高岭石表面酸碱反应的电位滴定实验研究

采用表面酸碱电位滴定法探讨高岭石表面酸碱性质,基于多位模式(即假定高岭石表面存在3种基团Al2 OH 、AlOH 和SiOH ) ,根据实验所得数据对高岭石表面的质子化和去质子化过程的相关参数进行拟合,讨论各个位点所发生的反应,并探讨了支持电解质浓度、高岭石溶解过程对表面酸碱电位滴定结果的影响。高岭石的表面零净质子电荷点(pHPZNPC,5 .2 )不等同于零电荷点,当pH <5 .2时,高岭石表面荷正电荷,主要由于表面富硅贫铝层的形成和Al位的质子化所致;当pH >5 .2时,高岭石表面荷负电荷,以Si位和Al的去质子化反应为主。

A study of surface acid-base properties of kaolinite on the basis of the multi-sites model

Surface acid-base properties of kaolinite were investigated by potentiometric surface titration. On the basis of the multi-sites model (assuming the presence of (Al-2OH)()(), (AlOH)()() and (SiOH)()()), relative parameters of proton adsorption/desorption were calculated according to the experimental data which had been corrected in consideration of the kaolinite dissolution. The reactions at every site were also discussed. The influence of various ionic strengths and kaolinite dissolution on the results of potentiometric surface titration was studied. The point-of-zero-net-proton charge of kaolinite (pH-(PZNPC),5.2) differed from the point of zero charge. Below pH 5.2, the positive charge at the kaolinite surface was mainly attributed to the formation of silica rich/aluminum deficient precursor complex and proton adsorption at aluminum sites, whereas above pH 5.2, the negative charge at the kaolinite surface was contributed chiefly by deprotonation of Si and Al sites.