Technical note
Comparative study of alternative methods
for the simultaneous determination of Fe +3and Fe +2
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in leaching solutions and in acid mine drainages
C.Paipa a ,M.Mateo b ,I.Godoy a ,E.Poblete c ,M.I.Toral
c,*,
T.Vargas
a
a
Center of Hydro-electrometallurgy,Faculty of Physical and Mathematical Sciences,University of Chile,P.O.Box 2777,Santiago,Chile
b
School of Biochemical Engineering,Catholic University of Valparaı
´so,Avda Brasil 2147,Valparaı´so,Chile c
Laboratory of Analytical Chemistry,Department of Chemistry,Faculty of Sciences,University of Chile,P.O.Box 653,Santiago,Chile
Received 11November 2004;accepted 29March 2005
Available online 3June 2005
Abstract
In leaching solutions coming from the hydrometallurgical processing of copper sulphides,it is necessary to determine the con-centrations of Fe total ,Fe +2and Fe +3.It is known that the 5-sulfosalicylic acid (SSA)forms a red-violet complex with Fe +3in acid media and a yellow complex with Fe +2and Fe +3in prence of ammonia at pH =10.In this study,the results obtained by the SSA method are statistically compared with tho obtained by 1,10-phenanthroline method,dichromate titration method and atomic absorption spectrometry.A statistical analysis demonstrated that the SSA method gives more exact and reprentative results than the other studied methods.The acid mine d江北水城
rainages and the leaching solutions,prent an extremely complex matrix becau to the high content of copper and arnic,showing relationships that vary from 1:30up to 1:1,depending on the stages of the hydromet-allurgical process.Under the considerations,the SSA method allows the determination of Fe +3directly in samples that have an iron content in the range 0.005g L À1–18g L À1with a relative standard deviation (RSD)<2%.Ó2005Elvier Ltd.All rights rerved.
Keywords:Acid rock drainage;Hydrometallurgy;Bioleaching;Process instrumentation and extractive metallurgy
1.Introduction
The leaching solutions from hydrometallurgical pro-cessing of copper sulphides have a high concentration of veral metallic sulphates.Usually,it is necessary to determine quantitatively the iron ions concentration of both oxidation states,which could be sometimes impre-ci becau two techniques are required;furthermore,copper is a very usual interferent in the colorimetric
determination of iron.The Fe +2determination is carried out by 1,10-phenanthroline method (APHA,1998).The Fe total determination is realid using potassium dichro-mate volumetric method and Atomic Absorption Spec-trometry (AAS)technique.In this n,in all of the cas the determi
nation of Fe +3is not direct and for in-stance,a quantitative determination of both oxidation states could be impreci.Recently,a simple and fast method has been described for the quantitative simulta-neous determination of Fe +3and Fe total with SSA in acid mine drainages (AMD)and other solutions (Kara-manev et al.,2002).The objective of this work was to compare the sulfosalicylic acid method with the other two described methods,with the aim of validating its u in monitoring of Fe(II)and Fe(III)in leaching
0892-6875/$-e front matter Ó2005Elvier Ltd.All rights rerved.doi:10.1016/j.mineng.2005.03.009
*
Corresponding author.Fax:+5622713888.E-mail address:analitic@uchile.cl (M.I.Toral).
This article is also available online at:
/locate/mineng
Minerals Engineering 18(2005)
1116–1119
solutions and in AMD which came from bio/hydromet-allurgical process.
2.Experimental满江红岳飞全文带拼音
In order to compare results,the following analytic methods were ud for the direct determination of Fe+2:Method of the o-phenanthroline(1,10-phenan-throline)(APHA,1998)and the titration method with potassium dichromate,and indirectly([Fe total]–[Fe+3]) by means of the method of the sulfosalicylic acid(SSA) like it is described.
For the direct determination of Fe+3the method of the SSA was ud,and indirectly Fe+3also was deter-mined by means o-phenanthroline method and potas-sium dichromate method([Fe total]–[Fe+2]).For the determination of Fe total the three previous methods were compared with tho of Atomic Absorption Spectrome-try(AAS)(APHA,1998).
The procedure ud in the SSA method was as fol-lows:Into a100mL volumetricflask,add an adequate volume of the sample.Then add3mL of10%(w/v)sul-fosalicylic acid solution and complete volume with Ultrapure MilliporeÒWater.Stir during2min and measure de absorbance at500nm.Then
add3mL of ammonia solution25%(w/v)and stir during2min and measure the absorbance at425nm(Karamanev et al., 2002).The other methods have been broadly described in the literature(APHA,1998).
3.Results and discussion
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A comparative study of the employed analytical methods by means of control chart was carried out (Fig.1).The obtained results allowed to establish that the average values obtained by the dichromate method were significantly different for the determination of Fe total and Fe+3.On the other hand,in the determina-tion of Fe+2with a confidence level of99%,the preci-sion of the three methods is statistically comparable. However,from the three subjected methods to statistical control,the o-phenanthroline method prents the biggest relative error(Fe+2=À3.76%,Fe+3=À2.28% and Fe total=À4.00%)and SSA method prents the smaller relative error(Fe+2=0.88%,Fe+3=À0.08% and Fe total=À0.09%).
A regression among the variable measured‘‘concen-tration’’(y axis)and the‘‘true concentration’’(x axis)
allows to study an analytic method to detect and to quantify its possible errors and also as correcting
them. In Fig.2,the correlation is prented from the methods subjected to statistical control.For the dichromate method a significant evidence of afixed systematic error exists for the determination of Fe(II)and Fe(III),since the confidence limit for the true intercept does not in-clude the zero value as much in the determination of Fe(II) 3.3452±2.7422,as in Fe(III)0.7578±0.4549 for a significance level of95%.On the other hand,the o-phenanthroline method and the sulfosalicylic acid method,include the zero value and therefore,significant
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C.Paipa et al./Minerals Engineering18(2005)1116–11191117
evidence offixed systematic error does not exist.The analysis of the confidence limits of the true slope,al-lowed to conclude that significant evidence of a relative systematic error does not exist in the methods subjected to control,since the confidence limits of the slope in-clude the value1for a significance of95%for critical values of the test t.
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On the other hand,the addition of standard method and calibration graph in aqueous medium were com-pared.The statistical treatment of comparison of this slopes allow establishing the matrix influence.A signifi-cant difference was found for the determination of Fe total for the o-phenanthroline method in prence of 30g LÀ1of Cu(II).This specie is a majority constituent of the leaching solutions and of the acid mine drainages, being in concentration levels that reach30g LÀ1with a pH between1and2.Applying the critical values in a ‘‘two tailed’’t-test with a95%of confidence,a3.18t value was found.On the other hand,the t experimental value was of3.88which corroborate the copper interfer-ence.Therefore,the analyd samples cannot be con-trasted directly with the standards prepared in water by the o-phenanthroline method.
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On the other hand,in the analysis of the method of SSA,it was found that both slopes are practically
simi-lar and as a result it can be contrasted the sample directly with the standards prepared in water.The same thing happens when the studied interference is the As(V),also studied by our group.Under the last con-siderations the method of the SSA is adapted statis-tically for the analysis of Fe+2,Fe+3and Fe total in leaching solutions and acid mine drainages.
Finally,it was decided to compare the SSA method and the ortho-phenanthroline method in samples taken from a respirometric equipment.Oxygen uptake was determined during the experiments using electrochemi-cal respirometer SAPROMAT.Six reaction vesls maintained at a constant temperature in a thermostatic bath compo the system.Each reactionflask is con-nected to an electrochemical cell and to a contact manometer in a clod system.Oxygen consumption in the reaction vesls produces a decrea of pressure in the system that is compensated by the same amount of oxygen generated by an electrochemical reaction.The electrochemical current that is directly proportional to oxygen uptake is integrated and recorded continuously. For this experiment,Thiobacillus ferrooxidans was inoc-ulated in100mL of the MC media,which contains 3g LÀ1of Fe(II).And then the experiment was made in duplicate.Periodical samples were taken and immedi-ately analyzed by the two methods for comparing their results with the curve obtained in the respirometer which gave us mg of O2and by a conversion we could obtain Fe(III)oxidized against the time by the bacterial culture.
The results shown that the ortho-phenanthroline method has a higher relative error than SSA method, specifically at higher[Fe(III)]concentrations.The direct measurement of Fe(III)is very important becau it con-stitutes a parameter of monitoring the oxidative capac-ity of the bacteria.
4.Conclusions
The fact of having a system of analysis under statisti-cal control,allowed to establish that the method of the SSA is which gives more exact and reprentative results among the studied methods.The acid mine waters and the leaching solutions,prent an extremely complex matrix becau the content of the interference,as copper for example,is in relationships which could vary from 1:30up to1:1depending on the stages of the hydromet-allurgical processing.Under the considerations,the method of the SSA allows the determination of Fe(III) directly in samples that have an iron content understood between0.005g LÀ1and18g LÀ1with a relative stan-dard deviation(RSD)<2%.This wide lineal range, includes samples coming from all the stages of the hydrometallurgical processing of copper.
1118 C.Paipa et al./Minerals Engineering18(2005)1116–1119
Acknowledgments
The authors thank Project OO-I-1050from FON-DEF for the support of this investigation. C.Paipa thanks to the German Service for Academic Exchange (DAAD)for her doctoral fellowship and to the Project PG-97-2002of the University of Chile.References
APHA,1998.Standard methods for the examination of water and wastewaters.
Karamanev,D.G.,Nikolov,L.N.,Mamatarkova,V.,2002.Rapid simultaneous quantitative determination of ferric and ferrous ions in drainage waters and similar solutions.Minerals Engineering15, 341–346.
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