XRD investigations of the structure changes of natural zeolite as a result of the heavy metals sorption

Abstract

Based on researches using an X-ray powder diffraction using the Rietveld method it was found that
zeolite tuff of Yagodninsky deposit consists of clinoptilolite – Na (23.0%), clinoptilolite – Ca (52.1%) and
mordenite (12.9%). As a result of heavy metal sorption the parameters of crystal mordenite grid changed, the
sizes in the direction of a and b axis decreased and the volume of elementary unit cell of processed zeolite in
comparison with original one in a row: Сu→Ni→Co→Fe decreased. Value of exchange capacity on nickel,
cobalt, copper and ferrum when processing zeolites with individual solutions as well as its mixture was calculated.
Value of exchange capacity changes from 9 to 18 mg-eqv/kg depending on the solution composition. In all cases there was an amount exceedance of substance of displaced cations over the amount of substance
of absorbed cations. When zeolite is saturated with cobalt the exchange cations are displaced more then 5%;
when zeolite is saturated with copper or ferrum – 11.9-12.0%, respectively. Maximum amount exceedance of
displaced cations substance over the amount absorbed cations substance is observed when zeolite saturating with nickel – to 25%. The authors note that solvent – water is involved in exchange reaction along with heavy metals, it is confirmed by pH change of eluate by 1-2 units. On the basis of comparison of substance amount of absorbed cations with substance amount of displaced cations, it was determined that the mechanism of ions exchange is predominant