D. J. M. Santosa, D. Hermawan, S. Surya Kusumah, D. S. Nawawi, and J. Sutiawan, “Optimizing Nitric Acid Leaching Conditions for Ash and Potassium Reduction in Empty Fruit Bunches-Based Biomass Energy”, J. Sylva Indonesiana, vol. 9, no. 01, pp. 126–135, Feb. 2026.