Dependence of Phosphorus Recovery on Acid Type during Dissolution–Precipitation Treatment of Incineration Ash of Chicken Manure

Abstract

To utilize chicken manure as a source of phosphorus, we employed dissolution–precipitation treatment to recover phosphorus from the incineration ash of chicken manure (IACM), which was used as fuel to power a boiler. To recover useful phosphorus-containing solids from IACM, the ash was dissolved in aqueous solutions of either nitric acid, hydrochloric acid, or sulfuric acid to elute phosphorus together with various component elements, followed adding aqueous NH₃ to yield a precipitate containing phosphorus. Using nitric acid and hydrochloric acid, calcium phosphate species such as calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) and monetite (CaHPO₄) were obtained following the precipitation treatment. By contrast, sulfuric acid resulted in the precipitation of magnesium ammonium phosphate (MAP) species, such as struvite (MgNH₄PO₄∙6H₂O) and dittmarite (MgNH₄PO₄∙H₂O). Both the calcium phosphate and MAP species could be used as a slow-acting fertilizer containing phosphorus, while the MAP species could be simultaneously used as a slow-acting fertilizer containing nitrogen. Notably, the calcium phosphate species obtained in the present study were equivalent to those found on a phosphate rock, which is widely used as a raw material in phosphorus-based industries, and the natural sources of this material could be depleted in the near future. Though IACM has not been used effectively thus far, it shows promise as viable alternative to the dwindling natural sources of phosphorus.