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Seventh Conference of Nuclear Sciences & Applications 6-10 February 2000. Cairo, Egypt En-4 Radioactivity Concentrations in some Industrial Ores and their Waste Products by Gamma Spectrometry.

N.M.Ibrahiem*,B.EI Ezaby,A-Nada, T.MAbd El-Maksoud & S.A.Abd El Azeem. Physics Department, Women's College, Ain Shams University, Cairo. National center for nuclear safety & radiation control, EAEA,. Cairo, Egypt.

ABSTRACT

Some industries as cement, ceramic and production use raw materials containing low concentrations of natural radioactivity, which concentrate and release radionuclides with enhanced concentrations to the environment. NORM wastes produced annually in huge amounts could reach levels so high that the existing low level radioactive waste (LLRAW) facilities would be readily occupied, if controlled disposal procedures were not adopted. Also NORM wastes may be used as raw materials in other industries especially in building and construction industries. Complete informations about NORM wastes are not enough in key industries. In this article raw materials in cement industry (raw meal), ceramic ore (kaolinite) and ceramic glaze (bauxite) as well as phosphate, and also waste products in cement industry (klinker and dust), and phosphogypsum were analyzed by high resolution gamma spectrometry to evaluate the natural radionuclide contents in such samples.

Key words: natural radioactivity, NORM, ceramic, kaolinite, bauxite, phosphate, phosphogypsum, cement.

INTRODUCTION

Naturally occurring radioactive material (NORM) wastes is the main source of about 80% of human exposures. Some industrial activities as the production of phosphate production, cement and ceramic industries produce unwanted byproducts. NORM cannot be ignored even being lower than the exempt concentration levels (ECL'S)(I). Construction industries need large low cost amounts, in the other hand large volumes of NORM wastes produced annually from industrial processes encourage the use of these byproducts for construction purposes. Some byproducts have higher concentrations of radionuclides than the raw materials used in these industries. These byproducts may increase the human exposure to natural radiation when used in construction industry. In this article high resolution gamma spectrometry were applied to measure the contents of radionuclides from the 238- 226,thorium232 and uranium235- actinium series as well as 40K in, [1] Raw meal, used in cement production which is a mixture of coal, [CaSO4.2H2O] cement rock and limestone [Ca COj]. Also three other samples, the produced cement , cement clinker for brick production ,and the dust which is a waste product in this industry. [2] Phosphate ore and its end product phosphogypsum produced from phosphorites manufactory. [3] Ceramic ore and ceramic glaze ( kaolinite [Al2Si2O5(OH),i]&bauxite [Al2O3.nH2O] respectively)(2).

All these raw materials belong to sedimentary rocks, which contains uranium and in variable concentrations and may be concentrated in the waste products. This may cause radiological hazards if used in construction industry or released to the environment .So it may need to be considered as radioactive wastes, and to be disposed under controlled procedures/1' 923 EG0100092 The aim of this study is to measure the concentrations of the individual natural gamma emitters in the uranium, thorium, actinium series and 40K in the previous samples. Also to compare the radionuclides concentrations in the waste products with the exempt levels put by the IAEA, which are of scientific interest to geochemists, radiological interest to health physists and of economic interest to manufacturers from the economic point of view.

SAMPLES AND MEASUREMENTS Cement, cemet products and cement waste products were provided by the Arabic Cement Company in Suez .The phosphate and phosphogypsum samples were provided by El Nasr Company of fertilizers and chemical industries, Abu-Zaabal. The ceramic samples were provided by the Arab ceramic productive company. The prepared samples were transferred to a 750 ml or 500ml Marinelli beakers for gamma measurements and sealed for eight weeks to ensure secular equilibrium between uranium-238 and thorium-232 and their radioactive progeny . A high resolution gamma spectrometer based on a hyper pure germanium detector from EG&G Ortec were used for the gamma analysis .The HpGe crystal has diameter of 64.5 mm and 69.9 mm length , relative effeciency of 50% ,peak to Compton ratio 62 ,FWHM of 1.9 keV at the 1.33 MeV 60Co transition and 753 eV at the 122 keV 57Co transition .

The effeciency calibration for the system has been explained in a recent publication [Ibrahiemetal.,1999](4).

For the uranium - 238 series gamma energies of 63.3 keV (3.8%)234Th 186.1 keV (3.3%) 226Ra (after the subtraction of the 185.7 keV 53% of 235U), the 295.1 keV(19.2%), and 352.0 keV (37.1%) 214Pb, and 609.3 keV (46.1%), 768.4 keV (5%), 934.0 keV (3.4%) and 1120.3 keV (15%) 214Bi, were taken to determine the concentrations of the assigned nuclides in the series (5).

For the 232Th series gamma energies of 463.1 keV (4.6%), 911.2 keV (29%) and 966.0 keV (2.3%) 228Ac, 727.3 keV (6.7%) and 1620.7 keV (1.5%), 212Bi and the 583.0 keV (30.9%) 208TI were taken to represent the concentrations of the assigned nuclides in the series(5)

For the actinium series gamma energies of 143.8 keV (10.5%), 163.4 keV (4.7%) and 205.3 keV (4.7%) were taken to represent the 235U concentrations^.

The 1460.8 keV (10.7%) gamma energy was taken to determine the 40K concentration^.

Exposure to radiation has been defined in terms of the radium equivalent activity (Raeq) which is given by Beretka and Mathew(6&7)

Raeq = ARa+ 10/7 An + 10/130 AK m

40 Where ARa, An, and AK are the specific activity of Ra,Th and K respectively in Bqkg'1 .For materials used in building constructions , to limit the annual external gamma -ray dose to 1.5m Gy. The external hazard index (Hcx) is determined from the equation

Hex = ARa /370 + A™ /259 + AK /4810 [II]

The internal exposure to 222Rn and its radioactive progeny ,is controlled by the internal hazard index H ;„ ,given by the equation

H in = ARa/185 + Ath/259 + AK/4810 [III]

924 RESULTS AND DISCUSSIONS

Eissa et al (8),analyzed a phosphate ore sample ,provided by Abu-Zaabal Company for fertilizers and Chemicals ,by prompt and delayed neutrons activation analysis .The measurements were done by high resolution gamma-ray spectrometry .They found the thorium-232 content (0.85 ppm) 3.4Bq kg "' and the uranium-238 concentration to be (52ppm) 644.8Bq kg"1 .In the present investigation thoium-232 in equilibrium with actinium- 228,was found to be 7.2 Bq kg"1 ,238U in equilibrium with 234Th was found to be 1.39 k Bq kg'1,while the235 U content was measured to be 19.4 Bq kg"1 (table I).

Table 1: Activity concentration for different nuclides in (Bqkg'1). Nuclide Concentration (Bqkg"1 ) Phosphate ore Phosphogypsum Kaolinite Bauxite Uranium series Th-234 1391.4+70.0 30.0+17.5 282.8+29.7 58.4+10.7 Ra-226* 470.5+18.8 407.1+5.4 148.5+3.7 41.1+2.2 Pb-214 391.0+20.0 313.2+6.2 75.2+5.6 23.0+1.0 Bi-214 373.0+3.5 285.1+5.7 67.2+18.1 22.0+2.0 Thorium series Ac-228 7.2+1.0 15.5+0.8 48.6+8.9 25.5+1.9 Bi-212 6.0+0.9 3.5+1.8 49.8+2.4 35.5+1.4 Tl-208 LLD LLD 47.7+1.8 27.7+0.6 Actinium Series U-235 19.4+3.5 LLD 3.8+0.6 LLD K-40 15.2+0.8 23.0+0.1 960.0+7.2 519.1+5.0 *226Ra concentration was calculated after the subtraction of the 185.7 keV(53%)gamma of235U

Analysis of the phosphogypsum sample (table I) shows that the 238U content is lower than the limit of detection (LLD), which is in agreement with the results obtained by Testa et al.(9) for samples from Togo and Boucraa .They explained the absence of uranium in the phosphogypsum samples to be due to the chemical process, with sulfuric acid H2SO4 precipitation of [Ca(Ra) SO4] and the formation of strong uranium phosphate complexes in the H3PO4 .Also 226Ra content in both phosphorite and phosphogypsum were found to be in the same order, which is also in agreement with the results obtained by Testa et al.(9). Results for 238U and 226Ra concentrations in the phosphate ore sample show state of disequilibrium, which can be explained by weathering occurring to phosphorites due to their sedimentary origin (3), the sample content of 235U is 19.4 Bq kg'1.

Table 1 gives also concentrations for the different radionuclides in the 238U-226Ra series, thorium 232 series as well as 40K,in ceramic raw materials, kaolinite and the bauxite used as glaze in ceramic industry. Both samples show state of disequilibrium in the natural radioactivity which can be explained also by the sedimentery origin for both samples'3' .

Table 2 represents the content in Bq kg'1 of different radionuclides in four samples in different stages in cement industry, the raw meal, cement, cement klinker which is used for cement brick production, and cement dust (cement waste product).

925 Table 2 : Activity concentration for different nuclides in (Bqkg*1).

Nuclide Concentration (Bqkg"1) Raw meal Cement Cement bricks Cement waste Uranium series Th-234 68.2+3.2 S7.+5.8 79.5+6.8 72.8+10.2 Ra-226 38.4+5.6 50.8+0.8 53.2+1.0 57.1+1.7 Pb-214 19.5=2.1 28.0+2.6 30.5+2.1 29.0+3.0 Bi-214 18.2+6.0 26.0+8.0 28.8+7.8 27.3+10.3 Thorium series Ac-228 7.0+2.0 10.2+2.9 13.4+0.9 11.8+3.4 Bi-212 9.5+2.7 13.6+0.4 14.2+0.5 12.2+1.0 Tl-208 7.3+0.1 10.6+0.1 12.0+0.2 10.0+0.3

K-40 84.5+0.6 69.4+0.8 75.2+0.9 1606.2+15.3

Ra-226 content in both the cement and the cement klinker are about the same range ,as well as both of the thorium-232 series and the 40K concentrations. For the cement dust the analysis shows about the same range for the uranium-radium 226 and the thorium series concentrations compared with that in cement ,but the 40K content is about 1.6 k Bq kg"1 (about twenty one times to that in both cement and klinker).

Table 3 gives the Raeq, the external hazard and the internal hazard indices Hex &H,n respectively, for samples, which may be used in building constructions. Racq for cement and cement klinker are about one fifth of the maximum recommended limit, which is 370 Bq kg"1(7)

Table 3 Ra<,q ,Hex &Hin in materials used as building materials .

1 Material Ra ea Bq kg" Hcx Hin Cement 70.6 0.19 0.33 Cement bricks 78.1 0.21 0.35 Phosphogypsum 430.9 1.16 2.26 Kaolinite 281.8 0.76 1.16 Bauxite 117.5 0.32 0.43

1 For the kaolinite sample Raeq is found to be about 282 Bq kg" and Hin > 1.For the 1 bauxite sample (ceramic glaze) the Raeq is found to be about 118 Bq kg" and both Hiri &Hex are less than one for each. Although Racq is less than the maximum permitted value for building materials, it is recommended to minimize the ceramic areas indoors to decrease human exposure to inhabitant as low as possible For phosphogypsum which may be used as gypsum plaster, also it may be added in both 226 cement and bricks production, it shows high content of Ra,which in tern increases Racq ,Hjn & Hex (table HI gives Hex >1 & Ra«,~430). So it has to be excloded to be used as gypsum plaster. But for cement and- bricks production, it may be used, taking in consideration the radioactivity concentrations in the final product as a whole depending on the percentage of the waste product added. The concentrations of the different radionuclides in phosphogypsum are less than the exempt level of radiation(l).

926 ACKNOWLEDGEMENT This work has been done at Dr Hosnia Abu-Zeid laboratory, Prof, of nuclear physics,Faculty of Girls ,Ain Shams University.One of the authers DrNagdya Ibrahiem is indepted to Prof Dr H. Abu-Zeid for offering her the facilities to go on with research work.

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