Study on the aluminum species and coagulation efficiency of high concentration PASC in diluted solutions

High-concentration (about 2.0mol-1) flocculants -polyaluminum silicate chloride (PASC) with different Si/Al mole ratio γ (Si/Al) and polyaluminum chloride (PAC) were prepared using NaAlO_2 as basification agent. The chemical species distributions of PASC and PAC were compared, which were determined by Al-Ferron complexation timed spectrophotometric and 27Al-NMR methods respectively. Jar-test was applied to evaluate the coaguation efficiencies. The experimental results show that the species distribution and transformation of PASC are different from those of PAC, due to the interaction of polysilicic acid and hydrolyzed aluminum species. The Al_ 13/Al_b and Al_ other/Al_s concentration decreased while the monomer species Al mono/Al_a concentration increased with the increasing of γ (Si/Al). The result of the jar-test shows high concentration PASC, which has great advantage in water treatment owing to its low dosage, high coagulation efficiency and wide pH value adaptation. However, it is not appropriate to express coagulation efficiency of PASC and PAC using Al_ 13/ Al_b concentration.