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TREATMENT OF COKE OVEN AND BLAST FURNACE EFFLUENTS TO INHIBIT FORMATION OF IRON-CYANIDE COMPLEXES Richard Prober, Associate Professor Peter B. Melnyk, Assistant Professor Lee A. Mansfield, Graduate Student Department of Chemical Engineering Case Western Reserve University Cleveland, Ohio 44106 INTRODUCTION Regulations concerning wastewater discharges of cyanides are under consideration in many areas. The more stringent proposals would require removal of total cyanides to residua] levels as low as 25 p.g/\. This lumping of iron-cyanide complexes together with the other much more toxic forms would have particularly significant implications for the iron and steel industry. Effluents from blast furnace gas washing and various coking wastewaters contain significant amounts of cyanides, both free and complexed, and iron. Ferricyanide and ferrocyanide are refractory species which would require new and potentially costly treatment methods, such as ozonation or ultraviolet irradiation for effective removal. An alternate approach may be preferable; for example, control of discharges of iron- cyanide complexes, or inhibition of the chemical reactions that form them. Free cyanide could then be removed by conventional treatments. This is a reaction engineering problem which involves specification of temperatures, pH values, concentrations and reactor configuration to minimize formation of the complexes for anticipated reaction times on the order of 1 hr. Previous studies of the reactions of interest by Southgate [1], Grieves, et al. [2,3] and Battelle Memorial Institute [4], provide data on conversion of free cyanide for initial cyanide 10-100 mg/l and CN/Fe M ratios 0.05-18. The data include some runs in the presence of zinc or copper. However, the reaction time, temperature and pH were not well defined previously. The data base has been expanded with the results of our studies, which covered conditions of total cyanide concentration 1 to 60 mg/l; CN:Fe M ratios 0.8 to 10; temperatures 1 to 55 C; and pH 4 to 12 for both reducing and oxidizing atmosphere. This included runs in the presence of copper, EDTA or zinc as inhibiting additives. Also, tests were run with simulated coking or blast furnace effluents. EXPERIMENTAL Our studies were batch runs in a 4-liter glass vessel, carried out with addition of iron salts into the reaction mixture, either as a dry powder or as a predissolved concentrate. Nitrogen sparging was used to maintain reducing conditions. Volatilization of hydrogen cyanide into the sparge gas was shown to be small, even for acidic conditions. Free cyanide analysis was carried out by an automated version of the standard color- imetric test, involving reaction with chloramine-T to form cyanogen chloride which gives a purplish complex with a solution of barbituric acid in pyridine [5]. Analysis for total cyanides was made via the ultraviolet digestion method of Goulden, Brooksband and Afghan [6]. REACTION DATA The reaction of interest has a complicated stoichiometry due to pH-dependent hydrolysis of the reactant species: 776
Object Description
Purdue Identification Number | ETRIWC197669 |
Title | Treatment of coke oven and blast furnace effluents to inhibit formation of iron-cyanide complexes |
Author |
Prober, Richard Melnyk, P. B. (Peter B.) Mansfield, Lee A. |
Date of Original | 1976 |
Conference Title | Proceedings of the 31st Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,27048 |
Extent of Original | p. 776-781 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-07-08 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 776 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | TREATMENT OF COKE OVEN AND BLAST FURNACE EFFLUENTS TO INHIBIT FORMATION OF IRON-CYANIDE COMPLEXES Richard Prober, Associate Professor Peter B. Melnyk, Assistant Professor Lee A. Mansfield, Graduate Student Department of Chemical Engineering Case Western Reserve University Cleveland, Ohio 44106 INTRODUCTION Regulations concerning wastewater discharges of cyanides are under consideration in many areas. The more stringent proposals would require removal of total cyanides to residua] levels as low as 25 p.g/\. This lumping of iron-cyanide complexes together with the other much more toxic forms would have particularly significant implications for the iron and steel industry. Effluents from blast furnace gas washing and various coking wastewaters contain significant amounts of cyanides, both free and complexed, and iron. Ferricyanide and ferrocyanide are refractory species which would require new and potentially costly treatment methods, such as ozonation or ultraviolet irradiation for effective removal. An alternate approach may be preferable; for example, control of discharges of iron- cyanide complexes, or inhibition of the chemical reactions that form them. Free cyanide could then be removed by conventional treatments. This is a reaction engineering problem which involves specification of temperatures, pH values, concentrations and reactor configuration to minimize formation of the complexes for anticipated reaction times on the order of 1 hr. Previous studies of the reactions of interest by Southgate [1], Grieves, et al. [2,3] and Battelle Memorial Institute [4], provide data on conversion of free cyanide for initial cyanide 10-100 mg/l and CN/Fe M ratios 0.05-18. The data include some runs in the presence of zinc or copper. However, the reaction time, temperature and pH were not well defined previously. The data base has been expanded with the results of our studies, which covered conditions of total cyanide concentration 1 to 60 mg/l; CN:Fe M ratios 0.8 to 10; temperatures 1 to 55 C; and pH 4 to 12 for both reducing and oxidizing atmosphere. This included runs in the presence of copper, EDTA or zinc as inhibiting additives. Also, tests were run with simulated coking or blast furnace effluents. EXPERIMENTAL Our studies were batch runs in a 4-liter glass vessel, carried out with addition of iron salts into the reaction mixture, either as a dry powder or as a predissolved concentrate. Nitrogen sparging was used to maintain reducing conditions. Volatilization of hydrogen cyanide into the sparge gas was shown to be small, even for acidic conditions. Free cyanide analysis was carried out by an automated version of the standard color- imetric test, involving reaction with chloramine-T to form cyanogen chloride which gives a purplish complex with a solution of barbituric acid in pyridine [5]. Analysis for total cyanides was made via the ultraviolet digestion method of Goulden, Brooksband and Afghan [6]. REACTION DATA The reaction of interest has a complicated stoichiometry due to pH-dependent hydrolysis of the reactant species: 776 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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