Development of a method for obtaining sorbent from bagasse of sweet sorghum for neutralization of soil contamination by heavy metal ions

Abstract

The object of research is the industrial waste of plant raw materials of sweet sorghum (lignocellulosic bagasse) and a modified sorbent created on its basis for cleaning soils contaminated with heavy metal ions. Traditionally, the modification of plant materials to obtain sorbents involves the oxidation (hydrolysis) of plant material under the action of strong mineral acids at high temperature. After acid treatment, alkaline activation and repeated washing of the sorbent is carried out until neutral wash water. The yield of the sorbent is 20–30 % by weight of raw materials. In addition, a significant amount of decomposition products and large volumes of hazardous wastewater are generated. Therefore in the course of the study, a mercerization method was used to obtain a sorbent – treating lignocellulosic bagasse with an alkali solution. The main components of lignocellulosic bagasse are lignin and cellulose, connected in biopolymer complexes. In their raw form, they have weak sorption properties through the fibrillary structure and low content of free functional groups in them. Under the conditions of the mercerization process, the molecular bonds between the fibers of the biopolymers are partially destroyed and the solution of low molecular weight polysaccharides is dissolved. The structural framework of the lignocellulosic matrix is preserved, and its ability to swell is growing. Integrity is preserved, vegetable fibers improve their structural-porous structure by increasing the internal adsorption surface. The optimal conditions for the mercerization process are a hydro module of 1:10 with an initial alkali concentration of 120 g/l. The maximum sorption values of heavy metal ions increase by a factor of 2–3. The sorbent yield reaches 60–80 %. In addition, the advantage of this method is the absence of harmful wastewater. The developed method can be used for processing waste and other plant materials (corn, sunflower, sugar cane, etc.), and the resulting sorbent is used in agricultural technologies for neutralization of soils contaminated with heavy metal ions.