Obtaining of iron-containing silicate composites for contaminated water purification from arsenic compounds

Abstract

The object of research is palygorskite – a natural clay mineral with a layered ribbon structure. It is characterized by high specific surface area, secondary porosity and sorption capacity for metal cations. However, due to the negative charge of the surface, palygorskite is inefficient when cleaning water from pollution that is in anionic form, in particular, from arsenic compounds. A significant drawback of the use of dispersed aluminosilicates as sorbents is the difficulty of their separation from the liquid phase after the process of sorption purification. Therefore, to increase the sorption properties of palygorskite by pollutants in the water in the form of anions, the authors used the method of modifying its surface with iron-containing compounds, including treating the prepared palygorskite with iron salts (III) in a weakly alkaline medium. Physical and chemical methods are used to study the structure of modified and initial samples of palygorskite, in particular, the method of infrared spectroscopy (IR spectroscopy) and the method of low-temperature nitrogen adsorption-desorption. The results indicate that the surface of the palygorskite is coated with iron compounds (III), which led to an increase in the specific surface area from 213 m 2 /g to 275 m 2 /g and a pore size from 1.9 nm to 2.25 nm. The obtained samples differ from the original mineral by increased sorption capacity with respect to arsenic compounds (V). The maximum sorption of arsenic by the modified sample is 7.8 mg / g, which is significantly higher than that for natural palygorskite – 0.2 mg/g. It has been shown that arsenic is removed by iron-containing silicate rather quickly and does not depend on the pH value of the aqueous medium in the range 3 – 8. This is due to the fact that when processing the surface of palygorskite by iron oxyhydroxides the latter acquires an increased reactivity by increasing the number of active sorption centers.