The Flocculation Performance Of Polyaluminium Chloride Prepared By Forced Hydrolysis And Spontaneous Hydrolysis

Flocculant plays a important role in the flocculation process, polyaluminum chloride is one of the widely used inorganic flocculant. Polyaluminum chloride is obtained by forced hydrolysis method and spontaneous hydrolysis method. The main products by forced hydrolysis method are K-Al13 and Al30 with core structure of AlO4. while the structures of P-Al13 which is the products by spontaneous hydrolysis is based on AlO6 without AlO4. It has been widely used in the process of flocculation for solution containing K-Al13. The application of Al30 solution is rarely, while, P-Al13 is not applied. The flocculation performance of K-Al13, Al30, and P-Al13 are studied comparatively in this thesis.Firstly, the preparation conditions of forced hydrolysis products of PAC, K-Al13 and Al30 were explored by slow base injection into A1C13 aqueous followed by SO4-/Ba2+ displacement method. It was founded that the product was either S-K-Al13 or Na-K-Al13 as the preparation conditions were different. So the preparation details of Na-K-Al13 were as followed:C(NaOH)=0.25mol/L, C(AlCl3)=0.25mol/L, T(reaction temp.)=80℃, V(dropwise)= 0.33mL/min,B=2.4, t(aging)=1h, C(Na2SO4)=0.50mol/L.Also, preparation conditions of high content of Al30 solution were explored and confirmedas followed:C(NaOH)=0.25mol/L, C(AlCl3)=0.25mol/L, T(reaction temp.)=80℃, V(dropwise)= 0.33mL/min, B=2.4, t(aging)=48h(T(aging temp.)=95 C), C(Na2SO4)=0.50mol/LP-Al13 was obtained under the guidance of the 25℃ phase diagram of AICl3-Al2O3-H2O. A certain amount of aluminium powder, concentrated hydrochloric acid and distilled water can conduct spontaneous hydrolysis polymerization reaction to get to a certain degree of alkalization. Theobtained solution was evaporated to gain the product crystallization at room temperature. The products were washed with anhydrous ethanol, and then dried, the P-Al13 solid was acquired with 95% content of P-A113.Coagulation contrastive experiments of the high Al13 content PAC solution, pure K-Al13 solution, high Al30 content solution, pure P-Al13 solution and solid were carried when the pH values of the water samples were 6.5,7.5 and 8.5. Coagulation performances indicated that flocculation effect of P-Al13 solid was better than PAC, K-Al13 and Al30. Flocculation mechanismof P-Al13 is mostly owing to adsorption bridging and sweep flocculation. Adsorption bridging and electric neutralization is given priority with Al13 solution, adsorption electrical neutralization and adsorption bridging and sweep flocculation work together with Al30 solution.Finally, a kind of crystal was obtained in the process of preparation of Al30, and its structure was analysed though a single-crystal X-ray diffraction method. The results show that the crystal structure is Al31, with two (AlO6)0.5 connectted to the four local alkalization degree of the uneven aluminum nuclear of Al30.