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An Efficient and Regenerable Quaternary Starch for Removal of Nitrate from Aqueous Solutions
- Chauhan, Kalpana, Kaur, Jasvinder, Singh, Prem, Sharma, Poonam, Sharma, Praveen, Chauhan, Ghanshyam
- Industrial & Engineering Chemistry Research 2016 v.55 no.9 pp. 2507-2519
- adsorption, anions, aqueous solutions, bicarbonates, carbohydrate structure, chlorides, correlation, derivatization, engineering, equations, ion exchange capacity, models, nitrates, pH, phosphates, quaternary ammonium compounds, sorption isotherms, starch, sulfates, thermodynamics
- This paper presents a study of NO₃– ions sorption from an aqueous solution using quaternary starch derivatives. For this, the derivatization was carried out by an improvised method for the synthesis of a gemini-like structure, which is unique and has two quaternary ammonium functionality per anhydroglucose units of starch. Mohr’s method was used to characterize the synthesized bis-quaternary starch as chloride ion content, and the results supported a chloride content of 13.5–14.4% with the total ion exchange capacity of 3.8–4.2 mequiv/g. A series of batch experiments were conducted to examine the effects of structure, contact time, concentration, pH, and effect of co-ions on the sorption of NO₃–. The results showed an increase in sorption capacity with an increase in the concentration of NO₃–, while the presence of competing anions such as PO₄³–, HCO₃–, and SO₄²– showed marginal effect on the NO₃– sorption capacity. The increase in pH from 4.0 to 6.5 also effected the NO₃– sorption process marginally. Moreover, the quaternary starch exhibited 78.5% efficiency even after the eighth sorption–desorption cycle. The kinetic and thermodynamic adsorptions of NO₃– ions from the aqueous solutions were also investigated for the synthesized quaternary starch derivative. The adsorption kinetics data were best described by the pseudo-second-order rate equation. The equilibrium data agreed well with the Langmuir model. The maximum capacity for quaternary starch can be deduced from the obtained correlation coefficients and was calculated at ≈205 mg/g in the isotherm model, which is preferential to the earlier reported commercialized Purolite technology. In conclusion, the bis-quaternary starch structure is successfully synthesized in uniform and high modification and shows significant potential for removal of NO₃– ions from aqueous solution.