Date post: | 05-Jul-2018 |
Category: |
Documents |
Upload: | trinhnguyet |
View: | 217 times |
Download: | 0 times |
Loesche Mills for
Metal Recovery and Filler Production from Steel Slag
2
This dry process developed by Loesche for recovering metals from
steel slag combines all the advantages of conventional processes:
• Efficientandcost-effectivemetalrecoveryinthecoarserange
• Virtually 100% metal recovery down to the finest fractions
range by means of optimised dry grinding, classification and
sorting technology
• Production of a high-quality mineral filler product with pre-
ciselydefinablegrainsizedistribution
Theprocessisparticularlysuitablefor
• Slagfromtheproductionofstainlesssteels
• LDslag
• Metallurgicallymodifiedslag
Followingcoarseslagprocessing (recoveryofmetale.g.+20mm,
crushingofthemineralcomponentsto-20mm)bymeansofcrush-
ing,screeningandsortingtechnologiessuchashandpicking,sen-
sor sorting, magnetic separation and/or dry density separation, a
pre-crushedslagfractionisfedintotheLoeschemill.
Selectivegrindingandclassificationof themineral fraction to the
desiredfineness,andtreatmentandpre-concentrationofthemetal
contentareperformedsimultaneouslyinthemill.Therangeoffine-
nessofthemineralfractioncanbevaried,therebyallowingfineness
levelsof-2mmaswellas5,000Blaineormoretobeadjusted.The
millsoperatingprinciplepermitstheutilisationofboththedifferent
levelsofgrindabilityandthedifferentspecificdensitiesofthesub-
stancescontainedinthegrindingstockforseparation.
While a defined filler product exits the mill through the classifier
situatedat the topof themill in thedirectionof the filterandsilo
plant,ahighgrademetalfractionisdischargedviaachuteoutletin
downwarddirection.
Iftheflowofmetaldoesnotyetachievethedesiredpurityof+90%
metal, furtherconcentrationstagesbymeansofsensor,magnetic
and/ordensityseparationareinstalleddownstream.Inthatcasethe
non-metallicproductof thesortingprocess is recycledto themill.
Thisway, it is possible to recover virtually 100%of themetal as
metalproductand100%ofthemineralproductaspreciselydefined
andmetal-freefiller.
TheLoescheprocessthereforeoffersthepossibilityofcreatingtwo
marketableproductsinasingleunitandadditionallyhastheadvan-
tage of avoiding the necessity to treat the residual slurry that is
otherwisecustomaryinwetprocesses.
Atypicalprocessvariationforspecialsteelslagreductionisdepict-
edinthefollowingflowdiagram.
FeaturesoftheLoescheprocessforthecomplete and dry processing of steel slag
Loesche Mill type LM 15.200 under construction
Loesche Mill type LM 15.200, Wolica, Poland, 2009
3
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
1
1110
2
12
3
13
4
14
5
15
6
16
7
17
8
18
9
19
20 21 22 23 24 25 26 27 28
Themetalliferousslagtobecomminuted ①isintroducedcentrally
orfromthesideintothemill.
Onthegrindingtable ②thematerialmovesundereffectofcentrif-
ugal force towards theedgeof thegrinding tableand in thisway
passes under the hydropneumatically spring-loaded grinding
rollers ③.
Themineralfractionisselectivelygroundbythemechanicalstrain
duringthecomminutionprocessunderthegrindingrollers,whilethe
metalparticlesareonlysuperficiallyliberatedfromadherentmineral
particles and their particle shape is retained to the greatest possible
extent.Theheaviermetalparticles ④ concentrate on the grinding
table,whilethemineralfraction ⑤concentratesabove.
Thegroundparticlesaretranportedoverthedamringintothegas
flow.
Thelightmineralfractioniscarriedbythegasflow ⑥ to the classi-
fier ⑦. Themetal particles – on account of their higher specific
density–arenotinterceptedbythegasflowanddescendagainst
thegasflowintothedischargesystem ⑧.
Material of the mineral fraction to which metal still adheres is
rejectedbytheclassifierandreturnedviatheso-calledgritcone ⑨
tothegrindingprocess.
Small amountsof themineral fraction still naturally adhere to the
metal fractiondischarged in thedownwarddirection. Ifnecessary
these mineral particles can be separated in subsequent sorting
steps.
Withthisoperatingprincipleitispossibletorecovernearly100%of
themetals.
Operating principle of metal recovery in a Loesche mill
44
M
MM
M
M
MM
M
M
M
M
1 2
3
4
5
5
67
7a8a
8
9
10
11
12
24
13 14 15 16
17211919
2022
23
18
25
26
27
28
31
2930
Example of a process flow diagram for the complete and dry processing of slag with the Loesche vertical mill 1 Wheel loader 2 Conveyor belt 3 Jaw crusher 4 Impact crusher or cone crusher 5 Conveyor belt 6 Screen 7 Handpicking, sensor sorting, magnetic
separation, dry density separation 7a Collecting container, coarse metal 8 Conveyor belt with metal detector 8a Collecting container, medium metal 9 Intermediate silo 10 Proportioning conveyor 11 Rotary star gate feeder 12 Loesche mill 13 Filter 14 Volumetric flow measurement 15 Mill fan 16 Stack with flap 17 Recirculation gas line with flap 18 Hot-gas generator 19 Rotary star gate feeder 20 Conveyor belt 21 Bucket elevator 22 Product silo, filler 23 Filler transportation 24 Discharge system, metal fraction 25 Conveyor belt, metal fraction 26 Magnetic separation 27 Sensor sorting 28 Dry density separation 29 Conveyor belt 30 Metal fraction 31 Conveyor belt, returning mineral
fraction to grinding circuit
55
M
MM
M
M
MM
M
M
M
M
1 2
3
4
5
5
67
7a8a
8
9
10
11
12
24
13 14 15 16
17211919
2022
23
18
25
26
27
28
31
2930
6
Coarse grain processing CG Metalrecoveryonlyinthecoarsesizerange(~+20mm)(metalrecovery:50–70%) bymeansofsimplesortingprocesses Products: Coarsemetal,pre-crushedmineralmatrixwithresidualmetal
andhardlydefinedgrainsizedistribution
Wet grinding WG Completewetfinegrindingofthemineralmatrix,(metalrecovery:>95%) separationofthemetalbymeansofclassification,
density separation and/or magnetic separation Products: Metal,de-wateredslimeswithhardlydefinedgrainsizedistribution
Process with wet pre-concentration WPC Concentrationofthemetalinpre-concentrates(metalrecovery:65–85%) (e.g.byjigging,risingcurrentsorters);
wetgrindingofthepre-concentratesonly Products: Metal,washedandclassifiedmineralaggregates(e.g.0/2,2/8,8/16…),
proportionoffinelyground,de-wateredslimeswithhardlydefinedgrainsizedistribution
Process with dry pre-concentration DPC Concentrationofthemetalinpre-concentrates(metalrecovery:60–85%) (e.g.byairjigs,fluidisedbedseparators);
drygrindingofthepre-concentratesonly Products: Metal,classifiedmineralaggregates(e.g.0/2,2/8,8/16…),
proportionoffinelygrounddustasdefinedfillerproduct
Dry grinding Loesche DGL Completedrygrindingofthemineralmatrix,(metalrecovery:>95%) separationofthemetalbymeansofclassification,
density sorting and/or magnetic separation Products: Metal,variablefillerproduct(e.g.fillerquality,5,000Blaine…)
EconomicComparison
Precondition:High-valueapplicationforthefillerproductcomparedtolow-valueapplicationofthedewateredslimesproductfrom wetprocessing.ExtensiveapplicationanalyseshaveshownthatdrygrindingbytheLoeschemillproducesahigh-qualityandversatilemineralfiller.
conventionalwetprocessing
dry processing
Loesche process
CG WG WPC DPC DGL
7
LM 24.2M
LM 21.2M
LM 19.2M
LM 17.2M
LM 15.2M
LM 12.2M
Productrate[t/h]asafunctionofLMsize
Finenessfine coarse
heavy lightGrindability
0 10 20 30 40 50 60 70 80 90 100
Product rate [t/h]
Model series and capacities
Gearboxes ready for shipment
Stainless steel slag with metal inclusions
Reflected light microscopy with typical phases of a stainless steel slag
Heavy product (metal) & light product after dry density separation (- 2 mm)
Loesche GmbHSales Ores & SlagsHansaallee 24340549 DüsseldorfTel. +49 - 211 - 53 53 - 777Fax +49 - 211 - 53 53 - 500E-mail: [email protected]/ores
Typical element distribution in a stainless steel slag
Filler product
Raw slag