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HYDROMETALLURGYHYDROMETALLURGY2 Leaching mechanisms2 Leaching mechanisms
Fathi HabashiFathi Habashi
Department of Mining, Metallurgical, and Materials EngineeringDepartment of Mining, Metallurgical, and Materials Engineering
Laval University, Quebec City,,CanadaLaval University, Quebec City,,CanadaFathi.abashi!arul.ulaval.caFathi.abashi!arul.ulaval.ca
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HydrometallurgyHydrometallurgy
Solid-LiquidSeparation
ConcentrationPurifcation
Precipitation
Oxidant Leaching agentre
Solidtowast
Solution
Pure Metalscompounds
Precipitantor electriccurrent
Leaching
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LEAH!"G #LEAH!"G #
Leaching Agents
Solubility$ Large and ra%id solu&ility o' the material to &e leached inthe leaching agent$
Cost$ An e(%ensi)e reagent is undesira&le &ecause any traces lostduring handling *ill re%resent a large economic loss$
Materials of construction$ !' the leaching agent is corrosi)e and hasto &e handled in tan+s made o' stainless steel, titanium, orHastalloy, the ca%ital cost *ill &e high, and there'ore its use *ill &eless desira&le$
Selectivity$ An ideal reagent *ill e(tract only the desired com%onent$
Regeneration$ A&ility o' regenerating the reagent 'or recycle is alsoan im%ortant criteria
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LEAH!"G 2LEAH!"G 2
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LEAH!"G -LEAH!"G -
.ases such as "aOH or "H/OH are more
e(%ensi)e than H20O/&ut they are used
&ecause o' the 'ollo*ing ad)antages1
"egligi&le corrosion %ro&lems$ More selecti)e, i$e$, suita&le 'or ores containing much
gangue *hich reacts *ith acids &ut not *ith the
&ases$ E(am%les o' such gangue minerals are
limestone, dolomite, iron o(ide, iron car&onate, etc$
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LEACH!" #
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LEAH!"G /LEAH!"G /
An o(idiing or a reducing agent is sometimesneeded during leaching to solu&ilie certainminerals *hich do not dissol)e other*ise$ 3or
e(am%le, during leaching o' gold, sul'ideminerals, uranium ores, etc$
ommonly used o(idiing agents are1 o(ygen4or air5, oone, hydrogen %ero(ide, 'erric ion,
manganese dio(ide, sodium nitrate, and sodiumchlorate
ommonly used reducing agents are 'errous ion,and sul'ur dio(ide$
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LEAH!"G 6LEAH!"G 6
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H$drometallurgicalH$drometallurgical
%eactions%eactions
Ph$sical processesPh$sical processes Chemical processesChemical processes
Electrochemical processesElectrochemical processes
Electrol$tic processesElectrol$tic processes
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Ph$sical ProcessesPh$sical Processes
Hydration
Na+Cl(s)+ (n+m)H2O Na(H2O)+n(aq)+ Cl(H2O)m(aq)
Speed o& agitation
'emperature
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Chemical ProcessesChemical Processes
!onic7co)alent solids!onic7co)alent solids
o)alent solidso)alent solids
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Chemic l Processes
hemic l Processes
Ionic-cov lentonic-cov lent
solids
olids
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Chemic l Processes
hemic l Processes
Ionic-cov lentonic-cov lent
solids
olids
"eutraliation"eutraliation om%le( 'ormationom%le( 'ormation
Dis%alcementDis%alcement
O(idationO(idation
8rotonation8rotonation
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Chemic l Processes. Ionic-cov lent solids
hemic l Processes. Ionic-cov lent solids
Neutr liz tion
eutr liz tion
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Chemic l Processes. Ionic-cov lent solids
hemic l Processes. Ionic-cov lent solids
Neutr liz tion
eutr liz tion
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Chemic l Processes. Ionic-cov lent solids
hemic l Processes. Ionic-cov lent solids
Complex form tion
Dissolution o' lead sul'ate in sodium chloride solution$ Lead
sul'ate has a lo* solu&ility in *ater1
PbSO4(s) Pb2+(aq)+ SO42 (aq)
!n %resence o' chloride ions, the chloro%lum&ate ion is 'ormed1
Pb2++ 4Cl [PbCl4]2
thus decreasing considera&ly the concentration o' 8&29ion$ This disru%ts
the e:uili&rium o' 8&29
in contact *ith the solid %hase, 8&0O/, thus moresolid goes into solution$ O)erall reaction 1
PbSO4+ 4Cl [PbCl4]2+ SO42
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Chemic l Processes. Ionic-cov lent solids
hemic l Processes. Ionic-cov lent solids
Complex form tion
The dissolution o' Hg0 in a solution o'
sodium sul'ide can &e re%resented
similarly1 Hg04s5Hg29 9 024a:5
Hg29 9 202;Hg02
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Chemic l Processes. Ionic-cov lent solids
hemic l Processes. Ionic-cov lent solids
Displ cement 1
The dissolution o' a sul'ide in a solution
containing a metal ion that 'orms a less
solu&le sul'ide is a dis%lacementreaction$ 3or e(am%le, the dissolution o'
=n0 in u0O/solution
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Displ cement
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Chemic l Processes. Ionic-cov lent solids
hemic l Processes. Ionic-cov lent solids
!xid tion
xid tion
The dissolution of sulfides in oxygenated
water. For exa!le" the aqueous oxidation
of Fe# to ferrous sulfate$Fe#(s)Fe2+(aq)+ #2(aq)
#2+ 2O2#O%2
O&erall rea'tion$Fe#(s)+ 2O2(aq)Fe2++ #O%2
Oxygen shares ele'trons with the sulfide ion
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Chemic l Processes. Ionic-cov lent solids
hemic l Processes. Ionic-cov lent solids
Proton tion 1
roton tion 1
rotonation rea'tions in&ol&e the dissolution
of 'o!ounds of wea a'ids in strong a'ids"
or foration of &olatile a'ids.
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Proton tion
roton tion
For exa!le dissolution of CaCO*in a'ids$
CaCO*(s)Ca2+(aq)+ CO*2(aq)
CO*2+ H+HCO*
HCO*+ H+H2CO*
H2CO*H2O + CO2
The o&erall rea'tion$
CaCO*+ 2H+Ca2++ CO2+ H2O
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Chemic l Processes
hemic l Processes
cov lent solidsov lent solids o)alent &ond, e$g$, that &et*een silicon and
o(ygen in silica and the silicates, is a strong
&ond that cannot &e &ro+en easily &y a:ueous
solutions
The strong #iO ond in sili'a is not soluili,ed y
oiling with 'on'entrated a'ids ex'e!t hydrofluori'
e'ause of the foration of #iF%whi'h is a gas thatay &olatili,e or rea't with water to for
fluorosili'i' a'id" H2#iF-.
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Electrochemical Processes
#
"he solid is a conductor, e.g., a metal, or a solid #ithpartially ionic and partially covalent bonds that possessessemiconducting properties, e.g., U$%, &n', and CuFe'%.
"here is a transfer of electrons from the solid phase or fromsolution to the reacting species, i.e., the process involvesan o(idation)reduction couple. "he ions or molecules insolution simply diffuse through the boundary layer to meetthe solid surface to pic* up or give a#ay electrons."he solid dissolves at certain locali+ed points #hile theelectron transfer ta*es place at other points usually muchfurther.
"he o(idation and the reduction reactions proceedsimultaneously.
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Electrochemical Processes
2
"he *inetics of these reactions areinfluenced by the presence of latticedefects in the solid andor the presence oftrace impurity #hich may increase or
decrease the electrical conductivity of thesolid, and hence the availability of theelectrons."he rate of dissolution increases #ith
increased reagent concentration and #ithincreased temperature. -hen t#oreagents are present, the rate dependsonly on one reagent at a time.
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Electrochemical Processes
Metals in oxygenated water
Metals in dilute acid
Metals by displacement
Metal with complex formation
$(ides
'ulfides
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ELEC!OL"#C P!OCESSESELEC!OL"#C P!OCESSES
An outside %otential 4EM35 is im%osed on
the solid *hich is made as anode in an
electrolytic cell to cause its dissolution$
3or a metal1 MMn99 ne7
3or a semiconducting di)alent sul'ide1 M0
M299 0 9 2e
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S(MMA%)S(MMA%)
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>inetics o'>inetics o'
$%&rometall'rgical !eactions$%&rometall'rgical !eactions
"heory of diffusion introduced by the"heory of diffusion introduced by the
/erman physicist 0dolf Fic* in 1233/erman physicist 0dolf Fic* in 1233 "he concept of the boundary layer"he concept of the boundary layer
introduced by the /erman chemistintroduced by the /erman chemist
-alther 4ernst in 1567-alther 4ernst in 1567
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(i))'sion(i))'sion
Diffusion is the tendency ofDiffusion is the tendency of
any substance to spreadany substance to spreaduniformly throughout theuniformly throughout the
space available to it. 8t is aspace available to it. 8t is a
result of molecular movementresult of molecular movement
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Fick's LawFick's Law
d.
dC/01dt
dn
*
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$E *O,(A!" LA"E!$E *O,(A!" LA"E!
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$E *O,(A!" LA"E!$E *O,(A!" LA"E!
-hen a solid C is agitated in #ater and the solution is-hen a solid C is agitated in #ater and the solution is
analy+ed at intervals, it #ill be found that the rate ofanaly+ed at intervals, it #ill be found that the rate of
increase of the solute concentration follo#s the e9uationincrease of the solute concentration follo#s the e9uation
( )2C32C3)1dt
d3C2s
33
/
1dt
dnCC
s
*
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$E *O,(A!" LA"E!$E *O,(A!" LA"E!
ConcentrationConcentration
4
n123C
= 333
CCV
A
dt
Cds
*
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Rate Determining 0te%Rate Determining 0te%
Diffusion:Diffusion:
controlledcontrolled
processesprocesses
Chemically:Chemically:
controlledcontrolled
processesprocesses
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Characteristics o) $%&rometall'rgicalCharacteristics o) $%&rometall'rgical !eactions!eactions
Effect of fluidEffect of fluid
velocityvelocity
2/315ate C
*
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Characteristics o) $%&rometall'rgicalCharacteristics o) $%&rometall'rgical
!eactions!eactions
Effect of temperatureEffect of temperature
r2
6
N
5T1*
+ , A e-E%'
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Change o) -echanismChange o) -echanism
Effect of concentrationEffect of concentrationDissolution of Cu$ in sulfuric acidDissolution of Cu$ in sulfuric acid
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Change o) -echanismChange o) -echanismEffect of temperatureEffect of temperatureReaction: PdReaction: Pd2+2++ Cu+ Cu Pd + CuPd + Cu2+2+
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0UMMARY0UMMARY
Di''usion o' reacting s%ecies to the
inter'ace
Adsor%tion at the inter'ace
Reaction at the inter'ace
Desor%tion o' the %roducts
Di''usion o' the %roducts 'rom the inter'ace
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0UMMARY0UMMARY
Diffusion-controlled processesCheically controlled processes
!nterediate-control processes
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