TRNG I HC CNG NGHIP TP

CHNG 1:TNG QUAN1.1. Tng quan v phn nhm1.1.1. Gii thiu chung v phn nhm [6,7]

Nhm sunfat sn xut t acid sunfuric v mt s vt liu cha nhm nh t st, cao lanh, qung bxit, nhm hydroxit. C cng thc chung l Al2(SO4)3.nH2O. Phn nhm l mt loi mui c cng thc chung l M2SO4.Al(SO4)3.xH2O ( M c th l ion kim loi kim hoc ion amoni).

Nu ch c nhm sunfat th l phn n v khi cho thm kali sunfat hoc amoni sunfat th gi l phn kp. iu ch sn phm ny ngi ta cho nhm sunfat vi mui sunfat ca kim li kim hoc amoni theo t l mol tng ng sau c n to vng ri kt tinh. Khi cho thm kali sunfat vo qu trnh phn ng, thu c nhm kali sunfat cng thc phn t l K2SO4.Al2(SO4)3.24H2O hay AlK(SO4)2.12H2O. Trng hp dng amoni sunfat thu c phn nhm amoni c cng thc phn t l Al2(SO4)3.(NH4)2SO4.24H2O hay Al(NH4)(SO4)2.12H2O.

l nhng phn nhm tn ti dng n phn t ngoi ra cn c loi phn nhm tn ti dng cao phn t (polyme) nh nhng phn sau: PAC, WAC, PASC, PASS. Phn PAC hay cn gi poly aluminum chlorite c cng thc phn t chung l (Aln(OH)mCl(3n-m)) vi m= 4-10, n= 2-5. Ta c th coi nhng cht poly aluminum chlorite (PAC) nh l sn phm to thnh bi phn ng khng trit gia axit clohydric v nhm hydroxit theo phng trnh:

Tng t, trong cng thc phn t Aln(OH)m(SO4)kCl3n-m-2k ca cht poly aluminum cloro sunfat (WAC) c mt s ion Cl b thay th bi nhng gc hydroxyl OH v nhng gc sunfat SO4-. Cn trong cng thc phn t ca nhng cht poly aluminum clorua silicat (PACS) v poly aluminum sillcate sulphate (PASS) li cha nhng gc silicat SiO3- hay nhng nhm silic oxit SiO2.1.1.2. Phn loi phn nhm

Phn nhm gm hai dng

- Dng n phn t

Phn nhm n: c cng thc chung ca nhm sunfat l Al2(SO4)3.nH2O, thng gp Al2(SO4)3.18H2O cha 15% Al2O3. Ty theo iu kin sn xut, c th thu c nhiu loi tinh th nhm sunfat hydrat ha khc nhau trong gi tr ca n c th l 18, 16, 27,...

Phn nhm kp: l mui kp ca nhm sunfat vi sunfat kim loi kim hoc amoni. V d nh phn K2SO4.Al2(SO4)3.24H2O, ...

Kali nhm sunfat hay (thng gi l phn chua) K2SO4.Al2(SO4)3.24H2O l nhng tinh th ln hnh bt din, trong sut, khng mu, v cht, cm gic se li, khi lng ring d =1,75 g/cm3, nhit nng chy 92oC, un nng n 200oC th mt nc kt tinh thnh phn khan dng bt trng, t tan trong nc.

Dung dch phn c tnh acid, khng c. Tinh th phn tan trong nc to mng hydroxit lng xung ko theo cc cht bn l lng trong nc. V vy n c dng lm trong nc, lm cht keo t trong x l nc, lm cht cm mu trong nhum vi, cht kt dnh trong ngnh sn xut giy, lm thuc th trong cc phng th nghim, dng lm thuc cm mu, lau ra b phn c th ra nhiu m hi, ra nim mc ming, hng, lm thuc rc k chn.

- Dng cao phn t: l loi phn nhm tn ti dng (polyme) v d nh phn poly aluminum chlorite (PAC), ... Cha 30- 31% Al2O3

Phn poly aluminum chlorite (PAC) c PAC rn v PAC dng lng. Dng rn l bt mu vng v dng lng c mu nu vng tan tt trong nc. C cng thc (Aln(OH)mCl(3n-m)) thng gp nht khi m=3 v n=2 cng thc phn t l (Al2(OH)3Cl3)

Trong bi n ny s dng phn kali nhm sunfat c cng thc phn t l: K2SO4.Al2(SO4)3.24H2O v phn poly aluminum chlorite (PAC) c cng thc (Al2(OH)3Cl3).1.1.3. c tnh ca phn nhm

Lm cht keo t trong x l nc thi, thc hin phn ng thy phn vi nc to thnh cc bng hydroxit kim loi c kh nng ht cc ht l lng trong nc ri theo lc trng trng, lng nhanh xung y. Qu trnh keo t din ra do phn ng thy phn ca mui nh sau:

Theo phn ng trn, hydroxit nhm keo t li ko cc cht l lng kt ta. Trong cng ngh x l nc (v mc nht nh cng ngh x l nc thi v mt s cng ngh khc) cng ngh keo t m theo truyn thng cht keo t l phn nhm Al2(SO4)3 ng vai tr quan trng.

Vai tr ca phn nhm l khi c a vo nc cn x l cha cn l lng, u tin n phi ha tan to Al3+ trung ho in tch cc ht keo m, sau mui nhm thy phn to bng cn l Al(OH)3. Trong b lng, bng cn kt ta ko theo cn l lng cn x l v lm trong nc. Trong thc t phn cng thc hin c cch to bng nu thit k khu vc to bng tt s to iu kin cho cc bng cn nh tip xc to cc bng ln. Cng on keo t lm trong nc l mt bc k thut quan trng trong dy chuyn cng ngh x l nc thi v cc loi nc c nhiu cn l lng khc.1.2. Tng quan v nc thi ngnh cng ngh dt nhum

1.2.1. Quy trnh cng ngh

Ngnh dt nhum l ngnh cng nghip c dy chuyn cng ngh sn xut phc tp, p dng nhiu loi hnh cng ngh khc nhau. Ty theo quy m ca c s dt nhum, tnh cht ca ngun nguyn liu, tnh cht ca sn phm, trnh cng ngh m cc cng on dt nhum ti cc c s cng khc nhau nhiu hay t. Quy trnh cng ngh dt nhum c trnh by nh sau:

Hnh 1.1. S chung quy trnh cng ngh dt nhum [1]1.2.2. Cc ngun nhim, c tnh dng nc thi ngnh dt nhum [1]

Cc cht gy nhim chnh trong nc thi ca cng ngnh dt nhum gm:

Cc tp cht tch ra t vi si nh du m, cc hp cht cha nit, cc cht bi bn dnh vo si (trung bnh 6% khi lng x si).

Cc ha cht s dng trong qu trnh cng ngh dt nhum nh h tinh bt, H2SO4, CH3COOH, NaOH, NaOCl, H2O2...Cc loi thuc nhum, cc cht tr ngm, cht cm mu, cht ty git. Lng ha cht s dng i vi tng loi vi, tng loi mu thng khc nhau v ch yu i vo nc thi ca tng cng on tng ng.

Dt nhum l mt trong nhng ngnh i hi s dng nhiu n nc v ha cht. Hin nay trong ngnh cng nghip dt nhum dng rt nhiu nc phc v cho cc cng on sn xut bnh qun 50-300m3/ tn sn phm. Trong ngun nhim chnh xut pht t cng on dt nhum v nu ty.

Hng nm, ngnh cng nghip dt nhum s dng hng nghn tn thuc nhum. Hiu sut s dng ca cc loi thuc nhum vo khong 70-80% v ti a l 95%. Ty theo tng loi vi, loi sn phm m ngi ta c th s dng nhiu loi thuc nhum thch hp nh thuc nhum hon nguyn, thuc nhum hot tnh, thuc nhum phn tn. Vi mi loi thuc nhum mi trng khc nhau th tnh cht nc thi cng khc nhau.

c trng quan trng nht ca nc thi t cc c s dt nhum l s dao ng rt ln v lu lng v ti trng cc cht nhim, n thay i theo ma theo mt hng sn xut v cht lng sn phm.

Thnh phn nc thi ca cng ngh dt nhum rt a dng bao gm cc cht nhim dng hu c v dng v c. Nhn chung nc thi t cc c s dt nhum c kim kh cao, c mu v hm lng cc cht hu c COD cao

Nc thi ty dt: c pH t 9-12, hm lng cht hu c COD t 1000-3000 mg/l do thnh phn cht ty gy nn. mu ca nc giai on u c th ln n 10000 Pt-Co, hm lng cn l lng khong 200mg/l nng ny gim nhng giai on cui. Thnh phn ca nc thi gm thuc nhum tha, cht hot ng b mt, cc cht oxy ha cellulose, xt, cht in ly ...

Nc thi nhum thng khng n nh v a dng, do hiu qu hp th thuc nhum ca vi ch t 60-70%, v 30-40% cc phm nhum tha dng nguyn thy hoc b phn hy mt dng khc. Ngoi ra mt s cc cht in ly, cht hot ng b mt, cht to mi trng cng tn ti gy ra mu rt cao ca nc thi nhum.

Thnh phn nc thi dt nhum thng cha cc gc nh RSO3Na, RSO3-, N-OH, R-NH2 ... Do cc phm nhum hot tnh, hon nguyn, v lng phm nhum tha ln dn n gia tng cht hu c v mu lm nc c mu rt cao i khi ln n 50.000 Pt-Co, hm lng COD thay i t 80 n 18.000 mg/l, pH ca nc thay i t 2-14.

Mc nhim ca nc thi dt nhum ph thuc rt ln vo loi v lng ha cht s dng, vo kt cu mt hng sn xut (ty trng, nhum, in hoa...), vo t l s dng si tng hp, vo loi hnh cng ngh sn xut (gin on, lin tc hay bn lin tc), vo c tnh my mc thit b s dng...Bng1.1. Cc cht gy nhim v c tnh ca nc thi ngnh dt nhum [1]Cng onCht gy nhim trong nc thic tnh dng thi

H si, gi hTinh bt, glucozo, cacboxy metyl, cellulozo, polyvinyl alcol, nha, cht bo v spBOD cao (34 50% tng lng BOD)

Nu tyNaOH, cht sp v du m, tro, soda, silicat natri v x sivn kim cao, mu ti, BOD cao (30% tng BOD)

Ty trngHypoclorit, hp cht cha clo, NaOH, AOX, axit kim cao, chim 5% BOD

Lm bngNaOH tp cht kim cao, BOD thp (di 1% tng BOD)

NhumCc loi thuc nhum, acid axetic v cc mui kim loi mu rt cao, BOD kh cao (6% tng BOD), TS cao

InCht mu, tinh bt, du, t st, mui kim loi v acid mu cao, BOD cao v du m

Hon thinVt tinh bt, m ng vt, muiKim nh, BOD thp, lng nh

1.2.3. Cc loi thuc nhum thng dng trong ngnh dt nhum [2]

Thuc nhum phn tn

Nhm thuc nhum ny c cu to phn t t gc azo v antraquinon v nhm amin (NH2, NHR, NR2, NR-OH), dng ch yu nhum cc loi si tng hp (si axetat, si polieste) khng a nc.

Thuc nhum acid

L cc mui sunfonat ca cc hp cht hu c khc nhau c cng thc l R-SO3Na khi tan trong nc phn ly thnh nhm R-SO3 mang mu. Cc thuc nhum ny thuc nhm mono, diazo v cc dn xut ca antraquinon, triaryl metan

Thuc nhum hot tnh

L nhng hp cht mu m trong phn t ca chng c cha cc nhm nguyn t c th thc hin mi lin kt ha tr vi vt liu ni chung v x dt ni ring trong qu trnh nhum. Thuc nhum hot tnh c gam mu, mu ti v thun sc, cng ngh nhum a dng v khng qu phc tp. Chng c s dng nhum v in hoa cho cc vt liu cellulozo, t tm, len, vt liu t x polyamit.

Cc loi thuc nhum hot tnh tuy c khc nhau v cu to phn t, phm vi s dng v hot c th trnh by di dng tng qut:

Trong :

S- nhm to cho phn t c ha tan cn thit trong nc, thng gp hn c l cc nhm: - SO3Na, - COONa, - SO2CH3.

R- phn mang mu ca phn t thuc nhum n khng nh hng n mi lin h gia thuc nhum v x m n quyt nh v mu sc, v bn mu vi nh sng v cng c tc ng n cc ch tiu v bn mu khc, nn vic chn gc R phi tha mn c cc yu cu k trn. Nhng gc mu c chn vo mc ch ny l: mono v iazo, phc cht ca thuc nhum azo vi ion kim loi, gc thuc nhum acid antraquinon, hon nguyn a vng, dn xut ca Ftaloxianin

T-X- nhm hot tnh c cu to khc nhau, c a vo cc h thng mang mu khc nhau.

X- nguyn t hay nhm phn ng, trong iu kin nhum n s tch khi phn t thuc nhum, to kh nng cho thuc nhum thc hin phn ng ha hc vi x. X khng nh hng g n mu sc nhng i khi cng c nh hung n ho tan ca thuc nhum. Nhng nguyn t ny thng l: -Cl, -SO2, -OSO3H, -NR3, -CH=CH2

T- nhm mang nguyn t (hay nhm) phn ng, n lm nhim v lin kt gia thuc nhum vi x v c nh hng quyt nh n bn lin kt ny, trc ht l bn mu ca thuc nhum vi gia cng t. Khng nhng th, hu ht cc trng hp s tng tc ca thuc nhum hot tnh vi x l phn ng nucleophin, nhm T s ng vai tr quyt nh tc phn ng nn vic la chn nhm T cho ph hp rt quan trng.

Nhng u im v nhc im ca thuc nhum hot tnh:

- u im: c gam mu rng, mu ti v thun sc, c bn cao vi gia cng t, d lm sch nc thi, gi thnh va phi.

- Nhc im: kh git sch phn thuc nhum b thy phn, tn nhiu ha cht, bn mu vi nh sng khng cao nht l mu v mu cam.

Thuc nhum trc tip

y l thuc nhum bt mu trc tip vi x si khng qua giai on x l trung gian, thng s dng nhum si 100% cotton, si protein (t tm) v si poliamid, phn ln thuc nhum trc tip c cha azo v mt s l dn xut ca dioxazin. Ngoi ra, trong thuc nhum cn c cha cc nhm lm tng bt mu nh triazin v salicylic acid c th to phc vi cc kim loi tng bn mu.

Thuc nhum hon nguyn

Thuc nhum hon nguyn gm hai nhm chnh: nhm a vng c cha nhn antraquinon v nhm indigoit c cha nhn indigo. Cng thc tng qut l R=C-O, trong R l hp cht hu c nhn thm, a vng. Cc nhn thm a vng trong loi thuc nhum ny cng l tc nhn gy ung th, v vy khi khng c x l, thi ra mi trng, c th nh hng n sc khe con ngi.

Thuc nhum lu hunh

L nhm thuc nhum cha mch d hnh nh tiazol, tiazin, zin trong c cu ni -S-S- dng nhum cc loi si cotton v viscose.

Thuc in, nhum pigmen

C cha nhm azo, hon nguyn a vng ftaoxianin, dn xut ca antraumon.1.3. Cc ch tiu nh gi cht lng nc [4]1.3.1. Cc ch tiu vt l1.3.1.1. c

Nc tinh khit trong sut khng mu, c kh nng cho nh sng truyn qua. Khi c cc tp cht huyn ph, cn rn l lng, cc vi sinh vt v c cc ha cht ha tan th kh nng truyn nh sng ca nc gim i.

Da vo ngi ta xc nh c ca nc. Nc c c cao tc l c nhiu tp cht cha trong v do vy kh nng truyn nh sng qua nc gim. n v o c thng dng l mg SiO2/l, NTU, FTU, trong n v NTU v FTU l tng ng nhau.

1.3.1.2. mu

Nc nguyn cht khng c mu, khi nc cha mt s cc cht ha tan th n tr nn c mu, cc hp cht st ha tan lm cho nc c mu nu , cc cht mn humic lm cho nc c mu vng, cc loi thy sinh to cho nc c mu xanh l cy Nc thi sinh hot v nc thi cng nghip thng to ra mu xm hoc mu en cho ngun nc.

n v o mu thng dng l theo thang mu platin - Coban. Nc thin nhin thng c mu thp hn 200 (Pt - Co). mu biu kin trong nc do cc tp cht l lng trong nc to ra v d dng loi b bng phng php lc. Trong khi , loi b mu thc ca nc (do cc cht ha tan to ra) phi dng cc bin php ha l kt hp.

1.3.1.3. Hm lng cht thi rn trong nc

Hm lng cht rn trong nc gm c cht rn v c (cc mui ha tan, cht rn khng ha tan nh huyn ph, t ct), cht rn hu c (gm cc vi sinh vt, vi khun, ng vt nguyn sinh, to v cc cht v c rn hu c v sinh nh phn, rc, cht thi cng nghip). Trong x l nc ngi ta a ra cc khi nim sau:

- Tng hm lng cn l lng TSS l trng lng kh tnh bng miligam ca phn cn li sau khi bay hi 1 lt mu nc trn ni cch thy ri sy kh 103oC ti khi c trng lng khng i, n v l mg/l.

- Cn l lng SS l phn trng lng kh tnh bng miligam ca phn cn li trn giy lc khi lc 2 lt mu nc qua phu, sy kh 103oC-105oC ti khi c trng lng khng i, n v l mg/l.

- Cht rn ha tan DS bng hiu gia tng hm lng cn l lng TSS v cn l lng SS:

DS = TSS - SS

- Cht rn bay hi VS l phn mt i khi nung 550oC trong mt thi gian nht nh. Phn mt i l cht rn bay hi, phn cn li l cht rn khng bay hi.

1.3.2. Cc ch tiu ha hc

1.3.2.1. Hm lng oxy ha tan DO

Mt trong nhng ch tiu quan trng nht ca nc l hm lng oxy ha tan, v khng th thiu c i vi tt c cc vi sinh vt sng trn cn cng nh di nc.

Oxy l cht kh kh ha tan trong nc, khng tc dng vi nc v mt ha hc. ha tan ca n ph thuc vo p sut, nhit v cc c tnh ca nc (cc thnh phn ha hc, vi sinh, thy sinh sng trong nc). Nng ca n khong 815mg/l nhit bnh thng. xc nh hm lng oxy ha tan trong nc ngun cng nh nc thi, ngi ta thng dng phng php iot (hay cn gi l phng php Winkler).

1.3.2.2. Nhu cu oxy sinh hc BOD

Nhu cu sinh ha oxy BOD l lng oxy cn thit vi sinh vt phn hy cc cht hu c trong mt n v th tch nc nht nh (1000 ml) trong mt n v thi gian nht nh, trong iu kin nhit l 20oC v khng c nh sng.

xc nh lng oxy cn phi cung cp cho nc thi mt lng oxy tha cho qu trnh phn hy cc cht hu c do cc vi sinh vt (qu trnh c th l: 5, 10, 15, 20 ngy ty theo yu cu nghin cu).

Lng oxy trong nc gim i so vi ngy u cho bit s mg oxy m cc vi sinh vt tiu th. Trong mi trng nc, khi qu trnh oxy ha sinh hc xy ra th cc vi khun s dng oxy ha tan.

Vn tc ca qu trnh oxy ha ni trn ph thuc vo s vi khun c trong nc v nhit ca nc. BOD cng l mt ch tiu dng nh gi mc nhim bn ca nc.

BOD c th c xc nh bng phng php ha hc khi s dng kali permaganat, xanh metylen, xc nh t COD. Hoc cng c th dng phng php sinh hc, dng chai BOD hay phng php h hp.

V qu trnh oxy ha hon ton cc hp cht hu c i hi phi tn nhiu thi gian nn ngi ta thng dng ch tiu BOD5 l lng oxy tiu th sau 5 ngy.

1.3.2.3. Nhu cu oxy ha hc COD

COD l lng oxy cn thit oxy ha ht cc hp cht hu c c trong nc, to thnh CO2 v H2O. COD l mt i lng dng nh gi s b mc nhim ca ngun nc. Phng php ph bin nht xc nh COD l phng php kali bicromat.

1.3.2.4. pH

pH l i lng c nh ngha theo phng trnh sau:

Tnh cht ca nc c xc nh theo cc gi tr khc nhau ca pH:

- Khi pH = 7 nc c mi trng trung tnh

- Khi pH > 7 nc c tnh kim

- Khi pH < 7 nc c tnh acid.

pH c th xc nh bng giy qu hoc bng cc my o pH (pH mt) in cc hydro hoc cc thy tinh.1.4. Phng php x l nc thi dt nhum [4]

Qu trnh x l nc thi l mt quy trnh cng ngh bao gm nhiu cng on nh, mi cng on ch c th x l c mt phn tp cht nht nh. Do chng ta phi tm hiu s b v cc cng on v phng php x l trong mt dy chuyn c bn.Do c th ca cng ngh, nc thi ngnh dt nhum cha tng hm lng cht rn l lng, mu, BOD, COD cao. Cc yu t c cn nhc khi la chn phng n x l thch hp cho nc thi dt nhum l hiu qu x l, hiu qu kinh t, tnh cht v lu lng nc thi, thnh phn v nng cc cht nhim c trong nc thi, c bit phng php x l phi ph hp vi iu kin sn xut. C rt nhiu phng php x l nc thi nh phng php ha hc (phng php oxy ha kh...), phng php c hc (lng lc...), phng php sinh hc, phng php ha l gm ng t v keo t, hp ph, tuyn ni... Trong bi n ny chng em chn phng php ha l keo t-to bng.1.4.1. Phng php keo t - to bng

Cc tp cht trong nc thng a dng v chng loi v kch thc, chng c th l cc ht ct, sinh vt ph du, sn phm hu c phn hy nh thuc nhum... Kch thc ht dao ng t vi phn triu milimet n vi milimet. Bng cc phng php x l c hc nh lng lc, tuyn ni, ch c th loi b c cc ht c kch thc ln hn 10-4 mm, vi cc ht c kch thc nh hn 10-4 mm, nu dng qu trnh lng tnh th phi tn rt nhiu thi gian v cng rt kh c th c c hiu qu cao, do vy cn phi p dng phng php x l ha l, l phng php keo t.

Keo t l phng php x l nc c s dng ha cht, trong cc cht rn gy c dng ht keo nh l lng trong nc nh tc dng ca cht keo t m lin kt vi nhau to thnh bng keo c kch thc ln hn d lng.

Cc cht keo t thng c s dng l phn nhm, phn st...di dng dung dch ha tan, cc cht in ly hoc cc cht cao phn t...

Cu to ca ht keo

Ty thuc vo ngun gc xut x, thng thng cc ht cn trong nc u c th mang in tch m hoc dng, v d ht cn gc silic, cc tp cht hu c u mang in tch m. Cc hydroxit nhm, st mang in tch dng. Khi th cn bng in ng ca nc b ph v cc thnh phn mang in tch s kt dnh vi nhau nh lc lin kt phn t v lc in t, to thnh mt t hp cc phn t, nguyn t hoc cc ion t do. Cc t hp to thnh c gi l ht keo. Ty thuc vo thnh phn cu to cc ht keo s c nhng tnh cht khc nhau. Ngi ta c th chia cc ht keo thnh hai loi: keo k nc v keo ho nc. Trong k thut x l nc bng qu trnh keo t, keo k nc ng vai tr ch o.

Ht keo c cu to rt phc tp gm:

- Nhn keo: l tp hp c th bng hng trm hoc hng ngn ty thuc vo phn tn, kch thc nguyn t hay phn t.

- Lp hp ph: c to ra do nhn keo c kh nng hp ph mnh v hp ph chn lc nhng ion c trong thnh phn nhn ht keo.

- Lp khuyt tn: to ra do cc ht keo cn ht nhng ion ngc du xa hn.

Hnh 1.2. Cu to ht keo [3,4]

Trong :

1. L nhn keo 2. Lp hp ph

3. L lp khuych tn4. Lp in tch kp

Qu trnh keo t xy ra theo cc c ch:

- Hp ph v trung ho in tch: khi mi trng pH ph hp cho qu trnh hp ph ca cc cu t nhm trn b mt cc cht gy c, hin tng keo t xy ra. Qu trnh hp ph xy ra trong mt h c phn tn cao nn tc hp ph rt ln. Nu h c khuy trn tt, thi gian t ti cn bng ch tnh bng pht.

- C ch li cun, qut: bn thn cht keo t phn nhm t n c th kt ta v lng. Khi nng huyn ph thp cc cht gy c kh to thnh tp hp ln lng. Nn kt ta ht h cn thm mt lng cht keo t.

Nng cht keo t cao, t mc siu bo ho s t n kt ta v lng, trong qu trnh n s cun theo cc ht c cng lng.

- C ch hp ph v to cu ni gia cc ht: sau khi ht huyn ph c kh in tch b mt, chng c th co cm li thnh cc tp hp ln, qu trnh ny din ra chm. thc y ngi ta b sung thm polyme tr keo t vo h, cc polyme ny s b hp ph trn b mt cht gy c theo kiu m neo, tc l mt phn t polyme c th b hp ph trn nhiu ht gy c. Chng ng vai tr chic cu ni ca cc cht gy c, ko chng li vi nhau to thnh cm ln. Tc ny xy ra rt nhanh ch chng vi pht.

- C ch keo t hp ph cng lng: cc ion kim loi ha tr cao s dng trong qu trnh keo t nh Al3+ to ra trong nc cc sn phm thy phn khc nhau nh Al(OH)4-, Al(OH)2+... cc gi tr cao v thp ca pH, cc lin kt ny tn ti v tch in, nhng mt gi tr pH trung bnh no th ch c mt cc hydroxyt nhm to ra lp tc chng lng xung. Trong qu trnh lng chng ko theo c cc bng keo v tp cht c trong h huyn ph nh cc ht keo khc, cc cn bn, cc cht hu c, cht mang mi tn ti trng thi ha tan hay l lng.

ng hc ca qu trnh keo t

- Khi h keo trong nc b cc cht keo t lm mt i trng thi n nh ca n tc to bng keo quyt nh bi s chuyn ng to ra s tip xc gia cc ht keo vi nhau nh s khuch tn v chuyn ng c hng. Khuch tn ch c tc dng hnh thnh bng keo nh, hnh thnh bng keo c kch thc ln phi c chuyn ng nh hng ca cc ht keo chng tip xc vi nhau.

- Di tc ng ca chuyn ng nhit, ban u cc ht cn c kch thc nh va chm v kt dnh to thnh ht c kch thc ln cho n khi chng khng khng cn kh nng tham gia vo chuyn ng nhit na. Lc ny tc ng khuy trn tham gia vo qu trnh to bng cn ln hn. 1.4.1.1. Phng php keo t dng cht in ly n gin

Bn cht ca phng php l cho vo nc cc cht in ly dng ion n gin ngc du. Khi nng cc ion ngc du tng ln th cng c nhiu ion c chuyn t lp khuch tn vo lp in tch kp, dn ti vic gim ln ca th in ng zeta, ng thi lc y tnh in cng gim i. Nh chuyn ng Brown cc ht keo vi in tch b khi va chm d kt dnh bng lc ht Vander Walls to nn cc bng cn ngy cng ln v d dng lng xung.

Qu trnh keo t bng cc cht in ly n gin c xem nh mt c ch keo t ti u v n gii thch qua s nn in trong lp khuch tn vo lp in tch kp ph v trng thi n nh ca h keo trong nc.

Trong thc t, qu trnh keo t dng cht in ly n gin t c ngha do nng cht in ly t ti vic ph v trng thi n nh ca h keo i hi rt cao. Kt qu thc nghim cho thy rng, khi s dng cht in ly vi cc ion c ha tr cao, hiu qu keo t cng ln v nng cht in ly i hi s gim i. Cng nh cc phng php keo t khc, keo t dng cc cht in ly n gin i hi liu lng cht in ly cho vo nc phi tht chnh xc. Nu nng cht in ly trong nc vt qu mc cn thit s dn n qu trnh tch in tr li vi cc ht keo, lm in th in ng zeta tng ln, hiu qu keo t gim i v h keo trong nc s tr v trng thi bn vng.

Do cc nhc im ni trn, trong thc t x l nc phng php keo t dng cht in ly n gin rt t khi v hu nh khng c s dng.

1.4.1.2. Phng php keo t bng h keo ngc du

Qu trnh keo t c thc hin bng cch to ra trong nc mt h keo mi tch in ngc du vi h keo cn bn trong nc v cc ht keo tch in tri du s trung ha ln nhau.

Trong qu trnh ny ngi ta s dng mui nhm hay cn gi l phn nhm lm cht keo t, l loi ha cht rt thng dng trong x l nc cp, nc thi nht l x l nc sinh hot. Mui ny c a vo nc di dng dung dch ha tan, trong dung dch chng phn ly thnh cc cation v anion theo phn ng sau :

Nh ha tr cao ca cc ion nhm kim loi, chng c kh nng ngm nc to thnh phc cht hexa [Al(H2O)6]+3. Ty vo gi tr pH ca mi trng m chng c kh nng tn ti cc u kin khc nhau, cc phc cht ny tn ti pH t 3 n 4

Khi tng pH cc phn ng xy ra nh sau:

Tng acid

Tng kim

Vi nhm khi pH bt u t 6 tr ln, cc phn ng dng li trng thi hydroxit Al(OH)3 kt ta lng xung. ha tan ca cc hydroxit Al(OH)3 qu nh nn pH ti u cc ion kim loi ny c tch ht ra khi nc. Qu trnh to thnh Al(OH)4- ch xy ra khi pH (( 7,5.

Cc sn phm hydroxit tan to thnh trong phm vi pH t 3 n 6, l cc sn phm mang nhiu nguyn t kim loi. Cc hp cht ny mang in tch dng mnh v c kh nng kt hp vi cc ht keo t nhin mang in tch m to thnh bng cn. Cc hydroxit nhm to thnh khc nhau ty thuc vo pH v cc iu kin ca qu trnh, song chng u l nhng hp cht mang in dng v c hot tnh to bng keo t cao nh hot tnh b mt ln. Cc bng keo ny khi lng xung s hp ph, cun theo cc ht keo, cn bn cht hu c, cht mang mu...tn ti trng thi ha tan hoc l lng trong nc. Mt khc, ion kim loi t do cn kt hp vi nc qua phn ng thy phn cng to thnh cc hydroxit nh sau:

Cc loi phn nhm thng c s dng trong qu trnh keo t nh nhm sunfat Al2(SO4)3.14H2O, Al2(SO4)3.18H2O, nhm clorua AlCl3.6H2O, aluminat natri NaAlO2

1.4.1.3. Phng php keo t hoc tng cng qu trnh keo t bng cc hp cht cao phn t

Qu trnh ny s dng cc cht cao phn t tan trong nc, chng c cu to mch di, vi phn t lng t 103-107g/mol v ng knh phn t trong dung dch vo khong 0,1m n 1m. Chng cng cn c s dng lm cht tr keo t, tc l s dng cng phn nhm l cht keo t chnh. Chng gip cho qu trnh keo t xy ra nhanh hn v to ra cc bng keo c kch thc ln hn c th tch ra khi nc mt cch d dng.

Da vo ha tr ngi ta phn chia cc loi cao phn t dng trong keo t ra thnh ba loi: loi anion, cation v loi khng ion. Ngoi ra cng c th phn chia chng theo cu to ha hc, theo ln phn t lng cng nh tch in ca chng. Ngoi cc cht cao phn t t nhin ngi ta s dng c cc cht cao phn t tng hp lm cht keo t.

Cc cht cao phn t khng ion mch thng, phn t lng rt cao v l mt trong nhng cht keo t tt nh polynatriacrylat (l sn phm trng hp ca natriacrylat), N-dimetylamino propylmethacrylat (c trng hp t acrylamit), polyacrylamit (l sn phm trng hp ca acrylamit). Cc polyme cu to mch di, phn t lng cao. Trong nc, chng keo t cc ht cn bn di dng lin kt chui. Cc lin kt ny to iu kin thun li cho vic hnh thnh v lng ta bng cn.

Trong x l nc hin nay thng dng nhiu cc cht polymer t nhin, cc polyacrylamit anion v khng ion. Lng polymer dng ti a n 0,5 mg/l. Tuy nhin cc loi polyme ny c nhc im l khng bo qun c lu, c bit khi ha tan trong nc, cng ngh sn xut tn km, gi thnh cao. V vy vic s dng polyme lm cht keo t nc ta cn b hn ch.

1.4.1.4. Cc yu t nh hng n qu trnh keo t [9]

Phng php keo t bng cc cht in ly hay cc hp cht cao phn t u t c s dng rng ri m ch yu l phng php keo t bng h keo ngc du hay gi n gin l keo t bng phn nhm.

Tr s pH ca nc

Nc thin nhin sau khi cho Al2(SO4)3 vo, tr s pH ca n b gim thp, v Al2(SO4)3 l mt loi mui to thnh t acid mnh v bazo yu. S thy phn c th lm tng tnh acid ca nc. Hiu qu keo t nh hng ch yu l tr s pH ca nc sau khi cho phn vo.

Tr s pH ca nc c nh hng rt ln v nhiu mt n qu trnh keo t

- nh hng ca pH i vi ha tan ca nhm hydroxit. L mt hydroxit lng tnh in hnh, tr s pH ca nc qu cao hoc qu thp u nh hng n qu trnh ha tan.

Trong mi trng acid: Mi trng acid yu:

Al(OH)2+ l ion to th, OH- l ion i ht keo (+)

Mi trng acid mnh (pH thp):

Kt qu dung dch keo chuyn thnh dung dch tht.

Trong mi trng kim:

Mi trng bazo yu:

Al(OH)2O- l ion ta th, H+l ion i ht keo (-)

Mi trng bazo mnh:

Khi OH- cao hn na, Al(OH)3 tan trong dung dch bazo to nn aluminat v dung dch keo tr thnh dung dch tht. Trong nc c ion SO42-, phm vi pH 5,5 - 7 trong vt kt ta c mui sunfat kim rt t ha tan. Khi gi tr pH bin i cao mui sunfat kim hnh thi Al2(OH)4SO4, khi gi tr pH bin i thp th hnh thi Al(OH)SO4. Tm li trong phm vi pH 5,5 - 7, lng nhm d trong nc u rt nh.

- nh hng ca pH i vi in tch ht keo nhm hydroxit

in tch ca ht keo trong dung dch nc c quan h thnh phn vi ion ca nc, c bit l vi nng ion H+. Cho nn tr s pH i vi tnh nng mang in ca ht keo c nh hng rt ln. Khi 5