Synthesis of Fe-containing aluminosilicate materials based on montmorillonite and an assessment of their sorption properties

Abstract

The article describes the results of the synthesis of Fe-containing aluminosilicate materials and a study of their physico-chemical and adsorption properties. The importance of the study is explained by the need to develop alternative effective sorbents based on inexpensive raw materials, which could replace expensive activated carbons and polymeric sorbents currently used for the purification of wastewater from anionic pollutants. Of all metal oxide sorbents the most interesting are iron oxides and hydroxides. They are quite common and therefore easily accessible, cheap, and environmentally friendly. Sorption capacity can be increased by immobilizing the particles of iron oxides on finely dispersed carriers, which results in a decrease in the size of the sorption-active oxide particles and an increase in their surface area. To synthesise Fe-containing aluminosilicate materials (Fe-AM) we used montmorillonite clay from the Tuldon deposit (Republic of Buryatia) as a carrier. A solution of the trinuclear acetate iron complex [Fe₃O(CH₃COO)₆(H₂O)₃]NO₃ (FeAc) was used for the deposition of iron. The FeAc solution was added to an aqueous suspension of clay and kept at room temperature for 3 hours. Then the solid phase was separated by centrifugation. The obtained materials were dried at room temperature and heat treated at 500^оС for 2 hours. The properties of the samples were studied using chemical analysis, the low-temperature adsorption of nitrogen method, IR spectroscopy, and XRD. The DSC method demonstrated that when heated, the FeAc complex disintegrates, resulting in the formation of a hematite, which is confirmed by the XRD data. We also studied the effect of the synthesis conditions on the physico-chemical properties of the obtained materials. The ultrasonic treatment of clay during the analysis allowed us to obtain materials with increased concentrations of iron and a larger specific surface area. Materials obtained with a Fe/clay ratio in the modifying solution of less than 18 mmol/g were characterised by larger specific surface areas as compared to the initial clay. The adsorption properties were studied in an aqueous solution of anionic dyes Acid Yellow 36 (AY) and Direct Blue, which can be found in large concentrations in wastewater from textile enterprises. The study demonstrated that Fe-containing aluminosilicate materials are more effective for the adsorption of the AY dye (up to 265 mg/g with initial concentrations of the dye in the range of 25-600 mg/dm³). They were determined to have greater adsorption capacity for the AY anionic dye as compared to some activated carbons and remain effective during the three adsorption-desorption cycles of the dye. The synthesised materials can be of great interest as cheap regenerable sorbents for anionic pollutants in wastewater.