| The hydrolyzed solution of aluminum salt is a complex system.Many questions remain a mystery,such as how does the aluminum monomer evolve into aluminum hydroxide step by step,how many polyaluminum species were produced during the evolution,what kinds of evolution processes were experienced and so on.The structures and their evolution laws of those polyaluminum species produced from the hydrolyzed solution of aluminum salt is not only the theoretical support for understanding the action mechanism of aluminum series flocculants and synthesizing the high efficiency coagulants,but also the theoretical basis for solving the environmental problems such as migration and transformation of aluminum,prevention and treatment of aluminum pollution,in earth ecology.Thus it inevitably become the most effective way to solve the problem that synthesize more pure polyaluminum compounds and solve their structures.In order to isolate more polyaluminum compounds from the very complex hydrolyzed solution,after years of exploration and innovation,a control theory was found which was regarded as the most effective way by ourselves so far,i.e.the solid-liquid equilibrium phase diagram.Therefore,in this paper,a solid-liquid equilibrium phase diagram of AlBr3-Al2O3-H2O ternary system at 50 ? was successfully draw by using the wet slag method.There are three spontaneous hydrolysates in this phase diagram except for the starting material,AlBr3·6H20,and the final product,Al(OH)3,of the hydrolysis reaction,they areAl6(OH)6Br12·24H2O,Al(OH)2Br·2H20 andAl5(OH)12Br3·6H2O.Thus,anyone existed in this phase diagram can be isolated as a pure compound through designing a reasonable crystallization path according to the phase diagram.In order to obtain well-crystallized polyaluminum compounds,it is also possible to improve the crystallization properties of the product by changing the anionic species.In this paper,we first prepared the polyaluminum stock solution basing on the phase diagram,and after the addition of 2,6-naphthalene disulfonate(2,6-NDS),two novel polyaluminum compounds were obtained,and the results of structural analysis show that their structural formulas are[Al30O8(OH)56(H2O)26](NDS)8Cl2·37H2O and[Al30O8(OH)60(H2O)23](NDS)6Br2·56H2O,respectively.The structure of the polycation in the former is similar as the Al30 species reported in the literatures,but because of the difference in preparation methods,its unit cell parameters and the number of water molecules filled in the cell are different,so it is a new polyaluminum compound with different crystalline form.The structure of the polycation in the latter can be regarded as the result after two pair of H20 molecules coordinated for the two pair of neighbor Al nuclei(in which their local basification degrees are the most unbalanced on the symmetry)in the two sides of the Al30 were replaced by two hemihydrated di-hydroxyls(OH--(H2O)0.5-OH-),it's firstly discovered that H2O molecule was associated on an Al30 species,and the positions where the two semi-water molecules associated to are also the positions where the two quarter-aluminum nuclei,the two semi-aluminum nuclei and the two aluminum nuclei combined to in Al30.5,Al31 and Al32,respectively.It may be speculated that the H20-associated Al30 is probably the precursor of Al30.5 in the evolution process of Al30?Al30.5?Al31?Al32.The discovery of this novel construction manner not only proves that the local basification.degree symmetrical equalization principle can correctly predict the active sites in further hydrolyzing reaction,but also enriches the construction manners of polyaluminum species,and provides a new evidence for the further improvement of the formation and evolution mechanism of polyaluminum species.In addition,in this paper an improved new gravimetric method was achieved to determine the aluminum content in polyaluminum compounds,especially for those samples who are difficult for depolymerizing. |
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