once every 2 weeks. The phosphate retention in these columns was much higher than could be expected from the pure Al(OH)₃ system experiments, indicating the occurrence of a long-term reaction. Column segments were analyzed for organic-, (Al + Fe)-, and Ca-P. Negligible Ca-P was formed. Electron microscopy and Xray analysis showed quartz particles, Al-containing particles with no detectable P, and particles containing Al, P, and Ca. Formation of the Al-P-Ca particles contributes to the capacity of soils to store or retain P.