葡聚糖分子对氢氧化铁矿化结晶的调制作用

通过对比五种不同葡聚糖浓度的Fe3＋/葡聚糖矿化作用体系中Fe(OH)3凝胶在早期矿化阶段的成核和相变过程来研究葡聚糖对铁矿物的结晶与转化的调控作用. 运用ICP-AES(等离子发射光谱仪)观察各个矿化体系中上清液的Fe3＋]浓度及相应pH的变化, 矿化产物运用FTIR、XRD进行表征. 结果发现, 上清液中Fe3＋]经历了两次下降过程, 在陈化的第三天突然回增. 与不含葡聚糖的矿化作用体系很快形成结晶良好的α-FeOOH不同, 在含有葡聚糖的矿化作用体系中最初形成的物相主要为β-FeOOH. 葡聚糖分子通过与Fe3＋配位吸附在铁氧化物颗粒的表面促进了β-FeOOH转化为α-Fe2O3. 相变是经过溶解-再结晶机制进行的. Fe3＋]第二次下降正是由于β-FeOOH转化为α-Fe2O3引起的. 葡聚糖浓度适当增大, β-FeOOH溶解加快, 有利于相变的进行. 因此葡聚糖的存在能显著影响在氢氧化铁凝胶中形成晶核的结构类型及其相变历程.

Effect of Dextran on the Crystallization of Ferric Hydroxide

The initial nucleation and phase transformatin process of the Fe(OH)3 gel in five different mineralization systems with different dextran concentrations(from 0～2.0%(w) and the same Fe3＋]=0.012 mol?L-1) have been investigated. The mineralizational phases in the initial stage were characterized by FTIR, XRD and ICP-AES spectrometry. The results showed that the concentration of Fe3＋ ions in supernatant increased suddenly in the third day during aging and then its secondary reduction stage occurred. There were the same chages of pH as Fe3＋] in these process. The initial phases formed in the systems with dextran were mainly β-FeOOH, not α-FeOOH which growing rapidly in the system without dextran. The dextran molecules were adsorbed on the surfaces of iron oxide particles by complexing with Fe3＋. The adsorbed dextran molecules would facilitate the phase transformation from β-FeOOH into α-Fe2O3 by a dissolution-recrystallization mechanism. The secondary reduction stage of Fe3＋] corresponded to the process of the phase transformation from β-FeOOH into α-Fe2O3. With the increasement of the concentrations of dextran (up to 2.0%(w)) in solution, the dissolution of β-FeOOH and the formation of α-Fe2O3 in these mineralization systems were accelerated. It was clear that dextran molecules could control the nuclei type and its phase transformation of the Fe(OH)3 gel.