combination of dft and c cp/mas nmr to determine anisotropy

Combination of DFT and 13C CP/MAS NMRto determine anisotropy tensors for

xanthates

Anna-Carin Larsson Sven Öberg Division of Chemical Engineering Department of Mathematics

in collaboration with

Zhong-Xi Sun Mats Lindberg Jinan University, China Division of Chemical Engineering

Possible species in a flotation pulp and on a mineral surface

Xanthate (KX) the collector used

Alcohol (ROH) X- + H2O → OH- + ROH + CS2 at pH<7 or

6X- +3H2O → 6ROH + CO32- + 3CS2 + 2CS3

2-

in highly alkaline solutions

Dixanthogen (X2) 2X- + 1/2O2 + H2O → X2 + 2OH- → 2X- + H2O2 at alkaline pH

X2 + 2SO32- → 2X- + S2O6

2-

See e.g. S. R. Rao, Surface Chemistry of Froth Flotation


Monothiocarbonate (KMTC)

Perxanthate (KperX)

Carbonate (ROCO2K) MTC- + 1/2O2 → ROCO2- + S0 has not been found

MTC- → ROH + COS preferential reaction

X- + 1/2O2 → MTC- + S0 or

S2O32- + X- → S2- + S0 + MTC- (not balanced)

X2 + 4OH- → 2MTC- + S0 + S2- + 2H2O

X- + H2O2 → PerX- + H2O

Surface needed for preadsorption of X- or O2.Surface ions (esp. Cu2+) function as catalysts

See e.g. S. R. Rao, Surface Chemistry of Froth Flotation


Insoluble metal xanthates Pb2+ + 2X- → PbX2 or

2Cu2+ + 4X- → 2CuX + X2

S-alkyl-monothiocarbonate (SMTCK) ROCS2-M → RSCOS-MRSCOS-M → RSM + COSRSM + CO2 → RSCO2-M or

ROCOS-M → RSCO2-M

PbX2 See e.g. S. R. Rao, Surface Chemistry of Froth Flotation

A. J. Vreugdenhil, et al., J Mol Struct, 1997, 405, 67-77.

13C CP/MAS NMR and DFT data

KiPrX exp DFT

δiso (ppm) 20.4 22.7 23.4 25.1 79.1 84.1 231.6 251.7

δaniso (ppm) 154.4±4.6 164.3

η 0.60±0.05 0.60

Ω (ppm) 278.2±8.2 295.7

Exp chemical shifts referenced relative to adamantane (38.48 ppm relative to TMS (0 ppm))DFT chemical shifts referenced relative to DFT chemical shift of TMS (0 ppm)

δiso = (δxx + δyy + δzz)/3

δaniso = δzz - δiso

η = (δyy - δxx) / δaniso

Ω = |δzz - δxx|


Pb(iPrX)2 exp DFT

δiso (ppm) 20.8 21.3 22.9 22.2 23.6 25.1 74.5/76.6 89.0 79.4/82.2 89.9 226.4 244.4/245.3

δaniso (ppm) 142.8±4.1 152.7/156.2

η 0.73±0.04 0.78/0.74

Ω (ppm) 266.0±7.0 288.3/291.9



CuiPrX exp

δiso (ppm) 21.8 23.6 24.9 82.9 223.2

δaniso (ppm) 142.3±8.7

η 0.63±0.10

Ω (ppm) 258.5±15.1


Structural fragment

13C CP/MAS NMR and DFT data(iPrX)2 exp DFT

δiso (ppm) 21.7 18.0 22.1 18.7 23.0 20.2 23.2 21.3 81.1 86.9 82.2 87.5 206.5 225.3 207.1 225.4

δaniso (ppm) 141.1±4.0 161.2 140.1±4.3 162.4

η 0.15±0.15 0.09 0.16±0.16 0.03

Ω (ppm) 222.5±12.5 234.1 221.6±13.2 240.8



KMTC exp1 DFT

δiso (ppm) 185 198.4

δaniso (ppm) 100 93.1

η 0.3 0.42

Ω (ppm) 164 159.4

KperX exp2 DFT

δiso (ppm) 227.7 247.1

δaniso (ppm) 163.0

η 0.43

Ω (ppm) 279.9

1 Methyl, D. Stueber, et al., SS NMR, 2002, 22, 29-49.2 Ethyl (aq), F. P. Hao, et al., Anal. Chem. 2000, 72, 4836-4845.

Pb(MTC)2 DFT

δiso (ppm) 198.0/198.6

δaniso (ppm) 82.4/82.5

η 0.86/0.87

Ω (ppm) 159.2/159.5

Pb(perX)2 DFT

δiso (ppm) 245.0/246.8

δaniso (ppm) 164.4/159.3

η 0.46/0.43

Ω (ppm) 284.6/273.2

All DFT results are for iso-propyl


SMTCK exp DFT (iPr)

δiso (ppm) 173.51 185.1 1752

δaniso (ppm) 642 61.7

η 0.62 0.72

Ω (ppm) 1162 114.81 Methyl, D. Stueber, et al., Inorg Chem, 2001, 40,1902-1911.2 Methyl, D. Stueber, et al., SS NMR, 2002, 22, 29-49.

RSCS2K2 δiso = 247 ppm; δaniso = -178 ppm; η = 0.6; Ω = 317 ppm

RSCOSK2 δiso = 210 ppm; δaniso = -108 ppm; η = 0.7; Ω = 200 ppm

13C CP/MAS NMR and DFT dataROCO2K exp exp DFT

δiso (ppm) 21.6/23.2 22.11 21.0 23.6/24.0 23.7/24.21 21.8 67.3/68.1 67.7/68.41 71.4 157.3 157.81 168.8 158.2 158.71

1572

δaniso (ppm) 76.5±1.6 742 72.2 75.7±1.3

η 0.39±0.05 0.32 0.08 0.32±0.05

Ω (ppm) 129.9±3.0 1202 111.3 125.5±2.8

1 iso-propyl, D. Stueber, et al., Inorg Chem, 2001,40, 1902-1911.2 Methyl, D. Stueber, et al., SS NMR, 2002, 22, 29-49.

Another compound (169.5 ppm)


13C CP/MAS NMR and DFT dataK2CO3 exp exp

δiso (ppm) 169.5 1691/171.22

δaniso (ppm) -52.0±2.4 -491

η 0.54±0.10 0.31

Ω (ppm) 92.1±4.5 821

(KHCO31 δiso = 160 ppm; δaniso = 56 ppm; η = 0.5; Ω =

97 ppm)

1 D. Stueber, et al., SS NMR, 2002, 22, 29-49.2 D. Stueber, et al., Inorg Chem, 2001, 40, 1902-1911.

Strong CP signal but no protons?Absorbs moisture from air?No alkyl chain.

After removing ROCO2K(dissolves in EtOH)

Summary of 13C isotropic chemical shifts exp DFT(TMS) DFT(KX)

KX 231.6 251.7 231.6

KperX 227.71 247.1 227.0

Pb(perX)2 245.9 225.8

PbX2 226.4 244.8 224.7

CuX 223.2

X2 206.8 225.4 205.3

KMTC 1852 198.4 178.3

Pb(MTC)2 198.3 178.2

SMTCK 1752 185.1 165

K2CO3 169.5

ROCO2K 157.8 168.8 148.7

K → Pb/Cu gives lower chemical shift valuesPbX2 and Pb(perX)2 can be distinguished by

anisotropyKMTC and Pb(MTC)2 can be distinguished by

anisotropy

1 Ethyl (aq), F. P. Hao, et al., Anal. Chem.

2000, 72, 4836-4845.2 Methyl, D. Stueber, et al., Inorg Chem,

2001, 40, 1902-1911.

Effect of alkyl chain length

3 mM Heptylxanthate (HX)pH 8 226.4 +182 + 173.2 + 166.7 ppm

3 mM Amylxanthate (AX)pH 8 226.4 + 182 + 173.2 + 166.7 ppm

3 mM Ethylxanthate (EX)pH 7.5 226.4 + 172.4 + 166.3 ppm

PbS

PbX2 at 226.4±0.5 ppm

Surface-PbX2 at 226.4±2 ppm,δaniso = 142±2 (142.8±4.1 for precipitate);η = 0.9±0.1 (0.73±0.04 for precipitate)

Adsorption of 13C-enriched xanthates

Broader lines than for PbX2 precipitate indicate surface bonded complex

More PbX2 forms (or stays stable) when thealkyl chain is longer.Shorter chains decompose easier.

Effect of alkyl chain length cont.

PbS

K2CO3 at 169.5 ppm

PbCO3 at 167 ppm (166.41)RSCO2K at 175 ppm2, 173.5 ppm3, 173.8 ppm4

Pb(RSCO2)2 at 173 ppm?KMTC at 185 ppm2

Pb(MTC)2 at 182 ppm?

1 H. W. Papenguth, et al., Am. Mineralogist, 1989, 74, 1152-1158.2 Methyl, D. Stueber, et al., SS NMR, 2002, 22, 29-49.3 Methyl, D. Stueber, et al., Inorg Chem, 2001, 40, 1902-1911.4 Ethyl, D. Stueber, et al., Inorg Chem, 2001, 40, 1902-1911.


3 mM Heptylxanthate (HX)pH 8 226.4 +182 + 173.2 + 166.7 ppm

3 mM Amylxanthate (AX)pH 8 226.4 + 182 + 173.2 + 166.7 ppm

3 mM Ethylxanthate (EX)pH 7.5 226.4 + 172.4 + 166.3 ppm

Effect of time

3 mM Ethylxanthate (EX)pH 7.1

PbS


After 5h there is a lot of PbX2 (226 ppm) and only a small amount of PbCO3 (167 ppm).Some MTC- (185 ppm) may be present but obscured by a spinning sideband.Some S-alkyl-MTC- (174 ppm) is present.

As time goes PbX2 is decomposed and after 45 h most of it has decomposed to PbCO3.

Conclusions

DFT calculations and experiments to determine chemical shift tensors giveresults which are in very good agreement

Combination of chemical shifts and chemical shift anisotropy can be used todistinguish surface species

13C NMR is sensitive enough to distinguish between different surface species

Xan are very easily decomposed (for comparison DTP almost does notdecompose at all) leading to loss of hydrophobicity

Conclusions

Longer alkyl chains adsorb more easily and stays stable for a longer time

The decomposition of EtXan on PbS could be followed

A route for the decomposition of Xan species were suggested:Pb-X → Pb-MTC → Pb-O2CSR → PbCO3

combination of dft and c cp/mas nmr to determine anisotropy

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