Influence of the monomer form of orthosilicic acid on the stability of polyalumosilicon coagulants and their efficiency in the treatment of drinking water

Abstract

The object of the study was polymeric alumino-silicon coagulants modified with the monomeric form of orthosilicate acid. The methods and precursors for obtaining stable solutions of composite alumino-silicon coagulants, as well as the effectiveness of coagulation treatment of a surface source of drinking water, were considered. The samples were obtained in two ways: 1) partial hydrolysis of medium-basic aluminum polyhydroxychloride together with sodium silicate solution (PolyAKKg); 2) mixing highly basic aluminum polyhydroxychloride together with a ready solution of orthosilicic acid with a high (above 50 %) monomer content (PolyAKKz). In the course of research, the problem of the short shelf life of composite alumino-silicon coagulants was solved, which had prevented their industrial implementation in drinking water preparation processes. It was established that the resulting composite coagulants had the following parameters: Al2O3, 8.075–8.725 %; SiO2, 0.058–0.725 %; Al/Si ratio, 20–250; basicity, 41.4–80.7 %. The effectiveness of the obtained composite coagulant and commercial coagulant was tested under laboratory conditions at a surface source of drinking water by reducing turbidity and by the concentration of residual aluminum in the water after coagulation. The results showed that composite coagulants of the PolyAKKz type with the addition of orthosilicic acid with a high monomer content (above 50 %) obtained using methanesulfonic acid hydrolysis as a precursor have higher solution stability compared to other precursors or coagulants of the PolyAKKg type. The study results could be used to design new composite coagulants for the preparation of drinking water from surface sources with high turbidity