Chemical interactions between Cr(VI) and concrete
particles in synthetic groundwater solutions were
studied. Results indicate that redox, adsorption, and
precipitation are the three major reactions occurring
at the concrete−water interface. The solution pH
plays
a significant role in determining the characteristics
of chromium reaction behavior with concrete
materials. In acidic systems, Cr(VI) species are
removed from the solution by reduction reactions. At
pH < 4.0, Cr(VI) reacts with aqueous Fe(II)
ion,
derived from the Fe-containing minerals of concrete
materials, and is subsequently reduced to Cr(III).
A simple stoichiometric relationship was observed for
Cr(VI) reduction by concrete particles. As
Cr(III)
is not adsorbable in this pH region, it becomes released
into the solution phase. The Cr(III)
concentration
is then governed by the solubility of Cr(OH)3(s)
and/or
Fe
x
Cr1
-
x
(OH)3(s)
precipitates as solution pH
increases. In the pH range from 4.0 to 9.0, an
adsorption
reaction is mainly responsible for Cr(VI)
removal.
Vesuvianite from Pajsberg, Sweden contains about one atom of Mn, based on 50 cations per formula unit, and small amounts of Be, B, and As. Optical absorption analysis suggests that the Mn is predominantly or entirely trivalent. Crystalstructure analysis indicates that Mn is housed at the general octahedral site Y3, which exhibits only minor distortion from ideal octahedral symmetry. Arsenic is housed at Y2 and Z2, and the formula derived from electron microprobe and LA-ICP-MS analyses suggests minor substitution of Al for Si, also at Z2. Beryllium and B are at T1, between the edge-sharing trimers Y3Y2Y3, as is the case for B in the boron-dominant vesuvianite species wiluite. The total content at T1 is interpreted as 0.82Be, 0.34B, and 0.037Fe 3þ .
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