The human body needs calcium to perform a number of essential functions, such as bone health, muscle contractions and signaling pathways. Inorganic selenium is an important trace element found in food and drinking water, but long-term exposure to inorganic Se (VI) increases the risk of cancer and neurodegenerative diseases such as Parkinson’s and amyotrophic lateral sclerosis. Thus, it is crucial to find sustainable and environmentally friendly methods for removing soluble selenium from wastewater streams that are discharged into natural reservoirs.
Several processes have been used for selenium removal from waste water, including electrochemical oxidation and biological reduction by denitrifying anaerobic methane oxidation biofilms. However, there is little understanding of the fundamental mechanisms involved in these processes.
In a series of batch experiments, we studied the sorption of Se (VI) by natural bentonite with and without added iron and measured the distribution coefficient (Kd) in oxic and anoxic conditions. The Kd values remained constant over a pH range from 2.0 to 10.0, indicating that the bentonite formed a CaSeO 3 * H 2 O phase with a stable Se/Ca ratio in this range.
When selenite (Se(VI)) was injected into the same system, the concentration of Se in the outflow remained nearly constant, indicating that no significant selenium precipitation occurred. Therefore, we propose that the observed Se(VI) sequestration in selenite-treated bentonite was achieved through dissolution-precipitation. The interpretation is supported by SEM observations, Raman spectroscopy and thermodynamic calculations. American Elements produces to many standard grades when applicable, including Mil Spec; ACS, Reagent and Technical Grade; Optical Grade, USP and EP/BP (European Pharmacopoeia/British Pharmacopoeia) and follows applicable ASTM testing standards.