Charles, D.A., et al. “Effect of Particle Size, NaOH Concentration, and S L Ratio on the Extraction of Humic Acid from Leonardite”. Journal of BioProcess and Chemical Technology (JBCT), vol. 17, no. 34, Apr. 2025, pp. 27-34, https://revistas.uadec.mx/JBCT/article/view/196.