Mefenamic acid stability and removal from wastewater using bentonite-supported nanoscale zero-valent iron and activated charcoal

Abstract

The low-cost composite, nanoscale zero-valent iron (nZVI) immobilized on bentonite clay (B), was prepared by using the NaBH4 reduction method. The morphology, structure, and composition of B-nZVI were investigated. The use of bentonite as a support material apparently decreased the extent of aggregation and the size of ZVI nanoparticles, thus increasing their surface reactivity and removal efficiency. The B-nZVI composite was used to remove a popular non-steroidal anti-inflammatory drug mefenamic acid (MA) from aqueous solution. For the sake of comparison, the removal of aqueous MA was investigated using activated charcoal and bentonite. Overall, B-nZVI was seen to lead to the best removal efficiency. Batch experiments showed that various parameters, such as time, initial concentration of MA, solid phase dosage, and temperature, can affect the removal of MA. Kinetic studies showed that the removal of MA by B-nZVI correlated well with the pseudo-second-order rate model. The removal process was seen to be endothermic, and the experimental data correlated well with Langmuir isotherm with Qmax being 92.6 and 108.7 mg/g for charcoal and B-nZVI, respectively, with a significantly larger binding affinity of MA by B-nZVI.