Alkaline leaching of phosphorous from poultry manure ash

Abstract

Phosphorous (P) is an essential element for all living organisms and predominantly serves as a vital component in phosphate fertilizers pivotal for agricultural purposes. With the projected depletion of phosphate rocks reserves within the next century, the quest for alternative phosphorous source is necessary. Poultry manure ash emerges as a promising substitute, offering a potential solution to mitigate future phosphorous demands. This study investigates the extraction of phosphorous from poultry manure ash via alkaline leaching with sodium hydroxide (NaOH). Factorial experimental designs and analysis of variance (ANOVA) were applied to investigate the impact of concentration, temperature, and their interactions on phosphorous extraction yield. The leaching mechanism was studied by coupling an extensive kinetic analysis with XRD and SEM-EDX of the solid residues. Alkaline leaching extracts maximum 60 % of P in 8 h when working at high concentration (10 M) and high temperature (75 °C) on the ash with the original particle size distribution. The NaOH concentration was the factor most affecting the P extraction yield. The extraction of P was found to be limited by diffusional kinetic control and re-precipitation of phosphorous with the calcium contained in the ash. The first hindering effect can be reduced by leaching smaller size fractions of the ash, thus increasing the extraction up 70 %. The activation energy of alkaline leaching was found to be 41.11–60.98 kJ/mol in the size range 500–160 μm while the reaction was found to proceed under enthalpic driving force. While alkaline leaching demonstrates high selectivity for phosphorus, challenges related to limited extraction efficiency still need to be addressed.