| Silicon, one of the four main nutritious elements necessary for agricultural crops, are the basic element of rock minerals. Silicon are distributed widely in the nature, of which almost are crystalline phase and amorphous structure. However, these nutrient elements can not be directly taken up by plants. Some surveys have shown that the soils are poor of silicon account for about 50% of the arable land in China. At present, the production capacity of China is not high, which is insufficient to meet agricultural demand. Therefore, it is imperative to using insoluble silicon-contained minerals to produce silicon fertilizer for satisfaction of domestic market needs.The silicon fertilizer are prepared by calcinating mixture of wollastonite,dolomite and fluxing agent. This experiment studied the effects of materials ratio,calcination temperature and reaction time on available silica content in wollastonite-dolomite reaction system. The molybdenum blue photometric method for determination of silicon dioxide content in silicon fertilizer was researched. The physical and chemical properties of raw material and roasted product were analyzed by XRD, SEM, FTIR, EPMA and TG-DSC. It has discussed the reaction mechanism of wollastonite and dolomite and investigated the effect of fuxing agent on wollastonite and dolomite reaction system using the kinetic method. The results are as followings:(1) The optimized molybdenum blue photometric method is simple, fast and accurate. The sampling weight is less than 0.2 g. and the oscilation frequency is 170-190 r/min. It has great real significance that using 2% citric acid as leaching agent to extract the available silica in silicon fertilizer. The standard deviation is less than 0.20%, and the recovery is from 98.5%-101.3%.(2) The optimum molar ratio of wollastonite, dolomite and fuxing agent is 1:0.3:0.4, and the reaction should be carried out at 1000°C for 1 hour. Under the optimum conditions, the content of available silica could reach 21.6%. The roasted wollastonite are in short column and the internal surface area are enhanced. Some parts of wollastonite have been active. The main phases of roasted products were CS, C2 S, C3MS2, C2MS2 and M2 S. The available silica, calcium and magnesium could be almost completely exsolved from C2 S, C3MS2 and C2MS2 in 5 g/L citric acid solution. It is technically feasible to produce silicon fertilizer by roasting wollastonite, dolomite and system added with fluxing agent and it is of practical significant to study this subject.(3) Fluxing agent has an important effect on wollastonite and dolomite reaction system. It can improve the reaction rate. Because of the addition of fluxing agent, the decomposing temperature of dolomite and the initial reaction temperature of wollastonite-dolomite system are dropped 22°C and 21°C, respectively. The thermal decomposition process of wollastonite- dolomite system with addition with fluxing agent follows the Gentling equation from the point of view of dynamics. The activation energy decreased from 106.89kJ/mol to 90.64kJ/mol when the addition of fluxing agent with the mole ratio of 0.4 was added to wollastonite–gypsum reaction system.(4) Silicon fertilizer has a great influence on plant height, root growth and biomass of little cabbage. The plant height, root weight and biomass of little cabbage with addition of 1‰ silicon fertilizer respectively increases 48.8%, 49.6%, 102.4% comparing with the blank control group. Proper silicon fertilizer can improve the germination rate of little cabbage. The fertilization index is 100 kilograms per mu based on economic considerations... |
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