Abstract

The interaction of heavy metals with sediments is complex and means are required to understand this matter more fully. Soil washing is among the methods available to remove heavy metals from sediments. This research was devoted to evaluating the performance of rhamnolipid for the removal of heavy metals, copper, zinc, and nickel, in batch and continuous flow configurations under different conditions, to investigate the mobility and availability of heavy metals by means of selective sequential extraction, and to find the mechanism for removal of heavy metals from the contaminated sediment obtained from the Lachine Canal, Quebec by using a rhamnolipid. The removal of heavy metals from sediments was up to 37% for Cu which was mostly from the organic, 13% of Zn which was mostly from the carbonate, and 27% of Ni which was mostly from oxide and carbonate fractions when rhamnolipid without additives was applied in the continuous flow configuration. By ion exchange experiments, complexation was found to be the major mechanism of removal for all three metals by rhamnolipid. Adding 1% NaOH elevated the role of ion exchange mechanism up to 67.1% for removal of zinc from the sediment. Rhamnolipid adsorbed to the sediment according to the Freundlich isotherm. The zeta potential of the sediment was measured at -24.3 mV for distilled water, -9.5mV for 2%, and -29.5 mV for 0.5% rhamnolipid. Scanning electron microscopy showed that washing with rhamnolipid does not change the texture of the sediment. Augmentation of the wetted surface area of the sediment improved the removal for all three metals (up to 3.5 times for copper), which emphasizes the role of this parameter in the removal process. A theory was established to explain the removal process of the metals, including wetting, contact of rhamnolipid to the surface of the sediment and detachment of the metals from the sediment. Rhamnolipid has proven its ability as a washing agent in heavy metals removal from sediments, but more research is required to improve the performance of the rhamnolipid before scale-up.