Respiration and Eco-toxicity Studies for Waste
Phosphogypsum
S.H. Park*, B. Han*, W.B. Lee* and J. Kim**
*Department of Environmental System Engineering, Chonnam National University, Yeosu, Jeonnam
550-749, Republic of Korea (E-mail: [email protected]) Tel: 82-61-659-3262, Fax: 82-61-652-6091
** Department of Environmental Education, Mokpo National University, Muan-gun Chungkye-myon,
Chonnam 534-729, Republic of Korea (E-mail: [email protected]) Tel: 82-61-450-2782, Fax: 8261-450-2780
ABSTRACT
The objective of this study was to investigate respiration and eco-toxicity of recycled
phosphogypsum (PG). Artemia salina and Oryzias latipes were selected for the
experiments. At a 24-hr acute toxicity test in a batch condition, immobilization rate of
the Artemia salina was 2.5% at 50% phosphogypsum used (PG50), whereas the rate
was increased to 5% at 100% phosphogypsum (PG100). The immobilization rate
ranged from 27.5 to 35% after 48 hr. The immobilization rate ranged from 27 to 35%
after 48 hr. For Oryzias latipes during a 24-hr and 48-hr test, the mobilization rates
at PG30 and PG50 were 100%, respectively. For the Artemia salina at the column
test, the addition of the phosphogypsum at 50% (PG50) decreased to pH 6.8. No
immobilization rates were observed for 13 weeks. As a result of respiration test, the
average of OUR for Artemia salina and Oryzias latipes were 9.29*10-4 mg/d/species
and 0.426 mg/hr/species. This study suggested that phosphogypsum generated
from fertilizer productions could be recycled at low concentrations with soils.
Keywords: Phosphogypsum, Artemia salina, Oryzias latipes, Toxicity
INTRODUCTION
Phosphogypsum (PG) is produced during the manufacture of phosphoric acid by a
chemical reaction of rock phosphate with sulphuric acid. Annually 1.6 million tons of
waste phosphogypsum have been generated as a result of the fertilizer production in
South Korea. Approximately 58% of the phosphogypsum have been recycled for
cement materials and gypsum boards. Garg et al. (1996) reported that a mixture of
phosphogypsum and lime could have sufficient durability for construction materials.
Azam et al. (2000) studied physical characteristics of gypsum with clays and
suggested the gypsum could be used for cement materials. In order to provide further
researches, ecotoxicity and environmental effect of the recycled phosphogypsum on
aquatic life are needed. The objective of this study was to determine the possibility
of phosphogypsum recycle as an embankment material by eco-toxicity experiments
in both batch and column tests. For the application of the phosphogypsum, several
characteristics such as pH, radioactive, acute toxicity and respirometric toxicity were
also investigated. Artemia salina and Oryzias latipes were selected for the ecotoxicity experiments.
MATERIALS AND METHODS
As shown in Figure1, three column reactors constructed of acrylic were made, each
having 74.2-L capacity (ID: 30 cm and height: 105 cm). The volume of mixed
materials was 105,975 cm3. A moisture content meter, a sprinkler, and timer were
installed with the reactors. The reactors were placed in a 20oC temperaturecontrolled environmental room. The reactors were filled with mixed PG and soil. The
experiment was conducted according to the mixing ratios of phosphogypsum to soil.
For instance, PG50 indicates 50% of phosphogypsum and 50% of soil were applied,
respectively. Leachate was collected from a column containing a mixture of
phosphogypsum and soil. The ecotoxicity of Artemia salina was analyzed according
to the Acute Toxicity Test Method of the Artemia salina suggested by US EPA (2002).
The heavy metals, pH, DO, and nutrients for PG samples were analyzed in
accordance with the Standard Methods. These samples were also analyzed for their
metal constituents as per standard test procedures using ICP/MS (ICPM-8500,
Shimadzu, Japan). The determination of radionuclide concentrations was performed
by gamma spectrometry analysis using the Natural Radioactivity Measurement
System (Canberra Industries Inc., USA)
RESULTS AND DISCUSSION
Characteristics of phosphogypsum
Physicochemical characteristics of the phosphogypsum waste are shown in Table 1.
The radioactive concentration of Ra-226 at 50% phosphogypsum used (PG50) was
7.97 pCi/g, which means below the U.S. EPA regulation (10 pCi/g). Mercury,
cadmium, and arsenic concentrations according to mixing ratio were ND (not
detected), 0.01 mg/L, and 0.001 mg/L, respectively. Initial total nitrogen and
phosphorus concentrations at PG50 condition were 14.8 mg/L and 0.059 mg/L,
respectively. The specific gravity of the phosphogypsum waste was 2.343.
Table 1. Characteristics of phosphogypsum waste according to mixing ratio.
Parameter
Cr
(mg/L)
5.0
Cd
(mg/L)
1.0
Hg
(mg/L)
0.2
As
(mg/L)
5.0
U-238
(pCi/g)
Ra-226
(pCi/g)
10
SL100
0.004
0.011
ND
ND
<0.567
0.783
PG30
0.001
0.001
ND
ND
1.188
4.131
PG50
0.003
0.010
ND
ND
1.485
7.965
PG100
0.003
0.010
ND
0.001
1.647
13.122
Standard in USA
Note: ND; Not detected.
PG is a chemical compound that also consists mainly of calcium sulfate dihydrate
(CaSO4·2H2O) and some impurities. Its physical and chemical properties are
comparable to those of gypsum, except for the presence of different minor
constituents, some of which are naturally occurring radioactive isotopes. This
preliminary investigation suggested that the phosphogypsum waste could be utilized
for an embankment material.
Acute toxicity test
A batch experiment was conducted according to mixing ratios during 48 hrs. At a 24hr acute toxicity test, the immobilization rate of Artemia salina was 2% at 50%
phosphogypsum used (PG50), whereas the rate was increased to 5% at 100%
phosphogypsum (PG100). The immobilization rate ranged from 27 to 35% after 48
hr. For Oryzias latipes during a 24-hr and 48-hr test, the mobilization rates at PG30
and PG50 were 100%, respectively. No mobilization of the Oryzias latipes was found
at PG100.
Tables 2 and 3 show the mobilization rates according to mixing ratios for Artemia
salina and Oryzias latipes in column test. Ten organisms were put in the begging of
the test. For the Artemia salina, the addition of the phosphogypsum at 50% (PG50)
decreased to pH 6.8. No immobilization rates were observed for 13 weeks. In other
words, no significant effect of mixing ratios on the Artemia salina was found. It was
observed that the effective concentration (EC50) of Artemia salina by leachate from
PG100 was 32.5 mg/L (Figure 2). The survival rate of Artemia salina and Oryzias
latipes were more than 50%, when the leachate from phosphogypsum mixed were
applied. Toxicity unit (TU) for the three organisms was less than 1, which indicated
that no significant effect on eco-toxicity was found. As results of the tests, a minor
effect on the eco-environment was found. This study suggested that phosphogypsum
generated from fertilizer productions could be recycled at low concentrations with
soils.
Table 2. The mobilization study for Artemia salina from column test.
Time
0 hr
DO
pH
24 hr
No. of
pH
Organism
48 hr
Mobil.
pH
(%)
Mobil.
(%)
Control
8.40
8.05
10
8.05
100
8.07
100
PG30, 1-week
8.07
7.03
10
7.07
100
7.96
100
PG30, 7-week
8.17
7.16
10
7.17
100
7.20
100
PG30, 13-week
8.23
7.23
10
7.23
100
7.28
100
PG50, 1-week
8.16
6.76
10
6.80
100
6.91
100
PG50, 7-week
8.19
7.02
10
7.06
100
7.13
100
PG50, 13-week
8.23
7.12
10
7.13
100
7.18
100
Note: Mobil.; Mobilization.
Table 3. Mobilization study for Oryzias latipes from column test.
Time
0 hr
DO
pH
24 hr
No. of
pH
Organism
48 hr
Mobil.
pH
(%)
Mobil.
(%)
Control
8.60
7.84
10
7.72
100
7.72
100
PG30, 1-week
8.46
6.08
10
6.26
100
6.39
100
PG30, 7-week
8.45
6.29
10
6.45
100
6.73
100
PG30, 13-week
8.36
6.46
10
6.57
100
6.85
100
PG50, 1-week
8.30
5.85
10
6.02
100
6.19
100
PG50, 7-week
8.24
6.05
10
6.16
100
6.34
100
PG50, 13-week
8.20
6.20
10
6.38
100
6.59
100
Respiration Test
For a respiration test, an acrylic reactor (350 mL) containing each organisms was used to
investigate oxygen uptake rate (OUR) of PG. The respiration test consisted of stirring a
solution containing PG mixtures and monitoring the utilization of oxygen using a DO
meter over time after oxygen was saturated in a water bath (23oC). 2,000 Artemia salina
and 1 Oryzias latipes were uesd in the beginning of experiment. The test was usually
terminated when the oxygen concentration in the reactor was about 4.0 mg/L. Figure 3
shows the change of OUR over time during the respiration test. The oxygen
concentrations in the PG mixture declined slowly to approximately 10% during 8 hours of
the test period. The average OUR for Artemia salina and Oryzias latipes were 9.29*10-4
mg/d/species and 0.426 mg/hr/species. The change in oxygen is also shown in Figure 3
for only soil as a control test (Blank). Respiration information from this test could provide
a recycle technology for use in assessing the potential application of PG.
Figure 1. A schematic diagram of column test.
Figure 2. The effective and lethal concentrations for Artemia salina and Oryzias
latipes.
15.0
Blank
SL100
PG30
(×10-4
mg/d/animal)
10.0
OUR
5.0
0.0
0
2
4
Elapsed time (hr)
6
8
Figure 3. Oxygen uptake rate (OUR) for Artemia salina.
References
H. Tayibi, M. Choura, F.A. Lopez, F.J. Alguacil, A. Lopez-Delgado, Environmental
impact and management of phosphogypsum, Environmental Management
90(2009) 2377-2386.
M. Singh, Treating waste phosphogypsum for cement and plaster manufacture,
Cement and Concrete Research 32(2002) 1033-1038.
M. Renteria-Villalobos, I. Vioque, J. Mantero, G. Manjon, Radiological, chemical and
morphological characterizations of phosphate rock and phosphogypsum from
phosphoric acid factories in SW Spain, Hazardous Materials 181(2010) 193-203.
W. Shen, M. Zhou, Q. Zhao, Study on lime-fly ash-phosphogypsum binder,
Construction and Building Materials 21(2007) 1480-1485.
C. Papastefanou, S. Stoulos, A. Ioannidou, M. Manolopoulou, The application of
phosphogypsum in agriculture and the radiological impact, Environmental
Radioactivity 89(2006) 188-198.
Azam, S. and Abduljauwad, S.N. (2000) Influence of gypsification on engineering
behavior of expansive clay. Geotech Geoenviron Engr. 126(6), 538-542.
Garg, M, Singh, M. and Kumar, R. (1996) Some aspects of the durability of a
phosphogypsum-lime-flyash binder. Construction Building Mater. 10(4), 273-279.
U.S. EPA (2002) Method for measuring the acute toxicity of effluents and receiving
waters to freshwater and marine organisms, EPA-821-R02-121, 275.