循环流化床粉煤灰无定形组分化学组成与结构特性

Chemical composition and structural characteristics of amorphous componentsin circulating fluidized bed-derived coal fly ash

循环流化床(CFB)粉煤灰较低的成灰温度使其无定形组分与传统的煤粉炉(PC)粉煤灰存在明显差异,目前对CFB粉煤灰无定形组分组成和结构的认识尚不深入。以4种CFB粉煤灰为研究对象,分别利用Retiveld全谱图拟合方法和酸碱交替化学溶解法,计算了粉煤灰无定形组分的质量分数;结合化学组成和物相定量结果,获得了灰中无定形组分的主要化学组成。利用^(27)Al和^(29)Si核磁共振(NMR)图谱分峰拟合的方法,揭示了无定形组分中硅铝的配位结构及其在酸碱处理时的分解过程。结果表明,4种CFB灰的物相均以无定形硅铝酸盐为主,其质量分数均在65%以上,其主要化学组成为SiO_(2)和Al_(2)O_(3),无定形组分的Si/Al低于粉煤灰中总的Si/Al。利用酸碱交替化学溶解法获得的无定形组分质量分数略低于Retiveld全谱图拟合计算的无定形组分质量分数。NMR结果表明CFB灰中的Si-O-Si和Si-O-Al结构是高度无序和不稳定的,其中铝主要以四配位([AlO_(4)])和六配位([AlO_(6)])的铝氧结构存在,硅主要以Q_(4)(0Al)结构为主,[SiO_(4)]之间通过桥氧连接,形成高聚合程度的Si-O-Si结构;[AlO_(4)]或[AlO_(6)]与[SiO_(4)]结合形成Q^(3)(1Al)或Q_(4)(1~2Al)的Si-O-Al结构。HCl溶液破坏[AlO_(4)]结构并使铝溶出,NaOH溶液破坏[SiO_(4)]结构并使硅溶出,利用酸碱交替化学溶解法可实现CFB灰无定形组分中铝硅的深度分离。

Due to the lower ash formation temperature of circulating fluidized bed fly ash(CFB-FA),its amorphous fractions are significantly different from conventional pulverized coal furnace fly ash(PC-FA).At present,the chemical composition and structure of the amorphous components in CFB-FA are not well understood.Taking four kinds of CFB fly ash as the research object,the Retiveld full spectrum fitting method and the acid-alkali-based alternate method were used to calculate the content of amorphous components in fly ash.Combining the chemical composition and mineral quantitative results,the main chemical composition of the amorphous components in the CFB-FA was obtained.Based on the^(27)Al and^(29)Si magic-angle rotating nuclear magnetic resonance(NMR)spectrum,the coordination structure of silicon and aluminum in the amorphous component was revealed using the rewind integral peak fitting method.The results show that the main phase of the four CFB ashes is amorphous aluminosilicate,the mass fraction of which is more than 65%,and the main chemical compositions of amorphous components are SiO_(2)and Al_(2)O_(3).The Si/Al(molar ratio)of amorphous component is lower than the total Si/Al of the raw fly ash.The contents of amorphous components in the CFB-FA obtained by acid-alkali alternate method are slightly lower than those calculated by Retiveld full spectrum fitting.NMR results reveal that the Si-O-Si and Si-O-Al structures of amorphous components in the CFB-FA are highly disordered and unstable.The aluminum in the amorphous component of CFB-FA ash mainly exists in four-coordinated([AlO_(4)])and six-coordinated([AlO_(6)])aluminum oxide structures.The silicon in the amorphous component is mainly Q_(4)(0Al)structure.[SiO_(4)]structures are connected by bridging oxygen to form Si-O-Si structure with high degree of polymerization;and[AlO_(4)]or[AlO_(6)]combines with[SiO_(4)]to form Si-O-Al structures of Q^(3)(1Al)or Q_(4)(1~2Al).The HCl solution destroys[AlO_(4)]structure and causes Al to dissolve,and the NaOH solution destroys[SiO_(4)]structure and causes Si to dissolve.The Si and Al in amorphous composition of CFB ash can be separated by the acid-alkali-based alternate method.