Naslov
Bisulfite-catalyzed Borohydride Reduction of Selected Azo Dyes

Autori
Koprivanac, Natalija ; Papić, Sanja ; Vujević, Dinko, Lončarić Božić, Ana ; Malojčić, Rajko

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Cholorchem 2000 / Nečas Miroslav - Pardubice : Research Institute for Organic Syntheses, 2000

Skup
8th Ba-annual International Conference on Dyes and Pigments

Mjesto i datum
Špindlerův Mlýn, Češka Republika, 14.05.2000. - 18.05.2000

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
azo dyes; reduction; wastewater decolorization

Sažetak
Water-soluble dyes and closely related by-products containing azo groups can be chemically reduced by different agents. Sodium borohydride, one of the strongest water-soluble reducing agent has not been extensively employed in dye reductions due to its rapid reaction with water and its tendency to reduce via hydride transfer mechanistic pathway. These deficiencies have been overcome by using an effective level of bisulfite in conjunction with borohydride [1,2]. In this paper, we studied the bisulfite-catalyzed borohydride reductions of selected azo dyes. The aim of our research is to apply this reduction process in dye wastewater decolorization. Experimental The six different azo dyes were used in this experiments (Direct Orange 39, Mordant Yellow 10, Acid Orange 7, Reactive Red 45, Stilben Yellow 3GX and Reactive Blue 137). Certain amount of sodium bisulfite (0,005-0,200 g) was added in 100 ml of dye solution (1 g/l). 1,2 % sodium borohydride solution was prepared by dilution of commercial solution containing 12 % NaBH4 and 40 % NaOH. After pH adjustment to 5-6, borohydride solution (0,25-5,00 ml) was added and stirring was continued for 15 minutes at ambient temperature. Obtained quality of treated water was estimated on the basis of determined ecological parameters. The reduction products , corresponding aromatic amines, were removed by commercial cationic flocculant Levafloc R. The reduction process efficiency was evaluated on the basis of spectrophotometric measurements. Results and Discussion The influence of the Na2S2O5/NaBH4 ratio at pH 5-6, ambient temperature and constant duration of mixing on the reduction of various mono- and diazo dyes was determined. Using this process, complete decolorization was possible in all cases. It was shown that bisulfite dramatically improves the efficiency of sodium borohydride in dye reduction. Effect of borohydride concentration on reduction of Mordant Yellow 10 at certain amounts of bisulfite is shown in Table 1. Complete decolorization of 100 ml dye solution was obtained with 0,020 g of bisulfite followed by addition of 2,00 ml of 1,2 % caustic solution of sodium borohydride. Amounts of bisulfite need for complete reduction with borohydride are approximately similar for all dyes used in experiments. Bisulfite could readily be air oxidized to sulfate. Therefore, it is important to use a minimal necessary amount of bisulfite in borohydride reduction process when applied in dye wastewater decolorization in order to avoid additional pollution with sulfate. This treatment technology could be flexible enough to accommodate differences in characteristics of wastewater containing various azo dyes. TABLE 1 Bisulfite-Catalyzed Borohydride Reduction of Mordant Yellow 10* % Reduction ml NaBH4 withoutNa2S2O5 0,005 gNa2S2O5 0,010 gNa2S2O5 0,020 gNa2S2O5 0,050 gNa2S2O5 0,100 gNa2S2O5 0,200 gNa2S2O5 0,25 4,39 27,23 39,39 88,56 88,83 65,99 92,57 0,50 8,10 - 50,29 90,08 89,08 99,98 96,38 1,00 5,72 28,10 69,79 92,08 99,99 99,99 94,97 2,00 7,93 - 86,66 99,98 99,98 99,99 96,55 3,00 13,35 54,99 - 99,99 - - 96,15 4,00 13,40 - 88,54 - - - 95,88 5,00 14,39 40,40 89,08 - - - 95,88 *Mordant Yellow 10, C.I. 14 010 (c0=1 g/l, V=100 ml) Besides color removal, the values of ecological parameters (Table 2) have not been changed after dye reduction. To improve water quality it is important to remove reduction products. TABLE 2 The values of ecological parameters determined in solution of Mordant Yellow 10: A, before reduction; B, after reduction and C, after removal of reduction products by cationic flocculant. Sample COD, mg/l BOD5, mg/l BOD5/COD TOC, mg/l IC50,vol % A 780 31,0 0,04 376 >62,5 B 600 21,8 0,04 376 >62,5 C 114 4,0 0,03 8 >75,0 Quality of water obtained after reduction followed by flocculation process is suitable for discharge to the sewage system. References [1] R.S. Stennick and M.M. Cook, Abstracts of Papers, 204th National Meeting of the American Chemical Society, Washington, 1992. [2] E.C. Chou, B.W. Wiegere, D.K.Huggins and E.I. Wiewiorowski, U.S. Pat. 4, 544,541, 1984.

Izvorni jezik
Engleski

Znanstvena područja
Kemijsko inženjerstvo

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