Regeneration with Complexation

Chelating resins are commonly regenerated with mineral acid, but in some cases the resin's affinity for the target metal is too great for this to succeed. In the Hg(II)-iminodiacetate system desorption with nitric acid failed because of the very strong complexation of Hg(II). Concentrated NaCl solution was an effective regenerant because CP ions convert Hg2 + to a series of chlorocomplexes (Figure 3). In other words, Hg2 + is adsorbed more strongly than H#, but can be displaced even by Na# because it is simultaneously complexed by Cl~. In this example, both adsorption and desorption steps are selective for Hg(II) over

Table 3 Selectivities at pH 4 of an iminodiacetate chelating resin, relative to Ca2 +

Ion

Ca2 +

Fe2 +

Co2 +

Cd2 +

Zn2 +

Ni2 +

Pb2 +

Cu2 +

Hg2 +

K"

1.00

4.0

6.7

15

17

57

1200

2300

2800

Table 4 Selective removal of Hg(II) on a chelating resina

Hg(II)

Zn(II)

Fe(III)

Cd(II)

Pb(II)

mgL

%

mgL

%

mgL

%

mgL

%

mgL

%

Feed 11.8

100

78

100

37

100

1.7

100

4.6

100

Bed volumes

23 <0.015

< 0.1

73

94

1

3

1.6

94

4.0

87

47 0.015

0.1

74

95

7

19

1.7

100

5.5

120

77 0.015

0.1

78

100

14

38

1.7

100

5.0

109

111 0.030

0.3

78

100

17

46

1.7

100

4.7

102

157 0.035

0.3

76

97

28

76

1.7

100

4.9

107

aMetal concentrations before and after treatment of a simulated smelter wastewater (pH 1.5) with an iminodiacetate resin. Reproduced with permission from Becker NSC and Eldridge RJ (1993) Reactive Polymers 21: 5.

aMetal concentrations before and after treatment of a simulated smelter wastewater (pH 1.5) with an iminodiacetate resin. Reproduced with permission from Becker NSC and Eldridge RJ (1993) Reactive Polymers 21: 5.

most elements, although Fe(III) shares the ability of Hg(II) to adsorb as a cation and desorb as a chloro-complex. The regeneration reaction can be written:

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment