The Separation And Purification Of Al₁₃ From Polyaluminum Chloride(PAC) And Its Properties

Based on the previous researches on Al₁₃ species, the more efficient methods for separation and purification of it from PAC are explored in this paper. Meanwhile, its distribution features, speciation stability, coagulation properties and coagulation mechanisms are described: The main research and conclusions are as follows:1. The polynuclear Keggin species, Al₁₂A1O₄(OH)₂₄ (H₂O) ₁₂⁷⁺(Al₁₃), was firstly separated and purified from PAC by the ultra-filtration and column chromatography method. The obtained Aln was characterized by Al-Ferron timed complexation spectrophotometry, ²⁷Al—NMR,TEM and ZATESIZER 3000HSA.The result showed that the purified sample by the ultra-filtration method was influenced by membrane pore radius and the concentration of PAC solution, high purity Al₁₃ would be obtained by choosing appropriate membrane and concentration of PAC. When using the column chromatography method, the bigger molecules were eluted first, then the smaller. Al₁₃ would be obtained by taking out the middle educt and the content of it could reach about 100%. The TEM and ZATESIZER 3000HSA results showed that Al₁₃ were mainly aggregated as line type and branch type in B=2.4 solution, and the size about it was about several decade and several hundred nm.2. The Al₁₃ species were separated and purified with column chromatography method, precipitation with adding ethanol method and acetone, and SO₄^2-/Ba²⁺ displacement method from a series of PAC solutions. The Al₁₃ species yielded were compared. Coagulation efficiency was tested by Jar tests for Aln, PAC and AlCl₃ in treating synthetic water samples. The results indicated that, gel column chromatographic method gave the highest efficiency compared to the other three methods, and the Al₁₃ species obtained by this method gave the best results for turbidity removal.3. Effects of different experimental conditions such as eluent flow rate, ionic strength, pH and B value on separation of Alu were investigated in gel-filtration chromatography method. Experimental results indicated'that molecule size exclusion was not the only parameter affecting the column chromatographic separation efficiency of AI13 but molecule charge as well. Reducing the eluent flow rate, increasing the ionic strength and suitable pH resulted in increasing the separation efficiency. Experimental results clearly indicated that by the varying experimental conditions, it is possible to produce high purity AI13 species (contain 100% Alb species) using a gel column chromatographic technique.4. The effect of various factors, such as the dilution, pH and aging, on the speciation transformation of Al|3 species, PAC and AICI3 was investigated. The experimental results showed that the most unstable species was Ala. Since the AICI3 carried a large amount of Ala, as the solution conditions changed, its species changed significantly. While the AI13 species was very stable for the extensive water qualities. Additionally, the results showed that there was great difference of the Alb species between the formation under pre-produced and the formation after it was dosed into water. The most probably reason was that they had different chemical constitution.5. Under different pH and concentration, the coagulation-flocculation behavior of All3 species, PAC and AICI3 was investigated by the use of photometric dispersion analyzer (PDA), the floe formation and re-aggregation potential and the effects of sulfate on coagulation were also studied. Jar tests were performed to test the coagulation efficiency of AI13 species, PAC and AICI3 in treating synthetic or actual water samples. It deeply confirmed that AI13, PAC and AICI3 had different speciation transformation under various solution conditions in the coagulation process because of their different speciation distribution. The floe recovery capacity for the AI13 after shearing was greatest which is likely a result of increased collision efficiency due to more effective charge neutralization capacity. The experimental results also showed that sulfate had a significant effect on coagulation. Sulfate promoted aggregation of hydrolyzed species for the AI13 species, causing significantly improved coagulationefficiency through an electrostatic patch effect. Compared with PAC and A1C13, AI13 gave the best results for turbidity, humic acid and color removal, and achieves the highest charge-neutralizing ability. AI13 species was a higher positive-charged and fitted for wide pH range application., it was much more steady in hydrolyzing process and the most effective polymeric Al species in water and wastewater treatment.