NGHIEN
CQU
CO CHE
GIAI
PHONG ASEN
RA
NUOC
NGAM - MO PHONG CAC QUA
TRINH KHLJ
YEM
KHI TU NHIEN
TRONG CAC TANG NGAM
NaOC
IRAN HONG CON,
NGUY£N
THI
HANH
Khoa Hoa hoc, Dai hoc
KHTN,
DHQG
Hd Ngi
Summary
In recent several, years there were publications of arsenic
contamination in groundwater. This event actuated us to study and
explain the mechanism of arsenic releasing into groundwater of
aquyfers under alluvial plains. Understanding of this mechanism
could
make clear of the relations between solid phase (arsenic-bearing
material) and water phase (arsenic dissolvable) in earth crust layers.
The investigation was implemented at the laboratory model
imitated

niii
thugng nguon sdng Ma da phat hien tha'y trong
nude
ciia mot vai
962
con sud'i ham
lugng
asen
cao
khae thudng. Cac khao sat tiep theo eho
tha'y day la vung cd su phan bd kha nhieu
loai
khoang
chfla
asen -
asenopyrit va pyrit giau asen. Qua trinh phong hda eae loai quang giau
asen da eung ea'p asen eho eae ddng sud'i chay qua khu vue nay. San
ph^m
asenat sau phong hda mot
ph^n
tao cac ket tua, mot phan bi hap
phu
len
nhung hat set phu sa va cac hat hidroxit sat (III) vfla hinh
thanh. Cac hat chat ran nay se
duge
cac ddng sdng mang ve boi dap
nen cac ddng bang. Day ehinh la nguyen nhan
tich luy
asen trong eae

ngam ciia mot so
gieng khoan kieu UNICEF tai Ha Ngi cd ham lugng asen kha cao, tfl
nam 1998
chiing
tdi da tien hanh khao sat
tuong
ddi he thd'ng va da
CO
ket qua ve su
nhidm
asen trong nude ngam khu
vue
Ha Ngi [4].
Ve ea che ciia su giai phdng asen ra nude ngam, mot so tac gia da
dua ra cac gia thuyet nhu su oxi hda eae khoang asenopyrit ed trong
cac tang da't ngam nude [5, 6, 7]; su trao doi gifla anion photphat va
asenat [8] hay su khii asenat [9, 10] nhung
cQng
cdn nhieu tranh
luan
xung quanh va'n de nay [2].
Dflng
trudc su de doa ve hiem hga ciia tinh trang
nhiem
asen trong
nude sinh boat va an udng [4, 6,
11];
ben
canh
viec nghien

chiia nude
va cac vi cha't
Cot yem
khi
Khoa
la'y
mSu
Bo
khir
oxy khong khi
Bom nhu
d6ng
-
tudn
hoan
May khuay
tir
Bom b6 sung dinh
duong
va vi chat
Cot yem khi cao 700 mm, dudng kinh 45 mm duge ea'u tao bdi 3
Idp.
Ldp
thfl
nha't day khoang 50 mm
chira
cha't mun duge la'y tfl
t^ng
da't mat nham tao ngudn vi sinh vat va mot phan cha't huu ca. Ldp
thii

1,0.10-'
2,4.10-'
3,0.10'
5,2.10'
1,2.10'
6,0.10-'
6,0.10-'
Bang 2.
Phuong
phap phan
tich
Thanh
phdn
Asen
Fe,
Mn
PP Phan tich
AAS-HVG
AAS
NO3-,
PO4'-,
NH4^
Colorimetry
SO4'-
Oxi hda tan
Do do
due
Colorimetry
(xanh metylen)
lodometry

Thi nghiem duge nghien cflu lien tue trong vdng 56 ngay dem. Su
bien
thifin
ndng do theo thdi gian trong pha nude ciia Fe, Mn, As duge
the hien tren hinh 2 va ciia
S04^-,
S^',
As the hien tren hinh 3.
10
';::,;.'
J,
•,;,•.,••
'
,;. •^^^„i <
>N.
•vm
•
n
-
•
,
•
/
•
• •
«
.
n
•
"

trong
pha
nudc.
Series
1:
Tong Fe
(mgIL);
Series 2: Mn
(IQ-'mglL);
Series 3: Tdng As
(IQ-^mg/L);
Series 4: DO
(lO'mgOJL)
Tfl do thi tren hinh 2 ta cd the thay rang qua trinh khu
Mn02
ve
Mn^""
da bat dau
xiy
ra sdm nhat; ngay tfl ngay thfl 3 (khi DO da giam
965
xud'ng chi cdn 2,4 mg/L) va sau dd ham lugng
Mn^""
trong pha nudc
tang dan do
Mn02
van tiep tuc bi khu. Den ngay thfl
31
trd di thi ham
lugng mangan hau nhu khong tang nfla. Day cd the la lugng mangan

su giai phdng
Mn^^.
Dieu
nay phu hgp ca ve mat the oxi hda cua cap
Mn02/Mn^^
Idn
han nhieu so
vdi cap
Fe(OH)3/Fe^^
trong mdi trudng nudc cd pH xung quanh 7 [12]
va ea ve mat ddng hge cua qua trinh phan flng oxi hda khu khi c6 mat
ca
Fe(in)
va
MnOz.
Qua giai doan tang nhanh tfl ngay thfl 14 den ngay
thfl
31,
ham lugng
Fe^^
sau dd lai giam dan rdi hau nhu khdng ddi d giai
doan cud'i. Khi ndng do
Fe^*
bat dau giam thi ddng thdi trong he thd'ng
eung xua't hien ket tua mau den ciia FeS. Tong ndng do sunphua trong
pha nude xae dinh duge tai thdi diem nay la xung quanh gia tri
0,25.10"*
M. Cac
CO
che chuyen hda trong mdi trudng khu yem khi ciia hgp cha't

H2O
Fe(0H)2 +
2CO2 =
Fe^"
+ 2HCO3-
,2+
, c2-
Fe'^
+
S'-
=
FeS
'2
+
~r"
— 1
c
-r
LYiii
-r
^n.2
Fe^^
-I-
Mn02
+
4W
=
Fe^^
+
Mn^^

Fe^*,
khi ham lugng
Mn02
trong mdi trudng cdn cao thi qua trinh oxi hda
trd lai cua
ASO3'-
tao thanh
ASO4'-
va tai ket tua asenat
eung
hoan
toan ed the
x^y
ra.
100
90
-
Series 1
-Series2
Series3
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52
Hinh 3.
Subie'n thien nong
do
siinphat,
sunphua
vd
asen trong
pha
nudc theo thdi

2ASO3'-
+
2H2O
AsO/- +
Mn02
+
2W
=
AsO/'
+
Mn^^
+
//,0
3Me^^
+
2
AsO/-
=
Me/AsO
J,
Sau ngay thfl
31,
ndng do cua asen giam trong khi ndng do Fe(II)
eung
giam, d day nhu chflng tdi da nhac tdi, hoan toan khdng phai do
qua trinh khfl Fe(III) dflng lai ma ed mdi lien quan den
sir
tao thanh
FeS va
Fe2AsS.

Idng
da't d cac tang
ngam nudc (aquyfer) lien quan mat thiet vdi ham lugng
Mn02
trong
da't, vdi qua trinh khu Fe(III) ve Fe(II) va ham lugng sunphua hinh
thanh. Khi ham lugng
Mn02
trong dat cao thi qua trinh khfl sat eung
nhu viec giai phdng asen bi flc che rd ret. Mdt thuc te ehung tdi da
gap khi khao sat mflc do
nhiSm
kim loai nang trong nudc
ng^m
khu
vue Ha Ngi dd la gan nhu cd mdt quy
luat
la nai nao ham lugng sat
cao thi ham lugng asen trong nudc eung cao va nai nao ham lugng
mangan cao thi ham lugng sat thap va ham lugng asen eung tha'p
(tham khao tren bang 3). Dieu nay gin nhu phu hgp vdi nhflng ket
qua nghien cflu cua
ehung
tdi. Day mdi chi la gia thuye't; thuc te' con
ra't nhieu cac mdi quan he va nhflng dieu kien phfle tap khae anh
hudng de'n nhflng can bang gifla cac pha trong cac
ting
ngap nude.
Chinh nhung
can

0.061
YP
4.776
0.379
0.396
PV
4.496
0.112
0.342
HD
8.329
0.128
0.264
TM
5.640
0.264
0.062
Ghi
chii:
MD: Mai Dich; NH: Nggc Hd; NSL:
Ngd
Sy Lien; LY:
Luang
Yen;
YP: Yen Phu; PV: Phap
Van;
HD: Ha Dinh; TM:
Tuang
Mai.
Qua 56 ngay dem nghien cflu tren he thd'ng thuc nghiem md

3.
Le Van Hdi. Luan an tot nghiep, Khoa Hda
hge,
Dai hge Khoa
hge Tu nhien, Dai hge Qude gia Ha Ngi, 2000.
4.
Michael Berg, Hong Con Tran et
al.
Arsenic Contamination of
Groundwater and Drinking Water in Vietnam: A Human
Health Threat, Environmental Science & Technology, Vol. 35,
No.
13, 2001 (2621-2626).
5.
S. Mallick, N. R. Rajagopal. Groundwater development in the
arsenic-affected alluvial belt of West Bengal - Some question.
Curr. Sci., 70, 1966 (956-958).
6. B. K. Mandal, T. R. Chowdhury, G. Samanta, D. Mukherjee, C.
R. Chanda, K. C. Saha, D. Chakraborti. Impact of safe water for
drinking on five families for 2 years in West Bengal, India, Sci.
Total Environ., 218, 1998 (185-201).
7.
S. K.
Acharyya.
Comment on Nickson et al. Arsenic poisoning
of Bangladesh
groundwater.
Nature, 401, 1999 (545).
8. P. Bhattacharya, D. Chatterjee, G. Jacks. Occurrence of
arsenic-contaminated groundwater in alluvial aquyfers from the

TCVN. Cac tieu
chudn
nhd nudc Viet nam ve moi trudng, Tap 1:
Chat lugng nude. Ha Ngi 1995.
971