Abstract
We examine the collection method for phosphate from volcanic ash soil type phosphorus adsorbent used in secondary effluent. The phosphorus in volcanic ash soil type phosphorus adsorbent is desorbed by 68.9% using 0.5 mol · l-1 H2SO4 solution at a space treatment speed (SV) of 2.5 for 6 h. Phosphorus in the extraction solution can be completely collected by adjusting the pH of the H2SO4 solution to 4.8∼8.7. The major components of the collected phosphorus extract are sodium, aluminum, iron and phosphorus. The total phosphate amount in the collected phosphorus extract is approximately 43.0 gP · kg-1, which is equal to that of a phosphate rock. The citrate-soluble phosphorus in the collected phosphorus extract is estimated to be 80% of the total amount of collected phosphate. Moreover, when the collected phosphorus extract is applied to the subsoil of andosol to grow Brassica campestris cv. Komatsu, its effect is identical to that of superphosphate application. As for the level of application of the collected phosphorus extract, it is found that 6% is suitable. It is proved that the collected phosphorus extract is very promising for soil reduction and reuse.
