Author(s)

Laksmita P. Santi¹, Didiek H. Goenadi¹, Donny N. Kalbuadi¹, Indah P. Sari¹,   Sulastri²

¹Indonesian Research Institute for Biotechnology and Bioindustry, Bogor, Indonesia.
²PT Pupuk Kalimantan Timur, Bontang, Indonesia.

This study deals with the pre-treatment of coal fly ash (CFA) by using alkaline substance to improve water solubility of Si which in turn readily available to the plants. Selected weight ratios of CFA/NaOH (s:s) were tested and the highest H₄SiO₄ yield ratio was selected for further study. X-ray diffraction and scanning electron microscopy analyses were performed to confirm the evidence of structural changes of the CFA upon alkaline treatment. To improve SiO₂ dissolution, seven Si-solubilizing fungi, i.e., Aspergillus niger BCC194, A. niger K0909, A. niger A1601, Trichoderma polysporum, T. viride, T. pseudokoningii, and Trichoderma spp, were each inoculated onto pre-treated ash. The results indicated that the relationships between ratio of CFA/NaOH and total and soluble Si were linier (R² = 0.97** and 0.96**, respectively). Total SiO₂ values range from 10.43% to 13.02%, whereas soluble Si contents were 2.30% - 2.64% improved about 300 times compared to un-treated CFA. Both XRD and SEM analyses indicated that alkaline treatment to CFA caused particle damages resulting in increasing soluble Si. Inoculation of pre-treated CFA by T. polysporum up to twelve days of incubation yielded the highest soluble Si. Each fungal species grown on Bunt & Rovira solid media enriched with CFA as Si-source expressed significantly different ability in solubilizing Si from CFA. Citric acid was shown to be stronger compared to acetic and oxalic acids in solubilizing Si from CFA.

Soluble Si, Si-Solubilizing Fungi, Si Fertilizer, Silicic Acid

Santi, L. , Goenadi, D. , Kalbuadi, D. , Sari, I. and Sulastri,  . (2021) Alkaline Pre-Treatment of Coal Fly Ash as Bio-Silica Fertilizer. Journal of Minerals and Materials Characterization and Engineering, 9, 180-193. doi: 10.4236/jmmce.2021.92013.