Prasetyo, E., and K. Toyoda. “Solid Phase Extraction of Thorium and Uranium and Their Separation from Lanthanides Using Humic Acid Silica Gel As a Low-Cost Adsorbent”. Journal of Engineering and Technological Sciences, vol. 49, no. 4, Oct. 2017, pp. 508-19, doi:10.5614/j.eng.technol.sci.2017.49.4.6.