In e na ional Jou nal o
En i onmen al Resea ch
and Public Heal h
A icle
En i onmen al Impac o Phosphogypsum-De i ed
Building Ma e ials
M. I. Rome o-He mida 1, V. Flo es-Alés2,* , S. J. Hu ado-Be múdez 3, A. San os 4and
L. Esqui ias 1,5
1Física de la Ma e ia Condensada, Uni e sidad de Se illa, 41012 Se illa, Spain;
isa ome [email p o ec ed] (M.I.R.-H.); [email p o ec ed] (L.E.)
2Cons ucciones A qui ec ónicas II, Uni e sidad de Se illa, 41012 Se illa, Spain
3CITIUS—S.G.I. Celes ino Mu is, Uni e sidad de Se illa, 41012 Se illa, Spain; [email p o ec ed]
4De Ciencias de la Tie a, Uni e sidad de Cádiz, 11519 Cádiz, Spain; [email p o ec ed]
5Ins i u o de Ciencia de Ma e iales de Se illa, CSIC—Uni e sidad de Se illa, 41092 Se illa, Spain
*Co espondence: [email p o ec ed]; Tel.: +34-954-556-656
Recei ed: 28 May 2020; Accep ed: 11 June 2020; Published: 14 June 2020


Abs ac :
The aim o he p esen wo k was o cha ac e ize he p oduc s ob ained om he ea men
o phosphogypsum esidue by means o wo eco e y ou es, and also o e alua e he concen a ions
o hea y me als and adionuclides in he ma e ials ob ained and hei leacha es. In his way, i
is possible o de e mine how he mos haza dous componen s o phosphogypsum beha e du ing
p ocedu es un il hei s abiliza ion h ough CO
2
ixa ion. This s udy p o ides an ini ial es ima e o
he possibili ies o eusing he esul ing p oduc s om a heal h and sa e y isk s andpoin and hei
po en ial pollu ing capaci y. The phases esul ing om he ans o ma ions we e con olled, and he
beha iou o s anda d mo a s manu ac u ed om he esul ing pas e lime was s udied. In all cases,
an addi ional con ol o he leacha e p oduc s was pe o med.
Keywo ds: phosphogypsum; lime pas e; mo a ; hea y me als; adionuclides
1. In oduc ion
One o he mos con amina ing indus ies is he phospho ic acid (H
3
PO
4
) indus y. This chemical
is widely used in ag icul u al e ilize s, de e gen addi i es, cleaning p oduc s, and insec icides.
Phospho ic acid is p oduced om he ea men o calcium phospha e ocks wi h sulphu ic acid. The
chemical eac ion o he indus ial p ocess is:
Ca3(PO4)+3H2SO4+6H2O→2H3PO4+3(CaSO4)·2H2O. (1)
The esidue gene a ed by his p ocess, ha is, mainly calcium sulpha e di-hyd a e, is commonly
known as phosphogypsum (PG) [1].
PG is no mally slu ed wi h wa e and hen pumped in eno mous amoun s o a nea by deposi .
The e ilize manu ac u ing indus y in he p o ince o Huel a (SW Spain) is based on an impo an
p oduc ion o phospho ic acid by we p ocessing o he phospho ic ock in an indus ial plan om he
1960s. In some cases, such as in Huel a (SW Spain), hese deposi s may be loca ed in he icini y o
popula ed owns o in coas al zones close o he phospho ic acid plan s whe e hey occupy la ge a eas
o land, hus ep esen ing a haza d o bo h he en i onmen and local popula ion [
2
–
4
]. In he case o
Huel a (SW Spain), he ma e ial s o ed eaches 120 million ons and occupies an a ea o 1200 hec a es
nea he es ua y o he Tin o and Odiel i e mou hs [
5
]. The g owing in e es in he es o a ion o he
en i onmen by emo ing land ills and was e s acks is an incen i e o sea ch o po en ial low-cos
applica ions o PG was es.
In . J. En i on. Res. Public Heal h 2020,17, 4248; doi:10.3390/ije ph17124248 www.mdpi.com/jou nal/ije ph
In . J. En i on. Res. Public Heal h 2020,17, 4248 2 o 17
Un ea ed PG could ce ainly be used in se e al indus ial applica ions. Howe e , i con ains
hea y me als and adionuclides, which a e ha m ul o he en i onmen and human heal h [
6
,
7
]. This
is an impo an d awback when i comes o einco po a ing PG in he indus ial p oduc ion ci cui
in acco dance wi h he p inciples o he clean ci cula economy [
8
]. Each yea , nea ly 200 M o PG
a e p oduced wo ldwide, bu only 15% o p is ine PG is e-used [
9
,
10
]. The p ope ies o he ma e ial
no only make i u gen o p ocess and e en ually emo e he deposi s en i ely, bu also o e many
signi ican oppo uni ies o eco e aluable ma e ials, hus suppo ing he ci cula economy and, as
men ioned, adding alue by CO2seques a ion.
The inco po a ion o cons uc ion and demoli ion was e in conc e e and cemen mo a s is al eady
a common p ac ice, and he aim is o ensu e he cons uc ion indus y assumes pa o he was e i
p oduces [
11
,
12
]. The goal o his s eam is o p omo e he use o conglome a es by inco po a ing was e o
p oduce so-called “g een conc e e”. To achie e his, app op ia e s anda ds a e u gen ly equi ed, as well
as in e disciplina y collabo a ions be ween he di e en s akeholde s in ol ed in cons uc ion [13].
PG is a sou ce o calcium, which, in addi ion o being a CO
2
seques e ing agen , is a cons uc ion
ma e ial [
14
,
15
]. Resea ch has demons a ed he high e iciency o po landi e p ecipi a ion by PG
dissolu ion using an alkaline soda solu ion [
16
]; PG, eac ing wi h ammonia, may be con e ed in o
ammonium sulpha e and p ecipi a ed calcium ca bona e [
17
], yielding eac ion con e sion e iciencies
o >95% [
18
]. By means o o he p ocesses wi h PG, was es, which a e unable o ix CO
2
by hemsel es,
can be success ully u ned in o e ec i e CO
2
sinks [
19
]. CO
2
seques a ion may also be achie ed
h ough mine al ca bona ion o was e PG using he echnique o memb ane elec olysis [
20
] and by he
PG educ ion he mal decomposi ion p ocess [21].
In his s udy, PG was ea ed in wo ways. The i s op ion (p ocedu e A) was based on i s
eac ion wi h sodium hyd oxide (Na(OH)) o ob ain po landi e (Ca(OH)
2
) in he o m o lime pas e in
a hena di e (Na2SO4) solu ion [20]. Then, he lime eac s apidly and comple ely wi h CO2, yielding
p ecipi a ed calcium ca bona e (PCC). The second op ion (p ocedu e B) was based on dissolu ion in a
highly alkaline liquid esidue om he aluminium anodizing indus y, ich in Na-Al. The esul ing
p ecipi a e consis ed o ka oi e (Ca
3
Al
2
(OH)
12
). Ka oi e has high ca bona ion e iciency (80–100%),
and p oduces a solid p ecipi a e mainly composed o calci e (CaCO
3
) and an aluminium hyd oxide
(Al(OH)3) solu ion [22].
Following he s eam o euse hese was es in he cons uc ion indus y, he slaked lime p oduced
can be used as a mo a componen . Ca(OH)
2
imp o es he deg ee o cohesion o he ma e ials by
means o he ca bona ion eac ion, hus educing po osi y. I s ca bona ion is a spon aneous p ocess
d i en by di usion and a ec ed by na u al a iables [23].
PG is classi ied, acco ding o he Uni ed S a es En i onmen al P o ec ion Agency (US-EPA),
2018 [
24
], as a Technologically Enhanced Na u ally Occu ing Radioac i e Ma e ial (TENORM). The
main oxic and adioac i e me als p esen in PG a e S , As, Y, Cu, Pb, and he adioac i e iso opes
226
Ra,
238
U,
230
Th,
210
Pb, and
210
Po [
25
–
27
]. Mino i y impu i ies, such as P, Cd, and C a e also d agged ou .
These ep esen a isk o en i onmen al con amina ion ha a ec s li ing beings. The concen a ions o
hese elemen s a y depending on he cha ac e is ics o he o iginal phospha e ock [28].
To es ablish he limi a ions o he use o PG ela ed o i s con en in he abo emen ioned elemen s,
i is necessa y o unde s and hei leaching p ocesses du ing ea men [
29
], om PG un il i s inal
s abiliza ion as calcium ca bona e. Thus, he en i onmen al impac gene a ed by i s ex ac ion om
PG a s and i s possible ecycling could be e alua ed.
The main aim o his wo k is he cha ac e iza ion and con ol o he phases esul ing om PG
was e ans o ma ion by wo p ocesses: P ocedu e A is based on ea men wi h Na(OH) in which he
con ols we e pe o med on he po landi e ob ained as lime pas e in he i s phase and also in he
calci e esul ing om ca bona ion. Addi ionally, lime mo a s we e manu ac u ed om lime pas e and
s anda dized siliceous sand o e i y he beha iou once he esul ing ma e ial was s abilized [
30
], as
well as i s possible iabili y as cons uc ion ma e ial. P ocedu e B is based on he eac ion wi h he
In . J. En i on. Res. Public Heal h 2020,17, 4248 3 o 17
esidual liquid o he aluminium indus y. I was ca ied ou on he ka oi e om he i s eac ion and
he inal calci e ob ained a e he ca bona ion p ocess.
In all cases, an addi ional con ol o he leacha e p oduc s in acco dance wi h he oxici y
cha ac e is ic leaching p ocedu e (TCLP) was ca ied ou [31].
2. Ma e ials and Me hods
C ude solid PG was supplied by Fe ibe ia om he s acks in Huel a, Spain. Fo i s cha ac e iza ion,
he esidue was homogenized by means o a spli e . Then, he mois u e con en o aw PG was
analysed, yielding a alue o 21%. Fo he di e en es s, he emaining mois u e was emo ed in an
o en a 40
◦
C o a ound 48 hou s o p ese e he s uc u al wa e o he gypsum. Once d y, i was
g ounded in a mo a and used in he expe imen s wi hou any o he ea men . The p ocess schemes
can be seen in Figu e 1.
In . J. En i on. Res. Public Heal h 2020, 17, x 3 o 17
In all cases, an addi ional con ol o he leacha e p oduc s in acco dance wi h he oxici y
cha ac e is ic leaching p ocedu e (TCLP) was ca ied ou [31].
2. Ma e ials and Me hods
C ude solid PG was supplied by Fe ibe ia om he s acks in Huel a, Spain. Fo i s
cha ac e iza ion, he esidue was homogenized by means o a spli e . Then, he mois u e con en o
aw PG was analysed, yielding a alue o 21%. Fo he di e en es s, he emaining mois u e was
emo ed in an o en a 40 °C o a ound 48 hou s o p ese e he s uc u al wa e o he gypsum.
Once d y, i was g ounded in a mo a and used in he expe imen s wi hou any o he ea men . The
p ocess schemes can be seen in Figu e 1.
Figu e 1. Schemes o bo h chemical p ocesses.
2.1. P ocedu e A
2.1.1. Syn hesis
Lime pu y was ob ained by using he Cá denas–Escude o me hod [16], wi h some
modi ica ions o scale he gene a ion o by-p oduc s.
In he i s s age, 300 g o PG was suspended in 500 mL o dis illed H2O unde magne ic s i ing.
To his suspension, 180 g o NaOH in a 9 M solu ion was slowly added o a ou he c ys alliza ion
o he solid phase. The mix u e was also s i ed o he nex 10 min. The eac ion associa ed wi h his
p ocess was:
CaSO4·2H2O + 2NaOH → Ca(OH)2 + Na2SO4 + 2H2O.
(2)
This p ocess esul ed in he p ecipi a ion o a whi ish solid phase iden i ied as pu y lime and
he Na2SO4 solu ion as a clea supe na an liquid. The solid phase was sepa a ed by cen i uga ion
and labelled C_S. The liquid phase was disca ded o his esea ch. Se e al samples o he solid phase
we e d ied in an o en a 40 °C in o de o hyd a e and ca bona e hem o p ese e hem om
humidi y and a mosphe ic CO2, so ha hey could be s udied.
2.1.2. Ca bona ion P ocess
Figu e 1. Schemes o bo h chemical p ocesses.
2.1. P ocedu e A
2.1.1. Syn hesis
Lime pu y was ob ained by using he C
á
denas–Escude o me hod [
16
], wi h some modi ica ions
o scale he gene a ion o by-p oduc s.
In he i s s age, 300 g o PG was suspended in 500 mL o dis illed H
2
O unde magne ic s i ing.
To his suspension, 180 g o NaOH in a 9 M solu ion was slowly added o a ou he c ys alliza ion o
he solid phase. The mix u e was also s i ed o he nex 10 min. The eac ion associa ed wi h his
p ocess was:
CaSO4·2H2O+2NaOH →Ca(OH)2+Na2SO4+2H2O. (2)
This p ocess esul ed in he p ecipi a ion o a whi ish solid phase iden i ied as pu y lime and he
Na
2
SO
4
solu ion as a clea supe na an liquid. The solid phase was sepa a ed by cen i uga ion and
labelled C_S. The liquid phase was disca ded o his esea ch. Se e al samples o he solid phase we e
d ied in an o en a 40
◦
C in o de o hyd a e and ca bona e hem o p ese e hem om humidi y and
a mosphe ic CO2, so ha hey could be s udied.
2.1.2. Ca bona ion P ocess
In he second s age, 2 g o he C_S sample was dispe sed in 40 mL o dis illed wa e unde
magne ic s i ing in a eac o (mass a io [C_S]/[H
2
O] =1/20). A low o CO
2
(1 ba , 20 cm
3
/s) was
In . J. En i on. Res. Public Heal h 2020,17, 4248 4 o 17
bubbled h ough he suspension o 15 min a oom empe a u e and p essu e [
1
]. The sample was le
o es o e nigh in his CO2- ich wa e .
The ca bona ion eac ion was:
Ca(OH)2+CO2→CaCO3+H2O. (3)
The esul ing solid phase, labelled Ca_S (mainly CaCO
3
,), was sepa a ed by cen i uga ion and d ied
in an o en a 80
◦
C. The supe na an was disca ded, and samples o he solid phase we e aken o s udy.
2.1.3. Lime Mo a Manu ac u ing
Mo a s we e manu ac u ed wi h lime pu y ob ained as desc ibed abo e, wi h 1:3 lime/sand and
0.5 by weigh wa e /lime a ios. They we e p epa ed wi h a wa e con en ha allowed a consis ency o
185 mm, measu ed in acco dance wi h he UNE-EN 1015-3/A1 s anda d [
32
] o ensu e i s wo kabili y.
P isma ic samples we e p epa ed in acco dance wi h UNE-EN 1015-2/A1 s anda ds [
33
]. The
samples we e hen deposi ed o 21 days in clima ic chambe s (New B unsaick Galaxy 170) o accele a e
ca bona ion unde ealis ic cu ing condi ions o 25
◦
C, 50–60% RH, and 10% ol. o CO
2
concen a ion.
2.2. P ocedu e B
2.2.1. Syn hesis
Ve insu S.A. (Je ez de la F on e a, Spain) p o ided he aluminium anodizing p ocess was e. This
was a clea solu ion wi h a pH o a ound 14, con aining a small amoun o a p ecipi a e phase. Fo
his s udy, he esidue was il e ed, and he p ecipi a e disca ded. The caus ic liquid was e had a
densi y o 1.32 g/cm
3
, and a composi ion o [Na] =110
±
2 g/L (4.78
±
0.09 M)) and [Al] =52
±
2 g/L
(1.93 ±0.07 M).
The caus ic liquid om he anodizing aluminium indus y eac ed wi h PG acco ding o he
eac ion [23]:
3(CaSO4·2H2O) +6Na+(aq) +12OH-(aq) +2Al3+(aq)
In . J. En i on. Res. Public Heal h 2020, 17, x 4 o 17
In he second s age, 2 g o he C_S sample was dispe sed in 40 mL o dis illed wa e unde
magne ic s i ing in a eac o (mass a io [C_S]/[H2O] = 1/20). A low o CO2 (1 ba , 20 cm3/s) was
bubbled h ough he suspension o 15 min a oom empe a u e and p essu e [1]. The sample was
le o es o e nigh in his CO2- ich wa e .
The ca bona ion eac ion was:
Ca(OH)2 + CO2 → CaCO3 + H2O. (3)
The esul ing solid phase, labelled Ca_S (mainly CaCO3,), was sepa a ed by cen i uga ion and
d ied in an o en a 80 °C. The supe na an was disca ded, and samples o he solid phase we e aken
o s udy.
2.1.3. Lime Mo a Manu ac u ing
Mo a s we e manu ac u ed wi h lime pu y ob ained as desc ibed abo e, wi h 1:3 lime/sand
and 0.5 by weigh wa e /lime a ios. They we e p epa ed wi h a wa e con en ha allowed a
consis ency o 185 mm, measu ed in acco dance wi h he UNE-EN 1015-3/A1 s anda d [32] o ensu e
i s wo kabili y.
P isma ic samples we e p epa ed in acco dance wi h UNE-EN 1015-2/A1 s anda ds [33]. The
samples we e hen deposi ed o 21 days in clima ic chambe s (New B unsaick Galaxy 170) o
accele a e ca bona ion unde ealis ic cu ing condi ions o 25 °C, 50–60% RH, and 10% ol. o CO2
concen a ion.
2.2. P ocedu e B
2.2.1. Syn hesis
Ve insu S.A. (Je ez de la F on e a, Spain) p o ided he aluminium anodizing p ocess was e.
This was a clea solu ion wi h a pH o a ound 14, con aining a small amoun o a p ecipi a e phase.
Fo his s udy, he esidue was il e ed, and he p ecipi a e disca ded. The caus ic liquid was e had a
densi y o 1.32 g/cm3, and a composi ion o [Na] = 110 ± 2 g/L (4.78 ± 0.09 M)) and [Al] = 52 ±2 g/L
(1.93 ± 0.07 M).
The caus ic liquid om he anodizing aluminium indus y eac ed wi h PG acco ding o he
eac ion [23]:
3(CaSO4·2H2 O) + 6Na+ (aq) + 12OH-(aq) + 2Al3+ (aq) ↔ 3Na2SO4 + Ca3Al2(OH)12 +
6H2O. (4)
The p ocess was ini ia ed by adding 12.5 g o PG o 25.0 mL o he aluminium-anodizing esidue
unde magne ic s i ing o 3 h in ambien p essu e and empe a u e condi ions [9,16]. The pH was
12.0 du ing he p ocess. The o ma ion o a g ey p ecipi a e was obse ed, labelled as PGAS, and a
yellowish supe na an was disca ded o his s udy. Bo h phases we e sepa a ed by cen i uga ion,
and hen he solid phase was placed in an o en a 80 °C o p ese e i om hyd a ion and ca bona ion.
Based on he chemical composi ion o he esidues, his speci ic mass a io co esponded o a
s oichiome ic mola a io o [Ca2+]/[Al3+] = 1.5, a ge ing he chemical eac ion (4). I should be no ed
ha o he s oichiome ic ela ionships wi h di e en addi ions o wa e we e es ed. In his s udy,
only he one ha p oduced he bes CO2 seques e ing esul s, which was he inal pu pose, is
p esen ed.
3Na2SO4+Ca3Al2(OH)12 +6H2O. (4)
The p ocess was ini ia ed by adding 12.5 g o PG o 25.0 mL o he aluminium-anodizing esidue
unde magne ic s i ing o 3 h in ambien p essu e and empe a u e condi ions [
9
,
16
]. The pH was
12.0 du ing he p ocess. The o ma ion o a g ey p ecipi a e was obse ed, labelled as PGAS, and a
yellowish supe na an was disca ded o his s udy. Bo h phases we e sepa a ed by cen i uga ion,
and hen he solid phase was placed in an o en a 80
◦
C o p ese e i om hyd a ion and ca bona ion.
Based on he chemical composi ion o he esidues, his speci ic mass a io co esponded o a
s oichiome ic mola a io o [Ca
2+
]/[Al
3+
]=1.5, a ge ing he chemical eac ion (4). I should be no ed
ha o he s oichiome ic ela ionships wi h di e en addi ions o wa e we e es ed. In his s udy, only
he one ha p oduced he bes CO2seques e ing esul s, which was he inal pu pose, is p esen ed.
2.2.2. Ca bona ion P ocess
In his s ep, 2 g om he PGAS sample we e dispe sed in 40 mL o dis illed wa e [
19
]. The
ob ained mix u e was subjec ed o a con inuous low o pu e CO
2
(
≈
1 ba , 20 cm
3
/s) unde magne ic
s i ing. The sample was ca bona ed acco ding o he ollowing eac ion:
Ca3Al2(OH)12 +3CO2→3CaCO3+2Al(OH)3+3H2O. (5)
The pH du ing he p ocess dec eased mono onously om 12.8 un il i s abilized a 6.7 a e 110 min.
This esul ed in a new solid–liquid suspension whose phases we e sepa a ed by cen i uga ion. The
solid phase was labelled PGAB, and he liquid phase disca ded. The ep oducibili y o he expe imen
was e i ied se e al imes.
In . J. En i on. Res. Public Heal h 2020,17, 4248 5 o 17
2.3. Cha ac e iza ion Techniques
Mine al cha ac e iza ion o he samples was pe o med by X- ay di ac ion. The di ac ion
in ensi ies we e measu ed on a B uke powde di ac ome e (model D8-Ad ance A25) equipped
wi h con en ional B agg–B en ano geome y and a Cu anode. X’Pe HighSco e so wa e (Mal e n
Panaly ical, Mal e n, UK) was used o analyse he esul s.
An ICP-MS/MS Agilen 8800 (Agilen Technologies, San a Cla a, CA, USA) was used o analyse he
elemen s and iso opes a ace and ul a- ace le els (ppm–pp anges). This equipmen was p o ided
wi h an oc opola eac ion sys em (ORS), designed o minimize di e en ypes o spec ome ic
in e e ence. The elemen a y concen a ions in liquid samples we e analysed wi h a con en ional
nebulize Sa illex X400 (ISC-Science. O iedo, Spain) coupled wi h a CETAC ASX 520 sample
in oduc ion sys em. A speci ic in e ace allowed he samples o be analysed in he p esence o high
concen a ions o hyd o luo ic acid. Quan i a i e analyses we e pe o med in acco dance wi h he
US-EPA 200.8 (1986) [
34
]. The solid samples we e subjec ed o mic owa e-assis ed acid diges ion in 9
mL o concen a ed HNO
3
and 3 mL o HF o 15 min a 200
◦
C. A e cooling, he con en s o he essel
we e il e ed and ans e ed o a 25 mL olume ic lask wi h ype I wa e om a Milli-Q In eg al-3
(Millipo e, Me ck, Spain).
The ac i i y concen a ions o he na u al adionuclides we e measu ed by high- esolu ion
gamma- ay spec ome y. The de ec ion sys em used consis ed o a Re e se-Elec ode Ge manium
(REGe) de ec o , model GR6040 (Canbe a. Mon igny-le-B e onneux, F ance) shielded by an ac i e
an i-coincidence sys em con aining an annula an i-Comp on NaI de ec o . Canbe a GENIE 2000
(Canbe a. Mon igny-le-B e onneux, F ance) so wa e was used o ob ain spec a and o subsequen
analysis. Canbe a LABSOCS so wa e (Canbe a. Mon igny-le-B e onneux, F ance) was used o
calcula e he coun ing e iciency o he ge manium de ec o . Cylind ical con aine s (liquid samples) and
Pe i dishes (solid samples) we e used in he expe imen al measu emen s and sealed unde acuum
o p e en he escape o adon gas, enabling achie emen o secula equilib ium be ween adon and
i s daugh e s (
226
Ra and
214
Pb). The ac i i y concen a ions o he gamma emi e s we e de e mined
h ough he ollowing ene gies: 210Pb (46.5 keV), 232Th (63.3 keV), 226Ra (351 keV o 214Pb), 235U (144
keV), and 40 K (1460 keV).
The TCLP (1311 US-EPA) leaching es was pe o med o assess he e ec i eness o he
immobiliza ion o he di e en componen s and ob ain he deg ee o oxici y associa ed wi h he
di e en esidues. This p ocedu e used an ex ac ion liquid o pH 2.88
±
0.05 consis ing o 5.7 mL o
glacial ace ic acid dilu ed wi h 1L wi h deionized wa e . O he solid sample, 100 g was added o an
amoun o ex ac ion liquid, main aining he 20 mL/g a io, and placed in a o a y sys em a 30
±
2 pm
o 18 hou s and a a empe a u e o 22 ±3◦C.
A Rh- ube Panaly ical X- ay Fluo escence Spec ome e (AXIOS model) (Mal e n Panaly ical.
Mal e n, UK) was used o apply he XRF echnique, enabling quali a i e and quan i a i e chemical
analysis om O o U in a wide ange o concen a ions, om majo componen s o aces.
3. Resul s and Discussion
3.1. E olu ion o En i onmen al Risk
3.1.1. E alua ion o Majo Elemen s and T ace Elemen s om he T ea men o PG wi h a Soda
in Solu ion
(a) Phosphogypsum
The XRD analysis con i med he almos exclusi e p esence o gypsum in he sample o unp ocessed
PG [17], wi h a esidual amoun o qua z (SiO2) o igina ing om he mo he phospha e ock.
Acco ding o he XRF analysis esul s, shown in Table 1, he PG was mainly composed o Ca
(32 w . %, as CaO) and S (46 w . %, as SO
3
). These esul s we e simila o hose epo ed in o he

In . J. En i on. Res. Public Heal h 2020,17, 4248 6 o 17
s udies [
1
] and co esponded o a Ca/S
≈
0.993 mola a io, e y close o he expec ed Ca/S
≈
1 mola
a io. The main impu i ies o he PG we e Si (2.52 w . %, as SiO2) and P (0.65 w . %, as P2O5).
Table 1. Majo i y elemen s in bo h chemical p ocesses.
Majo i y Elemen s (w . %) PG C_S PGAS PGAB
Fe2O3nd nd nd 0.01 ±0.01
MnO nd nd nd nd
MgO nd nd nd nd
CaO 32 ±1 49 ±2 21 ±1 32 ±2
Na2O 0.01 ±0.01 12.5 ±0.6 20.5 ±0.7 2.29 ±0.08
K2O 0.02 ±0.01 nd 0.02 ±0.01 0.03 ±0.01
TiO2nd nd nd nd
P2O50.65 ±0.02 1.02 ±0.01 0.38 ±0.01 0.47 ±0.01
SO346 ±3 13.6 ±0.2 27 ±2 14.4 ±0.9
Cl nd nd nd nd
F nd nd nd nd
S O nd nd nd nd
BaO nd nd nd nd
LOI 18.4 ±0.4 19.4 ±0.2 14.4 ±0.2 33 ±0.1
w . %: weigh pe cen age; PG: phosphogypsum; C_S: lime pu y; PGAS: ka oi e p ecipi a e; PGAB: calci e om
ka oi e ca bona ion.
The main hea y me als and adionuclides obse ed in he PG we e: S , C , As, Cu, Cd, Pb, U,
and Th. The mino i y elemen s iden i ied a e shown in Table 2, oge he wi h he PG sample leaching
esul s ob ained om TCLP.
Table 2.
Con en s o ace elemen s (mg/kg) in he PG (phosphogypsum) sample. Leaching esul s (mg/L)
ob ained om he applica ion o he TCLP (Toxici y Cha ac e is ic Leaching P ocedu e) echnique
o he PG sample (L_ : phosphogypsum leaching), and e e ence (mg/kg) o he global a e age
concen a ion o ypical uncon amina ed soils. The limi alues pe mi ed by he US-EPA (Uni ed
S a es- En i onmen al P o ec ion Agency) o me als in leacha es ex ac ed om he TCLP es and he
maximum pe missible limi s o hea y me als in wa e o domes ic use acco ding o he US-EPA, WHO
(Wo ld Heal h O ganiza ion), and EU (Eu opean Union) (acco ding o Ge man legisla ion).
Me al PG
(mg/kg) L_ (mg/L) Limi s Allowed
(mg/kg)
TCLP (U
S—EPA) U S—EPA WHO EU
V 2.9 ±0.7 0.0161 ±0.0001 97 0.05
C 6.3 ±0.2 <0.023 92 5.0 0.10 0.05 0.05
Co <0.6 <0.0024 17.3
Ni <3 0.026 ±0.001 47 0.02 0.02
Zn <42 0.600 ±0.007 67 5.0 3.0
As <0.6 0.0052 ±0.0004 4.8 5.0 0.05 0.01 0.01
Se <30 <0.006 0.09 1.0
S 360 ±10 1.89 ±0.03 320 4.0
Cd 1.8 ±0.4 0.0072 ±0.0007 0.09 1.0 0.005 0.003 0.005
Ba 37 ±1 0.0433 ±0.0008 628 100.0 2.0 0.30
Pb 1.8 ±0.1 0.0053 ±0.0001 17 5.0 0.015 0.01 0.01
Th 1.1 ±0.2 <0.0013 10.5
U 5 ±1 0.0081 ±0.0001 2.7
The concen a ions o V, C , Ba, Pb, and Th we e well below hose ypically ound in undis u bed
soils (Table 2) [
35
]. Howe e , he concen a ion o Cd was
≈
20 imes highe han he ypical alue, he
concen a ion o S was
≈
1.2 imes highe , and he con en o U was app oxima ely hal o i s alue in
uncon amina ed soils. I should be no ed ha he concen a ions o Cd and S we e lowe han di e en
PG sou ces analysed in he li e a u e (Idaho, Sou h A ica, and Tunisia) [
29
]. The concen a ions o
o he me als we e below he de ec ion limi .
In . J. En i on. Res. Public Heal h 2020,17, 4248 7 o 17
All hese esul s, when compa ed wi h he limi alues pe mi ed by he US-EPA o me als in
leacha es ex ac ed wi h he TCLP es (Table 2), we e well below he es ablished limi s. No in o ma ion
is a ailable o some me als, such as V, Co, Ni, Zn, and S . Mo e s ic c i e ia would be applicable i he
a o emen ioned numbe s a e compa ed wi h hose s ipula ed in legisla ion egula ing d inking wa e
o human consump ion. Fo his eason, he maximum pe missible limi s o he me als s udied we e
aken in acco dance wi h he US-EPA (1986), he Wo ld Heal h O ganiza ion, and he EU (D inking
Wa e Di ec i e, 1998) (Table 2) [
36
]. Addi ionally, o anadium, Ge man legisla ion was aken as a
basis o pu i ica ion [
37
,
38
]. E en so, he le el o leacha e concen a ion did no exceed he es ablished
limi s, excep o Ni, which sligh ly exceeded hese limi s (30%).
Conside ing he esul s ob ained, he PG analysed in his s udy does no gene a e majo
en i onmen al isks, and he e o e, no co ec i e measu es should be applied. Howe e , cau ion
mus be aken be o e any ca ego ical asse ion, because PG is he e ogeneous, and i s hea y me al and
adionuclide con en s depend on he dep h a which he PG is ound [39–41].
(b) Soda solu ion ea men by-p oduc s
The XRD di ac og am o he C_S sample is shown in Figu e 2. As expec ed acco ding o i s
composi ion (Table 1), he e was a majo p esence o CaO, co esponding o slaked lime and Na
2
O
and SO
3
due o he sodium sulpha e. The lime was composed o 65.3% Ca(OH)
2
, 13.5% SO
3
, silica
impu i ies (qua z), and phospha es (1.02% P2O5), and did no con ain MgO.
In . J. En i on. Res. Public Heal h 2020, 17, x 8 o 17
.
Figu e 2. XRD (X Ray Di ac ion o he samples Ca_S (calci e om lime pu y ca bona ion) (abo e)
and C_S (lime pu y) (below). C: Calci e, Q: Qua z, P : Po landi e, T: Thena di e.
The concen a ions o C , Co, Ni, Zn, and Th (Table 3) we e below he a e age concen a ions
ound in ypical uncon amina ed soils. Those o As and S we e highe by ac o s o ≈1.5 and 1.3,
espec i ely. Howe e , he concen a ions o Se, Cd, U we e subs an ially highe , as much as ≈37.5
imes highe in he case o Cd. The inc ease in he concen a ion o U, ≈4 imes highe han ha o
ypical soil, was no su p ising since i is a ma e ial ob ained om PG, which is conside ed a NORM
ma e ial, ha is, one which is ich in U-Th adionucleide se ies.
c) Ca bona ion by-p oduc s
The XRD analysis o his sample indica ed ha he po landi e ca bona ed comple ely, esul ing
only in calci e (Figu e 2). The cha ac e is ics o his sample ha e been epo ed elsewhe e [1].
In his case (Table 3), as may be expec ed, he concen a ions o ace elemen s and adionuclides
coincided almos comple ely wi h hose ound in he C_S sample.
d) Mo a p obes
As expec ed, he majo i y in he disca ded sand was calci e. The po landi e was ully
ca bona ed. Small e lec ions o esidual hena di e in he lime we e also obse ed (Figu e 3).
.
Figu e 3. XRD o mo a sample. C: Calci e, Q: Qua z, T: Thena di e.
Figu e 2.
XRD (X Ray Di ac ion o he samples Ca_S (calci e om lime pu y ca bona ion) (abo e)
and C_S (lime pu y) (below). C: Calci e, Q: Qua z, P: Po landi e, T: Thena di e.
The UNE-EN 459-2 s anda d [
42
] s a es ha lime con en mus always be highe han 55%,
al hough highe alues may be equi ed. Ne e heless, he UNE-EN 196-2: 2014 s anda d [
43
] equi es
ha sulpha e con en , gi en in e ms o SO
3
, mus be less han 2%. Rega ding he MgO con en ,
he s anda d equi es his o be less han 5%. The SO
3
con en exceeded he limi es ablished in he
egula ions, and he e o e, p e en i e measu es a e equi ed o co ec i .
The concen a ions o C , Co, Ni, Zn, and Th (Table 3) we e below he a e age concen a ions
ound in ypical uncon amina ed soils. Those o As and S we e highe by ac o s o
≈
1.5 and 1.3,
espec i ely. Howe e , he concen a ions o Se, Cd, U we e subs an ially highe , as much as
≈
37.5
imes highe in he case o Cd. The inc ease in he concen a ion o U,
≈
4 imes highe han ha o
ypical soil, was no su p ising since i is a ma e ial ob ained om PG, which is conside ed a NORM
ma e ial, ha is, one which is ich in U-Th adionucleide se ies.
In . J. En i on. Res. Public Heal h 2020,17, 4248 8 o 17
Table 3.
T ace elemen s o po landi e (C_S), calci e (Ca_S), and mo a samples. Leaching esul s
ob ained om he applica ion o he TCLP (Toxici y Cha ac e is ic Leaching P ocedu e) echnique o
he sample o po landi e (L_p), calci e (L_c), and mo a (L_m).
METAL C_S (mg/kg) L_p (mg/L) Ca_S
(mg/kg) L_c (mg/L) Mo a
(mg/kg) L_m (mg/L)
V<0.1 <0.007 <0.1 <0.007 0.3 ±0.1 0.109 ±0.001
C 13.8 ±0.2 0.083 ±0.003 11.5 ±0.4 <0.023 9 ±2<0.023
Co 0.275 ±0.004 <0.0024 0.23 ±0.01 0.0048 ±0.0002 0.165 ±0.03 0.0049 ±0.0002
Ni 1.80 ±0.02 0.023 ±0.001 2.3 ±0.1 0.046 ±0.001 0.347 ±0.05 0.039 ±0.001
Zn 10.1 ±0.2 0.67 ±0.02 9.7 ±0.5 <0.214 9.6 ±1.2 <0.221
As 7 ±2<0.002 5.2 ±0.4 <0.002 3.9 ±1.1 <0.002
Se 2.36 ±0.08 <0.0059 2.33±0.08 <0.006 1.2 ±0.7 <0.0061
S 413 ±6 2.17 ±0.05 353 ±1 3.03 ±0.04 170 ±20 2.31 ±0.01
Cd 3.37 ±0.04 <0.0008 3.6 ±0.1 <0.0008 1.4 ±0.4 <0.0008
Ba 83 ±2 0.062 ±0.002 72 ±1 0.1203 ±0.0009 36 ±2 0.0658 ±0.0004
Pb 3.25 ±0.05 0.0066 ±0.0003 3.5 ±0.2 <0.0009 1.43 ±0.04 <0.0009
Th 1.5 ±0.2 <0.0013 2.69 ±0.08 <0.0013 0.32 ±0.05 <0.0013
U 10.7 ±0.3 <0.0012 9.7 ±0.3 0.0508 ±0.0003 3.9 ±0.3 0.0302 ±0.0003
(c) Ca bona ion by-p oduc s
The XRD analysis o his sample indica ed ha he po landi e ca bona ed comple ely, esul ing
only in calci e (Figu e 2). The cha ac e is ics o his sample ha e been epo ed elsewhe e [1].
In his case (Table 3), as may be expec ed, he concen a ions o ace elemen s and adionuclides
coincided almos comple ely wi h hose ound in he C_S sample.
(d) Mo a p obes
As expec ed, he majo i y in he disca ded sand was calci e. The po landi e was ully ca bona ed.
Small e lec ions o esidual hena di e in he lime we e also obse ed (Figu e 3).
In . J. En i on. Res. Public Heal h 2020, 17, x 8 o 17
.
Figu e 2. XRD (X Ray Di ac ion o he samples Ca_S (calci e om lime pu y ca bona ion) (abo e)
and C_S (lime pu y) (below). C: Calci e, Q: Qua z, P : Po landi e, T: Thena di e.
The concen a ions o C , Co, Ni, Zn, and Th (Table 3) we e below he a e age concen a ions
ound in ypical uncon amina ed soils. Those o As and S we e highe by ac o s o ≈1.5 and 1.3,
espec i ely. Howe e , he concen a ions o Se, Cd, U we e subs an ially highe , as much as ≈37.5
imes highe in he case o Cd. The inc ease in he concen a ion o U, ≈4 imes highe han ha o
ypical soil, was no su p ising since i is a ma e ial ob ained om PG, which is conside ed a NORM
ma e ial, ha is, one which is ich in U-Th adionucleide se ies.
c) Ca bona ion by-p oduc s
The XRD analysis o his sample indica ed ha he po landi e ca bona ed comple ely, esul ing
only in calci e (Figu e 2). The cha ac e is ics o his sample ha e been epo ed elsewhe e [1].
In his case (Table 3), as may be expec ed, he concen a ions o ace elemen s and adionuclides
coincided almos comple ely wi h hose ound in he C_S sample.
d) Mo a p obes
As expec ed, he majo i y in he disca ded sand was calci e. The po landi e was ully
ca bona ed. Small e lec ions o esidual hena di e in he lime we e also obse ed (Figu e 3).
.
Figu e 3. XRD o mo a sample. C: Calci e, Q: Qua z, T: Thena di e.
Figu e 3. XRD o mo a sample. C: Calci e, Q: Qua z, T: Thena di e.
In he case o he mo a , since i is a e y he e ogeneous sys em on a millime e scale, i was
necessa y o ake di e en aliquo s o ob ain eliable in o ma ion because he masses ha can be
diges ed by ICP a e e y small, esul ing in a dispe sion o he concen a ions o he ace elemen s. The
a e age esul s o ou aliquo s aken a e p esen ed in Table 3. I can be obse ed ha , when mixing
he lime wi h sand, he ini ial concen a ions o mos o he ace elemen s dec eased. The a e age
concen a ions o As and S we e below he limi s es ablished by cu en egula ions. Howe e , hose o
Se, Cd, and U we e mode a ely abo e hose limi s. Besides he ace elemen concen a ions, he esul s
om he applica ion o he TCLP echnique a e shown o he L_p, L_c, and L_m samples in Table 3.
These esul s a e compa ed wi h he maximum pe missible limi s es ablished by he TCLP (US-EPA),
In . J. En i on. Res. Public Heal h 2020,17, 4248 9 o 17
indica ed in Table 2. I has been e i ied ha all he alues we e well below he es ablished limi s.
Thus, i can be concluded ha he moni o ed me als we e e ec i ely immobilized. I was also e i ied
ha hese alues we e below he pe missible limi s es ablished by TCLP (US-EPA). Howe e , he e is
no in o ma ion on pe missible limi s o some me als, such as Zn, Ni, V, and S . The concen a ions o
all he elemen s sc eened did no exceed he maximum pe missible limi s o d inking wa e . The V
limi exceeded he maximum pe mi ed by Ge man law by a ac o o ≈2.2.
3.1.2. Con en s o Majo and T ace Elemen s in he T ea men o PG wi h Aluminium Residue
(a) Aluminium was e
The densi y o he aluminium esidue was 1.32 g/cm
3
measu ed by Hg pycnome y wi h
pH =14
and [Na] =110
±
2 g/L (4.78
±
0.09 M) and [Al] =52
±
2 g/L (1.93
±
0.07 M), acco ding o ICP-OES esul s.
(b) Syn hesis
The XRD pa e n o he solid by-p oduc esul ing om an a ack o he PG wi h he aluminium
was e is ep esen ed in Figu e 4, labelled PGAS. The main associa ed e lec ions co esponded o ka oi e
and hena di e, as expec ed acco ding o Equa ion (3). I should be no ed ha no esidual gypsum
was de ec ed, indica ing ha he eac ion was comple e. The composi ional analysis o he PGAS
by-p oduc by XRF (Table 1) con i med he p esence o Ca, Al, S, and Na as he main componen s, in
he ela i e mola ac ions Ca:Al (1.51) and Na:S (1.96), ypical o ka oi e and hena di e, espec i ely,
con i ming ha he eac ion was indeed comple e.
In . J. En i on. Res. Public Heal h 2020, 17, x 10 o 17
.
Figu e 4. XRD o he samples PGAB: calci e (abo e) and PGAS: ka oi e p ecipi a e (below). C: Calci e,
Q: Qua z, K: Ka oi e, T: Thena di e.
c) Ca bona ion.
The XRD pa e n o he ca bona ed sample (Figu e 4) p esen s he calci e e lec ions
accompanied by hose o he emaining qua z impu i ies om he PG. No hena di e e lec ions we e
obse ed, con i ming i s comple e dissolu ion du ing he ca bona ion p ocess. Howe e , he XRF
analysis (Table 1) e ealed he p esence o subs an ial con en s o ce ain chemical species no
de ec ed by XRD, indica ing hei amo phous cha ac e . These we e mainly Al and S, and o a lesse
ex en , Na.
The con en s o ace elemen s p esen in he PGAS sample (Table 4), such as V, C , As, S , Ba,
and Th we e well below he concen a ions in undis u bed soils. Howe e , he concen a ion o Cd
(1.1 ± 0.2 mg kg) exceeded he ypical concen a ion by a ac o o 12.5. In con as , he concen a ion
o U (2.5 ± 0.3 mg / kg) was wi hin he limi pe mi ed o uncon amina ed soils.
Table 4. Con en s o ace elemen s in he PGAS (ka oi e p ecipi a e) and PGAB (calci e) samples.
Leaching esul s ob ained om he applica ion o he TCLP (Toxici y Cha ac e is ic Leaching
P ocedu e) echnique o he PGAS (L_k) and PGAB (L_ck) samples.
Me al
PGAS
(mg/kg)
L_k
(mg/L)
PGAB
(mg/kg)
L_ck
(mg/L)
V
8.0 ± 0.3
<0.007
5.8 ± 0.3
0,.0225 ± 0,04
C
5.3 ± 0.4
<0.023
6.7 ± 0.6
0.030 ± 0.004
Co
<0.6
<0.0024
<0.6
<0,0024
Ni
<3
0.0082 ± 0.0003
<3
0.0050 ± 0.0004
Zn
<41
0.0740 ± 0.0005
<41
<0.212
As
1.8 ± 0.8
<0.002
1.4 ± 0.2
<0.002
Se
<30
<0.006
<30
<0.0059
S
248 ± 10
1.69 ± 0.02
345 ± 5
1.46 ± 0.1
Cd
1.1 ± 0.2
<0.0008
1.6 ± 0.2
<0.0008
Ba
27 ± 3
0.0344 ± 0.0001
36 ± 1
0.0024 ± 0.02
Pb
1.5 ± 0.2
<0.0009
1.6 ± 0.1
<0.0009
Th
0.9 ± 0.1
<0.0013
1.1 ± 0.1
<0.0013
U
2.5 ± 0.3
<0.0012
2.9 ± 0.2
<0.0012
Figu e 4.
XRD o he samples PGAB: calci e (abo e) and PGAS: ka oi e p ecipi a e (below). C: Calci e,
Q: Qua z, K: Ka oi e, T: Thena di e.
(c) Ca bona ion.
The XRD pa e n o he ca bona ed sample (Figu e 4) p esen s he calci e e lec ions accompanied
by hose o he emaining qua z impu i ies om he PG. No hena di e e lec ions we e obse ed,
con i ming i s comple e dissolu ion du ing he ca bona ion p ocess. Howe e , he XRF analysis
(Table 1) e ealed he p esence o subs an ial con en s o ce ain chemical species no de ec ed by XRD,
indica ing hei amo phous cha ac e . These we e mainly Al and S, and o a lesse ex en , Na.
The con en s o ace elemen s p esen in he PGAS sample (Table 4), such as V, C , As, S , Ba, and
Th we e well below he concen a ions in undis u bed soils. Howe e , he concen a ion o Cd (1.1 ±
0.2 mg kg) exceeded he ypical concen a ion by a ac o o 12.5. In con as , he concen a ion o U
(2.5 ±0.3 mg/kg) was wi hin he limi pe mi ed o uncon amina ed soils.
In . J. En i on. Res. Public Heal h 2020,17, 4248 16 o 17
38.
Ma
í
nez-L
ó
pez, C.; Mej
í
a-A cila, J.M.; To es-Ag edo, J. Mej
í
a-de-Gu i
é
ez, R. E alua ion o he oxici y
cha ac e is ics o wo indus ial was es alo ized by geopolyme iza ion p ocess. DYNA
2015
,190, 74.
[C ossRe ]
39.
Mac
í
as, F.; P
é
ez-L
ó
pez, R.; Ruiz-C
á
no as, C.; Ca e o, S.; C uz-He n
á
ndez, P. En i onmen al assessmen and
managemen o phosphogypsum acco ding o eu opean and Uni ed S a es o Ame ica egula ion. P ocedia
Ea h Plane . Sci. 2017,17, 666–669. [C ossRe ]
40.
Ruiz-C
á
no as, C.; P
é
ez-L
ó
pez, R.; Mill
á
n, R.; Nie o, J.M. P elimina y s udy o Huel a phosphogypsum
s acks as a po en ial sou ce o elemen s o economic in e es . Geogace a 2017,62, 103–106.
41. Suá ez, F.M.; Pe ez-Lopez, R.; Ruiz-Cano as, C. E aluación Ambien al de los Fos oyesos de Huel a Según
No ma i as de Eu opa y No eamé ica. Mine al. Soc. J. 2015,20, 85–86. [C ossRe ]
42.
UNE-EN 459-2: 1994. Cemen and Lime Tes Me hods. Pa 1. De e mina ion o Mechanical Resis ance; UNE-EN:
Mad id, Spain, 1994.
43.
UNE-EN 196-2: 2014. Cemen and Lime Tes Me hods. Pa 2: Chemical Analysis o Cemen s; UNE-EN: Mad id,
Spain, 2014.
44.
Ca alho, F.P. Disposal o phosphogypsum was e con aining enhanced le els o adioac i i y. In
P oceedings o he In e na ional Las Con e ence on Managemen o Radioac i e Was e om non-powe
applica ions–Sha ing he IAEA-CN-87/6, Sain Paul’s Bay, Mal a, 5–9 No embe 2001; pp. 67–68.
45.
Boli a , J.P.; Ga c
í
a-Teno io, R.; Ga cia-Leon, M. On he ac iona ion o na u al adioac i i y in he p oduc ion
o phospho ic acid by he we acid me hod. J. Radioanal. Nucl. Chem. 1996,214, 77–78. [C ossRe ]
46.
In e na ional A omic Ene gy Agency-Annual Repo o 2004. A ailable online: h ps://www.iaea.o g/es/
publica ions/ epo s/annual- epo -2004 (accessed on 10 Decembe 2019).
47.
US-EPA. Recommended Wa e Quali y C i e ia. 2002. A ailable online: h ps://www.elaw.o g/es/con en /us-
%E2%80%93-us-epa-na ional- ecommended-wa e -quali y-c i e ia-2002 (accessed on 10 Decembe 2019).
48.
US-EPA. Guidelines o Exposu e Assessmen . 1992. A ailable online: h ps://c pub.epa.go /ncea/ isk/
eco display.c m?deid=15263 (accessed on 10 Decembe 2019).
49.
US-EPA. Na ional P ima y D inking Wa e Regula ions; Radionuclides; Final Rule. Pa II. 40 CFR Pa s
9, 141, and 142. 2000. A ailable online: h ps://nepis.epa.go /Exe/ZyPURL.cgi?Dockey=2000238H.TXT
(accessed on 10 Decembe 2019).
50.
Royal Dec ee, 314/2016, de 29 de Julio, po el que se Es ablecen los C i e ios Sani a ios de la Calidad del
Agua de Consumo Humano. O icial S a e Gaze e (S a e Agency BOE), n
º
183 (2016), Mad id (in Spanish).
A ailable online: h ps://www.boe.es/eli/es/ d/2016/07/29/314 (accessed on 10 Decembe 2019).
51.
Al A a , L.; Al-Ouda , M.; Kanak i, S.; Budei , Y.; Khalily, H.; Al Hamwi, A. Radiological impac s o
phosphogypsum. J. Een i on. Manag. 2011,92, 2151–2158. [C ossRe ]
52.
Bol
í
a , J.P.; Ga c
í
a-Teno io, R.; Vaca, F. Radio ecological s udy o and es ua ine sys em loca ed in he sou h
o Spain. Wa e Res. 2000,34, 2941–2950. [C ossRe ]
53.
UNSCEAR. Uni ed Na ions Scien i ic Commi ee on he E ec s o A omic Radia ion; Sou ces and E ec s o Ionizing
Radia ion: New Yo k, NY, USA, 1993.
54.
Mi
ó
, C.;
Á
ila, J.M.; Ga c
í
a, M.; Pas o -Villegas, S.J. Riesgos debido a la adiac i idad na u al de piza as de
cons ucción. In . Tecnol. 2010,21, 9–16. [C ossRe ]
55.
EC-Eu opean Commission, Radia ion P o ec ion. 112- adiological P o ec ion P inciples Conce ning he
Na u al Radioac i i y o Building Ma e ials, Di ec o a e-Gene al En i onmen , Nuclea Sa e y and Ci il P o ec ion;
EC-Eu opean Commission, Radia ion P o ec ion: B ussels, Belgium, 1999.
56.
Beli e mis, M.; Kilic, N.; Co uk, Y.; Topcuoglu, S. The e ec s o physicochemical p ope ies on gamma
emi ing na u al adionuclide le els in he soil p o ile o Is anbul. En i on. Moni . Assess.
2010
,163, 15–26.
[C ossRe ]
57.
Be e ka, J.; Ma hew, P.J. Na u al adioac i i y o Aus alian building ma e ials, was e and byp oduc s. Heal h
Phys. 1985,48, 87–95. [C ossRe ] [PubMed]
58.
El-Tahe , A. Gamma spec oscopic analysis and associa ed adia ion haza ds o building ma e ials used in
Egyp . Radia . P o . Dosim. 2009,138, 166–173. [C ossRe ] [PubMed]
59.
G
á
zquez-Gonz
á
lez, M.J. Ca ac e izaci
ó
n y Valo izaci
ó
n de Residuos Gene ados en la Indus ia de P oducci
ó
n
de Dióxido de Ti anio. Ph.D. Thesis, Uni e sidad de Huel a, Huel a, Spain, 2011.

In . J. En i on. Res. Public Heal h 2020,17, 4248 17 o 17
60. K iege , R. Radioac i i y o cons uc ion ma e ials. Be onw. Fe . Tech. 1981,47, 468.
61.
In e na ional Commission on Radiological P o ec ion. In e nacional Commision on Radiological P o ec ion.
Recommenda ions o ICRP; Publica ion 26; Pe gamon P ess: Ox o d, UK, 1977.
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