Enhanced flotation of heavy metal ion by perilla seed meal protein as a novel collector: Preparation, mechanism and performance

Heavy metal ions are potent environmental toxins that have accumulated above their natural levels due to human activity. This work investigated the effect of a natural plant protein, perilla seed meal protein (PSMP), on Pb(Ⅱ) removal from its wastewater through a novel flotation technology. This technology consists of the extraction stage, first-stage flotation and second-stage flotation, and a so-called waved internal component (WIC) is designed for the second-stage flotation. PSMP was extracted, enriched and fabricated from low-cost, readily available agricultural waste, namely, perilla seed meal (PSM), during extraction and first-stage flotation. The characterisation and mechanism of interaction between PSMP and Pb(Ⅱ) were examined using SEM-EDS, FTIR, fluorescence spectroscopy and XPS. PSMP bonded strongly to Pb(Ⅱ) via van der Waals interaction, and the primary binding sites were N and O atoms. In the second-stage flotation, PSMP could induce foaming and remove more than 97% of Pb(II) under the suitable conditions of PSMP concentration 500 mg/L, pH 6.0 and airflow rate 250 mL/min. The presence of our waved internal component (WIC) significantly improved drainage and decreased the liquid holdup. This protein obtained from agricultural waste is thus useful as a collector in treating wastewater containing heavy metals.