Department of Civil, Environmental and Geomatic Engineering, University College London, Gower Street, London WC1E 6BT, UK.
Water Res. 2011 Dec 15;45(20):6718-24. doi: 10.1016/j.watres.2011.10.016. Epub 2011 Oct 20.
Several polyaluminum chloride (PACl) coagulants were prepared, with different OH/Al ratios (B values), and characterized by Ferron assay. These were used in studies of floc formation, breakage and re-growth with kaolin suspensions under controlled shear conditions, using a continuous optical monitoring method. Particular attention was paid to the effect of small additional coagulant dosages, added during the floc breakage period, on the re-growth of broken flocs. The results showed that the re-growth ability was greatly dependent on the nature of the PACl species added as second coagulant. The re-growth ability of broken flocs was greatest when the second coagulant was PACl(0) (i.e. AlCl(3), with B = 0) and least with PACl(25) (B = 2.5). In the latter case there was no effect on floc re-growth, irrespective of the initial coagulant used. PACls with intermediate B values gave some improvement in floc re-growth, but less than that with PACl(0). Additional dosage of PACl(0) gave re-grown flocs about the same size or even larger than those before breakage. The re-growth of broken flocs is significantly correlated with the species Al(a) (monomeric) and Al(b) (polymeric), as determined by Ferron assay. The amorphous hydroxide precipitate formed from PACl(0), (mainly Al(a)) can greatly improve the adhesion between broken flocs and give complete re-growth. However, for PACl(25), mostly composed of Al(b), the nature of the precipitate is different and there is no effect on floc re-growth.
几种聚合氯化铝（PACl）混凝剂被制备出来，具有不同的 OH/Al 比（B 值），并通过 Ferron 法进行了表征。这些混凝剂在受控剪切条件下用于高岭土悬浮液的絮体形成、破碎和再生长研究，使用连续光学监测方法。特别关注了在絮体破碎期间添加少量额外混凝剂量对破碎絮体再生长的影响。结果表明，再生长能力极大地取决于作为第二混凝剂添加的 PACl 种类的性质。当第二混凝剂是 PACl(0)（即 AlCl(3)，B = 0）时，破碎絮体的再生长能力最大，而当第二混凝剂是 PACl(25)（B = 2.5）时最小。在后一种情况下，无论初始混凝剂如何，对絮体再生长都没有影响。B 值中等的 PACls 对絮体再生长有一定的改善，但不如 PACl(0)。PACl(0)的额外剂量可使再生长的絮体大小相同或甚至更大。破碎絮体的再生长与 Ferron 法测定的物种 Al(a)（单体）和 Al(b)（聚合体）显著相关。PACl(0)（主要是 Al(a)）形成的无定形氢氧化物沉淀可以大大改善破碎絮体之间的附着力，并实现完全再生长。然而，对于 PACl(25)，主要由 Al(b)组成，沉淀物的性质不同，对絮体再生长没有影响。
