207 journal homepage: www.fia.usv.ro/fiajournal Journal of Faculty of Food Engineering, Ştefan cel Mare University of Suceava, Romania Volume XII, Issue 2 – 2013, pag. 207 - 213 CON TRI BUT IONS TO THE DE VELO PME NT OF THE MA T ERIAL BA LANCE O F M IGRA TI ON PRO CESS OF M E TAL IONS FROM THE AIS I3 04 STAIN L ESS S TE EL I N A CE TI C AC ID S OL UT IONS *Silviu-Gabriel STROE1, Gheorghe GUTT1, Maria POROCH-SERIŢAN1 1 Faculty of Food Engineering, Stefan cel Mare University of Suceava, 13 Universitatii Street, 720229, Suceava, Romania *silvius@fia.us.ro; g.gutt@fia.usv.ro; mariap@fia.usv.ro *Corresponding author Received April 8th 2013, accepted May 15th 2013 Abstract: The aim of this work was the development of theoretical and real material balance by studying the diffusion phenomena of the metallic ions from AISI304 stainless steel samples in acetic acid solutions with 3%, 6% and 9% concentrations. The correlation of the quantities of substance which migrate from the metallic alloys in the food simulants through the interaction interface between the two environments can be accomplished through the materials balance developed for each component. To development the materials balance, we used the general stoichiometric equation of a chemical process. Within the comparative study of the theoretical and real mass balance, we have used the experimental data obtained after the migration tests, where the variables were represented by the working parameters: the temperature of the migration testing - T [°C], the exposure time - t [min.] and the stirring of the corrosive environment - n [rot·min-1]. The value of each parameter was varied on three levels, in accordance with the real situations met in practice. In order to express the quantitative stage of the interaction between the metallic material and the corrosive environment, at a certain moment, we have used the degree of dissolution δM of the metallic components such as Mn, Cr, 56Fe and Ni. The comparative study of the dissolution rates obtained allows to extrapolate and to elaborate in practice the optimization of the process which occurs at the interface of the two real food environments. Keywords: diffusion, stainless steel, acetic acid, mass balance, dissolution rate 1. Introduction The knowledge and study of chemical reactions which occur at the interface between a metallic material and a food environment, considered corrosive, play an important role in the manufacturing process of food raw materials. Thus, in order to design the equipment or to optimize the processes we must know the operation conditions, such as: the nature of the corrosive environment, the temperature at which the processes occur, the duration of the contact between the two environments and the stirring of the corrosive environment. 2. Materials and methods 2.1. Metallic samples and corrosive environments Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 2 – 2013 S i l v i u- G a b ri e l S T R O E , G he o rg he G U T T , M a ri a PO R O C H - S E R IŢAN, C o n t r i b u t i o n s t o t h e d e ve l o p m e n t o f t h e m a t e r i a l b a l a n c e o f m i g r a t i o n p r o c e s s o f m e t a l i o n s f r o m t h e A I S I 3 0 4 s t a i n l e s s s t e e l i n a c e t i c a c i d s o l u t i o n s , F o o d a nd E n v i r o n me n t S a f e t y , V o l u me X I I , I s s u e 2 – 2 0 1 3 , pa g . 2 0 7 - 2 1 3 208 For the development of theoretical and real mass balance we have used the metallic samples of AISI304 stainless steel grade, the chemical composition being shown in the Table 1 (according to EN 10088- 2:2005) [1]. The dimensions of the metallic samples used in the migration tests were of 40×40×1 mm. Table 1. Chemical composition of AISI304 stainless steel [wt %] Fe C Mn P S Si Cr Ni 67 0.08 2 0.045 0.03 1 18-20 8-11 As corrosive environments, we have used solutions of CH3COOH, with the following concentrations: 3%, 6% and 9%. 2.2. Experimental design The experimental design used for the migration tests in each of the three corrosive environments is presented in the Table 2. Tabel 2. Experimental design used to perform the migration tests Nr. exp. Temperatura T-[°C] Timp t-[min.] Agitare n-[rot·min-1] 1 22 30 0 2 22 30 125 3 22 30 250 4 28 30 0 5 28 30 125 6 28 30 250 7 34 30 0 8 34 30 125 9 34 30 250 10 22 60 0 11 22 60 125 12 22 60 250 13 28 60 0 14 28 60 125 15 28 60 250 16 34 60 0 17 34 60 125 18 34 60 250 19 22 90 0 20 22 90 125 21 22 90 250 22 28 90 0 23 28 90 125 24 28 90 250 25 34 90 0 26 34 90 125 27 34 90 250 After performing migration tests of the elements from the metallic samples in the acid solutions of the corrosive environments there have been identified and dosed, using mass spectrometry and inductively coupled plasma ICP-MS, the following metallic elements: Mn, Cr, 56Fe and Ni, according to the Table 3. Table 3. Concentrations of Mn, Cr, 56Fe and Ni elements found in CH3COOH solutions, used as corrosive environments No. exp. Chemical element, [mg·L-1] Mn Cr 56Fe Ni 3% 6% 9% 3% 6% 9% 3% 6% 9% 3% 6% 9% 1 0.003 0.00157 0.00122 0.004 0.005 0.001 0.990 0.32 0.08 0.0152 0.311 0.0033 2 0.003 0.00237 0.00182 0.004 0.007 0.001 0.660 0.40 0.10 0.0072 0.341 0.0058 3 0.022 0.00287 0.00222 0.077 0.012 0.003 6.120 0.54 0.26 0.0782 0.381 0.0064 4 0.003 0.00177 0.00072 0.005 0.012 0.002 0.390 0.20 0.02 0.0132 0.391 0.0056 5 0.004 0.00227 0.00102 0.009 0.015 0.004 1.170 0.28 0.04 0.0232 0.531 0.0066 6 0.005 0.00287 0.00142 0.007 0.019 0.005 0.730 0.58 0.10 0.0352 0.551 0.0071 7 0.002 0.00197 0.00082 0.005 0.014 0.002 0.760 0.36 0.02 0.0082 0.411 0.0057 8 0.003 0.00207 0.00132 0.007 0.018 0.005 0.860 0.74 0.06 0.0132 0.511 0.0060 9 0.005 0.00247 0.00182 0.019 0.022 0.007 1.040 1.22 0.28 0.0372 0.561 0.0076 10 0.003 0.01467 0.00092 0.005 0.011 0.001 0.690 0.22 0.06 0.0132 0.281 0.0038 11 0.004 0.00607 0.00122 0.005 0.013 0.002 0.400 0.60 0.14 0.0068 0.331 0.0053 12 0.041 0.00387 0.00152 0.188 0.020 0.003 9.220 1.08 0.68 0.1372 0.381 0.0066 13 0.003 0.00207 0.00112 0.007 0.014 0.008 0.880 0.22 0.18 0.0152 0.301 0.0073 Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 2 – 2013 S i l v i u- G a b ri e l S T R O E , G he o rg he G U T T , M a ri a PO R O C H - S E R IŢAN, C o n t r i b u t i o n s t o t h e d e ve l o p m e n t o f t h e m a t e r i a l b a l a n c e o f m i g r a t i o n p r o c e s s o f m e t a l i o n s f r o m t h e A I S I 3 0 4 s t a i n l e s s s t e e l i n a c e t i c a c i d s o l u t i o n s , F o o d a nd E n v i r o n me n t S a f e t y , V o l u me X I I , I s s u e 2 – 2 0 1 3 , pa g . 2 0 7 - 2 1 3 209 14 0.005 0.00377 0.00142 0.013 0.019 0.008 1.190 0.36 0.30 0.0192 0.321 0.0091 15 0.004 0.00357 0.00162 0.010 0.020 0.009 0.720 0.50 0.34 0.0282 0.367 0.0112 16 0.002 0.00227 0.00102 0.020 0.014 0.002 0.160 0.44 0.08 0.0072 0.231 0.0072 17 0.004 0.00287 0.00132 0.012 0.019 0.004 0.960 0.54 0.18 0.0202 0.276 0.0086 18 0.007 0.00367 0.00172 0.022 0.022 0.005 2.010 0.72 0.32 0.0322 0.306 0.0101 19 0.004 0.00257 0.00082 0.007 0.012 0.003 1.090 0.76 0.02 0.0132 0.301 0.0052 20 0.003 0.00267 0.00112 0.005 0.015 0.003 0.590 0.88 0.02 0.0082 0.331 0.0057 21 0.043 0.00297 0.00142 0.238 0.020 0.004 5.320 0.96 0.10 0.2372 0.361 0.0059 22 0.004 0.00387 0.00182 0.011 0.018 0.006 0.840 0.72 0.28 0.0172 0.121 0.0071 23 0.005 0.01167 0.00372 0.014 0.031 0.009 0.870 0.88 0.88 0.0172 0.141 0.0097 24 0.008 0.01267 0.00502 0.012 0.042 0.015 1.020 1.00 1.16 0.0302 0.172 0.0131 25 0.008 0.00147 0.00172 0.012 0.013 0.008 1.230 0.20 0.44 0.0262 0.160 0.0079 26 0.016 0.00357 0.00522 0.079 0.026 0.015 4.320 0.66 1.24 0.0752 0.211 0.0088 27 0.025 0.01567 0.00972 0.108 0.039 0.036 7.920 1.04 2.28 0.1072 0.241 0.0168 3. Results and Discussion 3.1. Theoretical material balance Assuming that the reaction kinetics is known, this paper presents the theoretical and real material balances of the diffusion processes which occur between the AISI304 stainless steel grade samples and the food simulants (acetic acid solutions - 3%, 6% and 9%). The correlation of the substance quantities which leave the metallic material and migrate in the food environment, at the interaction interface between the two environments, can be done by the use of the materials balance elaborated by components [2]. For the development of the material balance we have started from the stoichiometric equation of a chemical process, which can be written as (1) [2]:      m i iA n i iA AA ii 11  (1) where: iA  - the stoichiometric coefficient of the reactants; iA  - the stoichiometric coefficient of the reaction products; iA , iA - reactants, reaction products, respectively. At the interaction interface between the food environment and the metallic material, main chemical reactions, secondary chemical reactions and electrochemical reactions occur. In order to express the quantitative stage of the interaction between the aliment and the metallic material, at a certain moment, we have used a dissolution rate of a metallic contaminant or a certain component iA  [3], [4]. This parameter is defined as dissolution rate of the metallic contaminant and is expressed by the relation: 0 0 0 0 0 0 k k i ii k k i ii k kk k A A A AA A A A AA A AA A n nn n nn n nn                (2) where: 0 iA n , 0 kA n , 0 iA n  - is the composition of the initial reaction mass of the contaminant ( iA ), of a certain contaminant ( kA ), and of the reaction products ( iA ), respectively; iA n , iA n  - the composition of the reaction mass at a certain moment of the contaminant ( iA ), of the reaction products ( Ai ' ), respectively. The use of the dissolution rate variable for the quantitative characterization of the process allows the development of the stoichiometric calculation in a simple form Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 2 – 2013 S i l v i u- G a b ri e l S T R O E , G he o rg he G U T T , M a ri a PO R O C H - S E R IŢAN, C o n t r i b u t i o n s t o t h e d e ve l o p m e n t o f t h e m a t e r i a l b a l a n c e o f m i g r a t i o n p r o c e s s o f m e t a l i o n s f r o m t h e A I S I 3 0 4 s t a i n l e s s s t e e l i n a c e t i c a c i d s o l u t i o n s , F o o d a nd E n v i r o n me n t S a f e t y , V o l u me X I I , I s s u e 2 – 2 0 1 3 , pa g . 2 0 7 - 2 1 3 210 and the elaboration of the balance equation system in a form appropriate to their use for the quantitative description of the process. Starting with the composition of the reaction mass at a certain moment expressed through the sizes: nAA nn ... 1 ; nAA nn  ...1 (3) and for each component it can be written the following balance equations [2]: kk k i ii AA A A AA nnn    00 (4) kk k i ii AA A A AA nnn     00 (5) 0 ii AA nn   (6) The total number of moles in the reaction mass, at a certain moment, is expressed by the balance equation (7): kk k ii kk k i kkiii AA A n A m A TAA A m A AA k n is A m A n AT nnn n A A nnnn          011001 01 1 0 1 0 1 0         (7) The equation (7) can be written also as equation (8) [2]:   k k k k ii AT A T A A n A m A TT n n n nn                       1 1 0 0 0 110 (8) where: 0 11 T A A n i A m i A n n k k ii          (9) By replacing the number of moles by mass, the equation (2) can be written as equation (10): 0 0 0 0 0 0 k k i k i ii k k i k i ii k kk k A A A A A AA A A A A A AA A AA A m M M mm m M M mm m mm                (10) 3.2. Real material balance In case of AISI304 stainless steel grade, used in the processing of food raw materials, the initial mass of reaction is considered to be formed by the metals presented in Table 1 (according to EN 10088-2:2005) [1], from the composition of metallic material and the acetic acid (CH3COOH) [5]. The acetic acid has the following properties: 105,60  molgM , 76,4apK , at 25°C. The stoichiometric equation of the chemical process from the interaction interface between the acetic acid and AISI304 stainless steel, in case of obtaining the vinegar by acetic fermentation, is the following:   OHOHFeFeOHCNiOHC CrOHCMnOHCOOHCFeNiCrMn 2222322232 223222322242 0000 3)()( )()(2/582   (11) Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 2 – 2013 S i l v i u- G a b ri e l S T R O E , G he o rg he G U T T , M a ri a PO R O C H - S E R IŢAN, C o n t r i b u t i o n s t o t h e d e ve l o p m e n t o f t h e m a t e r i a l b a l a n c e o f m i g r a t i o n p r o c e s s o f m e t a l i o n s f r o m t h e A I S I 3 0 4 s t a i n l e s s s t e e l i n a c e t i c a c i d s o l u t i o n s , F o o d a nd E n v i r o n me n t S a f e t y , V o l u me X I I , I s s u e 2 – 2 0 1 3 , pa g . 2 0 7 - 2 1 3 211 and the secondary reaction is:   OHHOFeOHFe 224323  (12) In order to express the quantitative stage of the interaction reaction between the metallic material and the aliment, at a certain moment, it is used the dissolution rate Mn of a metallic contaminant (Mn), expressed by the relation: 0 0 Mn MnMn Mn m mm   (13) The mass of each component, in a certain moment, is expressed by the equation (13) [3], [4]. The theoretical masses calculated for the contaminants Mn, Cr, 56Fe and Ni which could result from the complete dissolution of the metallic samples are presented in Table 4. Tabel 4. Theoretical masses of the contaminants Mn, Cr, 56Fe and Ni [mg] Mn Cr 56Fe Ni 202.2 1819.8 6673.7 1011.0 Based on the relation (13) we have obtained the numeric values of the dissolution rate of the Mn, Cr, 56Fe and Ni contaminants (Table 5). Tabel 5. The dissolution rate of the contaminants Mn, Cr, 56Fe and Ni Nr. exp. δMn, [%] δCr, [%] δ56Fe, [%] δNi, [%] 3% 6% 9% 3% 6% 9% 3% 6% 9% 3% 6% 9% 1 0.0015 0.0008 0.0006 0.0002 0.0003 0,0055 0.0148 0.0048 0.0012 0.0015 0.0308 0.0003 2 0.0015 0.0012 0.0009 0.0002 0.0004 0,0055 0.0099 0.0060 0.0015 0.0007 0.0337 0.0006 3 0.0109 0.0014 0.0011 0.0042 0.0007 0.0002 0.0917 0.0081 0.0039 0.0077 0.0377 0.0006 4 0.0015 0.0009 0.0004 0.0003 0.0007 0.0001 0.0058 0.0030 0.0003 0.0013 0.0387 0.0006 5 0.0020 0.0011 0.0005 0.0005 0.0008 0.0002 0.0175 0.0042 0.0006 0.0023 0.0525 0.0007 6 0.0025 0.0014 0.0007 0.0004 0.0010 0.0003 0.0109 0.0087 0.0015 0.0035 0.0545 0.0007 7 0.0010 0.0010 0.0004 0.0003 0.0008 0.0001 0.0114 0.0054 0.0003 0.0008 0.0407 0.0006 8 0.0015 0.0010 0.0007 0.0004 0.0010 0.0003 0.0129 0.0111 0.0009 0.0013 0.0505 0.0006 9 0.0025 0.0012 0.0009 0.0010 0.0012 0.0004 0.0156 0.0183 0.0042 0.0037 0.0555 0.0008 10 0.0015 0.0073 0.0005 0.0003 0.0006 0,0055 0.0103 0.0033 0.0009 0.0013 0.0278 0.0004 11 0.0020 0.0030 0.0006 0.0003 0.0007 0.0001 0.0060 0.0090 0.0021 0.0007 0.0327 0.0005 12 0.0203 0.0019 0.0008 0.0103 0.0011 0.0002 0.1382 0.0162 0.0102 0.0136 0.0377 0.0007 13 0.0015 0.0010 0.0006 0.0004 0.0008 0.0004 0.0132 0.0033 0.0027 0.0015 0.0298 0.0007 14 0.0025 0.0019 0.0007 0.0007 0.0010 0.0004 0.0178 0.0054 0.0045 0.0019 0.0318 0.0009 15 0.0020 0.0018 0.0008 0.0006 0.0011 0.0005 0.0108 0.0075 0.0051 0.0028 0.0363 0.0011 16 0.0010 0.0011 0.0005 0.0011 0.0008 0.0001 0.0024 0.0066 0.0012 0.0007 0.0228 0.0007 17 0.0020 0.0014 0.0007 0.0007 0.0010 0.0002 0.0144 0.0081 0.0027 0.0020 0.0273 0.0009 18 0.0035 0.0018 0.0009 0.0012 0.0012 0.0003 0.0301 0.0108 0.0048 0.0032 0.0303 0.0010 19 0.0020 0.0013 0.0004 0.0004 0.0007 0.0002 0.0163 0.0114 0.0003 0.0013 0.0298 0.0005 20 0.0015 0.0013 0.0006 0.0003 0.0008 0.0002 0.0088 0.0132 0.0003 0.0008 0.0327 0.0006 21 0.0213 0.0015 0.0007 0.0131 0.0011 0.0002 0.0797 0.0144 0.0015 0.0235 0.0357 0.0006 22 0.0020 0.0019 0.0009 0.0006 0.0010 0.0003 0.0126 0.0108 0.0042 0.0017 0.0120 0.0007 23 0.0025 0.0058 0.0018 0.0008 0.0017 0.0005 0.0130 0.0132 0.0132 0.0017 0.0139 0.0010 24 0.0040 0.0063 0.0025 0.0007 0.0023 0.0008 0.0153 0.0150 0.0174 0.0030 0.0170 0.0013 25 0.0040 0.0007 0.0009 0.0007 0.0007 0.0004 0.0184 0.0030 0.0066 0.0026 0.0158 0.0008 26 0.0079 0.0018 0.0026 0.0043 0.0014 0.0008 0.0647 0.0099 0.0186 0.0074 0.0209 0.0009 27 0.0124 0.0078 0.0048 0.0059 0.0021 0.0020 0.1187 0.0156 0.0342 0.0106 0.0238 0.0017 After obtaining the numeric values (according to the Table 5), a comparative study can be done in relation to the influence of the working parameters on the dissolution rate of the contaminants. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 2 – 2013 S i l v i u- G a b ri e l S T R O E , G he o rg he G U T T , M a ri a PO R O C H - S E R IŢAN, C o n t r i b u t i o n s t o t h e d e ve l o p m e n t o f t h e m a t e r i a l b a l a n c e o f m i g r a t i o n p r o c e s s o f m e t a l i o n s f r o m t h e A I S I 3 0 4 s t a i n l e s s s t e e l i n a c e t i c a c i d s o l u t i o n s , F o o d a nd E n v i r o n me n t S a f e t y , V o l u me X I I , I s s u e 2 – 2 0 1 3 , pa g . 2 0 7 - 2 1 3 212 It is known the fact that the presence of manganese in the stainless steels has the role to ensure deoxidation and to prevent the formation of iron sulphide inclusions [6]. In which concerns the behaviour of manganese (Mn) in acid environments, the lowest dissolution rate (0,004%) was obtained by the 7 and 19 experiences: T- 34°C and 22°C, t-30 and 90 min. and stationary environments (n-0 rot·min-1). The highest dissolution rate (0.0124%) was obtained in the experience no. 27, where the working parameters were: T-34°C, t-90 min. and n-250 rot·min-1. Concerning the behaviour of the chrome in acid environments, it is known the fact that this is not a chemical element to present an important migration phenomenon in food environments. Due alloying chromium, the stainless steels are more resistant to corrosion [7]. The lowest dissolution rate (0.0001) can be noticed in case of experiences 4, 7, 11 and 16, where, as particularity, the corrosive environment was stationary, only in case of experience no. 11, the stirring of the environment being of 125 rot·min-1. The highest dissolution rate (0.0131) can be noticed in the case of experience no. 21, where the environment concentration was of 3% CH3COOH, T-22°C, t-90 min. and n-250 rot·min-1. Regarding the behaviour of the iron to corrosion (56Fe), the lowest dissolution rate were obtained in the case of experiences 4, 7, 19 and 20, where a stationary corrosive environment was used, the exception being the experience no. 20, where n-125 rot·min-1. The highest dissolution rate of iron is observed in case of experiment no. 12, where the concentration was of 3% CH3COOH, T-22°C, t-60 min. and n-250 rot·min-1. Amongst all studied metallic elements within this experiment, nickel presents the highest degree of risk on human health. The World Health Organization (OMS) recommends a maximum allowable dose of 0,005 mg/kg of body weight. OMS recommended also a value of nickel for the drinking water of 0,02 mg/l [8], and the daily intake of nickel from food products is estimated to 0,15-0,7 mg/day [8]. From studying the values of the dissolution rate for Ni, it is noticed that the minimum value of the degree of dissolution is met in case of the experience no.1, where solutions of 9% CH3COOH, T-22°C, t-30 min. and n - 0 rot·min-1 were used. The maximum value of the dissolution rate is noticed in case of experience no. 9, where the concentration was of 6% CH3COOH, T-34°C, t-30 min. and n-250 rot·min-1. 4. Conclusions The development of the theoretical and real mass balances of the migration processes of metallic acids in acid solutions, studied and presented in this paper, have had as main purpose the characterization of the migration processes from the interaction interface between acetic acid and AISI304 stainless steel grade samples through the calculation of the dissolution rate of the metallic contaminants Mn, Cr, 56Fe and Ni. By elaborating these balances, we have obtained very important information regarding the behaviour of these stainless steels in the studied experimental conditions. One can notice that minimum values of the dissolution rate of the elements Mn, Cr and 56Fe are obtained when solutions with 3% CH3COOH concentrations were used, and the minimum dissolution rate of Ni were obtained when the environment concentration was of 9% CH3COOH. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 2 – 2013 S i l v i u- G a b ri e l S T R O E , G he o rg he G U T T , M a ri a PO R O C H - S E R IŢAN, C o n t r i b u t i o n s t o t h e d e ve l o p m e n t o f t h e m a t e r i a l b a l a n c e o f m i g r a t i o n p r o c e s s o f m e t a l i o n s f r o m t h e A I S I 3 0 4 s t a i n l e s s s t e e l i n a c e t i c a c i d s o l u t i o n s , F o o d a nd E n v i r o n me n t S a f e t y , V o l u me X I I , I s s u e 2 – 2 0 1 3 , pa g . 2 0 7 - 2 1 3 213 The maximum levels of dissolution of Mn, Cr and 56Fe elements were obtained in case of the use of corrosive solutions with a concentration of 3% CH3COOH, and for the element Ni when solutions with 6% CH3COOH concentration were used. 5. References [1]. EN 10088 - 2 : 2005, Stainless steels. Technical delivery conditions for sheet/plate and strip of corrosion resisting steels for general purposes, (2005) [2].CALISTRU C., LEONTI C., Inorganic substances Technology, Ed. Didactică şi Pedagogică, Bucureşti, (1972) [3]. GUTT S., GUTT GH., Contributions to the mass balance and energy to electrochemical sharpening, Chemistry magazine, 44(11), 972 – 977, ISSN 0034-7752, (1993) [4].GUTT S., GUTT GH., Contributions to the material and energy balance sheet for the electrochemical nickel convection ultrasonic, Chemistry magazine, 6(48), 521 – 531, ISSN 0034-7752, (1997) [5].BUCULEI A., AMARIEI S., POROCH - SERIŢAN M., GUTT G., Study on the development of the material balance focused on the metal transfer between the system can- lacquering and canned vegetables, International Conference, Modern Technologies in the Food Industry-2012, 1-3 November, 2012, Chişinău (Republic of Moldova), Section 3, Chemistry and Microbiology of Food, (2013) [6].EHEDG - European Hygienic Engineering & Design Group, Materials of construction for equipment in contact with food, Trends in Food Science & Technology 18, Elsevier, (2007) [7].CODEX ALIMENTARIUS COMMISSION, Doc. no. CX/FAC 96/17. Joint FAO/WHO food standards programme. Codex general standard for contaminants and toxins in foods. Directive 91/338/EEC: Council directive 91/338/EEC amending for the 10th time Directive 76/769/EEC on the approximation of the laws, regulations and administrative provisions of the member states relating to restrictions on the marketing and use of certain dangerous substances and preparations. L 186 p. 59, (1995) [8].WORLD HEALTH ORGANIZATION - WHO Nickel in drinking-water. Background document for development of WHO Guidelines for drinking-water quality, Geneva, World Health Organization, (2005).