Effect of aluminum on the deposition of silica scales in cooling water systems

The formation of metastable aluminosilicates in the Al–Si–H2O system: Results from solution chemistry and solid-state NMR spectroscopy

“…In the presence of dissolved silica, Al(OH) 3 has been shown to be unstable at 90°C and it quickly forms both Al [6] and Al [4] silicate phases (Yokoyama et al, 2002). Based largely on those results, Yokoyama et al (2002) and Nishida et al (2009) proposed that the formation of Al(OH) 3 phases were necessary precursors to the formation of Al [4] phases in hydrothermal scales. The results of this current study suggest that these precursor phases may not be necessary, but more work is required to elucidate the mechanisms of aluminosilicate formation in these systems.…”

“…Allophane-like phases have also been implicated in controlling the bioavailability of Al (Doucet et al, 2001;Exley et al, 2002). Al [4] containing aluminosilicate phases have been identified as the dominant phases in hydrothermal scales (Gallup, 1997;Nishida et al, 2009) siliceous hot spring deposits (Yokoyama et al, 2004), biogenic silica (Gehlen et al, 2002), and inorganic opals (Brown et al, 2003;Paris et al, 2007). Houston et al (2008) indicated that metastable Al [4] dominant aluminosilicate phases form during uptake experiments performed at pH >5 and higher dissolved silica concentrations despite thermodynamic forces driving the formation of kaolinite.…”

“…/j.gca.2011 Solid-state nuclear magnetic resonance spectroscopy has been applied in numerous studies to provide basic characterization of the phases formed during reactions between Al and silica. Basic differences in the Al and Si coordination environments in allophane, imogolite, and other hydrous aluminosilicates can all be identified from solid-state 27 Al and 29 Si NMR techniques (Barron et al, 1982;Idlefonse et al, 1994;Gallup, 1997;Exley et al, 2002;Yokoyama et al, 2002Yokoyama et al, , 2004Brown et al, 2003;Paris et al, 2007;Nishida et al, 2009). Advanced techniques which exploit the couplings between neighboring elements can provide more detailed structural determination of these Al containing phases.…”

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

“…Fig. 1 shows a backscattered electron image of a silica scale from cooling water, which was investigated by Nishida et al [6], and the qualitative analytical results for zinc (Zn) that were determined using EPMA are shown for three points on the backscattered electron image.…”

“…In the cases of geothermal power plants or hot spring water, some reports suggest that aluminum may play an important role in silica scale formation [2][3][4][5]. Recently, Nishida et al [6] reported the characterization of silica scales, which formed from cooling water, and proposed a mechanism for their formation, in which aluminum participates. As zinc (Zn) compounds are also added into cooling water as an anticorrosive [7], the sorption of Zn into silica scales during their formation is possible [8].…”