Dac diem noi bat ve mat hoa hgc eua Mo va W la tinh khong In djnh, cac hgp chat hinh thanh de dang bj chuyin dii trang thai hoa trj qua lai [48, 55, 56, 104]. c a Mo va W deu eo kha nang tao phirc vdi nhilu phii tu vo co va hiru co de hinh thanh cac hgp chit nhan kep va da nhan qua cac cau (oxy, hydroxy, sunfua) cua phii tir hoac tnre tilp lien kit kim loai - kim loaị Tronc cac hgp chat do chiing thudng eo so phii tri tir 4 din 8 va tin tai o dang oxo- vdi mot hoac hai nguyen tir oxy eiia phoi tir lien kit vdi mot nguyen tu kim loai hoac qua cau nguyen tu (lien ket kim loai-kim loai). Net dac biet cua loai hgp chat nay la su nhudng dien tu p tir oxy cho kim loai da tao ra nhirng moi lien ket rat phirc tap va lam cho kieu hgp chat oxo- chi ha\ xuat hien a mire oxi hoa+5 va+6 la chinh [6, 55,56. 103, 134, 135].
Trong moi trudng axit yeu Mo(Vl) ton tai chu \cu a dang polyanion [Mo7024]^\ mac dii vay, van co hang loat thuoc thu phan img vdi Mo(\T) a dang cation MoO:'' nhu 8-oxiquinolin [101. 150]. thioxianat [46] \a dietxl dithiocacbamat [1, 6, 55, 91]. Dieu do chirng to trong dung dich. cung \ai polyanion [M07O24]'" van eo mot lugng cation MoO:" nhat dinh.
Dii vdi W(V1) cac qua trinh tmTng tu ciing xa> ra song thuong la \cu hon so vdi Mo(Vl) trong ciing dieu kien.
Nhin chung, cac dang ton tai cua Mo(Vl) \a \ \ ( \ ' l ) trong dung dich phu thuoc nit manh vao pH. nong do chat tan \a tinh chat cua dung moị Tu nhirng nghien ciru tong quan o tren chung toi co mot so nhan xet nhu sau;
- Trong tit ca eac dii tugng phan tich W tin ilurong h.\o gio ciing co
- Cac phep xac dinh mot trong hai nguyen t l luon bj anh hudng bdi su cd mat cua nguyen t l kia, vi ca hai thudng ciing co kha nang phan img. tao phuc... vdi cung mot tac nhan phan img. Hai phuong phap e l diln. tmyln thong va dugc sir dung nhieu nhat la thioxianat va dithiol dIu co nhirng han che kho khac phuc hoac khac phuc dugc rit phirc tap [25, 165]. Vi thi tim dugc phuong phap eo tinh chgn Ipc dl xac dinh mot trone hai neuven t l khi cd mat ca hai la mot nhiem vu kho khan eiia hoa hgc phan tich. Ro rang, de giai quyet nhiem vu kho khan nay khong phai chi la vAn d6 di6u cha thudc thu mdi [25, 57, 83..] hoac lira chgn thuoc thir co tinh chon Ipc tot ma con la tim dieu kien dc lam tang tinh chgn loc cua phuong phap [57...]. Cac qua trinh phan tich nhu the se rat co y nghTa doi vdi cong nghe tach va dieu che molypden va vonfram tinh khiet.
- Cac phuong phap xac dinh va tach chgn lgc mot trong hai nguyen to khi cd mat ca hai thudng co nhieu cong doan, phirc tap va de dan den sai sọ
- Cac irng dung ky thuat hoa ly hien dai de xac djnh chiing thudng dat tien, đi hoi phai co thiet bi tien tien va dac biet can sir thanh thao cua can bg phan tich. Sd lugng mau phan tich can phai du nhieu de co the tien hanh lam trong mot dgt thuc nghiem, nhu vay se kho dap ung \ eu eau phan lieh dinh hudng va hien trudng hoac phan tich mau don lẹ
- Trong thuc t<3, phuong phap trac quang van la phirang phap thich hgp
dh xac dinh molypden va xonfram. Nga\ cang eo nhieu thuoc thu huu co ket
hgp vdi cac ky thuat hien dai dugc ung dung \ao phan iieh trae quang de xac d i n h M o v a W[57, 83, 100. 123. 143..].
- Sir dung cac ky thuat chiet hoac trao doi ion eo the taeh \ a \ae dinh
dugc mot trong hai ngu\en to khi co mat ngu\en \o kia | P . 3^. S7. 126. 13^).
dang ciia Mo(VI) hoac W(VI) vl dang phuc trung hoa vl dien tich (trong trudng hgp su dung ky thuat ehilt) hoac vl dang eac phirc tan bin mang dien tich (trong trudng hgp sir dung ky thuat trao dii ion).
Cung da cd cac nghien ciru vl moi tnrdng nude - dung moi hiru eọ Nhimg nhin chung chi dirng d viec nang cao tinh chgn lgc va do nhay eua phep xac djnh [17, 68, 77, 124]. Cac nghien ciru nay cung da noi tdi dang tin tai khac nhau kha ro giira Mo(Vl) va W(V1) trong dung djch do tac dong cua mot so dung moi hiru co tan tot trong nudẹ Day chinh la mot ggi y r^t quan trgng cho chung tdi trong viec quyet dinh hudng nghien cim cua luan an.
Theo hudng nghien ciru tach va xac dinh Mo va W trong moi trudng nude - dung mdi hiru co, chung toi da trien khai de tai luan an theo cac ngi dung sau:
- Khao sat va khang dinh dang ton tai ciia phirc Mo(VI) va W(VI) vdi cac thudc thir hiru co trong mdi trudng nudẹ
- Nghien cuu xac dinh dieu kien tao ra sir khac biet giua dang ton tai ciia Mo(VI) va W(VI) trong moi trudng nude - dung moi hiru co cua cac mudi ngi phirc (phirc vong cang hay chelat) va phirc lien hgp ion giira Mo(\4) va W(VI) vdi cac bazo mau hiru cọ
- Lgi dung sir tdn tai khac biet giua Mo(VD va W(VI) trong moi tnrdng nude - dung moi huu co, nghien ciru xac dinh lugng nho Mo(\'l) \a \ \ ( \ ' l ) trong hon hgp bring phuong phap chiet-trac quang \a nghien cuu eac dieu kien, xay dung quy trinh tach trirc tiep hai ngu\en l6 na\ bang ky thuat trao đi ion thong thudng.
- Tach trirc ti6p lugng nho Mo trong lugng Ion W \a niiuoc lai bang ky
- Thir nghiem tach va phan tich lugng vlt Mo trong mau W kim loaị De thuc hien eac ngi dung tren, phuong phap nghien cim la tao cac dang ton tai khac biet phu hgp dl cd thi ehilt mot each chon loc hoac trao dii ion chgn lgc nham tach mot each hieu qua Mo va W ra khoi nhaụ phuc vii cho viec phan tich hoac tach rieng re hai kim loai naỵ Phuong phap phan tich phuc vu nghien cim la phan tich trie quang, ehilt - trie quang va ICP-MS.