The selective recovery of rhodium from wastewaters, in which the metal would be otherwise lost, would be highly profitable if the process were suitably low-cost. Current recovery processes are generally high maintenance and high-cost, whereas biological processes can be engineered to run with little external input in terms of cost and maintenance. Three emerging technologies were chosen based on their reported efficiency when removing base metals from wastewaters. The first technology screened, the sulphide-extraction membrane bioreactor (SEMB), consists of a sulphate-reducing prokaryote (SRP) anaerobic digester, in which a silicone membrane is submerged. Wastewater is passed through the membrane and metal ions are precipitated as metal sulphides by the hydrogen sulphide gas, which is capable of permeating the membrane. The second technology screened was a fluidized sand bed reactor in which metal ions are removed from solution via induction of nucleated precipitation by sodium carbonate onto the sand grains. The third, and most well established removal technology screened was a biosorption system using immobilized Saccharomyces cerevisiae biomass as the biosorbent. Experimental trials with each technology highlighted drawbacks with each; the SEMB system proved to be largely ineffective when challenged with the removal of rhodium from the wastewater as the rhodium precipitate fouled the membrane within hours, the fluidized bed system seemed unable to overcome the acidity of the wastewater and thus could not precipitate out the rhodium metal, and the efficiency of the biosorption process was hampered by the diversity of rhodium species present in the wastewater, which reduced the amount recovered. The outcomes of the trials with each technology indicated that further optimization of the technology or pretreatment of the wastewater is necessary before any of these options can be implemented. It could be concluded, however, that despite further optimization, both the SEMB and the fluidized bed system were not applicable in this case as precipitation would be non-specific, resulting in the necessity for further steps in order to purify the rhodium ions. Hence, the biosorption system was shown to be most applicable, and further optimization of the system could yield a highly efficient rhodium recovery process.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:rhodes/vital:3987 |
| Date | January 2005 |
| Creators | Mack, Cherie-Lynn |
| Publisher | Rhodes University, Faculty of Science, Biochemistry, Microbiology and Biotechnology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc |
| Format | xv, 164 p., pdf |
| Rights | Mack, Cherie-Lynn |
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