The Preparation And Crystal Structure Of Al₄(OH)₆(H₂O)₁₂Br₆·2Al(H₂O)₈Br₃, Morphological Analysis And Flocculation Of PAC Mother Solution

So far, in many complex forms of aluminum hydroxide molecules, only 6-7 forms of the crystal structures have been got through the crystal diffraction method. Therefore, trying to get more structure of aluminum hydroxide molecules has vital significance. Besides chloride and nitrates of M-Al13 with good solubility,pure aluminum hydroxide molecules powder is insoluble in water in our products.This insolubleness restricts the studies of the relationship between contrast and structure-activity of single form, so, we convert PAC systerm into a polyaluminum bromides system.In this thesis, the alkalization of bromide is controlled by aluminum powder, prompting aluminum bromide constantly hydrolysis and polymerization. Under conditions of raw material ratio, reaction temperature and crystallization, we have obtained single crystal of Al4(OH)6(H2O)12Br6-2Al(H2O)8Br3 and the crystal structure of it has been determined.The special structure shows that it's different from either Keggin style such asε-K-Al13,δ-K-Al13 and Al30 or so-called"flat"structure such as M-Al13 and Al8,it has a unique structure with 4 corner-sharing octahedron consisting of a bigger tetrahedron and a Al monomer surrounded by eight spliting water.This unique connection of the octahedron,the coordination of the Al monomer and the two exsiting in the same latice has the essential significance for deeping knowledges of formation transformation of the poly-aluminum forms and even for the laws of the migration and trasformation of aluminium in the living organisms and the Earth's environment.Flocculation performance of Al4(OH)6(H2O)12Br6-2Al(H2O)8Br3 was evaluated using Kaolin suspending solution as simulated water sample,for the good solubility of it.The results showed that Al4(OH)6(H2O)12Br6·2Al(H2O)8Br3 possessed flocculating property under weak acidic, neutral or alkaline conditions. Particularly, its flocculation performance under alkaline and neutral conditions was excellent.But its overall flocculation effect is next to the performance of M-Al13.The reason may be that there are a number of monomer [Al(H2O)8]3+in the structure of Al4(OH)6(H2O)12Br6·2Al(H2O)8Br3,and the charge number of [A14(OH)6(H2O)12]6+is smaller,the charge neutralization is weaker,and the molecular weight is smaller than M Al13,so that the bridging ability is weaker and the floculation performance is second to M-Al13.In the paper, we also investigated the flocculation performance of some of the PAC products with the corresponding mother liquids before they precipitated products instead of those insoluble ones. In adiition,the Chrome Azurol S method for the trace Al was improved. The stability and reproducibility of the method was enhanced so that it could be used for the determination of residual aluminum of the water sample after flocculation.