Efficient removal of contaminants from waste lubricant oil by nano-porous bentonite produced via microwave-assisted rapid activation: process identifications and optimization.

The low-cost Ca-bentonite was rapidly converted to a mesoporous adsorbent via microwave-assisted acidification and the obtained materials were employed for the removal of contaminants from waste lubricant oil. In order to understand the role of acid combinations on activation, the agent compositions were prepared according to the mixture design algorithm. The waste oil recovery was carried out in a batch system to determine the appropriate acid composition, optimum microwave power, radiation time, and powder/acid ratio. As power increased, the contaminant removal performance of the adsorbent was effectively raised to achieve appropriate clear base oil. The rise in power behind 600 W negatively affected the performance of the adsorbent in which the color of oil was changed from yellow to brown. The appropriate recovery of waste oil was readily achieved by employment of adsorbents in which the acidification was performed in 15 min. The microwave-assisted technique could shorten the residence time to achieve the maximum efficiency in comparison with the performance of those produced through the conventional method. Although sulfuric acid can be used for acidification of bentonite by microwave heat treatment, the combination of acetic acid, < 50 mol%, with the mentioned acid was identified as an efficient agent to improve the performance of adsorbents which is valuable from an engineering point of view.