Recovery of Water-Soluble Fertilizers from Biomass Boiler Ash Via Acid Leaching: Evaluation of Primary and Residual Effects on Maize Growth and Nutrient Uptake

Abstract This study evaluated the potential of water and acid-leached boiler ash (BA) as fertilizers by analyzing the elemental contents, recovery rates, and their effects on maize growth and soil nutrient dynamics. The resulting leachates were dried, and the molecular compositions of the materials were analyzed using XRD and FTIR. These materials were then applied to maize plants at a rate equivalent to 100 mg kg − 1 of P. Subsequently, maize plants were grown again in the same pots without further application, and the P and other plant nutrient levels in the plants were determined. Despite variations in leach methods, over 5% P, 7% K, 16% Ca, and 3% Mg remained in the filter residues, while H 3 PO 4 and HCl-leaching yielded the highest P concentrations in the leachates (7.45% and 5.95%, respectively). Water-leaching produced the highest K concentration (22%). As compared to control, the leachates significantly enhanced maize growth, with HNO₃-leached fertilizer producing the highest dry weight in the first crop and H 2 SO 4 and H 3 PO 4 -leached fertilizers being most effective for the second crop. Phosphorus and K uptake increased across all treatments, with P uptake peaking in the first crop with H 2 SO 4 and in the second crop with H 2 SO 4 and H 3 PO 4 . Soil analysis revealed elevated plant-available P, K, and Mg levels after fertilizer applications, especially with H 2 SO 4 and H 3 PO 4 , which persisted into the second crop. The results highlight the potential of BA-leachates as effective fertilizers for enhancing nutrient recovery and crop productivity, with tailored leaching treatments optimizing nutrient availability.