hallo Peter! I hope you're going well.
I have seen your question about polyaluminum chlorohydrate and I got interested immediately, since i find the topic really complicated. I worked sometimes with flocculant, but I learnt just a few: Al has high charge density, given is +3 oxidation state, and can interact with other negatively charged particles (organics?), stabilizing the medium. Indeed Al3+ is the real flocculant agent (like Fe3+); Unfortunately, at pH = 9.5 it is slightly soluble and so you add Al in your final reject. Today there are some polymers employed as flocculant agent.
I also would like to thank you Mr Hamada, since he was so kind to give us some interesting papers!!!