Comparison of silica-based poly(amine) containing ion exchangers and their guanidine derivatives for selective PGM recovery from authentic refinery process solutions

Dhladhla, Nomasonto Ellen (2006-12)

Thesis (MSc)--University of Stellenbosch, 2006.

Thesis

ENGLISH ABSTRACT: The platinum group metals (PGMs: Pt, Pd, Rh, Ir, Os and Ru) occur in nature in close association with other transition metals, such as Fe, Cu, Ni and Co in often large quantities. The separation and refinement of the PGMs largely uses solvent extraction, and ion exchange methods and finally incorporates precipitation and redissolution steps in order to obtain the pure PGM products at the end. During the refinement, precipitation and redissolution steps, PGM losses occur which give rise to process effluents which are termed authentic refinery process (ARP) solutions in this thesis. These process solutions have PGMs in low concentrations that could not be recovered by the present recovery processes. We have synthesised silica-based poly(amine)-containing ion exchangers (monoamine (N1); ethylenediamine (N2) and diethylenetriamine (N3)) and their corresponding dimethylguanidine derivatives (N1G-N3G) and have tested their Pt, Pd, Rh and Ir recovery behaviour from four ARP solutions. The ARP solutions vary considerably in compositions with the pH of the solutions ranging between -0.6 to 5.0. Palladium showed up to quantitative extraction from ARP solutions with the highest pH's (pH 3.2 and 5.0) with both types of ion exchangers. However, the Pt, Pd, Rh and Ir extractions were not so good under very acidic conditions (pH -0.6 and 0.2) for both types of ion exchangers. Maximum extractions were achieved at 60% (Ir), 54% (Pt), 46% (Rh) and 17% (Pd) with the N3 ion exchanger. A possible explanation for the incomplete PGM extractions was the high unbound chloride concentrations competing with the ion exchanger for the binding sites as well as the unknown speciation of individual PGM complexes in the ARP solutions. An increase in extraction followed a general trend from: N1 < N2 < N3. A very good PGM selectivity over Cu, Ni, Co and Fe under very acidic conditions was demonstrated by both types of ion exchangers. At increased pH, the selectivity dropped with the use of poly(amine) ion exchangers while the corresponding dimethylguanidine counterparts retained the selectivity due to their high pKa value. Quantitative desorptions were attained for Pd with the use of 5M HCI and the combination of 0.5M thiourea I 1 M HCI solutions for both types of ion exchangers, while 60%-90% Ir and Rh desorptions could be achieved with 2M HN03. In terms of the re-usability of the ion exchangers, the poly(amine) ion exchange material was more stable than the dimethylguanidine ion exchange material, under harsh desorption conditions (5M HCI). Overall, best successive recoveries were obtained for Pd (ca 35.0 mg/g ion exchanger) with the N3 ion exchanger after 5 cycles of adsorption and desorption.

AFRIKAANSE OPSOMMING: Die platinumgroepmetale (PGM's: Pt, Pd, Rh, Ir, Os en Ru) kom in die natuur te same met dikwels groot hoeveelhede ander oorgangsmetale soos Fe, Cu, Ni en Co voor. Vir die skeiding en rafinering van die PGM's word grootliks gebruik gemaak van vloeistofekstraksie, ioonuitruilings metodes en uiteindelik volg presipiterings- en heroplossingsstappe om suiwer PGM-produkte daar te stel. Tydens rafinering, presipiterings- en heroplossingsstappe kom PGM-verliese voor wat aanleiding gee tot proseseffluante wat outentieke rafineringsprosesoplossings (ARP) genoem word in die tesis. Hierdie prosesoplossings bevat PGM's in lae konsentrasies wat nie herwin kan word met die huidige herwinningsprosesse nie. Ons het silikagebaseerde poliamienbevattende ioonuitruilers (monoamine (N1 ); etileendiamien (N2) en dietileentriamien (N3)) en hul ooreenkomstige dimetielguanidienafgeleides (N1G-N3G) gesintetiseer en het hul Pt-, Pd-, Rh- en lr-herwinningseienskappe vanuit vier ARP-oplossings getoets. Die ARP-oplossings verskil aansienlik in samestelling met pH's wat strek van -0.6 tot 5.0. Palladium het die beste vertoon met tot kwantitatiewe ekstraksie met beide tipes ioonuitruilers vanuit die ARP-oplossings met die hoogste pH's (pH 3.2 en 5.0). Die Pt, Pd, Rh en Ir, het egter, nie so goed vertoon onder sterk suur kondisies (pH - 0.6 en 0.2) vir beide tipes ioonuitruilers. Die maksimum ekstraksie wat verkry is is 60% (Ir), 54% (Pt), 46% (Rh) and 17% (Pd) met die NJ ioonuitruiler. 'n Moontlike verklaring vir die onvolledige PGM-ekstraksie is die hoe konsentrasies van ongebinde chloried wat kompeteer met die ioonuitruiler vir die bindingsplekke sowel as die onbekende spesiering van indiwiduele PGM-komplekse in die ARPoplossings. 'n Toename in ekstraksie het 'n algemene tendens getoon van N1 < N2 < NJ. 'n Baie goeie PGM-seleksie bo Cu, Ni, Co en Fe onder suur kondisies is getoon deur beide ioonuitruilers. By hoer pH het die selektiwiteit verminder met die gebruik van die poliamien ioonuitruilers terwyl die ooreenkomstige dimetielguanidien ekwivalente selektiwiteit behou het as gevolg van hul hoe pK8-waarde. Kwantitatiewe desorpsie is verkry vir Pd met gebruik van 5M HCI en die kombinasie van 0.5M tioureum/1 M HCl-oplossings vir beide tipes ioonuitruilers, terwyl 60%-90% Ir en Rh desorpsie verkry is met 2M HN03. In terme van die hergebruik van die ioonuitruilers is die poliamien ioonuitruil-materiaal meer stabile as die dimetielguanidien ioonuitruilmateriaal onder strawwe desorpsiekondisies (5M HCI). Oorkoepelend is die beste agtereenvolgende herwinning verkry vir Pd (ca 35.0 mg/g ioonuitruiler) met die NJ ioonuitruiler na 5 siklusse van adsorpsie en desorpsie.

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