Pyrolysis temperature-dependent changes in dissolved phosphorus speciation of plant and manure biochars

Minori Uchimiya, Syuntaro Hiradate

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

Pyrolysis of plant and animal wastes produces a complex mixture of phosphorus species in amorphous, semicrystalline, and crystalline inorganic phases, organic (char) components, and within organo-mineral complexes. To understand the solubility of different phosphorus species, plant (cottonseed hull) and manure (broiler litter) wastes were pyrolyzed at 350, 500, 650, and 800 C and exposed to increasingly more rigorous extraction procedures: water (16 h), Mehlich 3 (1 mM EDTA at pH 2.5 for 5 min), oxalate (200 mM oxalate at pH 3.5 for 4 h), NaOH-EDTA (250 mM NaOH + 5 mM EDTA for 16 h), and total by microwave digestion (concentrated HNO3/HCl + 30% H2O 2). Relative to the total (microwave digestible) P, the percentage of extractable P increased in the following order: M3 < oxalate ≈ water < NaOH-EDTA for plant biochars and water < M3 < NaOH-EDTA < oxalate for manure biochars. Solution phase 31P NMR analysis of NaOH-EDTA extracts showed the conversion of phytate to inorganic P by pyrolysis of manure and plant wastes at 350 C. Inorganic orthophosphate (PO4 3-) became the sole species of ≥500 C manure biochars, whereas pyrophosphate (P2O74-) persisted in plant biochars up to 650 C. These observations suggested the predominance of (i) amorphous (rather than crystalline) calcium phosphate in manure biochars, especially at ≥650 C, and (ii) strongly complexed pyrophosphate in plant biochars (especially at 350-500 C). Correlation (Pearson's) was observed (i) between electric conductivity and ash content of biochars with the amount of inorganic P species and (ii) between total organic carbon and volatile matter contents with the organic P species.

Original languageEnglish
Pages (from-to)1802-1809
Number of pages8
JournalJournal of Agricultural and Food Chemistry
Volume62
Issue number8
DOIs
Publication statusPublished - Feb 26 2014
Externally publishedYes

Fingerprint

Manure
Manures
pyrolysis
Phosphorus
animal manures
Edetic Acid
Pyrolysis
oxalates
Oxalates
phosphorus
Temperature
temperature
pyrophosphates
Microwaves
Ashes
organomineral complexes
Water
cottonseed hulls
animal wastes
Crystalline materials

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Agricultural and Biological Sciences(all)

Cite this

Pyrolysis temperature-dependent changes in dissolved phosphorus speciation of plant and manure biochars. / Uchimiya, Minori; Hiradate, Syuntaro.

In: Journal of Agricultural and Food Chemistry, Vol. 62, No. 8, 26.02.2014, p. 1802-1809.

Research output: Contribution to journalArticle

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abstract = "Pyrolysis of plant and animal wastes produces a complex mixture of phosphorus species in amorphous, semicrystalline, and crystalline inorganic phases, organic (char) components, and within organo-mineral complexes. To understand the solubility of different phosphorus species, plant (cottonseed hull) and manure (broiler litter) wastes were pyrolyzed at 350, 500, 650, and 800 C and exposed to increasingly more rigorous extraction procedures: water (16 h), Mehlich 3 (1 mM EDTA at pH 2.5 for 5 min), oxalate (200 mM oxalate at pH 3.5 for 4 h), NaOH-EDTA (250 mM NaOH + 5 mM EDTA for 16 h), and total by microwave digestion (concentrated HNO3/HCl + 30{\%} H2O 2). Relative to the total (microwave digestible) P, the percentage of extractable P increased in the following order: M3 < oxalate ≈ water < NaOH-EDTA for plant biochars and water < M3 < NaOH-EDTA < oxalate for manure biochars. Solution phase 31P NMR analysis of NaOH-EDTA extracts showed the conversion of phytate to inorganic P by pyrolysis of manure and plant wastes at 350 C. Inorganic orthophosphate (PO4 3-) became the sole species of ≥500 C manure biochars, whereas pyrophosphate (P2O74-) persisted in plant biochars up to 650 C. These observations suggested the predominance of (i) amorphous (rather than crystalline) calcium phosphate in manure biochars, especially at ≥650 C, and (ii) strongly complexed pyrophosphate in plant biochars (especially at 350-500 C). Correlation (Pearson's) was observed (i) between electric conductivity and ash content of biochars with the amount of inorganic P species and (ii) between total organic carbon and volatile matter contents with the organic P species.",
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