60
Fig. 3.1 pC–pH diagram
for arsenate (top) and
arsenite (bottom) in pure
water. Total arsenic
concentration 5 μM,
25 °C. Around neutral pH
(6–8), the chemical form
of arsenate is as a negative
ion, 1 or 2 negative
charges. In contrast,
arsenite appears as a
neutral species
Fig. 3.2 pC–pH diagram
for fluoride in water with
the main components in
typical ground water. Total
concentration (mg/L)
F
− (5), Ca
2+ (10), Mg
2+ (2),
Na
1+ (1.5), K
1+ (1),
CO 3
2− (45), H 4 SiO 4 (15),
25 °C. Around neutral pH,
the predominant chemical
species is the single atom
anion (F
−
). However, in the
presence of metal cation
such as calcium and
magnesium, the
concentration of the
positive ionic pair becomes
significant
E. Vences-Alvarez et al.