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A Study on the Radioactivity Level in Raw Materials, Final Products and Wastes of the Phosphate Fertilizer Industries in Bangladesh

Md. Abdus Samad
Department of Physics, Jahangirnagar University, Savar, Bangladesh

Md. Abu Haydar
Health Physics and Radioactive Waste Management Unit, Institute of Nuclear Science and Technology, Atomic Energy Research Establishment, Savar, Bangladesh

Md. Idris Ali
Health Physics and Radioactive Waste Management Unit, Institute of Nuclear Science and Technology, Atomic Energy Research Establishment, Savar, Bangladesh

Debasish Paul
Health Physics and Radioactive Waste Management Unit, Institute of Nuclear Science and Technology, Atomic Energy Research Establishment, Savar, Bangladesh

Md. Mahbubur Rahman Bhuiyan
Department of Physics, Comilla University, Comilla, Bangladesh

Sheikh Mohammad Azharul Islam
Department of Physics, Jahangirnagar University, Savar, Bangladesh

Abstract/ Executive Summary:

A study on the detection of probable radionuclides and their activity concentrations in the raw material (phosphate rock), final product (fertilizer) and waste samples collected from all the phosphate fertilizer factories (total two factories: a Diammonium Phosphate, DAP and a Triple Super Phosphate, TSP factory) in Bangladesh were carried out. A total of seven types of samples (grossly divided into solid and liquid types); liquid waste, waste-mixed river water, normal river water, phosphate rock, phosphate fertilizer, solid waste and normal soil; were analyzed under this study. Raw material samples were collected only from the TSP fertilizer factory. Fertilizer, solid and liquid waste samples were collected from both the factories under study. Moreover, normal soil and natural surface water samples from the suitable areas adjacent to the factories were also collected for the comparison purpose. The samples were analyzed by gamma ray spectrometry technique using a Hyper-Pure Germanium (HPGe) detector of 40% relative efficiency. The analysis of the samples showed that only natural radionuclides such as ²²⁶Ra, ²³²Th and ⁴⁰K were present in the samples and no traces of artificial radioactivity were found in any of the samples. 40K was found below the detection limit in some samples. The analysis of the samples in the case of TSP fertilizer factory showed that the average activity concentrations of ²²⁶Ra and ²³²Th and ⁴⁰K in raw materials were 851.27 ± 7.10, 19.63 ± 6.57 and 54.06 ± 5.93 Bq/kg, respectively, in final product 211.90 ± 4.74, 42.48 ± 10.56 Bq/kg and ND (Not Detected), respectively, in solid waste 187.49 ± 4.88, 70.06 ± 11.76 and 289.27 ± 40.24 Bq/kg, respectively and in liquid waste 6.26 ± 0.63, 10.01 ± 1.39 Bq/L and ND, respectively. The measured results in the case of samples collected from DAP fertilizer factory showed that the average activity concentrations of ²²⁶Ra and ²³²Th and ⁴⁰K in the final product were 17.31 ± 3.92, 69.74 ± 9.88 and 48.46 ± 17.22 Bq/kg, respectively, in solid waste 24.47 ± 4.15, 164.62 ± 11.08, 191.52 ± 33.74 Bq/kg, respectively and in liquid waste 3.59 ± 1.05, 37.08 ± 3.30 Bq/L and ND, respectively. Considering the stored raw materials and wastes the part of the ambient environment of the factory, radium equivalent activity, radiation hazard index and external annual effective dose to the workers and public due to these materials were also calculated and compared with world average values.

Keywords: Radioactivity level; Phosphatic fertilizer, Rock phosphate , Contamination of soil, Radionuclides in raw materials

Location: Department of Physics, Jahangirnagar University, Savar

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Fertilizer

Objectives:

To determine the level of radioactivity in raw materials, final products and wastes generated from the phosphate fertilizer factories of Bangladesh and
To estimate the radiological impact due to the use of the phosphate fertilizer and release of the wastes in the environment.

Methodology:

The samples were collected from TSP and DAP fertilizer factories situated in Chittagong in the south-east region of Bangladesh. The factories stand on the bank of Karnaphuli river. Karnaphuli river is also the main source of water for local irrigation. Phosphoric acid, phosphate rock and NH₃ are used as the starting material for producing TSP whereas imported phosphoric acid and NH₃ are used for producing DAP fertilizer in Bangladesh. The phosphoric acid in TSP factory is produced by reacting concentrated sulphuric acid with phosphate rock. A total of 49 samples of seven different types namely 1) liquid waste, 2) waste-mixed water from the liquid waste disposal point of the Karnaphuli river, 3) normal water from Karnaphuli river, 4) phosphate rock (TSP only), 5) final product (fertilizer), 6) solid waste and 7) normal soil adjacent to the factory were collected from both the factory complexes and their nearby areas. Of these 49 samples, 22 were liquid and 27 solid. Of the 22 liquid samples, there were 10 liquid waste samples, six waste-mixed water samples and six normal water samples collected from the two factories. Whereas of the 27 solid samples, there were 5 raw materials samples, 10 solid waste samples, 6 fertilizer samples and 6 normal soil samples collected from both the factories. Equal numbers of samples were also collected from each factory for all the cases except in the case of raw material samples which were collected only from the TSP fertilizer factory. Standard methods were followed to process the samples for characterization.Marinelli type beakers (2 liter capacity) were used to process and measure the liquid samples. At the start of the sample processing steps, the beakers were made contamination free by cleaning those well using light hydrochloric acid solution and deionized water. The beakers were then dried using a temperature-controlled oven and the empty weights of the beakers were noted. The beakers were then filled with liquid samples. The net weights of the samples were found from the difference of weights of sample-filled and empty beakers. Finally, the beakers filled with samples were closed by caps, wrapped with thick vinyl tape about their caps and kept for 30 days for achieving the secular equilibrium between ga- seous and non-gaseous decay products of naturally occurring radioactive series.The solid samples were dried in the sun for several days. In order to obtain representative samples, they were thoroughly mixed, sieved to remove stones, pebbles, grass roots, straws etc. The samples were then crushed into small pieces and dried again in a temperature controlled oven at 100°C for 24 hours in order to remove the moisture content in the samples. The dried samples were ground to fine powder and passed through a sieve of mesh size of 200 μm. The samples were then filled in cylindrical plastic containers of 6 cm diameter and 7 cm height with a volume of 180 ml. The weights of all the samples were taken by an electronic balance and the net weights of the samples were noted. Finally, the plastic containers were closed by caps and wrapped with thick vinyl tape about their necks to seal the containers tightly. The samples were then stored for about 30 days to assure secular equilibrium between the ²³⁸U and ²³²Th series and with their daughters.The detection and measurement of radionuclides in the samples were carried out by gamma spectrometry technique using a vertical coaxial cylindrical HPGe detector of 172 cm³ active volume and of 40% relative efficiency. The p-type HPGe detector supplied by CANBERRA (Model-GC4020) had a resolution of 2 keV at 1332 keV of ⁶⁰Co gamma ray line. The detector was coupled to a 16 k-channel analyzer. The spectra of all samples were per-fectly analyzed using Genie-2000 spectra analysis soft-ware (which matched various gamma energy peaks to a library of possible radionuclides) to calculate the concentrations of ²³⁸U, ²³²Th and ⁴⁰K. The detector was en-closed in a cylindrical shielding container made of lead and iron with 11.3 cm thickness, 51 cm height and 28 cm internal diameter and having a fixed bottom and moving cover to reduce the external y-ray background. All the samples were counted for 10 ks. Prior to the measurement of samples, the environmental gamma background at laboratory site was determined with an identical empty Marinelli beaker and plastic container used in the sample measurement. The energy regions selected for the corresponding radionuclides were 295 keV and 352 keV of ²¹⁴Pb and 609 keV, 1120 keV and 1764 keV of ²¹⁴Bi for ²²⁶Ra, 583 keV and 2614 keV of 208Tl, 911 keV and 969 keV of ²²⁸Ac for ²³²Th and 1460 keV for ⁴⁰K.The efficiency calibration of the detector was performed by standard sources of solid and liquid matrices prepared using ²²⁶Ra standard solutions. The standard sources were prepared using identical containers used for the measurement of the samples, e.g., 2L Marinelli beakers for liquid and 180 ml plastic container for solid samples. The preparation process of standard sources had been reported elsewhere. The detector efficiency calibration curves as a function of energy for both liquid and solid matrices are shown. The energy calibration of the detector was performed by ¹³⁷Cs and ⁶⁰Co point sources.

Source of Information: Journal of Environmental Protection, 2012, 3, 1393-1402

Article Link (Online Journal): http://dx.doi.org/10.4236/jep.2012.310158

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The radionuclides detected in the solid and liquid samples were all natural and no artificial radionuclide was found in the study. The hazard index, H_ex and annual effective dose, E for the phosphate rock, wastes and normal soil samples were found within the acceptable limit except the hazard index for phosphate rock which was found higher than unity. This study could be useful as a baseline data on the radiological impact of the fertilizer industry on the public and the environment of Bangladesh.

Knowledge Management: Journal