extracting metals from scrap 8

8/14/2019 Extracting Metals From Scrap 8

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A series presenting industry-related science practicals for schools

8. Extracting Metals from Scrap

Devised byBill Harrison and David Wright, Pelsall School, Walsall

Haydn Poulsom, Shelfield School, Walsallin association with

Elkington Copper Refiners Ltd., Walsall, West Midlands

Published forThe Standing Conference on Schools' Science and Technology

byThe Association for Science Education,College Lane, Hatfield, Herts. AL10 9AA

SCSST1985 ISBN 0 86357 026 7

ice LearningCentres

N12004


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ForewordThe need to provide a framework which relates to everyday life, for science taught in schools, isnow widely accepted. Much existing science practical work relates only to an academic syllabus,expects a single 'right' answer and provides very limited opportunity for experimental design,problem-solving and group working.

The booklets in this series are based on the work of experienced science teachers who, during thesummer of 1984, were linked with industrial companies as part of a project initiated by SCSST incollaboration with ASE. Their brief was to devise experiments drawn from industrial processes,which illustrate scientific concepts and show how they are applied in industry. This developmentwas made possible by a generous donation from Lloyd's Register of Shipping.

Experiments described in the booklets aim to replace, within the existing curricula, some of thepresent school practical work. They allow opportunity for pupils to conduct challenginginvestigations which enhance their understanding, and there is a problem-solving and open-ended element.

The contribution of the teachers involved and the co-operation of the industrial firms who helpedwith the project is gratefully acknowledged. It is especially pleasing that medium-sized companiesas well as major international groups were involved. The project has shown once again the valueof effective links between schools and industry.

Sir Geoffrey Alien, FRSChairman

SCSST

Extracting Metals from Scrap ...Experimenting with Industry '


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The SeriesFurther Experimenting with Industry titles will be published during 1985, the complete seriesbeing detailed below. The teacher/industry partnerships which developed this material werewidely distributed throughout England and in Wales. The industrial participants ranged frommulti-national concerns well-known for their support of educational initiatives to companies inhighly specialized areas of technology with little experience of such activities.

Title

1 . Electrical TestingBob Cheyne, St. John's School, Marlborough

2. Optical Fibres in School PhysicsStephen Rutherford, Pimlico School, London

3. Industrial Use of Micro-organismsSteve Bowden, Whitchurch High School, Cardiff

4. Sugar ChallengeCharles Dalleywater, Ramsey Ailwyn CommunitySchool, Ramsey

5 . Chemicals for AgricultureLyn Bossons, Biddick School, Washington

6. Brake Fluid and School ScienceJames Dawber, Sharpies School, Bolton

7. Safety in Gas AppliancesPeter Hancock, Dame Alice Owen's School,Potters Bar

8. Extracting Metals from ScrapBill Harrison, Pelsall School, Walsall

9. Properties of MetalsHilary Laidler, Simon Balle School, Hertford

10. Electronics of Control SystemsVirginia Lavender, Collingwood School, Camberley

11. Chemistry of EstersDon Linnell, The Bramhall High School, Bramhall

12. Physics of Fluid FlowLinda Scott, Pate's Grammar School for Girls,Cheltenham

13. PlantTissue CultureTony Storr, Sharnbrook Upper School, Sharnbrook

Company

Square D Ltd., Swindon, Wiltshire

GEC Hirst Research Centre, Wembley, London

Nipa Laboratories Ltd., Pontypridd, Mid-Glamorgan

British Sugar pic, Peterborough, Cambridgeshire

ICI Agricultural Division, Billingham, Cleveland

Shell Chemicals, Carrington, Manchester

British Gas Eastern Region, Potters Bar, Hertfordshire

Elkington Copper Refiners, Walsall, West Midlands

British Aerospace, Stevenage, Hertfordshire

Marconi Command & Control Systems, Camberley,Surrey

Ciba-Geigy Industrial Chemical Division, Manchester

Dowty Services Ltd., Cheltenham, Gloucestershire

Unilever pic, Bedford

Elkington Copper Refiners LimitedECR Ltd. is a secondary copper refining company which was first established, in Birmingham, in1807. Its origins go back to Faraday's work on electroplating. ECR is now located near Walsall inthe West Midlands and recently became part of the IMI Group.

The company, which employs about 240 people, buys in some 60-80 0 0 0 tonnes/year oflow-grade metal scrap and recovers copper, silver and other metals.

The process developed by ECR is highly efficient in recovering a large percentage of by-productmaterials. For this reason, ECR's technology and experience is in demand worldwide and thecompany, as well as supplying equipment and plant, accepts consultancy contracts coveringcomplete feasibility studies, consultancy on existing installations and the training of personnel.

IVExtracting Metals from ScrapExperimenting with Industry


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ContentsTeachers' _

1 . Industrial background 1

2. Educational scope 6

3. Notes on experiments 6

Experiment 1: Assaying a gunmetal alloy scrap 6for copper content

Experiment 2 : Analysis of mixed furnace oxide 7

Experiments: Analysis of lead/tin alloy 8

Experiment 4: Electrolytic purification of copper 8

Experiments: Laboratory model of the commercial 9purification of copper

Experiments: Simulation of copper stripping and 10nickel recovery

Experiment?: Analysis of the acidified copper(ll) 1 1sulphate electrolyte

4. Appendix: Relationships to 16+chemistry syllabus 12

Students' worksheets

Experiment 1: Determining the percentage of copper in 13gunmetal alloy scrap

Experiment 2 : Analysis of mixed furnace oxide 16

Experiments: Analysis of lead/tin alloy 20

Experiment 4: Electrolytic purification of copper 23

Experiments: Laboratory model of the commercial 25purification of copper

Experiment6: Simulation of copper stripping and 2 7nickel recovery

Experiment?: Analysis of the acidified copper(ll) 30sulphate electrolyte

The material which follows may be reproduced without infringing copyright provided reproduction is for pupil-use only.The permission of the publishers must be obtained before reproducing the material for any other purpose.

Information in this publication is accurate to the best of the knowledge of the publishers and is given in good faith.However, no warranty is given or is to be implied with respect to the accuracy of such information. The publisherscannot accept liability for any accident or injury arising out of the use or application of the information and experiments.

Extracting Metals from ScrapExperimenting with Industry V


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Teachers' guide

ECR is a secondary copper refinery, that is only scrap orsecondary feedstock is used. The feedstock for the refineryranges from low grade residues, including certain catalysts andindustrial chemical wastes, generally with a lower copper limitof 5%, to clean copper turnings and other high grade scrap of96% plus copper content. In between these two extremes a re

various refining materials mixed brasses, gunmetal scrap,radiators, irony copper, burnt wire, brazier materials, etc. Theprocess used is shown in Figure 6 (p.5).

Low grade materials are generally screened, with the screeningsgoing directly to the blast furnace stockyard and the finematerials to the briquetting press. Here, the material is mixedwith lime and water and pressed into briquettes about the sizeof a house brick.

Figure

Furnace charge

The blast furnace charge consists of briquettes, low grade scrap,slags, residues, irony copper, etc., the object being to achieve an

overall copper content of approximately 35%. Coke is alsoadded with the charge and air is introduced via the tuyeres.

The furnace is operated on continuous tap and the moltencopper and slag leaves the bottom of the furnace and flows intoa holding furnace where the slag and metal are separated. Thefume from the top of the furnace is passed through a filteringsystem which separates out the heavy particles, eventuallyallowing low grade zinc oxide to be recovered. The heavyparticle fraction containing 1 5 % - 0% copper is recycled to theblast furnace.

The slag from the holding furnace is granulatedand

sold as shotblast material. After the blast furnace, the copper (black copper)contains about 80% copper, along with the bulk of the tin, lead,nickel and precious metals which have been charged to the blastfurnace.

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Figure 2The blast furnace

The black copper is then transferred, still molten, to theconverter. Coke and tin-bearing materials, together with a smallamount of irony material, a re added to the charge and themolten contents are air-blown via a row of tuyeres. During thisprocess the bulk of the tin, lead and zinc is fumed off andcollected in a bag house as converter oxide a mixture of tin,lead and zinc oxides. The slags a re removed and recycled to theblast furnace. The converter oxides are further processed in thetin/lead plant to produce very high quality tin/lead ingots soldfor solder manufacture and a higher grade zinc oxide.



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Figure3

Converter furnace

The resulting copper from the converter is termed rough copper(96% Cu) and is transferred to the anode furnace. Here, highgrade scrap is added and a fire refining operation carried outbefore the metal is cast as anodes (98.5% Cu). Again, the slagformed is recycled to the blast furnace.

Figure 4

Anode furnace



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FigureB

Electrolytic tank house

The anodes are then transferred to the tank house forelectrolytic refining to produce high purity cathodes. Currently,ECR operates on a 28-day cycle, that is each anode is used toproduce two cathodes at 14-day intervals. After the 28-day cycle,the remainder of the anodes are returned to the anode furnace.The solution circulating in the electrolytic tanks has to beconditioned to control the copper and nickel contents and it isduring this treatment that the crude nickel sulphate is obtained.After each 28-day cycle, the slimes which have accumulated inthe vats are pumped off and dried and this material whichcontains the precious metals gold, silver, platinum andpalladium is sold for recovery.

ECR believes that under normal economic circumstances theoptimum size for a secondary copper refinery is about 25 0 0 0tonnes per year cathode production. Such a refinery allowsoptimum manning and staffing and economic use of equipmentand does not create large logistic problems in respect offeedstock supplies.

Ideally, such a plant would require approximately 100000tonnes of material, averaging 25% copper content, per year. Apractical input of copper scrap to produce 2 5 0 0 0 tonnes peryear of electrolytic cathode would also provide the followingby-products:

Tin/lead ingotAnode slimeLow grade zinc oxideHigh grade zinc oxideImpure nickel sulphateGranulated slag

35% - 40% tin2.5% - 3.5% silver

5 0 % - 60% zinc75% - 80% zinc22% - 23% nickel

(tonne/year)2 3 0 - 803 0 0 - 5 01300- 1 7 0 0400 - 5 02 8 0 - 4012000- 15000



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Ingots

Alloys

IFurnace

CathodeWire bars

IngotsI

Converter slag

Anode furnace slag

Treatment of secondary copper and its alloysFlow sheet

ResiduesContaminated

alloys

Anode scrap

Figure

Copperscrap

Furnace

Srrii3lter

Wire barsIngots

By-products

Final slag

Low grade scrapSlags

ResiduesIrony copper

Coke

Blast furnace Low grade ZnO fume

Granulated slag

Black copper (80% Cu)

Scrap (2-6% Sn) -


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2 . E

Special noteAlthough the pyrometallurgical processes carried out at ECR areof primary importance in the overall process, practical work inthis area is not included in this series of experiments. Theseprocedures are much more complex than, for example, thereduction of iron ore in the blast furnace and, in addition, thehigh temperatures required are difficult to produce in the schoollaboratory without costly furnace equipment.

It should be noted that much of the assaying work at ECRinvolves the use of special instrumentation, particularly theatomic absorption spectrophotometer, and the use of chemicalswhich are difficult to handle in the school laboratory. For thisreason, some of the experiments described here tend to parallelthe ECR processes rather than to reproduce them.

The experiments which follow are aimed primarily a t the 14-16age group, i.e. pupils studying for CSE/O-level/16+ chemistrycourses. However, they could also be used in CEE, Science inSociety or A-level courses but some modification would beheeded in the latter case .

The practical work falls more or less into three categories:a) assaying/quality control of raw materials and products Experiments 1, 2 and 3;b) electrolysis processes Experiments 4, 5 and 6 ;c) process control/monitoring Experiment 7.

3. Notes on experimentsExperiment Assaying a gunmetal alloy scrap for copper content

Apparatus and chemicalsGunmetal alloy5 0 % nitric acid (by volume),

(10 cm 3/group)Sodium carbonate (solid)Beaker 100 cm 3 (2)FilterfunnelFilter pump & Buckner flask (if

available)Ashless filter paper (preferably

1 1 cm diameter, 542 Whatmangrade)

Evaporating basinMeasuring cylinder 10 cm 3Tripod and gauzeBunsen burnerBench matGogglesUse of top-pan balance (reading

to second place)Access to fume cupboard and

drying oven

Background notesIn this experiment students are asked to determine thepercentage of copper in a sample of gunmetal turnings. Such asample could be delivered to ECR from a local engineeringcompany as waste turnings from some machining process. Inorder to fix a price for the scrap it would be necessary for theanalysts to assay the material for copper content. With thisparticular sample they would also determine the tin content.Assaying is a vital part of the work of the laboratory and smallerrors could cost the company large amounts of money.

The gunmetal alloy used in this experiment containsapproximately 87% Cu; 10% Sn; 1.5% Zn; 0 .7% Pb; 0.3% Niand small traces of other elements. The alloy was supplied byBureau of Analysed Samples Ltd., Newham Hall, Newby,Middlesbrough, Cleveland TS8 9EA; catalogue no. BCS-CRM207/2; cost 1985) 10.50 per 100 g.

At ECR this sample of scrap would probably be dissolved in 5 0 %nitric acid plus a few cubic centimetres of 3 0 % hydrofluoric acidto eliminate the tin. The copper would then be determined byelectrolytic deposition using platinum electrodes. For safetyreasons in handling some of the above materials and becausethere are a number of electrolysis experiments in this series, asimple yet rough approximate method for use in the schoollaboratory was developed.



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Points of guidanceIn this experiment it is assumed that the gunmetal sample isprimarily 90% Cu, 10% Sn. If students a re aware of otherelements present, they will need to accept these as sources oferror. The advantage of choosing an alloy with tin is that the tinis precipitated out as Sn0 2 xH 20 in nitric acid, leaving thecopper in solution. The idea then is to precipitate the copper ascopper carbonate and then decompose to the oxide.

It is suggested that the first part of the experiment to take thealloy into solution is carried out in a fume cupboard by theteacher. Class samples can be placed on a hot plate. A simplehot plate can be made from a piece of caste iron supportedabove two or three Bunsen burners.

When filtering out the SnO 2 xH 20 it may be necessary to filtertwice in order to obtain a clear solution. Occasionally, afterfiltering out copper carbonate, the filtrate has a blue/green tinge.This may be due to the small amount of nickel present in thealloy. The copper carbonate should be washed thoroughly toremove all the solid sodium carbonate from it. If desired andparticularly if extending the experiment to a sixth form activity it would also be possible to determine the tin content byburning down to Sn0 2 as for the copper determination.

In a normal practical session it should be possible to reach thestage where the CuC0 3 has been filtered out. This can be driedin an oven or left to dry naturally until the next lesson, when itcan be decomposed to the oxide. Students may note, alongsidethe black oxide, a feathery copper deposit. This is probably dueto reduction of the oxide by the carbon in the filter paper.

-~ - y^Af^:^f*^.oiv ; ;^^,|p^?.i

pparatus and chemicals50% nitric acid (by volume),

(20 cm 3/group) Mixed oxides sample (40% ZnO;; 30% PbO; 30% Sn0 2 by mass):: (1 g/group); Sodium carbonate (powdered) (if

Part II is attempted); Beaker 100 cm 3 (3)ipilterfunnel (2){Ashless filter paper (preferably; 1 1 cm diameter, 542 Whatman; grade)Evaporating basin (3)KMeasuring cylinder 2 5 cm 3f Tripod

Bunsen burner: Bench matGogglesUse of top-pan balance (to second

place)Access to fume cupboard and

drying oven

Analysis of mixed furnace oxides

Background notesIn this experiment students are asked to determine thepercentage of zinc oxide, lead(ll) oxide and tin (IV) oxide in amixture. Such a mixture is produced by ECR from theirconverter furnace. A typical analysis is 30%-40% ZnO; 2%-25%PbO; 5%-25% Sn0 2 ; 2%-5% CuO. A suitable mixture for the

students' experiment is 40% ZnO; 30% PbO; 30% Sn0 2 bymass. A 1 g sample of this mixture should produce 0.3 g Sn0 2;0 .39 g PbSO 4 (0 .36 g PbCI2); 0.4 g ZnO.

At ECR the routine analysis uses atomic adsorption, but foraccurate work the lead and zinc a re determined using EDTA,with Xyanol Orange as an indicator.

Points of guidanceIt is suggested that the dissolution of the oxides is carried out ina fume cupboard by the teacher. Goggles should be worn. Fordetails of a simple hot plate, see Experiment 1 (above). Keeping

the filter papers in a desiccator for a few days should minimizeany inaccuracy caused by loss of moisture from the filter papers.

If Part I I is used to determine the percentage of zinc oxide,ashless filter papers must be used.



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pparatus and chemicalsCopper cathode(copper sheet

1 cm wide and of suitable: length)

Impure copper anode (suggestbrass, copper-nickel [nickelsilver], old pennies or even

: copper sheet);Beaker (suggest 100 cm 3)Power supply (suggest 6 V)Connecting wires, ammeter and

rheostat as necessaryBeaker of water (for rinsing

electrodes)Acidified copper(ll) sulphate

solution (approx 1.5M H2S0 4,0 .75M CuS0 4)

Use of top-pan balance (to secondplace)

Power sourceAmmeter

Copperwiresupports

Figure 7

Points of guidanceThese are listed under Experiment 5 (p.10). ;

To prevent the electrodes touching the beaker, the top 1 cmcould be bent over and suspended from stripped household ringmain cable bus bars (see Figure 7).

Experiment 5 Laboratory model of the commercial purification of copperBackground notesCommercially, the tank house contains 30 anodes and 31cathodes per cell and 2 0 cells to a tank. The cathodes a re thinpure copper sheets and the anodes contain about 98% copper,with up to 1 % nickel as well as lead, tin, zinc, antimony, arsenicwith small amounts of silver, gold, platinum and palladium.

During electrolysis the nickel goes into solution, while the

precious metals form solid compounds which a re known as theanode slime. The nickel is recovered by stripping the copperfrom the solution (see Experiment 6), while the anode slime issold to precious metal refiners. Any lead is precipitated in theslimes as lead sulphate.



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Impure copperanodes

Copper coveredwood

Connectedto negativeterminal Connected

to positiveterminal

Copper wirebus bars

Plastic

sandwichbox

Pure coppercathodes

Figure 8

Acidifiedcopper(ll) sulphateelectrolyte

pparatus and chemicalsClear, rigid plastic container(suggest lunch box)Wood strips, cut to slot on long

sides of container (2 )Thin copper sheet for contacts

(see Figure 8 for arrangement)Insulation tape (see Figure 8)Pure copper cathodes (suggest

copper sheet of suitable size, topbent over to act as a hook) j

Impure copper anodes (same size jas cathodes, preferably copper- 3nickel [nickel silver]) if

Thick copper wire bus bars :1(suggest household ring main fcable with insulation left on one |end see Figure 8) |

Power pack with suitable ffammeter and connecting wires J

Acidified copper(ll) sulphate |solution (approx. 1.5M H2S0 4, I0 .75M CuS0 4 ) ;j

Points of guidanceThe apparatus will need to run continuously for about a week a t0.1-0.2 A. This will enable students to see a noticeable thinningof the anode, a regular deposit of copper on the cathode and anappreciable colour change caused by nickel ions in the solution.

Make sure that the bus bars have good electrical continuity anduse the lid of the box to reduce evaporation.

Experiment 6 Simulation of copper stripping and nickel recoveryBackground notesAs the impure anodes contain nickel, the electrolyte becomescontaminated with nickel ions after several days. The electrolyteis pumped to a second, smaller tank house, where the copperions a re stripped from the electrolyte using lead anodes andpure copper cathodes. The copper content is regularlymonitored (see Experiment 7).

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pparatus and chemicals:iCopper cathode (copper sheet 1 cm wide and of suitable

length)Lead anode (lead sheet, as above,

but at least 1 mm thick)Beaker (suggest 100cm 3)

;Larger beaker (suggest 150cm 3)Power supply (to provide current

in the range 0.75-1.0 A)Connecting wires, ammeter and

rheostat as necessaryBeaker of water (for rinsing

electrodes)Propanone (for cleaning

electrodes)Copper(ll) sulphate-5-water

crystals

Nickel(ll) sulphate-6-watercrystals ;M sulphuric acidUse of top-pan balance (to second

place)

Experiment 7^ pparatus and chemicals

Burette (2 or 3) (see note)Beaker (suggest 100cm 3)FunnelConical flask (suggest 2 50 cm 3)Wash bottle of distilled water0.2M sodium hydroxide solution

(exactly)

0.1M sodium thiosulphatesolution (exactly)

Solid potassium iodideMethyl red indicator (water

soluble)Starch indicatorAcidified copper(ll) sulphate

solution (approx. 0.15M H2SO 4,0 .075M CuS0 4)

Dilute ethanoic acid with dropper

When most of the copper has been removed, the remainingsolution is largely nickel(ll) sulphate. This is then evaporatedand crude nickel(ll) sulphate crystallizes out and is then sold.

Points of guidanceMost of the copper should be removed if a current of about 0.8 Aruns for 45 minutes. A spongey deposit forms on the cathodeand, if treated carefully, very little, if any, falls off. Gassing

occurs initially, but soon stops.

During the experiment, the electrolyte changes colour from ablue-green to a lime green, reinforcing the fact that the copper isbeing removed.

The nickel(ll) sulphate solution contains sulphuric acid, which isconcentrated on evaporation to 4-5M. Students should bewarned of the dangers of this.

The crystals which are formed a re a slightly different colourfrom the original nickel(ll) sulphate. This is probably due to theacid conditions.

A lid placed over the cell is used to reduce acid spray.

Suggested additional demonstrationIf copper-nickel anodes a re used in Experiment 5 , these can beremoved a t the end of that experiment and replaced by onesmade of lead sheet, allowing stripping to occur in situ.

If copper-nickel anodes are not used, a previously madeelectrolyte containing nickel ions can be substituted instead.

The colour change can be demonstrated quickly (without goodadhesion of copper) if a higher current is used.

nalysis of the acidified copper(il) sulphate electrolyteBackground notesAt regular intervals it is necessary to test the tank-houseelectrolyte for acidity and copper content to maintain theelectrical conductivity and to prevent gassing. At least once aday the titration outlined in this experiment takes place, but onthe full-strength electrolyte.

Note: The experiment is quicker with two burettes, but it may benecessary to use one cleaned between titrations. It issuggested that, in addition, a teacher's burette is used todispense the electrolyte; alternatively, the students could use apipette, with a pipette filler.

Points of guidanceThe end point with the methyl red indicator is fairlystraightforward (pink to orange) but the end point in the copperestimation is more difficult to see, being partly masked by themethyl red coloration and the iodine suspension. It may beworthwhile to demonstrate the copper estimation before thestudents attempt it .

The copper estimation is not part of the 16+ syllabus, but itcontains some interesting chemistry from which more-ablestudents will benefit.


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4. AppendixRelationships to 16+chemistry syllabus

ExperimentAction of acids on metals/alloys; action of acids on carbonates;neutralization; precipitation of insoluble carbonates; thermaldecomposition of carbonates; calculations involving the mole.

Experiment 2Action of acids on metal oxides; precipitation of insoluble salts(PbSO 4 , ZnC0 3); thermal decomposition of carbonates;calculations involving the mole.

Experiment 3Action of acids on metals/alloys; formation of insoluble salts;calculations involving the mole.

Experiments 4 5General electrolysis; purification of copper.

Experiment 6General electrolysis; selective deposition; choice of electrodes(inert anode); crystallization; calculations involving the mole.

Experiment 7Neutralization; volumetric theory and practice; calculations; useof indicators; estimation of copper (probably A-level);calculations involving the mole; formation of insoluble salts.

These relationships are summarized in the table which follows.

Chemistry concepts covered

Concept

Action of acids on:metals/alloysmetal oxidescarbonates

Neutralization

Precipitation of salts

Thermal decomposition of:hydratescarbonates

Calculations involving the mole

General electrolysis:purification of copperselective depositionchoice of electrodes (inert anode)

Crystallization

Volumetric theory and practice

Use of indicators

Copper estimation (l2/thiosulphate)

Experiment

1

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2

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3

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Students' worksheets

Experiment

The following experiments were developed by a group ofteachers working with engineers and scientists a t ElkingtonCopper Refiners Ltd., in Walsall. The experiments demonstratesome of the industrial practices used in a large secondaryrefining plant.

It is hoped that from this practical work you will understandsomething of the ways in which the science you learn a t schoolis applied to the solution of real industrial problems.

Determining the percentage of copper in a sample of

The sample of gunmetal alloy scrap contains mostly copper, buthas a significant amount of tin.

Take a clean, dry 100 cm 3 beaker and label it. Accurately weigh itand then carefully add about 0.5 g of the gunmetal sample.Weigh the beaker and contents.

Mass of beaker + sample

Mass of beaker

Mass of sample

9

g

Take your beaker, with sample, to the fume cupboard, whereyour teacher will add 10 cm 3 of 50% concentrated nitric acid.

Q. What did you see occurring in the beaker?

Q. Why use a fume cupboard?

When the reaction slows, your teacher will cover the beaker witha watch glass and bring it to the boil on a hot plate.

Q. What do you now notice about the solution?

Continue the boiling for a few minutes until all of the alloy hasdissolved and no more gas is evolved. Your teacher will thenremove the beaker from the hot plate and allow it to cool. Makesure you a re wearing goggles, then carefully take the coolbeaker to your bench. Carefully add distilled water to yoursample up to the 2 5 cm 3 on the beaker. Gently bring thesolution to the boil and continue for no more than a minute.Allow it to cool.

Q . Look carefully a t your solution and describe what you see .


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Q . D o you have any idea what this solid could be ?

Filter the solution into a 100 cm 3 beaker, making sure to washout any solid left in the beaker, and also to wash the residue in

the filter paper. Use distilled water from a wash bottle.

Q . Why is it necessary to wash the residue?

Q . Where is the copper now?

Q . Where is the tin now?

Put the residue in the filter paper to one side in case yourteacher wants you to work on it later.

Take the filtrate and treat it in the following way. Make sure thatyou have a t least 50 cm 3 of filtrate in your beaker; if not, make itup to that amount with distilled water. Now, carefully add aspatula load at a time of solid sodium carbonate to yoursolution, and stir.

Q . Why is effervescence occurring?

Carry on adding the sodium carbonate until no furthereffervescence occurs and a thick green gelatinous precipitate isformed.

Q . What is this precipitate?

Q . Write down a word and symbol equation for the reaction.

Filter off the precipitate using ashless filter paper and a filterpump, if available. This will be quicker than the ordinarymethod. Wash the residue thoroughly with distilled water inorder to wash out any undissolved sodium carbonate. Makesure you get as much as possible of the solid out of the beakerotherwise it will cause an error in your calculations. If yourfiltrate comes through as a blue solution, you have notprecipitated all of the copper. You must add a little more sodiumcarbonate and filter and wash again.



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You must now dry the residue. This can be done either byplacing the residue in an oven or simply by leaving it to dry outfor the next lesson.

You a re now ready to decompose your copper compound byheating it. Weigh an evaporating basin. Place your sample still in the filter paper in the basin and put the basin, withsample, onto a tripod and gauze and heat from below. After a

little while, set the paper alight and allow it to burn away to ash.Then heat strongly from below for a few minutes until theresidue is completely black. Heat again from above to burnaway any remaining filter paper and to ensure complete thermaldecomposition. Allow to cool, and then weigh.

Mass of evaporating basin + residue = g

Mass of evaporating basin = g

Mass of residue = q

Q. What is the black compound produced on heating?

Q . Write a word and symbol equation for the thermaldecomposition of your copper compound.

Calculation

1 mole of CuO contains ............... mole of Cu atoms

............... g of CuO contains ............... g of Cu atoms

/. ............... g of residue contains ............... g of Cu

. . ......x...... g of original gunmetal contains ......y...... g of Cu

. . % of Cu in gunmetal alloy = x/y x 1 0 0 % = ............... % Cu

Extracting Metals from Scrap 15Experimenting with Industry


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Percentage of tin(IV) oxide in the sample

= mass of tin oxide/mass of sample x 1 0 0 %

= .............../............... x 1 0 0 %

= ............... % of tin(IV) oxide

Add dilute sulphuric acid to the filtrate to precipitate the lead aswhite lead sulphate.

Q. Write down the word equation and then the chemicalequation for the formation of the precipitate.

Filter off the precipitate into a weighed filter paper, carefullywashing all the white solid out of the beaker. Keep the filtrate ifyour teacher has told you to do Part I I of this worksheet.

Weigh an evaporating dish and add the filter paper plus theprecipitate and place it in a drying oven.

Mass of filter paper = g

Mass of evaporating dish = g

Mass of evaporating dish + filter paper = g

Weigh the evaporating dish, plus dry contents.

Mass of dish + filter paper + lead sulphate = g

Mass of dish + filter paper - g

Mass of lead sulphate = g

No. of moles of lead sulphate (PbS0 4 )

= mass of lead sulphate/mass of 1 mole of lead sulphate

= .............../...............

= ............... moles of lead sulphate

1 mole of lead sulphate (PbSO 4 ) is formed from 1 mole of lead(ll)oxide

.'. no. of moles of lead(ll) oxide is ............... mole

. . mass of lead(ll) oxide

= no. of moles x mass of 1 mole

= ............... x ............... g

= ............... g of lead(ll) oxide



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Percentage of lead(ll) oxide

mass of lead(ll) oxide/mass of sample x 100= ............... / ............... x 100

= ............... % of lead(ll) oxide

If Part I I is not to be carried out, then work out the percentage ofzinc oxide in the mixture as follows:

Percentage of zinc oxide

- 100 - % of tin(IV) oxide + % of lead(ll) oxide)

= 100 - ............... + ...............)

= ............... % of zinc oxide

.* . composition of the mixture is ....... % ZnO; ....... % PbO;

....... % SnO 2

Part IIAdd powdered sodium carbonate to the filtrate, a little at a time,until there is no more effervescence. Continue to add thepowder until no more zinc carbonate is precipitated.

Q . Write down the word equations and the chemical equationsfor the two reactions.

Filter off the white precipitate into an ashless filter paper,making sure that all the white powder is washed into the filterpaper. Wash the precipitate twice to dissolve out any sodiumcarbonate. Weigh an evaporating dish and place the filter paperplus contents in the dish in a drying oven. Burn off the filterpaper, when dry, and heat strongly to decompose the zinccarbonate into zinc oxide.

Q . Write down the word equation and chemical equation forthe reaction.

Weigh the cold dish and zinc oxide.

Mass of dish + zinc oxide = g

Mass of dish g

Mass of zinc oxide = q



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Percentage of zinc oxide in the sample

mass of zinc oxide/mass of sample x 1 0 0 %

- ............../ ............... x 1 0 0 %

= ............... % zinc oxide

The analysis of the mixed oxide is ....... % ZnO; ....... % PbO;....... % Sn0 2

Q . Does this add up to 100%?



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Experiment 3 Analysis of lead/tin alloyPartWeigh a clean, dry 100 cm 3 beaker. Add about 1 g of the alloyfilings and weigh the beaker and contents.

Mass of beaker + alloy filings = g

Mass of beaker = 9

Mass of alloy filings = g

Take your beaker to the fume cupboard, where your teacher willadd 2 0 cm 3 of 50% nitric acid. When the reaction stops, thebeaker is covered with a watch glass and boiled gently for twominutes (still in the fume cupboard).

Q . Why is the fume cupboard needed?

The white precipitate is hydrated tin(IV) oxide.

Q . Why was the watch glass used?

Note: If Part I I of this experiment is to be carried out, an ashlessfilter paper must be used.) Filter the cold solution through anashless filter paper. Carefully wash all the precipitate into thefilter paper. Place the filter paper in a weighed evaporating dishin a drying oven.

Dilute sulphuric acid is added to the filtrate to precipitate thelead as lead sulphate.

Q . Write down the word equation and then the chemical

equation for this reaction.

Filter off the white powder into a weighed filter paper andcarefully wash all the powder into the filter paper. Place the filterpaper in a weighed evaporating dish and dry in a drying oven.

Mass of filter paper = g


Mass of evaporating dish + filter paper



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When dry, reweigh the evaporating dish and contents.

Mass of evaporating dish + filter paper+ lead sulphate = g

Mass of evaporating dish + filter paper = g

Mass of lead sulphate = g

No. of moles of lead sulphate (PbSO 4 )

- mass of lead sulphate/mass of 1 mole of lead sulphate

= ............... / ...............

= ............... mole of lead sulphate

1 mole of lead produces 1 mole of lead sulphate

/. mole of lead weighs: (at. mass of lead x no. of moles) g= ............... x ............... g

= ............... g

. * . percentage of lead in the alloy

- mass of lead/mass of alloy filings x 1 0 0 %

- ............../..........,.... x 1 0 0 %

Percentage of lead is............... %

If Part II of this experiment is not being done, then percentage oftin

= (100 - percentage of lead) %

- 1 0 0 - ..............) %

Percentage of tin is ............... %

Part IITake the evaporating dish, plus filter paper containing hydratedtin(IV) oxide, and place it on a tripod and gauze. Burn off thefilter paper and reweigh.

Mass of evaporating dish + tin(IV) oxide = g


Mass of tin(IV) oxide = g

. * . no. of moles of tin(IV) oxide (Sn0 2)

mass of tin(IV) oxide/mass of 1 mole of tin(IV) oxide= .............. / ...............

= ............. mole of tin(IV) oxide



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1 mole of tin produces 1 mole of tin(IV) oxide

.*. mass of............... mole of tin weighs: (at. mass of tin x no. ofmoles) g

= (............... x ...........,...)g

Percentage of tin in the alloy

mass of tin/mass of alloy filings x 100

= .............../ ............... x 100

Percentage of tin is ............... %

Q . D o the two percentages add up to 100%? Explain youranswer.



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4 Electrolytic purification of copperPour the electrolyte into the beaker until it is about 1 cm fromthe top. Weigh the cathode and anode separately and recordtheir masses.

Mass of cathode

Mass of anode

g

g

Power sourceAmmeter

Copperwiresupports

Figure

Connect the cathode and anode to the ammeter and powersupply as shown in Figure 1. Make sure that the pure coppercathode is connected to the negative (black) terminal of thepower supply, and the impure copper anode is connected to thepositive (red) terminal.

Place the cathode and the anode into the electrolyte. They mustnot touch each other or the beaker. Switch on the power supplyso that the ammeter reads a current of 1 A.

Q. After about five minutes what change do you notice:

i) a t the anode;


23


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ii) at the cathode;

iii) in the electrolyte?

Q . After a further 3 0 minutes, look carefully a t the anode,cathode and electrolyte and explain any changes:

i) at the anode;

ii) a t the cathode;

iii) in the electrolyte.

Switch off the power supply and carefully remove the anodeand cathode. Wash them by dipping them into the beaker ofwater, dry them, then reweigh them.

Mass of cathode = g

Mass of anode = g

Q . Explain any change in the mass of the cathode.

Q . Explain any change in the mass of the anode.

At the beginning of the experiment, the anode was impurecopper.

Q . What has happened to the copper?

Q . What has happened to the impurities?



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Laboratory mode of the commercial purifecalion of cooper

Your teacher will demonstrate how copper is purifiedcommercially, using the apparatus shown in Figure 1.

Connectedto negativeterminal

Plasticsandwichbox

Figure

Impure, copperanodes

Copper coveredwood

Connectedto positiveterminal

Copper wirebus bars

Pure coppercathodes

Acidifiedcopper(ll) sulphateelectrolyte

Q . Why are so many electrodes used?

Q. How a re the cathodes connected to the power supply?

Q . At what voltage is the cell operating?

Q. Why is this voltage chosen?



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The apparatus will be left set up for a suitable length of time.

Q. How long was it left set up?

Q. Why was this time chosen?

Q. Describe the changes:

i) a t the cathode;

ii) at the anode;

iii) in the electrolyte.

Q . Explain these changes. . . ,

In the commercial process, the electrolyte is analysed regularlyfor acid and copper content.

Q . Why is this necessary? .



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Simulation of copper stripping and nickel recovery

Accurately weigh about 2.5 g of copper(ll) sulphate crystals.Record the mass and put the crystals in a small beaker.

Mass of copper(ll) sulphate = g

Weigh about 2.5 g of nickel(ll) sulphate crystals and add these tothe beaker. Add about 5 0 cm 3 of M sulphuric acid to the beakerand stir carefully until all the crystals have dissolved. Add moreacid until it is about 1 cm from the top of the beaker.

Clean the cathode and anode with propanone, weigh themseparately and record their masses .

Mass of cathode (copper)

Mass of anode (lead)

g

g

Power sourceAmmeter

Copperwiresupports

Figure

Make up a cell as shown in Figure 1, with the copper connectedto the negative (black) terminal of the power supply and the leadconnected to the positive (red) terminal. They should not toucheach other or the beaker.


2 7


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Q . Describe, as accurately as you can, the colour of theelectrolyte.

Switch on the power supply so that the current flowing is about0.8 A.

Q . What do you see:

i) at the cathode;

ii) at the anode?

Leave the apparatus set up for about 45 minutes then switch off.Carefully remove the cathode and anode, wash them by dipping

them in water, then leave them to dry. When dry, record theirmasses.

Mass of cathode = g

Mass of anode = g

Q . Describe the appearance of:

i) the cathode;

ii) the anode;

iii) the electrolyte.

Q . Explain what has happened to the cathode.

Q . Explain what has happened to the anode.

Q . Explain what has happened to the electrolyte.

Pour the electrolyte into a larger beaker and boil it gently untilcrystals start to appear (that is when 12-25 cm 3 is left). Stop

heating immediately, and leave to cool.

Warning: The liquid in the beaker is a concentrated acid. Treat itcarefully and wear goggles when heating.



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Q . Describe the crystals formed.

At the beginning of the experiment, the electrolyte containedcopper and nickel.

Q. Where is the copper now?

Q . Where is the nickel now?

The mass of copper in your original sample of crystals can becalculated. The relative molecular mass of copper(ll) sulphate -5 - water (CuSO 4 . 5H20) is 250 , and the relative atomic mass of

copper = 6 4.

Mass of copper in crystals

= mass of crystals x (64/250)

- .............. x (64/250)

= ............... g

Q . How much of the original copper did you strip from theelectrolyte?



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Experiment 7 Analysis of the acidified copper(ll) sulphate electrolyteYou will have available either a pipette or a burette containingthe diluted cell electrolyte. Carefully run exactly 2 5 cm 3 of thisinto a conical flask. Add three drops of methyl red indicator.

Q . What colour does the liquid go?

Use a funnel to fill a clean burette to above the zero mark with0.2M sodium hydroxide solution. Carefully run this liquid outinto a beaker until the bottom of the meniscus is resting on thezero mark.

Carefully run the sodium hydroxide solution from the buretteinto the liquid in the conical flask. After a while you will notice achange in colour in the indicator around the area where thesolution is being run in. Swirl the flask slowly until the new

colour disappears. When the colour takes a long time todisappear, wash around the inside of the conical flask withdistilled water, then add the sodium hydroxide solution slowlyuntil the colour changes with one drop added.

Q . What colour is the liquid now?

Make a note of the volume of sodium hydroxide solution used.D o not thow away this liquid. You will need it for the next part ofthe experiment.

3Volume of sodium hydroxide solution used = cm

Add dilute ethanoic acid drop by drop until the acid colourreturns. Weigh out 0.3 g of solid potassium iodide and add it tothe liquid in the conical flask.

Q . To what colour does the liquid change?

Fill a clean burette with 0.1M sodium thiosulphate solution asdescribed above. Run about 10 cm 3 of this solution into theliquid in the conical flask and add five drops of starch indicator.The liquid should now be purple in colour.

Wash around the inside of the conical flask with distilled water,then add more sodium thiosulphate solution, a drop at a time,until the purple colour disappears, leaving a pink liquid. Make anote of the volume of sodium thiosulphate used.

Volume of sodium thiosulphate used = cm 3

You may now use your results to calculate the mass of sulphuricacid and copper in the original sample.



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Calculation 1: mass of sulphuric acidQ . Write down the equation for the reaction between sulphuricacid and sodium hydroxide.

Mass of H2SO 4

= (volume of NaOH used/volume of H2S0 4 used) x (molarity ofNaOH/2) x (molecular mass of H2S0 4 )

= ............... x 1/25 x 0.2/2 x 98

= ............... gdrrT 3

Full-strength electrolyte contains 10 times this mass

= ............... gdrrT 3

Calculation 2: mass of copperThe chemistry of this is complicated but you do not need toknow it at this stage.

Mass of copper

= (volume of Na 2S 2O 3 used/volume of CuSO 4 used) x (molarityof Na 2S 2O 3) x (at. mass of Cu)

= ............... x 1/25 x 0.1 x 6 4

= ............... gdm 3

Full-strength electrolyte contains 10 times this mass

= ............... gdm" 3



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Experimenting with IndustryA series presenting industry-related science practicals for schools, developed as part of a 'teachers intoindustry' project organized by The Association for Science Education on behalf of The Standing Conferenceon Schools' Science and Technology.

Title

1 . Electrical Testing

2. Optical Fibres in School Physics

3. Industrial Use of Micro-organisms

4. Sugar Challenge

5 . ChemicalsforAgriculture

6. Brake Fluid and School Science

7. Safety in Gas Appliances

8. Extracting Metals from Scrap

9. Properties of Metals

10. Electronics of Control Systems

11. Chemistry of Esters

12. Physics of Fluid Flow

13. Plant Tissue Culture

Company

Square D Ltd., Swindon, Wiltshire

GEC Hirst Research Centre, Wembley, London

Nipa Laboratories Ltd., Pontypridd,Mid-Glamorgan

British Sugar pic, Peterborough, Cambridgeshire

ICI Agricultural Division, Billingham, Cleveland

Shell Chemicals, Carrington, Manchester

British Gas Eastern Region, Potters Bar,Hertfordshire

Elkington Copper Refiners, Walsall,West Midlands

British Aerospace, Stevenage, Hertfordshire

Marconi Command & Control Systems, Camberley,

Surrey

Ciba-Geigy Industrial Chemical Division,Manchester

Dowty Services Ltd., Cheltenham, Gloucestershire

Unilever pic, Bedford

Available from:The Association for Science EducationCollege Lane, Hatfield AL10 9AA

extracting metals from scrap 8

Documents