Alkaline Pre-Treatment of Coal Fly Ash as Bio-Silica Fertilizer

Abstract

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 H 4 SiO 4 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 SiO 2 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 (R 2 = 0.97** and 0.96**, respectively). Total SiO 2 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.