Study of buckwheat husk application for water demineralisation

Abstract

In the present paper, a brief review of the scientific literature on the main research directions in the field of sorption filters used for water demineralisation is presented. Materials used for these purposes, both of mineral and organic origin, are considered. Various natural materials, including waste products from wood processing and agriculture, are promising raw materials for the production of sorbents. Since these materials are typically characterised by low sorption ability in their raw form, additional activation processes are required. In this connection, research was conducted by the authors on the sorption of hardness salts (calcium and magnesium) from aqueous solutions in static conditions using raw and chemically modified buckwheat husk in a concentration range from 2 to 40 mEq/dm 3 . Hydrochloric and phosphoric acids, as well as sodium hydroxide, were used as modifiers. A study of the sorption kinetics demonstrated that the system achieves equilibrium within 5 min from the start of sorption. Additionally, the possibility of maximum demineralisation of aqueous solutions was studied. The best sorption properties with respect to hardness salts were demonstrated by buckwheat husks modified by sodium hydroxide, which had a maximum sorption capacity of 2.4 mEq/dm 3 as compared to 2.0 mEq/dm 3 for raw husks. For all types of obtained materials, mineral sorption isotherms were constructed in the range of studied concentrations. These isotherms were established to be of S4 type according to the Giles classification. Mathematical processing was carried out according to the sorption models of Langmuir, Freundlich, BET and Dubinin-Radushkevich. The sorption process for calcium and magnesium cations was revealed to be most accurately described by the Freundlich equation.