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A useful UV spectroscopic method for the determination of the concentration of diethylenetriamine (DETA) in aqueous mineral flotation solutions
Talanta 46 (1998) 145 – 148
A useful UV spectroscopic method for the determination of the concentration of diethylenetriamine (DETA) in aqueous mineral flotation solutions Heather J. Gass a, Ian S. Butler a,*, S. Ram Rao b, Zhenghe Xu b, James A. Finch b b
a Department of Chemistry, McGill Uni6ersity, Montreal, Quebec, Canada Department of Mining and Metallurgical Engineering, McGill Uni6ersity, Montreal, Quebec, Canada
Received 22 April 1997; received in revised form 4 August 1997; accepted 6 August 1997
Abstract An alternative method for the determination of the concentration of diethylenetriamine (DETA) in aqueous mineral flotation solutions is described. This method is based on the formation of a DETA-Ni(II)-sulphite complex, which shows a UV absorption maximum at 285 nm that varies linearly with the concentration of DETA throughout the 0–50 mg l − 1 DETA range. A high concentration of Ni(II) is used to offset the effect of any Cu(II) or Ni(II) ions that may already be present in the industrial plant solutions under analysis. The intensity of the absorbance maximum is dependent on the sulphite ion concentration, but this problem is overcome by measuring the absorbances when the test solutions are spiked with different concentrations of DETA and then extrapolating the absorbance versus DETA concentration plot to zero absorbance to obtain the original concentration of DETA in the test solutions. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Diethylenetriamine; Concentration; Aqueous
1. Introduction Diethylenetriamine [N-(2-aminoethyl)-1,2-diaminoethane, HN(CH2CH2NH2)2, DETA] has been suggested as a reagent for the depression of pyrrhotite (FeS) in industrial flotation circuits [1,2]. It can be analyzed by means of a UV spectroscopic method in which the absorption maximum at 386 nm for the complex formed
* Corresponding author. Fax: +1 514 3983797.
between DETA and fluram (4-phenylspiro[furan2(3H),1%-phthalan]3,3%-dione) is monitored [3]. The absorbance of the DETA-fluram complex at this wavelength varies linearly as a function of the concentration of DETA. The method is only accurate and reliable provided the plant solutions being tested do not contain any interfering species. In our experience, however, the results obtained by this method are subject to significant variations if the plant solutions contain any ionic species that can interact with DETA. In the presence of Ni(II) ions, we have found that the absorbances recorded are significantly lower than
0039-9140/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 3 9 - 9 1 4 0 ( 9 7 ) 0 0 2 5 9 - 2
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H.J. Gass et al. / Talanta 46 (1998) 145–148
Fig. 1. UV absorbance spectra of: (a) Ni/DETA/Metabisulfite; (b) [Ni(DETA)2]Br2; (c) [Ni(H2O)6]SO4.
those in the absence of Ni(II) ions. These absorbance differences are attributable to the formation of Ni(II)-DETA coordination complexes and can be compensated for by using reference blanks having the same Ni(II) concentrations as the test
solutions. In routine industrial operations, however, this is not an easy procedure. While it is relatively simple to determine the concentration of Ni(II) by atomic absorption spectroscopy, the chemical state of the Ni(II) ions depends on which
H.J. Gass et al. / Talanta 46 (1998) 145–148
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absorbance values. As with any standard addition procedure, it is best that the additions be comparable to those expected in the test solutions. If the range is too large, the relationship is no longer linear, too small and the results are not relevant.
2. Experimental The following stock solutions were prepared: NiSO4 · 7H2O, 5 g Ni(II) l − 1 1; simulated industrial plant DETA solutions containing 1 g l − 1 sodium metabisulphite and set to pH 9.0–9.5 by adding lime; reference blank solution containing 1 g l − 1 sodium metabisulphite and set to pH 9.0– 9.5 by adding lime; standard DETA solution, 0.955 g l − 1 DETA.
2.1. Procedure Fig. 2. Variation of absorbance (285 nm) with added DETA concentration mg l − 1 (all correlations have r values of 0.933 or better). Laboratory test trials use an artificial unknown DETA sample, plant test trials are the simulated flotation ciruit samples.
other ionic species are present in the solution. For example, in the presence of sulphite or metabisulphite ions, Ni(II) forms a Ni(II)-DETA-sulphite complex, which shows significantly different absorbances in its UV spectrum (Fig. 1a) than those for Ni(II)-DETA mixtures in the absence of sulphite or metabisulphite ions, e.g. [Ni(DETA)2]Br2 · H2O (Fig. 1b) or from [Ni(H2O)6]2 + itself (Fig. 1c). We have now developed an alternative method for the quantitative determination of DETA in aqueous mineral flotation solutions by UV spectroscopy. The analysis is based on monitoring the variation of the absorbance of the UV maximum at 285 nm of the complex formed when DETA interacts with Ni(II) in the presence of sulphite ion at alkaline pH 8.5 – 9.5. The presence of varying amounts of Ni(II) ions in solution is overcome by having a large excess of Ni(II) (by addition a soluble nickel salt) in the test solutions. This alternative procedure has also been designed to offset the effect of sulphite ions on the measured
Nickel sulphate solution (10 ml) and the reference blank solution (85 ml) were mixed together in a 100-ml volumetric flask. The volume was then made up to the 100-ml mark with distilled water. The mixture was centrifuged on an International Micro-Centrifuge for 6 min and a sample of the resulting green solution was decanted into a 1.00cm quartz cuvette and the background UV absorbance at 285 nm was determined. The time between mixing the solutions and recording the UV spectrum was set at 10 min in each case, as the absorbance does decrease with time. The same procedure was repeated for 85 ml samples of the industrial plant test solutions by adding known quantities of the standard DETA solution to the mixtures before making up to the 100-ml mark with distilled water. The concentration of the DETA added was in the 0–50 mg l − 1 range. The absorbances measured at 285 nm for the different solutions were plotted as a function of the concentration. The concentration of the DETA in the plant test solutions was determined by extrapolating the graph to zero absorbance and dividing the
1 This concentration is about ten-fold in excess of that required in order to minimize the effect of any Cu(II) or Ni(II) ions already present in the industrial solutions under analysis.
H.J. Gass et al. / Talanta 46 (1998) 145–148
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Table 1 Concentrations of DETA from the Ni(II)-DETA-sulphite absorbance measurements Actual DETA concentration (mg l−1)
DETA concentration from our method (mg l−1)
Range of added DETA used in trial (mg l−1)
10.0 1.20 3.87 1.22b
10.1a 1.14a 4.18 1.02
0 – 48.0 0 – 48.0 0 – 10.0 0 – 40.0
a b
Average of three replicate trials. Value determined by fluram method.
value of the x-axis intercept by 0.85 (to account for the volume dilution from 85 to 100 ml).
3. Results and discussion The UV spectrum of the Ni(II)-DETA-sulphite complex is shown in Fig. 1a. The 285-nm absorption band is clearly characteristic of the complex and increases proportionately with increasing concentration of DETA. Fig. 2 is a typical plot of the results obtained for an initially unknown concentration of DETA. The concentration of DETA measured by this method compares well with that determined by the fluram method. The results given in Table 1 show that our alternative UV spectroscopic procedure is reliable over the tested
.
range of 1–50 mg l − 1 DETA, which is the range normally expected in flotation plant solutions and effluents. Moreover, it will probably prove to be the method of choice for industrial situations where varying concentrations of Ni(II) ions are already known to be present in the pulp solutions.
References [1] M.A. Marticorena, G. Hill, A.N. Kerr, D. Liechti, D.A. Pelland, INCO develops new pyrrhotite depressant, in: T. Yalcin (Ed.), Innovations in Mineral Processing, Laurentian University, Sudbury, Ontario, Canada, 1995, pp. 15 – 33. [2] S. Kelebek, S.O. Fekete, P.F. Wells, Proceedings of the Fourteenth International Mineral Processing Congress, SME, New York, 1995, pp. 181 – 187. [3] S. Udenfriend, Science 178 (1972) 871.
.
A useful UV spectroscopic method for the determination of the concentration of diethylenetriamine (DETA) in aqueous mineral flotation solutions Heather J. Gass a, Ian S. Butler a,*, S. Ram Rao b, Zhenghe Xu b, James A. Finch b b
a Department of Chemistry, McGill Uni6ersity, Montreal, Quebec, Canada Department of Mining and Metallurgical Engineering, McGill Uni6ersity, Montreal, Quebec, Canada
Received 22 April 1997; received in revised form 4 August 1997; accepted 6 August 1997
Abstract An alternative method for the determination of the concentration of diethylenetriamine (DETA) in aqueous mineral flotation solutions is described. This method is based on the formation of a DETA-Ni(II)-sulphite complex, which shows a UV absorption maximum at 285 nm that varies linearly with the concentration of DETA throughout the 0–50 mg l − 1 DETA range. A high concentration of Ni(II) is used to offset the effect of any Cu(II) or Ni(II) ions that may already be present in the industrial plant solutions under analysis. The intensity of the absorbance maximum is dependent on the sulphite ion concentration, but this problem is overcome by measuring the absorbances when the test solutions are spiked with different concentrations of DETA and then extrapolating the absorbance versus DETA concentration plot to zero absorbance to obtain the original concentration of DETA in the test solutions. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Diethylenetriamine; Concentration; Aqueous
1. Introduction Diethylenetriamine [N-(2-aminoethyl)-1,2-diaminoethane, HN(CH2CH2NH2)2, DETA] has been suggested as a reagent for the depression of pyrrhotite (FeS) in industrial flotation circuits [1,2]. It can be analyzed by means of a UV spectroscopic method in which the absorption maximum at 386 nm for the complex formed
* Corresponding author. Fax: +1 514 3983797.
between DETA and fluram (4-phenylspiro[furan2(3H),1%-phthalan]3,3%-dione) is monitored [3]. The absorbance of the DETA-fluram complex at this wavelength varies linearly as a function of the concentration of DETA. The method is only accurate and reliable provided the plant solutions being tested do not contain any interfering species. In our experience, however, the results obtained by this method are subject to significant variations if the plant solutions contain any ionic species that can interact with DETA. In the presence of Ni(II) ions, we have found that the absorbances recorded are significantly lower than
0039-9140/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 3 9 - 9 1 4 0 ( 9 7 ) 0 0 2 5 9 - 2
146
H.J. Gass et al. / Talanta 46 (1998) 145–148
Fig. 1. UV absorbance spectra of: (a) Ni/DETA/Metabisulfite; (b) [Ni(DETA)2]Br2; (c) [Ni(H2O)6]SO4.
those in the absence of Ni(II) ions. These absorbance differences are attributable to the formation of Ni(II)-DETA coordination complexes and can be compensated for by using reference blanks having the same Ni(II) concentrations as the test
solutions. In routine industrial operations, however, this is not an easy procedure. While it is relatively simple to determine the concentration of Ni(II) by atomic absorption spectroscopy, the chemical state of the Ni(II) ions depends on which
H.J. Gass et al. / Talanta 46 (1998) 145–148
147
absorbance values. As with any standard addition procedure, it is best that the additions be comparable to those expected in the test solutions. If the range is too large, the relationship is no longer linear, too small and the results are not relevant.
2. Experimental The following stock solutions were prepared: NiSO4 · 7H2O, 5 g Ni(II) l − 1 1; simulated industrial plant DETA solutions containing 1 g l − 1 sodium metabisulphite and set to pH 9.0–9.5 by adding lime; reference blank solution containing 1 g l − 1 sodium metabisulphite and set to pH 9.0– 9.5 by adding lime; standard DETA solution, 0.955 g l − 1 DETA.
2.1. Procedure Fig. 2. Variation of absorbance (285 nm) with added DETA concentration mg l − 1 (all correlations have r values of 0.933 or better). Laboratory test trials use an artificial unknown DETA sample, plant test trials are the simulated flotation ciruit samples.
other ionic species are present in the solution. For example, in the presence of sulphite or metabisulphite ions, Ni(II) forms a Ni(II)-DETA-sulphite complex, which shows significantly different absorbances in its UV spectrum (Fig. 1a) than those for Ni(II)-DETA mixtures in the absence of sulphite or metabisulphite ions, e.g. [Ni(DETA)2]Br2 · H2O (Fig. 1b) or from [Ni(H2O)6]2 + itself (Fig. 1c). We have now developed an alternative method for the quantitative determination of DETA in aqueous mineral flotation solutions by UV spectroscopy. The analysis is based on monitoring the variation of the absorbance of the UV maximum at 285 nm of the complex formed when DETA interacts with Ni(II) in the presence of sulphite ion at alkaline pH 8.5 – 9.5. The presence of varying amounts of Ni(II) ions in solution is overcome by having a large excess of Ni(II) (by addition a soluble nickel salt) in the test solutions. This alternative procedure has also been designed to offset the effect of sulphite ions on the measured
Nickel sulphate solution (10 ml) and the reference blank solution (85 ml) were mixed together in a 100-ml volumetric flask. The volume was then made up to the 100-ml mark with distilled water. The mixture was centrifuged on an International Micro-Centrifuge for 6 min and a sample of the resulting green solution was decanted into a 1.00cm quartz cuvette and the background UV absorbance at 285 nm was determined. The time between mixing the solutions and recording the UV spectrum was set at 10 min in each case, as the absorbance does decrease with time. The same procedure was repeated for 85 ml samples of the industrial plant test solutions by adding known quantities of the standard DETA solution to the mixtures before making up to the 100-ml mark with distilled water. The concentration of the DETA added was in the 0–50 mg l − 1 range. The absorbances measured at 285 nm for the different solutions were plotted as a function of the concentration. The concentration of the DETA in the plant test solutions was determined by extrapolating the graph to zero absorbance and dividing the
1 This concentration is about ten-fold in excess of that required in order to minimize the effect of any Cu(II) or Ni(II) ions already present in the industrial solutions under analysis.
H.J. Gass et al. / Talanta 46 (1998) 145–148
148
Table 1 Concentrations of DETA from the Ni(II)-DETA-sulphite absorbance measurements Actual DETA concentration (mg l−1)
DETA concentration from our method (mg l−1)
Range of added DETA used in trial (mg l−1)
10.0 1.20 3.87 1.22b
10.1a 1.14a 4.18 1.02
0 – 48.0 0 – 48.0 0 – 10.0 0 – 40.0
a b
Average of three replicate trials. Value determined by fluram method.
value of the x-axis intercept by 0.85 (to account for the volume dilution from 85 to 100 ml).
3. Results and discussion The UV spectrum of the Ni(II)-DETA-sulphite complex is shown in Fig. 1a. The 285-nm absorption band is clearly characteristic of the complex and increases proportionately with increasing concentration of DETA. Fig. 2 is a typical plot of the results obtained for an initially unknown concentration of DETA. The concentration of DETA measured by this method compares well with that determined by the fluram method. The results given in Table 1 show that our alternative UV spectroscopic procedure is reliable over the tested
.
range of 1–50 mg l − 1 DETA, which is the range normally expected in flotation plant solutions and effluents. Moreover, it will probably prove to be the method of choice for industrial situations where varying concentrations of Ni(II) ions are already known to be present in the pulp solutions.
References [1] M.A. Marticorena, G. Hill, A.N. Kerr, D. Liechti, D.A. Pelland, INCO develops new pyrrhotite depressant, in: T. Yalcin (Ed.), Innovations in Mineral Processing, Laurentian University, Sudbury, Ontario, Canada, 1995, pp. 15 – 33. [2] S. Kelebek, S.O. Fekete, P.F. Wells, Proceedings of the Fourteenth International Mineral Processing Congress, SME, New York, 1995, pp. 181 – 187. [3] S. Udenfriend, Science 178 (1972) 871.
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