Industrial-Scale Manufacturing of Phosphoric Acid Using Sewage Sludge Ash
Nippon Phosphoric Acid Co. Ltd. (NPA) started to use sewage sludge ash (SSA) for the industrial manufacturing of phosphoric acid (PA) in 2013. NPA purchases SSA from wastewater treatment plants (WWTP) equipped with a Bio-P process to remove phosphate (Pi) from sewage. In the NPA’s manufacturing plant, SSA is blended with roller-milled Pi rock and is dissolved in concentrated sulfuric acid to generate phosphogypsum slurry. Then the slurry is filtered to separate PA from gypsum which is recycled for the manufacture of plasterboard and cement. Currently, NPA accepts a total of 1300 t/a of SSA for the manufacture of PA and gypsum. In full operation, the manufacturing plant has the capacity to accept 3000 t/a of SSA. The blend ratio of SSA with roller-milled Pi rock is currently limited to a maximum of 2.5% (<97.5% Pi rock). This is needed to guarantee the quality of both PA and by-product gypsum for customers. NPA could accept SSA from WWTP without the need to modify its existing facilities and save material costs by partially replacing Pi rock with SSA.
KeywordsSewage sludge ash Phosphoric acid Wet acid process Phosphogypsum
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