Guidelines for Recycling Precious Metals

7/30/2019 Guidelines for Recycling Precious Metals

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Guide1nestorn I 8 n 8Iiecyc Ing Prec0Metals

ByAndrew Catchmark

Maximizing the returnof precious metals means knowing something aboutsegregating scrap, assaylng, and refining, among other activities-ecycling precious metals begins with the identificationand collection of scrap generated in product manufac-turing Reclamation of valuable metals is required notonly from solid matter, but also from liquids such asplating solutions, rinses, and strippersA s a result of manufacturing or assembling electronic parts,for instance, the accumulation of scrap containing preciousmetals can bring a sizable monetary return S ome of the mate-rials from which metals can be recovered include printed circuitboards, transistors, diodes, wave guides, silver batteries, blank-ing scrap, punchings, brazing alloys, clad bimetal parts, contacts,relays, and connectors Many of these contain silver, gold, plati-num or palladium-all high-priced commoditiesInthe plating industry, scrap may consist of hooks or racks,anodes, chemical salts, filters, rinses, sludge, precipitates, ion-exchange resin or stripping solutions In addition, manufacturersof jewelry, flatware, holloware or optical goods have scrap mate-rials such as floor-sweepings, punchouts, rejected plated uten-sils, trimmings, brazing alloys, sterling silverware, jewelrygrindrngs, buffing residue, sludge, crucibles, and wastewater

Gold turnings from lathes and dust and filingsfrom metalworkingmachines are class ified as high-yield scrapIn the metal finishing industry, elfctroplaters can recover dol-la,s from spent plating solutions containing gold platinum, palla-dium silver and rhodium J ewelers. too can recycle usedcrucibles, bench filings, sink residues, filters and sweeps, and

silversmiths can collect articles damaged in production.The unfortunate occurrence in many of these installations sthat the precious metal sometimes misses the refinery and endsup in the garbage. However, the conscientious manager cantake better advantage of the refiner's capabilities by establishiWhouse rules for preparation of scrap and familiarizing himselfvdnsampling and refining procedures. To this end, some cf the m Wconsiderations are spelled out below.Value fquals Concentration-The value of the materz!bearing precious metal is equivalent to the extent to which It?metaLcan be recovered in pure form, In otherwords, he hi@the concentration of the precious metal in the scrap, the grea,jethe econbmic return. Shipping costs will be lower and dc!'arreturns will be higher.Segregate Materia&-The astute metal finisher will rea%greater returns by segregating, preparing and purifying It'metal-bearing material prior to shipping it to the refinery. Ifsgood idea to separate the scrap into basic metallic r;rouPs.Frexample, ferrous and non-ferrous materials should be keC'separate, and, if feasible, metallic and nonmetallic produc"should be segregated,too.Cyanide solutions, of course, mustEseparated as a safety measure. The key point to rememberthat the recovery process may vary with the complexltY 0 If *scrap. Some segregation techniques are magnetic SeParat'crphysical, mechanical or hand sorting, or crushing followed''physical separation.

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Recovery Alternatives-Once the segregatedpaterials have been accumulated, three options are available to,&metal finisher: (1) outright sale to a precious-metal dealer;(2),n.house preparation followed by in-house refining or shipment13 a refiner; and (3) blending the segregated scrap with a similarpaterialto achieve maximum return.Analyze the Sample-An appropriate sample should beto estimate the amount of precious metal contained inte sc,~:, Because scrap varies widely in content, samplingproceduresalso will differ. For instance, sweeps, powder andddst should be ground toa fine powder, screened and blended toachievehomogeneity before sampling Also, metallics must bemelted to homogeneity in special furnaces prior to assaying.From this molten material, a dip sample may be taken or thematerial may be poured into bars, from which a drilled portionmaybe assayed. For liquids such as electroplating and strippingsolutions, thorough agitation and extraction of a representativesample (with a sampling tube) is required.Selecting Assay Method-The assay method often is amatter of straightforward economics dictated by the number oftests reijLiired, the time spent on each test, and the cost ofequipment and materials The electrolytic method (metal platedout on a platinum cathode and weighed) commonly isemployedfor plating baths, the gravimetric method for standard gold com-pounds, and the spectrographic, atomic absorption or X-rayfluorescence or high-purity materials. In any case, it is of utmostImportance that the sample is representative of the scrap lot.Thelarger the sample, the more uniform the material, the higher thegold content, the more valid the assay will be. An accurate assaycan be made on a spurious sample, but, at the same time, anmvalid quantitative measure of the metal for the entire lot ofsalvagcd material also may result.Procedure for Gold-Gold-plated parts are likely to vary indeposit thickness from lot to lot. If at all possible, these rejectedparts should be segregated by type and lot; in essence, indis-criminate mixing of scrap parts should be avoided. Valid assayscan be obtained from filtered gold solutions that have beenthoroughly stirred and analyzed by taking a thief sample with aglass tube from the surface to the depth of the solution. However,extreme care must be taken when sampling stripping solutionsand some proprietary gold formulations. In these cases, tmay benecessaryto dilute a solution to redissolve precipitated crystals.Furthermore, solutions should not be stored in metal containersbecause gold immersion deposits and/or crystals may form and-..dhere !o the sulface of the vessel.Miscellaneous Assays-C arbon, wet sludge, carbon tubes,ion-exchange resin, and filter pads are difficultto sample; hence,the assay is often invalid. The best bet, however, is to sample andassay when the gold is still in solution. If not, sludge and precipi-tate should be dried, ground, screened, thoroughly mixed andtoen coned and quartered. This procedure provides a fairly good,

Selecting a Refiner-The selection of a prime refiner or amiddleman can mean money gained or lost. If both are equallynt, the finisher probably will do better to deal directlywith the prime refiner because the middleman's charge will beexcluded.importance of Representation-R epresentation is the wit-nessing Of the buyer's operation in the evaluation of the seller'sand is conducted in behalf of the sellei. Representationverifies the procedures and events that will occur in the:e'ining operation. This agreement is then reported tothe shipperI' his reassurance regarding the refining process Most"';pPers want to know if their material was received intact,s~c~fical lyith respect toweight, and an explanation if there isad ! s ~re P ~~cy .ome shippers will require a report of observations

made during processing, sampling or melting, whereas othersw'ttrequest the presence of a representative.Limitations of Reps-R epresentation can establish goodand confidence between the refiner and the seller. The'jUties of the representative are to inspect the shipment, witnessweighings of containers or net weights of bullion, andmake decisions handling Gr processing the ma!eriai,fiOw.ever, because most operating procedures are generalized and

sample and assay.

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not customized for each lot,the role ofthe representative may belimited in the determination ofsampling procedures. On the otherhand, in the preparation of future shipments. the representative'sobservations and recommendations can be extremely helpful toshipper and refiner.At the Refinery-If the scrap material is sealed when itarrives at the refinery, the seal number is verified against theshipping order. After verification, the seal is broken, the containeropened, and the contents inspected to verify that they corre-spond to the shipper's description. The shipment is weighed asreceived and weighed again after the containers have beenemptied. The result, of course, is the net weight of the refiningshipment.Making the Settlement-During this exercise, the represent-ative and the refiner place their respective seals on a reserveportion and the umpire's portionof the sample. Each forwards hisown portion to his respective laboratory for analysis. When theanalyses are complete, the parties usually exchange them bymail and a settlement is made. But, if the analyses are beyondthe contractual splitting limit, he umpire's portion of the sample isforwarded to the umpire's laboratory.J udging the Value-The value of the refining lot is deter-mined by fire assaying, wet chemical analysis, electrolyticmeans or a combination of all three. With classic fire assaying,actually a miniature refining process, the material first is melted na special furnace. The basis metal is forced into a slag and theprecious metal is collected with lead at the bottom of a crucible.The lead is then oxidized and removed, eaving a bead contain-ing only precious metals-a precise sample of the entire lot.Thisis then weighed as a basis for calculating the amount of preciousmetal in the refining shipment. In all cases, multiple samples arecross-checked for accuracy.Refining Techniques-At the refinery, here are a number ofways to refine a precious metal. Electrolytic purification is themost widely employed for gold and silver, but pyrometallurgy (firetechniques) and hydrometallurgy (chemical separation) are alsoused P latinum metals are purified by chemical precipitation anddissolution. Because they are usually obtained as a sponge orpowder, platinum-group metals are often melted into ingots.Getting the Return-In the final settlement, the shipperreceives a return in the form he specifies: (1)a check from therefiner, who would be the purchaser of the material; (2)a con-signment account for the value of the reclaimed material. minusrefining charges; (3) delivery of reconstituted scrap material inthe form of bars, strip, grain, wire, sheet, iflgets or salts; or (4 ) ashipment elsewhere per the buyer's instructions.Additional Information-The following publications arerecommended for those who have a continued interest in con-serving precious metals.1. Recycling Precious Metals, National Assoc. of RecyclingInd., Inc., 330 Madison Ave., New York, NY 10017.2. Sampling and Assaying of Precious Metals, InternationalP recious Metals Institute, 333 J ay St., Brooklyn, NY 112013. C. M. Hoke, R efining Precious Metal Wastes, MetallurgicalPublishing Co., 123 William St., New York, NY.4. "Precious Metals," chapter in Operations in the NonferrousScrap Metal lndustry Today, National Assoc. of R ecycling Ind.,New York, NY. 0

About the Author Andrew Catchmark is senior prolect engi-neer for ihe Advanced Automated svs-tems Division of AM P lnc, M a / / Slation140-41, Box 3608 Harrisburg PA 17105He has more than20yedrs of experiencein refining precious metals and plating inthe electronics industry Mr Catchmarkholds a BS degree in chemistry andmathematics from Albright CollegeReadino PA and studied enaineerino atLafayette C ollege, Easton H gis a past president of &e A E S ~ O S

secretary of ASTM Subcommittee B 08 09 on precious metalsAn n o l o r R r D n r h r r i r r o n t mom h o r n f th o I 3 n r D r t o r R r Q n c h gnrlI > I t3b)Ud Y # I ", I , " L,", I _ I I , I I ,L,, l l U L , , " I , I I + L " , #bL'd,blY l < O _ # 8 U I "

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,71ilate Recovery Alternatives-Once the segregated., a ,Ia (1 outright sale to a precious-metal dealer; (2)

" followed by in-house refining or shipmentI -,;finer, and (3) blending the segregated scrap with a similar,q;,,31 to achieve maximum return.,'Aqa,yze the Sample-An appropriate sample should bee3 to estimate the amount of precious metal contained inise scrap varies widely in content, sampling

ureS a i s p will differ. For instance, sweeps, powder and. ,oJ ld be ground to a fine powder, screened and blendedto.-: homogeneity before sampling. Also, metallics must be;. .?! to homogeneity in special furnaces prior to assaying.

- . !hlS molten material, a dip sample may be taken or the,,a1 may be poured into bars, from which a drilled portion. : I

assayed. For liquids such as electroplating and stripping: -.. n~,horough agitation and extraction of a representative. (with a sampling tube) is required.'",e/ecting Assay Method-The assay method often is ahtforward economics dictated by the number ofthe time spent on each test, and the cost of=+ aqenta m materials. The electrolytic method (metal plated_ - a platinum cathode and weighed) commonly isemployed...p'ating baths, the gravimetric method for standard gold com-2: and the spectrographic, atomic absorption or X-rayI -s,escence for high-purity materials. In any case, it is of utmost:,Dqance that the sample is representative of the scrap lot. The-?':.:the sample, the more uniform the material, the higher the-2 content, the more valid the assay will be. An accurate assay:-e made on a spurious sample, but, at the same time, an-.atid quantitative measure of the metal for the entire lot of

5' ,aged Iraterial also may result.Proreaure for Gold-Gold-plated parts are likely to vary in:-:33sit thickness from lot to lot. Ifat all possible, these rejectedc a s should be segregated by type and lot; in essence, indis-:'Tinate mixing of scrap parts should be avoided. Valid assays: a? be obtained from filtered gold solutions that have beenroughly stirred and analyzed by taking a thief sample with a3 3ss tube from the surface tothe depth of the solution. However,!reme Care must be taken when sampling stripping solutionssome proprietary gold formulations. In these cases, itmay beo dilute a solution to redissolve precipitated crystals.!hermre, solutions should not be stored inmetal containersgold immersion deposits and/or crystals may form and

MiscellaneousAssays-Carbon, wet sludge, carbon tubes,ange resin, and filter pads are difficult to sample; hence,assay is often invalid. The best bet, however, s to sample andwhen the gold is still insolution. Ifnot, sludge and precipi-should be dried, ground, screened, thoroughly mixed andconed and quartered. This procedure provides a fairly good,Selecting a Refiner-The selection of a prime refiner or acan mean money gained or lost, If both are equally

I the finisher probably will do better to deal directly*cI t h f - Wme refiner because the middleman's charge will beimportance of Representation-Representation is the wit-of the buyer's operation in the evaluation of the seller'sis conducted in behalf of the seller. Representationso verifies the procedures and events that will occur in theJ 'inln9 operation. This agreement is then reportedtothe shipper

- ' his reassurance regarding the refining process Mostto know if their material was received intact,iflcally with respect toweight, and anexplanation if there is a!screP ~Qcy.ome shippers will require a report of observationsriiiring processing, sampling or melting, whereas othersrequest the presence of a representative.' immo ns of Reps-Representation can establish goodand confidence between the refiner and the seller. TheOf the representative are to inspect the shipment, witnessweighings of containers or net weights of bullion, anda h d - - : - : - - - - L - A L - - ,:-- ---_-- mq+n r ; o l

because most operating procedures are generalized and

0 r k c s have been accumulated, three options are available tor -

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not customized for each lot,the role of the representative may belimited in the determination of sampling procedures.Onthe otherhand, n the preparationof future shipments, the representative'sobservations and recommendations can be extremely helpfultoshipper and refiner.!At the Refinery-If the scrap material is sealed when itarrives at the refinery, the seal number is verified against theshipping order. After verification, the seal is broken, the containeropened, and the contents inspected to verify that they corre-spond to the shipper's description. The shipment is weighed asreceived and weighed again after the containers have beenemptied. The result, of course, is the net weight of the refiningshipment.Making the Settlement-During this exercise, the represent-ative and the refiner place their respective seals on a reserveportion and the umpire's portion of the sample. E ach forwards hisown portion to his respective laboratory for analysis. When theanalyses are complete, the parties usually exchange them bymail and a settlement is made. But, if the analyses are beyondthe contractual splitting limit, he umpire's portion of the sample isforwarded to the umpire's laboratory.J udging the Value-The value of the refining lot is deter-mined by fire assaying, wet chemical analysis, electrolyticmeans or a combination of all three. With classic fire assaying,actually a miniature refining process, the material first is melted na special furnace. The basis metal is forced into a slag and theprecious metal is collected with lead at the bottom of a crucible.The lead is then oxidized and removed, leaving a bead contain-ing only precious metals-a precise sample of the entire lot.Thisis then weighed as a basis for calculating the amount of preciousmetal inthe refining shipment. In all cases, multiple samples arecross-checked for accuracyRefining Techniques-At the refinery, there are a number ofways to refine a precious metal. Electrolytic purification is themost widely employed for gold and silver, but pyrometallurgy (firetechniques) and hydrometallurgy (chemical separation) are alsoused. P latinum metals are purified by chemical precipitation anddissolution. Because they are usually obtained as a sponge orpowder, platinum-group metals are often melted into ingots.Getting the Return-In the final settlement, the shipperreceives a return in the form he specifies: (1) a check from therefiner, who would be the purchaser of the material; (2) a con-signment account for the value of the reclaimed material, minusrefining charges; (3) delivery of reconstituted scrap material in!he form of bars, strip, grain, wire, shee?. ngots nr salts: or (4)shipment elsewhere per the buyer's instructions.Additional Information-The following publications arerecommended for those who have a continued interest in con-serving precious metals.1. Recycling Precious Metals, National Assoc. of R ecyclingInd., Inc., 330 Madison Ave., New York, NY 10017 .2. Sampling and Assaying of Precious Metals, InternationalPrecious Metals Institute, 333 J ay S t., Brooklyn, NY 112013. C. M.Hoke, R efining Precious Metal Wastes, MetallurgicalPublishing Co., 123 William St., New York, NY.4. "Precious Metals," chapter in Operations in the NonferrousScrap Metal lndustry Today, National Assoc. of Recycling Ind.,New York, NY.

About the Author Andrew Catchmark is senior prolect engi-neei for the Advanced Automated Sys-tems Division of AMP lnc , Mail Sralion140-41, Box 3608, Harrisburg, PA 17105He has more than 20years of experiencein refining precious metals and plating inthe electronics industry Mr Catchmarkholds a BS degree in chemistry andmathematics from Albright College,Reading, PA, and stud/ed engineering atLafayette College,Easton He is a past presidentof the AES LosA,nge!es Era,nCh a current ,memberof he LancFis?erBranchandsecretary of ASTM Subcommittee 50809 on precious metals

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Guidelines for Recycling Precious Metals