CONDITIONS OF COMBINED SEDIMENTATION OF SILICON AND HUMIC SUBSTANCES FROM NATURAL WATERS IN THE PRESENCE OF CAUSTIC MAGNESITE

Abstract

The relevance. Ground sources of drinking water supply in the West Siberian region are characterized by high content of iron ions, silicate ions and organic substances of humus origin. These impurities lead to formation of a stable colloidal system. When using water as a cooler and in heating systems, silicate deposits are formed on the surface of the pipes, due to the ability of silicic acid to form insoluble compounds with calcium and magnesium cations, as well as with aluminum, iron and sodium cations. The combined presence of silicates and organic impurities reduces the effectiveness of existing water purification technologies. The aim of the research is to study the conditions of formation of silicon compounds with humic substances and the kinetics of interaction with caustic magnesite. Objects of research are natural waters and model solutions containing silicon compounds and dissolved humic substances, natural caustic magnesite. Methods: photocolorimeter, pH-meter, titrometry, inductively coupled plasma atomic emission spectrometry (ICAP-6000). Results. The authors have established the concentration ratio of silicate ions/humic substances in which colloidal particles are formed at concentrations of silicate ions 20 mg/L and humic substances 80 mg/L at pH=5…9. The size of the resulting colloidal particles is 200 nm, and the value of ζ-potential is –38 mV. It is shown that in the range of рН values from 7,0 to 10 the colloidal compounds are stable. When using caustic magnesite as a precipitant reagent, the interaction in the «silicate–humic substances» system proceeds in two stages, which determine the technological feasibility of simultaneous removal of silicates and humic substances from water.

Keywords

• natural water
• silicon compounds
• organic-mineral substances
• particle size
• water purification
• caustic magnesite