Conclusions and recommendations
This study was aimed at comparing the selective liquid-liquid Ag+ sorption capacities of normal and thiolated: palm oil (PO), palm kernel oil (PKO) and soybean oil (SBO), respectively.
It was found that TF-SBO had the highest sorption capacity, followed by TF-PO and then TF-PKO, while the normal oils were ineffective. Sulfur-modification of oils renders them effective for extraction of heavy metals like silver in aqueous media. The concentration of heavy metal sorption active (TF) sites in the sulphur-modified oil, favorably determines its sorption capacity. The choice of bio-oil for sulfur-modification should be one with relatively high total unsaturated bonds.
Future works should focus on scaling up and optimizing the extraction process. This study relied on bench-scale experiments. It is also necessary to determine the effects of stirring speed and other process conditions on the extraction process in order to optimize the use of TF-VO in extracting heavy metals.
Finally, implementation of the outcome of this study in remediating heavy metal-contaminated water is recommendable, and is already in progress. We propose a heavy metal remediation plant based on the process flow diagram shown in Figure 4. TF-VO would be prepared or purchased and stored. Contaminated water and TF-VO would be pumped respectively to the arms of a long passive T-mixer with bends (M-1). Studies have shown that this kind of mixers are effective for contacting fluid phases down to molecular level [13,14]. Further mixing could be achieved with active stirred tank with residence time of about 1 hour, as against the 6 hours spent in laboratory. The mixed fluid could be separated using a hydro-cyclone (or series of it, if necessary) at high feed pump pressure. It is recommended that used TF-VO (with trapped metals) be treated and recycled for process sustainability.