Interactions of Silicate Ions with Zinc(II) and Aluminum(III) in Alkaline Aqueous Solution

Abstract

We present (29)Si, (27)Al, and (67)Zn NMR evidence to show that silicate ions in alkaline solution form complexes with zinc(II) (present as zincate, Zn(OH)(3)(-) or Zn(OH)(4)(2-)) and, concomitantly, with aluminate (Al(OH)(4)(-)). Zincate reacts with monomeric silicate at pH 14-15 to form [(HO)O(2)Si-O-Zn(OH)(3)](4-) and with dimeric silicate to produce [HO-SiO(2)-O-SiO(2)-O-Zn(OH)(3)](6-). The exchange of Si between these free and Zn-bound sites is immeasurably fast on the (29)Si NMR time scale. The cyclic silicate trimer reacts relatively slowly and incompletely with zincate to form [(HO)(3)Zn{(SiO(3))(3)}](7-). The concentration of the cyclic trimer becomes further depleted because zincate scavenges the silicate monomer and dimer, with which the cyclic trimer is in equilibrium on the time scale of sample preparation. Identification of these zincate-silicate complexes is supported by quantum chemical theoretical calculations. Aluminate and zincate, when present together, compete roughly equally for a deficiency of silicate to form [(HO)(3)ZnOSiO(2)OH](4-) and [(HO)(3)AlOSiO(2)OH](3-) which exchange (29)Si at a fast but measurable rate.

Alkaline aqueous electrolytes for secondary zinc-air batteries: an overview

“…From the other side, in systems with alkaline electrolytes with lower value of pH (between 9.3 and 12.3), intermediate species such as Zn(OH) y 2 − y are formed, where ‘y’ varies from 0 to 4. Among this species, Zn(OH) 3 − (reaction ) and Zn(OH) 4 2− (reaction ) have been reported as the most predominant . M. Cai et al assigned two anodic peaks to the oxidation of zinc to Zn(OH) 4 2− and to Zn(OH) 3 − by cyclic voltammogram which has also been observed at the authors' facilities (Figure ) .…”

“…Peak A1 (Figure ) corresponds to the zinc oxidizing to Zn(OH) 4 2− (freely soluble , reaction ), while peak A2 corresponds to Zn(OH) 3 − (reaction ) formed as a consequence of the OH − depletion close to the electrode and it presents significant local solubility . …”

Utilization of aluminum sludge (AS) to enhance mine tailings-based geopolymer

“…It can be seen from the figure that when Na/Al [ 1.1, the water loss ratio decreases significantly with higher Na/Al ratio at both 0 and 10 % AS contents. This is mainly because the rate of condensation between silicate species themselves is slower than that between aluminate and silicate species [38][39][40][41]. Due to the high Si/Al ratios, 3.38 and 2.71 at respectively 0 and 10 % AS, and the large amount of NaOH at high Na/Al ratio [1.1, the dissolved Si is much more than the dissolved Al.…”

Formation of a silicato complex of zinc in aqueous solution and its accelerating effect on the formation of silica scales in cooling water systems

“…According to the thermodynamic considerations, Zn 2+ is present as tetrahedral species at pH 9. Consequently, the SCZ structure may be [Zn(-OSi(OH) 3 ) n ] 2Àn (n = 1-4), which is an analogue of complexes that were detected only in strong alkaline solutions by Anseau et al [10].…”