Effects Of Acid Pretreatment On Leaching Of Metal Impurities In Rice Husk And Characteristics Of Rice Husk Ash

Rice husk is one of the biomasses in nature which has a huge production and contains about 10%-21% amorphous silica. Rice Husk Ash(RHA) is the combustion product of rice husk in which silica with high activity is more than 90%, and RHA has a wide range of applications in industry. Research indicates that metal impurities in rice husk and combustion temperature are important elements that affect the quality of RHA, acid pretreatment of rice husk can remove the metal impurities and RHA with higher activity and purity can be obtained after combustion.Based on above ideas, rice husk as raw materials in this paper, the effects of acid pretreatment on leaching of metal impurities in rice husk and characteristics of RHA were studied. The specific research methods were as follow: rice husk was soaked in 5 different kinds of acid(hydrochloric acid, sulfuric acid, nitric acid, citric acid, oxalic acid) at different concentrations(0.05, 0.1, 0.5, 1, 1.5mol/L)under different immersion time(0.25, 0.5, 1, 2, 3h), ICP-OES was used to measure the content of metal impurities in leaching solution so as to reach the leaching rate of metal impurities, then the effects of acid pretreatment on the leaching result of metal impurities were studied; Rice husk after acid pretreatment was combusted in a fluidized bed at different temperature(600, 700, 800, 900℃), SEM, BET and EDS were used to analyse the effects of acid pretreatment and combustion temperature on the microstructure, specific surface area, content of elements of RHA.At first, Orthogonal design was used to design the experiments, and the experimental results were under range analysis and variance analysis, the optimal level combination of acid pretreatment conditions were as follow: the best kind of acid is sulfuric acid and citric acid, the optimum concentration of the acid is 0.5 mol/L, the optimum pretreatment time is 2h. Then,the influence of acid concentration and pretreatment time on the leaching rate of K, Ca, Na was studied, the leaching rate of K, Ca, Na increases with the increase of pretreatment time, when pretreatment time is 3 hours or more, the leaching rate does not change substantially; With the increase of acid concentration, the leaching rate of K, Ca first increases and then decreases, when acid concentration is 0.5mol/L, the leaching rate reaches a maximum; the leaching rate of Na decreases with the increase of acid concentration; Acid pretreatment can increase the specific surface area and pore volume of rice husk ash and weaken the inhibition of combustion temperature on the specific surface area and pore volume of rice husk ash;Combustion temperature has no significant influence on the content of elements of rice husk ash.