The Study Of Preparation And Adsorption Of Sulfur Dioxide On Modified Rice Husk RHA

Rice husk is considered as a raw material of rice husk ash(RHA) preparation, Experiments were conducted to study the influence of pretreatment for rice husk ash(RHA) preparation. Then, RHAs were modified with nitric acid and calcium-based materials on the basic properties. Meanwhile, adsorption capacity and desulfurization efficient of RHA treated either by nitric acid or by calcium-based materials were investigated.The main achievements show that:The best RHA is prepared from rice husk that smashed by planetary ball mill firstly, then keep being dipped in lmol·L-1 hydrochloric acid about 4 hours, afterwards pured with water and dried out before burning in two steps. By the calcination method, white and porous RHA with high specific surface area as much as 227m·g-1, containing noncrystalline SiO2 without any special surface functional groups can be produced. Crystalline state of the RHA treated by nitric acid almost characterized as before and the detections for specific surface area showed 129 to 160 m·g-1. Acid-modified rice husk ash appeared little change in pore structure. Pore size distribution of the RHA treated by calcium-based materials with specific surface area which is 28 m2·g-1 are mainly concentrated nearby 16 nm, and calcium silicate hydrate(C-S-H) gel and crystalline tricalcium silicate(C3S) was found in the sample treated by calcium-based materials. The absorption ability of the sulfur dioxide(SO2) of RHA is mainly enhanced by calcium silicate hydrate gel.For SO2 adsorption on RHA, it is known that the better sample treated by nitric acid is prepared from rice husk ash dipping in 6mol·L-1 HNO3 and lasting for 4 hours. The adsorption capacity of samples range from 0.08 to 0.12mg·g-1, it turns smaller with temperature increment and larger with increasing inlet concentration of SO2. Adsorption curve was fitted well with the pseudo-first order kinetics model, and this adsorption was an exothermic and nonspontaneous process with the entropy decreases.while the temperature down, the nospontaneous trend of adsorption process is reduced, and the lower temperature can promote to adsorption process.Better adsorption capacity was found in adsorption, especially the chemical adsorption, of SO2 by sample treated with calcium-based materials. The optimum sample, named CR-2, was prepared from rice husk ash which hydrated with calcium-based materials of mass ratio in 1:2 and keepped hydrating 16 hours under 60 ℃. The adsorption capacity of sample turns larger first then smaller with temperature increment and larger with increasing inlet concentration of SO2. Adsorption curve was fitted well with the pseudo-second order kinetic equation, and this adsorption was an endothermic and nonspontaneous process with the entropy decreases. As the temperature growing up, the nospontaneous trend of adsorption process is reduced, appropriate temperature scope can promote the adsorption process. The change of enthalpy and entropy is greater than zero at the same time, it shows that the adsorption reaction is irreversibly. Therefore, calcium silicate hydrate gel in RHA treated with calcium-based materials could enhance the chemical adsorption of SO2 of RHA.