Contreras, E., Leal, E., & Martínez, M. (2010). Effect of temperature, oxidation time and substrate: oxidant agent ratio in the yield and composition of humic acids derived from coal, monitored by 1H NMR and FT-ir. Revista Técnica Da Faculdade De Engenharia Da De Zulia, 27(2). Obtido de http://www.produccioncientificaluz.org/index.php/tecnica/article/view/5841