Hydrophobicity/Oleophilicity of Autoclaved Aerated Concrete (AAC) Grains Coated with Oleic and Stearic Acids for Application as Oil/Water Separating Filtration and Adsorbent Materials in Vietnam

Abstract

Separation of oil and water is an effective technique to treat oily wastewater. For examining the applicability of porous grains coated with hydrophobic agents (HA) as low-cost and easily available filtration and adsorbent materials in the separation of oil and water, this study assessed the hydrophobicity/oleophilicity of porous grains made from autoclaved aerated concrete scrap coated with low-cost and harmless hydrophobic agents such as oleic and stearic acids. Tests using a sessile droplet method showed unique relationships between the contact angles (CA) of water droplets in air (CAwa), oil droplets in water (CAow) and coated HA concentrations. The CAwa increased linearly with increasing HA concentration and then became almost constant and/or gently increased after a specific point, indicating that a minimum coating amount gives the maximum hydrophobicity to HA-coated porous grains exists. The CAow gradually decreased exponentially with increasing HA concentration. In particular, the CAow of porous grains coated with stearic acid decreased with increasing of HA concentration in a two-step process. Furthermore, analyses of the Pearson correlation showed that both CAwa and CAow correlated well with the specific surface area (SSA), implying that the SSA is a good indicator as a quick assessment of hydrophobicity/oleophilicity of HA-coated porous grains.