A New Method for Quantifying Phosphorus of Various Occurrence Forms in Solid Fuels

Quantification of phosphorus (P) and determination of the occurrence forms of P in solid fuels are important to thermochemical processing of P-containing solid fuels. This study has developed a new three-step method for separating and quantifying the total P in a solid fuel into five major P-containing fractions. These consist of three organic P-containing fractions (i.e., acid-soluble organic P, two acid-insoluble organic P including P in lipids and P in nucleic acids and other acid-insoluble organic structures) and two inorganic P-containing fractions (i.e., acid-soluble inorganic P and acid-insoluble inorganic P). The first step of this new method uses cold 0.6 M HClO 4 to extract the acid-soluble P species. The extracted solution is then neutralized, followed by selectively converting the acid-soluble organic P in the solution into orthophosphate (PO 4 3– ), pyrophosphate (P 2 O 7 4– ), and tripolyphosphate (P 3 O 10 5– ) by UV irradiation in the presence of H 2 O 2 . The second step of this new method uses an ethanol/chloroform mixture to extract the residue from the first step to yield a solution for quantifying the contents of P in acid-insoluble phospholipids using an inductively coupled plasma optical emission spectrometer (ICP-OES). The third step of this new method uses buffered NaCl solution at 100 °C to extract P in nucleic acids and other acid-insoluble organic structures from the residue of the second step into a solution for subsequent quantification using ICP-OES. The acid-insoluble inorganic P in the residue is then quantified using ICP-OES after HF/HNO 3 /H 2 O 2 acid digestion. The new method is validated with a comprehensive set of standard samples loaded with known amounts of single or mixed P-containing species with known occurrence forms. Compared to the large errors of the conventional Standards, Measurements and Testing method, complete P recovery is achieved with minimal errors. Further applications of the new method to seven different solid fuels also achieve close to 100% mass balance of P. The results demonstrate that the new method is suitable for quantifying various forms of P in solid fuels.