Magnesium activation affects the properties and phosphate sorption capacity of poultry litter biochar
Joshua T. Padilla , Donald W. Watts , Jeffrey M. Novak , Vasile Cerven , James A. Ippolito , Ariel A. Szogi , Mark G. Johnson
Biochar ›› 2023, Vol. 5 ›› Issue (1)
Magnesium activation affects the properties and phosphate sorption capacity of poultry litter biochar
Biochars with a high affinity for phosphorus (P) are promising soil amendments for reducing P in agricultural runoff. Poultry litter (PL) is an abundant biochar feedstock. However, PL-derived biochars are typically high in soluble P and therefore require chemical modification to become effective P sorbents. This study investigated the effect of magnesium (Mg) activation on extractable P (EP) and P sorption capacities of PL-derived biochars. Biochar was produced at 500–900 °C from PL activated with 0–1 M Mg. Three differentially aged PL feedstocks were evaluated (1-, 3–5-, and 7–9-year-old). Increased Mg activation level and pyrolysis temperature both resulted in EP reductions from the biochars. Specifically, biochars produced at temperatures ≥ 700 °C from PL activated with ≥ 0.25 M Mg had negligible EP. X-ray diffractograms indicated that increased Mg loading favored the formation of stable Mg3(PO4)2 phases while increasing temperature favored the formation of both Mg3(PO4)2 and Ca5(PO4)3OH. Maximum P sorption capacities (Pmax) of the biochars were estimated by fitting Langmuir isotherms to batch sorption data and ranged from 0.66–10.35 mg g−1. Average Pmax values were not affected by PL age or pyrolysis temperature; however, biochars produced from 1 M Mg-activated PL did have significantly higher average Pmax values (p < 0.05), likely due to a greater abundance of MgO. Overall, the results demonstrated that Mg activation is an effective strategy for producing PL-derived biochars with the potential ability to reduce P loading into environmentally sensitive ecosystems.
| • | Magnesium activation of poultry litter biochar reduced extractable phosphorus and allowed for additional phosphorus sorption. |
| • | Extractable phosphorus was reduced via the formation of solid Mg3(PO4)2 and Ca5(PO4)3OH phases. |
| • | Phosphorus sorption capacities were the highest for biochars produced from 1 M Mg activated poultry litter. |
U.S. Environmental Protection Agency
/
| 〈 |
|
〉 |
PDF
