Simatupang, L., Oktavia, D. P., & Doloksaribu, M. (2017). The adsorption of heavy metal Pb(II) by silica based adsorbent from volcanic ash of mount sinabung. Jurnal Pendidikan Kimia, 9(2), 330–335. https://doi.org/10.24114/jpkim.v9i2.7682