Abstract:
The physicochemical and adsorption properties of granular sorbents based on
natural bentonite and modified sorbents based on it have been studied. It was found
that modification of natural bentonite with iron (III) polyhydroxocations (mod. 1_Fe_5
GA) and aluminum (III) (mod. 1_Al_5 GA) by the “co-precipitation” method leads to
a change in their chemical composition, structure, and sorption properties. It is shown
that modified sorbents based on natural bentonite are finely porous (nanostructured)
objects with a predominance of pores measuring 1.5–8.0 nm, with a specific surface area of
55–65 m2/g. Modification of bentonite with iron (III) and aluminum compounds by the
“co-precipitation” method also leads to an increase in the sorption capacity of the obtained
sorbents with respect to bichromate and arsenate anions and nickel cations by 5–10 times
compared with natural bentonite. The obtained sorption isotherms were classified as
Langmuir type isotherms. Kinetic analysis showed that at the initial stage the sorption
process is controlled by an external diffusion factor, i.e. refers to the diffusion of sorbent
from solution into a liquid film on the surface of the sorbent. Then the sorption process
begins to proceed in a mixed diffusion mode, when it limits both the external diffusion
factor and the internal diffusion factor (the diffusion of the sorbent to the active centers
through the system of pores and capillaries). To determine the contribution of the chemical
stage to the rate of adsorption of bichromate and arsenate anions and nickel(II) cations
with the studied granular sorbents, kinetic curves were processed using the equations
of chemical kinetics (pseudo-second-order model). As a result, it was found that the
adsorption of the studied anions by modified sorbents based on natural bentonite is best
described by a pseudo-second-order kinetic model. It is shown that the use of natural
bentonite for the development of technology for the production of granular sorbents based
on it has an undeniable advantage, firstly, in terms of its chemical and structural properties, it is easily and effectively modified, and secondly, having astringent properties, granules
are easily made on its basis, which turn into ceramics during high-temperature firing. The
result is a granular sorbent with high physical and mechanical properties. Since bentonite
is an environmentally friendly product, the technology of recycling spent sorbents is also
greatly simplified.
