| dc.description.abstract | Selective Extraction and Recovery using Volatile Organic compounds is an
emerging technology developed during the 1970s. This process can achieve the
extraction of heavy metal contaminants from a matrix using a volatile organic
reagent which passes through the feed material and reacts selectively with the desired
metal salt, producing a volatile metal complex, removed from the matrix by a carrier
gas. Such complexes may be decomposed to produce a pure metal product and
regenerate the organic reagent for recycle. Previous studies demonstrated the
possible extraction of nickel from low grade laterite ores using ß-diketones (2,4-
pentanedione (Hacac)) and Schiff bases (bis(pentan-2,4-dionato)propan-1,2-diimine
(H2pnaa).
The current research is directed towards the selective extraction of different metals
such as zinc, lead, cadmium, molybdenum, and vanadium from contaminated
sediments and industrial wastes (Orimulsion ash, Municipal Solid Waste fly ash
(MSW), Pulverized Coal Combustion technology fly ash (PCC)).
New extractants and their metal complexes have been synthesised to determine their
thermal stability and their volatility. Of those synthesised the metal complexes of
tetra-propyldithiophosphoramide (Hprps) are the most thermally stable.
Using a thermogravimetric analyser the reaction kinetics of the SERVO process have
been studied. Equipment to study the SERVO process on a laboratory scale has been
designed and constructed. This equipment has been used to study the extraction of
metals from four different matrices (sediments, Orimulsion ash, and two types of fly
ash) using three different extractants, with promising results. These sources have
been ranked from the best to the least applicable for the technology: Orimulsion ash
> sediments > MSW fly ash > PCC fly ash.
Of the three extractants studied, Hacac, H2pnaa and Hprps, the latter is the most
efficient in terms of the range of metals which can be extracted, the volatilisation
temperature, the extent of degradation and reaction time, but unfortunately is also the
most expensive. For the fly ashes, of the three ligands studied, Hprps is the preferred
extractant followed by H2pnaa. Hacac is not recommended for these sources because
extraction is too low. | en_US |
