Chemija / Chemistry
 ISSN 0235-7216 ISSN 2424-4538 (online) |
2016 m. Nr. 2 Removal of aqueous cyanide from alkaline solutions using a weak base anion exchanger in comparison with a strong base anion exchanger
The gel weak base anion exchanger Purolite A847 has been proofed and compared with the macroporous strong base anion exchanger Purolite A500PS as a suitable adsorbent for the simultaneous removal of free cyanide and Ag-CN complex from an alkaline aqueous mixture under batch and fixed bed conditions. The determined capacities of Purolite A847 are apparently lower than those of Purolite A500PS and depend on the concentration of free cyanide in a solution: at higher concentrations of free cyanide the total capacity of an anion exchanger is lower. The experimental adsorption data obtained in batch were interpreted in terms of the pseudo-second-order reaction rate (qe, initial sorption rate h, rate constant k2) and intraparticle diffusion kinetic models. The values of qe, h and k2 for free cyanide on Purolite A847 were lower than those of the Ag-CN complex. Sorption of free cyanide and the Ag-CN complex from the alkaline mixture on Purolite A847 corresponds to the general selectivity order for weak base anion exchangers. Column dynamic behaviour peculiarities were studied with the selected breakthrough concentration in an effluent of 0.1 mg/L of silver or free cyanide. The experimental data were analyzed using the Yoon and Nelson empirical model parameters (rate constant K, time required for 50% breakthrough τ, removal capacity Q). The increase in free cyanide influent concentration parameters τAg(I) and QAg(I) for Ag-CN complex sorption on Purolite A847 decreases markedly when KAg(I) increases, while on Purolite A500PS τAg(I) and QAg(I) increase with slight changes in KAg(I). The regeneration of both the anion exchangers Purolite A847 and Purolite A500PS using 5% NaOH is sufficiently effective, with a higher recovered amount of free cyanide and a lower amount of the Ag-CN complex from Purolite A500PS.
: Keywords: sorption, anion exchanger, free cyanide, silver cyanide complex |
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