The pollution with nitrate/nitrite ions is a serious problem for Moldova and many
countries, especially with the developed agro-industrial complex. Excess of these ions in water
and food is dangerous for the human and animal species health. Removal of nitrate/nitrite ions
from liquids is a very actual problem. Nitrate ions are removed either by physicochemical or
biological methods. The nitrate and nitrite ions are reduced by hydrogen on catalysts (noble
metal palladium or palladium activated with copper). The products of the reaction are gaseous
nitrogen and dissolved ammonia, which is undesired in drinking water. Anion exchangers,
especially strongly basic anion exchangers, for nitrate and nitrite ions removal from water have
been used. Sorption of anions, including NO3
- or NO2
-, on strongly basic anion exchangers is not
selective because is conditioned by Coulomb’s (electrostatic) interactions and the modern
technologies of purification of various categories of fluids and gazes, concentration and
separation of substances require new selective sorbents.
In our investigation the commercial strongly basic anion exchanger AV-17 (containing
_N(CH3)3Cl groups has been used. The gel-type resin had a polystyrene-divinylbenzene matrix
and full exchange capacity 3.4-4.0 mequiv/g [1]. Before the sorption investigation the polymer
was modified with Cr(III)-containing compounds according to reference [2]. For investigation
polymer AV-17 containing 35.46 mg Cr/g was used. Continuous flow adsorption studies were
conducted in a column taking into consideration the previous investigation of nitrite ions
sorption by Cr(III)-containing polymer [3]. The column contained 3 layers - the first layer (upper
layer) consisted of granulated metallic Cd, second layer consisted of Cr-jarosite containing AV-
17 and third layer consisted of carboxylic cation exchanger (Purolite C-104) in Na-form. In the
first layer transformation of nitrate ions into nitrite takes place. In the second layer nitrite ions
were selective captured by Cr-jarosite containing AV-17. Carboxylic exchanger was used for the
selective sorption of Cd2+ cations (and Cr3+ ions that could possibly come out of the polymer
phase). Our investigation was carried out using response surface methodology. The influencing
factors were concentration of NaNO3, KCl, K2SO4, NaHCO3 and filtration peed.
There were measured and calculated the following responses of the system: dynamic
sorption capacity, (value of sorption until the appearance of the nitrate/nitrite ions into filtrate),
mg NO3
-/ g, total dynamic sorption capacity (sorption value when sorbent was saturated), mg
NO3
-/ g and relative rate of sorption. The obtained results were used for calculation of the
coefficients of the regression equations.
The investigation showed that strongly basic anion exchangers modified with Cr(III)-
containing compounds can be successfully used in selective removing of nitrate ions from liquids
after their reduction with metallic Cd.
References:
[1] Lurie, A. A. Sorbents and Chromatographic Carriers. Nauka, Moscow, 1972.
[2] Gutsanu, V.; Drutsa, R. Patent MD 1027. BOPI. 1998, 9. 23
[3] Gutsanu, Vasile; Tutovan, Elena; Cotsofana, Ludmila; Bulicanu, Vladimir. In: Ion. Exch..
Lett. 2012, 5, 6-12.