Preliminary study on feasibility of basaltic glass as prospective for slow fertilizer by evaluating the release rate of phosphate | Preliminary study on feasibility of basaltic glass as prospective for slow fertilizer by evaluating the release rate of phosphate

Improving soil fertility has been the main goal for increasing crop production in order to feed the increasing world population. Phosphorus is one of the major chemical elements commercially produced as phosphate to increase the fertility of the soil. Phosphate rock is considered the main raw material to produce phosphate type fertilizer. Looking for other viable sources of phosphorus, however, is an indispensable task in order to maximize food productivity by improving soil fertility for the increasing world population. Hence, this study examined the potential of basaltic glass to be used as a fertilizer mainly serving as a source of phosphorus. In order to evaluate the potential of basaltic glass, the dissolution rate of basaltic glass that was obtained from Stapafell Mountain, Iceland was studied using mixed flow through reactor. The dissolution rate of basaltic glass was calculated by measuring the amount of phosphate and silica species released in the bulk solution. Ion Chromatography (IC2000) was used to determine cations and anions in the reacted bulk solution while Auto analyzer was used for measuring aqueous silica and phosphate. The solid samples, before and after reaction, were examined using Scanning Electron Microscopy (SEM). The unreacted basaltic glass and reacted basaltic glass products were also inspected using X-ray Powder Diffraction (XRD). Matlab software program was used to simulate how the dissolution of particles of basaltic glass with different grain size distribution changes the specific surface area and hence the release rate of essential chemical species into the solution. Different values of specific kinetic rate constants, particle size distribution and time were used to simulate the optimum possible condition for dissolution of basaltic glass. The result from the first experiment shows that, the rate of dissolution of micronized basaltic glass at neutral pH and 800C was 1.2*10-9 mol.m-2.s-1. This dissolution rate of natural glass is too slow to release the expected amount of phosphorus (28 kg Phosphorus per hectare required for one harvest season) needed to fertilize the soil. Hence, another experiment was performed to explore the full potential of basaltic glass. In this experiment, basaltic glass was reacted with HCl, HNO3 and H2SO4.The complete dissolution of basaltic glass in acidic medium was observed. This confirms that the complete release of phosphate ion into the bulk solution from the basaltic glass structure. Treating basaltic glass with acidic solution, therefore, maximizes the release of phosphate and its feasibility to be used as a fertilizer source rock. Pure amorphous silica was also formed as a byproduct as a result of the complete digestion of basaltic glass in acidic media as solid phase. This may open the possibility of using basaltic glass for dual purpose (fertilizer and silica source). This study shows the potential of basaltic glass as a fertilizer when it goes to complete dissolution, however additional studies should be performed in large scale to promote the use of the basaltic glass as fertilizer.