Rapid adsorption of Ammonium on coffee husk and chicken manure-derived biochars: Mechanisms unveiled by chemical speciation, physical, and spectroscopic approaches

Authors: DE MORAIS, EVERTON G - Federal University Of Lavras; SILVA, CARLOS A - Federal University Of Lavras; Gao, Suduan; MELO, LEONIDAS C A - Federal University Of Lavras; BENEVENUTE, PEDRO A N - Federal University Of Lavras; LAGO, BRUNO C - Federal University Of Lavras; TEODORO, JESSICA C - Federal University Of Lavras; GUILHERME, LUIZ R G - Federal University Of Lavras

Submitted to: Sustainability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2025
Publication Date: 2/15/2025
Citation: De Morais, E., Silva, C., Gao, S., Melo, L., Benevenute, P., Lago, B., Teodoro, J., Guilherme, L. 2025. Rapid adsorption of Ammonium on coffee husk and chicken manure-derived biochars: Mechanisms unveiled by chemical speciation, physical, and spectroscopic approaches. Sustainability. 17:1616. https://doi.org/10.3390/su17041616.
DOI: https://doi.org/10.3390/su17041616

Interpretive Summary: Biochar can be one of the sustainable technologies for crop production by converting waste into stable carbon products, enriching soil carbon, and retaining nutrients in soil. This study evaluated the rapid retention of ammonium-nitrogen in biochars produced from coffee husk and chicken manure at different pyrolysis temperatures (300–900 °C) and investigated the mechanisms of ammonium retention. A rapid sorption experiment was conducted in laboratory by passing an ammonium chloride solution through the biochar and then determined the changes in chemical properties and N retention as well as solid formation using speciation software (Visual Minteq). The results indicated different mechanisms involved in ammonium retention by different biochar products. These mechanisms include electrostatic interactions with negative charges for coffee husk-derived biochar produced at 300 °C, solid formation for chicken manure-derived biochar produced at 400 °C, and physical trapping in the pores of the coffee husk-derived biochar produced at 900°C. The results imply that retention of ammonium-nitrogen by biochar can be achieved via various pathways, which can potentially enhance soil N retention, reduce N leaching, and improve N availability for crops.

Technical Abstract: Biochar has emerged as a sustainable technology for converting waste into high-value, stable carbon products. Depending on its properties, biochar can retain various elements, including nitrogen (N) as ammonium (N-NH4'). This study aimed to evaluate the rapid retention of N-NH4' in biochars produced from coffee husk (CH) and chicken manure (CM) at different pyrolysis temperatures (PT) (300°C, 400°C, and 900°C) and investigate the mechanisms involved. A rapid N-NH4' sorption experiment was conducted, in which an NH4Cl solution was passed through the biochars. The following analyses were performed: cation exchange capacity (CEC), total N content, N retention, infrared analysis (ATR-FTIR), and leachate solution analysis, followed by chemical speciation using Visual Minteq software. The results indicated that different mechanisms were involved in N-NH4' retention. In CH-derived biochars produced at 300°C, N-NH4' retention occurred primarily through electrostatic interactions with negative charges (CEC), as confirmed by ATR-FTIR analysis. In CM-derived biochars produced at 400 °C, the N-NH4' retention was mainly through the formation of struvite (NH4MgPO4·6H2O), as confirmed by chemical speciation in Visual Minteq. In CH-derived biochars produced at 900 °C, N-NH4' ions were trapped in the pores of the charred matrix due to increased biochar surface area when there were no N precipitates predicated with a reduction in CEC, likely due to the loss of functional groups at the highest PT. The biochars studied proved effective in retaining N-NH4' through different mechanisms, suggesting that biochars can enhance soil N retention, reduce N leaching, and be potentially used as a source of N for crops.