Near Quantitative Removal of Selenate and Sulfate Anions from Wastewaters by Cocrystallization with Chelating Hydrogen-Bonding Guanidinium Ligands

Abstract

Selenium (Se) has become an environmental contaminant of aquatic ecosystems as a result of human activities, particularly mining, fossil fuel combustion, and agricultural activities. By leveraging the high sulfate concentrations relative to Se oxyanions (i.e., SeO n 2– , n = 3, 4) present in some wastewaters, we have developed an efficient approach to Se-oxyanion removal by cocrystallization with bisiminoguanidinium (BIG) ligands that form crystalline sulfate/selenate solid solutions. The crystallization of the sulfate, selenate and selenite, oxyanions and of sulfate/selenate mixtures with five candidate BIG ligands are reported along with the thermodynamics of crystallization and aqueous solubilities. Oxyanion removal experiments with the top two performing candidate ligands show a near quantitative removal (>99%) of sulfate or selenate from solution. When both sulfate and selenate are present, there is near quantitative removal (>99%) of selenate, down to sub-ppb Se levels, with no discrimination between the two oxyanions during cocrystallization. Reducing the selenate concentrations by 3 orders of magnitude or more relative to sulfate, as found in many wastewaters, led to no measurable loss in Se removal efficiencies. This work offers a simple and effective alternative to selective separation of trace amounts of highly toxic selenate oxyanions from wastewaters, to meet stringent regulatory discharge limits.

Steric and Geometrical Frustration Generate Two Higher-Order CuI12L8 Assemblies from a Triaminotriptycene Subcomponent

“…We infer that the poor solubility of the triptycene backbone in methanol, together with the high polarity of methanol, drive the formation of 1, consistent with the multiple noncovalent interactions between building blocks that are observed in the structure (see above). 20 The same framework could be prepared using the parent 2-formylpyridine C instead of B, which generated a structure designated 1 H instead of 1 F , but the fluorine atoms of 1 F aided in its characterization, as noted below.…”

Near-quantitative Removal of Oxalate and Terephthalate from Water by Precipitation with a Rigid Bis-amidinium Compound

“…Figure 1 Dicationic sulfate precipitants reported by Custelcean's group [23][24][25] and our group. 26…”

“…[23][24][25] Very recently, Einkauf and Custelcean reported that these BIG 2+ precipitants could also precipitate selenate and selenite anions: while no selectivity was observed between the very similar sulfate and selenate anions, > 99% of sulfate and/or selenate could be removed by using an excess of precipitant. 25 Inspired by Custelcean's work, we recently reported that the simple bis-amidinium compound 1 2+ could remove > 95% of sulfate from aqueous solution and was selective for this anion even in the presence of competitive divalent anions. 26 Like Custelcean's precipitants, 23-25 1 2+ could be regenerated for subsequent reuse.…”

Silk/Polyamidoamine Membranes for Removing Chromium VI from Water

“…Cr(VI) anions are known to strongly interact with guanidinium cations through a combination of ionic and hydrogen bonding [41][42][43][44][45][46][47][48][49][50][51][52]. Theoretical studies have indeed demonstrated that the hydrogen bond interactions between the bidentate guanidinium and oxyanion-charged species produce very strongly bound complexes [48].…”

“…Furthermore, the guanidine moiety of arginine is responsible for the strong arginine-phosphate interactions of proteins [42]. Thanks to its peculiar molecular geometry, charge distribution, and hydrogen bonding ability, the guanidinium ion can indeed strongly bind bidentate oxyanions, including, inter alia, carboxylate, phosphate, sulfate, nitrate, and selenate [43][44][45][46][47][48][49]. Unsurprisingly, it has been reported that polyhexamethylene-guanidine modified natural zeolitic materials [50], and guanidinium-based ionic organic covalent nanosheets [51,52] uptake considerable amounts of Cr(VI) oxyanions from aqueous solutions.…”