The Effect of Freezing on Reactions with Environmental Impact

Abstract

The knowledge that the freezing process can accelerate certain chemical reactions has been available since the 1960s, particularly in relation to the food industry. However, investigations into such effects on environmentally relevant reactions have only been carried out since the late 1980s. Some 20 years later, the field has matured and scientists have conducted research into various important processes such as the oxidation of nitrite ions to nitrates, sulfites to sulfates, and elemental mercury to inorganic mercury. Field observations mainly carried out in the polar regions have driven this work. For example, researchers have found that both ozone and mercury are removed from the troposphere completely (and almost instantaneously) at the time of Arctic polar sunrise. The monitoring activities suggested that both the phenomena were caused by involvement of bromine (and possibly iodine) chemistry. Scientists investigating the production of interhalide products (bromine and iodine producing interhalides) in frozen aqueous solutions have found that these reactions result in both rate accelerations and unexpected products. Furthermore, these scientists did this research with environmentally relevant concentrations of reagents, thereby suggesting that these reactions could occur in the polar regions. The conversion of elemental mercury to more oxidized forms has also shown that the acceleration of reactions can occur when environmentally relevant concentrations of Hg(0) and oxidants are frozen together in aqueous solutions. These observations, coupled with previous investigations into the effect of freezing on environmental reactions, lead us to conclude that this type of chemistry could potentially play a significant role in the chemical processing of a wide variety of inorganic components in polar regions. More recently, researchers have recognized the implications of these complementary field and laboratory findings toward human health and climate change. In this Account, we focus on the chemical and physical mechanisms that may promote novel chemistry and rate accelerations when water-ice is present. Future prospects will likely concentrate, once again, on the low-temperature chemistry of organic compounds, such as the humic acids, which are known cryospheric contaminants. Furthermore, data on the kinetics and thermodynamics of all types of reaction promoted by the freezing process would provide much assistance in determining their implications to environmental computer models.

A review of air–ice chemical and physical interactions (AICI): liquids, quasi-liquids, and solids in snow

“…5. Schematic representation of how the amount of liquid represented by the blue area adjusts to temperature and how it may be trapped in veins forming micro-inclusions (O'Concubhair and Sodeau, 2013). Reprinted with permission from Takenaka et al (1996).…”

An RNA‐Cleaving Catalytic DNA Accelerated by Freezing

“…Many organic reactions, such as N‐nitrosation of dimethylamine and nitrite and ammonium nitrite denitrification, are accelerated in ice. Significant environmental effects of freezing on chemical reactions were also recently reviewed . In addition to chemical transformations, freezing has also been used in materials science and nanoscience .…”

Influence and CFD analysis of cooling air velocity on the purification of aqueous nickel sulfate solutions by freezing

“…Pollutants are excluded from the ice crystals when wastewater freezes, owing to constraints of their size/charge . Therefore, freeze crystallization (FC) has a wide range of applications in wastewater purification processes, as well as fruit juice concentration, protein crystallization, chemical and petroleum industry, pulp and paper industry, the desalination process, food processing industry, biotechnology and waste minimizatio, efficient recovery of different salts from reverse osmosis retentate of complex brine, removal of pharmaceutically active compounds from water, to polish secondary effluents in refineries (Gao et al, 2008), and for inactivate pathogens …”