Experimental and theoretical study on removal of organic contaminants with various function groups via suspension freezing separation

Attention is drawn to the freezing method for separating organic contaminants from industrial wastewater and simultaneously recovering valuable materials, but the mechanism regarding functional group of organic contaminants how affect ice purity remains unclear. In this work, four types of organics, including hexane, hexanoic acid, N-hexanol and N-hexanal, with various oxygen functional groups were selected as organic contaminants and studied to be separated from aqueous solutions by the suspension freezing method. Experimental results revealed that their separation efficiencies were 67.07%, 87.75%, 94.71% and 95.32%, respectively, after freezing 30 min at 200 rpm and -0.9 degrees C. The presented theoretical work reveals that hexane, as a non-polar organic contaminant without function group, unable to form hydrogen bonds with water clusters, making it more readily to precipitate and stick on ice surface during freezing, which significantly increased ice impurities with the lowest separation efficiency. Presence of functional group promotes organics to solute in concentrate via forming H-bond with water clusters, and thus improves ice purity by avoiding of precipitation. Hexanoic acid with the largest absorption energy with ice crystal tend to adsorb on ice surface but not stay in concentrate and showed the highest ice impurity corresponding to lowest separation efficiency. This work provides new sight for understanding declination of ice purity and separation efficiency caused by functional group of organic contaminants during freezing.

Automated summary

This study investigated the separation of four organic compounds in aqueous solutions using suspension freezing method and found that the presence of functional groups in organic contaminants affects ice purity and separation efficiency. Non-polar organic contaminant hexane, without functional group, showed the lowest separation efficiency due to its tendency to precipitate on ice surface during freezing, while organic contaminants with functional groups could solute in concentrate via forming hydrogen bonds with water clusters, leading to improved ice purity.