Chen Zhaoyang, Luan Zhaokun, Jia Zhiping, Li Xiaosen
Key Laboratory of Renewable Energy and Gas Hydrate, CAS, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, China.
J Environ Manage. 2009 Jun;90(8):2831-40. doi: 10.1016/j.jenvman.2009.04.001. Epub 2009 May 5.
The hydrolysis/precipitation behaviors of Al(3+), Al(13) and Al(30) under conditions typical for flocculation in water treatment were investigated by studying the particulates' size development, charge characteristics, chemical species and speciation transformation of coagulant hydrolysis precipitates. The optimal pH conditions for hydrolysis precipitates formation for AlCl(3), PAC(Al13) and PAC(Al30) were 6.5-7.5, 8.5-9.5, and 7.5-9.5, respectively. The precipitates' formation rate increased with the increase in dosage, and the relative rates were AlCl(3)>>PAC(Al30)>PAC(Al13). The precipitates' size increased when the dosage increased from 50 microM to 200 microM, but it decreased when the dosage increased to 800 microM. The Zeta potential of coagulant hydrolysis precipitates decreased with the increase in pH for the three coagulants. The iso-electric points of the freshly formed precipitates for AlCl(3), PAC(Al13) and PAC(Al30) were 7.3, 9.6 and 9.2, respectively. The Zeta potentials of AlCl(3) hydrolysis precipitates were lower than those of PAC(Al13) and PAC(Al30) when pH>5.0. The Zeta potential of PAC(Al30) hydrolysis precipitates was higher than that of PAC(Al13) at the acidic side, but lower at the alkaline side. The dosage had no obvious effect on the Zeta potential of hydrolysis precipitates under fixed pH conditions. The increase in Zeta potential with the increase in dosage under uncontrolled pH conditions was due to the pH depression caused by coagulant addition. Al-Ferron research indicated that the hydrolysis precipitates of AlCl(3) were composed of amorphous Al(OH)(3) precipitates, but those of PAC(Al13) and PAC(Al30) were composed of aggregates of Al(13) and Al(30), respectively. Al(3+) was the most un-stable species in coagulants, and its hydrolysis was remarkably influenced by solution pH. Al(13) and Al(30) species were very stable, and solution pH and aging had little effect on the chemical species of their hydrolysis products. The research method involving coagulant hydrolysis precipitates based on Al-Ferron reaction kinetics was studied in detail. The Al species classification based on complex reaction kinetic of hydrolysis precipitates and Ferron reagent was different from that measured in a conventional coagulant assay using the Al-Ferron method. The chemical composition of Al(a), Al(b) and Al(c) depended on coagulant and solution pH. The Al(b) measured in the current case was different from Keggin Al(13), and the high Al(b) content in the AlCl(3) hydrolysis precipitates could not used as testimony that most of the Al(3+) was converted to highly charged Al(13) species during AlCl(3) coagulation.
通过研究絮凝剂水解沉淀物的颗粒尺寸发展、电荷特性、化学形态及形态转变，考察了水处理絮凝典型条件下Al(3+)、Al(13)和Al(30)的水解/沉淀行为。AlCl₃、聚合氯化铝（PAC(Al13)）和聚合氯化铝（PAC(Al30)）水解沉淀形成的最佳pH条件分别为6.5 - 7.5、8.5 - 9.5和7.5 - 9.5。沉淀物的形成速率随投加量的增加而增大，相对速率为AlCl₃>>PAC(Al30)>PAC(Al13)。当投加量从50μM增加到200μM时，沉淀物尺寸增大，但当投加量增加到800μM时，沉淀物尺寸减小。三种絮凝剂水解沉淀物的ζ电位均随pH升高而降低。AlCl₃、PAC(Al13)和PAC(Al30)新形成沉淀物的等电点分别为7.3、9.6和9.2。当pH>5.0时，AlCl₃水解沉淀物的ζ电位低于PAC(Al13)和PAC(Al30)。在酸性条件下，PAC(Al30)水解沉淀物的ζ电位高于PAC(Al13)，而在碱性条件下则低于PAC(Al13)。在固定pH条件下，投加量对水解沉淀物的ζ电位无明显影响。在未控制pH条件下，ζ电位随投加量增加而升高是由于絮凝剂投加导致的pH降低。铝铁试剂研究表明，AlCl₃的水解沉淀物由无定形Al(OH)₃沉淀组成，而PAC(Al13)和PAC(Al30)的水解沉淀物分别由Al(13)和Al(30)的聚集体组成。Al(3+)是絮凝剂中最不稳定的形态，其水解受溶液pH显著影响。Al(13)和Al(30)形态非常稳定，溶液pH和老化对其水解产物的化学形态影响很小。详细研究了基于铝铁试剂反应动力学的絮凝剂水解沉淀物研究方法。基于水解沉淀物与铁试剂络合反应动力学的铝形态分类与传统铝铁试剂法测定的结果不同。Al(a) / Al(b) / Al(c)的化学组成取决于絮凝剂和溶液pH。本文测定的Al(b)与Keggin Al(13)不同，AlCl₃水解沉淀物中高含量的Al(b)不能作为AlCl₃混凝过程中大部分Al(3+)转化为高电荷Al(13)形态的证据。
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