Obtaining granular adsorbents based on biopolymers and clay minerals

Abstract

The development of granular, low-cost adsorbents represents an important environmental challenge. Natural clay minerals show promise in this area, as they exhibit adsorption capacity a range of pollutants. Nevertheless, the high dispersion of aluminosilicates limits their widespread use. To enhance the processability of these materials, they are subjected to granulation using natural biopolymers, such as sodium alginates. Concurrently, the adsorption capacity of the granules can be increased by the application of modifiers to the surface of natural silicates, in particular iron oxyhydroxides, which are efficacious in the removal of heavy metals from water. The aim of this study is to obtain granular adsorbents based on saponite and biopolymer that are stable in water and capable of removing heavy metal ions from the water environment. The rheological behavior of the suspensions was investigated in order to ascertain the optimal conditions for high-quality granulation. The phase composition of the modified saponite was determined by X-ray diffraction analysis. The structural-sorption characteristics of the samples were investigated using the method of low-temperature nitrogen adsorption-desorption, and their thermal properties were studied by differential thermal and thermal gravimetric analyses. The present study demonstrates that the viscosity of saponite and sodium alginate-based suspensions with varying mass ratios is dependent on the clay mineral content of the mixture, at a fixed polymer quantity. The conditions for granulation were determined, and it was established that the stability of the granules in the aqueous medium is influenced by the quantity of sodium alginate incorporated into the mixture. It was established that the specific surface area of the modified sample decreases during the granulation process. This value is 109 m2/g, which is less than the 173 m2/g that observed for the powdered adsorbent. The processes and phase transformations occurring in granular materials during heating were studied. As a result of the study of the rheological characteristics of suspensions based on saponite and sodium alginate, it was found that these systems are thixotropic. It was also discovered that the stability of the granules in an aqueous medium is significantly affected by the amount of sodium alginate added to the suspension. The potential applications of the obtained adsorbents in the purification of water from heavy metal ion contamination are shown.