The potential use of volcanic deposits for geopolymer materials

D J Ilham1, F R Kautsar1, J Januarti1, U Anggarini2, and D Fiantis1*
1Department of Soil Science, Faculty of Agriculture, Andalas University, Limau Manis,
Padang, Indonesia
2Department of Chemical Engineering, Universitas Internasional Semen Indonesia, Gresik,
Jawa Timur, Indonesia
E-mail: dianfiantis@faperta.unand.ac.id

Abstract

Volcanic deposits are abundant in the vicinity of an active and inactive volcano. They are produced from the cooling of magma during explosive volcanic eruptions. They have varying physical properties and can range in size from sub-millimetric ash up to boulder size. As Indonesia is considered as an active volcanic region, volcanic materials are abundant but they are still unexploited to full capacity such as geopolymer raw material. Geopolymers are generally understood as alkali-activated aluminosilicates. They may be considered as an inorganic two-component system which consists of: [1] a reactive solid source of SiO2 and Al2O3, and [2] an alkaline activation solution. The aim of the research is to identify the chemical and mineralogical properties of Merapi and Mt. Sinabung volcanic ashes as the raw material of geopolymers. Results showed that Mt. Merapi contained amorphous volcanic glass and crystalline [feldspar] minerals with 61.13% SiO2; 17.78% Al2O3; 3.47% Fe2O3; 6.22% CaO. Mount Sinabung deposit contains amorphous volcanic glass also and crystalline [feldspar] minerals with an oxide content of 49.33% SiO2; 15.93% Al2O3; 6.48% Fe2O3; 5.87% CaO. The high content of silica and alumina in this material showed that it was pozzolan material which can be synthesized to geopolymers. The molar ratio of SiO2/Al2O3 was high, Merapi is 5.84 and Sinabung is 5.26.

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