Spectral Study of Modified Humic Acids from Lignite Sergey Zherebtsov, Natalya Malyshenko, Ludmila Bryukhovetskaya and Zinfer Ismagilov E3S Web Conf., 21 (2017) 02022 Published online: 10 November 2017 DOI: 10.1051/e3sconf/20172102022