cong nghe dien hoa

8/3/2019 Cong Nghe Dien Hoa

1/68

1

CHNG 1

CC KHI NIM CBN

Pin scp: pin

Leclanch

Pin thcp: Ni-Cd;

Bi ging CNin ho-n mn TS. L Minh c

in ha

Phn

tch

in

ha

Tinh luyn kim loi

c in

Min

Chng n mn

Sn xut cc cht v c, hu c

Xl mi trng

Nghin cu cc qu

trnh chuyn cht

qua mng t bo,

kim sot cc qu

tnh pht trin

Nng

lng

Sinh -

in

ha

Cng ngh

in

ha

1.Khi nim vin haC th hnh dung cc chuyn nghnh ca Cngnghin ha trong s .

2. Bn cht in ha ca n mn trong dung dch nc


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Qu tnh n mn ca hu ht cc kim loi u lin quan n s vn chuyn

electron. V vy cn thit phi nghin cu bn cht in ha ca n mn.

Cc phn ng in ha

Xt phn ng n mn gia Zn v HCl. Phn ng vit nh sau:

Zn + HCl = ZnCl2 + H2 (1)

Ta vit di dng ion :

Zn + 2H+

+ 2Cl-= Zn

2++ 2Cl

-+ H2 (2)

hay Zn +2H+

= Zn2+

+ H2 (3)

C ngha trong acid H2SO4 phn ng n mn cng c biu din nh phn

ng (3). Phn ng (3) c tch thnh hai phn ng

Phn ng anode: Zn = Zn2+

+ 2e (4)

Phn ng cathode: 2H+ + 2e = H2 (5)

Trong phn ng anode, s oxi ha ca km tng t 0 n +2; phn ng cathode

s oxi ha ca hydro gim t +1 n 0.

V vy tt c cc phn ng n mn u l phn ng in ha. Kim loi n mn

th hin bng phn ng:

M Mn+ + ne (6)

V d: Fe Fe2+ + 2e (7)

Ni Ni2+ + 2e (8)

Al Al3+ + 3e (9)

Acid HCl

M2+

H2

Kim loi

H+

H+H

+



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3

Phn ng cathode quan trng i vi n mn l rt t. Phn ng n gin v

hay gp nht l phn ng thot hydro trong mi trng acid. Ngoi ra c cc phn

ng kh khc nh:

Fe3+

+ e Fe2+ (10)

Sn4+

+ 2e Sn2+ (11)

l cc phn ng khng quan trng v t gp. Phn ng ca oxi ha tan thng gp

trong dung dch acid v trung tnh:

O2 + 2H2O + 4e 4OH-

(12)

v O2 + 4H+

+ 4e 2H2O (13)

2.1.Phn ccS dch chuyn in thin cc v pha m hn c gi lphn cc cathode

(cathodic polarization).Tng t, nu elecltron trn b mt phn chia c gii

phng nhanh s chuyn in th v pha dng hn v c gi lphn cc anode.

Khi phn cc ln, kh nng ha tan anode s ln. V vy phn cc anode c c

trng nh l ng lc ca qu trnh n mn.

Trong dung dch, b mt st thn mn n nh Ecorr.

2.2.Thng

i vi mt vi kim loi (st, niken, titan, coban) tc n mn gim trn gi tr

th Ep. Kh nng chng li n mn trn vng th Ep c gi l thng.

Hat ng

Tc n mn

Thng

Th

Ep



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4


CHNG 2

NHIT NG HC N MN

Kim loi khi tip xc vi dung dch s hnh thnh mt b mt tip xc. Phn tnc phn cc khng i xng s b ht vo b mt, hnh thnh mt l p solvat,

ngn cn cc ht mang in trong dung dch tin gn b mt kim loi. Mt mt

phng gn nht ca cc ion dng so vi b mt mang in m gi l lp Helmholt

ngoi. Hnh thnh nn mt lp in tch kp, ging nh mt tin v xut hin

mt bc nhy th. in trng hnh thnh gia hai bn tin s khng ch cc

qu trnh chuyn in tch trn b mt (cc phn ng in ha).

1.Nng lng tdo v thin ccXt phn ng Zn trong acid HCl: Zn + HCl = ZnCl2 + H2

Khi xy ra phn ng, nng lng t do G s thay i . Khi sn phm c nng

lng t do thp hn cht phn ng, G < 0, phn ng t xy ra.

Bin thin nng lng t do G quan h vi thin cc ti trng thi cn

bng

G = - n. F. E

Vi n l s electron trao i trong phn ng; F hng s Faraday. Hai na phn

ng

Zn = Zn2+

+ 2e ea

2H+

+ 2e = H2 ec

ea, ecc gi l th oxi ha, kh hay thin cc n ng vi hai na phn

ng. Khi cht phn ng v sn phm xc nh trng thi tiu chun, c hot l

1 n v ta c eao

; eco.

1.1. Dy thin cc tiu chunDo khng tho gi tr tuyt i ca thin cc (phn ng n), nn phi

o s chnh lch th ca phn ng n vi mt in cc so snh. Thng s dng

in cc hydro lm in cc so snh. Tuy gi tr tuyt i ca n l khc 0, nhng

ngi ta quy c l 0.


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in cc so snh hydro tiu chun (SHE) gm mt tm Pt nhng trong dung dch

acid c hot bng 1. H2 thi vo di p sut l 1 atm. Thng in cc Pt c

ph mt lp mui Pt tng din tch in cc v khng ch gii phng H2. Th

in cc Zn khi ni vi SHE l 0,763 V.

1.2.Nng nh hng n thin ccXt phn ng tng qut:

aA + mH+

+ ne bB + dH2O

Bin thin nng lng t do trng thi tiu chun Go v khng tiu chun

G c tnh:

Go = (bGoB + dGoH2O ) - ( aG

oA + mG

oH+)

G = (bGB + dGH2O ) - ( aGA + mGH+)

Bin thin G gia hai trng thi:

G - Go = [b(GB + GoB ) + d(GH2O - G

oH2O)] [a(GA - G

oA ) + m( GH+ -

GoH+)]

i vi cht A, hot ca A quan h vi G qua biu thc:

a(GA - GoA ) = aRTln(A) = RTln(A)

a

Vi R l hng s kh; T l nhit tuyt i; (A) l hot ca A.Thay vo:

G - Go = R.T.ma

db

).(H(A)

.(H2O)(B)ln

+

Thay G = -nFe ; Go = -nFeo; ta c

e = eo

-nF

RTma

db

).(H(A)

.(H2O)(B)ln

+

Hay c vit di dng khc:

e = eo

+nF

RT3,2d

2

b

ma

O).(H(B)

).(H(A)log

+

y l phng trnh Nerst . Khi thay pH = -log (H+) ta c

e = eo

+n

059,0b

a

(B)

(A)log -

n

m. 0,059 pH



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Trong trng hp ny, b qua nh hng ca hot cc cu t trong dung dch

1.3. in cc so snh SHE v cc loi khcMt mu Pt nhng trong dung dch acid c hot bng 1. Bng kh hydro sch

thi vo v thit lp trng thi kh hydro tiu chun P=1 atm.

in cc so snh hydro ni vi mt na pin khc thng qua cu ni mui c

tm ngn bng thy tinh x p, ch cho php chuyn in tch, khng cho chuyn

cht.

Thin cc ePt3+/Pt cho ha tan Pt l +1,2V rt dng hn so vi eH+/H2. Pt ch

ha tan th rt dng, xa vi th kh ca phn ng 2H+ + 2e = H2, Pt khng hatan, ch l cht xc tc cho phn ng ny hnh thnh trn b mt.

in cc so snh hydro tiu chun SHE (Standard Hydrogen Electrode) gi l

in cc so snh loi 1. in cc so snh loi 2 hay s dng hn, th hin bng

di y:

Tn in cc Phn ngTh V

(SHE)

Hg-HgSO4HgSO4 + 2e =2Hg + SO4

2-

eHg/HgSO4 = 0,615 0,0295log(SO42-)

+0,615

Cu CuSO4CuSO4 + 2e = Cu + SO4

2-

eCu2+/Cu = 0,340 - 0,0295log(Cu2+)

+0,318

Calomen bo haHg2Cl2 + 2e = 2Hg + 2Cl

-

ecal. = 0,268 - 0,059log(Cl-)

+0,241

Ag-AgCl bo ha

AgCl + e = Ag+ + Cl-

eAg/AgCl = 0,222 + 0,059pH

( thay Cl- bng H+)

+0,222

Hydro tiu chun 2H+ + 2e = H2 0,0


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CHNG 3

NG HC N MN

ng hc nghin cu tc ca cc phn ngn mn. n mn trong dungdch trc tin quy nh bi cc phn ng in ha. Nghin cu ng hc l cn

thit to ra cc hp kim chng n mn v pht trin cc phng php chng n

mn.

1.nh lut FaradayPhn ng in ha to ra hoc tiu th electron . V vy tc ca dng

electron n hay i khi vng tip gip din ra phn ng c xem l tc phn

ng. Dng electron o bng dng in (ampe). Mt ampe tng ng 6,2.108

electron /giy.

nh lut c th hin : m =F.n

a.t.I

F l hng s Faraday; n : sng lng trao i; a : khi lng nguyn t; t

l thi gian. m l khi lng cht sinh ra hoc mt i. nh lut c biu din

cch khc:

r =A.t

m=

F.n

a.i

Vi i l mt dng in v bng I/A. Biu thc cho thy mt dngn

mn t l vi tc n mn, cng mt dngin tp trung vo din tch nh hn s

c tc n mn ln hn.

1.1.Mt dng trao iXt phn ng : 2H

+

+ 2e = H2

Ti th oxi ha kh hay thin cc n tiu chun eo H+/H2, phn ng t trng

thi cn bng th tc phn ng thun bng tc phn ng nghch, lc ny:

rthun = rnghch =F.n

a.i o

io l mt dng in trao i (Exchange Current Density) ti cn bng.



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C nng lng t do v io khng th tnh ton bng l thuyt m ch xc nh

bng thc nghim.Bn cht bmtnh hng ln n mt dngin trao i.

Bmt trn din ra phn ng khngnh hngn thin cc, ngc li io b

nh hng kh mnh ca bmt.Hay ni cch khc G khng bnh hng bi

tnh cht bmt nhng khi io th rt nhy vi cc tnh cht ca bmt.

1.2.Phn ccPhn cc l sdch chuyn in thin cc (E e) khi thcn bng e - gy

ra do phn ng tng trn bmti vi cc phn ngn.

Phn cc cathode c : cc electron cp n b mt do phn ng chm v gy nn

in th b mt E m hn e. Do vy cc xc nh l m.

Phn cc anode : electron ly ra khi b mt, s thiu ht electron gy ra s thay

i in th. in th chuyn v pha dng hn, do vy a dng.

C hai dng phn cc quan tm: phn cc hot ha (activation) v phn cc nng

(concentration).


1.3.Phn cc hot haKhi mt giai on no ca phn ng chm skhng ch tc dng electron

,lc ny ta ni phn ng b khng chbi schuyn in tch v gy ra sphncc hot ha.

Xt phn ng : 2H+ + 2e = H2

Trn b mt s c ba giai on:

-H+

phn ng vi electron trn b mt kim loi, hnh thnh Hh.phtrn b mt.

H+

+ e =H h.ph

-Hai Hh.ph phn ng vi nhau to H2

Hh.ph + H h.ph = H2

-Cc phn t lin kt vi nhau li thnh bng kh hydro trn b mt kim loi.

Mi quan h gia phn cc hot ha hay qu th v tc phn ng c trng

bi ia, ic. a = ao

a

i

ilog ; c = c

o

c

i

ilog

i vi qu th anode, a l dng do vy a dng. Tng t cho qu th

cathode, c m v c m. a, c l cc hng s Tafel cho cc phn ng n.


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Xt phn ng 2H+ + 2e = H2

Phn ng t cn bng ti eH+/H2, lc ny tc phn ng thun bng tc phn

ng nghch. Nng lng t do tng ng c th hin trn hnh. G*thun ,

G*nghch

tng ng l barier nng lng ca phn ng thun, nghch. bin thin

nng lng t do quan h vi thin cc:

G*thun - G*nghch = GH+/H2 = -nFeH+/H2

Theo nh lut phn b Maxwell v nng lng ca cc ht phn ng: rthun v

rnghch l hm ca nng lng hot ha.

rthun = Kt. exp(-RT

*G thun)

rnghch = Kn. exp(-RT*G nghch )

Kt, Kn l cc hng s phn ng cho phn ng thun v nghch. Ti gi tr cn

bng: rthun = rnghch =nF

a.io

io = Kt. exp(-RT

*G thun) = Kn. exp(-

RT

*G nghch)

G*thu

Trng thi hot

G*n

(1-)Fnc

nFc

G=-nFe

Trng thi

phn cc2H+ +2e = H2

H2 = 2H+ +2e

Trng thicn bng

Nng

lng

t do

Ta phn ng hay khong cch

tin cc


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R rng io l mt hm ca nng lng hot ha. Khi phn cc cathode hay c

qu thc trn b mt in cc, tc phn ng phng in gim v qu trnh ion

ha tng ln. iu ny c c bng vic gim nng lng hot ha cho phn ng

phng in mt lng nng lng nFc v tng cho phn ng ion ha mt lng

(1-)nFc.Tha s v 1- l t l ca c tham gia vo phn ng phng in v

ion ha. Tc phng in cathode v anode s trthnh:

ic = Kt . exp(- )RT

nF*G cthun

i a = Kn. exp(- )

RT

nF)1(*G cnghch +

Khi phn ng cathode xy ra thun li, dng tng s l:

itng.c = ic - ia = io .exp( )RT

nF c - io . exp( )RT

nF)1( c

Khi phn ng anode thun li ( ion ha thnh H+ thun li)

itng.a = ia - ic = io .exp( )RT

nF a - io . exp( )RT

nF)1( a

l phn ca a mt i bi phn ng ion ha anode

n gin li: itng.c = ic - ia = io. exp( )RT

nF c

khi c cao v hot ha, c = c log(ic/io) vi c =nF

RT3,2

Khi a cao: hot ha,a = a . log (ia/io)

y l phng trnh Butler- Volmer

1.4.Phn cc nng tc phn ng cao, phn ng kh cathode s lm gim nng cc ht mang

in trong dung dch gn in cc. S thay i nng H+ c th biu din nh

hnh di. CB l nng H+

trong ton dung dch v l chiu dy ca gradient

nng trong dung dch. eH+/H2 tnh theo phng trnh Nerst l hm ca nng H+

hay hot (H+).



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eH+/H2 = eoH+/H2 +

nF

T.R.3,2log(

2H

2

P

)H( +)

Nng H+ trong dung dch b khng ch bi phn cc nng

R rng e gim khi (H+) gim ti b mt. S gim ny gi l phn cc nng ,

nl mt hm ca mt dng in.

n =

L

c

i

i

1lognF

RT3,2

Biu din quan h (n- logi) cho thy n thp khi t n mt dng gii

hn iL. iL l tc phn ng cc i, t c v tc khuch tn ca H+

trong

dung dch b gii hn. iL c th tnh:

iL =

BC.F.n.D

D l khuch tn ca ht tham gia phn ng (H+ trong v d ny). Do vy iL

tng khi nng CB dung dch cao; nhit cao; khuy trn dung dch.

CB

CB = 0

Khong cch

Nng

1.5.Phn cc kt hpPhn cc cathode tng tng,c l tng ca phn cc nng v hot ha

tng,c = hot ha,c + nng ,c

Khai trin ra ta c:



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12

tng,c = c.logo

c

i

i+

o

c

i

i1log

nF

T.R.3,2

V phn cc nng thng khng tham gia trong phn cc nng ca phn

ng ha tan kim loi.

a = a.logo

a

i

i

1.6.ng cong phn cc


ioM/M+

i .m

nhnh

anode

nhn

h

1.6.1.Phn cc cathodeGa s h trong c hai na phn ng

Zn = Zn2+

+ 2e

2H+

+ 2e = H2

Hy gi thit, c mt dng e tha (mt dng iapp.c) c p t ln in cc

n

mn Zn trong acid c E.m v i.m xc nh bng in th hn hp.

Dng e tha gy cho in th chuyn v m hn t E.mn E. Th di chuyn

mt khong c = E - E.m - c xc nh l qu th. Dng k hiu phn bit

vi qu th t thn mn; l qu th t thin cc cn bng e.

eM ia ic

i .m

ioH

io

ia

ioH+/H2

logiaplog


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a)Mt dng p t, iapp.c, ln kim loi c th E.m v i.m ; gy ra qu thc ;

b)ng cong phn cc c c t th a.

Dng e tha lm gim tc phn ng anode t i.mn ia v tng tc phn

ng kh t i.mn ic .Theo nguyn l bo ton in tch (tc trnh tch in trn b

mt), s chnh lch gia tng tc kh cathode v gim tc oxi ha anode do

qu thc phi bng nhau:

iapp.c = ic - ia

Hnh trn biu din dng iapp.cng vi cc gi tr khc nhau ca c. Khi c thp

th ic ch b hn ia mt t v iapp.c rt b. Khi tng c, ic tng trong lc ia gim. ia

gim n lc rt b so vi ic , lc ny ng cong phn cc cathode trng vi

ng gch cho na phn ng cathode ca phn ng 2H+ + 2e = H2 . V vy

ng cong phn cc cathode (v vi logiapp.c) s cong ti vng qu th thp, nhng

li thng vng qu th cao. Phn thng, ngi ta gi l tun theo Tafel.

1.6.2.Phn cc anodeElectron b ly i khi kim loi v dng in s theo hng ngc li. S thiu

ht electron khin in th chuyn v pha dng hn so vi E.m. Tc oxi ha

tng trong khi tc kh ic gim do vy dng p vo:

iapp.c = ia - ic

Nhnh phn cc anode cng gii thch tng t nh nhnh phn cc anode.


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CHNG 4

THNG

1.Mng thngThng c nh ngha l s chng li n mn do hnh thnh mt lp mng

mng trn b mt kim loi hay hp kim trong cc iu kin oxi ha vi phn cc

ant ln.

2.Trng thi, biu din n mn thng - hot ngTh 3

2

1

i

ipEp

logi

Kim loi v hp kim c cc tnh cht thng lun c cc biu hin ring bit

khi phn cc ant. Dung dch axt tch kh th thp, tc n mn (mt dng

ant) tng cao.

Pha trn th thng Epp, mng thng trnn bn, n mn thp trng

thi thng vng 2). Dng n mn trng thi thng c th nh hn 106 ln

so vi dng n mn trng thi hot ng ic. Ti th cao hn, mng thng b

ph vv tc ant tng qu vng qu thng (vng 3). Vi thp khng r,

hp kim Cr-Ni, qu thng din ra vng gn th thot oxi, lc ny mng th

ng giu Cr l khng bn.



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2.1.nh hng ca nng cht oxi haTng nng cht oxi ha s tng th oxi ha kh ca phn ng n theo

phng trnh Nernst. L thuyt in th hn hp don s nh hnh cho hp kim

thng- hat ng.

Khi nng tng t 1 n 2, tc v thn mn tng t A-B nh thng thy

cc hp kim v kim loi. Nng 3, hp kim c th tn ti trng thi thng

D hay hot ng C.

Vng chuyn ti p hot ng th

ng, ti y dng gim khi tng th,l vng to ra khi o thng k hiu

gch gch. im X l trng thi th

n nh v khng bao gi quan st

c khi thng c thit lp bi

cht oxi ha ha tan trong thc t.

Nng tng t 4 5, trng thi th

ng n nh, tc n mn gim

n gi tr hot ng thp gn im

D. Tng 6 7 gy ra chuyn trng thi

n qu th ng v tc n mn

tng t E F.log

4

3

2

1

Th

A

C

D

E

F

7

6

5

B

Quan h tc n mn theo nng th hin theo hnh. Khi nng cht oxi

thi hot ng ban u. Trong vng BCD, c th hot ng hay thng, mng thng cha hnh thnh cho n D khi chn lc ny mng thng n nh v tc

n mn gim ng k.

Tn mn duy tr gi tr thp trong vng thng v tng trong vng

qu thng khi tng cao na nng . Khi qu trnh ngc li, nng long i

do pha long th tc n mn gim theo ng c t qu thng n thng.

Tuy nhin khi mng thng hnh thnh th n vn duy tr nng thp.



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V vy trong vng DCB, thng bin xut hin. Khi b mt b co xc, s

ph n nh mng thng v n mn s tng trng thi hot ng C.

2.2.nh hng ca tc chuyn ng dung dch th biu din n mn thp khng r trong dung dch axt pha long nh nc

bin. Dung dch c tch kh. phn ng kh:

2H2O + 2e = H2 + 2OH-

v hp kim n mn trong trng thi hot ng. Tc thot H2 ca phn ng trn l

thp i vi hu ht kim loi, v tc n mn rt thp trong dung dch trung tnh

tch kh, ngay ctrng thi hot ng.

Khi c sc kh phn ng cathode su tin:

O2 + 2H2O + 4e = 4OH-

Th

logi

Epass

2H2O+2e=H2+

= n++

O2+2H2O+4e=4OH-

1 2 3 4 5 6

Eam1

Eam2

Tng tc dung dch, s tng dng khuch tn gii hn t 1 6. Tc n mn

v thn mn trong trng thi hot ng cng tng dn n 4, ni y thn mn



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tng ng kn Epass v tc n mn gim t icn ipass trong trng thi th

ng nh hnh.

2.3.Cu trc v hp phn mng thngCu trc m nhiu nh nghin cu a ra ca mng mng thng trn st l

lp di Fe3O4, lp ngoi l - Fe2O3. Lp trong Fe3O4c cho l cu tc khuyt

tt v v th dn in

Mng thng thng c c tnh ca bn dn loi n, mang cc in tch m

tha. Mng thng ca nhiu hp kim cha ng cc nguyn t hp kim, c bit

l Cr hnh thnh mng oxt rt bn vi Fe. Cc hp kim v kim loi nguyn cht

khc c nhng tnh khc nhau v hay thay i nh l mt hm ca th p t vo v

thnh phn hp kim.

Evans ng gp nhng cng trnh u tin trong vic a ra l thuyt mng

oxt thng, tch mng, cch ly mng oxt dy khi b mt st trong hp kim

v Cr dung dch.. C hai c cng cu trc v thnh phn. Nhng mng cromat c

hnh thnh do ph mng thng trong sut qu trnh cch ly.

Uhlig v ng nghip nhn mnh tm quan tng ca oxi hp ph ha hc

trong vic hnh thnh mng thng. Mng hp ph khng ch l mt ro ngn cn

s ha tan ant m gii hn ng hc gim mt dng trao i io cho phn ng

hon tan oxi h p ph ha hc thun li kh c mt cc electron phn l p d cha

ghp i trong kim loi chuyn tip. Trong hp kim Fe-Cr, Cr l hp cht nhn cc

electron phn lp d cha ghp i t Fe. Hp kim vi Cr nh hn 12%, khong

trng electron d cha ghp i trong Cr b lp y t Fe d v hp kim ging nh

st khng hp kim, m khng b thng trong sung dch pha long tch kh.

Ln hn 12% Cr, hp kim b thng trong dung dch nh th, v cc electron phnlp d cha cp i lun sn c cho hp ph thun li, mng dy ln, cation kim loi

c gi si vo mng t kim loi nm di cng nh H+ t dung dch.

H+

(H3O+) hay OH

-ng vai tr trong vic hnh thnh mng thng. Do Fe

trong dung dch amniac, cc dung dch tng t khng phi nc, khng thy th

ng hot ng. Mc d in th oxi ha kh c tho c cho oxi . Hin tng

hot ng thng khng c trong cc dung dch trng t khc.


18/68

18


Phn ng ant tng :

Fe + 2H2O = Fe(OH)2 + 2H+ + 2e

Fe(OH)2 c th c hoc khng c trong cu trc mng. Lorenz v cng s gi

thit

Fe + H2O = (FeOH)h.ph + H+

+ e

(Fe(OH))h.ph = (FeO)h.ph + H+

+ e

(FeO)h.ph + H2O = (FeOO)h.ph + H+

+ e

Hp ph l giai on u trong qu trnh hnh thnh v pht trin mng, Tc

n mn bc ch trong vng th thng l v mng oxt hay gii hn ng hc

l vn ang thao lun hin nay. Mng oxt c th gim io v mng hp ph c

th hnh thnh ro cn.


19/68

19

CHNG 5

PHNG PHP PHN CC O TC N MN

C hai phng php ang s dng hin nay o tc n mn bng phn ccin ha : ngoi suy Tafel v in trphn cc. Phng php phn cc c nhiu

thun li:

- Cn thi gian ngn ( vi pht) xc nh tc n mn, cn phng phptrng lng cn vi ngy.

- Rt thun li trong nghin cu ng hc hay kim tra n mn trong nh myang hot ng.

- Phng php c nhy cao, khng cn cc yu t tng tc nh nhit.

- Phng php khng ph vkt cu, lp li php o trn cng mt in cc.

1.Ngoi suy TafelPhng php ny c gii thiu m t l thuyt in th hn hp n mn

trong dung dch nc. ngoi suy ng, yu cu phn ng n phi c khngch bng qu trnh chuyn in tch. Trn ng cong phn cc t ra phi c mt

on thng c chnh xc cc xc nh i.m bng ngoi suy Tafel.



20/68

20

iu ny thc s kh t c trong dng dch long lc ny phn cc nng

v in trOhm nh hng ging nhau mt dng cao hn. Tuy nhin mt cch

tng i trong gii hn ca ngoi suy Tafel i.m lun bng mt dng gii hn iL

trong phn cc nng khi khuch tn khng ch qu trnh.

Th phn cc ni chung ph thuc vo thi gian v cn xem xt cn thn c

c g cong phn cc n nh phn nh phn cc n mn thc. Trong mt

chng mc, ni chung phn cc cathode nhanh v thun nghch hn phn cc

anode, ph thuc nhiu vo thi gian v tr.

2.Phng php in trphn ccPhng php in trphn cc (TPC) c c t l thuyt in th hn hp.

Xt ng cong phn cc vi qu trnh anode, cathode b khng ch bi qu trnh

chuyn in tch.

iapp.c = ic - ia

ic l mt dng cathode; ia l mt dng anode. ; iapp.c l mt dng cathode

p t ti ti cng gi trin th E. Tng t: iapp.a = ia ic

th thp gn to, phn tuyn tnh r rng. Phm vi tuyn tnh ph thuc vo

gi tr hng s Tafel chn la. Khi phn cc t thn mn E.m vi ic, ia p vo:

c= c. log(ic/i.m)

a= a. log(ia/i.m)

Khi phn cc t thn mn E.m, a,c l cc hng s Tafel anode cathode( phncc hot ho) v i.m l tc n mn. c=ac xac nh nh l q th v n

biu din s thay i th khi thn mn trng thi n nh E.m.

Bin i ta c: iapp.c = i.m (10-c/c - 10-a/a )

V vy i app.c l s khc bit gia hai hm m m tin ti ) khi 0. Sp xp v

ly vi phn ta c:

Rp =app.capp.c idi

d

=

0

mama i

B

cai

ca

.. )(.3.2

.=

+=



21/68

21

V vy dc (d/diapp.c) 0 ti gc ng cong phn cc xc nh nh l

in trphn cc Rp l t l nghch vi tc dn mn

B)(.3.2

.

. cai

ca

ma

+=

l hng s t l .

Nhn thy hng s Tafel chn c gi tr ln s c phn tuyn tnh gc. Tuy

nhin phn tuyn tnh xut hin qu th th p khi hng s Tafel thp a,c =

30mV. Chn a c gy ra s bt i xng qua gc to nh hnh 5.2 vi

a=30mV ,c = 118mV.

Ly logarith ta c: log Rp = log B - log i .m

V vy v quan h log Rp logi.m l mt n thng c dc l -1 v im ct

quy nh bi hng s t l B. Phn tuyn tnh trn mt di rng.

Ti liu tham kho

[2]. D. Pletcher, F. C. Walsh,Industrial Electrochemistry , 1993.

[3]. V. S. Bagotsky, Fundamentals of Electrochemistry, 2006.

[4]. C. M. A.Brett, A.M. O.Brett,Electrochemistry-Principles, Methods and

Applications, 1993.

[5]. Philippe Marcus, Corrosion Mechanisms in Theory and Practice, 2002



22/68

1


IN PHN SN XUT NaOH Cl2

1.Phng php ho hc1.1.Sn xut bng sa vi

Na2CO3 + Ca(OH)2 = 2NaOH + CaCO3

1.2.Sn xut t qung pyrit: chia lm hai giai onNa2CO3 + Fe2O3 = Na2O.Fe2O3 + CO2

Na2O.Fe2O3 + H2O = 2NaOH + Fe2O3

em c c, ta c NaOH, Fe2O3 tun hon trli trong qu trnh sn

xut. u im ca phng php l khng c sn phm tha. NaOH c hnphng php sa vi. Nhc im l tn nhiu nguyn liu.

1.3.Phng php VentonMnO2 + 4HCl = MnCl2 + Cl2 + 2H2O

Hon nguyn MnO2

MnCl2 + Ca(OH)2 = Mn(OH) + CaCl2

Thi khng kh v cho tha sa vi th Mn(OH)2b oxi ho to kt taMnO2.

2Mn(OH)2 + Ca(OH)2 + O2 = CaO.2MnO2 + 3H2O

CaO.2MnO2 + 10HCl = CaCl2 + 2MnCl2 + 5H2O + 2Cl2

2.Phng php in ho*Dch in phn: Mui n NaCl (cha 39,4% Na, 60,6%Cl). Mui uc

ho tan n gn bo ho v a v thng in phn ( 45 -55oC).

*Nc mui cn x l trc khi a vo thng in phn, tch hm

lng Mg2+, Ca2+, SO42-

, . . .

SO42-

: h p ph ln anode, cn tr phng in ca Cl, to iu kin O

phng in, anode bn mn.

Cho php: Ca2+


23/68

2

2.1.Phng php tinh ch nc mui2.1.1.Phng php xa-kim

Ca2+

+ Na2CO3 = CaCO3 + 2Na+

Mg

2+

+ NaOH = Mg(OH)2 + 2Na

+

2.1.2.Phung php sa vi-xaMgCl2 + Ca(OH)2 = Mg(OH)2 + CaCl2

MgSO4 + Ca(OH)2 = Mg(OH)2 + CaSO4

Ca(HCO3)2 + Ca(OH)2 =2CaCO3 + 2H2O

CaCl2 + Na2CO3 = CaCO3 + NaCl

CaSO4 + Na2CO3 = CaCO3 + Na2SO4

2.1.3.Phng php sa vi-sunfatGm 2 giai on:

+Tch Mg, Ca nhsa vi

+Gia cng sunfat lng trong dung dch bng xa

Na2SO4 + Ca(OH)2 = NaOH + CaSO4

CaCl2 + 2NaOH = Mg(OH)2 + 2NaCl

MgSO4 + 2NaOH = Mg(OH)2 + Na2SO4

CaSO4 + 2NaOH = CaCO3 + Na2CO3 +2H2O

CaCl2 + Na2SO4 = CaSO4 + 2NaCl

+Trao i ion

2R-Na + Ca2+

= R2-Ca2+

+ CaCl2

R l gc nha. Sau khi trao i, nha c mang i ti sinh

2.2.Cc phn ng in ccS phn ly:

NaCl = Na+

+ Cl-

H2O H+

+ OH-

Cathode : in phn nc



24/68

3

2H2O + 2e = 2H + 2OH-

2H = H2

OH-+ Na

+= NaOH

Na phng in trn in cc c khng?Trong mi trng pH=7, H+ phng in -0,41V

Phng trnh Nernst :+

+= Na

o ClnnF

RTEE , E

0=-2,7V

Thay vo ta c: CNa+ = 3,8.1038

mol/l

Anode: Cl phng in to kh Cl2, OH-cng c th tham gia

2Cl--2e = Cl2

4OH- - 4e = O2 + 2H2O

hoc 2H2O -4e = O2 + 4H+

Chn loi in cc sao cho: qu th thot clo nh hn, clo su tin

tham gia phn ng trc. Loi in cc ph hp: graphit, Ti m Pt, Ti ph

RuO2,TiO2.

Cc phn ng ph

-ion OH- tham gia phn ng anode

4OH-- 4e = O2 + 2H2O

Oxy thot ra anode, ln vo kh Cl2. Oxy phn ng vi grapht, tiu

hao anode

-Ho tan Cl2 vo dung dch

Cl2 + H2O = HClO + HCl

Cl2 + OH-

= HClO + Cl-

-ClO-phng in trn anode

6ClO-+ 6OH

-= 2ClO3

-+ 4Cl

-+ 3/2 O2 + 3H2O + 6e

3.Cu to thng in phn NaOH, Cl2 mng ngn



25/68

4

Nguyn l hot ng ca mng ngn aming

Aming ph trc ti p ln in cc cathode Fe (dng li). in cc

anode t gn mng ngn, nc mui 30% chuyn vo khoang anode, Cl2

sinh ra trn anode. Nc mui khuch tn qua mng ngn xp, H2 v NaOH

hnh thnh pha bn kia ca mng ngn. Anode l Ti c ph lp xc tc.

Cathode Fe c ph l p xc tc (Ni din tch ln) lm gim qu th

hydro.

Dng mng ngn aming gp phi mt s vn :

+Khi c s chnh lch nng , tt c cc loi ion u c th khuch tn

qua mng ngn. Na+ di chuyn t khoang anode sang khoang cathode bng

khuch tn, i lu v in di. Hu ht lng Clo tng ng i cng vi Na+

vo khoang cathode v vy NaOH ln nhiu Cl. Ngoi ra, nng NaOH ch

t di 12%, khuch tn ca OH- t khoang cathode n khoang anode tr

nn ng k. iu ny dn n mt mt Cl do in phn thnh hypocloride vhnh thnh oxy anode, lm bn sn phm Cl. NaOH c nng thp nn

cn thit b c c nng ln nng 50%.

+in tr ri IR trn mng ngn ln. in th thun nghch ca thng

in phn l -2,2V, ca thng in phn c mng ngn l -3,2 n -3,8V, in



26/68

5

th ny ri ch yu trn mng ngn. Theo thi gian, IR mng tng do cc cht

kt ta hyroxit ca Mg, Ca trong cc l xp ca mng. Nc mui cn phi

lc sch trc khi vo thng.

+Mng cn thay sau vi thng. Trong qu trnh thay mng vn phi mbo hot ng ca nh my.

Do in trca thng in phn mng ngn ln, tiu hao nng lng khi

hot ng mt dng cao l khng kinh t. Thng lm vic 0,15 0,2

A/cm2. Khi thit k phi m bo din tch in cc ln nht trn mt n v

th tch.

Sp xp in cc anode



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6

Thng cathode



28/68

7

Thng in phn mng ngn, kiu MDC 55 ca Oxy Tech Systems, Inc

Thng MDC 55 c kch thc 3 x 16 x 2 m, nng khong 7 tn. in cc

l loi n cc, dng in 120 kA, in th 3,4 V, nng sut 3,5 tn Cl2 mi

ngy.S cng nghin phn sn xut NaOH, Cl2 c th hin hnh

Dy chuyn cng ngh

Chun b dung dch un nng Kt ta Mg, Ca Lc

RaLm sch

Ho lng

Axt ho un nngThng in phn

Tng hp HCl

Sy Lm lnh Bc hi Ly tm

Phn ly

NaCl

NaCl

NaCl

Na2SO4

NaOHNaClH2SO4 Cl

2H

2

HCl

4.Thng in phn cathode thu ngn4.1.Thng in phn, dy chuyn cng ngh



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8

S cng nghin phn NaOH, Cl2 vi cathode thu ngn

4.2.Cc phn ng trn in cc2Cl- -2e- = Cl2

Na+ + Hg + e- = NaHg

Phn ly hn hng

2NaHg + 2H2O = H2 + 2Na+ +2OH- + 2Hg

Kch thc thng 15 x 2 x 0,3m, bng st, y nghing Hg chy t

u ny n u kia. Anode lm bng vt liu bn, ph Ti. Kch thc 30 x

30 cm t song song vi b mt Hg (khong cch 1cm). Thng c khong 250

anode.



30/68

9

Nng mui vo 25%, 60oC. Chy qua cell. Kh Cl2 thot ra nh,

hn hng Hg nm y. Hn hng c tch hon ton NaCl v i vo thit

b tch (denuder). L mt thit b hnh tr, c nhi cht bng graphit c

gn cc kim loi chuyn tip Fe hay Ni lm xc tc phn hu hn hng.NaHg e- = Na+ + Hg ; 2H2O + 2e

- = H2 + 2OH-

5.Cng ngh mng trao i5.1.Cng ngh



31/68

10

Ti liu tham kho[1]. D. Pletcher, F. C. Walsh,Industrial Electrochemistry , 1993.


[3]. C. M. A.Brett, A.M. O.Brett, Electrochemistry-Principles, Methods

and Applications, 1993.



32/68

1


BIN TNH B MT KIM LOI

1.Oxi ha nhum mu nhm bo v nhm v hp kim nhm, ngi ta to trn b mt n mt lp oxit

bng phng php ho hc hoc in ha. Mng oxit dy hoc mng theo

iu kin oxi ho. Mng c th dy n hng trm m. Mng c rn cao,

c kh nng hp th mu, thm du m tt nn c th lm vic ni c ma

st cao. Sau khi oxi ho, mng c em i nhum mu v choc hu c.

Mng Al2O3 c th hnh thnh trn b mt nhm bng phng php in

ha hay ha hc. Mng c th dy n hng trm micron.1.1.Phng php ha hc

Phng php ny to bn ca mng khng cao, t s dng. Thnh

phn dung dch oxi ha nh sau:

Na2CO3 : 50g/l

NaOH : 2 2,5 g/l

Na2CrO4 : 15 g/lThi gian : 5 30 pht

1.2.Phng php in ha1.2.1.Ccu mng oxit

Mng c hai lp: lp mng, st cht st b mt Al. Cu to t oxit nhm

ngm nc, chiu dy 0,01 0,1m. Lp bn ngoi ngm nc nhiu hn.

Khi nhng nhm vo dung dch, anode nhm c qu trnh ha tan in

ha nhm

Al = Al3+

+ 3e

ng thi nhm tc dng vi dch in phn theo phn ng

2Al + 3H2SO4 = Al2(SO4)3 + 3H2

Din ra ng thi vi qu trnh ha tan nhm l qu trnh thot oxi theo

phn ng


33/68

2


4OH-- 4e = O2 + 2H2O

Qu trnh gii phng oxi c th qua cc bc:

2OH-

= H2O + O- -

O

2-

= O

-

+ eO

-= O + e

2O = O2

Cc sn phm trung gian O2-, O tc dng vi nhm anode (vt cn oxi ha)

2Al3+

+ 3O2-

= Al2O3

2Al + 3O = Al2O3

Qu trnh hnh thnh mng nhanh chng, mng to c st, mng chiu

dy hu nh khng thay i trong sut thi gian oxi ha. Qu trnh ha tan

mng s xy ra ng thi:

Al2O3 + 3H2SO4 = Al2(SO4)3 + H2O

Ha tan mng ny s to ra cc l xp. cathode, qu trnh kh :

H+ + 2e = H2

Khi hnh thnh l xp: O2-

, O khuych tn qua mng y cc l xp vhnh thnh Al2O3. Phn ny s tip tc pht trin lm dy thm mng oxt.

ng thi phn mng pha trn s b ha tan do vy chiu dy mng hu

nh khng i, phn trn cc l xp c dng hnh cn.

Trong cc l xp c cc phn ng hydrat ha

Al2O3 + H2O = Al2O3.H2O

Al2O3 + 3H2O = Al2O3.3H2O

Al2O3.nH2O + H2SO4 = Al2(SO4)3 + (n+3) H2O

1.2.2.Dung dch v chin phn :H2SO4 : 180 200g/l

Nhit : phng

Mt dng anode Da : 1,5 2 A/dm2

Thi gian oxi ha : 40 50 pht


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1.3.Nhum mu nhm:Mng Al2O3 xp nn c kh nng hp ph cc cht mu hu c. i khi

cc cht mu tc dng vi mng oxt to cc hp cht ha hc. Cc cht mu

v chnh thnh do cc phn ng to cht mu.V d: nhum vng da cam nhm c tin hnh nh sau:

-X l b mt nhm trc khi oxi ha

-oxi ha in ha nhm trong acid, ri nhng vo dung dch K2Cr2O4 trong

30 pht. Sau li nhng vo dung dch AgNO3. Mu vng da cam c c

do phn ng:

2AgNO3

+ K2Cr

2O

4= Ag

2CrO

4+ 2KNO

3

Ag2CrO4 kt ta mu vng da cam

-Thnh phn dung dch nhum mu

Mu Dung dch 1Thnh phn

g/l

Dung dch

2

Thnh

phn

(g/l)

Hp cht

mu

Xanh FeCl2 10 100 K4Fe(CN)6 10 50

Nu CuSO4 10 100 K4Fe(CN)6 10 50 Cu2 Fe(CN)6

en Pb(CH3COO)2 40 100 KMnO4 15 25 CoO

Vng Pb(CH3COO)2 100 200 K2Cr2O7 50 100 PbCr2O7

Vng

nht

Pb(CH3COO)2 10 50 Na2SO4 10 50 PbSO4

Cc mu sau khi nhum mu phi sy kh.

Cht hu chay s dng l Alizarin t 2 5 g/l, nhum nhit 50

60oC. Mu ph thuc thi gian ngm mu.


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2.Pht pht ha kim loiPht pht ha (PPH) l qu trnh to mng bo v trn b mt chi tit.

Mng gm cc mui pht pht ca Fe, Mn, Zn hay hn hp cc mui ny.

Mng PP c bn khng cao do xp, nn bn n mn km. Nhng lic kh nng hp ph tt nn lm nn sn hoc gia cng thm trong dung

dch cromat ri thm du bt kn cc l xp s tng bn n mn.

Mng PPH r tin, to nn tt cho sn. Tnh bo v ca mng PP ph

thuc: nng mui PP trong dung dch, thi gian, thnh phn thp v trng

thi b mt trc khi PP. Lp PP tan trong nc 25oC l 1,5mg/l; 90oC l

10,6g/l; tan mnh trong acid v kim.

2.1.Pht pht ho nngChia lm hai loi: PPH thng v PP nhanh

-PPH thng

Nhng mu thp vo dung dch mui PP dng ha tan nh km, mangan,

thng dng l mui Majep (hn hp mui st va Mn pht pht) hay dng

mono photphat Me(H2PO4)2

nhit thng, c phn hy nhng khng ng k:

Me(H2PO4)2 = MeHPO4 + H3PO4

Khi un nng:

5Me(H2PO4)2 = 2MeHPO4 + Me3(PO4)2 + H3PO4

Nhng thp vo dung dich pht pht ho xy ra 2 qu trnh:

Anode : Fe = Fe2+

+ 2e

Cathode 2H+

+ 2e = H2

Ion H+

do s phn ly ca H3HPO4 t do hay do:

Me(H2PO4)2 = Me2+

+ 2H2PO4-

H2PO4-

= H+

+ HPO42-

HPO42- = H+ + PO4

3-


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5


Kt qu l l p dung dch gn b mt mu thp giu ion Fe2+ cng nh

HPO42-

; PO43-

; Fe3(PO4)2 ; Mn3(PO4)2. Bi vy lp dung dch y t qu

bo ho v kt tinh ln b mt thp tho thnh lp ph pht pht:

Fe2+

+ HPO42-

= FeHPO4

Mn2+

+ HPO42-

= MnHPO4

Zn2+

+ HPO42-

= ZnHPO4

Hay

3Fe2+

+ 2PO43-

= Fe3(PO4)2

3Mn2+

+ 2PO4

3-= Mn

3(PO

4)

2

3Zn2+

+ 2PO42-

= Zn2(PO4)2

Nhit cao th mui monophtpht d phn hu do MeHPO4 v

Me3(PO4)2 c th kt ta trn b mt thp v ngay c trong dung dch. Nu

khng ch nhit thp th thi gian PPH ko di. Thi gian PPH ph thuc:

- Thnh phn kim loi- Phng php gia cng b mt trc khi PPH- T s axt chung v axt t do- Nhit Thnh phn v ch PPH

[nFe(H2PO4)2.[mMn(H2PO4)2] : 30 - 35 g/l

Nhit : 97 99oC

Thi gian : 40 - 80 pht

-PPH nhanh

tng tc PPH kim loi en, thng thm vo dung dch PPH cht

kh hay cht hu c. Thi gian PPH gim cn 10 15 pht

Cc cht thm vo l cht kh phn cc, thc y qu trnh cathdode.

Cht oxi ho thng dng l mui nitrit, nitrat. Cht kh l mui bisulphit,

sulphit.. Cht hu cnitrobenzen; hydroxylamin; thioure.


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Thnh phn (g/l):

[Fe(H2PO4)2][Mn(H2PO4)2] : 30

NaNO3 : 4- 6

Zn(NO3)2.6H2O : 60H3PO4 t do : 0,1 1

Nhit : 92 - 96 oC

Thi gian : 8 10 pht

Dung dch khc

Zn(H2PO4)3.2H2O : 35 37

Zn(NO3)

2.6H

2O : 52- 53

H3PO4 t do : 15 - 16

T l axit chung/ axit t do = 5/1 : 6/1

Nhit : 85 - 95oC

Thi gian : 15 20 pht

2.2.Pht pht ho lnhTin hnh nhit thng, khng cn khng ch nhit nghim. Mng

PPH mng dng lm lp lt cho sn.

Trong dung dch c cc cht lm tng nhanh tc ho tan kim loi

nh Zn(NO3)2; KClO3 ; NaF. Thnh phn (g/l):

Dung dch 1 :

Majep : 35 45 g/l

Zn(NO3)2 : 70 90

NaF


Dung dch 2

H3PO4 t do : 80 85

ZnO : 15 17


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NaNO2 : 1 2

pH: 2,7 - 3,1


3.Cromat ho b mt kim loiLp cromat ca cc b mt kim loi Al, Mg, Zn, Cd, Sn, Cu, Ag bm tt,

bn n mn. Mu sc: xanh lam, vng, xanh lc, en l nhng hp cht Cr3+

c mt Cr6+. Kh nng chng n mn ca lp cromat khng phi do s th

ng b mt kim loi m khi c mt cromat lm mt tc dng ca m mi

trng. Hm lng cromat trong lp b mt cng cao, chiu day cng dy,

bn n mn cao. Cng mu ca lp cromat ph thuc t l Cr3+/Cr6+.

Phng php cromat ho gm hai giai on:

+X l b mt kim loi

+ Nhum mu trong dung dch c ca axit cromic v H2SO4. Sau

nhum xanh trong dung dch kim.

Phng php ny c nhc im l tc ho tan kim loi qu nhanh. C

th dng phng php cromat ho mt giai on trong dung dch: H2SO4: 5-

10g/l, CrO3: 10-20g/l, thi gian 180s.


39/68

1

PHNG PHP NG TIN HO XL NC THI

1.Khi nim chungPhng php ng keo t, to bng l mt phng php c s dng rng

ri trong vic x l nc thi ni chung, nc thi cng ngh dt nhum ni ring.

Csca phng php l s dng mui kim loi c kh nng hnh thnh cc bng

keo t. Cc bng keo t ny s hp ph cc cht bn trong nc thi v c tch ra

bng cc phng php n gin. Bng phng php ny cc tp cht tn ti trong

nc thi di dng keo, dng t tan c tch ra. Cc ht keo mun tch ra mt

cch c hiu qu, trc ht cn trung ho in tch ca chng v sau lin kt

chng li vi nhau, hnh thnh khi keo t ln hn. Qu trnh trung ho in tch

gi l qu trnh ng t, cc bng keo tp hp thnh khi bng ln hn gi l qu

trnh to bng. Cc cht ng t thng s dng l mui ca nhm, st hoc s

dng hn hp. Hay s dng nht l mui nhm Al2(SO4)3 - mt mui tan tt trong

nc, gi thp, hot ng trong gii hn pH rng t 6-8. Cc mui st hay c s

dng: Fe(SO4)

3.2H

2O, Fe

2(SO

4)

3.3H

2O, FeSO

4.7H

2O v FeCl

2.

ng tin vi anode nhm ho tan l mt phng php to ra cc cht keo

t nh Al(OH)3, Fe(OH)2, Fe(OH)3 gy keo t, hnh thnh cc bng keo c kh

nng keo t nhiu cht hu c, cht mu trong dung dch. Bn cnh , kh H2, O2

thot ra hai in cc cathode v anode lm tuyn ni, khuy trn dung dch lm

tng thm hiu qu x l. Lp bn nho Al(OH)3 hp ph cc cht mu, cht hu

c, cc tp cht khc trong dung dch di tc dng ca tuyn ni s ni ln trn

mt dung dch .

2.Cc c tnh chung ca ht keo v c2.1.Cu trc ca ht keo v ctrong dung dch: ht keo gm ba phn :

-Nhn ht keo: l tp hp nhiu phn t rn lin kt vi nhau, c bao

bc bi mt lp v ion. S hp ph mt loi ion no trong dung dch to nn lp

v ion ny.

-Lp in tch kp: hnh thnh bi cc ion tri du vi lp v ion.

-Lp ion khuch tn hnh thnh phn ngoi ca lp in tch kp.



40/68

2

Cu trc ht keo th hin trn hnh 4.1 .

Ht mang in tchm

Lp in tch kp

Lp khuch tn ccion tri du

Mng bao quanh ht keo

Thin ngzta

Th nng xung quanhht keo

Thin ng tng

Hnh 1: M t cu trc ht keo. Khi nim v lp in tch kp

2.2.Tnh cht ca cht keo:-Cc ht keo tn ti l lng trong dung dch , chu tc ng bi hai lc i

nhau: lc ht phn t Van der Waals c khuynh hng kt hp cc ht keo li khi

chng mt khong cch rt gn nhau. Lc y tnh in ngn cn s kt hp cc

ht keo tch in cng du.

-Tn ti mt in thin ng zta -l in th tnh t mt trt ca ht v

trong lng dung dch.

2.3.Cch ph bn ht keo2.3.1.Nn p lp khuch tn:

Khi trong dung dch c cc cht in ly l, lp khuch tn ca ht keo s b

nn p li, to iu kin cho cc ht huyn ph tip cn nhau, tnh bn ca h keo skm i. B dy lp khuch tn gim khi ha tr v nng ca ion i cao. S keo

t theo cch ny ch din ra ch yu vi cc h keo c th nng cao, dy lp

khuch tn khng ln v nng ion ca dung dch nh. S keo t ch din ra khi

nng cht in ly t mt gi tr ti thiu no gi l ngng keo t. Ngng

keo t quan h vi ha tr v nng ion theo cng thc:

C = K662

53 ).(

ZCA

TKp



41/68

3

Vi K l hng s, A l hng s tng tc ht tnh in, l hng sin mi, Z ha

tr ca ion i.

2.3.2.Hp ph v trung ha in tchS ph bn ca h keo do hp ph v trung ha in tch khi s dng Fe3+ v

Al3+

din ra nh sau: qu trnh thy phn ca cc ion kim loi to thnh phc

hydroxo Al(OH)2+

, Al(OH)2+, Fe(OH)2

+. . .sau hnh thnh cc polyme hydroxo

v cui cng l kt ta hydroxt kim loi. Cc ion dng trn hp ph gy trung ha

in tch m trn b mt ht keo, gim lc y ca cc ht, to iu kin thun li

cho cc ht keo tin gn nhau hn to cc ht keo ln. Cch ny ch din ra khi

h huyn ph mang in tch m ng vi gi tr pH ln hn pH ng in ca hhuyn ph.

Cc ht keo nhm hay st c th lm o du in tch lm h huyn ph bn

trli. Nguyn nhn ny l do s dng tc nhn keo t qu liu lng. Lc tng

tc l t hp cc lc tnh in v lc ha hc lm cc ht huyn ph o du tch

in v gy ra s ti bn h.

2.3.3.Cchdnh bm vo kt taKhi cc mui st, nhm hay cc oxit, hydroxit kim loi dng lm cht keo t

c nng cao chng s kt ta nhanh di dng cc bng keo hydroxit. Cc ht

keo c th dnh vo khi kt ta cc hydroxit ty thuc qu bo ha ca dung

dch. kt ta nhanh, th t s:

s

nn

K

OHMe ]][[ + 100

[Men+

], [OH-] l nng mol ca ion kim loi, hydroxyl trong dung dch; Ks

l tch s tan ca ion Me(OH)n.

Khi cc ht kt ta tch in dng, kt ta s tng vi s c mt ca cc

anion trong dung dch. Cc ht keo c xem nh l cc tm to thnh kt ta.

2.3.4.Cchkt ta qut, hp ph to cu ni.Ngoi hai cch trn, qu trnh keo t cn xy ra theo cch kt ta qut, hp

ph to cu ni gia cc ht keo. Theo cch kt ta qut, qu trnh thy phn v

to polyme xy ra khi nng trng thi siu bo ha. Khi lng chng li cun



42/68

4

cc ht keo lng theo. Khi cc polyme hnh thnh trong h hay c b sung t

ngoi vo, chng c hp ph ln b mt ht keo v to nn cu ni gia chng,

to thun li hnh thnh tp hp ln hn.

2.3.5. Cc phn ng xy ra trn in ccKhi c dng in mt chiu i qua dung dch, trn anode, cathode xy ra cc

phn ng nh sau:

anode:

.Ho tan nhm : Al - 3e Al3+

.Thot oxy:

pH7: 4OH- - 4e O2 + 2H2O

cathode

pH7 : H2O + 2e H2 + 2OH-

Ion Al3+

va mi hnh thnh trn lp dung dch st anode nhm, chng tham

gia cc phn ng thy phn:

.pH


43/68

5

Dng hydroxo Al tn ti mt cn bng vi Al(OH)3 v c ho tan ph thuc pH.

pH 10 Al(OH)4-c hm lng ln

nht.

2.3.6. Sto thnh keo nhm bng ho tan anodei vi dung dch c pH= 5-7, khi in phn do s thot kh O2 trn anode, H2

trn cathode, nhm ion b thy phn nn pH dung dch thp, thnh phn ch yu l

Al(OH)2+

v Al(OH)2+

ngoi ra cn c Al3+

v Al(OH)3. Nu dung dch c tnh

acid, hm lng phc hydroxo tch in dng kh cao, chng nm phn tn, chm

lin kt li to ht keo ln hn.Khi tng pH>6, ion Al3+ va hnh thnh s b thu phn hon ton, phc

hydroxo Al(OH)2+

, Al(OH)2+

tip tc thu phn, sn phm thu phn l Al(OH)3.

n pH=7-8 Al(OH)3t nng cc i. Nh vy khi tng pH, hm lng cc ht

keo dng gim dn, cc sn phm thu phn d lin kt vi nhau li hn to thnh

cc ht keo ln hn. Th t cc phn ng thu phn nh sau:

Al3+

.6H2O + H2O Al(OH)2+

.5H2O + H3O+

Al(OH)2+.5H2O + H2O Al(OH)2+.4H2O + H3O

+

Al3+

.6H2O + 2H2O Al(OH)2+.4H2O + 2H3O

+

Al(OH)2+.4H2O + H2O Al(OH)3.3H2O + H2O

+

Trong qu trnh in phn, pH ca lp dung dch st anode gim dn do to ra

keo nhm v thot O2 nn cc hydroxo tch in dng c phn tn rt cao.

Trong in trng, H+ chuyn v cathode s trung ho cc ion OH-chuyn t

cathode sang anode, gip cho qu trnh thu phn hnh thnh cc hydroxo d dng.Trong khong pH =5,7-7,0 cc thnh phn chnh l Al(OH)2+, Al(OH)2

+. . . v

Al(OH)3. Tng pH v thi gian in phn, cc phn t lin kt to cc ht a

nhn:

kAl(OH)2+

+ mAl(OH)2+

+ nAl(OH)3 Alp(OH)qr+

p=k+m+n; q=k+3n+2m; r=2k+m



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6

V th c th xem ht keo Alp(OH)qr+

l ht keo a nhn c trng trong

khong pH= 5,7-7,0. in tch ht ny ty thuc lng Al(OH)2+; Al(OH)2+

c

ngha l ph thuc pH dung dch v lng Al3+.

Khi gi tr pH nm trong khong 7-8, cc hydroxo Al(OH)2+, Al(OH)2+

v

Al(OH)3 hnh thnh lp dung dch st anode Al ho tan theo cc phn ng nh

sau:

Al3+

.6H2O + H2O Al(OH)2+

.5H2O + H3O+

Al(OH)2+

.5H2O + H2O Al(OH)2+.4H2O + H3O

+

Al(OH)2+.4H2O + H2O Al(OH)3.3H2O + H3O

+

H3O+

+ OH- 2H2O

Ion OH- chuyn sang anode, kt hp vi ion H+ to ra nc. Al3+ tham gia

phn ng thy phn thun li nn nng Al(OH)2+, Al(OH)2+

rt nh, lng

Al(OH)3 t 90-95%, bt u c s hnh thnh Al(OH)4-. Tt c cc ion dng, m

kt hp vi Al(OH)3 hnh thnh ht a nhn in tch dng nh:

kAl(OH)2+

+ mAl(OH)3 + nAl(OH)4- [Al(OH)3]mAln+k(OH)4n+2kk-n

Ht keo c th zeta xp x bng khng nn cc ht c phn tn gim, chng

d tng tc vi nhau to thnh cc khi huyn ph v nh hnh kch thc ln.

pH t 8,0 -8,5 lc ny lng OH- cao, tham gia phn ng vi H+ hnh thnh

nc, to iu kin thun li thu phn cc phn t hydroxo thnh Al(OH)3. Cc

ht Al(OH)3 tip tc thu phn to thnh cc ht mang in m:

Al(OH)3.3H2O + H2O Al(OH)4-.2H2O + H3O

+

Trong khong pH ny, ht keo c th zeta nh nht. Keo nhm tch in m do

hp ph cc anion Al(OH)4-. Ht keo a nhn c cng thc

mAl(OOH).nAl(OH)4-

2.3.7. Stn ti ca cht keo mu trong nc thiTrng thi phn tn ca thuc nhum lin quan n cu trc, bn cht ha hc

ca chng v chu nh hng ca bn cht dung mi, pH mi trng v c mt ca

cc cht ph gia.



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7

2.3.7.1.nh hng ca dung mi:Dung mi c nh hng ln n kh nng ha tan v phn tn ca thuc

nhum. Dung mi khng cc ha tan cc cht khng cc, dung mi c cc c kh

nng ha tan cc cht c cc.

Nc l dung mi phn cc ph bin nht do cu trc c cha nhm -OH. Cc

phn t cht mu c cha cc nhm phn cc nh: -SO3Na, -COOH, -OSO3Na,

-N+H2-HCl, -N

+R3Cl . . .th d tan trong nc. Cc cht mu khng cha cc nhm

tan hay cc nhm trn b chuyn v dng mui canxi, bari th khng tan trong nc.

tng ha tan ca thuc nhum, ngi ta nghin chng siu mn v b sung

thm cc cht ph gia vo hn hp.

2.3.7.2.Sbin i tnh cht thuc nhumDo c mt cc cht ph gia, pH mi trng thay i, nhit . . .m cc cht

mu c th tham gia cc phn ng ha hc lm thay i tnh cht ban u ca mnh:

nh tham gia phn ng ha hc lm thay i mu sc ca phn ng gia thuc

nhum hot tnh vi vt liu; thay i tnh cht ca thuc nhum hon nguyn.

2.3.7.3.Tnh cht keo ca cht mu hu ca s cc cht mu tn ti trong nc dng keo hoc bn keo. Ty thuc vo

bn cht, cu to, kch thc v khi lng phn t ca cht mu hu cm n

dng ha tan hay phn tn trong dung dch.

Khi cc phn t c phn khng phn cc ln v phn phn cc nh th phn t

thuc nhum ring l c th to thnh mixen keo. S lin kt xy ra i vi nhng

thuc nhum m phn t cha nhiu nhm k nc, v d nh thuc nhum

polymethine. Mt vi loi ca thuc nhum ny khng lin kt trong ru nhng

lin kt trong nc to thnh cc mixen lm cho nht tng, di ph hp th mu

b thay i.

Cc phn t thuc nhum c nhiu vng ccbua hydro k nc v mt s

nhm phn cc a nc nh -SO3Na, -OH, -COONa . . . c th tan trong nc,

ru, axeton. . .Ty khi lng v cu to phn t m chng c th tn ti dng

keo a nc hay ha tan to thnh dung dch thc. Cc phn t kh nh nh metyl



46/68

8

da cam m bao gm mt s t vng thm v nhiu nhm phn cc mnh nh -OH, -

SO3Na th khng to thnh mixen.

Cc iu kin khc nh nng cht mu, cht in ly, nhit dung dch c

thnh hng n bn ca cht mu: nng cht mu tng lm gim bn

keo. S c mt ca cc cht in ly c th lm thay i bn ca h keo mu.

Nhit tng lm tng ha tan ca cht mu nn bn keo tng ln [3]. Mixen

ca cc loi thuc nhum - naphton orange kh nh khng to thnh mixen keo

bn mc d xy ra sng t khi c mt NaCl. S lin kt to thnh mixen bn vi

cc kch thc v hnh dng khc nhau c quan st vi benzopurpurin. S to

thnh mixen ph thuc vo nng thuc nhum, mui NaCl: khi nng NaCl

ln th nhng mixen khng l ca benzopurpurin xut hin, nhit cao hn 60o

C

th khng thy to thnh mixen. S to thnh mixen c nhn thy vi thuc

nhum mu vng.

Tm li, s lin kt to thnh mixen ca cc thuc nhum khc nhau dng

nhc khng ch bi cc qu trnh tng t nh s kt hp ca cc phn t cht

ty ra, cc phn t bao gm cc nhm c cc - khng cc . . .

2.3.7.4.Tng tc vi dung miCc keo phn cc th bn trong mi trng phn cc, ngc li cc keo khng

phn cc th bn vng trong mi trng khng phn cc v km bn trong mi

trng phn cc. tng bn phn tn ca cc cht keo trong mi trng khng

c cng bn cht, ngi ta s dng cc cht keo a dung mi, cc cht keo ny c

mt phn hp ph bm dnh vo phn t ca cht cn bo v, phn kia nhng vo

dung mi to thnh h keo bo v.

2.3.7.5.Hiu ng bn ca keo a ncCc cht keo a nc c th lm bn cc sol k nc vi dung mi khc nhau

nh x phng, cht ty ra. . . Cc hiu ng bn hay bo v c vai tr quan trng

trong vic ch to cc h phn tn bn m ui k dung mi dnh vo ht cn lm

bn, cc u phn cc quay vo dung dch. Khi ht va c tch in va b

solvat ha.

Cc cht khc nhau khng c bo v nh nhau, s bo v ph thuc vo

i lc gia cc ht keo. Wiliam, Chang [3] thy rng i lc ca mt s cht keo vi



47/68

9

keo vng khc vi keo cng g rubin, cch bo v l cc ht keo k dung mi b

bao bc bi cc cht a nc, lp lm bn c kch thc cphn t.

Lin kt ca cht lm bn vi b mt k dung mi c th do lc hp dn Van

der Waals hoc lc lin kt ion nu cu t tch in. Tng tc gia cc cu ta

v k dung mi c th gy ra hin tng lm bn hay mt tnh bn gy ra sng t.

Trong trng hp ht c ph kn mt lp cht bo v th cht keo c tc dng

lm bn. Trong trng hp cht keo hp ph km th bn ca ht keo gim v tc

dng bo v nh, cht keo c th gy keo t theo cch to cu ni. Nng cht

keo bo vnh hng n bn keo: nng cht bo v tng th bn ca h

keo tng.

2.3.7.6.Sto bng ln nhau ca cc cht keo tch inH keo c th bn hay km bn khi c mt cc cht in ly v cht keo khc.

ph bn h keo a nc, ngi ta c th s dng cc cht keo tch in tri du

vi u phn cc ca cht keo bo v. S to bng c th xy ra khi cht keo tch

in m c trn ln vi cht keo tch in dng. Khi hai cht keo tch in tri

du tng tc nh vy th s to bng lun lun xy ra. Hin tng tng t xy ra

khi mt cu t ca h l k nc cn cu t kia l a nc yu v c hm lng

khng nhiu qu.

S to bng cng xy ra khi cc cht a in ly b solvat rt km hay chng c

kch thc ln v rt khng i xng. S lng v s phn bin tch cng l

nhng vn quan trng trong s to bng.

2.3.8.c trng ca cchkeo tin ha cht muS keo t xy ra do cht mu hp ph ln cc phc hydrox nhm. Cc phc

hydroxo ny tip tc b thy phn, khi v nh hnh nhm hydroxit hnh thnh,

cng to iu kin thun li cho cc cht mu hp ph vo. Nhm hydroxit phn

t lin kt to thnh bng keo ln hn, li cun cht mu theo cch keo t qut.

Cc yu tnh hng n vic tch loi mu:

-Bn cht tch mu: phng php keo t bng mui nhm ch c hiu qui

vi cc cht mu hu cphn tn, khng tan trong nc. i vi cc thuc nhum

hon nguyn tan hoc hot tnh, nu cc phn t cht mu cng knh, phc tp , c



48/68

10

kh nng to phc vi nhm th phng php ng tin vn c th p dng

c. y c l l hn ch p dng ca keo nhm.

-Cc dng khc nhau ca keo nhm: ty thuc vo gi tr pH m cc dng tn

ti ca phc hydroxo cng khc nhau. Do vy m hiu qu x l cng thay i theo

gi tr pH. Khi pH= 6-8, cc ht keo nhm mang in dng, rt d tng tc vi

cc cht mu mang in tch m hay trung tnh nn hiu qu x l rt cao.

-Cc yu t khc nh: khuy trn dung dch, nhit . . . nh hng n tnh

bn ca cc ht keo, hay ni cch khc snh hng n hiu qu x l.

Bn pha cathode, ion OH-

to ra do phn ng thot kh H2 s chuyn sang

anode cng vi cc phn t cht mu nhng vi tc ln hn do c kch thc b

hn. Cc ion H+

, hydroxo, v keo nhm s chuyn sang cathode. Ion H+

do c kchthc b hn nn chuyn ng nhanh hn cc phn t cht mu, khng tng tc

trung ha in tch vi cht mu. Chng nhanh chng trung ha cc ion OH-. Cc

hydroxo, keo nhm di chuyn chm hn s tham gia cc phn ng hp ph v trung

ha in tch cc phn t cht mu. ng thi cc hydroxo tip tc thy phn nn

tip tc h p ph, trung ha in tch cc anion mu. Cc phn t cht mu nm

trong khu vc anode, s khng b tng tc va chm vi cc ion H+ nn xc sut va

chm c hiu qu vi cc phc hydroxo, keo nhm l rt ln.

Trong khong pH=8 , cc ion OH-ng thi tham gia phn ng thot oxy v

tng tc vi H+, thc y qu trnh to phc hydroxo v keo phn tn tch in

dng.

Keo nhm sau khi hp ph cht mu, di tc dng tuyn ni ca cc bt kh

hai cc anode v cathode s ni ln trn b mt dung dch. Cch hp ph v

trung ha in tch khng ch ch yu qu trnh ng tin

2.3.9.Li ch ca phng php ng tin trong xl nc thi dt nhumNc thi dt nhum c thnh phn phc t p do tnh cht a dng ca ha

cht v cng ngh nhum. c c hiu qu cao trong x l nc thi nhum

cn thit phi s dng kt hp nhiu phng php. S dng ring r cc phng

php ha l, ha hc hn ch tnh u vit ca cc phng php khc.

p dng phng php ng tin trong x l nc thi mang li nhng li

ch sau:



49/68

11

-Chi ph u t cng ngh thp.

-Tiu tn nng lng thp.

-Khng s dng cc ha cht b sung.

-C kh nng tng cao v di lm vic rng.

-Khi nng t p cht, thnh phn trong dng thi thay i ln, ngi vn

hnh h thng x l khng phi iu chnh nhiu.

-Kt qu x l ng tin cy.

-Lng bn gim rt nhiu so vi cc phng php khc. Thun li trong vic

x l bn.

-X l c nhiu loi tp cht trong dng thi.

2.3.10. Cc kt qu nghin cu ca phng php ng tin trong v ngoi ncVit nam, cc tc giTrng Ngc Lin (i hc Bch khoa H Ni),ng

B Trinh, H Vn Khnh (Vin Ha hc) cng b nhiu cng trnh lin quan n

vic ng dng phng php ng tin vi nhm, st anode ha tan x l mt

s cht mu hu c. Cc l thuyt v cch ca qu trnh cng c cc tc gi

t p trung nghin cu nh bn cht ca qu trnh ng t in, cu trc ht keo

nhm. . . . Song vic trin khai thc t vn cn nhiu hn ch.

nc ngoi, ng tin c ng dng rng ri, a lnh vc. Di y l

mt sng dng c th:

a.Xl nc thi ca tu bin

p dng ng tin x l nc thi ca tu bin mang li nhiu kh quan.

X l nc thi c cha kim loi nng, du m, cht rn llng nhm gim chng

n mc quy nh. Vi phng php ny, c th tit kim c 150.000 USD/ tu

bin trong vic x l nc thi nhim. Nc thi c th thi trc tip ra bin, chi

ph gim t 75 - 90% [29]. Mt vi thng s ca nc thi sau x l ghi bng 4.1.



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12

Bng 4.1c tnh nc thi sau x l

Tp cht Trc x l (mg/l) Sau x l (mg/l)

Tng du & m

Cd

Pb

Cu

Ni

Zn

Toluene

Xylenes

Phenol

2500

25

22

2,5

2,0

6,2

23

168

3,4


51/68

13

Leland G. Cole, Jerry Kolodzik, Joseph T, Bishop nghin cu trn thit b

pilot s dng phng php ng tin x l nc thi nhum. Cc i tung

nghin cu y: mu, SS, kim loi nng, du m. Kt qu nghin cu: quan st

bng mt thng th nc sau x l rt trong, mt mu hon ton.

Trc x l Sau x l

COD 1896 mg/l 37 mg/l

TSS 356 mg/l Khng pht hin c

Chi ph 0,72 - 0,99 USD/1000 gallons nc x l

e.Raintech International ( M) tung ra th trng thit bng tin -

Powell Electrocoagulation Systems - ng dng trong x l nc thi. Mt s kt

qu di y thu c khi nghin cu trong phng th nghim v thc t:Cc thng s Hiu sut tch %

BOD

TSS (t st, than, ph sa...)

Du, m, nht trong nc

Nc trong bn

Kim loi nng

Pht pht

Vi khun, virus, nguyn sinh vt

90

99

93 - 99

50 - 80

95 - 99

93

99,99

Tnh a dng v hiu qu ca phng php ng tin cn c th thy qua

cc con sbng di y.

Bng 4.3: Kh nng v hiu sut x l ca phng php ng tin

Tp cht Ngun nc

thi n/cu

Trc x l

(mg/l)

Sau x l

(mg/l)

Hiu sut x l

(%)

BOD C.bin thy sn 40500 750 98,1

TSS n.thi sinh hot 5620 25 99,6

ng Min 287 0,484 99,8

Km - 221 0,14 99,9



52/68

14

Cadimi - 31 0,338 98,9

Nhm S/ x h p 0,30


53/68

1


A. IN PHN SN XUT NHM

1.Gii thiuNhm c bit t nm 1825. Nm 1887 ngi ta sn xut Al bng

phng php in phn. Sn lng Al trn th gii khong 2x107 ton/nm,

in phn sn xut nhm chng th 2 sau in phn NaOH-Cl.

Nhm l kim loi nh, bn nn c ng dng nhiu trong cng ngh. S

dng nhm r tin, b mt nhm c th x l bng oxi ho to nn b mt

chng n mn.

Phn ln Al s dng dng hp kim vi Mg, Cu, Si, Zn, Ni, Fe. Nhng hpkim quan trng nht dura (94% Al, 4%Cu, 1,5% Mg, 0,5% Mn), silumin (hp

kim c Al + 12% Si).

Khng th sn xut trc tip Al t Al2O3 v Al2O3 nng chy nhit rt

cao (2050oC), khng dn in. Nhm c sn xut t qung bauxite, c th

cha Si, cc oxit kim loi khc c bit l st. Qung chuyn thnh nhm

nguyn cht bng phn ng sauAl2O3.3H2O + 2NaOH = 2NaAlO2 + 4H2O

u tin qung c x l bng NaOH, p sut cao. Nhm ho tan thnh

dng aluminate, oxit st khng tan, Si cn li dng natri aluminium silicate,

lm mt mt nhm. Hm lng Si cng t cng tt. Sau khi lc, oxit nhm

ngm nc kt ta, NaOH c ti s dng. Al c ra sch v gia nhit

1200oC tch nc. Bc tip theo l chun b dch in phn. Nu s dng

C kh Al th ch phn ng nhit rt cao. Hu ht Al c sn xut

bng in phn Al nng chy vi Na3AlF6.

Nhm nng chy 2020oC, to nn dung dch nng chy khng dn in.

Nu ho thm 15% khi lng Na3AlF6, nhit ch 1030oC, mi trng

ny s dn in. y l cng ngh ca Hall (M) v Heroult (Php).


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2.Cc yu cu i vi Al2O3-Rt tinh khit, khng cha nhng nguyn t c in th tiu chun dng

hn Al.-C hot tnh cao, tnh cht ny th hin tnh tan cao trong cryolite. Nu

ho tan thp th Al2O3 lng ng xung y b.

-Khng ht nc. Do mng tinh th Al2O3 khc nhau nn tinh th ht nc

khc nhau. Khi nung nng Al2O3 s mt nc v mng tinh th bin i.

Al2O3.3H2O Al C225o

2O3.H2O .Al C500o

2O3 .Al C950o

2O3

Al(OH)3 (AlOOH) 2 .Al 2O3 .Al 2O3

3.Sn xut cryolite3.1.Sn xut bng phng php acid

CaF2 + H2SO4 = 2HF + CaSO4

SiO2 + 6HF = H2SiF6 + 2H2O

H2SiF6 + Na2CO3 = Na2SiF6 + CO2 + H2O

12HF + Na2CO

3+ 2Al(OH)

3= 2(3NaF.AlF

3) + 3CO

2

3.2.Sn xut bng phng php kimBc 1:

CaF2 + Na2CO3 + SiO2 = CaO.SiO2 + 2NaF + CO2

CaF2 + Na2CO3 + Fe2O3 = CaO.Fe2O3 + 2NaF + CO2

Bc 2

NaAlO2 + 2 H2O Al(OH)3 + NaOH

Al(OH)3 + NaF AlF3 + NaOH

AlF3 + NaF 3NaF.AlF3

Cryolite khng cha cc nguyn t c in th dng hn Al, ho tan tt

Al2O3, khng tc dng ho hc vi in cc.

3.3.Mt s tnh cht ca hn hp cryolite v Al2O3



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-Hai thnh phn chnh l Al2O3 v 3NaF.AlF3, nhiu nghin cu thay bng

cht khc nhng khng c kt qu.

-Tnh dn in cao, nht thp, khi lng ring nhit cao nh hn

Al-Trong dung dch in phn nng chy Al, thnh phn NaF v AlF3 khng

phi lc no cng ph hp vi l thuyt ca cryolite, trong qu trnh in

phn n gim dn. Theo chiu cao ca bin phn thnh phn ca hai cu t

ny khng ng nht. T s NaF : AlF3 thng bng 3. Khi nh hn 3, dung

dch c tnh acid.

-Trong sn xut, lng Al2O

3thng 8%. Qu 8% Al

2O

3bt u kt tinh

to ra cn y bin phn. Thm AlF3, CaF2, MgF2iu chnh cc nh

hng xu.

-Khi lng ring ca hn hp

1000oC :

NaF : 1,961 g/cm3

Na3AlF6 : 2,112 g/ cm3

Al : 2,289 g/ cm3

Khi lng ring ca cryolite c tnh theo cng thc

Klr = 2,088 0,00088 (t-1000)

Khi lng ring ca Al lng

Klr= 2,382 0,000273 (t- 659)

4. Cchin phn4.1.Cch

Hin c 2 cch

+ ion Na+ phng in trc cathode ri t mi xy ra cc phn ng

khc

2 Na3AlF6 6 NaF + 2 AlF3

6 NaF 6 Na+ + 6 F-



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cathode

6 Na+

+ 6e 6 Na

6 Na + Al2O3 2 Al + 2 Na2O

anode :6 F

-- 6 e 3 F2

3 F2 + Al2O3 a Al2O3 + 1,5 O2

O2 + C 2CO

O2 + C CO2

Khng gian cathode giu Na2O, vng anode giu AlF3

3 Na2O + 2 AlF3 6 NaF + Al2O3

+ ion Al3+

phng in cathode

Phn hu cryolite

3NaF.AlF3 3 Na+

+ AlF63-

Al2O3 Al3+

+ AlO33-

Cathode : Al3+

+ 3 e Al

Anode :

2 AlO33-

- 6 e Al2O3 + 1,5 O2

O2 + C 2 CO

O2 + C CO2

Trong mi trng nng chy, c nhiu cation, anion. Chuyn n cathode

c Al3+

, Na+,Al

+. Chuyn n anode c F-, AlF6

3-, O

2-, AlO3

3-.

4.2. Cc phn ng cathodeAl

3++ 3 e Al

Na+

+ e Na (khi mt dng in cao)

Cc phn ng khc

Al3+

+ 3 e Al

2 Na+

+ e Na2+



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Al+ + e Al

Na2+

+ e 2 Na

Cc phn ng anode

2 AlO33-

- 6 e Al2O3 + 1,5 O2

AlO2-

- 2e Al2O3 + 0,5 O2

4.3.Cc phn ng ph-Al cathode nng chy tan trong criolite to ra hp cht Al ho tr 1

Al + Na3AlF6 3AlF + 3NaF

-Na to ra vng cathode tc dng vi dung dch in phn sinh ra NaF

-To ra Al4C3 4 Al + 3C Al4C3

5.Thng in phnHnh di l thng in phn nng chy Al t qung Al2O3 vi cryolite.

Thng in phn lm bng thp khng r, bn trong bc nhm, cch nhit tt

m bo khng tn tht nhit. y thng c ph bng C khi, c li l

cc thanh thp gim in tr. y chnh l tip in cho cathode nhm.

Hai bn thnh c ph bng than antracite.


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Thin cc tng t -4,5V n -40 - -60V do hnh thnh lp kh, F hay CF3

trn b mt anode. Thng thng gm 200 cell, tng din tch anode l 15 m2.

Mt dng ti thiu l 1A/ cm2, dng tng cng l 150KA. in thin

cc ph thuc vo nng Al v n s quyt nh lng cu t trong dung

dch. V dng in ln, nn t trng to ra cng s ln. Dng t trng s

to nn b mt tip xc pha Al/ dung dch in phn.

Hiu sut dng in 85 90%. Nng lng cn thit 14000 16000 kWh /

tn nhm.



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B. TINH LUYN Zn

1.L thuytn phn tinh luyn kim loi da trn nguyn tc: in phn dung dch

hoc mui nng chy ca kim loi . Thng s dng anode khng ho tan.Phn ng:

Phn ng trn anode

Dung dch in phn thng l mui sunfat ca kim loi. Acid H2SO4c

la chn v r tin. Trong nhiu qu trnh, kim loi thng cha trong qung

oxit hoc sunfit vi hm lng khng ln. Vic lm giu l cn thit. in

phn tinh luyn l bc sau cng.

Chun b nguyn liu thng qua cc bc

-Lm giu qung: tch cht thi bng tuyn ni, lm tng nng ca mui

sulfit hay oxit kim loi.

-Nung: chuyn kim loi dng sunfit sang dng oxit c th tan trong acidH2SO4.

-C c cht tan: dung dch thu c dng sulfate, c cc tp cht khc.

-Tinh ch: loi b cc tp cht c in th dng hn (c th kt ta cng

vi kim loi, gim tinh khit ca kim loi, hydro phng in). Loi b cc

tp cht bng cch tng pH ca dung dch, kt ta bng H2S.

-in phn: kt ta kim loi ln cathhode trong thng phn ng. Khi O2 cmt anode, nng ion kim loi gim, acid ca dung dch in ly tng

ln, dn n gii phng H2ng thi vi kt ta kim loi. Thng thng phi

b sung lng ion kim loi.



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2.Tinh luyn ZnLuyn Zn thng dng nht l in phn dung dch Zn sulfate. Sn phm Zn

thu c c tht c 99,99%, t mt mt Cd hn cc phng php tinh

luyn cin khc.

Phn ng cathode, kt ta Zn:

Oxy thot ra trn in cc khng tan

Do qu th H2 trn Zn rt cao nn Zn c th kt ta trong mi trng acid

vi hiu sut rt cao. Th kh ca Zn2+ m hn in th kh ca H+.

C mt cc tp cht khc, chng s kt ta ng thi vi Zn. Trn cathode

c nhng v tr c qu th H thp. Qu trnh thot H xy ra mnh ng thi

vi ho tan Zn c kt ta (theo cch pin cc b). Cc tp cht nh Cu,

Bi, Ge v Sb khng ch lm gim hiu sut dng m cn ngn khng cho Znkt ta. V vy mc ch x l qung Zn to ra dung dch Zn sulfate khng

c tp cht, nh hng khng tt n phn ng cathode.

K thut in phn

Cc thnh phn c trong qung Zn nh hng n phng php x l dung

dch ZnSO4. ZnSO4 tch ra theo phn ng

Vi qung sulfide, cn phi nung chuyn thnh dng oxit

Tp cht trong qung Zn c chia lm 3 nhm chnh

1.Fe, Si, Al, Sb, Bi, Ge, Sn

2.Cu, Cd, Ni, Co



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3.Pb, Ag, SiO2

Khi ho tan ZnSO4, acid t do gim, pH tng. Nh vy Fe(III) s kt ta,

Al v mt phn Cu dng hydroxit. Fe(OH)3 c din tch b mt ring ln,

Sb, Bi v Ge s h p th ln b mt Fe(OH)3 v tch khi dung dch. As dng khng tan Fe4O5(OH)5As. Fe(OH)2 kt ta pH 6,5, ti gi tr pH ny

Zn(OH)2 cng kt ta. Do vy, nn oxi ho Fe2+

thnh Fe3+

.

Ni2+

, Co2+

cng phn ng vi MnO2pH thp hn, to nn ion vi ho tr

3, kt ta dng hydroxit, Co(OH)3 v NiOOH cng c tch ra mt phn.

Trong qu trnh in phn, MnO2 to ra do phn ng

Cc tp cht nhm th 3 s khng tan, nm trong dung dch lc ra.

Kt ta cha cc tp cht nhm 1, 3 v mt phn nhm 2, tch ra bng cch

lc. Tch tp cht nhm 2 b kh bi Zn bt

Sau khi x l, nng Zn trong khong 120 170 g/dm3

, acid t do 150-200 g/dm

3. Nng ion kim loi trong dung dch in ly th hin bng sau



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Vt liu cathode thng l tm Al, dy 4-8mm. Zn bm ln Al km nn d

dng tch ra sau khi in phn. Anode ch dy 5-10mm, kch thc 100 x 600

mm. Thi gian lm vic 1,5 2 nm. Khi anode ch c 1-2%Ag, thi gian s

dng 3-4 nm. Thi gian in phn 10 24 h, nng Zn gim xung 45 -55d/dm

3. iu kin in phn

Mt dng cathode :400 700 A/m2

Hiu sut dng : 88 92%

Th : 3,3 -3,6 V

Nhit : 30 40 oC

Tiu thin nng : 3000 3500 kWh / tn

Sn xut 1 tn Zn cn : 4kg MnO2, 16 kg Zn bt, 62 kg H2SO4.

i



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C. TINH LUYN Cu

1.L thuytng sn xut bng cc qu trnh luyn kim cha nhiu tp cht, thng

0,5 2%. Tp cht nh hng xu n tnh cht c, in ca Cu. 0,15% Phoc 0,5 % As s gim ng k dn in. V vy, ci thin tnh cht in

ca Cu l l do chnh ca in phn tinh luyn.

L do th 2 ca tnh luyn in ho l tch cc kim loi qu nh Au, Ag,

Pt, Pd . . .

Cc tp cht c chia lm cc nhm

1.Ni, Co, Fe, Sn, Zn, Pb

2.Cu2O, Cu2S, Cu2Se, Cu2Te

3.Au, Ag, Pt, Pd, Se, Te

4.As, Sb, Bi

Cc phn ng chnh in cc

T p cht nhm 1: thin cc m hn ca Cu, s ho tan cng vi Cu,

chuyn vo dung dch. Do c anion sulfate trong dung dch nn ch sulfate to

nn bn ca anode. Cc kim loi khc nh Ni, Co, Sn v Zn s tch lu trong

dung dch, v th ca n m hn th ca cathode. Tuy khng c nh hng

xu nhng cn phi nh k tch chng ra khi dung dch. Ion Fe2+ do ho tan



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anode to ra, nhng s khng kt ta do th m hn so vi th ca cathode.

T phng trnh Nernst

th ph thuc vo t s Fe2+ / Fe3+. Nu nng Fe3+ thp hn Fe2+, in

th cn bng s m hn in th anode, Fe2+ b oxi ho thnh Fe3+. Nng

Fe2+

gim, nng Fe3+ li tng. Fe3+ li b kh thnh Fe2+ ti cathode. Nu

hai phn ng ny xy ra s tiu hao nng lng in ca c qu trnh.

Cc tp cht khng tan ca nhm th 2 nh Cu2S, Cu2Se, Cu2Te khng b

ho tan anode nhng sa lng, to bn anode. Ch Cu2O c th b ho tan theo

phn ng

V th, mt na lng Cu b ho tan trong dung dch in ly dng ion

Cu2+

, mt na kia to thnh bt mn, c th phn ng vi O2 v H2SO4, mt t

to mn anode.

Kim loi nhm 3 nh Au, Ag, Pt, Se v Te cng to mn anode. Chng bn

hn Cu, khng tan v hnh thnh mn anode.

Cc tp cht nhm 4 nh As, Sb, Bi lm gim ng k cht lng ca Cu

cathode. Chng kh tch v thin cc xp x vi Cu, nm gia th ca H v

Cu. Tuy nhin, nng ca chng nh do vy, th kt ta m hn so vi th

ca cathode. Trong mt iu kin no y, chng khng b kt ta. Khi nng

ion Cu gim, n kh kt ta. Mc khc, Sb, Bi c th phn ng vi As tp

mun arsenate tan, to bt mn trn dung dch, lm kh khn trong thao tc.



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2.K thut in phnAnode Cu 99 95%. Din tch khong 1 1,5 m2, rng 40 50 mm, khi

lng 300 350 kg. Anode dy 1mm, nng 5 kg. S lng in cc ph

thuc nng sut ca nh my.

iu kin in phn

-Mt dng cathode :200 300 A/m2

-Hiu sut dng : 94 96 %

-in th : 0,25 0,35 V



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-Nhit : 55 -60 oC

-Nng lng tiu hao : 250 360 kWh/t

Sau in phn, cathode Cu t 99,97 99,99 %.

Trong qu trnh in phn, dung dch s tch lu dn Ni, Sb, As. Cc tp

cht ny s ly ra trong giai on ti sinh. Bn anode chuyn i x l tip.

in phn tinh luyn Cu l mt qu trnh in ho, v l thuyt thnh phnca dch in phn khng thay i trong qu trnh. Nhng thc t l c bin

i. Trc ht, dch in phn acid s ho tan mt lng Cu anode khi c O2,

iu ny s lm tng nng ion Cu2+, nng acid t do s gim. Th 2, tp

cht trong anode Cu khng i vo bn m lu li trong dung dch, gp phn

lm gim nng acid t do.



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3.iu chnh dung dchThc t c 2 cch hiu chnh thnh phn v lm giu dung dch.

Cc th 1 bao gm vic tch loi Cu, As v Sb bng kt ta cathode trong

mt thng in phn khc vi anode khng ho tan. Qu trnh ny lm tngnng acid t do sau khi dung dch c c c, ti y Ni, Fe v Cu sulfate

s kt tinh.

Phng php th 2 : trung ho acid H2SO4 t do bng qu trnh ho tan Cu.

Cu sulfate s kt tinh trong dung dch bo ho. Dung dch cn li mang i

in phn trong thng c mng ngn tch Cu, As v Sb. Tch Ni, Zn, Fe

bng c c.

Sau tinh luyn, dung dch in phn thng ch c acid sulfuric, tip tc

hiu chnh dung dch bng qu trnh ho tan Cu.

X l mn anode

Mn anode cha nhiu kim loi qu him, hp kim nh nhm Pt, Au,Ag,

Se, Te, . .

Cu tch ra khi mn, ho tan trong H2SO4 long nng, c khng kh, sau

, Se v Te c tch ra. Tip theo, sau khi thm natri cacbonat, natri nitrat,

ct thch anh, mn c nng chy to nn hp kim 93% Ag, 3% Au, 1% Cu,

0,05% Pd, 0,03% Pt, cc kim loi vt khc.

Ag vi tinh khit 99,99% c tch ra khi hp kim bng qu trnh ho

tan anode trong dung dch Ag nitrate. Do mt dng trao i cao nn Ag kt

ta ln in cc vi bm dnh rt km, cu trc thng in phn tinh luyn

c cu trc c bit thu mn anode.

Sau x l tinh luyn Ag, mn anode cha 95% Au, 5% Ag, 1% Cu, Pd, Pt

v cc kim loi khc. Sau khi nng chy v cn tm, anode a vo bin

phn, dung dch HAuCl4 v acid HCl t do. in th kt ta Au cao 1,4V, tt

c cc tp cht tr Ag dng AgCl, s b ho tan v lu li trong dung dch.


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Khi lng Pt, Pd t c 75 g/dm3, dung dch cn thay th. Cc kim loi

ny thu hi dng mui ammonium ; (NH4)PdCl6, (NH4)2PtCl6. Kh cc

mui kim loi ny, thu c Pd v Pt.

Ti liu tham kho

[1]. Konstantin I. Popov, Branimir N. Grgur , Stojan S. Djokic,

Fundamental aspects of electrometallurgy, 2002.

[2]. D. Pletcher, F. C. Walsh,Industrial Electrochemistry , 1993.


[4]. C. M. A.Brett, A.M. O.Brett, Electrochemistry-Principles, Methods

and Applications, 1993.

cong nghe dien hoa

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