Optimisation of the emulsion liquid membrane composition and demulsification for rhodium extraction
- Authors: Moyo, Francis , Tandlich, Roman
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76743 , vital:30626 , https://doi.org/10.1515/lwr-2015-0002
- Description: This study was aimed at designing an optimised emulsion liquid membrane (ELM) for the extraction of rhodium from precious metal refinery wastewaters. The demulsification process and the structure of the optimised ELM are reported on. Two optimised ELMs were prepared. The first one contained a 30 % solution of toluene in kerosene as diluent with the following concentrations of the ELM components: 30.000 g/L (w/v) polyisobutylene, 10.870 g/L (m/v) of trioctyl amine and 51.001 g/L (m/v) of SPAN 80. The second ELM contained the same diluent, but the concentrations of the other ELM components in it were as follows: 20.000 g/l of polyisobutylene, 10.268 g/l trioctyl amine and 50.024 g/l of SPAN 80. The stripping phase was the same in both optimised ELMs, namely a 2 M solution of HNO3. The stripping phase and the diluent solution were mixed together in ratios of 1:1 and 2:1, respectively. Two methods were used to characterise the microdroplet diameters, i.e. optical microscopy and the Zeta-sizer. For the t-test, the p-value of 0.3018 at 5 % level of significance showed that there was statistically no significant difference in the mean micro-droplet size for 1:2 ELMs containing 20 g/l and 30 g/l of polyisobutylene after 40 minutes of emulsification. The best demulsification results were obtained using the chemical demulsification with polyethylene glycol with molecular weight of 400 g/mol (PEG 400) at 50 ± 1 °C for 24 hours. However, significant carryover of toluene, trioctyl amine and polyethylene glycol into the aqueous phase was observed.
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- Date Issued: 2015
Mini-review on the use of liquid membranes in the extraction of platinum group metals from mining and metal refinery wastewaters/side-streams
- Authors: Moyo, Francis , Tandlich, Roman
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/75960 , vital:30487 , DOI: 10.4172/2155-6199.1000228
- Description: The current mini-review focuses on the use of liquid membranes in the platinum group metal (PGM/PGMs) extraction from various types of wastewaters to prevent environmental pollution; and for the metal recovery to address the scarcity of the PGMs in the industrial cycles. The bulk liquid membranes have been used to the extracted PGMs from the (acidic) aqueous media with recoveries of up to 96.3 ± 2.5% of the original PGM amount. The extraction time generally ranges from 2 to 24 hours. The bulk membrane liquid in the PGM extraction will depend on the covalent structure of the extractant, the feed phase PGM concentration and the complex of the PGM in question that is actually extracted from the aqueous environment. The advantages of this type of liquid membrane include its operational simplicity, but the disadvantages include limited possibility to improve the extraction performance of the system. Literature data are encouraging as they indicate that extraction of PGMs from mining and metal-refinery side-streams does not suffer from interference from metal contaminants that are commonly found in the mining and metal refinery side-streams, e.g. iron. Thus further research should focus on the application of ELM to extraction of PGMs from said wastewaters and major research drive should focus on the use of the Taylorvortex column and the non-Newtonian ELMs. With the supported liquid membranes, 78-82% of the original PGM content could be recovered from model side-streams. The selectivity of the extraction for individual PGMs can be controlled by the extractant used.
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- Date Issued: 2014
Sorption of hydrophobic organic compounds on natural sorbents and organoclays from aqueous and non-aqueous solutions: a mini-review
- Authors: Moyo, Francis , Tandlich, Roman , Wilhelmi, Brendan S , Balaz, Stefan
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/71614 , vital:29925 , https://doi.org/10.3390/ijerph110505020
- Description: Renewed focus on the sorption of hydrophobic organic chemicals (HOCs) onto mineral surfaces and soil components is required due to the increased and wider range of organic pollutants being released into the environment. This mini-review examines the possibility of the contribution and mechanism of HOC sorption onto clay mineral sorbents such as kaolinite, and soil organic matter and the possible role of both in the prevention of environmental contamination by HOCs. Literature data indicates that certain siloxane surfaces can be hydrophobic. Therefore soils can retain HOCs even at low soil organic levels and the extent will depend on the structure of the pollutant and the type and concentration of clay minerals in the sorbent. Clay minerals are wettable by nonpolar solvents and so sorption of HOCs onto them from aqueous and non-aqueous solutions is possible. This is important for two reasons: firstly, the movement and remediation of soil environments will be a function of the concentration and type of clay minerals in the soil. Secondly, low-cost sorbents such as kaolinite and expandable clays can be added to soils or contaminated environments as temporary retention barriers for HOCs. Inorganic cations sorbed onto the kaolinite have a strong influence on the rate and extent of sorption of hydrophobic organic pollutants onto kaolinite. Structural sorbate classes that can be retained by the kaolinite matrix are limited by hydrogen bonding between hydroxyl groups of the octahedral alumosilicate sheet and the tetrahedral sheet with silicon. Soil organic carbon plays a key role in the sorption of HOCs onto soils, but the extent will be strongly affected by the structure of the organic soil matter and the presence of soot. Structural characterisation of soil organic matter in a particular soil should be conducted during a particular contamination event. Contamination by mining extractants and antibiotics will require renewed focus on the use of the QSAR approaches in the context of the sorption of HOCs onto clay minerals from aqueous and non-aqueous solutions.
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- Date Issued: 2014