Session: Radiation Protection of the Public and the Environment

THE RADIOLOGICAL IMPACT OF THE BELGIAN PHOSPHATE INDUSTRY

Vanmarcke H. and Paridaens J. Belgian Nuclear Research Centre, SCK•CEN, Boeretang 200, 2400 Mol,

Abstract

The Belgian phosphate industry processes huge amounts of phosphate ore (1.5 to 2 Mton/year) for a wide range of applications, the most important being the production of phos- phoric acid, fertilizers and cattle food. Marine phosphate ores show high specific activities of the natural uranium decay series (usually indicated by Ra-226) (e.g. 1200 to 1500 Bq/kg for Moroccan ore). Ores of magmatic origin generally contain less of the uranium and more of the thorium decay series (up to 500 Bq/kg). These radionuclides turn up in by-products, resi- dues or product streams depending on the processing method and the acid used for the acidu- lation of the phosphate rock. Sulfuric acid is the most widely used, but also hydrochloric acid and nitric acid are applied in Belgium.

For , the northern part of Belgium, we already have a clear idea of the production processes and waste streams. The five Flemish phosphate plants, from 1920 to 2000, handled 54 million ton of phosphate ore containing 65 TBq of radium-226 and 2.7 TBq of thorium- 232. The total surface area of the phosphogypsum and calcium fluoride sludge deposits amounts to almost 300 ha. There is also environmental contamination along two small rivers receiving the waste waters of the hydrochloric production process: the Winterbeek (> 200 ha) and the Grote Laak (12 ha).

The data on the impact of the phosphate industry in the Walloon provinces in Belgium is less complete. A large plant produced in 2004 0.8 Mton of phosphogypsum, valorizing about 70 % of the gypsum in building materials (plaster, cement), in fertilizers, and in other prod- ucts such as paper. The remainder was stored on a local disposal site.

The radiological impact of the Belgian phosphate industry on the local population will be dis- cussed. At present most contaminated areas are still recognizable as waste deposits and inac- cessible to the population. However as gypsum deposits and other contaminated areas quickly blend in with the landscape, it is important to take regulatory measures to prevent a change in land use. The most adverse scenario would be the conversion of contaminated sites into resi- dential areas.

1. NORM in the Belgian industry

Problems with NORM (naturally occurring radioactive materials) are not limited to the proc- essing of raw materials containing high specific activities of the uranium or thorium decay series. In fact, almost every industry with a large turnover of materials has some problems with NORM, because of the selective concentration of certain radionuclides in by-products, residues or product streams. A recent comprehensive study identified ten industries within Belgium where processing of NORM can cause environmental contamination, waste prob- lems or an increased exposure of workers and members of the public (Vanmarcke, 2003):

• phosphate industry; • non-ferro industry; • zircon sands and refractory materials; • steel industry; • coal-fired power plants; • cement production; • use of thorium compounds; • extraction and purification of drinking water; • former mining area of alum shale; • waste dumps of coal-mines; Also other industrial activities in Belgium, like the titanium dioxide pigment production and the oil and gas industry were identified and there relevance for generating by-products or residues with enhanced natural radioactivity was checked.

Widely divergent exposure scenarios apply to the various NORM industries and even within the same industry. The phosphate industry, which is the main source of enhanced natural ra- dioactivity in Belgium, is discussed in this paper. It is an excellent example to illustrate this point. The nature of the NORM problems differs widely from one phosphate plant to another and simple protective measures are in most cases sufficient to reduce the occupational and public exposures (Vanmarcke, 2005). That's why the European Legislation on work activities is kept deliberately flexible (EU-BSS, 1996). Furthermore there is a vast legacy from past NORM practices. Many of the historical sites were contaminated before present standards of radiological protection were developed.

2. Overview of the Belgian phosphate industry

Phosphate ores contain different amounts of natural radionuclides, according to their origin. Marine (or sedimentary) phosphate ores show radionuclide concentrations from the uranium decay series which are a factor 10 to 100 higher than the typical values of the Belgian soil. Ores of magmatic origin contain less of the uranium and more of the thorium decay series. The natural radioactivity of the phosphate ores used in Belgium is shown in table 1. Most of the information was collected on the request of the Flemish Environment Agency (Paridaens, 2001 and 2002).

Table 1. Range of specific activities of the natural uranium and thorium decay series in phos- phate ores used in Belgium. The typical range for Belgian soil is also indicated.

Origin U-238 (Ra-226) Th-232 Bq/kg Bq/kg Marine phosphate ore 500 - 5000 10 - 100 Morocco 1200 - 1600 10 - 30 Florida 1500 - 2000 20 - 60 Magmatic phosphate ore 30 - 150 20 - 500 Kola (Russia) 30 - 60 60 - 100 Palfos (South Africa) 150 500 Belgian soil 10 - 50 10 - 50

The natural radioactivity of phosphate rock is only an ‘annoying’ property that is mostly com- bined with the presence of heavy metals. The production process determines where the radio- activity of the ores turns up. The acidulation of phosphate rock with sulfuric acid (H 2SO 4) is the most widely used method. The by-product is insoluble calciumsulphate or (phos- pho)gypsum (CaSO 4), which contains the bulk of the radium-226 activity. The five plants in Belgium using, or having used, this production process are: • UCB, Ostend (1953 - 1987); • Prayon , Puurs (1963 - the basic phosphoric acid production facility moved to Mo- rocco in 1992); • Rhodia Chemie, Zelzate (1925 - up to now); • BASF, (1967 - 1993); • Prayon, Engis (1973 - up to now).

Tessenderlo Chemie produces dicalciumphosphate through acidulation with hydrochloric acid (HCl). The main by-product is a sludge of calciumfluoride (CaF 2). Two thirds of the radium went into the solution and was evacuated with the effluent waters in two small rivers: the Grote Laak and the Winterbeek. In 1991 a decontamination stage, based on dissolved barium salts, was put into operation, decreasing the radium contents of the effluent waters by about an order of magnitude, at the expense of tripling the radium activity of the waste sludge. The two production units of Tessenderlo Chemie are located in the neighboring villages of Tes- senderlo (1920 - 1995) and Ham (1931 - up to now).

BASF Antwerp uses since 1980 also nitric acid (HNO 3) as dissolution agent. Here no substan- tial waste flows are being produced. This implies that the radioactivity is transferred from the ore towards the end products, which are in this case fertilizers (1980 - up to now).

3. The phosphate industry in Flanders

The five phosphate plants, which were active in Flanders during the last 100 years were stud- ied in a similar way. Firstly, the plant was contacted with specific questions on the turn over of materials, production processes, radioactive mass balances, by-products, waste deposits... Then we visited the plant to have an impression of the actual situation. With a portable gam- ma detector we measured the dose rates on the plant's premises and on the disposal sites. Samples were taken where enhanced dose rates were observed. They were analyzed with high resolution gamma spectroscopy to determine the specific activities of the uranium and tho- rium decay series. Track etch radon detectors were placed for a period of 6 months on the disposal sites at 1.5 m above ground level.

3.1 UCB Ostend

UCB produced between 1953 and 1987 phosphoric acid (P 2O5) through wet acidulation of marine phosphate rock with sulphuric acid. The phosphate rock was of Moroccan origin con- taining typically from 1200 to 1500 Bq/kg radium-226. For each ton of phosphate ore, 0.3 ton of phosphoric acid and 1.5 ton of by-product gypsum was produced, diluting the radium-226

activity with about the same factor, with respect to the ore (from 800 to 1000 Bq/kg). On the basis of the available production figures of phosphoric acid, 6 Mton of gypsum should have been produced. 4 Mton was stored on two separate gypsum deposits. It is unclear what hap- pened to the rest, if ever produced. • Deposit Zandvoorde (1970 - 1987): 3.1 Mton phosphogypsum on 16 ha, 15 m high; • Deposit Oudenburg (1953 - 1970): 0.9 Mton phosphogypsum on 8.5 ha, 7 m high.

3.2 Prayon Rupel Puurs

Prayon Rupel

Potaarde in Niel

Recreational area in Boom

Hollebeek in Rumst

Company premises in Puurs

Polders-Hoeykens in Puurs 0 1 2 3 km

Figure 1. Overview of the many gypsum deposits around the production plant in Puurs men- tioning the five deposits that we investigated on the request of the Flemish Envi- ronment Agency (Paridaens, 2001 and 2002).

Prayon Rupel produces since 1963 phosphoric acid in Puurs from Moroccan phosphate ore. The production process on the basis of diluted sulfuric acid shows large resemblance with that of UCB. The specific radium-226 activity of the by-product gypsum is from 800 to 1000 Bq/kg. The basic phosphoric acid production facility moved to Morocco in 1992, after the authorities rejected the renewal of the disposal license for the phosphogypsum. 12 Mton of phosphogypsum were produced between 1963 and 1992, of which 10 Mton were disposed of and 2 Mton were sold to the building industry, mainly for the production of plasterboards. The valorization of phosphogypsum began in 1972 and reached a top with 0.23 Mton in 1980.

As a result of an increasing debate in the Netherlands about radioactivity in plaster – at that time the most important customer of the plasterboards – this practice stopped in 1985. 70 % of the disposed phosphogypsum was put in a number of well defined deposits. The other 30% has been disposed of on various sites around the production plant, mostly in abandoned clay pits of former brickyards. A lot of these terrains are no longer recognizable as deposits, be- cause they are leveled and covered with soil, overgrown or given a new land use. One exam- ple of this is the deposit of “Potaerde” in Niel, which looks like any ordinary piece of wood- land, and which might easily be converted into a residential area in a near future. Another ex- ample is the area for daytime outdoor recreation “De Schorre” in Boom. Here about 1.2 Mton of gypsum was disposed of in various sites, before these terrains were converted into a recrea- tional area. By the looks of it, it is very difficult to see where gypsum was deposited and where not. Figure 1 shows the locations of the known phosphogypsum deposits. Five of these were visited and investigated to a certain extent. • Company premises in Puurs: 1.4 Mton phosphogypsum on 18 ha, 8 m high; • Disposal Polders-Hoeykens in Puurs: 2.1 Mton phosphogypsum on 14.3 ha, 16 m high; • Disposal Potaerde in Niel: 0.12 Mton phosphogypsum on 6.3 ha, no elevation; • Disposal Hollebeek in Rumst: 3.6 Mton phosphogypsum on 32 ha, 11 m high; • Recreational area De Schorre in Boom: 1.2 Mton phosphogypsum on 75 ha, various sites.

3.3 Rhodia Chemie Zelzate

Figure 2. Air photograph of the 70 ha gypsum deposit of Rhodia Chemie. The residential area at the bottom right is the hamlet “Klein Rusland” of the municipality of Zelzate.

The phosphoric acid production of Rhodia Chemistry (former Rhône-Poulenc) situated along the canal Ghent-Terneuzen goes back until 1925. In the past marine as well as magmatic phosphate ores were acidulated with sulphuric acid. Since 1985 only magmatic ores from Pal- fos in South Africa and Kola in Russia were used containing less of the uranium and more of the thorium decay series. The specific thorium activity of the recent phosphogypsum varies

between 300 and 400 Bq/kg. Since the seventies 0.45 to 0.5 Mton of phosphogypsum are pro- duced annually and placed on one huge gypsum deposit of 70 ha. In 2000 the deposit con- tained already 20 Mton of gypsum with a maximum height of 35 m above ground level (see figure 2). The deposit is surrounded by a double ditch for recycling the transport and percola- tion water. The slopes were sown and planted, as a result of which they are now completely overgrown with grass and bushes.

3.4 Tessenderlo Chemie

Tessenderlo Chemistry produces dicalciumphosphate from phosphate ore, mainly for the pro- duction of cattle food. They had two production units, one in Tessenderlo from 1920 until 1995 and another in Ham from 1931 up to now. Hydrochloric acid (HCl) is used to acidulate the Moroccan phosphate ore, with a specific radium-226 activity from 1200 to 1600 Bq/kg. 1 ton of phosphate ore results in 0.134 ton of calcium fluoride sludge and a large quantity of waste water. Till the beginning of the nineties, the specific radium-226 activity of the (old) sludge amounted to 3000 to 4000 Bq/kg. Since then, the addition of barium salts results in a decrease of the radium concentration of the waste water from 20 Bq/l, with a flow rate of 1500 m³/h, down to 2 Bq/l, with a flow rate of 1000 m³/h; at the same time increasing the ra- dium contents of the (recent) sludge to almost 10 000 Bq/kg. Figure 3 shows the yearly ra- dium emissions of Tessenderlo Chemie in the surface waters.

300 270 260 250

200 170

150 100 100 56

Radiumemission (GBq) 50 28 26 26 19 19 15 15 15 15 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2002 2003 2004

Figure 3. Yearly emissions of radium-226 by Tessenderlo Chemie into the small rivers Grote Laak and Winterbeek. In 1991 a decontamination stage was put into operation.

The current sludge production of Tessenderlo Chemie amounts to 0.05 to 0.06 Mton per year and is put on the 55 ha large deposit “Veldhoven” in Ham. The total sludge production of 2.4 Mton for the period 1920 - 2000 is divided over four deposits: • Deposit Kepkensberg: 0.55 Mton old sludge on 19.7 ha, uncovered; • Deposit Spoorwegstraat: 0.12 Mton old sludge on 2.5 ha, covered with 1.5 m of soil; • Company premises in Ham: 0.15 Mton old sludge on 5.6 ha, uncovered;

• Deposit Veldhoven in Ham: 1.5 Mton old and recent sludge on 55 ha. The dose rates and the radon concentrations increased to 2.6 µSv/h and 300 Bq/m³ because of the higher spe- cific activity of the recent sludge.

Tessenderlo Chemie

Belgian nuclear waste agency Olen radium facility Deposit Veldhoven and production unit in Ham Deposit Kepkensberg and Spoorwegstraat

Production unit in Tessenderlo Valley of the Grote Laak

Valley of the 0 10 20 km Winterbeek

Figure 4. Excerpt from the aerial gamma map of the Belgian Geological Service from 1994 with indication of the locations contaminated with radium-226 from the activities of Tessenderlo Chemie. The environmental contamination of the former Olen ra- dium facility and the storage facilities for radioactive waste by the Belgian nuclear waste agency are also visible on the gamma map.

Most of the radium released into the Winterbeek and Grote Laak absorbs on the suspended particle matter. The fate of the particle-bound radium differs from that of the radium in solu- tion due to particle setting. The periodic dredging of the bottom sediments has contaminated the river banks. The area contaminated by the dredged sediments is mostly confined to a 10 m strip along the river. In flooding zones, where flow turbulence is low, the sedimentation proc- ess is stimulated and vast areas can get contaminated. The gamma map of the border area of the provinces Limburg, Antwerp and gives a good overview of the environ- mental radium contamination of Tessenderlo Chemie (figure 4).

3.5 BASF Antwerp

BASF Antwerp processes since 1967 phosphate ores of various origin for the production of fertilizers. From 1967 till 1993 mainly Moroccan phosphate ore was used through acidulation with sulphuric acid. 9.6 Mton of phosphogypsum was produced during that period with a spe- cific radium activity of 750 to 1000 Bq/kg. The gypsum was dumped into the estuary of the , the tidal river that flows through Antwerp.

BASF Antwerp uses since 1980 also nitric acid and since 1993 it is the only production method. No significant by-products are produced, which implies that the radioactivity is transferred from the ore to the end products, in this case fertilizers About 0.4 to 0.45 Mton of phosphate ore are processed annually to produce about 2 Mton of fertilizer resulting in a dilu- tion of the radioactivity in the end products. The substitution of marine ores by magmatic ores decreases the radium content and increases the thorium content of the fertilizers.

4. The radiological impact of the phosphate industry in Flanders

Figure 5 gives an overview of the quantities of ore that the phosphate industry in Flanders has processed between 1950 and 2000. The annual use of ore has decreased since the eighties with a third down to 1.1 Mton. This was due to the closing of UCB in Ostend in 1987 and the moving of the basic phosphoric acid production facility of Prayon Rupel to Morocco in 1992.

2.000 BASF 50 Tessenderlo 1.500 40 Rhodia Prayon 30 1.000 UCB 20 Total 500 10

Ore consumptionOre (kton/plant) 0 0 Total ore Total consumption ore (Mton) 1950 1960 1970 1980 1990 2000

Figure 5. Yearly and cumulative use of phosphate ores in Flanders.

The five Flemish phosphate plants, from 1920 to 2000, handled 54 million ton of phosphate ore containing 65 TBq of uranium-238 (radium-226) and 2.7 TBq of thorium-232 in radioac- tive equilibrium with their decay products. In which by-products, residues or product streams this radioactivity turns up, is dependent on the processing method. The radioactive mass bal- ance of the Flemish phosphate industry is given in figure 6. The total surface area of the phosphogypsum and calcium fluoride sludge deposits amounts to almost 300 ha. There is also environmental contamination in the valleys of the two small rivers receiving the waste waters of the hydrochloric production process: the Winterbeek (> 200 ha, banks and flooding zones) and the Grote Laak (12 ha, mainly banks).

5 phosphate plants processed 54 Mton of ore over the period 1920 - 2000 containing 65 TBq radium-226 and 2.7 TBq thorium-232

End products Waste

Among other things 48 Mton gypsum 2.4 Mton Discharges to Fertilizers containing CaF 2 sludge surface water containing 36 TBq radium and deposits (Grote Laak and 6 TBq radium and 2.3 TBq thorium (82 ha) containing Winterbeek) 0.4 TBq thorium 10 TBq radium (13 TBq radium)

200 ha of gypsum Gypsum Gypsum Sedimentation Carried deposits (36 Mton): valorized discharged in river valleys: down ∼ UCB Ostend (25 ha) 2 Mton in Scheldt ∼ Grote Laak . to sea (gypsumboard) (10 Mton) ∼ Rhodia Zelzate (70 ha) (about 12 ha) ∼ ∼ Prayon Rupel: Winterbeek

around the (> 200 ha) production plant in Puurs

(about 100 ha)

Figure 6. Overview of the impact of the phosphate industry in Flanders.

An environmental contamination with radium-226 can expose the local population to ionizing radiation in various ways. The dominating exposure pathways are (the conversion factors are for adults. They are derived from the UNSCEAR 2000 report) : • external irradiation at the contaminated area (0.32 (nSv/h)/(Bq/kg)) ; • internal exposure through the consumption of contaminated food (2.8 10 -7 Sv/Bq) ; • inhalation of the short lived radon decay products (9 (nSv/h)/(Bq/m³) . This conversion fac- tor has to be multiplied by a typical equilibrium factor of 0.6 outdoors and 0.4 indoors if radon and not its decay products is measured). When determining the population exposure one has to make all sorts of assumptions on dose rate, exposure duration, dietary habits... The values selected for these parameters determine to a great extend the result. Realistic scenario's for the most exposed members of the population (critical group) for accessible areas with a radium contamination of the soil from 1000 to 10 000 Bq/kg result in external exposures of a few mSv/year at the most. Living mainly of the crops grown on the contaminated soil can add another few mSv/year from internal exposure. Radon in open air is mostly no problem because of the dilution. Converting the contaminated areas into residential areas or industrial areas implies the risk of infiltrating radon accumulat-

ing in the buildings. High radon concentrations are then to be expected resulting in radon ex- posures up to several tens of mSv/year.

The radiological impact of the phosphate industry on the local population today is still rather limited because most contaminated areas are still recognized as disposal sites and are inacces- sible to the public The most important exposure pathways, like external irradiation and indoor radon, are avoided in this way. Prudence is called for as some gypsum deposits blend in seamlessly into their environment. With an inventory of more than 500 ha of contaminated areas it is unavoidable that the radiological impact will increase with time. In some places, restriction of land use, or even restoration would be advisable. Local, regional and federal au- thorities have an important role to fulfill in establishing these measures.

5. The phosphate industry in the Walloon provinces

The data on the impact of the phosphate industry in the Walloon provinces in Belgium is less complete. Prayon Engis produced in 2004 0.8 Mton of phosphogypsum, valorizing about 70 % of the gypsum in building materials (plaster, cement), in fertilizers, and in other prod- ucts such as paper. The remainder was stored on a local disposal site with a capacity of 9 Mton of which 3.75 Mton was used in the middle of 2002. Most of the current phosphate ores are of magmatic origin, mostly originating from Russia (Kola) with low specific radium-226 and thorium-232 concentrations.

Knauf Engis is largest buyer of the phosphogypsum of Prayon Engis. In 2004 0.4 Mton of phosphogypsum were valorized for the production of plaster. Since 2002, the specific activity of the plaster is very low, about 30 Bq/kg radium-226 and 50 Bq/kg thorium-232.

References

European Commission (EU-BSS) “Council Directive 96/29/EURATOM of 13 May 1996 Lay- ing down the Basic Safety Standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation” Official Journal of EC, Series L, No. 159, 1996. Paridaens J., Vanmarcke H. “Inventarisatie en karakterisatie van verhoogde concentraties aan natuurlijke radionucliden van industriële oorsprong in Vlaanderen” Two SCK reports on behalf of VMM; part 1: BLG 884, June 2001; part 2: BLG 916, June 2002 (in Dutch). UNSCEAR “Sources and effects of ionizing radiation” Report to the General Assembly of the United Nations with Scientific Annexes, United Nations publication E.00.IX.3, New York, 2000. Vanmarcke H., Paridaens J., Froment P., Van Cauteren J., Timmermans C. “Overzicht van de NORM problematiek in de Belgische industrie” SCK, NRG and AV-Controlatom report on behalf of NIRAS, R-3775, Mol, October 2003 (available in Dutch and in French). Vanmarcke H., Paridaens J. “De NORM problematiek in de fosfaatindustrie” NORM conf. Belgian Society for Radiation Protection, Brussels 25 February 2005, Annalen Belg. Ver. voor Stralingsbescherming, Vol. 30, 2005 (in Dutch).