| In recent years, biomass energy has been drawing more and more attention in China. There have been great developments in technologies related to biomass energy utilization. Among those technologies, direct combustion has become the main method to make full use of biomass resources. The development of biomass direct combustion technology provides technical assurance for direct combustion power generation industry. However, with the rapid expansion of biomass power generation industry, the amount of biomass ash is increasing tremendously. And there has not been comprehensive utilization of biomass ash yet, thus leading to not only environmental pollution, but also waste of resource. Biomass ash contains amorphous silica and large amounts of nutrients required by crops, very low content of heavy metals, making it an excellent source of silicon and raw material for preparation of fertilizer. In this paper, experimental methods, including liquid leaching and solid calcining, was used to extract potassium, phosphorus, and SiO2 from a kind of corn straw ash collected from a biomass power plant, on purpose of ash comprehensive utilization.Firstly, extraction of potassium was conducted. The efficiency of different extractants and conditions was compared to aquire the optimum condition, which was that the raw ash was burned at 500℃, then leached in water at room temperature under L/S 3 for 30min. The concentration of potassium was 17.2g/L, and dissolution rate and the extraction rate were 82.0% and 62.6%respectively. The higher efficiency potassium recovery, higher purity of potassium leachate, less content of heavy metals, simpler operation process, lower cost, made the process more advantageous when compared to those results of research about extracting potassium from marginal sources of potassium.After large part of potassium was removed from the corn straw ash, there was a certain amount of phosphorus in it. Thus, the ash was then leached in hydrochloric acid and nitric acid respectively to recover phosphorus, under the best condition that the ash was soaked in hydrochloric acid at 50℃ with L/S 3 for 1h and pH less than 1, but for nitric acid as extractant, at room temperature, L/S 3, the reaction time 20min, pH less than 0.3. The best results were the concentrations were 1.53g/L and 1.53g/L, and dissolution rates were 90.23% and 89.85% respectively.After water and acid leaching, the main component in the residual ash was amorphous silica, making it a kind of silicon source with high quality. NaOH was selected as extractant to abstract SiO2. Many factors, such as reaction mode, SiO2 and Na2O molar ratio, mixture mode of NaOH and ash, the reaction time and temperature, were investigated in the extraction of the silica. After comparison, within the range of experiments, the conclusion was achieved that the optimum condition for high-temperature calcination was SiO2/Na2O molar ratio equal to 1, at 330℃ calcined for 2h, and SiO2 dissolution rate was 72.6%; for the liquid phase reaction, molar ratio of SiO2/Na2O equal to 1, heated at 80℃ with stirring for 3h, and dissolution rate was 74%.This study was conducted to extract phosphorus and potassium by liquid leaching method, and to extract SiO2 by both solid phase and liquid phase procedures. The experiments obtained some optimum corresponding conditions for extraction process. These conditions can provide a certain reference value on ash comprehensive utilization. |
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