Xác định lượng vết Asen bằng phương pháp điện hoá hoà tan

d u n g d i c h nong do dang oxi boa trong dung dicb nong do kim loai trong tbuy nga n h| so khueeh tan cua dang oxi hoa trong dung dicb he so kbuecb tan cua kim loai trong tbuy ngan die

TRl/OliCx ±)hl PiOG I'ObG HUP H^i - i^OI

T r a n - Hiiu - E o a n

f S ^ > , V.L^///^/lJ

x l c ± J i m LU^dNG 7ilT Aol!;W

X *

Ql^(} GAG PLbdEG PEAP ±>IEb hO^ KG A 'J^^NT

( 1 04 03 - Hoa pban tieb )

Luan an pho tien si kboa hoc

3W-^

Nb5ng ngufdi budng dan kboa hoc :

Tran CbUdng Huyen , Pbo tien si , Pbo giao sif

Tii Vong Kgbi , Pho tien si , Pho gieo su'

Cbu Xuan Anb , Pbo tien si

Ha-noi - 1984

3 - 0 / Cac phu'dng p b a p d i n b bijfdng n g b i e n cu'u

3 - C l - Phu'dng p b a p cu'c pbo 2 3

3 0 2 - Phiidng p b a p von-ampe vong 2 5

4.0.3 - Pbam vi sxl dung cac dien cue so sanb 57

4.1 / Tinb chat dien boa cua asen 59

4.2 /Xac dinh asen bSng pbu:dng pbap dien boa boa tan anot

4.2.1 - Cac tin bieu boa tan anot cua dong 67

4.2.2 - Hoa tan anot he Cu-As 72

4.2.3 - Hoa tan anot be Cu-Au 73

4.2.4 - Hoa tan anot be Cu-As-Au 75

4.2.5 - £'ieu kien xac dinb asen tbeo be Gu-As-Au

bS.ng pbtfdng pbap dien the tbdi gian hoa tan anot 76 4.3 / Xac dinb asen bang pbifdng pbap dien hoa boa tan catot

4.3.1 - Xac dinb asen tbeo he Gu-As bSng pb^idng pbap

von-ampe boa tan catot 81 4.3.2 - Xac dinh asen tbeo be I-Gu-As bSng pb\:fdng pbap

von-ampe boa tan catot , dung dien ciic tbuy

ngan tinb 85 4.3.3 - Xac dinb asen theo he I-Cu-As bling phudng pbap

dien the tbdi gian boa tan catot , dung dien

ci/e mang t b u y n g a n 9 5

4.4 / Xac dinb asen bSng pbi:fdng pbap von-ampe boa tan

xoay cbieu boa tan bae bai 100

4.5 / So sanb cac pbiidng pbap di ngbien cu'u

Ban ve cd ebe 101

5 AP DbNG THUG T^

5.1 / Xac dinb triic tien luldng vet asen trong cac mau

tbT^c te 110 5.1.1 - Pban tich boa chat tinh kbiet 113

5-1.2 - Pban tieb nufde 115

5.1.3 - Pban tieb cac doi tu:dng sinb b9e 116

5.2 / Xac dinb bam l-\X6nQ: asen sau khi cat dudi dang AsH^ 119

6 idlT LUAN 120

— 0

-1984

d u n g d i c h

nong do dang oxi boa trong dung dicb nong do kim loai trong tbuy nga n h| so khueeh tan cua dang oxi hoa trong dung dicb

he so kbuecb tan cua kim loai trong tbuy ngan dien the tbdi gian boa tan ( phudng pbap ) the dieu ci;c ; bien gidi tin cay

the oxi boa kbit tieu ehuan the ti2& song cua song cu:c pbo ;' the itng vdi nUa tbdi gian cbuyen the dien pban

the dinh the dinh anot va catot • ' •

bien gidi tin cay bieu dien tbeo 6.6n vi tijfdng doi tbuy ngan ; dien ciic tbuy ngan tinb ( dang tree ) dien ci/c mang tbuy ngan tren dia than tbuy tinb dong boa tan trong pbiidng pbap ±)THT

dong boa tan anot va catot trong phu^dng pbap BTHT dong dinb

dang khu' cua chat boat don^: dien dang oxi boa cua chat boat dong dien dien lu'dng , tij:dng ditdng vdi ludng kim loai da bi ket tua tren dien ciic

; do nbay ve dong dien cua may ghi : dien eiic ealomen bao boa ( dung dicb KCl ) : dien cu'c cbi sunfat

: nbiet do dung dicb

: dong dien trung binh trong pb;:rdng pbap cu'c phS

: dong kbuecb tan gidi ban trung binh : bing so toe do cua pban u'ng dien hoa d dien the tieu ehuan

: cbieu day cua mang tbuy ngan

*

: toe do ehay cua tbuy ngan trong mao quan cua dien eiie giot tbuy ngan

so electron tham gia phan ling d dien cu:e ;

so Ian tbi nghiem doc lap ban kinh gi9t tbuy ngan giay \ sal so binh pbiidng trung binh bay

do lech ehuan

•

: so vdi : tbdi gian ; cbu ky giot tbuy ngan : tbdi gian dien pban

: toe do quet the : gia tri trung binii cong cua n Ian thi ngbiem : he so cbuyen cua phan u'ng dien cue

: cbieu day Idp kbuecb tan : tbdi gian cbuyen

= 1.10'^ %

1.10 -4 ol

1.1C~^ m l.lC 1.10

•9

• o

0

-J ^ n g ed the dong vat va thuc vat c6 asen Vdi lUdng

rat nbo , asen c6 tac dung kieb tbieb qua trirJri song NbUng

neu vUdt qua mot gdi ban nao do , no trd tharih chat doc HgUdi

bi ngo doe asen kinh nien se roi loan bo may tieu hoa , cac

niem mac bi hoai va eo the tu: vong -Asen ehiem -10 i khoi

a • •

lUdng vo qua dat , cbu yeu ton tai dUdi dang sunTua nbu: reanga ( As^S ) , oepimen ( As^S^ ) va mim Ian Ion vdi quang kim

loai kbae Khi Ifehai tbac qu|ng , pbai cbu y den asen Asen

dude sU dung trong y hoc ,^tbuoe da , san xuat tbuy tinln , v

vat lieu ban dan v.v Trong nong ngbiep , dan xuat cua asen lam thuoe trU sau cbo cay trong Trong boa hoc pban tich ,

asen la thanb pban quan trong cua nhieu tbuoc tbu; huu ed quy

nbu : asenazo , berilon IV , sunfaxazen , thoron I v.v

San ludng asen cua the gidi tu bin nSm 1940 la 46.000 T / 57 /• Asen va cae ebe pbam cua no d^^X^c san xuat hang nam' , bSng

nbieu con dUdng kbae nbau , bi thai dan ra song , ho , bien

Xac dinb ludng vet cac nguyen to , trong do c6 asen , la mot trong nbung van de tbdi sU cua boa hoe pban tich nude ta nb§m phuc vu nbieu cbUdng trinh phat trien kinh te , kboa hoc

ky tbuat va bao ve moi trudng Be laioi viec nay , ehung ta

thudng dung pbUdng pbap tr§c quang , pban tich quang pbo pbat

xa I^oSc hap tbu nguyen tu! Phudng pbap dien boa boa tan da bat dau phat buy tac dung d mot so phong thi nghiem , nbung

nhin ehung , no chUa dii6c pho bien rong rai

Tren the gidi , dien boa boa tan da tr5 tbanlj mot phudng pbap pban tieb vet quan trong trong khoang 20 n^m nay tfu diem noi bat cua phudng pbap nsj la do nbay rat cao ^

CO the so sanb d\l6o vdi do nbay cua pbudn^

pbUdng pbap kieb boat ndtron / 3914,35^^,55 / ina trang bi

va ky tbuat lam viec lai kha ddn gian I'o eo the tbUe bien ngay ca tren cac m.ay cue pbo thong tl!iudng da eo tai nbieu pbong tbi ngbiem thuoe cac bo Bing phudng pbap dien hoa boa tan , ngudi ta da xac dinh dude nbieu nguyen to trong nbieu doi tUdng f 3»14,53 7 • Tuy nbien , viec xac dinh mot so nguyen to , trong do eo asen , can pbai ngbien euu Jhem

Hien nay , viec xac dinb asen thUdng dude tbue bien bllng pbUdng pbap tr4c quang dung bae-diaylditbioeacbamat / 1,18,

44, 47 7 - Bo la pbUdng pbap tieu ehuan cua nbieu nude va nbieu tS chuc quoc te / 18,24,25,47 / Bo nbay -5-10"''^mo 1/1

TbUc te ngbien cUu va Ung dung trong nUde mUdi nSm qua ehung to la , b^ng phudng pbap dien boa boa tan , cbu yeu la von-ampe boa tan , ehung ta da xac dinb dude nbieu nguyen to

d vung nong do 10"- lC"\ol/l , tru asen va vai nguyen to kbae Neu ngbien euu thanb cong mot phudng pbap xac dinh asen c6 do nbay , do ebon loc vao ed nbu cac phudng pbap xac dinb Gu,Pb,Cd,Zn ( cac nguyen to sd trudng cua dien boa boa tan ) thi ta de dang tboa man nbieu nbu eau thue te cua dat nudc , trong do c6 nbu eau cua cong tac bao ve^moi trudng 3di vay , ehung toi ebon de tai ngbien eUu la :

Xac dinb lUdng vet asen

bSng cae pbUdng pbap dien boa boa tan

Asen c6 kboi ludng nguyen tu la 74,92 d.v.6 , mang.so tbu tu : 33 trong bang tuan bo^n Mendeleep m thuoe nb6m

V A , cbu ky 4 , n5.m gilia Ge va oe Asen eo tinh chat trung gian giua a kim va kim loai l'o c6 nhieu tinh chat dien boa d^c biet , pban ung dien cue kbong tbuan nghich Do

kbong giong nhu viec xac dinb Cu,Pb,Gd,Zn Sau khi khao

sat nhieu he , dSe biet la eac be bae ba C U - A S - A U va I-Gu-As,

a ' a a a a '

ehung toi ebon ra mot pbUdng pbap xac dinh ludng vet asen dap

ung dude cac yeu eau da neu a I^o da dude dung de xac dinh

ham ludng asen trong mot so mau tbue te

Trong qua trinb ngbien cUu , ehung toi con phat bien

mot so van de eo y nghia cbung trong linh vUe pban tich dien

boa boa tan

0 0

-2 T6i^ G ^b M T A I LI^U

2.0 / 2£l_l2£^lL-gẬ ^^^^^^ ^^^^ ^^^ ^^^-^ l^<JJ^g ^ê asen

» Nbung thong tin quan trong ve cae pbUdng pbap bien dai xac dinh ludng vet eac nguyen to , trong do eo asen , de

dang tim tbay trong eac tai lieu cua Korenman ỊM / 15 /,

BAoracbevxki lụ V / ^0 / va Koch 0 .^ / 44 / Sau phudng pbap trie quang eo y nghia nbat trong viec xac dinb lUdng vet asen da dude mo ta ty my trong cbuyen khao cua Bavko A K

va Pilipenko Ạ T / 1 7

Asen CO the dudc xac dinh 3 dang xanb cua pbuc di da

axit asenomolipdic vdi chat kbu la bidrazinsuniat boae SnCl^

f 1 7 ' Tinh chat phUc nay tUdng tu tinh chat pbuc di da cua •

Ge , Si, dS.c biet rat giong phUc di da cua P Trong eac doi tUdng tu nbien va ky tbuat , ham ludng photpho thudng Idn bdn asen vai ebiie den vai tram Ian Bdi vay,phudng pbap nay trong tbue te pbai di kem vdi mot pbUdng pbap taeh kbae ,

thudng la chiet hoSc cat Gong viec nay cbiem nbieu tbdi gian

va can dung moi bUu cd nbu GHClv , CCl^ v.v

PbUdng pbap xac dinb ludng vet asen dung tbuoc tbu dietylditbiocaebamat la pbUdng pbap tot , dude cong nban la phudng pbap tieu ehuan cua ISO , SEV , Lien xo , hy { 18, 24,25,47 7 v^-v- • luan 'kxi sU dung phudng pbap nay lam pby:dng pbap doi ehung

bac-NgUdi ta dung kem kim loai khu asen trong moi trUdng axit thanb asin ( AsH^ ) roi bap tbu no bIng dung dieb bac-dietylditbiocacbamat pha trong piridin Pban Ung xay ra nhu

7 (G2H^)^NGSS 7^As

Kbi AsH-z trUde khi vao dung dich hap fhu dude dan qua Idp

3

giay ( bo§c bong ) tam cbi axetat de lam sach vet H^S Gudng

do mau cua dung dicb hap tbu ty le vdi nong do asen Bo

nbay -5.10"'^ mol/1 - Bung dicb thuoe tbu eo mui h^e va rat doc - No de bi pban buy dudi tac dung cua anb sang va nbiet do,gay kbo khan cbo viec bao quan

Co tbf xac dinb asen bSng pbUdg_pbap so mau vet tren

giay 7 1 7 • ^ ^ay ^ asen dude khU bing kem kim loai trong

moi trudng axit thanb asin Khi nay di qua giay tam cbi

axetat de lam sacb vet H^S roi den giay tarn HgBr^ boae

HgCl^ Ham ludng asen dUdc danb gia qua viec stb sanb cudng

do mau cua giay tam muoi tbuy ngan Ung vdi mau phan tich va mau doi cbieu - Cong viec nay lam bing m§t thudng , sai so

cbu quan Idn Koch 0- G. £ ^^ J kbong xep pbUdng pbap nay vao hang cac pbUdng pbap dirib ludng asen Tuy theo ludng asen bi hap tbu tren giay , cae hdp chat c6 mau kbae nbau

se d^i6Q. tao thanb [ \ 7 '- H(HgBr)^As - mau vang , (HgBr)-,;As • mau nau , Hg^As^ - mau d^ii Hien nay cac pbong tbi nghiem

trong nude sU dung bai loai tbiet bi Gbung kbae nbau cbu yeu d each d|t giay tam muoi tbuy ngan PbUdng pbap nay

kbong du do nbay de xac dinh asen trong toe va mau vi bam

ludng asen trong cae doi titdng nay qua nbo va ludng mau can pban tieb qua Idn , kbong eo dieu kien cung cap Kbi pban tieb nude , pbai dung bang lit va qua giai doan boc bdi rat

au

/

Cac pbUdng pbap kbae it c6 y nghia trong tbiie tien

nude ta Chang ban phudng pbap dung di thiol va butylrodamin

bi P va Si can trd

PbUdng_nba£_auan2_pbo_ba2_tbu_ngu2|n_tU

Binh luat Kiecsop la ed s3 cua pbUdng pbap nay - Tbeo

do , moi nguyen tU se bap tbu bUc xa c6 do dai song ehinh

bing do dai song cua bUe xa ma no phat ra kbi d trang thai kieb tbich Cudng do bap tbu ty le vdi nong do nguyen tu can xac dinb Be tbUc hien pbUdng pbap nay , ve nguyen tac ,

ta pbai c6 moi den rieng cbo moi nguyen to can xac dinb Ca tot cua den nay dudc ebe tao bing ehinh nguyen to can xac d dinb NgUdi ta dUa mot nguyen to nao do den trang thai nguyen

tu bing nbieu each , pho bien nbat la dung ngon lUa

Phudng pbap quang pbo hap tbu nguyen tu eo do ebon loc cao, toe do pban tich nbanh nen dUdc sU dung rong rai d cac nude ti'en tien Vdi ngon lUa axetylen - kbong kbi va den ca-tot asen cbo vacb 189,042 nm ,c6 the pbat bien dUdc nong do asen trong dung dicb thap den 1.10" % , tuc -lCu^^;;r2C7 •

S nUde ta , cbi vai pbong tbi ngbiem dau nganh va mot

so trUdng dai hoc Idn mdi thUc bien dvl^c phudng pbap nay vi tbiet bi rat dit Hdn nua , viec s ^ du bo den kbong pbai

de , ma tuoi tbo cua moi den lai eo ban

' a a

?^!i^-S_E^ap_quang_pbo_£h8t_xa_nguyen_tu

Nguyen tu kbi dUdc dUa len trang thai kieb tbieb tfhi pbat xa DUa vao viec ngbien cUu pho vacb cua bUc xa , ta

CO the dinh tinh va dinh ludng mot nguyen to nao do Tuy

tbeo tinb chat nguyen to can xac dinb , doi tudng phan tieb

, eau tao tbiet bi ma n,gudi ta dung cac nguon kieb tbieb

kbae nbau : ngon lUa ( 2.000 - 3-000 ^K ) , bo quang 6.000 "^K ) , tia dien ( 10.000 - ^0.000 ''K ) , laser (7-000-8.000 ^K ) Koch 0 G / 4 4 7 cbo biet , lUdng asen thap nbit CO the pbat hien khi dung nguon ho quang li 1 (ug -Tbeo Indicbenko L N 7 10 7 ,c6 the pbat bien dUdc 0;i^03 % As

(4.000-trong khoang vat nbd vacb 23^,984 ma , eUdng do manh nbat

Hien nay 5 nUde ta,cae may quang pbo eo nguon laser rat hiem Vdi eac may quang pbS pbat xa thong tbUdng dung nguon

bo quang tbi do nbay kbong tboa man de pban tich nbieu doi tUdng tbue te ma 5 do ham lUdng asen cbi vao khoang 1 ppm -

1 ppb

PbUdng 2i^a£_kich hoat_ndtron

PbUdng pbap kieb boat ndtron la mot trong eac phudng

pbap pban tich pbong xa 8 pbUdng pbap nay , ngUdi ta bien cae nguyen t6 can xac dinh tbanli cac dong vi pbong xa nban tao nbd eac pban Ung bat nban kbi cbieu mau ngbien cUu bBng cac bat • electron , ndtron , proton , hat nban heli v.v

CO nSng ludng cao va tiep sau do , do do pbong xa cua ehung Phudng 'pbap nay eo do nbay rat cao ( 0,01 ppm - 0,1 ppb ) /" 15,20,44 7 • KHi cbieu mau bing dong ndtron 10 n-em'^^.s" , gidi ban dUdi cua sU xac dinb asen la 2 ng /" 44 7 • i^9 -^ nbay nay tboa man nbu eau xac dinh asen trong bau bet cac doi tudng Vdi pbUdng pbap kieb boat ndtron , Vasen da cbo biet

•

bam ludng asen trong mot it toe eon sot lai cua Napoleong

Idn bdn trong toe ngUdi binh thudng 13 Ian Tu do dan den mot each bieu kbae ve nguyen nban lam cbo vi cUu boang de

•

kia chet mot each dot ngot

Huon phan tieb bing pbUdng pbap kieb boat ndtron ,

can CO nbung tbiet bi rat pbUc tap , dit tien Ngoii ra , nbung cong trinb pbong , ebong nhiem xa cung kha ton kem Bdi vay , cbi nbung ed sd dau nganh cua nba nUdc mdi xay

di^ng dude pbUdng pbap nay

NgUdi ta biet rat nbieu nen cue pho asen /17,^0 ] Tuy nbien , do do Idn cua dong tu dien va phan ung dien cue cua asen kbong tbuan ngbich , pbUdng pbap cUc pho c6 dien kbong the xac dinb nguyen to nay d nong do dUdi lO'-^mol/l Nam

1981 , Le LUdng ( Vien boa hoc cong ngbiep , Tong cue boa chat ) da dung cUc pho song vuong xac dinh asen ; do nbay chUa vUdt qua 1.10"-^ mol/1 Sd di nhu: vay vi may cUc pbo song vuong OH-104 chi nbay doi vdi cac nguyen to eo pban

Ung dien cUc tbuan ngbich Cac may cUe pbo tast , cue pbo xung cbo do nbay xac dinb cao bdn , song do ebUa eo thiet

bi nay nen cbUa tbu nghiem dUdc

Nam 1983 , Le v^n Bi-oh ( luan an tot ngbiep dei I'.oc

Tong hdp Ha noi ) da xac dinb du:de asen thap den 1.10"

mol/1 dUa vao song xue tac bidro trong nen LiCl 0,llu

-s-Fe (III) 5,8.1C~\ol/l ( pH = 3,2 ) Bo nbay nl-y cbUa

tboa man yeu eau thUe te

eon dude goi la pbUdng pbap cue pbo eo lam giau , cue pbo n^Ude ( Inverse Polarogrspby ) hay von-ampe n^\i6c ( Inverse Voltammetry ) Tbeo Koch 0 G 7 44 7 , pbUdng pbap dien boa boa tan c6 the xac dinb nhieu nguyen to d nong do thap den 1 ng/ml NbU vay , ve m§t do nbay , pbUdng pbap nay so sanb dUde vdi pbUdng pbap kieb boat ndtron va bdn ban cac pbUdng pbap kbae da trinb bay d tren Nhieu tac gia nUdc ngoai da dung pbUdng pbap dien hoa boa tan ngbien cUu van

de xac dinb asen Ho da dat d-\l6Q, mot sd ket qua dang kbieb le , song cung eon nhieu van de pbai ban crude kbi ap dung vao boan canb cu the nUdc ta bien nay

Trong nbung nam ebong My cu:u nUde , vdi nhUng bai bao

le te trong cac tap cbi tbieu so , ehung toi biet the gidi bit dau phat trien phudng pbap pban tieb dien boa mdi nay Bdi vay , dau nSm 1973 i i^gsy sau kbi hiep dinb Pari ky ket , tu gia ndi sd tan trS ve Ha noi , ehung toi da lam nbung viec can tbiet de xay dUng pbUdng pbap nay Bai bao dau tien trong nude tbuoc linh vuc nay viet ve viec xac dinb bae trong cbi tinb kbiet /^ 62 7 • ^"^1 may ^'^^ P^o OH-

102 va dien cue Pt tu ebe , Tr^n Huu Hoan va con^^ sU da

xac dinb dude bam lUdng Ag thap den n.lO"^ o ma kbong qua eac giai doan taeb boSe lam giau Gong trinh nay da dUdc pbuc vu viec ngbien euu nang cao chat ludng acqai chi va viec tinh ebe chi bing phudng pbap nong ehay vung Trai qua nam thing , phUdng pbap pban tich dien boa boa tan da dudc xay dung "s va pbat trien d mot so cd sd nbu : Bo mon pban tich cua Kboa boa Trudng dai hoc T^ng hdp Ha noi , Phong phan tieb cua Vien boa Vien kboa hoc Viet nam ,Pbong pban tich cua Vien boa boc cong ngbiep Tong cue boa chat

tu , quang pbo pbat xa nguyen tU deu kbong du do nbay de

xac dinh asen d lUdng nbo bdn 100 ng hoSe 0,1 ppm Luon sU dung dude cac phudng pbap do pbai lay ludng mau Idn va qua giai doan lam giau rat pbUc tap Hdn nua , van de cung cap , nbap tbiet bi vat tU can tbiet cbo mot so pbUdng pbap von dUde Ua ebuong tren the gidi ( nbu quang pho bap tbu nguyen

tu ) gap kbo khan,khien cbo ehung kbo ap dung rong rai d

nude ta Phudng pbap kieb boat ndtron dat do nbay ly tudng , CO the tboa man dude moi yeu eau thUc te ve viec xac dinh asen Song ehung toi kbong du trinb do va tbiet bi de tbue hien phudng pbap nay Va lai , luan an eo mue dieb tim

mot pbUdng pbap xac dinb asen du nbay va de dang pbo cap den

cac cd sd de mong dap ung d\i(ic rxhieu yeu eau da dang trong

n\X6c Trong cac phUdng pbap con lai thi pbUdng pbap dien boa boa tan eo by vong hdn ca Chung toi ebon phudng pbap nay vi ngoai nbung uu diem cua no da ke tren , trude bet

cbung toi CO phudng tien vi da tich luy dude it nhieu kinh ngbiem •

Muon ngbien euu tot , trUde tien ta can biet cac thong tin da eo ve tinb chat dien boa cua asen vi tinh binh xac dinb asen tren the gidi bing phudng pbap da ebon

>fH

0

'«tfr-.^;K^>a:3»"-"-2 1 / Tinb chat dien hoa cua asen

Tinb chat dien boa cd ban cua asen ( tren dien cUc giot

tbuy ngan ) da trinh bay trong cac tai lieu / 17,20,34,45

7-NbUng thong tin nay eo the soi sang pban nao ed ebe cua cae pbUdng pbap dien boa boa tan xac dinb asen va giup ta dinb budng ngbien cUu tiep theo

/

2.1.1 - Asen boa tri V

NgUdi ta tbay vai song nbo cua asen (V) trong HCl 6M boae 8M vi mot song kbU kep trong HCl 11,5 M , cbieu cao cua no giam theo nong do axit va mat ban trong HCl 9 ^ /48 7-Nbung , nhin cbung , asen (V) kbong bi khu tren dien cue gi,t tbuy ngan / 17,^5 7 •

Trong tu nbien , asen c6 the ton tai d dang boa tri (V),

do do muon xac dinb no pbai cbuyen ve boa tri (III) nhd phan Ung boa hoc

2.1.2 - Asen boa tri III

• Tinh chat dien boa cua asen (III) , trfen dien eUc giot tbuy ngan , trong moi trudng HCl da d\l(5c ngbien cUu ky nbat

va cung tbu d\X6c nbieu thong tin mau tbuati nbat TRong moi trudng nay , asen ton tai d nbieu dang kbae nbau Theo

Arnold f3^ 7 GO tac gia cbo rang , trong HCl , asen (III)

CO the ton tai d cae dang sau : AsCl^ , As(OH)Gl-, ,As(0H).-Cl, As(OH)^^ , H^AsO^ , kbong c6 anion phUc eloroasen Trong HCl 12 M , dang Uu tien li AsGl- , trong HCl 9 K li AsCl, va

"o As(0H)Cl2 , con trong HCl 5M , c6 tat ca 3 dang ke tren c6 tac gia lai cbo ring , trong HCl 4M c6 cac anion pbuc cloro

vi du AsCl^ Tai lieu sac ky trao dgi ion / 20 7 cbo tbay

13

trong HCl tU 0 den 12 mol/1 he so pban bo cua asen tren tionit Dowex-50 be bdn 1 Bieu do congbia la , asen neu ton tfi d dang ion dUdng dien tbi cung cbi vdi ty le rat nbo Tren anionit Bov/ex-1 , he so pban bo cua asen be bdn 1 kbi

ea-nong c?o Eei be bdn 4mol/l , vi Idn bdn 10 khi ea-nong do HCl Idn hdn 8 mol/1 Bieu do c6 nghia la , khi nong do HCl Idn hdn

4 mol/1 , trong dung dicb eo anion pbuc eloroasen va ty le pbuc anion cbiem Uu the kbi nong do HCl Idn hdn 8 mol/1 Ket hdp bai tii lieu sic ky trao doi ion tren , ta suy ra ring , trong dung dicbHGl tu 0 den 4 mol/1 , asen ton tai cbu yeu

3 dang hdp chat trung tinb Tim bieu dang ton tai cua asen trong dung dieb HCl eo Idi cbo viec thao luan ket qua ngbien eUu sau nay

Tbeo Kriukova T A / 17 7 , i^ot; so tac gia thay , tron^ moi trudng HCl , asen (III) cbo 4 song cue pbo , dang vi the cua ehung tbay doi tbeo nong do axit Song tbu nbat Ung vdi

sU tao thinb asen nguyen to ( elemental arsenic ) , song tbu bai va tbu ba Ung vdi sU khu cua H^AsO^, va AsjO- , con song tbu tu Ung vdi sU khu cua asen nguyen to den A S H - Vi sii phue tap cua pb6 nen eac tac gia nay cbo ring moi trudng HCl kbong tbieb hdp cbo mue dieb pban tieb

Koltboff I. h 7 ^3 7 cbo biet , mot so tac gia kbae

thay , Trong HCl IM chUa 0,01 % gelatin , asen (III) cbo mot song pbuc tap bit dau t'u" -0,4 V ( sv SCE ) va dong g^idi ban dUdng nbu dat d\t6c d -0,8 V den -0,9 V ung vdi sU khu du 6 electron thanb asin ( A S H ^ ) Tuy nbien ho ban kboan la ,sau dong gidi ban do eon eo mot song kbae.nen ngbi ngd ehinh ~-ia tbuyet cua minb

Tbeo Milner G.'V.C / 48 7 i Kaxirkova cbo rang , trong HCl BI , asen(III) cbi cbo 2 song 3 vung -0,3 va -0,6 V ( sv SCE ) , song thU nbat kbong dinb lUdng va eo the ung vdi sU t tao tbinb asen nguyen to eon song tbu bai Ung vdi sU khu asen nguyen to tdi asin , cbieu cao song niy ty levdi nong do asen trong dung dieb Cung theo IVIilner G.V;/.C , ileites thay asen (III) ebo bai song trong dung dieb HCl Song tbU nbat eo

E-, yp » - 0,428 V ( sv SCE ) , cbieu cao cua no ty le vdi nong

do asen trong khoang 1,8.10"^ - 9*10 mol/1 Kbi nong do asen tang , cbieu cao song nay kbong bien doi nUa Tac gia do giai tbieb la , asen nguyen to d\L6o sinb ra da tao thanb mang ( film)

vi bi hap phu tren be mat dien cue giot tbuy' ngan Song thU bai chi bieu bien tot kbi nong do asen (III) tang den 5«10"''^

' Khi nong do asen cao bdn , song nay eo cue dai kep ky

di Khi dung xanbmetylen de ebong cUc dai , Leites tbay ring^ bing so dong kbuecb tan ( i^- C" m"^*^ t" ""^^^ ) cua song tbu bai gap doi bing so nay cua song thU ribat Ngbien cUu sau sic hdn , tac gia niy cbo ring , trong HCl lii , asen bi khu thanb bai bude , moi bude tbu 3 electron Neu nbunn ket luan ed

ban cua Meites phu bdp thUc te , tbi ta c6 the xac dinh asen bing pbUdng pbap dien boa boa tan dUa vao sU dien pban lam

giau no d dang boa tri (0)

Qua trinb khu asen (III) tren dien cue giot tbuy ngan

rat pbuc tap Nbieu cd ebe c6 ging giai tbich qua trinh niy

da dudc neu ra Boi vdi song tbu nbat , cd ebe sau day c6 le tbich Yi^-g bdn cs, f ':>^ / : '

As(OH)J ^ Gl" -^ e -SilMk^ •As(0H)Gl ^ OH"

As(OH)Cl ^ e _cham_^ ^^ ^^^ ^ ^^^-. ^ ^^^

As (I) ^ e ^ ^ ^ ^ > As

do khong tbuan nghich NbU the , phudng pbap eUc pbS song vuong xac dinh asen ( xem mac 2.0 ) kbong tbich hdp Luon dung phudng pbap nay , pbai tim dUdc nen sao sho asen phan Ung dien o^c du tbuan ngbich

Su kbu asen (III) trong cae moi trudng kbae cung dudc ngbien cUu f 17,^5,^8 7 Trong H^SO^ 0,5 Ivi chUa o,01 ^i ge-'latin , asen cbo bai song Cbieu cao song thU nbat ty le vdi nong do asen (III) Cac song nay xuat hien d the am

bdn trong moi trUdng HCl vdi the nu?a song Ian ludt la -0,7

V vi -1,0 V ( sv SCE ) IsTbu vay , muon lam giau asen

trong moi trudng HpSO^ pbai dien pban d the am hdn trong moi trudng HGl , do do nbieu kim loai bi dien pban theo nen

do ebon loc se kem hdn Trong HNO^ IM , asen cung cbo bai song vdi the ntfa song tudng tu trong H ,S0_^ Trong moi tr trUdng rudu -f axit sunfurie , asen cung cbo eac song ro vdi the HL^a song Ian ludt la -0,6 V , -0,88 V va -1,15 V Asen (III) kbong bi khu trong moi trUdng kiem , trung tinb boSe kiem tatrat Trong moi trUdng kiem manh , asen (III) cung bi oxi boa den asen (V) Nbu vay , ta tbay moi trudng kiem va trung tinb -kbong Idi cbo phudng pbap xac dinb dUa vao each lam giau asen S dang boa tri (C)

Su kbu asen (III) trong dung dieb KI cung dude xem xet

r '5^ 7 ' Trong KI 0,1 M ehUa chat ebong cue dai , asen cbo

bai song ro kbi nong do cua no thap h(5n 8.10" mol/1 Trong

KI 0,1 M ( pHaa 2,0 " ^,4 ) , cbieu cao song ty le vdi nong

do asen (III) cbo den I.IO"'^ mol/1 Neu nong do asen Idn bdn , quan be tren kbong eon nUa Cbieu cao song dat gia tri gidi ban kbi nong do asen vudt qua 4.10"'^mo 1/1 Nbd tinb toan ly tbuyet , ngUdi ta tbay , d day eo bien tudng bap phu ding nbiet -

Trong eac moi trUdng eo chat tao pbUc manh nbu pirogalol , axit oxalic , axit tatric , EBTA -t KCN v.v , the nife song cua asen dicb ve phia am boae mat bSn Bdi vay , eac moi trudng ay cung kbong tbieb bdp vdi phudng pbap dien

boa boa tan xac dinb asen

Tu nbung dieu da trinb bay , ta rut ra may nban xet

nbu sau :

1 ) M S I trudng HCl eo le la moi trudng tbieb hdp hdn ca cbo viec xac dinh asen bing phudng pbip dien boa boa tan

2 ) Trong dung dicb KI , asen c6 bap phu ding nbiet

3 ) Muon xac dinb asen (V) , pbai kbu no den boa tri (III) bing eac pban Ung boa hoc tbieb bdp

17

2.2 / Cac pbUdng pbap dien boa boa tan xac dinb asen

Tbeo eac thong tin ve tinh chat dien boa cua asen da

trinb bay d mue tr-ude , ta thay ring , cae phudng pbap dien boa boa tan xac dinh asen deu dUa tren kha nang dien pban

lam giau asen d dang As (0) Nbung tai lieu xac dinh asen

da eng bo d nudc ngoai eo the chia lam bai nbom nhu sau :

2.2.1 - PHUdng_£ba£_dien_hoa_boa_tan_anot

Cac pbUdng pbap dien hoa boa tan anot deu dua tren kha nang oxi boa dien hoa As (0) da tao tbqnb trong giai doan

lam giau den As(III)

Cic moi trudng HGIO^ 7 ^2 7 , H^SO^ £ 5^ 7 , K^SO^ ^ HNO^ £ IS J CO the dung lam moi trudng dien pban Tuy nbien, HGl 1 Iv! la moi trudng dudc sU dung nbieu hdn ca /" 11,12,13, 21,32,42,54 7

Bo nbay xac d^inh phu tbuoc nbieu vao loai dien cue lam viec d-i/dc sU dung , Vdi dien cUe Pt , dung moi trudnfe HCl Uvl , Truebina L.P / 32 7 c6 the xac dinh dude nong do asen

thap den 2.10'^^ mol/1 , eon Gustaf,; P. £^2 7 da dat tdi

do nbay 2.10 ^ mol/1 Bien cue vang dxt6o sU dung nbieu nbat / 11,12,13,21,42,46,54 7 va cung dat do nbay cao nbat / 12, 13,42,46 7 • Ching ban , kbi dung dien cue vang , trong moi trudng HGl lii^ , Kaplin A.A / 12 7 dat dudc do nbay 6.10"^ mol/1 , con Gustaf F ^ 42 7 cong bo pbat hien dUdc 0,02

ng/ml , tuc "3.10*"^^ mol/1 Kaplin n.k. thay Cu cin trd sU xac dinb Asen rat nhieu ngay ca kbi £ On(11) 7 : £ ks{lll) 7

Idn bdn 1 : 2 Trong eac doi tUdng tu nbien va ky tbuat

\-\16n^ Cu thudng Idn bdn ludng As Nbu vay , neu dung dien cue vang pbai ket bdp vdi mot qua trinb tach tbich hdp

l,H_Ml^^

Kbi dung dien cue Pt va Au , Gustaf E / 42 7 i^ban thay cbung

de bap phu oxi , gay trd ngai ebo sU xac dinb Ngoai ra , e

cac dien cUc nay c6 do ben cd hoc kem nen kbo sU dung Bien

cue graphit kbong nbay / 11, 32 / - Cbing ban , vdi dien cue

do , khao sat d moi trUdng H G I M vi H^SO^ 0,5 M , Trushina L

P 7" 32 7 kbong the xac dinh asen 3 nong do be bdn 1.10" mol/1

Tuy nbien , neu van dung dien cUc graphit mi cbo asen cung

dudc lim giau vdi dong trong giai doan dien pban tbi trong giai

doan boa tan ngUdi ta tbu dude tin bieu pban tich c6 cUdng do

manh bdn ro ret / 11,16,^3 7 • Roizenblat E M. £ 2.7 7 ^ | ^

tbay , ngay ca lUdng vet Cu (II) trong nude cat cung lam tang

dong dinb boa tan anot cua asen - Fnieu tac gia cbo ring £ 16,

23,27 7 kbi Ou va As cung bi dien pban 3 dang boa tri ( 0 ) ,

tren be mat dien cue da tao thanb hdp chat gian kim loai bae

bai Cu-As eo boat tinh dien boa manh Khi dung dien eUc

gra-phit ket hdp vdi be bae bai Cu-As , Krapivkina T A. £ 16 7

va Neiman E Ya 7 25 7 c6 the xac dinh asen d nong do 10"

-10"-^ mil/l

Thong tbUdng , pbUdng pbap'xung vi pban boa tan nbay bdn

pbUdng pbap von-ampe boa tan khoang 100 Ian Tuy nbien , doi

vdi asen , pbUdng pbap xung vi pban boa tan kbong the hien uu

viet ve mat do nbay so vdi phudng pbap kia 7" ^2 7" •

Be tang do ebon loc , doi kbi ngUdi ta eon su dung ky

tbuat doi itfoi trUdng Muon lam viec nay , dau tien nguyen to

can xac dinh dxL6Q, lim giau 3 moi trudng tbich hdp , sau do dudc boa tan d mot moi trudng cb9n lo^ kbae - Vdi ky tbuat nay ,

Toropova V P. £ 31 7 da xac dinb asen trong hon hdp vdi 10 Ian

Cu(II) , 100 lin Bi(III) , Sb(III) , Sn(II) ya Pb(II) T^e gii

nay sU dung moi trudng dien phan la HCl 5 - 8 M , moi trudng

boa tan li KOH IM vi dien cUe tbuy ngan tinh Tuy njrjien , do

19

nbay cua phudng pbap kbong dat tdi 1.10 mol/1

Kbi doc cae tai lieu pban tieb asen bing cac pbUdng pbap

dien boa hoi tan anot , ta eo mot so suy ngbi xung quanh van

de dung dien cue so' sanb va do nbay rat cao mi nbieu tac gia

da cong bo Tran HUu Hoan / 63,64 7 da nban thay cae dien cue

ealomen va bae elorua loai tbUdng mai c6 the dUa vao dung dieb

do mot ludng vet Hg(II) boae Ag(I) - Trong cae moi trudng axit

vo cd , tin bieu boa tan anot cua tbuy ngan , bae , asen gan

nbu trung nbau nen de gay nbami Ian Ii.ac dau , ngudi ta dinb

kha nbieu giay mo ta viec xac dinh seen asen , song kbong eo mot cbu tbich nio ve viec dung dien eUc so sar±i NbU tren da

neu , Gustaf F cong bo phat bien dudc As 0,02 ng/ml , song

cbi dUa ra pb6 von-ampe boa tan cua dung dicb 1 (ug/ml , tUc

50.000 Ian Idn bdn Mae dau vay , tin bieu nay cung cbi li mot dinb kbong dep , tu , cbieu rong nua dinh do dUde tdi -140 mV

2.2.2 - 5iJl?^5S_Eiii2_Sil^ ^22_-^2§_5§2-_2552!^

Cac phudng pbap dien boa boa tan catot dUa tren kha nang

khu dien boa As(0) thanb asin ( AsH^ )

Nam 1980 , Brainina Kb Z / 4,29 / dung dien eUc mang tbuy ngan tren graphit xac dinh d\i6c nong do asen thap den 1.10"^mol/l bing pbUdng pbap von-ampe boa tan catot Tac gia nay sU dung dung dicb nen nbu sau : HCl 1,5 M ^ 2 M -s- KI 0,4 M -s- Esi^O^).^

3,5 10" - 5 95-10" M Phudng pbap nay eo do ebon loc tot ,

nbieu nguyen to , trong do eo cac kim loai kiem , kiem tbo •, ^'e (II) , Co , S O " , Cl~ Ya PO^" kbong can tr3 Tuy nbien , Cu(Ii; can trd ; ngay ca khi nong do Gu(II) gap 10 Ian As(III) , tin

bieu pban tich cung bien mat Tac gia c6 dUa ra vai Ung dung tbUe te , nbung kfeong cbu y den kha nang mat asen lue xu ly mau

bing hon bdp HpSO^ •!• HF / 29 7 - Theo Bolezal ^.£77 » nbd sU dung dong vi As^ , tu lau , ngudi ta biet eo den 45 %

asen bi mat khi dung hon hdp axit do

Belova T Ya /" 2 7 sU dung be bae ba I-Gu-As dau tien vao nam 1975 • lac gia niy dung dien cUc tbuy ngan tinb xac d dinb asen trong nen HCl 3M -s- KI 0,015 M ^ CuSO^ 5.10"^ M ,

3 nbiet do 80 - 180 ^ C Neu tinb den do ben cua KI vi tbuy ngan kim loai trong moi trUdng axit manb , nbiet do cao , ta tbay pbUdng pbap niy rat kbo thUe hien Vdi phudng pbap von-ampe boa tan catot dong xoay cbieu , h9 xac dinli dudc asen d vung nong do 1.10 ' mol/1 Phan ung xac dinb asen nay d\i6Q,

gia tbiet li theo cd che xue tac

2.3 / Cac van de ngbien eUu trong luan an nay

Tu phan tong quan tren , ta rut ra dUdc nhSng nban xet tong quat nhU sau :

1) Ngudi ta CO ging tang do nbay bing each dung cae dien cue che tao tii kim loai qui nbu Au , Pt boae su dung cae bdp chat gian kim loai Cu-As kbi dung dien cue graphit , tbuy ngan tinb 2) Moi trudng dien pban thudng dung la HCl HI ( boa tan anot ) boae HCl 1 3 M ( boa tan catot ) Co le HGl li chat dien ly tbieb bdp nbat cbo viec xac dinh asen bing cac phudng pbap

dien boa boa tan Nban xet nay phu bdp vdi dieu da rut ra tu tinb chat dien boa cua asen , neu 3 mue 2-1

3) Trong cae doi tudng tu nbien va ky tbuat , feem ludng vet

Cu tbUdng Idn bdn ludng vet As Cae dien cue lam bing kim 1 loai qui cbo do nbay cao song bi Cu gay tr3 ngai Bdi vay , trong sU dung tbue te pbai qua mot giai doan taeh pbuc tap Kbi dung he Cu-As , ngudi ta pbai them mot ludng muoi Gu(II) vao dung dieb do , do do tren tbue te , Gu (II) trong mau

21

kbong can tr3 , nen kbong can taeh trude

4) CbUa CO mot phudng pbap dien boa boa tan xac dinh asen boan ehinh , du 6n dinb va tin tu3ng di giai quyet cac yeu eau tbue

te 3 nude ta vi con nhieu van de ton tai trong each dung dien ci^c so sanb , each xU ly mau tbue te Qung nbung kfeo khan ve dieu kien thUe nghiem va thiet bi -

5) Phudng pbap dien the tbdi gian hoa tan ehUa dudc sU dung

de xac dinb lUdng vet asen

• ^

Tu nbung dieu da trinb bay , ehung'toi thay c6 nl^iem vu pbai xem xet lai lei mot so pbUdng pbap da c6 , cai tien cbung boae ngbien euu phudng pbap mdi nbim dat tdi mue tieu cua luan

an la tim dudc mot phUdng pbap xac dinh lUdng vet asen nbay den 10" mol/1 va eb9n loc ( cbu yeu la doi vdi Gu ) dong tbdi pbai

CO du dieu kien ap dung rong rai 3 trong nude Muon lam dUdc dieu do , can di sau xem xet cac be chUa Gu(II) Ta xac dinb asen theo cae be niy se eo bai dieu Idi ehinh : mot la , tan duns: boat tinb dien boa manb cua eac hdp chat gian kim loai Cu-

As de tang do nbay ,; bai la , kbong bi Gu trong mau can tr3 He_Cu-As : Wciom Krapivkina T A , Neiman E Ya dung dien ci/c graphit ngbien euu he Cu-As bang phUdng pbap von-ampe boa tan anot Kha nang xae dinb asen tbeo budng boa tan catot he nay , kbong eo I~ , chUa ai biet Bdi vay , cbung toi xem xet lai he nay bing cac pbUdng pbap boa tan anot va ca catot Bien

\ ^ cue lam viec la dien cue tbuy ngan boae ran , tuy tung trudng bdp cu the

He Cu-As-Au : tfu diem n6i bat ve do nbay cua dien cue Au va bieu qua tang do nbay doi vdi dien cue graphit kbi dung be Cu-

As lam cbung toi ngbi den kha nang xac dinb asen tbeo he bae

ba Cu-As-Au vdi cae loai dien cue than He nay chUa dudc tac

gia nao ngbien cUu - Chung toi kbong dung dien eUc Au , vi

do ben ed h9e cua no kem vi bdn nUa no de hap phu Oxi gay kbo

khan cbo sU xae dinb Phutdng pbap dien the tbdi gian boa fan

vdi uu diem n^i bat ve do pban giai ph6 cao , dSdc sU dung cbu yeu de ngbien eUu be nay

He I-Cu-As : Nbom Belova T Ya ngbien cUu he nay dap tien Cung giong nhU be Cu-As , he I-Cu-As s^l dung boat tinb dien

boa manb cua hdp chat gian kim loai de tang do lihay Ngoii ra, tbeo Belova T Ya , pban ung xac dinh asen tbeo he nay c6 cd

che xue tac - Tu do suy ra , be I-Cu-As pbai eo do nbay cao

bdn be Cu-As - Tuy nbien , do nbay ma Belova T Ya, dat dudc

kbi ngbien eUu he I-Gu-As kbong hdn Krapivkina T A va

Nei-man E Ya khi ngbien eUu he C U - A S - Co sU mau tbuan nay , pbai Chang vi ky tbuat dong xoay cbieu mi Belova T Ya 4a

dung ehUa phu hdp , bay c6 che cua tac gia ehUa tboa dang bay

vi mot ly do nao kbae Bdi vay , cbung toi tbay can ngbien cUu

ky lai he nay , by vong tim dudc cac dieu kien tbich hdp hdn

de tang do nbay , do ebon loc cung nbu giam bdt kbo khan ve

trang bi va thao tac so vdi cong trinb xuat xu

-Chung toi ebon Hei lam moi trudng dien ly cbu yeu di ngbien cUu cae he tren vi ba le sau ; mot , day la moi trUdng da dudc nbieu tac gia sU dung , c6 the do la moi trudng tbich bdp nbat vdi asen ; bai , trong dung dich HCl , the ni/a song cua nbieu nguyen to da dude thong bao /17,207 , do do neu can cu vao the dien phan ta eo the du doan ve kha nang gay nbieu cua cac nguyen

to kbae \ ba , HCl li axit de tinb ebe nbat de eo do tinb kbiet can tbiet

-0-23

•

3 CAC PHUdNG PHAP NGHI.SN GU\) VA BI£iU KIEN THUC NGHIEM

3.0 / Cac phudnp; pbap dinh bUdng ngbien euu

Mot so tinb chat dien boa cua chat can xac dinb c6 the

a •

biet dude nbd phudng pbap cUe pho va von-ampe vong a Nbung bieu biet ay giup ta dinh budng nbanh ebong viec ch9n eac dieu kien tbuan Idi ebo pban tich dien hoa boa tan

a •'

-Kbi ngbien eUu bing pbUdng pbap cue pho , von-ampe vong cung nbu dien boa boa tan , ta dung cac dung dieb chUa chat dien ly trd 3 nong do du Idn nbim nbung mue dieb ehinh sau : 1) Loai tru sut the ohm trong dung dieb de eo the xem the dat vao cac dien cue bing bieu so dien the giUa anot va catot , tao dieu kien tbuan Idi ebo viec su dung cae may cue pho eo be thong bai dien cUc

2) Loai trU dong dicb cbuyen cua chat boat dong dien

3) Giu cbo be so boat do cua chat boat dong dien khona: ddi trong suot qua trinh do

3.0.1 - Etodng_pbap_sUc_;2bQ

Neu mot chat boat dong dien ( trong dung dicb chUa chat dien ly trd va chat ebong cUc dai ) tbue bien phan ung dien hoa nh\t sau tren dien cue giot tbuy ngan :

Ox + ne = Kb ' ( 1 ) thi vdi eac may cue pho thong thudng , ta se tbu dudc mot song ei^c pha' CO dang bae thang tren toa do dong dien / dien the

Neu phan ung ( 1 ) tbuan ngbich , toe do cbuyen electron nbanh hdn toe do cbuyen chat , tbi toe do kbuecb tin Ox tu dung dicb den dien cUc qui dinh dong dien qua binh dien phan Lue d6 , cbieu cao song cue pbo , (in^ vdi dong kbuecb tin p-idi

ban trung binh , eo the tinh tbeo phUdng trinb Ilkovie 3 dang sau / 6 y :

I^ = 607nDl/2 ^2/3 ,1/6 ^^^ ^ ^ ^

( trong do ; i^ tinb ra ^ A , B — cm /s , t — s ,m — mg/s )

Neu toe do cbuyen electron cham hdn toe do cbuyen chat

va kbong ebe phan Ung ( 1 ) lam cbo qua trinh dien cue kbong tbuan ngbich , tbi dong dien trung binh tbu dudc se be bdn

dong dien trung binh trong trUdng hdp pban ung tbuan nghich Tuy nbien , tu pbUdng trinb Weber - Kouteeky ( theo £ 6 7 ) suy

ra ta thay , khi the dien cue tang dan ve phia am toe do cbuyen electron tang dan , lue the dien cUc dat gia tri ung vdi dong gidi ban song cUc pho thi toe do cbuyen electron nbanh bdn toe

do cbuyen chat , lue nay toe do kbuecb tan lai qui dinh dong gidi lien Bdi vay , ta eo the sU dung phudng trinb ( 2 ) trong mot so tinh toan gan dung ebo eac phan ung kbong tbuan ngbich

do toe do cbuyen electron cham gay ra , Luan an sU dung pbUdng trinb nay de tinb he so kbuecb tan cua asen (III)

Tbeo Heyrovsky J 7 o 7 ? song cue pb6 catot kbong tbuan ngbich eo the dudc bieu dien bing phudng trintj sau :

Tu ( 3 ) suy ra , sU phu tbuoc cua dUdng Ig / I /(I-,- i)/ vao -E CO tinb chat ty le tbuan Budng thing do c6 be so goe la

^ n P / (2,3RT) NTiu vay ,qua phan tich logarit song cue pho ,

ta eo the xae dinh dude o< de danb gia mUe do tbuan ngbich cua pban Ung dien cue

Co nbieu yeu to anb bu3ng den dong gidi ban va binh dang song cue pbo nhu : sU tao phUe , sU bap phu v.v Neu qua trinh khu dang Ox eo ion bidro ( H^G^) tham gia tbi sU tbay doi nong

do cua no se lam dicb cbuyen the tlSCi song theo pbUdng trinh sau:

duy tri trong khoang 10"-^ - 10 mol/1 , tue la tudng dUdng vdi nong do mi phudng ph ap cue pbo c6 dien cbo tin bieu ro rang Neu pban ung dien cUc du tbuan ngbich , tren pbo eo mot dinb ca- • tot va mot dinb anot dudng bdn Vi tri eac dinh nay trung vdi

vi tri tin bieu pban tich trong pbUdng pbap von-ampe boa tan Neu pban ung dien cue tbuan ngbich , khoang each giUa bai dinb

la / 5 / :

^pa ~ V ^ ^'^^^ / n ( V ) , 3 25 ""C ^ ( 5 ) •

Neu phan ung dien cxic kbong tbuan ngbich , khoang each do Idn bdn va cung tang kbi tang toe do quet the B3i vay , khi khao sat cae qua trinb dien cue , da so la kbong tbuan ngbich , ta

can giu toe do quet the cham , tbUdng bing toe do quet the trong

'^'h.-\l6n]^ pbap cue pho ed dien

Qua trinb pban tieb dien boa boa tan gom bai giai doan

7" 3,55 7 :

Giai doan 1 : dien phan trong mot th5i gian tbieb hdp tai

dien the xae dinb ( thudng la lin^g vdi dong gidi ban song eUc

pbo ) de lam giau chat can xac dinh

Giai doan 2 : boa tan chat da dUde lam giiu khoi be mat dien cue bing sU pban cue anot ( boae catot ) , dong tbdi ghi tin bieu hoa tan do

GiUa bai giai doan do , eo mot tbdi gian ngbi chUng 30

giay de thiet lap trang thai on dinh cua ket tua tren Sien eUc

vi ngung sU doi lUu dung dieb Nbd' giai doan lam giau bing

dien pban , dien boa boa tan eo do nbay cao hdn cac pbUdng pbap cue pho tudng Ung khoang 100 - 1000 Ian Tuy theo tin bieu boa tan dxC6c tbeo doi li dai lUdng nio vi ky tbuat nao dung de theo doi , ta eo eac phUdng pbap dien boa boa tan kbae nbau -Luan an cbi sU dung eac pbUdng pbap dien hoa boa tan mi cbung toi CO dieu kien thUe hien nbU sau :

a a '

i) PbUdng pbap von-ampe boa tan ( V A H T )

B phudng pbap nay , ta tbeo doi sU pbm thuoe cua dong dien vao the cua dien eUc lam viec ( so vdi dien cUc so sanb ) kbi

no dudc pban cue bing the mot cbieu bien tbien vdi toe do kbong d6i de hoa tan chat Neu the cua dien cUc bien tbien tbeo cbieu dudng dan , ta eo phudng pbap VAHT anot Neu the bien tbien tbeo cbieu am dan , ta eo pbUdng pbap VAHT catot Cac tin bieu" pban tieb tren pho VAHT anot vi catot deu c6 dang dinh nbung ngUde cbieu nbau Bien tieb ( boae cbieu cao ) dinh ty le vdi nong do chat pban tich The dinh c6 dae trUng dinli tinh

tram (uA ) qua be gom dien cue lim viec vi dien eUc ho trd d%

boa tan chat Neu dong dien di tu dien cUc lam viec den dien cue bo trd , ta co phudng pbap BTHT anot Neu dong dien di theo cbieu ngUde lai , ta eo phudng pbap BTHT catot Tin bieu pban tieb tren pho BTHT anot va catot c6 cbieu ngUde nbau , nbUng deu CO dang bae thang , gan giong song cue pbo Tbdi gian boa tan chat kboi be mat dien cue g9i la tbdi gian cbuyen Bai

ludng nay ty le vdi nong do chat phan tieb /" 8,9,56 7 • The Ung vdi nUa tbdi gian cbuyen g9i la the nUa song ( E-, y ) , eo dae trung dinb tinb / 58 7 • BTHT eo do phan giai cao bdn VAHT , nbung CO do nbay thap bdn mot chut

3) PbUdng pbap von-ampe boa tan xoay ehieu ^

Cach tbue hien phudng pbap nay tudng tu phudng pbap VAHT

da trinh bay tren , trU the dat vao dien cUc lim viec la the mot cbieu da dieu bien bing the xoay cbieu binh sin ( bien do

tu vai den vai ebuc mV ) vdi tan so tu vai 4e*i chuc den vai tram Hz ( tan so cd ban ) Bong qua binh dien phan la mot hon bdp cac dong eo tan so la boi cua tan so cd ban Bong vdi tan

so gap doi tan so cd ban ( dong h9a tan bae bai ) eo y nghia pban tich vi no loai trU dddc dong tu dien,nen GO dieu ki^n tang do nbay Neu dung bo 190 dien PC vi diet de taeh va tbu dong nay , tbi tin bieu tbu d\X6c c6 dang dinh va kbong pban

biet dau / 69 7

-Vdi nbung Uu nbude diem rieng , ba phudng pbap tren se

ho trd nbau trong qua trinh ngbien cUu sau nay

3-1.1 - NhUng_van_d|_li|n_quan_den_giai_doan_l^

3,1-1.1 ) Cac pban \ing lam giiu

NgUdi ta tbUdng dung cac pban ung sau day de lim giau

chat can xac dinb / 55 7 •

1) Cac ion ma trang thai kim loai cua no de tan trong tbuy

ngan dudc lam giau bing each dien phan thanb kim loai tren

dien cue tbuy ngan tinli Gu,Pb,Gd,Zn tbUdng dudc lem giiu th tbeo loi niy

2) Cac ion kim loai dudc khu dien hoa den trang thai kim loai tren be mat eac dien cue trd ribu Pt ,Au,graphit Cach niy thudng dung de lim giiu tjiuy ngan , eac kim loai qui va cae kim loai kbong tao hon bong

3) Co the lam giiu chat can xac dinb dudi dang bdp chat it tan theo bai cach sau ;

- Hdp chat it tan dudc tao thanb kbi ion cua nguyen lieu dien cue tudng tac vdi ion can xaE dinh TrUdng bdp nay , the

dien pban dat d gia tri xay ra sU oxi boa nguyen lieu dien cue

- Chat can xac dinh tao thanb hdp chat it tan tren dien cue

kbi tudng tac vdi tbuoc tbu eo trong dung dich nen TrUdng b bdp nay , ngUdi ta dien phan d the xay ra sU oxi boa boae khu chat can xae dinb den mUe oxi boa c6 the tham gia pban ung boa hoc de tao thanb ket tua

4) Co the dung cac chat boat dong be mat de lim giau chat can xac dinb mi kbong can dien pban

5) Co the chiet nguyen to can xae dinh vao mot the tich d^ung moi be , sau do lam giau no bing eac each tren trong tudng

bUu cd

Boi vdi asen , luan an sU dung pban Ung lam giau loai 1

va 2 khi ngbien euu eac be Cu-As , Gu-As-Au va ket bdp loei

1 , ^ kbi ngbien cUu be I-Cu-As

29

3.1.1.2 ) Qua trinb dien boa

Qua trinh dien boa trong giai doan lam giau chat rat pbUc tap , song CO the tam chia thinb ba giai doan seu :

1) Su cbuyen chat boat dong dien tdi dien cue lim viec

2) Su cbuyen dien tich giUa chat boat dong dien va dien cUe 3) Su cbuyen san pbam cua phan ung di|n cite vao dung dicb boae

sU tao thanb bon bong bay mang tren be mat dien eUc

Tuy tung trUdng bdp cu the , giai doan nao cham nbat se

la giai doan quyet dinb toe do cua ca qua trinb Ciai doan tao tbinb ket tua tren dien cue c6 y nghia Idn , nbat la trUdng bdp dung cae dien cUc rin SU ket tua bing dien tUdng tU sU ket tua boa b9c Trong qua trinh ket tua boa b9e eo bien tUdng qua bao boa - Trong qua trinb ket tua bing dien c6 bien tudng qua the /" 55 7 • ^'^i ^ay , trong thUe binh , kbi lam giiu cac nguyen to , chang ban Cu,Pb,Gd,Zn , ngUdi ta pbai dien pban 3 the ami hdn the bat dau co dong gidi ban song cue pho it nbat

li ©,3 V 7 3,55 7

3.1.1.3 ) Tinh chat hon bong

Hon bong la mot he kim loai ma mot hdp pban cua no la

tbuy ngan Hon bong eo the dUde binh tbinb khi dien phan cac dung dicb chUa ion kim loai bing dien eUc tbuy ngan tinb b9ae mang tbuy ngan tren dien cUc rin Luan an eo dung bai loai dien eUc niy nen viec tim bieu tinh chat cbung cua hon bon^ li can tbiet

Cac kim loai tan trong tbuy ngan 3 nbung mUe do kbae nbau

va phu tbuoc vao nbiet do Lien ket cua cbung vdi tbuy ngan

CO the mang dae trUng lien ket kim loai ho^e lien ket ion GiUa kim loai va tbuy ngan co the tao thanb eac bdp chat gian kim loai ( intermetalic compound ) Neu nbieu kim loai cung

tan vao tbuy ngan , tbi giUa ehung cung eo the tao tbanh cac h hdp chat kieu nbu the Thanh phan eac bdp chat gian kim loai tbUdng kbong theo qui luat boa tri - B9 tan cua cae hdp chat gian kim loai tbUdng rat be Bo do , kbi tao tbanh eac bdp chat lo^i niy thudng eo bi|n tudng taeb pha -

Gac kim loai kbi tan vio tbuy ngan deu it nlilexx thay ddi tinfe chat dien boa 7 55 7 • Cbing ban , kbi nong do kim loai vUdt qua do tan thi kim loai tinh kbiet bit dau taeb ta tu hon bong bao boa - Lue nay , the cua bon bong bing the cua kim loai tinh kbiet - The cua bon hong chUa bdp chat gian kim loai A^B^ nim giua cae gia tri tUdng ung vdi hon bong ehUa tung bdp phan rieng le V.v - Nbung bien dil xay ra trong bon bong co the bieu hien tren dUdng cong pban cue dong dien / dien the - Chang ban , neu boa tan anot m.ot hon hong phue tap , thi moi bdp phan

se bi boa tan 3 the Ung vdi the bea tan moi hon bong dong the rieng le Neu bdp chat gian kim loai binh thinb , tbi tren dudng phan eUc dong dien / dien the , nbung dinb ban dau bien

di va CO the xuat hien dinb mdi Ung vdi hdp chat mdi da binh

tbinb / 55 7

3.1.1-4 ) Tinb chat mang kim loai tren dien cue rin

Luan an co dung bai loai dien cue ran li dien cUc than

tbuy tinh vi dien cue than mem Noi ehung , eac dien cUc ran

CO be mat kem hoan bao so vdi dien eUe tbuy ngan va kbo lap lai trang thai ban dau sau moi Ian d^i mdi - Tuy vay , cbung dude

sU dung rong rai de xac dinb nbieu nguyen to ma tin bieu pTlan tich nam d vung the dudng , tai do tbuy ngan bi boa tan anot

Mang kim loai tren dien cue rin cung co nbung tinh chat tudng tu tren dien cue tbuy ngan , song no cung co nbung net rieng Noi cbung , cae mang niy thudng mong , xop GiUa kim

31

loai va dien cue co the binh tbanh may loai tudng tac dang cbu

y nbu sau /" 55 7 =

1) Lien ket kim loai - dien cUc manb bdnlien ket giUa eac

nguyen tU kim loai - Luc dien phan , dau tien be mat bi phu bdi

ddn Idp tbu nbat , sau do d6n Idp tbu bai binh tbanh

2) Lien ket giUa cac nguyen tU kim loai manb bdn lien ket

kim loai - dien cUc Kbi do , kim loai se ket tua tren nfciing '

trung tam cua eac nguyen tu kim loai da ket tua trude

-Kbi boa tan mot chat da ket tua tren dien cue , trong nbieu

trudng bdp , ngudi ta ghi dude mot dinh ehinh , Idn , ro ring

vi vai dinh phu nim 3 the dudng bdn the boa tan tinb tbeo phudng

trinb Nernst Gac dinb phu tbUdng ung vdi sU boa ten cua ddn

Idp tbu nbat co lien ket vdi be mat dien cue manh hdn lien ket

giUa cae nguyen tu kim loai

3.1-2 - NhUng_van_d|_lien_guan_den_giai_doan_b

Mot so van de dinb tinh lien quan den qua trinb boa tan

ket tua da dude de cap d phan trUdc Phan nay ebi gidi tbieu

sd lude , cbu yeu bing cac bieu tbue toan h9e , sU phu tbuoc

cua tin bieu pban tich vao eac dai ludng dae trung ebo moi

phudng pbap se dung de ngbien eUu

3-1-2.1 ) PbUdng pbap von-ampe boa tan

1) Hoa tan kim loai tu dien cue tbuy ngan tinb va dien cue

mang tbuy ngan ' Phudng trinb bieu dien dong cUe dai boa tan tu dien cue

tbuy ngan tinh ( dang tree ) trong trudng bdp pban ung dien cue

tbuan ngbich co dang sau /357 :

( trong do : kj^ , k^ — cac bing so )

The dinb co the bieu dien nbu sau :

prp

Boi vdi dien cUc ming tbuy ngan , Eoe B K ( theo £ y:> 7 )

dat dieu kien ring , sU kbuecb tan trong mang tbuy ngan be ,

CO the bo qua ; dung dieb dude kbuay vdi toe do kbong d^i , va

cuoi cung da tinh dude : #

( trong do : e — Ed so logarit tU nbien

E '— the dien eUc hinlj tbue 1ieu diwln ) 2) Hoa tan kim loai tu dien cue trd phing

Giai pbUdng trinb lien quan den dinb luat tbu bai cue Pic

khi cbu y den donfe b9c phan ung cbuyen dien tich , boat do kim

loai tren be mat dien eUc , toe do cbuyen san pbam phan ung

dien boa kboi dien eUc , Brainina Kb Z /~ 3 7 da tim thay

nbung bieu thUe cuoi cung cbo mot so tru'dng hdp nhu sau :

1 - Qua trinh dien cue tbuan ngbich :

B : the can bing

E : the bit dau ghi

Q' : ludng dien ngoai suy trong tinti toan

£^ : boat do ket tua ldp day

Y : be so ty le trong bieu thUc ve tudng quan giUa boat

do ket tua cua ldp day vi ldp mong

(p = 1 - oC

Cae ky bi|u kbae eo trong bang cbu tit , 3 A^M luan an

3.1.2.2 ) PbUdng pbap dien the tbdi gian boa tan

Trong phudng pbap dien the' tbdi gian , nong do

chat kbu cUc ty le tbuan vdi can bae bai tbdi gian cbuyen £ 39 7

Con trong pbUdng pbap BTHT,tbdi gian cbuyen ty le tbuan vdi

nong do chat ngbien euu 7 55 7 * ^'^ l^uldng 7 56 7 cung xac nhan

dieu do Zakbarov M C vi cong tac vien 7" S,9 7 da ngbien

cUu ly tbuyet mot each he thong phudng pbap nay ( co doi cbung tbue nghiem ) Budi day la nbung ket luan cuoi cung cua ^o

trong mot so trudng b^p co lien quan den luan an

mang tbuy ngan 7 9 7

a) Bien cUc mang tbuy ngan ( phing )

J : kieb tbude dae t n m g cua dien eUc , tinb ra cm ^

doi vdi dien cUc mang tbu;^ ngan , do li cbieu day ming, doi vdi dien cUe tbuy ngan tinh , do la ban kinh giot -

Z tinb ra giay ; B-^ — cm / s

2) Hoa tan kim loai tU be mat dien cUc trd phang 7 8 7

Q ty le vdi ludng kim loai da ket tua tren be mat dien

cue nen tbdi gian cbuyen dudc tinb nbu sau :

r = Q / I ( 19 )

Biet ring : Q = ^ ^ ^ C x ^d ^^ ( 20 )

Trong pbUdng pbap BTHT , do Idn cua dong dien pbong qua

ldp dien kep ( dong tu dien ) tao nen pbong Khi xem xet anb

budng cua pbong den tin bieu phan tieb , Zakbarov M G da rut

ra cong tbue tinb nong do cUc tieu ma BTHT eo the xae dinb dudc

Trong nbung dieu kien phan tieb binh thudng nbiU t^ = 30 pb ,

n = 2 ^ gia tri noi tren la 1,15-10" mol/1 £8/ •

dl%n nen nbay bdn o\lo pho eo dien chut it Ngay nay , the gidi

CO cue pb6 xung vi pban vdi do phan giai va do nbay hdn hSn eUc ph6 dong xoay cbieu , vi the eac tac gia ve dien hoa boa tan kbong quan tam den ky tbuat nay nUa Iran HUu Hoan va cae cong

sU trong nude £ S3 7 dung ky tbuat boa tan bae bai xae dinb Cd tbeo pbUdng pbap dien boa boa tan , da dat den do nbay 5.10

1/1 Cie tic gia niy dung nen NK^Gl IM ^ im^OH 0,5 M

^-2

mo

HgClo 2.10 M va dien cue ming tbuy ngan tren than mem Ho da dUa ra mot bieu thUe thUe ngbiem ve quan he giua dong hoa tan boa tan bae bai ( I ) vdi cae dai ludng dae trUng cua phudng pbap nhu : bien do the xoay cbieu , toe do quet the , tbdi gian dien pban v.v Nban tbay su phu tbuoc ty le tbuan giUa I ^ va nong do chat pban tieb

Qua nbung dieu triiih bay tren , ta thay cac phudng pbap pban tieb dung trong luan an eo dae diem cbung la : giUa tin bieu pban tieb ( I , "C , I 2 ) ^^ nong do cbst can xac dinb co si^ phu tbuoc ty le tbuan Tuy nbien , ^o cac phudng trinb ly tbuyet cbUa de cap den mot so van de nhu la su tao tbanh bdp chat gian kim loai , anb budng cua chat b9at dong be mat v.v ,

nen trong tbUe te , moi quan be tren chi ton tai trong k h o ^ g nong do hep vdi nbung dieu ki|n nio do pbai tim bing tbue ngbem

0