NOVEL RECOVERY PROCESS OF PHOSPHATE FROM SEWAGE SLUDGE ASH BY CARBON DIOXIDE BLOWING

摘要

Sewage sludge ash contains a lot of phosphorus, and hence, it is important that it be recycled. However, sewage sludge ash also contains many heavy metals, making it difficult to recover the phosphorus. We found that group-Il-eiement phosphates are preferentially dissolved by blowing CO_2 into the suspension. We think that the dissolution mechanism involves the formation of soluble hydrogen carbonate through the CO_2-blowing process. Hence, only group-Il phosphates that form hydrogen carbonate were dissolved. We attempted to extract phosphoric acid from sewage sludge ash by this method. The CO_2-blowiń? process facilitated the elution of phosphoric acid fromthe sewage sludge ash, but heavy met?? ions, such as Fe, were not eluted. The powders were dried by evaporation and the phosphate did not contain much of the heavy metals.