Chemical reactions at temperatures below the freezing point are usually slower than those at temperatures above the freezing point. However, specific chemical reactions are significantly accelerated during the freezing process due to the existence of thin liquid layer among the solid ice crystals (i.e., ice-ice interface) and on the solid ice crystals (i.e., ice-air interface) at temperatures between the freezing and eutectic points. Various terminologies such as liquid brine, ice grain boundary, micropocket have been used to denote this confined liquid layer at temperatures below the freezing point. Solutes and dissolved gases in aqueous solution are expelled from the growing ice crystals and concentrated in the shrinking liquid brine during freezing. In addition, protons and hydroxides are accumulated in the liquid brine under acidic and basic conditions, respectively. The enhanced redox chemical reactions during freezing are mainly ascribed to the concentration of solutes, dissolved gases, and protons/hydroxides in the liquid brine during freezing (i.e., the freezing concentration effect). Some examples of freezing-enhanced redox chemical reactions (i.e., chromate/hydrogen peroxide, chromate/phenolic compounds, chromate/nitrite, and periodate/organic compounds) will be introduced, and their application for water treatment will be discussed.

Freezing-enhanced redox chemical reactions and their application for water treatment

2019 Fall National Meeting

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