2002 年 9 巻 297 号 p. 76-83
It has recently become necessary to develop a new process for recovery of phosphorus component from the incineration ash of sewage sludge which is becoming difficult to be disposed. The condition of leaching process was investigated, because the leaching process of phosphoric acid was one of the most important process in recycling the incineration ash. The results can be summarized as follows :
1) Sulfuric acid solution was preferred to sodium hydroxide solution for leaching of phosphorus ions from incineration ash of sewage sludge. It should be paid attention that for leaching process, (1) sulfuric acid concentration is comparatively high, (2) ratio of solid to solution is low, (3) processing temperature makes it high, (4) the leaching rate was fast and leaching time less than 30 minutes
2) The phosphorus component in incineration ash of sewage sludge is existing as calcium phosphate, mainly. It was found that it was possible to prevent from substantial decline by making the ratio of solid to solution comparatively high to control the concentration of Ca2+ ion.
3) The residue after leaching treatment with sulfuric acid solution was not suited to the cement resources, because it included calcium sulfate. By washing treatment with sodium hydroxide, the quantity of SO3 in the residue was reduced and the residue is possible to be utilized as cement resources.