RecoveryandThenIndividualSeparationofPlatinum,Palladium ... · 2019. 9. 25. · catalytic converter brought from an end-of-life car man-agementcompany) ... 3.1. Individual Separation

Research ArticleRecovery andThen Individual Separation of PlatinumPalladiumand Rhodium from Spent Car Catalytic Converters UsingHydrometallurgical Technique followed by SuccessivePrecipitation Methods

Ahmed M Yousif 12

1Chemistry Department College of Science and Arts Jouf University Al-Qurayyat Saudi Arabia2Chemistry Department Faculty of Science Menoufia University Shebin El-Kom Egypt

Correspondence should be addressed to Ahmed M Yousif amm_yousif_000hotmailcom

Received 7 July 2019 Revised 7 August 2019 Accepted 30 August 2019 Published 25 September 2019

Academic Editor Antonio de Lucas-Consuegra

Copyright copy 2019 Ahmed M Yousif is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Recovery of PGMs (especially rhodium platinum and palladium) from different spent manufactured products (like catalyticconverters) is considered as an important task as they are rarely found in nature and they possess high economic value In thiswork the honeycomb of a car catalytic converter was primarily processed by crushing grinding and then treating in a hydrogenatmosphere In order to establish an economic and ecofriendly method for the recovery of studied PGMs different experimentalconditions of changing HClH2O2 (as a leaching solution) ratio temperature and contact time were studied through batchexperiments to obtain the optimum leaching conditions e use of 08 vol H2O2 and 90M HCl mixture at 60degC for a contacttime of 25 hours during the leaching process may be considered as the best conditions to be followed to save chemicals energyand time (about 86 96 and 98 of Rh Pt and Pd were recovered respectively) Individual separation of PGM ions from eachother using precipitation technique from their leaching liquor was performed where purity values of 995 993 and 955 wereobtained for Pt Pd and Rh respectively

1 Introduction

In order to reduce the nitrogen oxide hydrocarbon andcarbon monoxide emissions (they are considered as harmfulgases) produced by different vehicle engines it has been amustfor all vehicles produced since 1993 to be fitted with catalyticconverters A catalytic converter contains precious metals (asactive components) such as palladium platinum and rhodium(referred to as PGMs) in order to convert harmful gasesemitted from vehicle engines to relatively harmless ones byboth the reduction of nitrogen oxides (NOx) into nitrogen N2and the oxidation of hydrocarbons and CO to CO2 [1]

Catalytic converters consist of honeycomb skeleton unitswhich possess PGMs on its large surface (as the honeycombskeleton of each unit increases the contact area between theunit and the vehicle exhaust emissions) [2] During themanufacturing process salts of PGMs are impregnated into

the surface of honeycomb skeleton using their solutions andthen they are reduced to their metallic form [3] Dependingon the manufacturer the concentrations of PGMs in the unitvary widely In recent car catalytic converters Pt concen-tration ranges from 300 to 1000 μgmiddotgminus 1 for Pd the con-centration ranges from 200 to 800 μgmiddotgminus 1 and for rhodiumthey vary from 50 to 120 μgmiddotgminus 1 erefore in all cases thepercentage of total content of PGMs in the samples shouldalways be smaller than 01 [4]

Because of the production of PGMs by limited quantitiesand their high value there is an increasing demand for theirrecovery from different spent manufactured products as asecondary source Besides from an environmental point ofview such a recovery process should be correctly managedto avoid health and environmental risks [5 6]

Spent catalytic converters are good candidates for suchrequirement Several works have been conducted to recover

HindawiJournal of ChemistryVolume 2019 Article ID 2318157 7 pageshttpsdoiorg10115520192318157

PGMs from spent catalytic converters using different met-allurgical and refining methods through the use of smeltingfurnaces hydrogen pretreatment andor direct leaching ofPGMs [4 7ndash9] Several leaching processes have been de-veloped based on the selective dissolution of the honeycombunit consisting of PGMs after its crushing and milling [10]One of the obstacles faces the dissolution process is the factthat PGMs are inert erefore they are hardly dissolved inordinary acids Instead a mixture of a strong acid (mainlyHCl) and a suitable strong oxidizing agent (such as nitricacid chlorate hypochlorite perchloric acid bromated ni-trate and cupric ions) is required in relatively large amountsto dissolve PGMs during a long period of time estimated inhours [11ndash13]

Since the leaching processes are usually performed by theuse of strong oxidizing agents their potential effects must betaken into consideration regarding their environmental andsafety issuese use of chlorine compounds requires specialcare because of their poisoning effect e use of aqua regiaand other HClHNO3 mixtures produces nitrous vaporsemission due to several intermediate and final speciesgeneration such as NOCl NO NO2 and HNO2 besides Cl2generation as mentioned elsewhere e use of cupric ionsleaves behind copper compounds in the leaching liquorwhich are themselves considered as contaminants hardlyseparated from leached PGMs [12 14] erefore these factslead us to think about the use of efficient and ecofriendlyleaching processes

In the present study efforts were directed to recoverPGMs from processed spent catalytic converters (afterpretreatment in a hydrogen atmosphere) using harmlessleaching mixtures of hydrochloric acid and hydrogen per-oxide as an oxidant (without any harmful gas emission or aresidual byproduct generation during the process) Differentexperimental conditions of changing HClH2O2 ratiotemperature and contact time were studied for the leachingprocesses to obtain the optimum leaching conditions Otherexperiments were conducted to individually separate PGMsfrom each other in the leaching liquor using the pre-cipitation technique

2 Experimental

21 Chemicals and Materials Reagents used in the experi-ments (36 HCl (12M) and 30 H2O2 (ww) solutions)were Sigma-Aldrich products and used as received All otherchemicals were purchased from Prolabo and Merck andused as received Double distilled water was used throughoutthe experimental work e catalyst used in this study is ofhoneycomb supports (found in a spent three-way gasolinecatalytic converter brought from an end-of-life car man-agement company) which are formed by a cylindrical bodytraversed by many straight channels and coated with a washcoat on which the PGMs are located

22 Preparation of the Catalyst Powder and HydrogenPretreatment e honeycomb unit was crushed and thenground using a cutting mill (IKA MF10) until the powder

size reached 03mm e obtained powder was mixed well(to make it more homogeneous to reduce misleading resultsduring analysis) and then was stored in a desiccator to avoidside reactions 1 gram of the powder is used in the elementalanalysis after digestion with an acid mixture (firstly withHClHNO3 31 (vv) and then HF) in a Teflon vessel at110 psi relative pressure using a microwave digester

Hydrogen pretreatment for obtained powder stabilizesthe PGMs in their metallic form in order to be easy todissolve with the studied leaching mixtures [1] Accordinglythe powder was treated with a constant hydrogen gas flow(8 H2) for 20 hours at 100degC

23 Leaching and Experimental Techniques Different ex-perimental conditions of HClH2O2 ratio contact time andtemperature were studied for the leaching processes toobtain the optimum leaching conditions through the fol-lowing batch techniques

For each experiment solid powder and working leachingsolution (solidsolution ratio is 1 20 wv respectively) wereput in a 250mL flask e flask was conditioned on avibromatic shaker at 250 rpm and was immersed in an oilbath at the working temperature and pH for 3 hours (severalpreliminary experiments were performed to conclude thatthe contact time of 3 hours was sufficient for an experimentto reach the optimum leaching capacity) At the end of theexperiment leached PGM ion concentrations in the solutionwere calculated quantitatively (after clarifying a small por-tion of the leaching solution through centrifugation) andwere compared with the PGM content in the solid powderEach measurement reading was an average of threereplicates

For monitoring the effect of contact time for the leachingexperiment small portions of the leaching solution werecollected throughout the experiment at different time in-tervals and then centrifuged en the clarified solutionswere sent to analysis to record the leaching efficiency as afunction of the contact time

After applying the optimum leaching conditions for abatch experiment leaching solution containing PGM ionswas directed to another treatment to individually separatePGM ions from each other using precipitation technique asillustrated in the following section

24 Individual Separation of PGM Ions from Each OtherUsing Precipitation Method is method is based onselecting suitable precipitating agents to be successivelyadded to PGM ions found in their pretreated leaching so-lution in order to separate them individually as insolublesubstances which may be treated after filtration to obtaintheir pure metallic form as illustrated in the forthcomingsection (Section 31)

25 Instruments e elemental analysis as well as con-centration measurements was performed by using in-ductively coupled plasma-atomic emission spectrometry(ICP-AES Horiba Jobin-Yvon Ultima)

2 Journal of Chemistry

3 Results and Discussion

Elemental analysis of Pd Pt and Rh in the powder is listed inTable 1 e difference in readings for the same metal in theanalysis may be attributed to the heterogeneity of sampleserefore in all cases the percentage of total content ofPGMs in the samples was found to be smaller than 01 asmentioned in the literature [4]

Conditioning of HClH2O2 mixture with differentcompositions to the powder during the batch experimentyields a leaching solution of reddish color is color isconsidered as a primary evidence of the existence of PGMsin the powder that they form colored chlorocomplexes asillustrated in the following equations [11]

Pt(s) + 2H2O2(aq) + 6HCl(aq)⟷ PtCl61113858 11138592minus

(aq) + 2H+(aq)

+ 4H2O(1)

Pd(s) + H2O2(aq) + 4HCl(aq)⟷ PdCl41113858 11138592minus

(aq) + 2H+(aq)

+ 2H2O(2)

2Rh(s) + 3H2O2(aq) + 12HCl(aq)⟷ 2[RhCl6]3minus

(aq)

+ 6H+(aq) + 6H2O

(3)

To study the effect of changing HClH2O2 ratio on theleaching efficiency 30 H2O2 was added to 12degM HCl ofratios up to 24 100 vv respectively and the leaching ef-ficiencies were recorded through batch experiments and areshown in Figure 1 It is obvious that by increasing H2O2HClratio up to 08 100 vv the leaching efficiency increaseddramatically Afterwards there was no significant increaseobserved Gas bubbles were observed after the addition ofH2O2 to the leaching solutions which were considered as aprimary evidence of the formation of chlorine gas activespecies (which react with PGMs to produce their chlor-ocomplexes in acid solutions) as illustrated in the followingequation

H2O2(aq) + 2HCl(aq)⟷Cl2(g) + 2H2O (4)

Based on the facts listed above the following experimentswere conditioned by holding 08 vol H2O2 as a constantratio during a series of experiments through which HClconcentration was varied from 1 to 12M using distilled watere obtained leaching efficiencies are shown in Figure 2 Asillustrated in the figure PGM dissolution efficiencies in-creased dramatically with increasing HCl concentration tillreaching the value of 90M Afterwards slight increases of theleaching efficiencies were observed For all experiments theobserved leaching efficiencies order of PGMs wasPdgtPtgtRh By using 117MHCl the leaching efficiencies ofPd Pt and Rh were 100 96 and 88 respectively

Figure 3 illustrates the effect of changing the temperatureon the leaching efficiencies of PGMs from the powder samplesusing optimum conditions of H2O2 volume ratio and HCl

concentration (08 vol H2O2 and 90M HCl) e tem-perature was varied in a wide range from 20degC to 80degC ebatch experiments were conducted using well-sealed 250mLflasks to avoid evaporation of liquids at high temperatures tomaintain the constant solidsolution ratio for all experimentse results obtained showed that at all temperatures theleaching efficiencies followed the order PdgtPtgtRh For Ptand Pd curves the leaching efficiencies increased significantlytill reaching a temperature of 60degC Afterwards there was noobservable increase in the efficiency values For Rh curve theleaching efficiencies increased constantly till reaching atemperature of 60degC after which there were no considerableincreases in recorded efficiencies

Figure 4 illustrates the effect of contact time of the batchexperiments on the leaching efficiencies of PGMs from thepowder sample using optimum conditions of H2O2 volumeratio HCl concentration and temperature (08 vol H2O290MHCl and 60degC)e leaching processes possessed highkinetics Pd and Pt reached equilibrium leaching values after2 hours while Rh reached that value after 25 hours Morethan the mentioned equilibrium times leaching time gaveno effect to the PGM dissolution

A comparison between the various variables examinedduring the leaching experiments is tabulated in Table 2 Interms of an economic feasibility study based on the bestconditions that save chemicals energy and time selectivelythe use of 08 vol H2O2 and 90M HCl mixture in theleaching process at 60degC for a contact time of 25 hoursrespectively may be considered as the best conditions to befollowed in the leaching process as about 86 96 and 98of Rh Pt and Pd were recovered respectively

31 Individual Separation of PGM Ions from Each OtherUsing Precipitation Method A simplified flow sheet of thefollowed leaching and precipitation techniques is shown inScheme 1 Primarily the leaching solution is directed tosome treatments before being suitable for individual sepa-ration of PGMs from each other e first step was thedistillation of the excess HCl by evaporation at 190degC enthe dilution of the hot solution with water until a solution of200mgL Pt was obtained (a suitable precipitation con-centration for Pt species) [15] During dilution hydrolysis ofmetal species occurred e complexes formed remaineddissolved in the mother liquor as these species possess highsolubilitye hydrolysis probability seemed to be higher forPd and Rh than Pt which is the reason for their completeseparation from Pt at the precipitation step mentioned in thefollowing section [16] It is important to say that the dis-tillation temperature must be high enough (not below190degC) to ensure effective hydrolysis of Pd and Rh species

Table 1 Elemental analysis of Pt Pd and Rh of the spent catalystunit under study

Content (μgmiddotgminus 1)Pt Pd Rh

Range 251ndash277 391ndash419 112ndash126Average 264 405 119

Journal of Chemistry 3

Samplepowder

Leaching solutioncontaining PGMs

Spentcatalyst

Hydrogen pretreatmentLeaching with HClH2O2 mixture

Crushing and grinding

(NH4)2 [PtCl6] ppt

(NH4)2 [PdCl6] ppt

Filtrate containing Pdand Rh species

Calcination at 800degC

Platinum

Palladium


KOHFiltration

Discarded filtrateRh(OH)3ppt Calcination1150degC

Rhodium

Filtrate containing Rhspecies

(i)(ii)

HydrolysisNH4Cl (240gL) 40degCFiltration

(i)(ii)

NaClO3Filtration

(i)(ii)

(i)(ii)

(iii)

Scheme 1 Simplified flow sheet of the followed leaching and precipitation techniques

00 04 08 12 16 20 24 2840

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

H2O2 (vol)

RhPtPd

Figure 1 Effect of changing H2O2HCl volume percentage onPGM leaching efficiencies at 60degC for 3 hours

0 2 4 6 8 10 120

10

20

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

[HCl] (M)

RhPtPd

Figure 2 Effect of changingHCl concentration with addition of 08vol H2O2 on PGM leaching efficiencies at 60degC for 3 hours


e individual precipitation of Pt over Pd and Rh fromeach other was performed by adding NH4Cl (290 gL) at 40degCto their solution under vigorous stirring A yellowish Ptprecipitate of (NH4)2[PtCl6] was obtained e precipitatewas filtered and then washed with a dilute NH4Cl solution(140 gL) e filtrate was set aside for later use e contacttime between the mother liquor and the precipitate was keptsmall to avoid coprecipitation of the impurities with Pt toensure high purity of the precipitate Pt precipitate was cal-cined at 800degC washed several times with hot distilled waterand then dried to obtain a fine Pt powder of more than 995puritye calcination processmay be summarized as follows

3 NH4( 11138572 PtCl61113858 1113859⟶800degC 3Pt(s) + 2NH4Cl + 16HCl + 2N2

(5)

To precipitate Pd individually from Rh found in the fil-trate it was evaporated to concentrate the solution To the hot

solution below boiling temperature was slowly added about3 grams of sodium chlorate (NaClO3) crystals (as they vig-orously reacted to the solution due to the presence of organicmaterials in the solution) with continuous stirring until thebright red precipitate of insoluble (NH4)2[PdCl6] was com-pletely formed instead of the former soluble form of(NH4)2[PdCl4] e precipitate was filtered and then washedthoroughly with distilled water and the filtrate was set aside toextract remaining Rh as a next step e dried precipitate wascalcined at 900degC where a Pd powder of more than 993purity was obtained and stored in a closed vessel e cal-cination process may be illustrated as follows

3 NH4( 11138572 PdCl61113858 1113859⟶900degC 3Pd(s) + 2NH4Cl + 16HCl + 2N2

(6)

Remaining dissolved rhodium species in the filtrate wasprecipitated as a lemon yellow rhodium hydroxide

RhPtPd

0 10 20 30 40 50 60 70 80 9020

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

Temperature (degC)

Figure 3 Effect of changing temperature on PGM leaching efficiencies using 08 vol H2O2 and 90M HCl for 3 hours

RhPtPd

20

10

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

00 05 10 15 20 25 30 35Time (hours)

Figure 4 Effect of contact time on the PGM leaching efficiencies using 08 vol H2O2 and 90M HCl at 60degC for 3 hours


(Rh(OH)3) precipitate using KOH solution by slow additionwith stirring until complete precipitation occurred eprecipitate was filtered washed thoroughly with distilledwater and then dried in air e complete decomposition inthe air for Rh(OH)3 to Rh2O3 and then Rh metal wasperformed by ignition at 1150degC to produce a grey Rh metalpowder of 954 purity Other refining processes may befollowed in a forthcoming work (low purity percentage of Rhmay be due to some impurities found in the leaching so-lution or due to various treatments performed to the in-dividual separation process)

4 Conclusions

Selectively the HClH2O2 mixture was used as a suitableleaching mixture as it did not cause any harmful gasemission or any residual byproduct generation during theleaching process of PGMs from catalytic converters Dif-ferent experimental conditions of changing HClH2O2 ratiotemperature and contact time were studied for the leachingprocesses to obtain the optimum leaching conditions euse of 08 vol H2O2 and 90M HCl mixture at 60degC for acontact time of 25 hours during the leaching process may beconsidered as the best conditions to be followed in order tosave chemicals energy and time (about 86 96 and 98of Rh Pt and Pd were recovered respectively) Pt Pd andRh were separated individually from the leaching liquor with purity values of 995 993 and 95 respectively by usingthe precipitation technique

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that they have no conflicts of interest

References

[1] D J de Aberasturi R Pinedo I R de LarramendiJ I R de Larramendi and T Rojo ldquoRecovery by hydro-metallurgical extraction of the platinum-group metals fromcar catalytic convertersrdquo Minerals Engineering vol 24 no 6pp 505ndash513 2011

[2] P Lucena J M Vadillo and J J Laserna ldquoMapping ofplatinum group metals in automotive exhaust three-waycatalysts using laser-induced breakdown spectrometryrdquo An-alytical Chemistry vol 71 no 19 pp 4385ndash4391 1999

[3] M Moldovan M M Gomez and M A Palacios ldquoDe-termination of platinum rhodium and palladium in car ex-haust fumesrdquo Journal of Analytical Atomic Spectrometryvol 14 no 8 pp 1163ndash1169 1999

[4] M Faisal Y Atsuta H Daimon and K Fujie ldquoRecovery ofprecious metals from spent automobile catalytic convertersusing supercritical carbon dioxiderdquo Asia-Pacific Journal ofChemical Engineering vol 3 no 4 pp 364ndash367 2008

[5] A M Yousif M Nishioka Y Wakui and T M SuzukildquoAdsorption of Pd(II) Pt(IV) and Rh(III) on a ligand en-capsulated polymer resin assisted by thermal heating ormicrowave irradiationrdquo Solvent Extraction and Ion Exchangevol 30 no 1 pp 77ndash87 2012

[6] A M Yousif M Nishioka Y Wakui and T M SuzukildquoRapid adsorption of Rh(III) by polyamine-functionalizedcellulose fiber combined with microwave irradiationrdquoChemistry Letters vol 39 no 12 pp 1317-1318 2010

[7] Y Cao S Harjanto A Shibayama et al ldquoKinetic study on theleaching of Pt Pd and Rh from automotive catalyst residue byusing chloride solutionsrdquo Materials Transactions vol 47no 8 pp 2015ndash2024 2006

Table 2 Effect of the various variables examined during leaching process on the PGM leaching efficiencies

Variables studied Leaching efficiency ()Temp (degC) H2O2 (vol) [HCl] (M) Time (hours) Rh Pt Pd60 02 1192 30 48 53 6760 03 1188 30 61 67 7860 04 1184 30 71 76 8760 05 1180 30 80 89 9360 08ndash24 1168ndash1136 30 88-89 96-97 10060 08 100 30 20 30 6060 08 200 30 38 47 6960 08 300 30 52 63 7760 08 500 30 64 76 8560 08 600 30 73 83 9060 08 700 30 80 90 9560 08 900ndash1168 30 86ndash88 96 98ndash10020 08 900 30 40 70 7530 08 900 30 54 79 8340 08 900 30 66 86 8950 08 900 30 77 92 9460ndash80 08 900 30 86ndash90 96 98-9960 08 900 05 35 50 6060 08 900 10 60 73 7660 08 900 15 75 90 9360 08 900 20 80 95 9860 08 900 25ndash30 86 96 98


[8] C Fontas V Salvado and M Hidalgo ldquoSeparation andconcentration of Pd Pt and Rh from automotive catalyticconverters by combining two hollow-fiber liquid membranesystemsrdquo Industrial and Engineering Chemistry Researchvol 41 no 6 pp 1616ndash1620 2002

[9] C H Kim S I Woo and S H Jeon ldquoRecovery of platinum-groupmetals from recycled automotive catalytic converters bycarbochlorinationrdquo Industrial and Engineering ChemistryResearch vol 39 no 5 pp 1185ndash1192 2000

[10] H Dong J Zhao J Chen Y Wu and B Li ldquoRecovery ofplatinum group metals from spent catalysts a reviewrdquo In-ternational Journal of Mineral Processing vol 145 pp 108ndash113 2015

[11] S Harjanto Y Cao A Shibayama et al ldquoLeaching of Pt Pdand Rh from automotive catalyst residue in various chloridebased solutionsrdquo Materials Transactions vol 47 no 1pp 129ndash135 2006

[12] M Massucci S L Clegg and P Brimblecombe ldquoEquilibriumpartial pressures thermodynamic properties of aqueous andsolid phases and Cl2 production from aqueous HCl andHNO3and their mixturesrdquo 5e Journal of Physical ChemistryA vol 103 no 21 pp 4209ndash4226 1999

[13] J S Yoo ldquoMetal recovery and rejuvenation of metal-loadedspent catalystsrdquo Catalysis Today vol 44 no 1ndash4 pp 27ndash461998

[14] C A Nogueira A P Paiva P C Oliveira M C Costa andA M R da Costa ldquoOxidative leaching process with cupric ionin hydrochloric acid media for recovery of Pd and Rh fromspent catalytic convertersrdquo Journal of Hazardous Materialsvol 278 pp 82ndash90 2014

[15] G Schreier and C Edtmaier ldquoSeparation of Ir Pd and Rhfrom secondary Pt scrap by precipitation and calcinationrdquoHydrometallurgy vol 68 no 1ndash3 pp 69ndash75 2003

[16] C Saguru S Ndlovu and D Moropeng ldquoA review of recentstudies into hydrometallurgical methods for recovering PGMsfrom used catalytic convertersrdquo Hydrometallurgy vol 182pp 44ndash56 2018


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Submit your manuscripts atwwwhindawicom

PGMs from spent catalytic converters using different met-allurgical and refining methods through the use of smeltingfurnaces hydrogen pretreatment andor direct leaching ofPGMs [4 7ndash9] Several leaching processes have been de-veloped based on the selective dissolution of the honeycombunit consisting of PGMs after its crushing and milling [10]One of the obstacles faces the dissolution process is the factthat PGMs are inert erefore they are hardly dissolved inordinary acids Instead a mixture of a strong acid (mainlyHCl) and a suitable strong oxidizing agent (such as nitricacid chlorate hypochlorite perchloric acid bromated ni-trate and cupric ions) is required in relatively large amountsto dissolve PGMs during a long period of time estimated inhours [11ndash13]

Since the leaching processes are usually performed by theuse of strong oxidizing agents their potential effects must betaken into consideration regarding their environmental andsafety issuese use of chlorine compounds requires specialcare because of their poisoning effect e use of aqua regiaand other HClHNO3 mixtures produces nitrous vaporsemission due to several intermediate and final speciesgeneration such as NOCl NO NO2 and HNO2 besides Cl2generation as mentioned elsewhere e use of cupric ionsleaves behind copper compounds in the leaching liquorwhich are themselves considered as contaminants hardlyseparated from leached PGMs [12 14] erefore these factslead us to think about the use of efficient and ecofriendlyleaching processes

In the present study efforts were directed to recoverPGMs from processed spent catalytic converters (afterpretreatment in a hydrogen atmosphere) using harmlessleaching mixtures of hydrochloric acid and hydrogen per-oxide as an oxidant (without any harmful gas emission or aresidual byproduct generation during the process) Differentexperimental conditions of changing HClH2O2 ratiotemperature and contact time were studied for the leachingprocesses to obtain the optimum leaching conditions Otherexperiments were conducted to individually separate PGMsfrom each other in the leaching liquor using the pre-cipitation technique

2 Experimental

21 Chemicals and Materials Reagents used in the experi-ments (36 HCl (12M) and 30 H2O2 (ww) solutions)were Sigma-Aldrich products and used as received All otherchemicals were purchased from Prolabo and Merck andused as received Double distilled water was used throughoutthe experimental work e catalyst used in this study is ofhoneycomb supports (found in a spent three-way gasolinecatalytic converter brought from an end-of-life car man-agement company) which are formed by a cylindrical bodytraversed by many straight channels and coated with a washcoat on which the PGMs are located

22 Preparation of the Catalyst Powder and HydrogenPretreatment e honeycomb unit was crushed and thenground using a cutting mill (IKA MF10) until the powder

size reached 03mm e obtained powder was mixed well(to make it more homogeneous to reduce misleading resultsduring analysis) and then was stored in a desiccator to avoidside reactions 1 gram of the powder is used in the elementalanalysis after digestion with an acid mixture (firstly withHClHNO3 31 (vv) and then HF) in a Teflon vessel at110 psi relative pressure using a microwave digester

Hydrogen pretreatment for obtained powder stabilizesthe PGMs in their metallic form in order to be easy todissolve with the studied leaching mixtures [1] Accordinglythe powder was treated with a constant hydrogen gas flow(8 H2) for 20 hours at 100degC

23 Leaching and Experimental Techniques Different ex-perimental conditions of HClH2O2 ratio contact time andtemperature were studied for the leaching processes toobtain the optimum leaching conditions through the fol-lowing batch techniques

For each experiment solid powder and working leachingsolution (solidsolution ratio is 1 20 wv respectively) wereput in a 250mL flask e flask was conditioned on avibromatic shaker at 250 rpm and was immersed in an oilbath at the working temperature and pH for 3 hours (severalpreliminary experiments were performed to conclude thatthe contact time of 3 hours was sufficient for an experimentto reach the optimum leaching capacity) At the end of theexperiment leached PGM ion concentrations in the solutionwere calculated quantitatively (after clarifying a small por-tion of the leaching solution through centrifugation) andwere compared with the PGM content in the solid powderEach measurement reading was an average of threereplicates

For monitoring the effect of contact time for the leachingexperiment small portions of the leaching solution werecollected throughout the experiment at different time in-tervals and then centrifuged en the clarified solutionswere sent to analysis to record the leaching efficiency as afunction of the contact time

After applying the optimum leaching conditions for abatch experiment leaching solution containing PGM ionswas directed to another treatment to individually separatePGM ions from each other using precipitation technique asillustrated in the following section

24 Individual Separation of PGM Ions from Each OtherUsing Precipitation Method is method is based onselecting suitable precipitating agents to be successivelyadded to PGM ions found in their pretreated leaching so-lution in order to separate them individually as insolublesubstances which may be treated after filtration to obtaintheir pure metallic form as illustrated in the forthcomingsection (Section 31)

25 Instruments e elemental analysis as well as con-centration measurements was performed by using in-ductively coupled plasma-atomic emission spectrometry(ICP-AES Horiba Jobin-Yvon Ultima)






(aq) + 2H+(aq)

+ 4H2O(1)


(aq) + 2H+(aq)

+ 2H2O(2)


(aq)

+ 6H+(aq) + 6H2O

(3)


H2O2(aq) + 2HCl(aq)⟷Cl2(g) + 2H2O (4)











Samplepowder


Spentcatalyst



(NH4)2 [PtCl6] ppt

(NH4)2 [PdCl6] ppt



Platinum

Palladium


KOHFiltration


Rhodium


(i)(ii)


(i)(ii)

NaClO3Filtration

(i)(ii)

(i)(ii)

(iii)


00 04 08 12 16 20 24 2840

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

H2O2 (vol)

RhPtPd


0 2 4 6 8 10 120

10

20

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

[HCl] (M)

RhPtPd





(5)




(6)


RhPtPd

0 10 20 30 40 50 60 70 80 9020

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

Temperature (degC)


RhPtPd

20

10

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

00 05 10 15 20 25 30 35Time (hours)




4 Conclusions


Data Availability




References


























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls








(aq) + 2H+(aq)

+ 4H2O(1)


(aq) + 2H+(aq)

+ 2H2O(2)


(aq)

+ 6H+(aq) + 6H2O

(3)


H2O2(aq) + 2HCl(aq)⟷Cl2(g) + 2H2O (4)











Samplepowder


Spentcatalyst



(NH4)2 [PtCl6] ppt

(NH4)2 [PdCl6] ppt



Platinum

Palladium


KOHFiltration


Rhodium


(i)(ii)


(i)(ii)

NaClO3Filtration

(i)(ii)

(i)(ii)

(iii)


00 04 08 12 16 20 24 2840

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

H2O2 (vol)

RhPtPd


0 2 4 6 8 10 120

10

20

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

[HCl] (M)

RhPtPd





(5)




(6)


RhPtPd

0 10 20 30 40 50 60 70 80 9020

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

Temperature (degC)


RhPtPd

20

10

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

00 05 10 15 20 25 30 35Time (hours)




4 Conclusions


Data Availability




References


























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




Samplepowder


Spentcatalyst



(NH4)2 [PtCl6] ppt

(NH4)2 [PdCl6] ppt



Platinum

Palladium


KOHFiltration


Rhodium


(i)(ii)


(i)(ii)

NaClO3Filtration

(i)(ii)

(i)(ii)

(iii)


00 04 08 12 16 20 24 2840

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

H2O2 (vol)

RhPtPd


0 2 4 6 8 10 120

10

20

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

[HCl] (M)

RhPtPd





(5)




(6)


RhPtPd

0 10 20 30 40 50 60 70 80 9020

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

Temperature (degC)


RhPtPd

20

10

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

00 05 10 15 20 25 30 35Time (hours)




4 Conclusions


Data Availability




References


























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls






(5)




(6)


RhPtPd

0 10 20 30 40 50 60 70 80 9020

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

Temperature (degC)


RhPtPd

20

10

30

40

50

60

70

80

90

100

Leac

hing

effic

ienc

y (

)

00 05 10 15 20 25 30 35Time (hours)




4 Conclusions


Data Availability




References


























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls





4 Conclusions


Data Availability




References


























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls



















Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls









Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




Documents

RecoveryandThenIndividualSeparationofPlatinum,Palladium ... · 2019. 9. 25. · catalytic converter brought from an end-of-life car man-agementcompany) ... 3.1. Individual Separation