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Heritage Science

Table 1 Solubility products, Ksp, and overall stability constants, logβ n, for common cleaning agents

From: Effective cleaning of rust stained marble

Solubility products

β n = [MLn]/[M][L]n; β n = K1 × K2 × ⋯Kn a

Species

Ksp

Metal ion

Citrate

Oxalate

Tartrate

EDTA

tpen

tga

cys

MgCO3

10−5

Mg(II)

3.4

4.2

1.4

8.8

1.7

–

2.7

CaCO3

10−8

Ca(II)

3.5

2.7

1.8

10.6

4.3

–

2.5

Fe(OH)2

10−14

Fe(II)

4.4

5.2

2.5

14.3

14.6

10.9

11.8

FeOOH

10−41

Fe(III)

11.5

18.5

12.3

25.0

11*

32.0

32.7

  1. Solubility products taken from Ref. [29], FeOOH from [7]. Overall stability constants taken from: citrate, oxalate and tartrate [24], edta [25], and tpen [26]
  2. aThe stability constant for Fe(III) is calculated from the reduction potential e° = 0.74 V vs SCE [27]. The values 0.98 V vs NHE and Fe(III)/Fe(II) = 0.77 V is used. Thioglycolate, tga, Fe(II) [24] and Fe(III) [28]. Cys, Mg(II) and Ca(II) [21], Fe(II) and Fe(III) [28]. The overall stability constants for Fe(II) and Fe(III)-cys refers to the bis-complexes, n = 2. For other n-values, consult refs
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