Effects Of Pretreatment And Calcination Conditions Of Rice Husk On The Activity Of Rice Husk Ash

In rice-growing countries rice husk has long been regarded as agricultural waste.However,it is actually a source of SiO₂,because rice husk contains about 20%of SiO₂.Researches show that amorphous silica in rice husk ash can be used as a resource for recycling,and it has a certain activity in the chemical reaction.For example,it can be used for producing silica-containing compounds such as sodium metasilicate,amorphous silica,silica gel,etc,and it also can be used as silicon fertilizer in agricultural production.Therefore,how to increase the content of amorphous silica in rice husk ash for obtaining high reactivity rice husk ash is of great significance for agriculture and industrial production.In this paper,the effects of temperature and time on rice husk ash in the process of calcining rice husk were investigated to determine the best calcination condition of rice husk.The necessity of pretreatment of rice husk before calcination was also studied.The best condition in the pretreatment process wasobtained by experiments,which provided theoretical basis and effective solutions for large-scale practical production.The main results of this research are as follows:?1?Method for determiningsilica contented in rice husk ash:Based on the testing method of silicon-containing fertilizerreleased by the Japan Center for Food and Agricultural Materials Testing?FAMIC?,some of the steps were appropriately streamlined to obtain a new method for testingthe amorphous silica in rice husk ash.?2?The best condition for calcining rice husk:The experiment results showed that rice husk can be completely calcined at 700?for calcining about 90 minutes,and the content of soluble silica in rice husk ash can reach about58.9%.If the calcination time was further increased,the effect on rice husk ash was not significant.In addition,when the calcination temperature exceeded over 800?,the silica in the rice husk ash was crystal transformed,the amorphous silica transformed into crystalline silica and lost the utilization value.?3?The best condition for pretreatingthe rice husk:The rice husk was washed at room temperature for 2.5 hours under the condition that the solid-liquid ratio of the rice husk to the reagent was 1:50,using 1%H₂SO₄ solution as a pretreatment reagent.The content of soluble silica in the rice husk ash obtained by calcination can reach about 95.5%.Further,the sulfuric acid solution as a pretreatment reagent can be reused about 7 times.