纤蛇纹石焙烧去金属氧化物制备纤维状二氧化硅

Preparation of Fibri-Form Silica via Extraction of Metal Oxide by Mix-roasting from Chrysotile Fibers

以纤蛇纹石纤维为前驱体,采用硫酸氢铵焙烧法去除金属氧化物制备纤维状Si O2,研究了不同温度条件下的化学反应过程,对焙烧过程中不同反应阶段所形成产物、去除可溶盐后水浸残骸的结构和谱学特征进行分析和表征,以揭示纤蛇纹石去金属氧化物过程和纤维状Si O2的形成机理。结果表明:在焙烧过程中,130~270℃范围内,纤蛇纹石结构中镁氧八面体片的外羟基被破坏,Mg2+离子形成(NH4)2Mg2(SO4)3和(NH4)2Mg(SO4)2可溶性盐;随着反应温度增加,纤蛇纹石结构中镁氧八面体片的内羟基被破坏,(NH4)2Mg(SO4)2转变为(NH4)2Mg2(SO4)3;当焙烧温度达到380℃,镁氧八面体片被完全破坏,(NH4)2Mg(SO4)2全部转变为晶态(NH4)2Mg2(SO4)3,仅保留纤维状硅氧四面体片骨架;当焙烧温度为500℃时,(NH4)2Mg2(SO4)3全部转变为Mg SO4,硅氧四面体骨架进行重组,焙烧产物经水浸后获得纤维状Si O2。

The fibri-form silica was prepared via the removal of metallic oxide in chrysotile fibers with chrysotile fibers as a precursor by an ammonium bisulfate roasting method. The chemical reaction process of thermal effect of chrysotile fibers and the change of phases at different temperatures were investigated. The structure and spectroscopic characteristics of the washed residues in different stages of mix-roasting were analyzed. The formation mechanism of fibri-form silica by removing metallic oxide was revealed. The result shows that(NH4)2Mg2(SO4)3 and(NH4)2Mg(SO4)2 can be formed due to the ionization of Mg2+ when the temperature in roasting process is increased from 130 to 270℃ ℃. The inner hydroxyl of magnesia octahedron in chrysotile fiber decomposes and the(NH4)2Mg2(SO4)3 transforms into(NH4)2Mg(SO4)2 as the temperature increases。 At 380℃, magnesia octahedron in chrysotile fibers completely decomposes, and(NH4)2Mg(SO4)2 transforms into(NH4)2Mg2(SO4)3 crystal, but the Si—O tetrahedron retains. At 500℃,(NH4)2Mg2(SO4)3 transforms into Mg SO4 and the Si—O tetrahedron recombines, finally extracting fibrous silica by washing with mix-roasting washed residues.