| 摘要 |
The objective of the present invention is to prevent clogging of a filter medium used in solid-liquid separation of a phosphorus extraction liquid and processed ash after extracting phosphorus in incinerated ash into an alkaline solution. This method for extracting phosphorus separates a solid component and a liquid component using a filter medium in a solid-liquid separation step performed after first performing a phosphorus extraction step for extracting phosphorus by mixing an alkaline reaction liquid (1) and incinerated ash (2) containing P. Of the incinerated ash (2), the P alkalinity dependence of the elution concentration of ionic silica on the alkaline reaction liquid (1) is measured, and the P alkalinity of the alkaline reaction liquid (1) is caused to be no greater than a predetermined P alkalinity of ionic silica at which the tendency for the P alkalinity dependence of the elution concentration of ionic silica changes. Of the incinerated ash, the P alkalinity dependence of the elution concentration of phosphorus on the alkaline reaction liquid (1) is also measured, and the P alkalinity of the alkaline reaction liquid (1) is caused to be at least the P alkalinity that is 1.0 (equivalents/kg) lower than a predetermined P alkalinity of P at which the tendency for the P alkalinity dependence of the elution concentration of phosphorus changes. |
