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.