By Futoshi Nagata, Katsuya Inoue, Kozo Shinoda, Shigeru Suzuki and Yoshio Waseda

Transcript

1 13 Green Rust(Cl ) *1, * 1*2, *1, *1, * 1 Synthesis of Green Rust(Cl ) and Characterization of its Oxidation Process By Futoshi Nagata, Katsuya Inoue, Kozo Shinoda, Shigeru Suzuki and Yoshio Waseda Chloride-containing green rust, GR(Cl ) with formula [Fe II 3 FeIII (OH) 8 ] + [Cl nh 2 O], was synthesized from the solutions of ferric chloride, ferrous chloride, and sodium hydroxide. The suspension containing GR(Cl ) was oxidized by passing oxygen gas into the aqueous solution, in which GR(Cl ) was transformed into α-feooh and γ-feooh. In order to clarify the influence of reaction conditions on the formation of iron oxyhydroxides and oxides obtained from GR(Cl ), the X-ray diffraction method was used for analyzing the solid particles formed during conversion. The ph and oxidation reduction potential(orp) values of the aqueous solution were monitored during the transformation of GR(Cl ). In addition, transmission electron microscopy was used for analyzing the morphology of the solid particles separated from the suspension. The oxidation of hydroxysulfate green rust, GR(SO 2 4 ), was also investigated in the similar way in order to compare the oxidation of GR(Cl ) with that of GR(SO 2 4 ). These results indicate that the formation of different structures of iron oxyhydroxides in aqueous solution strongly depends on the reaction conditions. (Received December 12th, 28) Keywords: green rust, aqueous solution, iron oxyhydroxides, X-ray diffraction, transmission electron microscopy 1 [1] Fe(III) Green Rust(GR) GR 2 3 Fe FeO 6 2 Fe 3 Fe [1] Cl SO 4 1 Green Rust1(GR1)2 Green Rust2(GR2) GR GR1(Cl ) [Fe II 3 Fe III (OH) 8 ] + [Cl nh 2 O] [2]GR(Cl ) (Cl ) GR(Cl ) GR(Cl ) GR(Cl ) GR(SO 2 4 ) Green Rust(Cl ) FeCl 2 nh 2 O (n=4.23) FeCl 3 nh 2 O (n=7.65) ICP *1 *2

2 14 Green Rust(Cl ) 64 1, ml.5 mol/l 2 NaOH 25 ml 5 C 5 ml/min GR1(Cl ) 1 NaOH FeCl 2 FeCl 3 GR1(Cl ) 3 X XRD(Rigaku RINT 22/PC, Mo Kα keV, 5kV, 3mA) 2.2 GR(Cl ) 5 C 25 C 2cc/min N 2 O 2 P O2 :21% (ORP) ph X TEM(JEOL JEM-12EX II, 12kV) GR2(SO 2 4 ) GR2(SO2 4 ) [Fe(II)]/[Fe(III)]=3, [OH ]/{[Fe(II)] + [Fe(III)]} = ml GR2(SO 2 4 ) 2ml 5ml.75mol/l [3] GR(Cl ) XRD (a) [OH - ] / [Fe] = 2.5 a.u. Intensity / (b) [OH - ] / [Fe] = 2. (c) [OH - ] / [Fe] = 1.8 (d) [OH - ] / [Fe] = 1.6 (e) [OH - ] / [Fe] = 1.5 a.u. Intensity / (a) [Fe(II)] / [Fe(III)] = 4.5 (b) [Fe(II)] / [Fe(III)] = 4. (f) [OH - ] / [Fe] = 1.3 GR1(Cl - ) Fe 3 O 4 (c) [Fe(II)] / [Fe(III)] = 3.5 GR1(Cl - ) Fe 3 O 4 2 / degree Fig.1 XRD patterns of particles separated from the suspension that were mixed under the conditions: [Fe(II)]/[Fe(III)]=4.5, and [OH ]/[Fe] = (a)2.5, (b)2., (c)1.8, (d)1.6, (e)1.5, and (f)1.3. Fe(OH) 2 2 / degree Fig.2 XRD patterns of particles separated from the suspension that were mixed under the conditions: [OH ]/[Fe] = 1.5, and [Fe(II)]/[Fe(III)] = (a)4.5, (b)4., and(c) [Fe(II)]/[Fe(III)] 4.5 NaOH [OH ]/[Fe] XRD

3 2 12,,,, 15 Fig.1 GR(Cl ) [Fe II 3 Fe III (OH) 8 ] + [Cl nh 2 O] [Fe(II)]/[Fe(III)]=3. GR(Cl ) 2 [Fe(II)]/[Fe(III)]= mol/l3.99mol/l [OH ]/[Fe] [OH ]/[Fe] GR(Cl ) 16.1 C magnetite : Fe 3 O 4 [OH ]/[Fe] 1.6 (II): Fe(OH) 2 [OH ]/[Fe] Fe(OH) 2 [OH ]/[Fe] = 1.5 GR(Cl ) [OH ]/[Fe] = 1.5 [Fe(II)]/ [Fe(III)] GR(Cl ) XRD Fig.2 [Fe(II)]/[Fe(III)] Fe 3 O 4 [OH ]/[Fe] = 1.5[Fe(II)]/[Fe(III)]=4. XRD Fig.3 Fe 3 O 4 GR(Cl ) Fe 3 O 4 GR(Cl ) y / a.u. Intensit 2 / degree GR1(Cl - ) Fig.3 XRD pattern of particles separated from the suspension that were mixed without centrifugal washing under the conditions: [OH ]/[Fe] = 1.5, and [Fe(II)]/[Fe(III)]= GR1(Cl ) GR2(SO 2 4 ) Green Rust GR(Cl ) GR(SO 2 4 ) 5 C 25 C GR(Cl ) GR(SO 2 4 ) XRD Fig.4 GR(Cl ), 5, 1, 3, 6, 9min GR(SO 2 4 ), 1, 3, 6, 9min X X X Fig.4 GR GR Goethiteα-FeOOH α-feooh GR GR α-feooh 5 C,α-FeOOH Lepidocrociteγ-FeOOH 3 GR(Cl ) 5 C GR(Cl ) 25 C GR(Cl ) GR(SO 2 4 ) 5 C GR(SO 2 4 ) 25 C GR(SO2 4 ) GR(Cl ) GR(SO 2 4 )

4 16 Green Rust(Cl ) 64 1,2 (vi) 9 min (vi) 9 min Intensity / a.u. (v) 6 min (iv) 3 min (iii) 1 min (ii) 5 min Intensit y / a.u. (v) 6 min (iv) 3 min (iii) 1 min (ii) 5 min (i) min (i) min Intensity / a.u. -FeOOH -FeOOH 2 / degree (v) 9 min (iv) 6 min (iii) 3 min (ii) 1 min (i) min -FeOOH -FeOOH 2 / degree Intensity / a.u. -FeOOH -FeOOH 2 / degree (v) 9 min (iv) 6 min (iii) 3 min (ii) 1 min (i) min -FeOOH -FeOOH 2 / degree Fig.4 XRD patterns of particles separated from the suspensions containing (a)gr(cl ) oxidized at 5 C, (b)gr(cl ) oxidized at 25 C, (c)gr(so 2 4 ) oxidized at 5 C, and (d)gr(so2 4 ) oxidized at 25 Cby nitrogen gas containing 21% oxygen. [4] GR(Cl ) GR(SO 2 4 ) 9 GR 2 XRD Fig.5 GR(Cl ) NaCl.u. Intensity / a -FeOOH -FeOOH 2 / degree (a) GR1(Cl - ) : 5 - (b) GR1(Cl ) : 25 (c) GR2(SO 4 2- ) : 5 (d) GR2(SO 4 2- ) : 25 Fig.5 X-ray diffraction patterns of freezedried particles separated from the suspension containing (a)gr(cl ) oxidized at 5 C, (b)gr(cl ) oxidized at 25 C, (c)gr(so 2 4 ) oxidized at 5 C, and (d)gr(so 2 4 ) oxidized at 25 Cby nitrogen gas containing 21% oxygen. 5 C γ-feooh ORP ph Fig.6

5 2 12,,,, E / mv (vs. SHE) 2-2 (i) 5 (ii) 25 ph (i) 5 (ii) 25 E / mv (vs.she) Oxidation Time, t / min (i) 5 (ii) 25 ph Oxidation Time, t / min (i) 5 (ii) Oxidation Time, t / min Oxidation Time, t / min Fig.6 (a)orp and (b)ph of the suspension containing GR(Cl ) as a function of oxidation time that was oxidized by nitrogen gas containing 21% oxygen (i)at 5 Cand (ii)at 25 C. (c)orp and (d)ph of the suspension containing GR(SO 2 4 ) that was oxidized in the similar way. GR FeOOH 2 3 ORP FeOOH GR 2 FeOOH ORP ORP 1 3 α-feooh Fig.4 GR(Cl ) 2 ORP γ-feooh 3.3 Fig.7 TEM α-feooh γ-feooh [1, 5]GR(Cl ) 5 C Fig.5 γ-feooh (a) TEM (b) (c)(d) γ-feooh GR(Cl ) γ-feooh γ-feooh Fig.7 γ-feooh α-feooh α-feooh 1nm γ-feooh 4nm GR(Cl ) α-feooh GR2(SO 2 4 ) α-feooh

6 18 Green Rust(Cl ) 64 1,2 Fig.7 Transmission electron micrographs of freeze-dried particles obtained from the suspension containing (a)gr(cl ) oxidized at 5 C, (b)gr(cl ) oxidized at 25 C, (c)gr(so 2 4 ) oxidized at 5 C, and (d)gr(so 2 4 ) oxidized by nitrogen gas containing 21% oxygen at 25 C. 3.4 GR(Cl ) [OH ]/[Fe] = 1.5[Fe(II)]/[Fe(III)]=4. GR(Cl ) X XRD Fig.8 TEM Fig.9 GR(Cl ) NaCl / a.u. Intensity -FeOOH -FeOOH 2 / degree Fig.8 XRD patterns of particles of GR(Cl ) that was oxidized at 25 Cin air. Fig.9 Transmission electron micrograph of particles of GR(Cl ) that was oxidized at 25 Cin air.

7 2 12,,,, 19 α-feooh Akaganeiteβ-FeOOH β-feooh [1, 6]TEM Fig.7 β-feooh β-feooh [2,7 9] GR(Cl ) β-feooh 4 GR(Cl ) FeCl 2 FeCl 3 NaOH (=[OH]/[Fe]) XRD GR(Cl ) [OH ]/[Fe] = 1.5[Fe(II)]/[Fe(III)]=4. XRD magnetite : Fe 3 O 4 XRD Fe 3 O 4 GR(Cl ) Fe 3 O 4 [OH ]/[Fe] = 1.5[Fe(II)]/[Fe(III)]=4. GR(Cl ) GR(Cl ) 25 C α-feooh 5 C α-feooh γ-feooh GR2(SO 2 4 ) GR(Cl ) α-feooh β-feooh [1] :, (23), [2] P. Refait, J.-M.R. Genin : Corros. Sci., 39 (1997), 539 [3] :, (27) [4] 1,, (1996), [5] Sang-Koo Kwon, Shigeru Suzuki, Masatoshi Saito, Yoshio Waseda : Corros. Sci., 48 (26), 3675 [6] Hongbo Fu, Xie Quan : Chemosphere, 63 (26), 43 [7] C. Remazeilles, Ph. Refait : Corros. Sci., 49 (27), 844 [8] M. Yamashita, H. Konishi, T. Kozakura, J. Mizuki, H. Uchida : Corros. Sci., 47 (25), 2492 [9] Kenny Stahl, Kurt Nielsen, Jianzhong Jiang, Bente Lebech, Jonathan C. Hanson, Poul Norby, Jettie van Lanschot : Corros. Sci., 45 (23), 2563