聚硅酸铁水解规律及混凝机理的探讨

Hydrolysis Law and Coagulation Mechanism of Poly-silicic-ferric Sulfate(PSF) Coagulant

以水玻璃、硫酸亚铁及氯酸钠为原料，用共聚法制备聚硅酸铁混凝剂（PSF），同时研究PSF的水解过程以及PSF与聚合硫酸铁（PFS）、复合铝铁（PFA）的微观品质（微观结构、形态尺寸及Zeta电位）及混凝性能，并结合水解形态分布及微观品质对PSF的混凝机理进行初步探讨．结果表明，PSF是由许多链节样物种连接而成的分维数很大的敞开式枝状结构，其平均粒径比PFS、PFA分别大近5、11倍，而PFS、PFA是由一些低分维数及尺寸很小的棒状或球状形态组成，PSF、PFS的Zeta电位相近，远远低于PFA（为PFA的1／20左右），PSF的形态尺寸及Zeta电位分布不均．在较宽的pH范围内（浊度为5．5—12NTU，Uk为5．5—10cm^-1），PSF的混凝效果明显优于PFS、PFA．PSF在纯水中的水解可以代表在地表水中的水解过程．PSF具有的特征微观品质使其在不同pH值范围内具有不同的水解形态分布，导致混凝机理差异很大．在宽泛的pH范围内（5〈pH〈9），PSF的3种水解形态Fe（OH），Fe（OH）^2＋及Fe^3＋稳定存在于水体中，是PSF在较宽pH范围内具有优异混凝性能的根本原因，也是PSF同时具有增强电中和／脱稳及架桥混凝机理的内在原因．微观品质、水解形态分布及混凝效果的对比合理解释了电中和／脱稳是混凝的前提条件，架桥是必要条件，二者要紧密配合才能取得高效的混凝效果。

A new type of inorganic coagulant, pely-silicic-ferric sulfate（PSF） was prepared using water glass, ferrous sulfate and sodium chlorate with co-pelymerized method, and the hydrolysis process of PSF was studied. The microproperties （microstructure, size of species and Zeta potential） and coagulation performance of PSF were explored compared with pelyferrlc sulfate（PFS） and pelyferric aluminum（PFA）, and coagulation mechanism of PSF was analyzed primarily using hydrolysis species distribution and microproperties. The results show that the morphology of PSF is characterized by having multi-branched structures with larger size, wider molecular weight and bigger fractal dimension, while PFS and PFA are some conglomerate of some sphere or stick shapes with almost the same molecular weight and lower fractal dimension. The average diameter of PSF is more than 5 or 11 times the size of PFS or PFA, respectively, and Zeta potential of PSF is almost equal to that of PFS but is far lower than that of PFA. The hydrolysis process of PSF in surface water can be surrogated by that in pure water. The distribution of hydrolysis species of PSF at different pH value is different due to its characteristic microproperties, which causes the distinction of coagulation mechanism. Three kinds of hydrolysis products [Fe（OH）3,Fe（OH）^2＋ and Fe^3＋] in wider pH range （5 〈 pH 〈 9） is approximately constant, which is the essential reason that PSF has superior coagulant efficiency in water treatment with wider pH range and that the coagulation mechanism of PSF is the cooperation of enhanced charge-neutralization/destabihzation and bridging. The comparison between hydrolysis species distribution and coagulation performance reveals reasonably that charge-neutralization/destabilization is the precondition and bridging is the necessary condition in coagulation process, and efficient coagulation can be obtained only by the close cooperation of that two stages.