Ci a ion: Sánchez-España, J.; Ilin, A.;
Yus a, I. Me allic Coppe (Cu[0])
Ob ained om Cu2+-Rich Acidic
Mine Wa e s by Two Di e en
Reduc ion Me hods: C ys allog aphic
and Geochemical Aspec s. Mine als
2022,12, 322. h ps://doi.o g/
10.3390/min12030322
Academic Edi o s: Radoslaw Pomykala,
Ba ba a To a and Ka e ina Adam
Recei ed: 31 Janua y 2022
Accep ed: 1 Ma ch 2022
Published: 4 Ma ch 2022
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2022 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
mine als
A icle
Me allic Coppe (Cu[0]) Ob ained om Cu2+-Rich Acidic Mine
Wa e s by Two Di e en Reduc ion Me hods: C ys allog aphic
and Geochemical Aspec s
Ja ie Sánchez-España 1,* , And ey Ilin 2and Iñaki Yus a 2
1Mine Was e and En i onmen al Geochemis y Resea ch G oup, Depa men o Geological
Resou ces (IGME-CSIC), Cale a 1, T es Can os, 28760 Mad id, Spain
2Depa men o Geology, Uni e si y o he Basque Coun y (UPV/EHU), Facul y o Science and Technology,
Apdo. 644, 48080 Bilbao, Spain; and ey[email p o ec ed] (A.I.); [email p o ec ed] (I.Y.)
*Co espondence: [email p o ec ed]
Abs ac :
The eco e y o aluable me als om di e en ypes o was es has become o p ime s a egic
in e es gi en he sca ci y o p ima y c i ical aw ma e ials a in e na ional scale. Implemen a ion o
new me hods o e inemen o classical echniques wi h mode n echnological ad ances is, he e o e,
an ac i e esea ch ield. Mine was es a e o special in e es because hei high me al concen a ions
make hem en i onmen ally ha m ul and economically p o i able a he same ime. In his s udy, we
e alua ed wo di e en me hods o Cu eco e y om ex emely acidic mine wa e s seeping om
was es and abandoned mines in SW Spain. Th ough a se ies o di e en ba ch expe imen s, we
compa ed he me hod e iciency and c ys allog aphic p ope ies o elemen al coppe (Cu[0]) ob ained
by educ ion o Cu
2+
ions by (1) chemical educ ion using asco bic acid a di e en en i onmen al
condi ions o pH (1.50–3.95), empe a u e (25–80
◦
C) and asco bic acid concen a ion (10 mM o 0.1 M),
and (2) classical cemen a ion me hod wi h sc ap i on a pH 1.50 and 25
◦
C. Ou s udy demons a es
ha he p ecipi a ion o Cu[0] can ake place a pH 3.95 and low AA concen a ions (0.1 M), esul ing
in la ge (
µ
m-scale), pe ec ly de eloped c ys als o coppe wi h pseudop isma ic o acicula habi
a e 24 h o aging, likely h ough o ma ion o a ansien compound consis ing in Cu
2+
-asco ba e
and/o cup i e (Cu
2
O) nanocolloids. Reduc ion expe imen s a highe AA concen a ions (0.1 M)
showed as e p ecipi a ion kine ics and esul ed in high-pu i y (>98%) coppe suspensions o med
by sub ounded nanopa icles. The AA me hod, howe e , yielded e y low eco e y a es (15–25%)
because o he low pH alues conside ed. The cemen a ion me hod, which p oduced ee-like
agg ega es o med by sub-mic on c ys als a anged in di e en di ec ions, p o ed o be much mo e
e icien (>98% eco e y) and cos -e ec i e.
Keywo ds:
coppe ; chemical educ ion; acidic mine wa e s; seconda y aw ma e ials; me al eco e y
1. In oduc ion
Coppe is o pa amoun impo ance in mode n echnology, being widely used in
mic o/nanoelec onics [
1
]. Coppe nanopa icles and nanowi es a e also o majo in e es
o hei use in di e se ields, such as ca alysis, op oelec onics, and liquid phase o gas
senso s [
2
–
4
]. Coppe nanopa icles a e also used o p oduce conduc i e inks o elec odes
o silicon c ys al sola cells and in he p in ed elec onic indus y [
5
]. O he po en ial
applica ions o coppe nanopa icles aim o ake ad an age o hei known an ibac e ial
p ope ies in he ood o medical indus y, o o p oduce lub ica ing subs ances o he
ab ica ion o di e se composi e ma e ials [
2
]. Coppe nanopa icles ha e been adi ion-
ally ob ained by educ ion o Cu
2+
ions in solu ion, which does no equi e expensi e
equipmen and allows he con ol o pa icle size and mo phology h ough a ia ion o
ce ain pa ame e s [
2
]. This me hod usually equi es an alkaline pH o be e icien , since
he elec ode po en ial o AA is much lowe a alkaline medium (+80 mV compa ed o
Mine als 2022,12, 322. h ps://doi.o g/10.3390/min12030322 h ps://www.mdpi.com/jou nal/mine als
Mine als 2022,12, 322 2 o 18
+166 mV a pH 4 [
2
]). A p esen , coppe nanopa icles may be syn hesized by di e en
educ ion me hods using mic owa es, as well as sonochemical, elec ochemical, he mal,
and chemical echniques, whe eas coppe nanowi es a e cu en ly p oduced by di e en
me hods such as elec ochemical deposi ion/elec opla ing (commonly he easies and
cheapes echnique, and highly e icien a e y acidic pH), pulsed lase deposi ion, o
chemical apo deposi ion [
3
,
6
–
8
]. In chemical educ ion, he use o se e al educ an s in
ea ly imes, such as hyd azine o sodium hyd ophospha e, which we e seen o be ei he
highly oxic (e.g., hyd azine) o echnically ine icien (e.g., sodium hyd ophospha e), has
been p og essi ely eplaced by o he educing agen s, such as asco bic acid and o he
o ganic educ an s such as glucose [
2
,
3
,
5
]. The an ioxidan p ope ies o AA (which p e en
he esul ing coppe om unde going oxida ion in oxygena ed en i onmen s) make his
compound ad an ageous wi h espec o o he educ an s [
3
]. The con ol o size and
mo phology o Cu[0] and Cu
2
O nanoc ys als and nanos uc u es h ough he use o di e -
en o ganic and ino ganic addi i es, wi h o wi hou s abilizing agen s, has also become
a common p ac ice in ma e ials chemis y o p oduce nanoma e ials wi h e y speci ic
conduc i e p ope ies (e.g., supe conduc o s) [9].
In he con ex o a high demand o aw ma e ials o he mode n indus y and he
implemen a ion o ci cula economy concep s a global scale, he eco e y o aluable and
c i ical me als om mine was es has become o g owing in e es [
10
]. Acidic mine wa e s
seeping om mine was es (e.g., ailings, was e piles) o abandoned mine po als o open
pi s, usually e e ed o as acid mine d ainage (AMD), is among he majo en i onmen al
p oblems o he me al and coal mining indus y, due o i s se e e acidi y and high concen-
a ion o sul a e and many oxic me als [
11
,
12
]. A he same ime, howe e , hese acidic
liquo s may con ain aluable me als, such as Cu, Zn, Co, o Ni, a such high concen a ions
ha can make hem a esou ce o seconda y aw ma e ials mo e han a was e [
13
–
15
]. The
acidic mine wa e s o he Ibe ian Py i e Bel , in SW Spain, wi h AMD leacha es exceeding
concen a ions o 440 ppm (mg/L) [
16
] and wi h pi lakes showing ex eme con en s up
o 1350 mg/L Cu
2+
[
17
–
19
], p obably ep esen a pa adigma ic case a in e na ional le el.
Al hough i s bene i a indus ial scale by mode n echniques is s ill u opic, he eco e y o
coppe by he classical cemen a ion me hod using sc ap i on was widely used in he egion
du ing he 19 h and 20 h cen u ies [
20
], being also applied a p esen in some AMD si es
and pi lakes in o he mining dis ic s o he wo ld [21].
Despi e he ple ho a o s udies on di e en me hods o coppe p oduc ion om
solu ions o a iable chemis y and o igin, he e is an appa en lack o s udies compa ing he
e iciency o di e en me hods po en ially applicable o he eco e y o coppe om AMD,
and bo h he s uc u al/c ys allog aphic p ope ies o he ob ained coppe by educ ion o
Cu
2+
ions, and he geochemical con ols on Cu[0] c ys alliza ion, a e s ill no su icien ly
well known. Any Cu
2+
- educ ion me hod needs o be cos -e ec i e and mus p o ide
a high-quali y p oduc in o de o be p o i able and implemen able a indus ial scale.
In he p esen s udy, we aimed o e alua e he e iciency o Cu
2+
educ ion in Cu- ich,
acidic mine wa e s by (1) chemical educ ion using asco bic acid (a widely known educing
agen in Cu syn hesis s udies), and (2) classical cemen a ion me hod using sc ap i on as
educing agen . Bo h me hods we e es ed a low pH condi ions (<4.0) unde oxygenic
a mosphe e and wi hou any s abilize , since he main goal o ou in es iga ion was o
e alua e possible on-si e ea men s in abandoned mines wi hou he need o complex o
expensi e in as uc u e. We we e especially in e es ed in con as ing he geome y and size
o he coppe pa icles and/o c ys als o med by hese wo di e en me hods, o which
we used a combina ion o X- ay di ac ion and scanning elec on mic oscopy. Geochemical
modeling based on solu ion chemis y was also used o e alua e he dis ibu ion and mola
abundance o Cu aqueous species in solu ion and he sa u a ion s a e o he acidic solu ions
wi h espec o elemen al coppe and o he coppe compounds. The p ac ical implica ions
a e discussed.
Mine als 2022,12, 322 3 o 18
2. Ma e ials and Me hods
2.1. Field Wo k and Sampling
Wa e samples (1 L each) we e aken om h ee di e en loca ions in he p o ince o
Huel a (SW Spain), a egion se e ely a ec ed by acid mine d ainage (AMD) pollu ion [
16
].
These acidic mine wa e s included a leacha e om a big was e ock pile in he Rio in o mine
(TI), an e luen om an abandoned mine po al in Tha sis mine (CA) and an ou low om
an acidic pi lake in a big open pi in San Telmo mine (ST). The pH and Cu concen a ion o
hese samples a e p o ided in Table 1. A common ea u e o hese h ee mine wa e s was
hei high acidi y (pH 2.5–2.9). They di e ed, howe e , as ega ds o hei oxida ion s a e
(Eh = 570–750 mV), as well in sul a e and me al concen a ion, including dissol ed coppe
(23–183 mg/L Cu).
Table 1. Selec ed chemical pa ame e s o he h ee samples o acidic mine wa e used in his s udy.
Sample pH Eh SO4Fe Cu
mV mg/L mg/L mg/L
TI 2.6 570 23,300 1290 183
CA 2.5 615 3700 1250 124
ST 2.9 750 3350 125 23
These wa e s we e all il e ed on si e h ough 0.45
µ
m po e size, ni ocellulose mem-
b ane il e s (Millipo e) and s o ed a 4
◦
C du ing anspo o he labo a o y. Once in he
IGME Geochemis y lab, he wa e s we e used o di e en expe imen s aimed a educing
he dissol ed Cu
2+
ions p esen in he acidic liquo s o ob ain me allic, ze o- alence coppe
(Cu[0]). We used wo di e en educ ion me hods, namely: (1) educ ion wi h asco bic acid
(C
6
H
8
O
6
) as he educing agen , and (2) classic cemen a ion me hod using sc ap me allic
i on (Fe[0]) as he educing agen . To assess he e ec o pH and empe a u e on c ys al-
liza ion kine ics, as well as on he c ys allini y and pa icle size o me allic coppe , he i s
me hod (asco bic acid) was conduc ed a a ying pH (1.50–3.95), empe a u e (25
◦
C o
80
◦
C), and asco bic acid concen a ion (10 mM o 0.1 M C
6
H
8
O
6
). The second me hod was
solely conduc ed a pH 1.50 and 25
◦
C. Bo h educ ion me hods a e b ie ly desc ibed below.
2.2. Ba ch Expe imen s o Cu2+ Reduc ion
2.2.1. Reduc ion wi h Asco bic Acid
The selec ed acidic mine wa e s (500 mL in olume) we e pou ed in glass lasks and
placed in a magne ic s i ing s age se a 400 pm, whe e hey we e pa ially neu alized
by d opwise addi ion o 1 M NaOH o inc ease he pH o he wa e s o alues a ound
3.90–3.95 (Figu e S1 in Supplemen al Ma e ial). The goal o his pa ial neu aliza ion was
o emo e all dissol ed e ic i on in solu ion (Table 1) so ha he expe imen s could be
conduc ed wi hou he p esence o any colloids o Fe(III) mine als, such as schwe manni e,
which a e o en o med in hese solu ions upon pH inc ease [
22
–
25
]. This pH limi , in
addi ion, ensu ed he absence o aluminum p ecipi a es ha o m in AMD sys ems a
pH > 4.0 [26,27]
. The i a ed solu ions we e il e ed in a acuum il a ion uni (Millipo e)
using 0.45 µm po e size il e s o emo e all Fe(III) p ecipi a es (Figu e S1).
The pa ly neu alized (pH ~3.95), acidic mine wa e s we e subsequen ly i a ed by
d opwise addi ion o an asco bic acid solu ion (1 M, pH 2.5). This asco bic acid solu ion
had been p e iously p epa ed by dilu ion o pu e ( eagen -g ade), d y c ys alline asco bic
acid (C
6
H
8
O
6
) om Me ck in ul apu e dis illed wa e (Millipo e). The addi ion o asco bic
acid (AA) o he MilliQ wa e esul ed in an immedia e acidi ica ion, and he inc ease
o he AA concen a ion in he solu ion ended o a ain an appa en equilib ium pH
a ound 2.5 o AA concen a ions g ea e han 1 g/L (Figu e S2 in Supplemen al Ma e ials).
This acidi ica ion was p o oked by apid dep o ona ion o AA and pa ial con e sion o
asco ba e h ough Reac ion (1) [28]:
Mine als 2022,12, 322 4 o 18
C6H8O6→C6H7O6−+ H+(1)
Bo h AA and asco ba e can e ec i ely educe Cu(II) and Fe(III) ions, hough AA eac-
ions wi h ansi ion me als such as Fe(III) o Cu(II) ha e a e cons an s ha di e by up o
se e al o de s o magni ude, wi h he eac ions o asco ba e usually being as e [
28
]. In any
case, in his s udy we e e o ‘asco bic acid’ o conside he o al amoun o he p o ona ed
o m, AA, and he dep o ona ed o m (asco ba e) p esen in he educing solu ions.
The pH o he solu ions was con inuously measu ed du ing he educ ion expe i-
men s wi h p e iously calib a ed CRISON pH me e s, and isual changes o colo and
u bidi y we e eco ded and anno a ed. When a me allic coppe p ecipi a e was appa en ly
o med (based on colo change o u bidi y o ma ion), he solu ions we e immedia ely
il e ed h ough 0.45
µ
m po e size il e s and he ob ained solids we e washed se e al
imes by MilliQ wa e , and ai -d ied a ambien empe a u e o u he mo phological,
mine alogical, and c ys allog aphic analysis (Figu e 1).
Mine als 2022, 11, x FOR PEER REVIEW 4 o 19
acidi ica ion was p o oked by apid dep o ona ion o AA and pa ial con e sion o asco -
ba e h ough eac ion (1) [28]:
C
6
H
8
O
6
→ C
6
H
7
O
6−
+ H
+
(1)
Bo h AA and asco ba e can e ec i ely educe Cu(II) and Fe(III) ions, hough AA e-
ac ions wi h ansi ion me als such as Fe(III) o Cu(II) ha e a e cons an s ha di e by
up o se e al o de s o magni ude, wi h he eac ions o asco ba e usually being as e
[28]. In any case, in his s udy we e e o ‘asco bic acid’ o conside he o al amoun o
he p o ona ed o m, AA, and he dep o ona ed o m (asco ba e) p esen in he educing
solu ions.
The pH o he solu ions was con inuously measu ed du ing he educ ion expe i-
men s wi h p e iously calib a ed CRISON pH me e s, and isual changes o colo and
u bidi y we e eco ded and anno a ed. When a me allic coppe p ecipi a e was appa -
en ly o med (based on colo change o u bidi y o ma ion), he solu ions we e immedi-
a ely il e ed h ough 0.45 µm po e size il e s and he ob ained solids we e washed se -
e al imes by MilliQ wa e , and ai -d ied a ambien empe a u e o u he mo phologi-
cal, mine alogical, and c ys allog aphic analysis (Figu e 1).
Figu e 1. (a) Na u al Cu- ich aqueous solu ion om AMD-a ec ed acidic s eam mixed wi h 10 mM
AA (pH = 3.95, T = 25 °C) and con aining an unde e mined ansien Cu complex; (b) Me allic coppe
p ecipi a e o med on he il e a e il a ion o he solu ion shown in (a) a e 24 h; (c,d) Re lec ed
ligh mic oscope pho omic og aphs (a 500× magni ica ion) aken on he il e shown in (b), showing
a ne wo k o small acicula mic oc ys als o me allic coppe (Cu[0]) along wi h spa se la ge ans-
lucen c ys als o gypsum which could no be a oided (due o high Ca and SO
4
concen a ion in he
AMD wa e s).
The abo e explained expe imen s a pH 3.95 and 25 °C we e epea ed a condi ions
o lowe pH (1.5–2.5) and highe empe a u e (40–80 °C), as well as a di e en AA con-
cen a ion (10 mM o 0.1 M) o in es iga e he e ec o hese pa ame e s on he kine ics o
Cu[0] c ys alliza ion (see Figu e S3 in Supplemen al Ma e ial). All expe imen s we e con-
duc ed unde oxygenic condi ions.
Figu e 1.
(
a
) Na u al Cu- ich aqueous solu ion om AMD-a ec ed acidic s eam mixed wi h 10 mM
AA (pH = 3.95, T = 25
◦
C) and con aining an unde e mined ansien Cu complex; (
b
) Me allic coppe
p ecipi a e o med on he il e a e il a ion o he solu ion shown in (
a
) a e 24 h; (
c
,
d
) Re lec ed
ligh mic oscope pho omic og aphs (a 500
×
magni ica ion) aken on he il e shown in (
b
), showing a
ne wo k o small acicula mic oc ys als o me allic coppe (Cu[0]) along wi h spa se la ge anslucen
c ys als o gypsum which could no be a oided (due o high Ca and SO
4
concen a ion in he
AMD wa e s).
The abo e explained expe imen s a pH 3.95 and 25
◦
C we e epea ed a condi ions o
lowe pH (1.5–2.5) and highe empe a u e (40–80
◦
C), as well as a di e en AA concen a-
ion (10 mM o 0.1 M) o in es iga e he e ec o hese pa ame e s on he kine ics o Cu[0]
c ys alliza ion (see Figu e S3 in Supplemen al Ma e ial). All expe imen s we e conduc ed
unde oxygenic condi ions.
Mine als 2022,12, 322 5 o 18
2.2.2. Reduc ion wi h Sc ap I on
A second se o expe imen s was pe o med o ob ain Cu[0] by he classical cemen a-
ion me hod using i on as educing agen . Ins ead o sc ap i on we used clean nu s and
sc ews (p e iously sonica ed and insed wi h e hanol and MilliQ wa e o emo e any
dus o con amina ion om he ha dwa e su aces) which we e subme sed in he Cu
2+
-
con aining acidic liquo s (Supplemen al Figu e S4). These expe imen s we e conduc ed a
condi ions o pH = 1.5 (a e p e ious adjus men o he acidic solu ions wi h H
2
SO
4
1 M)
and T = 25
◦
C, wi h in e mi en shaking and in he p esence o oxygen, un il he pH and
Eh alues (which we e con inuously measu ed) we e ully s abilized ( he ime elapsed in
hese ials was be ween 80 and 90 min). The pH o hese expe imen s was adjus ed o
pH 1.5 ollowing p e ious esea ch which epo a high e iciency o Cu[0] cemen a ion a
hese e y acidic condi ions [
4
,
20
] and also o a oid he p esence o solid-phase Fe(III) (e.g.,
mine als such as ja osi e) which may also o m in hese wa e s a pH > 2.0 [
16
,
17
]. When
he solu ions had been s abilized, he i on pieces appea ed ully coa ed by a eddish-b own
colo ed ilm, and abundan blackish pa icles had been o med in he aqueous solu ion
(Figu e S4). These black, elonga ed pa icles we e sepa a ed om he aqueous solu ion by
acuum il a ion as discussed abo e. The il e s we e also ai -d ied a ambien T and we e
s udied by XRD and SEM-EDX, as desc ibed below.
2.3. X- ay Di ac ion, Op ical Mic oscopy and Elec on Mic oscopy
The me allic coppe p ecipi a es we e analyzed by di e en echniques a he SGIke
acili ies o he Uni e si y o he Basque Coun y (UPV/EHU). Cu[0]-coa ed il e s we e
i s ly examined unde e lec ed ligh op ical mic oscope Nikon Eclipse 50i/POL using
a LV-UEPI Uni e sal Epi Illumina o . X- ay di ac ion (XRD) was ca ied ou on a PAN-
aly ical X’Pe P o di ac ome e (Mal e n Panaly ical L d., Almelo, The Ne he lands),
wi h g aphi e monoch oma o , a p og ammable di e gence sli , and a solid-s a e PIXcel
de ec o . The wo king condi ions we e 40 kV and 40 mA, Cu K
α
adia ion and a con inu-
ous scan ange o 2–90
◦
2
θ
. Samples we e inely g inded in an aga e mo a , dispe sed in
e hanol and placed on ze o-backg ound Si holde . The goniome e was calib a ed wi h
a silicon s anda d and di ac ion da a p ocessed using X’Pe High Sco e so wa e wi h
ICDD da abase.
The ob ained p ecipi a es we e u he s udied by Scanning Elec on Mic oscopy
(SEM). A JEOL JSM-7000F ield emission elec on mic oscope (JEOL L d., Tokyo, Japan)
coupled o Ene gy Dispe sion X- ay Spec oscope (EDX) was used. Wo king condi-
ions included 20 kV beam ol age, 1 nA beam cu en , 10 mm wo king dis ance, ac-
uum
< 8.35 ×10−4Pa
. Samples we e examined in bo h seconda y elec on (SE) and
backsca e ed elec on (BSE) modes wi h acquisi ion ime in ange o 60 o 100 s a e -
e y poin o in e es . P io o SEM analysis, samples we e moun ed on C s ab, passed
h ough plasma cleaning p ocess (3 min), and me alized wi h ca bon, a oiding in oducing
any addi ional me al o he sys em.
2.4. Me al Concen a ion in he Aqueous Solu ions
Me al concen a ions in he aqueous solu ions be o e and a e he expe imen s we e
also conduc ed o quan i y Cu emo al du ing Cu(II) educ ion. These analyses we e
pe o med by Induc i ely Coupled Plasma A omic Emission Spec ome y (ICP-AES) in a
Va ian Vis a-MPX spec ome e (Agilen Technologies Inc., San Cla a, CA, USA).
2.5. Geochemical Modeling
The geochemical so wa e package PHREEQCI (Ve sion 3.0.5-7748, US Geological
Su ey, Res on, VA, USA [
29
]) was used o (1) modeling o coppe ionic species in solu ion
a a ying pH and edox condi ions (Eh), and (2) calcula ion o sa u a ion indices (SI) o
selec ed Cu-bea ing mine als. All he calcula ions we e conduc ed using he MINTEQA2
he modynamic da abase (Ve sion 4.0, USEPA, Washing on, DC, USA) [
30
]. The sa u a ion
indices o selec ed coppe -con aining mine al phases we e calcula ed using he co espond-
Mine als 2022,12, 322 6 o 18
ing solubili y p oduc s (log K
sp
alues) included in he MINTQA2.V4 da abase, as well as
he known composi ion o he acidic wa e s and he expe imen al condi ions.
3. Resul s
3.1. Reduc ion o Cu2+ Ions wi h Asco bic Acid
The i s ba ch educ ion expe imen s we e conduc ed a low AA concen a ion
(10 mM), pH = 3.95 and T = 25
◦
C (Figu e 1). A hese condi ions, he solu ions u ned o a
yellowish colo a e a ew minu es (Figu e 1a). The colo o he solu ion did no change
a e il a ion h ough 0.45 and 0.1
µ
m po e size. The e o e, his colo was in e p e ed o
be diagnos ic o he o ma ion o ei he a ansien colloidal (nano-sized) compound o an
ionic complex con aining Cu
2+
o Cu
+
ions chela ed wi h asco ba e anion. No c ys alliza-
ion was obse ed o hou s, and hese solu ions we e le o e ol e o e nigh a ambien
empe a u e (25
◦
C). A e 24 h, he solu ion had u ned colo less, and a pinkish p ecipi a e
had been accumula ed in he lask bo om. This solid, which was emo ed by acuum
il a ion (Figu e 1b) and subsequen ly s udied by op ical mic oscopy and XRD, consis ed
almos exclusi ely in me allic coppe (Cu[0]) ha was p esen in he o m o elonga ed,
eddish, mic ome ic c ys als o up o 50
µ
m, some imes isible o he naked eye as small
e lec ions (Figu e 1c), mingled up wi h much smalle equidimensional c ys als (a e age
a ound 2 ×2µm).
The XRD analyses e ealed he majo peaks diagnos ic o me allic coppe (e.g., ace s
such as 111, 200, 220, o 311), al hough aces o cup i e (Cu
2
O) could be also deduced by
he p esence o iny peaks a a ound 38
◦
2
θ
, co esponding o he mos in ense 111 ace s o
his mine al (Figu e 2). XRD analyses o he p ecipi a es o med in o he ba ch expe imen s
a highe AA concen a ions e ealed ha me allic coppe was always he inal and s able
mine al p oduc esul ing om he in e ac ion o he Cu
2+
ions wi h he added AA, hough
some iny peaks sugges i e o some mino p esence o cup i e could be obse ed in
some samples (Figu e 2). Due o he use o AA in he expe imen s, which is a well-
known an ioxidan compound p e en ing Cu[0] oxida ion [
2
–
5
], we belie e ha hese ace
amoun s o Cu
2
O ep esen emnan s o a ansi ional cup i e nanocolloidal p ecu so ,
a he han he esul o pos -expe imen al Cu[0] oxida ion.
Mine als 2022, 11, x FOR PEER REVIEW 6 o 19
The sa u a ion indices o selec ed coppe -con aining mine al phases we e calcula ed using
he co esponding solubili y p oduc s (log Ksp alues) included in he MINTQA2.V4 da-
abase, as well as he known composi ion o he acidic wa e s and he expe imen al con-
di ions.
3. Resul s
3.1. Reduc ion o Cu2+ Ions wi h Asco bic Acid
The i s ba ch educ ion expe imen s we e conduc ed a low AA concen a ion (10
mM), pH = 3.95 and T = 25 °C (Figu e 1). A hese condi ions, he solu ions u ned o a
yellowish colo a e a ew minu es (Figu e 1a). The colo o he solu ion did no change
a e il a ion h ough 0.45 and 0.1 µm po e size. The e o e, his colo was in e p e ed o
be diagnos ic o he o ma ion o ei he a ansien colloidal (nano-sized) compound o an
ionic complex con aining Cu2+ o Cu+ ions chela ed wi h asco ba e anion. No c ys alliza-
ion was obse ed o hou s, and hese solu ions we e le o e ol e o e nigh a ambien
empe a u e (25 °C). A e 24 h, he solu ion had u ned colo less, and a pinkish p ecipi-
a e had been accumula ed in he lask bo om. This solid, which was emo ed by acuum
il a ion (Figu e 1b) and subsequen ly s udied by op ical mic oscopy and XRD, consis ed
almos exclusi ely in me allic coppe (Cu[0]) ha was p esen in he o m o elonga ed,
eddish, mic ome ic c ys als o up o 50 µm, some imes isible o he naked eye as small
e lec ions (Figu e 1c), mingled up wi h much smalle equidimensional c ys als (a e age
a ound 2 × 2 µm).
The XRD analyses e ealed he majo peaks diagnos ic o me allic coppe (e.g., ace s
such as 111, 200, 220, o 311), al hough aces o cup i e (Cu2O) could be also deduced by
he p esence o iny peaks a a ound 38°2θ, co esponding o he mos in ense 111 ace s
o his mine al (Figu e 2). XRD analyses o he p ecipi a es o med in o he ba ch expe i-
men s a highe AA concen a ions e ealed ha me allic coppe was always he inal and
s able mine al p oduc esul ing om he in e ac ion o he Cu2+ ions wi h he added AA,
hough some iny peaks sugges i e o some mino p esence o cup i e could be obse ed
in some samples (Figu e 2). Due o he use o AA in he expe imen s, which is a well-
known an ioxidan compound p e en ing Cu[0] oxida ion [2–5], we belie e ha hese
ace amoun s o Cu2O ep esen emnan s o a ansi ional cup i e nanocolloidal p ecu -
so , a he han he esul o pos -expe imen al Cu[0] oxida ion.
Figu e 2. XRD pa e ns o Cu[0] ob ained in he di e en ba ch expe imen s conduc ed in his s udy:
(I) la ge Cu[0] c ys als o med by educ ion o Cu(II)- ich solu ions wi h asco bic acid 10 mM a pH
3.95 and 25 °C (TI; bo om), (II) Cu[0] nanopa icles o med by educ ion wi h asco bic acid 0.1 M a
pH 3.95 and 80 °C (CA, ST; cen e ), and (III) Cu[0] nanopa icles o med by educ ion wi h Fe[0]
(sc ap i on) a pH 1.5 and 25 °C (ST; op).
Figu e 2.
XRD pa e ns o Cu[0] ob ained in he di e en ba ch expe imen s conduc ed in his s udy:
(I) la ge Cu[0] c ys als o med by educ ion o Cu(II)- ich solu ions wi h asco bic acid 10 mM a pH
3.95 and 25
◦
C (TI; bo om), (II) Cu[0] nanopa icles o med by educ ion wi h asco bic acid 0.1 M
a pH 3.95 and 80
◦
C (CA, ST; cen e ), and (III) Cu[0] nanopa icles o med by educ ion wi h Fe[0]
(sc ap i on) a pH 1.5 and 25 ◦C (ST; op).
Mine als 2022,12, 322 7 o 18
The expe imen s conduc ed a pH 3.95 and AA concen a ions o 0.1 M showed much
as e p ecipi a ion kine ics. A dense b ownish- ed-colo ed suspension con aining Cu[0]
pa icles was o med a ound 5–10 min a e he addi ion o AA (Figu e S3). The educ ion
expe imen s ca ied ou a highe T (40–80
◦
C) did no show a signi ican change in he
p ecipi a ion kine ics as compa ed o he ones conduc ed a oom empe a u e, hough he
eddish-b own suspensions we e dense in he o me case a compa able pH alues. On
he o he hand, educ ion expe imen s pe o med a low pH (1.5–2.5) did no p oduce ei he
me allic coppe o any o he mine al p oduc a e 1 h eac ion ime. This is consis en wi h
he inc eased elec ode po en ial o AA a e y low pH [
2
], which could ha e signi ican ly
dec eased he eac ions kine ics.
The lowe in ensi y o majo Cu[0] peaks (e.g., 111, 200, 220) in he XRD pa e ns
ob ained in he educ ion expe imen s a highe AA concen a ion, along wi h as e
p ecipi a ion kine ics sugges ed lowe c ys allini y deg ee and/o size o he Cu[0] pa icles
(Figu e 2). This hypo hesis was u he con i med by he SEM-EDX s udies epo ed in he
nex sec ion.
3.2. Tex u al and C ys allog aphic P ope ies Re ealed by Elec on Mic oscopy
Unde SEM, he Cu[0] c ys als o med in he slow c ys alliza ion expe imen s a low
AA concen a ion appea ed wi h di e se mo phology anging om acicula -elonga ed,
pseudop isma ic o isomo phic (e.g., cubes, unca ed cubes, cuboc ahed a), e ahed al
o unca ed e ahed a, and apezoidal polyhed a (Figu es 3and 4). The la e anged in
size be ween 2–7
µ
m (wid h) and 1–4
µ
m (leng h), wi h a e y good co ela ion be ween
bo h dimensions (Figu e 4d,e). On he o he hand, pseudop isma ic and acicula -elonga ed
c ys als showed wid hs o a ound 1–4
µ
m bu anged la gely in leng h be ween 2 and
50
µ
m (Figu e 4b), some imes appea ing as e y hin ben needle-like c ys als (
Figu e 3a–e
).
Some bigge c ys als showed much smalle c ys alli es (wi h a ying shapes and diame-
e s smalle han 200 nm) showing o ien ed g ow h in some o hei edges o aces (e.g.,
Figu e 3 ), sugges ing he e ogeneous, su ace-con olled c ys al g ow h. The EDX analy-
ses o hese c ys als yielded composi ions o almos pu e, elec oly ic coppe
(>99% Cu
;
no shown).
In con as o he slow kine ics–low AA concen a ion expe imen s, he as kine ics–
high AA concen a ion expe imen s p oduced a p ecipi a e o med by nanome ic, sub-
ounded pa icles o me allic coppe anging in size be ween 40 and 200 nm (Figu e 5).
These SEM obse a ions we e in ag eemen wi h he lowe c ys allini y deg ee sugges ed by
he XRD spec a o hese samples, as desc ibed abo e (Figu e 2). The disc e e nanopa icles
coalesced oge he in la ge agg ega es (wi h diame e o up o ew mic ons) ha could
con ain ens o hund eds o smalle pa icles (Figu e 5).
3.3. Reduc ion o Cu2+ Ions wi h Sc ap I on
The educ ion expe imen s using sc ap i on a 25
◦
C and pH 1.5 esul ed in he
simul aneous o ma ion o black pa icles in he acidic solu ion and a b ownish- ed-colo ed
coa ing on he me allic pieces as he eac ion p oceeded (Figu e S4). A high densi y o gas
bubbles was also obse ed in hese expe imen s, consis en wi h he p oduc ion o a gaseous
phase (likely hyd ogen [H
2
], as discussed below). Fil a ion o he solu ion a e 30 min o
eac ion ime p oduced a dense, black-colo ed p ecipi a e (Figu e S4). SEM examina ion
o hese solids e ealed ha hese we e o med by almos pu e (>99%) me allic coppe .
In his case, me allic coppe was gene ally p esen as pine- ee-like o ms composed o
a ays o submic on c ys alli es g owing in di e se di ec ions (Figu e 6a–e). Less abundan
o ms o me allic coppe p oduced by he cemen a ion me hod included pseudo-sphe ical
agg ega es composed by coalesced, nanome ic pa icles (<100 nm, Figu e 6 ) and di e se
enc us ing agg ega es showing po ous g ow hs as boxwo k- ype o hin cu ed ilms
(Figu e 6e).
Mine als 2022,12, 322 8 o 18
Mine als 2022, 11, x FOR PEER REVIEW 8 o 19
Figu e 3. Scanning elec on mic oscopy (SEM) images o he Cu c ys als ob ained in ba ch educ ion
expe imen s wi h Cu(II)- ich acidic solu ions (pH 3.95, 25 °C) and asco bic acid 10 mM. Pic u es (a–
) display di e en ex u al and c ys allog aphic ea u es in a single sample (same sample as in Fig-
u e 1b,c).
Figu e 3.
Scanning elec on mic oscopy (SEM) images o he Cu c ys als ob ained in ba ch educ ion
expe imen s wi h Cu(II)- ich acidic solu ions (pH 3.95, 25
◦
C) and asco bic acid 10 mM. Pic u es
(
a
–
) display di e en ex u al and c ys allog aphic ea u es in a single sample (same sample as in
Figu e 1b,c).
Mine als 2022,12, 322 9 o 18
Mine als 2022, 11, x FOR PEER REVIEW 9 o 19
Figu e 4. Geome ic cha ac e is ics o di e en ypes o Cu[0] c ys als o med in asco bic acid e-
duc ion expe imen s (10 mM AA, pH 3.95, 25 °C) as deduced om he SEM pic u es shown in Figu e
3: (a,b) Pseudop isma ic-elonga ed-acicula c ys als, (c) Isomo phic polyhed a, (d,e) Te ahed al-
apezoidal polyhed a.
In con as o he slow kine ics–low AA concen a ion expe imen s, he as kine ics–
high AA concen a ion expe imen s p oduced a p ecipi a e o med by nanome ic, sub-
ounded pa icles o me allic coppe anging in size be ween 40 and 200 nm (Figu e 5).
These SEM obse a ions we e in ag eemen wi h he lowe c ys allini y deg ee sugges ed
Figu e 4.
Geome ic cha ac e is ics o di e en ypes o Cu[0] c ys als o med in asco bic acid educ-
ion expe imen s (10 mM AA, pH 3.95, 25
◦
C) as deduced om he SEM pic u es shown in
Figu e 3
:
(
a
,
b
) Pseudop isma ic-elonga ed-acicula c ys als, (
c
) Isomo phic polyhed a, (
d
,
e
) Te ahed al-
apezoidal polyhed a.
Mine als 2022,12, 322 16 o 18
The high yield o Cu eco e y in hese assays (>98%) in sho eac ion imes o a ound
90 min, along wi h he e y low cos o he educing agen , makes his mechanism much
mo e e icien and cheape han he ones based in chemical educ ion using AA o any
o he educing agen , such as glucose o hyd azine hyd a e. The high pu i y o me allic
coppe agg ega es (>99% Cu[0]) ob ained by his echnique and he e y li le equi emen s
(e.g., good pe o mance e en a e y low pH, no need o expensi e chemical eagen s,
no need o high empe a u e o in ense s i ing, e c.) makes cemen a ion he easies and
simples me hod o Cu eco e y om Cu- ich mine wa e s and hei acidic leacha es.
5. Conclusions
The cu en p ac ices in di e en indus ial sec o s ocused on Cu eco e y om
di e en was es include Cu
2+
educ ion by asco bic acid as a easible and appa en ly
e icien echnology. A he same ime, he e is an impo an need o de elop cos -e ec i e
s a egies o me al eco e y in abandoned mine si es wi hin he amewo k o ci cula
economy and mine was e ecycling [
10
,
15
]. An ob ious ques ion, he e o e, eme ges abou
he con enience o asco bic acid-based p ocedu es o eco e Cu om acidic mine wa e s
con aining high concen a ions o his me al as dissol ed loadings.
We p o ide he e, o he i s ime, a compa ison o me allic coppe p oduc s ob ained
by wo di e en educ ion me hods om Cu- ich acid mine wa e s. The p esen wo k has
shown ha high-pu i y me allic coppe can also be ob ained om highly acidic, me al- ich
mine d ainage solu ions by educ ion o dissol ed Cu
2+
by asco bic acid. This p ocedu e
may esul in he o ma ion o ei he (i) well-de eloped la ge c ys als o (ii) much smalle
ounded pa icles o sub-mic on o nanome ic diame e , depending on he c ys alliza ion
kine ics and sa u a ion s a e, which ha e been obse ed o a y wi h he asco bic acid
concen a ion used, as well as wi h o he pa ame e s such as pH o empe a u e. Compa ed
o p e ious s udies [
2
–
9
,
34
–
36
], we ha e iden i ied a su p isingly high di e si y o c ys al
geome ies (e.g., om acicula o polyhed al) and sizes ( om <200 nm o >50
µ
m) when
using low concen a ions o AA and slow c ys alliza ion kine ics. Howe e , his p ocedu e
shows a low e iciency as ega ds o me al eco e y a es (<25%) a he pH condi ions
(
1.50–3.95
) and AA concen a ions (10 mM–0.1 M) conside ed in his s udy. This me hod
p esen s some o he disad an ages, such as he need o a p e ious pa ial neu aliza ion
o inc ease he Cu- educ ion kine ics, o he undesi able emo al o Cu
2+
by adso p ion
on Al colloids o med in hese wa e s a pH > 4.0. These wo limi a ions lea e a na ow
ope a ional pH window o on-si e ea men s in abandoned mine si es. In any case, he
possibili y o con olling c ys al geome y o pa icle size as a unc ion o a ying expe i-
men al condi ions (e.g., pH, T, [Cu/AA] a io) could make his p ocedu e s ill in e es ing i
u he imp o emen s a e conduc ed o inc ease i s e iciency.
In con as , he classical cemen a ion me hod o Cu
2+
educ ion by sc ap i on, his o i-
cally applied in he IPB and o he mine dis ic s [
20
,
21
], o e s an easie , cheape , and mo e
e ec i e op ion o Cu eco e y om mine wa e s. The me allic coppe p oduced by his
me hod is also highly c ys alline, al hough commonly o ms agg ega es o smalle c ys al-
li es han hose o med by he slow kine ics asco bic acid me hod. The big ad an ages o
he cemen a ion me hod a e: (i) i can be applied a e y low pH ( hus, wi h no need o
alkaliza ion), and (ii) i does no equi e expensi e eagen s. The e o e, his me hod could
be used in combina ion wi h some o he echniques in a mul i-me al eco e y scheme aimed
a ob aining seconda y aw ma e ials o a leas a de aying emedia ion ea men cos s.
Supplemen a y Ma e ials:
The ollowing suppo ing in o ma ion can be downloaded a : h ps://
www.mdpi.com/a icle/10.3390/min12030322/s1, Figu e S1: Pic u es on pa ial neu aliza ion o
AMD wa e p io o Cu
2+
educ ion expe imen s; Figu e S2: Plo o pH s asco bic acid concen a ion;
Figu e S3
: Cu
2+
educ ion expe imen s a highe pH and asco bic acid concen a ion;
Figu e S4
: Pic-
u es showing one o he expe imen s o Cu
2+
educ ion using i on (Fe[0]) me allic pieces;
Figu e S5
:
Eh/pH diag ams o he Cu-O-H sys em using di e en he modynamic da abases.
Mine als 2022,12, 322 17 o 18
Au ho Con ibu ions:
Concep ualiza ion, J.S.-E.; Me hodology, J.S.-E.; Valida ion, J.S.-E., I.Y. and
A.I.; Fo mal Analysis, J.S.-E., I.Y. and A.I.; In es iga ion, J.S.-E., I.Y. and A.I.; Resou ces, J.S.-E. and I.Y.;
Da a Cu a ion, J.S.-E. and A.I.; W i ing—O iginal D a P epa a ion, J.S.-E.; W i ing—Re iew and
Edi ing, J.S.-E., I.Y. and A.I.; P ojec Adminis a ion, J.S.-E.; Funding Acquisi ion, J.S.-E. All au ho s
ha e ead and ag eed o he published e sion o he manusc ip .
Funding:
This esea ch was unded by he Spanish Minis y o Science and Inno a ion h ough g an
numbe CGL2016-74984-R.
Acknowledgmen s:
We acknowledge he echnicians and s a a he Geochemis y Labo a o y a
IGME-CSIC o hei kind help and suppo du ing he expe imen al wo k. We also hank he
pe sonnel a he SGIke acili ies a UPV/EHU o hei suppo du ing he XRD and SEM analyses.
We a e g a e ul o wo anonymous e iewe s who helped imp o e his manusc ip .
Con lic s o In e es :
The au ho s decla e no con lic o in e es . The unde s had no ole in he design
o he s udy; in he collec ion, analyses, o in e p e a ion o da a; in he w i ing o he manusc ip ,
and in he decision o publish he esul s.
Re e ences
1. Ghosh, S. Elec oless coppe deposi ion: A c i ical e iew. Thin Solid Films 2019,669, 641–658. [C ossRe ]
2.
Saiko a, S.V.; Mu ashe a, K.S.; Vo obye , S.A.; Kochma e , K.Y.; Ka imo , E.E.; E emina, A.D.; Mikhlin, Y.L. Syn hesizing highly
concen a ed hyd osols o coppe nanopa icles ia educ ion by asco bic acid in he p esence o gela ose. Chem. Sus . De .
2013
,
21, 403–409.
3.
Andal, V.; Bu aneswa i, G. E ec o educing agen s in he con e sion o Cu
2
O nanocolloid o Cu nanocolloid. Eng. Sci. Technol.
2017,20, 340–344. [C ossRe ]
4.
Kuma , S.; Kuma , V.; Sha ma, M.L.; Chaka a i, S.K. Elec ochemical syn hesis o me allic mic o- ose ha ing pe als in nanome e
dimensions. Supe la ice Mic os uc . 2008,43, 324–329. [C ossRe ]
5.
Tsai, C.-Y.; Chang, W.-C.; Chen, G.-L.; Chung, C.-H.; Liang, J.-X.; Ma, W.-Y. A s udy o he p epa a ion and p ope ies o
an ioxida i e coppe inks wi h high elec ical conduc i i y. Nanoscale Res. Le . 2015,10, 357. [C ossRe ] [PubMed]
6.
Vi k, H.S. Fab ica ion and cha ac e iza ion o me allic coppe and coppe oxide nano lowe s. Pak. J. Chem.
2011
,1, 148–154. [C ossRe ]
7.
Vi k, H.S.; Kisho e, K.; Balou ia, V. Fab ica ion o coppe nanowi es by elec odeposi ion using anodic alumina and polyme
empla es. J. Nano Res. 2010,10, 63–67. [C ossRe ]
8.
Sa ka , J.; Khan, G.G.; Basumallick, A. Nanowi es: P ope ies, applica ions and syn hesis ia po ous anodic aluminum oxide
empla e. Bull. Ma e . Sci. 2007,30, 271–290. [C ossRe ]
9.
Zhang, D.-F.; Zhang, H.; Guo, L.; Zheng, K.; Han, X.-D.; Zhang, Z. Delica e con ol o c ys allog aphic ace -o ien ed Cu
2
O
nanoc ys als and he co ela ed adso p ion abili y. J. Ma e . Chem. 2009,19, 5220–5225. [C ossRe ]
10. Lo e mose , B.G. Recycling, Reuse and Rehabili a ion o Mine Was es. Elemen s 2011,7, 405–410. [C ossRe ]
11.
No ds om, D.K.; Alpe s, C.N. Geochemis y o acid mine wa e s. In The En i onmen al Geochemis y o Mine al Deposi s, Pa A;
P ocesses, Techniques, and Heal h Issues; Plumlee, G.S., Logsdon, M.J., Eds.; Socie y o Economic Geologis s: Li le on, CO, USA,
1999; Volume 6, pp. 133–156.
12.
Gelle , W.; Klappe , H.; Schul ze, M. Na u al and an h opogenic sulphu ic acidi ica ion o lakes. In Acidic Mining Lakes–Acid Mine
D ainage, Limnology and Reclama ion; Gelle , W., Klappe , H., Salomons, W., Eds.; Sp inge : Be lin/Heidelbe g, Ge many, 1998;
pp. 3–14.
13.
Ba hen, R.; Sulonen, M.L.K.; Pe äniemi, S.; Jain, R.; Lakaniemi, A.M. Remo al and eco e y o me al ions om acidic mul i-me al
mine wa e using was e diges ed ac i a ed sludge as bioso ben . Hyd ome allu gy 2022,207, 105770. [C ossRe ]
14.
Isosaa i, P.; Sillampää, M. Use o Sul a e-Reducing and Bioelec ochemical Reac o s o Me al Reco e y om Mine Wa e . Sep.
Pu i . Re . 2014,46, 1–20. [C ossRe ]
15.
León, R.; Macías, F.; Cáno as, C.; Pé ez-López, R.; Ayo a, C.; Nie o, J.M.; Olías, M. Mine wa e s as a seconda y sou ce o a e
ea h elemen s wo ldwide: The case o he Ibe ian Py i e Bel . J. Geochem. Exp. 2021,224, 106742. [C ossRe ]
16.
Sánchez-España, F.J.; López Pamo, E.; San o imia, E.; Adu i e, O.; Reyes, J.; Ba e ino, D. Acid Mine D ainage in he Ibe ian Py i e
Bel (Odiel i e wa e shed, Huel a, SW Spain): Geochemis y, Mine alogy and En i onmen al Implica ions. App. Geochem.
2005
,
20, 1320–1356. [C ossRe ]
17.
Sánchez España, J.; López Pamo, E.; San o imia, E.; Diez-E cilla, M. The acidic mine pi lakes o he Ibe ian Py i e Bel : An app oach
o hei physical limnology and hyd ogeochemis y. App. Geochem. 2008,23, 1260–1287. [C ossRe ]
18.
López-Pamo, E.; Sánchez-España, J.; San o imia, E.; Diez-E cilla, M.; Reyes, J. Co as Mine as Inundadas de la Faja Pi í ica: In en a io
e Hid oquímica; Ins i u o Geológico y Mine o: Mad id, Spain, 2009; 279p.
19.
Sánchez-España, J.; Diez, M.; San o imia, E. Mine pi lakes o he Ibe ian Py i e Bel : Some basic limnological, hyd ogeochemical
and mic obiological conside a ions. In Acidic Pi Lakes: The Legacy o Coal and Me al Su ace Mines; Gele , W., Ed.; Sp inge :
Be lin/Heidelbe g, Ge many, 2013; pp. 315–342.
Mine als 2022,12, 322 18 o 18
20.
Taylo , J.H.; Whelan, P.F. The leaching o cup eous py i es and he p ecipi a ion o coppe a Rio Tin o, Spain. T ans. Ins . Min.
Me all. 1943,52, 35–96.
21.
Tucci, N.J.; Gammons, C.H. In luence o coppe eco e y on he wa e quali y o he acidic Be keley Pi lake, Mon ana, U.S.A.
En i on. Sci. Technol. 2015,49, 4081–4088. [C ossRe ]
22.
Bigham, J.M.; No ds om, D.K. I on and Aluminum Hyd oxysul a es om Acid Sul a e Wa e s. In Sul a e Mine als: C ys allog a-
phy, Geochemis y, and En i onmen al Signi icance. Re . Mine al. Geochem. 2000,40, 351–403. [C ossRe ]
23.
Sánchez-España, J. The beha io o i on and aluminum in acid mine d ainage: Specia ion, mine alogy, and en i onmen al
signi icance. In The modynamics, Solubili y and En i onmen al issues; Le che , T., Ed.; Else ie : Ams e dam, The Ne he lands, 2007;
pp. 137–150.
24.
Sánchez-España, J.; López-Pamo, E.; San o omia, E.; Reyes, J.; Ma ín-Rubí, J.A. The emo al o dissol ed me als by hyd oxysul-
pha e p ecipi a es du ing oxida ion and neu aliza ion o acid mine wa e s, Ibe ian Py i e Bel . Aqua . Geochem.
2006
,12, 269–298.
[C ossRe ]
25.
Sánchez-España, J.; Yus a, I.; López, G. Schwe manni e o ja osi e con e sion in he wa e column o an acidic mine pi lake.
Mine al. Mag. 2012,76, 2659–2682. [C ossRe ]
26.
No ds om, D.K. The e ec o sulpha e on aluminum concen a ions in na u al wa e s: Some s abili y ela ions in he sys em
Al2O3-SO3-H2O a 298 K. Geochim. Cosmochim. Ac a 1982,46, 681–692. [C ossRe ]
27.
Sánchez-España, J.; Yus a, I.; Bu gos, W.D. Geochemis y o dissol ed aluminum a low pH: Hyd obasalumini e o ma ion and
in e ac ion wi h ace me als, silica and mic obial cells unde anoxic condi ions. Chem. Geol. 2016,441, 124–137. [C ossRe ]
28.
Shen, J.; G i i hs, P.T.; Campbell, S.J.; U inge BKalbe e , M.; Paulson, S.E. Asco ba e oxida ion by i on, coppe and eac i e
oxygen species: Re iew, model de elopmen , and de i a ion o key a e cons an s. Sci. Rep.
2021
,11, 7417. [C ossRe ] [PubMed]
29.
Pa ku s , D.L.; Appelo, C.A.J. Use ’s guide o PHREEQC ( e sion 2)—A compu e p og am o specia ion, ba ch- eac ion,
one-domensional anspo , and in e se geochemical calcula ions. In U.S. Geological Su ey Wa e -Resou ces In es iga ions Repo
99-4259; U.S. Geological Su ey: Den e , CO, USA, 1999; 312p.
30.
Allison, J.D.; B own, D.S.; No o-G adac, J. MINTEQA2/PRODEAFA2, A Geochemical Assessmen Model o En i onmen al Sys ems:
Use Manual Supplemen o Ve sion 4.0; U.S. En i onmen al P o ec ion Agency: A hens, GA, USA, 1999.
31.
Sánchez-España, J.; Yus a, I. Low-c ys allini y p oduc s o ace-me al p ecipi a ion in neu alized pi -lake wa e s wi hou e ic
and aluminous adso ben : Geochemical modelling and mine alogical analyses. Mine al. Mag. 2015,79, 781–798. [C ossRe ]
32.
Takeno, N. A las o Eh-pH diag ams: In e compa ison o he modynamic da abases. In Geological Su ey o Japan Open File Repo
No. 419; Na ional Ins i u e o Ad anced Indus ial Science and Technology: Tokyo, Japan, 2005; 285p.
33. Mys kowski, E.M. The oxida ion o asco bic acid in he p esence o coppe . Biochem, J. 1942,36, 494–500. [C ossRe ]
34. Hacise kí, A. An o e iew o asco bic acid biochemis y. J. Fac. Pha m. Ank. 2009,38, 233–255.
35.
Goçal es, T.A.; Bo elho, A.B.; de Mo aes, V.T.; Espinos, D.C.R. S udy o pH In luence in he Syn hesis o Coppe Nanopa icles
Using Asco bic Acid as Reducing and S abilizing Agen . In P oceedings o he TMS 2020 149 h Annual Mee ing & Exhibi ion,
San Diego, CA, USA, 23–27 Feb ua y 2020; The Mine als, Me als & Ma e ials Socie y, Ed.; The Mine als, Me als & Ma e ials Se ies;
Sp inge Na u e: Cham, Swi ze land, 2020; pp. 1547–1557.
36.
Liu, Q.M.; Yasunami, T.; Ku uda, K.; Okido, M. P epa a ion o Cu nanopa icles wi h asco bic acid by aqueous solu ion educ ion
me hod. T ans. Non e ous Me . Soc. China 2012,22, 2198–2203. [C ossRe ]
37.
Songping, W. P epa a ion o ine coppe powde using asco bic acid as educing agen and i s applica ion in MLCC. Ma e . Le .
2017,61, 1125–1129. [C ossRe ]
38.
Sánchez-España, J. C ys alliza ion in acidic media: F om nanopa icles o mac oc ys als. Semin. Soc. Esp. Mine al.
2017
,13, 15–34.
39.
Jacukowicz-Sobala, I.; S anisławska, E.; Baszczuk, A.; Jasio ski, M.; Kociołek-Balawejde , E. Size-Con olled T ans o ma ion o
Cu
2
O in o Ze o Valen Coppe wi hin he Ma ix o Anion Exchange s ia G een Chemical Reduc ion. Polyme s
2020
,12, 2629.
[C ossRe ]
40.
Fo d, W.E. Dana’s Tex book o Mine alogy: Wi h an Ex ended T ea ise on C ys allog aphy and Physical Mine alogy, 4 h ed.; CBS
Publishe s: New Delhi, India, 2006; 851p.
41.
Ünale o˘glu, C.; Me , Y.; Züm eo˘glu-Ka an, B. Syn hesis and cha ac e iza ion o coppe asco ba e. Syn h. Reac . Ino g. Me .-O g.
Chem. 2001,31, 1531–1543. [C ossRe ]
42.
S e anowicz, T.; Osinska, M.; Napie alska-Zagozda, S. Coppe eco e y by he cemen a ion me hod. Hyd ome allu gy
1997
,47,
69–90. [C ossRe ]
