Analytical related problems in metal and trace elements determination in industrial waste landfill leachates

The Science of the Total Environment, 133 (1993) 285-298 Elsevier Science Publishers B.V., Amsterdam

285

Analytical related problems in metal and trace elements determination in industrial waste landfill leachates M. Gallorini a, M. Pesavento b, A. Profumo b and C. Riolo b aCNR, Centro di Radiochimica, Analisi per Attivazione Neutronica, V. le TarameUi, 12.27100, Pavia, Italy hDipartimento di Chimica Generale. V. ie Taramelli, 12.27100 Pavia, Italy (Received January 13th, 1992; accepted April 2rid, 1992)

ABSTRACT The periodic analytical control of waste landfill leachate is of fundamental importance not only to check the presence of possible toxic substances, but also to assess changes in concentration levels and behaviour with time. This work identifies some of the difficulties which arise during the analysis of some heavy metals and trace elements in leachate samples from a controlled industrial wastes landfill located in north Italy. The analytical problems encountered using both electro-thermal atomic absorption spectroscopy (ETAAS) and neutron activation analysis (NAA) for the determination of a series of elements, Cu, Cd, Pb, Ni, Mn, V, As, Se, Sb, Th, Sn, Cs, W, Cr, with concentration often at nanogram levels, are presented and evaluated. To solve these problems two selective chemical procedures have been developed to separate and to eliminate the matrix interfering compounds or elements (i.e., organic matter, complexing agents, Cl-, Br-~ S ~-, Na ÷) which reduce and in ~ome cases impair the sensitivity of the technique. For the analyses by ETAAS a preliminary preconcentration and separation proceduret based on the ion exchange resin Chelex-100 has been developed to determine Pb, Cd, Co, Cu, Ni and Sn. In the case of NAA a specific radiochemicai separation had to be studied for the analysis of Sn, V, W, Mn, Cr, As, Sb, Se, Th in pre~nce of high bromine and sodium concentrations. Procedures blanks and yields have been controlled and evaluated and quality assurance measurements have been carried out analyzing, with the proposed methods, standard reference materials from BCR and NIST. Furthermore, different mineralization procedures using both microwave and Teflon bomb have been cc~mpared and evaluated.

Key words: waste; landfill; metals and trace elements; precipitation; atomic absorption spectroscopy; neutron activation analysis INTRODUCTION

In the studies related to the environmental impact of waste landfills, one of the most important items is leachate production and its composi~ion. The 0048-9697/93/$06.00 © 1993 Elmvier Science Publishers B.V. All rights reserved

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M. GALLORINI ~ AL.

liquid waste represents the transfer path through which the landfill interacts with the surrounding environment [1]. A series of physical, chemical and microbiological processes occur in the landfills and the subsequent leachates can change in composition and concentration with time. Thus, the control of these effluents becomes essential not only to check the presence of possible toxic substances, but also to assess their behaviour in order to select the most suitable depuration procedure. The analytical controls of this kind of matrix, due to its very complex composition (high amounts of organics, chlorides, sulphides, bromides, complexing agents, etc.), is not an easy task. In the analysis of metals and trace elements, which are often present at nanogram levels, accurate determinations can be conveniently carried out only if s~ecific analytical procedures are followed. For many elements highly sensitive and specific methods of analysis, such as ETAAS and NAA, suffer from matrix effects and element or compound interferences: i.e. high chloride concentration can seriously affect the determination of cadmium and lead at trace levels by ETAAS, while, in the case of NAA, the presence of high amounts of sodium and bromine simply prevents the quantitative analysis of many trace elements. This paper identifies some of the main difficulties which arise in the analyses of leachates using these two analytical techniques. Specific chemical separation procedures to overcome these difficulties and to reinstate the original sensitivity and selectivity of the two analytical techniques are presented.

Characteristics of leac.~ate The industrial waste landfill leachate which has been studied here differs from typical municipal waste landfill leachate since its refuse composition is very different [2]. Moreover, according to the Italian National and Regional rules the industrial refuse allowed to be discharged in these 'controlled' landfills must follow specific leaching te~ts with very low concentration limits (see Table 1) [3]. Analysis of trace elements in the subsequent leachate is difficult, due to the very low concentrations (nanograms) present in a very complex matrix. In Table 2, ranges of the main chemical parameters of the leachate analyzed during a period of 18 months are reported.

Metals and trace eb.ments analysis An ion exchange pre-separation procedure, based on Chelex-10e ~ and a radiochemical separation with inorganic-ion exchangers have been developed to allow the determination of some trace metals by ETAAS a~d RNAA, respectively.

287

METAL AND TRACE ELEMENTS DETERMINATION IN INDUSTRIAL WASTE

TABLE 1 Some metal concentration ranges in industrial refuses (mg/kg) and corresponding concentration ranges (mg/l) obtaine~ in leaching tests Element

conc. ranges (mg/kg) dry wt (105°C)

Leaching test by acetic acid (0.5 N)

Leaching test by CO2 sat. H20

National law conc. limits

Cd Co Cr Cu Hg Mn Ni

0.5-35 1-50 10-3800 5 - ! 800 0.5-15 10-3000 10-1600 125-14 500 35-12000

< 0.01-0.17 < 0.1-0.2 < 0.1-0.2 < 0.05-0.07 < 0.005-0.05 <0.1-0.2 <0.4-8 < 0. I --0.4 <0.1-5

< 0.01 < 0.1 < 0.1 < 0.05-0.4 < 0.005 <0.1-0.3 <0. !-0.6 < 0.0 ! -0. I <0.1-0.12

0.02 -0.2 0.1 0.005 2 2 0.2 0.5

Pb Zn

AAS technique Reliable analysis of metals at ppb levels can be seriously affected by different types of interference and matrix effects whose controls requires special attention. By AAS only a few elements can be determined directly in the leachate. The presence of interfering species such as chlorides (present at % level), sulphides, bromides and organic matter reduces the sensitivity and precision of the measurements.

TABLE 2 Constituents concentration changes of the landfill leachate over 18 months (conc. in mg/l) Constituent

May 89

Sept. 89

May 90

Oct. 90

Dec. 90

pH COD CINH4 + NO2-

7.75 950 2300 165 < 0~0i 5.4 140 180 230 1.5 0.5

8.40 1440 3500 212 < 0.0 ! 6 135 300 248 2.2 i.2

8.40 2500 5000 581 0.05 28 160 560 320 3.75 13.5

8.40 2800 6300 600 0.1 160 180 670 3i 5 3.25 6.50

8.30 4750 7000 650 0.08 175 165 830 360 3.8 12.8

NO 3SO42S 2BrP tot. Phenol tot.

288

M. GALLORINI ET AL

The main interferences encountered during the leachate analysis for the determination of Cu, Cd, Co, Pb by ETAAS were chlorides, sulphides and the organic matter whose interference is indicated in Table 3. The determination of these elements is seriously affected by these interferents, even at low concentrations: not only is the signal suppression very high, but also the absorbance values lay in a very wide values range (up to ± 50% S.D.).

Neutron activation analysis The analysis by this technique, which is one of the most sensitive for many trace metals, is subject to considerable problems, mainly arising from the very high content of sodium and bromine (0.5-1%). During neutron irradiation considerable amounts of 24Na and S2Br are produced and their gamma energies heavily interfere with the gamma lines of the other radio-elements under investigation [4,5]. The determination of elements such as As Se, V, Cr, W, Ni, Sn, Th, present at ppb levels, becomes possible only if appropriate and selective radiochemical separations are carried out on the neutron irradiated samples (RNAA) [6]. REAGENTS AND METHODS All reagents were of high purity grade from British Drug House (BDH). Solutions were prepared in triple distilled water. Chelex 100 (100-:200 mesh) NH4 + form, from BIORAD, the inorganic ion exchanger tin dioxide (TDO) and hydrated manganese dioxide (HMD) from C. Erba. Measures in Atomic Absorption Spectrometry were carried out with an AA spectrometer IL 551 and a Shimadzu GFA-4B Graphite Furnace. All neutron irradiations were made in the TRIGA MARK II Research Nuclear Reactor of the University of Pavia. Microwave dissolutions were performed in Microwave Milestone

TABLE 3 Matrix interference (CI- S 2-, organic matter) in the AAS signal of Cd, Cu, Co and Pb Element

Conc. (#g/I)

CI0.1%

S201%

Organic matter COD 5000 mg/l

Cd Ca C3 P~

I 20 10 10

-25% -5 - 10% -5% -25%

-20 - 25% +!0% -55% -10%

100% suppression no interferences 30 - 40% -40 - 50%

-, signal suppression; +, signal enhancement.

METAL AND TRACE ELEMENTS DETERMINATION IN INDUSTRIAL WASTE

289

Mod ML 1200 (Teflon vessel Mod HPV 80) and in conventional pressure Teflon bombs. Standard reference materials used to check accuracy and precision were BCR CRM Lagarosiphon Major 060 distributed by the Community Bureau of Reference-Bruxelles (Belgium) [7] and NBS-SRM 1566 Oyster Tissues from the National Inst;tute of Standards and Technology, Washington DC (USA) [8].

Chelex separation procedure The proposed separation procedure has been developed to allow the determination of elements such as Co, Mn, Cd, Pb, Cu in the leachate samples by AAS and Mn and V by NAA, this technique was also used for the separation of W, Sn, Ni, Zn and Co which have also been conveniently determined by the specific radiochemical separation adopted in the RNAA of the leachate sample. The Chelex-100 pre-separation (Fig. 1) consisted of four steps. (i) An aliquot of 50 ml of each leachate was added of 5 ml high purity conc. HNO3 and then evaporated at 80°C in a clean hood overnight. (ii) The dry residues were then dissolved in 3 ml cone. HNO3 using both microwave digestion and a conventional Teflon lined dissolution bomb. (iii) After mineralization the solutions were brought to a final volume of 50 ml with triple distilled water and the pH was adjusted to 5 by dropwise addition of high purity I mM KOH. The solutions were passed through a Chelex100, 30 cm height, 1 cm i.d. plastic columns; the resin had previously transformed to the NH4 ÷ form and conditioned with 0.5 M ammonium acetate (pH 5). (iv) The columns were then washed with 3 column volumes of 0.5 M ammonium acetate and triple distilled water; the elements were recovered with 4 ml x 3 of I M HNO~. The nitric solutions were finally brought to 50 ml with triple distilled water and submitted to ETAAS measurements. For the analysis by NAA, 20 ml of the solutions were carefully dried at 60-70°C and the resulting residues neutron irradiated. For these conditions Cd, Co, Cu, Ni, V, Zn, W are separated onto the Chelex-100 column and completely recovered in the final nitric solution.

Procedure checks and blanks control t h e separation technique has been checked in its various stages to control recover3! yields and contribution from blanks. Due to the quite high CI" and Br" concentrations present in the leachates, a series of experiments with known amounts of the elements to be analyzed have been carried out to control the possible losses during the evaporation-drying step, in presence of 1%

290

M. GALLORIN!El" AL.

LEACIIATE SAMPLES ~_ 50 m l

EVAPORATION, DRY 80"C, 5 ml cone. HNO 3

I TEFLO;; BOMB DISSOLUTION I 3 ~ conc. HNO3

Jr20 DILUTION and pll ADJ. at 5

ELUTION WITH I 4 x 3 ml IM HNO 3 [ Cl, S, Br, Ha, P,...

,,

[, IL'~, Ni, Pbt

H20 DILUTION 35 ml FINAL VOL > AAS:

Cd, W, Co, V, Snr Zn, Cu

Fig. 1. Pre-separation and concentration Chelexl00 procedure for the determination of trace elements in landfill leachate samples by AAS.

CI" and 0.6% Br'. The same samples have been also utilized to cheek the recovery yields on the Chelex-100 separations; blank values were obtained by using high pure triple distilled water as a sample. The determh~ations of Cd, Co, Cu and Pb were carried out by AAS while V, Zn, Ni, Sn, Mn and W were analyzed by NAA. The results are presented in Table 4.

291

M E T A L A N D T R A C E ELEMENTS D E T E R M I N A T I O N IN INDUSTRIAL W A S T E

TABLE 4 Chelex separation procedure: yields and blanks values in ng Element

Amount added

Amount recovered

Yield %

Overall blank procedure

Cd a Co a Cu a Mn a'b

250 100 5000 5000 1000 1000 1000 1000 1000 500

246 4. 964. 4890 4. 4930 4. 970 4. 980 4. 965 4. 975 4. 965 4. 4604-

>95 >95 > 95 > 95 >95 >95 >95 >95 >95 >92

64.1 <5 604.9 204.5 354. 6 404.3 604- 10 84-2 504. 8 94.2

Ni a'b

Pb a Sn b Vb Z n a'b

Wb

15 88 150

150 45 30 30 40 45 25

aBy ETAAS. bBy NAA. Values obtained from five ~ndependent experiments.

In o r d e r to reduce the n u m b e r o f steps o f the p r o c e d u r e , an a t t e m p t to avoid the d i s s o l u t i o n step o f the d r i e d phases after e v a p o r a t i o n , w a s c a r r i e d o u t by direct t r a n s f e r o f the e v a p o r a t e d samples o n t o Chelex c o l u m n s after their r e c o n s t i t u t i o n w i t h w a t e r a n d K O H at p H 5. T a b l e 5 s h o w s the results obt a i n e d a p p l y i n g the C h e l e x p r o c e d u r e to l e a c h a t e s a m p l e s t r e a t e d in different conditions. (i) L e a c h a t e samples w h i c h were not s u b m i t t e d to chemical t r e a t m e n t , but only to p H a d j u s t m e n t . TABLE 5 Chelex-100 separation applied to leachate sample~ (50 mi) treated in different conditions {conc. in ~g/I) Element

Cd Co Cu Pb

No chemical treatment Evaporation, drying (f0*C conc. Drying(80*C,conc. HNO~,} only pH adj. at 5 HNO3) and redissolut~on at pH5 bombdissolution (final pH5) Column eluate

i M HNO 3 Colamn final eluate eluate

n.d. 35±5 74-1.5 84.1

0.4 3 I 10

4. 0.1 4-1 4- 0.3 4.2

0.1 8 8 9

I M I INO 3 final eiuate

4. 0.05 0.4 4.1.5 !0 4.2 16 4.2 IG

4. 0.| 4-2 4.3 4.2

Column eluate

! M HNO 3 final eluate

<0.05 <0.1 <0.5
I.i 42 28 41

4. 0.2 4-3 4.4 4.3

n.d. = not detectable. Determination by ETAAS. Values from 3 indeoendent exl~;riments. All values corrected for blank contribution.

292

M. OALLORINI ET AL.

(ii) Leachate samples which have been dried in presence of concentrated HNO3 at 80°C and reconstituted with water. (iii) Leachate samples which have been dried as described above and then dissolved in a Teflon bomb. The complete dissolution and mi,~eralization of the leachate samples must be carried out in order to obtain complete Cd, Co, Cu and Pb absorption onto the Chelex columns and their quantitative recovery in the final nitric acid solutions.

Dissolution procedures Two different dissolution procedures have been used to mineralize the dried leachate deriving from the evaporation of the initial 50-ml samples. (i) Microwave dissolution with 3 ml conc. HNO3. (ii) Conventional pressure Teflon dissolution bomb with 3 ml conc. HNO3. The mj,:rowave dissolution has been carried out a~:cording to the following conditions: 10 min at 25% power; 5 min at 40% power; 10 min at 20% power and 5 min cooling time. The Teflon bomb dissolutiGns were carried out overnight ate! 50°C. In both cases after dissolution, the Teflon vessels were' opened and the resulting solutions brought to a final volume of 50 ml; pH was adjusted to 5 by adding dropwise high purity KOH solution. The Chelex separation was then applied and the final 25 ml 1 M HNO3 eh~ed fractions were submitted for analysis. For the determinations by NAA, the solutions were dried at 60-70°C and weighed amounts of solid residues were neutron irradiated. In the case of the solid standard reference material (BCR CRM Lagarosiphon Major 060) weighed amounts of about 300 mg were transferred in the Teflen dissolution vessels with 5 ml of conc. HNO3 and 0.5 ml of conc. H F - then treated according to the two different dissolution techniques and then g'.,bmitted to the separation procedure. In Tables 6 and 7 Oata are reported for the analysis of BCR and leachate samples, respectively. In both cases the results from the microwave dissolution are lower than those from bomb dissolution; for many elements, such as Cd, Ni, Zn, V, W, the losses were quite consistent. As also reported by other authors [9], the dissolution of samples by microwave systems may result in non-quantitative recovery. In one case we believe that a possible adsorption onto the Teflon walls of the microwaves lissolution vessels, due to their interior 'wrinkledness', not present in the Teflon bomb, can be the main cause of these losses. The possibility of an incomplete dissolution with a formation of very small undissolved particles that car~ be retaiaed onto the columt~, has been investigated by neutron irradiation of Chelex resins and, in our experiments seems not to be consistent. Further investigations with radiotracers are now in progres.s.

293

METAL AND TRACE ELEMENTS DETERMINATION IN INDUSTRI!ALWASTE

TABLE 6 Results obtained in the analysis of BCR C R M 0~i!~by Che|ex-100 procedure and different dissolution methods (conc. in/~g/g) Element

Microwave dissolution

Cd a

1.29 1.49 31.45 1316 51.3 48.0 260

Co a Cu a Mn b Ni b Pb a Z,n b

4. 4. 4. 4. 4. 4. 4.

0.25 0.30 2.5 55 3 2.6 18

Teflon b It~ 3 m b dissolutic~n

Certified values

2.25 4. 0.20 2.02 4. 0.15 52.70 4. 2.1 1709 4. 62 60.604. 2.8 64.81 4. 2.5 330 4. 15

2.2 4. 0.1 n.c. 51.2 4. 1.9 1759 4. 51 n.c. 63.8 4. 3.2 313 4. 8

aBy ETAAS. bBy FAAS. n.c., not certified. Values obtained from 4 independent analyses.

Radiochernical neutron acyivation analysis

The high concentrations of sodium and bromine are the main element~ which are responsible in reducing the sensitivity in NAA in determining many trace elements i~ leachate samples. Elements such as As, Cr, Th, V, Se, Sn, Sb cannot be reliably determined at low levels (ppb) without a specific

TABLE 7 Results obtained in the analysis of leachate samples by Chelex-100 procedure and different dissolution methods (cone. in ~tg/l) Element

Microwave dissolution

Teflon bomb dissolution

Results obtained from "RNAA and hAAS analysis

Cd Co Cs Cu Me Ni Pb Sn Zn W

0.6 4. 34 43.5426 4. 1900 4. 500 4. 34 4. 150 4. 480 4. 28 4.

1.1 4. 42 4. 3.6± 28 4. 2200 4. 860 4. 41 4. 198 ~ 1260 4. 38 ~

n.d. 46 4. 5 a 44Ia n.d. 2300 4. 160 b 950 4. 80 a'b n.d. 220 4. 40 a 13904. 150a', b 42 4. 6 a

0.15 2 0.5 3 150 55 2 30 35 8

0.2 3 0.5 4 150 60 3 28 95 6

All values (obtained from 3 independent experiments) are corroded for the blank contribution.

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M. GALLORINIEl" AL.

radiochcmical separation in order to isolate the radioisotopes of interest from 24Na, S2Br, 32p whose activities interfere in the gamma spectrum. A selective radiochemical separation based on the use of inorganic ion exchangers tin dioxide (TDO) and hydrate of manganese dioxide (HMD) has been developed and used. In Fig. 2 the overall flow chart of the separation is illustrated; 50-ml aliquots of leachate were evaporated at 60-70°C and the /

-! EVAPORAT~0N, DR~ 80°C ,,

5 ml conc.

ID~O3

i

I NEUTRON IRRADIATION

1013 n cm-2 s - 1 (25 h)

f TEFLON B(~NB DISSOL~EION 3 ml HN0~ 0.5 ml HF ,

,

|

!

I 74Asr 75Se e l l 7 m s n w 124Sbr 187W, Th(232pa)

51Cr

24Ha , 82Br ' 32p, 59Fe e 86Rb ' 60Co ' Nl(58Co)w 134Cs w 65Zn

Fig. 2. Radi~hemical separation procedure for trace elements determination in landfill ieachate samples by NAA.

295

METAL AND TRACE ELEMENTS DETERMINATION IN INDUSTRIAL WASTE

resulting residues, sealed in quartz vials, were neutron irradiated together with primary and reference standard materials (NBS oyster tissue 1566) in the central thimble facility of the nuclear reactor at a nominal neutron flux o f 1013 n e m -2 s -I for 25 h. After a period of 2 days cooling time the vials were opened and the samples dissolved with carriers amounts of the elements considered (100-200 /zg) in Teflon dissolution bombs using 3 ml conc. HNO3 and 0.5 ml conc. HF. The mineralized samples diluted with distilled water to a final 1 M H N O 3 , w e r e passed through TDO and HMD plastic columns (10 cm height and 0.8 cm i.d.) in series, which had been previously conditioned with 3 column volumes l M H N O 3 . Under these conditions As, Se, Sb, Th (as Pa), W and Sn were retained onto TDO while Cr is retained in the HMD column. The columns were then washed with 3 column volumes of I M HNO3 to completely recover other elements of interest, such as Ni, Zn, Co, Cs and then dismantled to aIllow the gamma counting of the TDO and HMD phases. The other element:; contained in the eluted fractions were counted after the radioactive decay of 24Na, 82Br and 32p. In Table 8 data of 14 elements determined by RNAA in leachate samples

TABLE 8 Some metals and trace elements determined by RNAA in landfill leachP,te samples and m NIST (NBS-SRM 1566 Oyster Tissue). Concentration in ttg/ml ano ~g~g, respectively. Element

Landfill ieachate

NIST (NBS-SRM 1566 oyster tissu¢~ Found ill this work

As Co Cr Cs Mn a Ni Rb Sb Se Sn Th Va

0.250 4-0.035 0.046 4. 0.005 0.063 4.0.015 0.004 4.0.0018 2.2 4. 0.25 0.95 4-0.08 2.02 4. 0.30 0.118 4. 0.035 0.013 4. 0.006 0.220 4. 0.040 0.0006 4. 0.0002 0.054 4.0.018

14.3 4. 0.030 4. 0.610 4. 0.033 4. 18.1 4. 0.91 4. 4.38 4. < 0.020 !.85 4. n.d. 0.120 4. 2.1 4.

Zn

1.39

806

W

0.042 4. 0.006

4. 0.15

< 0.015

0.6 0.003 0.105 0.006 2.5 0.08 0.25

Certified 13.4 ±

1.9

(0.4) 0.69 i

0 27

~.C,

I'/.f 4. 1.2 1.03 4. 0.19 4.45 4. 0.09 n.c.

0.23

0.030 0.4 4. 25

2.1 4. 0.5 n.c.

0.10) (2.8) 852 ± 14 n.c.

aDc~ermined by Chelex-100 pre-irradiation separation. n.c., not certified. Values in parentheses are informative values. Values obtained from 3 independent analyses, n.d., not detectable.

296

M. GALLORIN! El" AL

are reported; the results have been obtained from 4 independent analytical runs and the same p~-ocedure has been used for the analysis of the NBS-SRM 1566 oyster tissues ~.o check accuracy and precision. Determination of v~adium and manganese

These two elements can be determined with very good sensitivity by neutron activatio~ analysis via their short radionuclide half-lives 4sV and 56Mn (tl/2 3.6 mi, and 2.58 h, respectively). Unfortunately in this case, the high concent,,~dons of chloride and sodium, through the activity of the corresp~:~ ding 3SCl and 24Na (tin/2 38 min and 15 h, respectively), mask the gamma spectrum preventing the correct determination of traces of 4sV and 5%~n. Separation after irradiation is rather difficult and a pre-separation procedure should be followed. Since both vanadium and manganese showed a good selective behaviour in the Chelex-100 separation, this procedure has been used for their determination by neutron activation analysis as previously reported. The corresponding results are reported in Tables 8 and 9. TABLE 9 Some metals and trace elements in landfill leachat~ determined by different procedures and analytical techniques (cone. in ~g/I) Element

AAS

Chelex procedure and AAS

Chelex procedure and NAA

RNAA TDO-HMD

As Cd Co Cr Cs Cu Mn Ni Pb Rb Sb Se Sn Th V Zn W

n.d. n.d. n.d. 60 n.d. n.d. 2300 920 n.d. n.d. n.d. n.d. n.d. n.d. n,d. 1100 n.d.

n.d.

n.d n.d. 42 4. 1 n.d. 3.6 4. 0.5 n.d. 2200 4. 250 940 4. 60 n.d. n.d. n.d. n.d. 198 4. 28 n.d 54 4. 18 1220 :t: 80 38 4. 6

250 ± n.d. 46 4. 63 4. 4 4. n.d. n.d. 950 4. n.d. 2020 4. 1184. 13 ~ 220 4. 0.6 4. n.d. 1390 4. 42 4.

4.

5a

4. 160 b 4. 90 b

4.

'By ETAAS. bBy FAAS. n,d., not determined,

90 b

1.1 4. 42 4. n.d. n.d. 28 4. 2100 4. 900 4. 41 4. n.d. n.d. n.d. n.d. n.d n.d. 1300 4. n.d.

0.2 a 3a

4a 100 b 50 b 3a

95 b

35 5 15 0.18

80 300 35 6 40 0.02 150 6

METAL AND TRACE ELEMENTS DETERMINATION IN INDUSTRIAL WASTE

297

RESULTS AND DISCUSSION

Table 9 shows the overall results obtained with the different proposed analytical procedures in the trace elements analysis of the leachate samples. Seventeen elements have been determined and, except for Mn, Ni, Zn and Rb, present at ppm levels, the concentration of the other elements is in the nanogram range. Four elements (Cr, Mn, Ni and Zn) can be directly determined by AAS in the leachate samples, while for all the others a chemical separation must be applied. The results obtained after determining the same elements by different analytical techniques are in excellent agreement, as in the case of Co, Mn and Ni; only in the case of Zn the values are quite scattered (S.D..-- 15% of the medium values). The results for those elements which have been determined by NAA coupled to either the Chelex-100 pre-irradiation separation or TDO-HMD after irradiation separation, are also in good agreement; nevertheless, the higher values obtained by TDO-HMD seem to be more valuable, due to a better ~recovery which derives from the possibility of adding carriers. CONCLUSIONS

The proposed procedures meet the principal requirements necessary to trace element ~lalysis in samples of landfill leachate and allows the determination of several elements at ppb level. Both the adopted chemical separations gave good results in selectivity, efficiency and recovery yield as has been demonstrated in the analysis of standard reference materials. The Chelex-lO0 separation combines the advantage of very low blank values with a high decor~tamination factor from the interfering elements; it was found to be very relial:~e for Mn and V pre-irradiation separation, suggesting its application to oilier difficult matrices, such as biological tissues and fluids with high sodium, chlorine and phosphorous content. REFERENCES 1 D.J. Lisk, Environmental effects of landfills. Sci. Total Environ., 100 (1991) 415-468. 2 J.M. Lema, R, M~ndez and R. Blazquez, Characteristics of landfill leachates and alternatives for their treatment: A review. Water Air Soil Pollut., 40 (1988) 233-250. 3 Italia Low: Gazzetta U~ciale no. 141, May 29, 1976. Law n 319/76. 4 M. Gallorini, E. Orvini, A. Roll a and M. Burdisso, Destructive neutron activation analysis of toxic elements in suspended ~n~erials released from refuse incinerators. Analyst, 106 (1981) 328-331. 5 M. Gallorini and E. Orvini, The role of the radiochemical neutron activation analysis in certifying selected trace elements content in biological related matrices. Tr~.e Element Analytical Chemistry in Medicine and Biology, P. Bratter and P. Schramel (EdsL W. de Gruyter, Berlin, 1980, pp. 675-699.

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6 P. Pietra, E. Sabbioni, M. Gallorini and E. Orvini, Environmental, toxicological and biomedical research on trace metals: radiochemical separation for neutron activation ano aiysis..I. Rad. Nucl. Chem., 102 (1986) 69-98. 7 BCR, Reference Materials Catalog, Commission of the European Community, (1992) p. 12. 8 NIST, Standard Reference Materials Catalog, NIST Special Publication 260. Dept of Commerce, Gaithersburg, MD, USA, 1991, p. 51. 9 R,R. Greenberg, H.M. Kingston, R,L. Watters and K.W. Pratt, Dissolution problems with botanical reference materials. Fres. J. Anal. Chem., 338 (1990) 394.