Martínez, Gustavo A., Samuel J. Traina, and Terry J. Logan. “Evaluation of Proton and Europium (III) Binding Reactions in a Sewage Sludge Humic Acid”. The Journal of Agriculture of the University of Puerto Rico 82, no. 3-4 (October 1, 1998): 121–140. Accessed December 22, 2024. https://revistas.upr.edu/index.php/jaupr/article/view/4071.