A new treasure in industrial solid waste-coal fly ash for effective oil/water separation

Coal fly ash (CFA) as an industrial solid waste has an extremely adverse influence on the environment. The high value utilization of CFA was a hot research topic with sustainable development for years. In this work, we found that CFA exhibits underoil superhydrophobicity and underwater superoleophobicity due to the special microstructures and chemical composition. And for the first time, CFA was used as a filter material for the separation of various oil/water mixtures and emulsions under the driven of gravity without any further chemical modification. Both light oil/water and heavy oil/water immiscible mixtures can be completely separated through CFA with almost 99.9% efficiency. More importantly, due to the size-sieving effect, CFA was capable of purifying various emulsions with high separation efficiency. After being pre-wetted with water, CFA displayed excellent separation capacity more than 92% and good flux as fast as 1050 L m(-2) h(-1) for water-in-oil emulsions. After being pre-wetted with oil, CFA exhibited a higher separation efficiency of 99.5% and a flux of over 935 L m(-2) h(-1) for water-in-oil emulsions. Therefore, this work provided an innovative, green, and low-cost approach for various oil/water mixtures and emulsions separation, which can also be widely used in wastewater treatment. (c) 2020 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

Coal fly ash (CFA) was found to exhibit excellent separation capabilities for oil/water mixtures and emulsions without further chemical modification. Light and heavy oil/water immiscible mixtures can be completely separated through CFA with almost 99.9% efficiency, and various emulsions can also be purified with a separation efficiency of 99.5% and a flux of over 935 L m(-2) h(-1) using pre-wetted CFA.