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, N G U Y £ 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 natural anaerobic conditions similar those in the ac/uyfers with present ofFe(OH)j, Mn02 and AsO/' as co-precipitated compounds The results were obtained after 56 days continues study Following the running time, Mn^* was released firstly and then Fe'* and arsenic were done about some days later when mainly part ofMn02 was reduced The decrease of iron and arsenic concentration in water phase was determined as consequence of the forming of FeS and FeAsS in experimental system The results also showed the relations between species of concerning elements and their interaction in the system Mci dau Nam 1993, Dang Van Can [1] mot chuyen khao sat tai viing niii thugng nguon sdng Ma da phat hien tha'y nude ciia mot vai 962 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 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 Cac hat chat ran se duge cac ddng sdng mang ve boi dap nen cac ddng bang Day ehinh la nguyen nhan tich luy asen eae tSng phu sa bdi tich va giai phdng asen nude ngam [2] Viet Nam, dac biet la khu vue phia Bae ed md pyrit ra't Idn d phia Tay Bdc each Ha Ngi khoang 60 km va ra't nhieu eae diem md vang rai rae; dd khoang arsenopyrit phan bd kha day Trong nhieu nam gan day vice khai thae vang diln rat manh va tren mot dien rdng khap khu vue vung niii phia Bae Cac khoang giau asen duge dua len va phan tan rdng tren mat da't Neu qua trinh phong hda nhu da nhac tdi d tren la nguyen nhan that su eung ea'p asen eho cac ddng sdng thi day qua thuc se la mot tham hoa Nam 1999, tien hanh phan tich ham lugng asen nude sdng Hong eho tha'y ehiing dao ddng khoang - ag/L; cd len tdi 90 ag/L va bun phu sa len tdi 38 mg/kg [3] Nam 1997, sau phat hien tha'y ngudn nude 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 nude ngam khu vue Ha Ngi [4] Ve ea che ciia su giai phdng asen nude ngam, mot so tac gia da dua cac gia thuyet nhu su oxi hda eae khoang asenopyrit ed 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 [2] Dflng trudc su de doa ve hiem hga ciia tinh trang nhiem asen nude sinh boat va an udng [4, 6, 11]; ben canh viec nghien eflu tim cac giai phap cdng nghe nham loai bd an toan asen, ehiing tdi eung quan tam tdi viec tim hieu ea che thuc te giai phdng asen mdi trudng nude dieu kien mot nude nhiet ddi nhu d Viet Nam 963 Qua trinh thuc nghiem De nghien cflu ca che ciia qua trinh giai phdng asen nude ngam, ehiing tdi da thiet ke va lap dat mot thiet bi thir nghiem khep kin nhu tren hinh Hinh I Sa thiet bi nghien cAu Binh chiia nude va cac vi cha't Cot yem Khoa la'y mSu Bo khir oxy khong Bom nhu d6ng - tudn hoan May khuay tir Bom b6 sung dinh duong va vi chat Cot yem cao 700 mm, dudng kinh 45 mm duge ea'u tao bdi 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 hai day 50 mm la mot ldp sdi hat to dudng kinh - mm Ldp thfl ba day 600 mm chfla cat sach duge trgn vdi 0,001%As (so vdi khd'i lugng eat khd) dudi dang ASO4' ddng ket tua vdi 0,1% Fe d dang Fe(0H)3 va 0,005% Mn d dang Mn02 va duge bam tren be mat cua cac hat cat Pha nude duge md phdng theo phan gan dung ciia nude tu nhien va ed phan nhu tren bang [12] Bang Thanh phan cua pha nu6c Thanh phan Canxi HCO3- Nong (M) 1,0.10-' 2,4.10-' NO3 3,0.10' SO42- 5,2.10' 1,2.10' 6,0.10-' 6,0.10-' Na-glutamat PO4'- Mg^^ 964 Bang Phuong phap phan tich Thanh phdn Asen Fe, Mn PP Phan tich AAS-HVG AAS NO3-, PO4'-, NH4^ Colorimetry Do due SO4'Colorimetry (xanh metylen) lodometry Oxi hda tan De qua trinh yem duge bao dam, ehung tdi su dung bam nhu dgng bom nude tfl binh chfla (1) vao cot yem (2) theo Id'i tfl day cot, qua tang mun, tang sdi, tang eat chfla As, FeOOH, Mn02 rdi quay trd lai binh chfla Mau nude duoc la'y deu dan sau nhung khoang thdi gian lien tiep each la 24 gid d phia dau cot nhd mot khoa ba thong (3) va duge dem phan tich cac chi tieu can thiet Lugng miu la'y se lam giam ap sua't he thd'ng Ap suat duge dieu hda bang each eho khdng vao sau da khu het oxi qua bd khu (4) Cac chi tieu phan tich duge thuc hien theo cac phuang phap duge cdng bd "Standard Methods for Examination of Water and Waste water" [13] va TCVN [15] Ket qua va thao luan Thi nghiem duge nghien cflu lien tue vdng 56 dem Su bien thifin ndng theo thdi gian pha nude ciia Fe, Mn, As duge the hien tren hinh va ciia S04^-, S^', As the hien tren hinh ';::,;.' J, • , ; , • , • • ' ,; • ^ ^ ^ „ i - - < >N .• Mi n • " ^ - Series • / -.:-—-— — • -Series2 Series3 • • • ** Series4 • • • • • « • « • • • n - 10 •vm • ^ « • • • • , • 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 Hinh Subie'n thien nong theo thdi gian ciia Fe, Mn vd As 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 thi tren hinh ta cd the thay rang qua trinh khu Mn02 ve Mn^"" da bat dau xiy sdm nhat; tfl thfl (khi DO da giam 965 xud'ng chi cdn 2,4 mg/L) va sau dd ham lugng Mn^"" pha nudc tang dan Mn02 van tiep tuc bi khu Den thfl 31 trd di thi ham lugng mangan hau nhu khong tang nfla Day cd the la lugng mangan dua vao tfl dau da duge chuyen het ve Mn^* Ndng cua Fe nhflng dau tang rat cham; chflng to qua trinh giai phdng Fe dudi dang Fe^* di6u kien van cdn mot ham lugng Idn MnOj ben canh la rat ban che mac du d dd mdi trudng da la mSi trudng yem (DO < 0,2 mg/L) Su khu Fe(in) bat dau tang rd rft sau khoang 14 ngay; dd lugng Mn^^ da duge giai phdng ban 80% moi trudng nude So vdi qua'trinh giai phdng Fe^^ thi hSu nhu vong tuan dau qua trinh khfl yem uu tien eho su giai phdng Mn^^ Dieu phu hgp ca ve mat the oxi hda cua cap Mn02/Mn^^ Idn han nhieu so vdi cap Fe(OH)3/Fe^^ mdi trudng nudc cd pH xung quanh [12] va ea ve mat ddng hge cua qua trinh phan flng oxi hda khu c6 mat ca Fe(in) va MnOz Qua giai doan tang nhanh tfl thfl 14 den thfl 31, ham lugng Fe^^ sau dd lai giam dan rdi hau nhu khdng ddi d giai doan cud'i Khi ndng Fe^* bat dau giam thi ddng thdi he thd'ng eung xua't hien ket tua mau den ciia FeS Tong ndng sunphua pha nude xae dinh duge tai thdi diem la xung quanh gia tri 0,25.10"* M Cac CO che chuyen hda mdi trudng khu yem ciia hgp cha't sat, mangan va luu huynh thi nghiem tren cd the minh hga mot phdn bang cac phan flng hda hge sau: Chat hflu CO va SO4'- ^^ ^^""^ ^^^ • CH4 + COj + NH4" + S'" + MnOj + 2e + 4W = Mn'^ + 2H2O Fe(0H)3 + e + H^ = Fe(0H)2 + H2O Fe(0H)2 + 2CO2 = Fe^" + 2HCO3,2+ , c2- Fe'^ + S'- = FeS Fe^^ -I- Mn02 + '2 + + 4W ~r" = — Fe^^ 1c -r Mn^^ LYiii + -r 2H,0 ^n.2 Fe^^ + 3H2O = Fe(OH)j + 3H* S^ +H2O HS +W Su giai phdng asen nhu tren hinh eho thay nd x^y g^n nhu song song vdi su giai phdng cua Fe(ll) Gia thiet eho rang khdi ngudn ciia hau het asen pha ran (nhu cac tang da't phu sa bdi tich tU 966 nhifin) tdn tai dudi dang asenat va ehii yen duge hap phu tren eae hat sat(III) hydroxit Khi Fe(III) bi khu ve Fe(II) va tan dudi dang mudi bieacbonat thi ddng thdi asen(V) eung bi khu ve asen(III) va tan vao nudc la hoan toan hgp ly Ddng thdi eung nhu ddi vdi Fe^*, ham lugng Mn02 mdi trudng cdn cao thi qua trinh oxi hda trd lai cua ASO3'- tao ASO4'- va tai ket tua asenat eung hoan toan ed the x^y 100 90 - Series -Series2 Series3 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 Hinh Subie'n thien nong siinphat, sunphua vd asen pha nudc theo thdi gian Series 1: Siinphat, (mg/L); Series 2: Sunphua, (10'mg/L); Series 3.: Asen, (lO'^mg/L) FeAs04 + 3e + 2H^ Fe'^ + ASO3'- + H2O Me3(As04)2 + 4e + 4H^ o 3Me2^ + 2ASO3'- + 2H2O AsO/- + Mn02 + 2W = AsO/' + Mn^^ + / / , 3Me^^ + AsO/- = Me/AsO J, Sau thfl 31, ndng cua asen giam ndng Fe(II) eung giam, d day nhu chflng tdi da nhac tdi, hoan toan khdng phai qua trinh khfl Fe(III) dflng lai ma ed mdi lien quan den sir tao FeS va Fe2AsS Ket qua phan tich dinh tinh phan ket tua mau den hinh he thd'ng eho tha'y cd ea ba phan Fe, As va S va theo 967 ket qua phan tich ban dinh lugng thi ham lugng S mau trung binh ga'p khoang 1000 Mn so vdi As Nhung qua trinh tren chflng to su gan bd hihi ea gifla cac hgp cha't cua asen, sat va mangan neu chflng ed mat ddng thdi mdt m6i trudng gidi han Cac mdi quan he gifla ehung da quyet dinh su tdn tai va hanh vi cua cac dang tdn tai ciia chflng mdi trudng Khae vdi Fe, Mn va As, pha nudc ndng ion sunphat giam sau dau, sau dd cfl giam dan gan nhu tuyen tinh Ddng thdi tdng sunphua eung bat dau tang sau thfl nha't va tang deu eho tdi khoang thfl 31 Mdt dieu rat trflng hgp dd la ndng Fe(II) giam thi ddng thdi tdng asen va tdng sunphua eung giam Su hinh sat sunphua da duge chflng minh rd rang qua phan tich ket tiia mau den cua FeS Song su giam ham lugng asen pha nudc thi tao asenua sat hay asen, nhu da ndi den d tren, chua duge chflng minh cu the Nhu vay su giai phdng asen pha nudc dieu kien c6 su phan buy yem cac hgp cha't hflu ca nhu Idng da't d cac tang ngam nudc (aquyfer) lien quan mat thiet vdi ham lugng Mn02 da't, vdi qua trinh khu Fe(III) ve Fe(II) va ham lugng sunphua hinh Khi ham lugng Mn02 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 khao sat mflc nhiSm kim loai nang 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 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 gin nhu phu hgp vdi nhflng ket qua nghien cflu cua ehung tdi Day mdi chi la gia thuye't; thuc te' ra't nhieu cac mdi quan he va nhflng dieu kien phfle tap khae anh hudng de'n nhflng can bang gifla cac pha cac ting ngap nude Chinh nhung can bang da quye't dinh su tdn tai cua cac ion nude ngam 968 Bang Ham lugng trung binh ciia sat, mangan va asen nudc ngam tai bai gieng chinh a Ha Noi (so lieu phan tich nam 1999) ^ ^ ^ ^ Bai gieng MD NH NSL LY YP PV Tong Fe 0.310 0.622 1.203 2.149 4.776 4.496 8.329 5.640 Mn'^ 0.951 1.627 0.858 0.366 0.379 0.112 0.128 0.264 Tdng asen 0.036 0.041 0.402 0.061 0.396 0.342 0.264 0.062 HLK.loai^^^^ (mg/L) HD TM 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 dem nghien cflu tren he thd'ng thuc nghiem md phdng mdt each dan gian qua trinh khfl yem cac tang ngam nudc tu nhien dudi long da't; bang cac ket qua phan tich eae phan ehinh va eae phan lien quan, ehung tdi manh dan neu mdt each so luge cac ca che' khu cac hgp chat oxit, hydroxit hay mudi it tan cua sat, mangan va asen cac hgp chat de tan hon nudc Ddng thdi cac qua trinh ket tua, tai tao eung nhu cac mdi quan he gifla ehung eung duge thao luan Chung tdi by vong day la nhung tu lieu bude dau hflu ieh eho nhflng quan tam de'n va'n de Tai lieu tham khao Dang van Can Preliminary assessment of the distribution, removal and accumulation of arsenic in hydrothermal depond bearing high arsenic content Scientific Technical Communication on Geology Department of Geology and Minerals of Vietnam, Hanoi 2001 (53-57) J M McArthur, P Ravenseoft, S Safiulla, M F Thirlwall 969 Arsenic in groundwater: Testing pollution mecnamsms lor sedimentary aquyfers in Bangladesh, Water Resources Research, Vol 37, No 1, January 2001 (109-117) Le Van Hdi Luan an tot nghiep, Khoa Hda hge, Dai hge Khoa hge Tu nhien, Dai hge Qude gia Ha Ngi, 2000 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) S Mallick, N R Rajagopal Groundwater development in the arsenic-affected alluvial belt of West Bengal - Some question Curr Sci., 70, 1966 (956-958) 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 years in West Bengal, India, Sci Total Environ., 218, 1998 (185-201) S K Acharyya Comment on Nickson et al Arsenic poisoning of Bangladesh groundwater Nature, 401, 1999 (545) P Bhattacharya, D Chatterjee, G Jacks Occurrence of arsenic-contaminated groundwater in alluvial aquyfers from the Delta Plain, eastern India: Options for a safe drinking water supply Water Res Dev., 13, 1997 (79-92) R T Nickson, J M McAthur, W G Burgess, P Ravenscroft, K Z Ahmed, M Rahman Arsenic poisoning of Bangladesh groundwater Nature, 395, 1998 (338) 10 R T Nickson, J M McAthur, W G Burgess, P Ravenscroft, K Z Ahmed Mechanism of arsenic poisoning of groundwater in Bangladesh and West Bengal, App Geochem., 15, 2000 (403-413) 11 Kris Christen The arsenic threat worsens, Environmental Science & Technology, July 1, 2001 (286 A-291 A) 970 12 Urs von Gunten, Jurg Zobrist Biochemical changes in groundwater-infiltration systems: Column studies Geochimica et Cosmochimica Acta, Vol 57, 1993 (3895-3906) 13 Mary Ann H Franson (Managing Editor) Standard Methods for the Examination of Water and Waste water, Amer Pub Health Association, Washington DC, 1995 14 Beat Myller ChemEQL Manual, Limnological Center EAWAG/ETH Switzerland, 1996 Research 15 TCVN Cac tieu chudn nhd nudc Viet nam ve moi trudng, Tap 1: Chat lugng nude Ha Ngi 1995 971 ... md pyrit ra' t Idn d phia Tay Bdc each Ha Ngi khoang 60 km va ra' t nhieu eae diem md vang rai rae; dd khoang arsenopyrit phan bd kha day Trong nhieu nam gan day vice khai thae vang diln rat manh... 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. .. nhu su oxi hda eae khoang asenopyrit ed 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