USE OF PHOSPHOGYPSUM AS AMMEND FOR RECLAIMED MARSH SOILS

Applied Nuclear Physics Group, University of Seville, Spain

Environmental and Radiation Physics Group, University of Huelva, Spain

Presented by: Juan Pedro Bolivar. Huelva University.Email: bolivar@uhu.es

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HIGHTLIGTHS

A ) What is the Phosphogypsum (PG)? Theresource of PG in South-West of Spain

B) Materials and Methods followed for thestudy of the agricultural area treated with PG

C) The radiological impact associated to theuse of PG as soil amendment

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WHAT IS PG?

2CO2FHO2·2H411CaSO4PO36HO221H4SO211HCa3CO2F6)4(PO10Ca

Phosphate rock (PR) + Sulphuric acid (SA) Phosphoric acid (PA) + Phosphogypsum (PG)

By-product generated in the production of phosphoric acid by the so-called “wet acid method” with sulphuric acid

AVERAGE ACTIVITY CONCENTRATIONS   (Bq/kg)238U 226Ra 210Pb 210Po

PHOSPHATE ROCK (PR) 1500 1600 1600 1600PHOSPHOGYPSUM (PG) 50‐200 500‐1000 400‐1000 400‐1500

SOILS 20‐50 20‐50 20‐50 20‐50

3High acidity of PG: pH ≈ 1.5-2

THE SOURCE OF PG

(Location)

50 km04

THE  SOURCE OF  PG IN SOUTH WEST  SPAIN

(Fertilizers plants location)

A part of Huelva City

Fertlizers plants

Odiel River Estuary

SaltworksSalt marshes(Nature Reserve)

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THE RESOURCE OF PG

ANNUAL CONSUMPTION – PRODUCTION(1968 to 31 Dec. 2010)

PR ~ 2·106 Tm

PG ~ 3·106 Tm

PHOSPHOGYPSUM MANAGEMENT HISTORY

1968-1997- 20% RELEASED DIRECTLY TO THE ODIEL RIVER

- 80% STORED IN PILES OVER MARSHLANDS OF THE TINTO RIVER

(the sea waters used to transport the PG to the piles were draining to theTinto river)

1998-2010- DIRECT RELEASES TO THE NEARBY ENVIRONMENT FORBIDDEN

- NEAR 100% STORED IN THE PILES (the fresh waters used to transport the PG follows a closed circuit)

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THE SOURCE OF PG

The PG wastes are covering 1200 Ha. of

marshlands.

Around 120 millions tons of PG are stored in the

area.

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External irradiation:gamma - beta

Internal irradiationdust inhalation

Internal irradiation222Rn + daughters

Indirect routeingestion

(In progress)

Radiological pathways of impact

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YZ1

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Radon Exhalation Map (Zone YZ1)

Bq m-2 h-1

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B) Materials and Methods used tostudy the agricultural area treatedwith PG

Agricultural Area treated with PG

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PG Stacks

Reaclaimed agriculture

area

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Agricultural Area treated with PG

It is allowed the use of PG as soil amendment?

- PG has been used widely by the farmers as a Ca-ammendment toreduce the Na saturation in saline-sodic marsh soils. PG has provedalso to increase P absorption by the crops.

- PG can be used as a soil amendment for highly weathered soils withrelatively low exchange capaities and/or low levels of extractablenutrients; for soils with high sodicity; for acid soils with levels of Al andfor calcareous soils.

WHY PG IS USED AS SOIL AMENDMENT ?

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The short-term radiological impact associated to the use of PG as soil amendement

Desague

Des

ague

C1 C2 C3Y1 Y2 Y3

1 ha 1 ha 1 ha

20 m 40 m

250

m

Desague

Des

ague

C1 C2 C3Y1 Y2 Y3

1 ha 1 ha 1 ha

20 m 40 m

250

m

Three year field experiment

Year 1 and Year 3 treated with PG

Rate of PG supplied :25 Tons/ha·yr

Control plots

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Treatment Number of samples

Depthcm

226Ra(Bq/kg)

238U(Bq/kg)

212Pb(Bq/kg)

137Cs(Bq/kg)

40K(Bq/kg)

Control 3 0 – 30 35.3 ± 0.8 25.3 ± 0.4 33.1 ± 0.7 2.8 ± 0.6 767 ± 20

Control 3 30 – 60 27.7 ± 0.4 23.5 ± 0.5 32.3 ± 1.0 0.9 ± 0.5 760 ± 50

Control 3 60 – 90 26.2 ± 0.7 19.4 ± 1.0 31.9 ± 0.7 N.D. 750 ± 20

PG 25 Tons/Ha 3 0 – 30 39.3 ± 2.3 23.9 ± 1.0 32.2 ± 1.0 2.3 ± 1.0 789 ± 27

PG 25 Tons/Ha 3 30 – 60 29.6 ± 1.8 25.2 ± 2.1 32.8 ± 0.4 1.0 ± 0.2 814 ± 11

PG 25 Tons/Ha 3 60 - 90 24.0 ± 0.9 21.7 ± 2.6 32.3 ± 1.0 N.D. 780 ± 50

The radiological impact associated to the use of PG as soil amendement

1. No statistical differences between control and PG treated plots2. Higher concentrations of Ra-226 in the uppermost layers of all the

plots3. Ra-226/U-238 activity ratios higher than one in all the plots

NO RADIOLOGICAL IMPACT18

The radiological impact associated to the use of PG as soil amendement

226Ra (mBq/L) in drainage watersControl Manure PG

(25 t ha-1)7.0 ± 0.7 6.6 ± 0.7 6.2 ± 0.76.4 ± 0.8 6.2 ± 0.9 7.3 ± 1.16.9 ± 0.6 4.7 ± 0.5 7.2 ± 0.66.1 ± 1.0 6.3 ± 0.7 6.2 ± 0.87.3 ± 0.4 6.1 ± 1.0 6.2 ± 0.77.2 ± 1.0 6.7 ± 0.5 4.4 ± 0.45.8 ± 0.5 6.1 ± 1.0 3.8 ± 0.36.7 ± 0.6 6.1 ± 0.7 5.9 ± 1.3

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210Po 234U 226RaPG TREATED SOILS

T1 0.43 ± 0.06 < MDA < MDAT2 0.90 ± 0.09 < MDA < MDAT2 0.75 ± 0.11 < MDA < MDAT4 1.9 ± 0.2 < MDA < MDAT5 0.68 ± 0.07 0.15 ± 0.04 < MDAT6 0.45 ± 0.10 0.24 ± 0.04 < MDA

CONTROL SOILSC2 0.45 ± 0.06 < MDA < MDAC10 0.43 ± 0.04 < MDA < MDA

SOIL TO PLANT TRANSFER EXPERIMENTS

TOMATOE (Bq/kg wet)

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226Ra BEHAVIOUR

FORCED LEACHING EXPERIMENTS3 grams of PHOSPHOGYPSUM

+60 ml of WATER

STIRRING(variable time)

FILTERING(0.8 m)

RADIOCHEMICAL SEPARATIONU Ra

(226Ra) (234U,238U)

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FORCED-LEACHING EXPERIMENTS

226RaFRESH-WATER MARINE WATER238U

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0 500 1000 1500 2000 2500 30000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5Fa

ctor

de

trans

fere

ncia

226 R

a (%

)

Tiempo (minutos)

FORCED-LEACHING EXPERIMENTS

226RaFRESH-WATER MARINE WATER226Ra

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FINAL REMARKS

1. A deep characterization (physical, mineralogical, chemical, radioactive) of the PG stored in the stacks of Huelva has been developed.

2. The environmental impact of PG piles of Huelva has been evaluated by analyzing the different pathways of pollutants dispersion: air (aerosols and radon), aquatic, and external direct radiation.

3. The main conclusion of the previous study was that there is no a significant radiological impact on the health of people living in the surroundings of these repository. But there is a significant radioactive impact on the surrounding environment.

4. The radiological study on the use of PG to recover saline soils has been developed in reclaimed salt marshes used mainly to rice crops.

5. A study of the soil to plant transfer has been done, finding that there are not statistical significant increases of radionuclides from the treated soils into the crops (tomatoes, peppers, and rice).

6. It has been demonstrated that PG can be used as amendment in reclaimed saltmarshes for agricultural soils without radiological implications.

MANY THANKS

Work finnanced by:

- Regional Governement of Andalucia

- Spanish Nuclear Safety Council

- Spanish Nuclear Waste Company

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Table 1. Average activity concentrations (Bq/kg) in products stored in PG stacks.Sample 226Ra 228Ra 137Cs 40K 210Pb 234,238U 228Th

Zone 1 (soils) 21 ± 7 22 ± 3 < 0.5 290 ± 60 24 ± 9 20 ± 8 21 ± 2

Zone 1 (PG) 620 ± 70 11 ± 4 < 0.7 0 – 20 450 ±20 24 ± 5 6.3 ±

0.8

Zone 2 (soils) 23 ± 5 28 ± 6 < 0.5-2 360 ±120 20 ± 5 19 ± 5 27 ± 7

Zone 2 (PG) 670 ± 50 9 ± 2 < 0.7 0 – 15 520 ±60

220 ±170

8.2 ±1.8

Zone 3 (PG) 620 ±130

9.4 ±1.8 < 0.7 0 – 18 500 ±

60 100 ± 30 10 ± 4

Zone 4 (PG) 630 ± 40 16 ± 2 < 0.8 0 - 13 442 ±21 18 ± 4 12 ± 3

Zone 4 (soils) 27 ± 8 28 ± 6 < 0.5 460 ±120 30 ± 7 23 ± 5 27 ± 7

Table 2. Average effective external dose rates at 1 m above surface received in PG piles. N = number of measuring points

Zone N Average (mSv y-1) Range (mSv y-1)1 (restored) 9 0.31 ± 0.09 0.15 - 0.52 (active) 17 1.6 ± 0.4 0.64 – 2.53 (un-restored) 10 2.3 ± 0.5 1.90 – 3.14 (un-restored) 8 2.1 ± 0.3 1.8 – 3.0

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muestra Tasa exhalación Error Meida putno Desv. Estad.YZ1-P11 413 21YZ1-P12 467 23 712 472YZ1-P13 1255 61YZ1-P21 303 16YZ1-P22 55 6 277 210YZ1-P23 473 24YZ1-P31 234 12YZ1-P32 549 27 913 917YZ1-P33 1956 94YZ1-P41 2291 110YZ1-P42 381 19 1018 1103YZ1-P43 381 19YZ1-P51 418 21YZ1-P52 1048 51 923 455YZ1-P53 1302 63YZ1-P61 684 33YZ1-P62 436 21 508 153YZ1-P63 405 20YZ1-P71 203 10YZ1-P72 408 20 482 323YZ1-P73 835 41YZ1-P81 87 4YZ1-P82 155 8 150 61YZ1-P83 208 11YZ1-P91 527 26YZ1-P92 105 6 479 352YZ1-P93 805 39YZ1-P101 234 12YZ1-P102 1600 77 673 804YZ1-P103 184 9MEDIA 613 559

Range of values: 55 - 2300 Bq m-2 h-1

Average: 613 ± 286 Bq m-2 h-1

Point Exh. rate Uncert. Mean St. Desv.

Rn Exhalation (Bq h-1 m-2)ZONE Average 1σRestored 100 ± 130Ploughed 510 ± 470

Non ploughed 250 ± 270Sloped 360 ± 170

Smaller than EPA recommendation (20 pCi·m-2·s-1)

(2660 Bq·m-2·h-1)