Simatupang, Lisnawaty, Devy Putri Oktavia, and Maryati Doloksaribu. 2017. “The Adsorption of Heavy Metal Pb(II) by Silica Based Adsorbent from Volcanic Ash of Mount Sinabung”. Jurnal Pendidikan Kimia 9 (2):330-35. https://doi.org/10.24114/jpkim.v9i2.7682.