Electrospinning bicomponent nanofibres for platinum ion extraction from acidic solutions

Willemse, Abraham Cilliers (2013-03)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Trace amounts of soluble Pt(II/IV) ions are not recovered using current refining processes. There are both economic and environmental incentives to recover these Pt(II/IV) ions from effluent. The work presented in this dissertation was aimed at producing functionalised electrospun nanofibre webs for the extraction of trace amounts of Pt(II/IV) ions in the form of [PtCl6]2- from acidic solutions. An insoluble, low molecular weight oligomeric compound, poly(N-terephthaloylthiourea)-N’,N’-piperazine, was synthesised from relatively inexpensive starting reagents using a “one-pot” two step synthesis procedure. Interest in this compound lies in its ability to extract Pt(II/IV) ions from acidic, chloride-rich solutions, as may be encountered in real process solutions in platinum group metal refineries. The product was isolated and characterised with an array of techniques, including GPC, elemental analysis, 1H and 13C NMR, as well as FTIR, and it was found to be a mixture of various molecular weight fractions with a degree of chemical variance between oligomer chains. The poly(N-terephthaloylthiourea)-N’,N’-piperazine was blended with polyacrylonitrile (PAN) and electrospun using both the classical single needle approach as well as a high throughput free-surface electrospinning process, called ball electrospinning. The nanofibres consisted of the oligomer which provided the affinity for [PtCl6]2- while PAN provided sufficient polymer chain entanglement which allowed the formation of fibrous structures. Two different solutions were found to produce nanofibres with the desired dimensions, namely: 6 wt% and 8 wt% PAN solution, both having a PAN to oligomer ratio of 7:3. The fibres produced by needle electrospinning and ball electrospinning had average fibre diameters of 172 ± 35 nm and 210 ± 49 nm, respectively. The ball electrospinning process had 86 times greater fibre production rates compared to needle electrospinning. The effects of three experimental conditions on the recovery of Pt(II/IV) ions by the poly(N-terephthaloylthiourea)-N’,N’-piperazine-containing nanofibres were determined. The conditions were: (i) the effects of specific surface area and available coordination sites over time, (ii) the effect of extraction temperature, and (iii) the effect of hydrochloric acid (HCl) concentration on [PtCl6]2- extraction. Increased availability of coordination sites caused an increase in Pt ion extraction. The Pt ion extraction also increased from 0.007 g to 0.023 g for each gram of nanofibres used as the temperature was increased from 20 °C to 60 °C when using a 114 mg/L Pt stock solution. The HCl concentration had no effect on Pt ion extraction when varied between 1.0 x 10-3 M to 1 M, while increased extraction as well as fibre damage was caused at HCl concentrations greater than 1 M. Nanofibres containing an oligomeric compound with affinity for [PtCl6]2- in acidic solutions were successfully synthesised and used to extract trace amounts of Pt(II/IV) ions from solutions under various conditions.

AFRIKAANSE OPSOMMING: In huidige verfynings prosesse word spoorelemente van oplosbare Pt(II/IV) nie herwin nie. Daar is beide ekonomiese en omgewings insentiewe om hierdie Pt(II/IV) ione te verhaal uit die afval oplossings. Hierdie tesis was gemik daarop om funksionele elektrospinde nanovesel webbe te produseer vir die herwinning van Pt(II/IV) ioon spoorelemente in die vorm van [PtCl6]2- uit aangesuurde oplossings. ‘n Onoplosbare oligomeriese verbinding met ‘n lae molukulêre gewig, poly(N-terephthaloylthiourea)-N’,N’-piperazine, was uit relatief goedkoop begin reagense gesintetiseer deur gebruik te maak van ‘n “een-pot” twee stap prosedure. Die belangrikheid van die verbinding lê in sy vermoë om Pt(II/IV) ione uit aangesuurde, chloried-ryke oplossing te onttrek, soos wat in alledaagse afval oplossings van platinum-groep metalurgiese raffinaderye ondervind kan word. Die sintese produk was geisoleer en gekarakariseer deur gebruik te maak van ‘n verskeidenheid tegnieke, waaronder GPC, elementêre analise, 1H en 13C NMR sowel as FTIR, en daar was bepaal dat die produk bestaan uit ‘n mengsel van verskeie molukulêre gewig kettings met ‘n mate van chemiese variansie tussen hulle. Die gesintetiseerde oligometriese verbinding was gemeng met poliakrielonitriel (PAN) en elektrospin deur gebruik te maak van beide die klasieke naald spin proses, sowel as ‘n hoë-produksie vrye oppervlak spin proses, genaamd die bal elektrospin proses. Die nanovesels bestaan uit die oligomeer wat die affiniteit vir die [PtCl6]2- voorsien terwyl die PAN genoegsame polimeer ketting verstrengeling veroorsaak het om die veselagtige struktuur te vorm. Nanovesels met die gewensde dimensies was gevorm deur die elektrospin proses toe te pas op twee verskillende oplossings, naamlik: ‘n 6 massa persent PAN en ‘n 8 massa persent PAN oplossing, beide met ‘n PAN tot oligomeer verhouding van 7:3. Die vesels geproduseer deur die naald en bal elektrospin prosesse het ‘n gemiddelde vesel deursneë gehad van 172 ± 35 nm en 210 ± 49 nm, onderskeidelik. Die bal spin proses het egter ‘n 86 keer groter produksie kapasiteit van vesels gehad in vergelyking met die naald spin proses. Die effek van drie verskillende toestande op die effektiwiteit van die nanovesels, wat poly(N-terephthaloylthiourea)-N’,N’-piperazine bevat, om Pt(II/IV) ione te onttrek uit die oplossings was ondersoek. Die toestande was: (i) die effekte van spesifieke oppervlak area asook beskikbare ontginnings setels oor tyd, (ii) die effek van die ontginnings temperatuur, en (iii) die effek van die soutsuur (HCl) konsentrasie op die Pt ioon ontginning. ‘n Toename in die beskikbaarheid van die ontginnings setels het gelei tot ‘n toename in die Pt ioon ontginning. Die Pt ioon ontginning het toegeneem van 0.007 g tot 0.023 g vir elke gram van nanovesels gebruik soos die temperatuur verhoog was van 20 °C tot 60 °C wanneer ‘n 114 ppm (m/v) Pt ioon oplossing gebruik was. Daar was geen effek op die Pt ioon ontginning toe die HCl konsentrasie tussen 1.0 x 10-3 M en 1 M HCl varieer was nie, alhoewel daar by konsentrasies hoër as 1M ‘n verhoogde ontginning sowel as vesel skade was. Nanovesels wat ‘n oligemetriese verbinding bevat met ‘n affiniteit vir [PtCl6]2- in ‘n aangesuurde oplossing, was suksesvol gesintetiseerd en gebruik om spoorelemente van Pt(II/IV) te onttrek onder verskillende omstandighede.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/80028
This item appears in the following collections: