The First International Proficiency Testing Conference Sinaia, România 11 th − 13 th October, 2007 276 THE DETERMINATION OF METAL CONTENT IN THE SLUDGE PROCEEDING FROM OIL REFINERIES. PROPOSAL FOR NEW STANDARD METHOD Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica Rompetrol Quality Control, Navodari, DJ 226 Km 23,905700 e-mail: [email protected]; [email protected]Abstract The sludge proceeding from oil refineries is different from other types of sludge (e.g. municipal wastewater treatment plants).The presence of hydrocarbon in high concentration (up to 20% wt.) and the high content in metals require adapted analysis methods. Following a previous study on the methods for the determination of metals in sludge and in oil products and residues, we can now propose a new method. This is appropriate for the analysis of metal content in sludge proceeding from the wastewater treatment plants of oil refineries. The novelty consists on the sample preparation for analysis. The preparation has in view the drying followed by the calcination for the hydrocarbon decomposition without exceeding a certain temperature (550 o C), thus avoiding the loss of some organo- metallic compounds in volatiles. Then, the ash is treated with a mixture of acids for complete mineralization. In this mixture, the presence of HF seems to be important. For the complete dissolution of the ash, the microwaves action is required and some boric acid must be added in order to avoid the crystallization of fluorides in solution. Then, the appropriate dilution must be done and the sample is ready for the spectrometric analysis. The validation of the method was worked out by an inter-laboratory test. The results for the repeatability and reproducibility were good enough taking into account the complexity of the matrix. Key words Sludge, metal content determination FAAS,ICP-MS, ICP-AES
Transcript
The First
International Proficiency Testing Conference
Sinaia, România 11th − 13th October, 2007
276
THE DETERMINATION OF METAL CONTENT IN THE SLUDGE PROCEEDING FROM OIL REFINERIES. PROPOSAL FOR NEW
STANDARD METHOD
Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica
Abstract The sludge proceeding from oil refineries is different from other types of sludge (e.g. municipal wastewater treatment plants).The presence of hydrocarbon in high concentration (up to 20% wt.) and the high content in metals require adapted analysis methods. Following a previous study on the methods for the determination of metals in sludge and in oil products and residues, we can now propose a new method. This is appropriate for the analysis of metal content in sludge proceeding from the wastewater treatment plants of oil refineries. The novelty consists on the sample preparation for analysis. The preparation has in view the drying followed by the calcination for the hydrocarbon decomposition without exceeding a certain temperature (550 oC), thus avoiding the loss of some organo- metallic compounds in volatiles. Then, the ash is treated with a mixture of acids for complete mineralization. In this mixture, the presence of HF seems to be important. For the complete dissolution of the ash, the microwaves action is required and some boric acid must be added in order to avoid the crystallization of fluorides in solution. Then, the appropriate dilution must be done and the sample is ready for the spectrometric analysis. The validation of the method was worked out by an inter-laboratory test. The results for the repeatability and reproducibility were good enough taking into account the complexity of the matrix. Key words Sludge, metal content determination FAAS,ICP-MS, ICP-AES
Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica : The determination of metal content in the sludge proceeding from oil refineries. Proposal for new standard method
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1 INTRODUCTION The determination of heavy metal content in the sludge is a matter of environment and a concern for managers since the environment legislation hardens. In order to have a right evaluation of the risk at the disposal of this waste, it is important to have a valid method for its characterization. In a previous work [1] we made the characterization of the sludge proceeding from a typical oil refinery (the dry residue, the water content, the loss on ignition of dry mass, the petroleum product content , the calorific power , the major elements and the trace elements). The specific composition of this sludge, conducted us to a method very different from those described in standards and studies for the sludge proceeding from municipal wastewater treatment [2-10]. A comparative study of the methods for the heavy metal determination, especially for the sample preparation process [11] proved without doubt that the preparation of the sample is better to be done as in case of metals determination in petroleum products. The preparation has in view the drying followed by the calcination for the hydrocarbon decomposition without exceeding a certain temperature (550 oC), thus avoiding the loss of some organo- metallic compounds in volatiles. Then, the ash is treated with a mixture of acids for complete mineralization. In this mixture, the presence of HF is very important. For the complete dissolution of the ash, the microwaves action is required and some boric acid must be added in order to avoid the crystallization of fluorides in solution. Then, the appropriate dilution must be done and the sample is ready for the spectrometric analysis. The goal of the present work was to have a validation of this method by an inter-laboratory test. 2 EXPERIMENTAL
2.1 Materials and equipment
The equipment in the reference laboratory was a flame atomic absorption spectrophotometer (FAAS) produced by Analytic Jena, model ZeeNit 700. The used technique was the flame absorption in case of Cu, Zn, Fe, Mn, Mg, Al, Ca, Ni, Pb and the graphite oven for less concentrated metals: Cd, Co, Cr. The standards were Merck solutions , 1000 mg/l for each metal. The other laboratories participating in the test used their own equipment and technique. The majority used also FAAS but two of them detain ICP-AES and ICP-MS, respectively. In the second column of the Table 3, one can find the specific equipment and procedure of each participant. All the laboratories in the inter-laboratory test are authorised and are representative in the region. A bigger number of laboratories should be necessary but we had to have in view their availability.
2.2 Procedures In order to have homogenous and stable samples for the analysis, a great quantity of sludge was dried and calcinated in the reference laboratory. The ash was finely grounded and mixed. In order to verify the homogeneity and the stability, 10 samples were collected and analyzed in the reference laboratory for the determination of 12
Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica : The determination of metal content in the sludge proceeding from oil refineries. Proposal for new standard method
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metals in the ash. The test started on 21st October 2006 with the drying and calcination of the sludge. During November and December, the stability was checked out in consecutive 10 samples observing the concordance of the standard deviation of the series with that of the laboratory. Then, the ash was divided in 10 portions and shared with the other participants. They also received instructions concerning the preferred method. We indicated the following procedure for the dissolution of the mineral part: adding 2 mL HCl + 2 mL HNO3 + 1 mL HF. Then, the content is sealed in a teflon phial and kept for 30 minutes in a microwave oven, at max.200oC. After filtration, dilution and pouring in the 100 ml flask, 0.2 g of boric acid is added for preventing the florides precipitation. Then, water to 100 ml is added. The instructions were specific to the expected concentration range in the prepared solution.
The participants were free to use their own mineralization procedure but they had to specify it when sending the results, following the codes in the Table 1:
Table1- Mineralization procedures used in the inter-laboratory test
Technique Digestor Digestion type Sample quantity
A1. Graphite oven B1. Microwaves C1. HNO3 D1. <0.5 g
- - C6. HNO3+HCl+HF - 3 RESULTS AND DISCUSSIONS In the Table 2, there are shown the results of the stability and repeatability test in the reference laboratory. The samples of ash obtained from sludge were mineralized and analysed during two months after the calcination and the results proved no systematic tendency to increase or decrease the metal content. Also, the standard deviation was satisfactory. The repeatability coefficient variation was very good, according to the SR EN 13346 for all metals found in the standard, as seen in the Table 5.
Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica : The determination of metal content in the sludge proceeding from oil refineries. Proposal for new standard method
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Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica : The determination of metal content in the sludge proceeding from oil refineries. Proposal for new standard method
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Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica : The determination of metal content in the sludge proceeding from oil refineries. Proposal for new standard method
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Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica : The determination of metal content in the sludge proceeding from oil refineries. Proposal for new standard method
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Table 5-Repeatability coefficient of variation, VCr , in comparison with that required by the standards [12]
Metal Standard limits for
VCr, % Actual VCr, %
Cu 1.7-4.6 2.7 Zn 1.9- 5.3 5.2 Cd 4.8-24.4 4.5 Cr 3.3-12.3 5.8 Ni 3.6-11.7 9.0 Pb 4-11.5 4.6
The reproducibility coefficient of variation, VCR ,was good for some metals and poorer for others than in the standards (see Table 6), but we can take into account the relatively small number of available laboratories for the test and the complexity of the matrix. Since the standard was validated for sludge proceeding from water treatment in mixture with sludge from municipal wastewater plants or industrial sludge in mixture with the above, in our study, the sludge proceeding from oil refineries had greater loading. There were also metals very likely to be in our sludge: V, Pt, Re, Pd, Mo which weren’t analysed here and can interfere. Table 6-Reproducibility coefficient of variation VCr in comparison with that required by
the standards [12]
Metal Standard limits for VCR, %
Actual VCR, %
Cu 5.4-18.7 26 Zn 7.5-15.1 28 Cd 21.5-116 26.9 Cr 11.6-17.4 10.2 Ni 10.9-23.7 26.8 Pb 29.6-76.3 33.5
In the Table 3, all the participant laboratories determined the lead at the wavelength 283 nm, except the reference laboratory where the lead was determined at 217 nm, this being recommended as more selective wavelength for Pb, however, the reference laboratory made comparatively 9 analyses at 283,3 nm too, and the content in lead resulted greater, as expected (373 mg/kg with 39 mg/kg standard deviation comparing with 284 mg/kg and 12 mg/kg standard deviation at 217 nm), this confirming us the presumptive interference. From the Table 3, it is obvious the effect of the microwaves on the complete dissolution of the sample in the acid, when comparing the metal content in the results of the laboratories working without microwaves (L2, L3) with those of the laboratories using them.
Claudia Irina Koncsag, Monica Grigore, Maria Mirela Velicu, Anca Birladeanu, Vasilica Chirica : The determination of metal content in the sludge proceeding from oil refineries. Proposal for new standard method
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4 CONCLUSIONS
Following this study, we can recommend the following method for the metal content determination in the sludge proceeding from oil refineries: drying to constant weight followed by the calcination without exceeding a certain temperature (550oC), thus avoiding the loss of some organo- metallic compounds in volatiles. Then, the ash is treated with a mixture of acids for complete mineralization. In this mixture, the presence of HF seems to be important. For the complete dissolution of the ash, the microwaves action is required and some boric acid must be added in order to avoid the crystallization of fluorides in solution. Then, the appropriate dilution must be done and a spectrometric method can be applied. The dissolution of the ash can be made as well with the mixture HCl +HNO3 1:3 and in the absence of microwaves but for Co, the dissolution seems to be complete only with the recommended acid formula, the present study confirming the conclusions in a previous work [11]. Also, the microwaves effect on the complete dissolution of the sample is obvious. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
Grigore M., Koncsag C. and Ioan C., Proceedings Chemical Industry and Environment V, Viena, ISBN 3 900 554 57 9, 251-257, (2006) Sandroni V., and Smith M.M.C., Analytica Chimica Acta, 468, 335-340, (2002) Sandroni V., et al., Talanta, 60, 715-718, (2003) J.Sastre, et al, Analytica Chimica Acta, 462, 59-62, (2002) B.Perez Cid, et al., Analytica Chimica Acta, 431, 209-214, (2001) Bettinelli, M, et al., Analytica Chimica Acta, 424, 289-295, (2000) ***STAS 13094/ mai 1992 – Nămoluri rezultate de la tratarea apelor de suprafaţă şi epurarea apelor uzate. Determinarea conţinutului de nichel. ***SR 13181/1994- Nămoluri rezultate de la tratarea apelor de suprafaţă şi epurarea apelor uzate. Determinarea conţinutului de zinc ***SR 13225/1995- Nămoluri rezultate de la tratarea apelor de suprafaţă şi epurarea apelor uzate. Determinarea conţinutului de plumb *** SR 13179/1994- Nămoluri rezultate de la tratarea apelor de suprafaţă şi epurarea apelor uzate. Determinarea conţinutului de cupru Grigore M., et al., Ovidius University Annals of Chemistry, 17(2), 213-216, (2006) *** SR EN 13346: 2002- Caracterizarea namolurilor. Determinarea elementelor in urme si a fosforului- Metode de extractie in apa regala
