Factors affecting ammonium capture by some Victorian lignites

Abstract

ABSTRACT Nitrogen (N) loss from intensive animal husbandry leads to economic loss and environmental damage. Lignite has a demonstrated capacity to suppress ammonia (NH3) volatilisation from manure and this has been attributed to the pH, cation exchange capacity (CEC), pH buffer capacity and labile carbon (C) content of the lignite. Whilst lignite is effective in mitigating NH3 loss, the capacity for N retention and how this is influenced by the lignite's properties are not well studied. It is unclear if lignites from different mines will have comparable N retention under similar conditions. In this study, we characterised five Victorian lignites for their C-containing functional groups, surface morphology and chemical properties. These were then related to the ammonium () adsorption capacity of the lignites using a batch isotherm technique. The contribution of biological immobilisation to the N retention capacity of the lignites was determined using 15N tracing in an incubation study. All lignites were acidic (pHH2O: 3.3–5.8; pHCaCl2: 3.0–5.4). The lignite had similar patterns of distribution of C functional groups with the carboxyl C between 2.8% and 5.3%. The maximum adsorption capacity (Qmax ) varied with the composition of the lignite and correlated positively with the lignites’ CEC, pH and carboxyl groups. Increase in pH, especially from pH >5, resulted in up to 3-fold increase in Qmax (25.6 mg g−1), likely due to deprotonation of carboxyl groups. Compared to adsorption, the biological immobilisation of did not play a substantial role in the overall lignite's N retention capacity. Highlights Victorian lignites were assessed for their retention capacity using adsorption isotherms and 15N tracing. adsorption capacity of lignites increased (up to 3-fold) with pH, especially from pH 5 to 7. Biological immobilisation did not play a substantial role in the retention capacity of the lignites. pH-dependent adsorption was the dominant means by which lignite retained .