Mining PDF

Mi ning Miningi st heprocessofext ract ingusef ulmi neralsfrom t hesur faceoft heEarth, i ncludingtheseas.Or esrecoveredbymi ningincludeme...

Mi ning Miningi st heprocessofext ract ingusef ulmi neralsfrom t hesur faceoft heEarth, i ncludingtheseas.Or esrecoveredbymi ningincludemet als,coal,oil shal e, gemst ones,l imestone,chalk,di mensi onst one, r ocksal t ,potash,gr avel,andclay. Miningi sr equiredtoobtainanymat erialthatcannotbegr ownt hroughagr i cult ural processes,orfeasi blycreatedarti fi ciallyinal aboratoryorfactory.Mini nginawi der sensei ncl udesextracti onofanynon- renewabl eresourcesuchaspet r oleum,natural gas. Ty pesofmi ning:Mi ningt echni quescanbedi vi dedi ntot wo commonexcav ati ont ypes: sur facemi ningandsub- sur face( under ground)mi ning. I. Sur facemi ning Surfaceminingisdonebyr emovingorst r ippingt heov erbur dent hatl i esabovea miningarea.Inmi ning,overbur deni ssurfacev egetati on, soil,di rt,l ay ersofbedrockin ordertoreachbur i edor edeposit st hatl aysabov eanar ea,suchast herock,soi l,and ecosystem thatl iesabov eacoal seam oror ebody.Overbur denisr emov ed duri ngsur f acemi ning, butisty picallynotcont ami natedwi thtoxiccomponent s. Overburdenmayal sobeusedt orestoreanexhaust edmi ningsi t e.Ithasbeen esti mat edthatmor et hantwo-thi rdsoft hewor ld’ sy earl ymi neralproductionis extr actedbysur f acemi ni ng. Techni quesofsur facemi ningi ncl ude: 1.Open- pitmi ning: Open- pitoropen- castmi ningi sasur facemi ningt echni queof extr actingrockormi ner alsf rom t heear thbytheirremov alfrom anopenpitorborrow. Open-pitminesareusedwhendeposi tsofcommer cial lyusef ulor eorrocksarefound nearthesurface.Iti sappli edtooreorr ocksfoundatt hesur facebecause theoverburdenisrel ativ elyt hinorthemat eri alofinterestisst r uctur all yunsui tabl ef or tunnel ing(aswoul dbethecaseforsand, ci nder,andgr avel).Thel ar gestopen- pit operati onscanmov ealmostonemi l l iont onsofmat erial( bot horeandwaste)perday. Insmalleroperati onstherat emaybeonl yacoupl eoft housandt onsperday. Mechani sm ofOpen- pitmi ning: A)Pi tgeomet ry Deposit smi ned byopen- pittechniquesar egeneral l ydi vi dedi nto hor izont allayers call edbenches.Thet hi ckness( t hati s,t heheight )ofthebenchesdependsont het ype ofdeposit ,forlargeminesi tisont heorderof12t o15met ers(about40t o50f eet). Miningi sgener all yconductedonanumberofbenchesatanyonet i me.Thet opofeach benchisequivalentt oawor ki nglevel,andaccesstodi ffer entlevelsi sgainedthrougha system oframps.Thewi dthofar ampdependsont heequipmentbei ngused,but typi calwidthsarefr om 20t o40met er s(65to130f eet).Mini ngonanewlevelisbegun byextendingarampdownward.Thi sini ti al, ordr op, cutist henpr ogr essi vel ywi denedto formthenewpi tbott om. Thewal l sofapi thaveacer tainslopedet er minedbyt hest rengthoft herockmassand otherf actors.Thestabili tyofthesewal l s,andev enofi ndivi dualbenchesandgr oupsof benches,i sv eryimportant—particularl yast hepitget sdeeper.Increasi ngt hepitslope anglebyonl yaf ew degreescandecr easestri ppi ngcost st remendouslyori ncrease revenuest hroughincreasedor er ecovery,butitcanal sor esultinanumberofsl ope fai luresonasmal lorl ar gescal e.Mi ll i onsoft onsofmat eri almaybei nvolvedinsuch sli des.Fort hisreason,mi neshav eongoing sl ope-stabili typr ogramsi nvolv ing the coll ect i onandanal ysisofst ructuraldata,hydrogeol ogi cinformation,andoper ati onal practices.Itisnotunusualf orf i veormor ediff er entslopeangl estobei nvolvedinone l argepi t. Asapi tisdeepened,mor eandmor ewast erockmustbest ri ppedawayi norderto uncovertheore.Ev entual lytherecomesapoi ntwher etherev enuef r om t heexposed oreislessthanthecost sinvolv edi nit srecovery.Mini ngthenceases.Ther at ioofthe amountofwast er ockst r ippedtoor er emovedi scall edtheov er allst rippi ngrati o. Thebreak-evenstr ippingrati oisaf unct ionoforev al ueandthecost sinvolved. B)Or ereser ves Thef i rststepi ntheev aluati onanddesi gnofanopen- pitmi neist hedeter mi nationof reserves.Informati onr egardingt hedepositiscoll ectedt hrought hedr i l lingofpr obe holes.Thel ocati onsoft hehol esareplot tedonapl anmap, andsect i onst akenthrough thehol esgiveagoodi deaoft heor ebody’ sv er ti calextent.From thesev er t i calsecti ons thetent at ivelocati onsoft hebenchesar eselected.Economi cfactorssuchascost s andexpect edr ev enues, whichv ar ywithgradeandbl ocklocation, aret henapplied. C)Uni toper ati ons I nmostofthesemi nest her ear efouruni toper ati ons:dr il li ng,bl ast ing,l oadi ng,and haul ing. Inlargemi nesrotarydr i ll sar eusedt odri llholeswi thdiamet ersrangingf r om 150t o 450mm ( about6t o18i nches).Thedri llbi t,madeupoft hreeconescont ai ningeither steelort ungstencar bi decut t ingedges,isr otatedagai nstthehol ebot tom undera heavyl oad,br eaki ng the rock by compr ession and shear.Anai rcompr essoron thedrill i ngmachi nef orcesairdownt hecentreoft hedril lstr ingsot hatt hecutti ngsar e remov ed.I nsmal l erpi tsholesar eoft endr il l edbypneumat icorhy drauli cper cussion machi nes.Theser igsmaybet r uck-orcrawler- mount ed.Holedi ametersareof t enint he rangeof75t o120mm ( about3t o5inches). Hol es ar e dr il led i n speci al pat ter ns so t hatbl ast ingpr oduces t he t ypes of fragmentat iondesir edf orthesubsequentl oadi ng,hauli ng,andcr ushingoperat ions. Thesepat t ernsaredefi nedbyt hebur den( theshortestdi stancebetweent heholeand theexposedbenchface)andthespacingbet weentheholes.Gener ally, theburdenis25 to 35 times the diameter of t he blasthol e,depending on t he type of rock andexplosivebei ngused,andthespacingisequaltotheburden. Thereareanumberofexpl osi vesused,butmostar ebasedonasl ur ryofammoni um ni trateandfueloil ( ANFO),whichist ransport edbyt ankertruckandpumpedi nt ot he holes.Whenfil ledwi t hANFO, ablasthole400mm ( about16i nches)indi ameterand7. 5 met r es(about25f eet)deepcandev elopaboutonebi l li onhor sepower.Iti sincumbent upon those invol ved int he dril l ing and blast i ng tot ur nt his powerinto usef ul fr agment at ionwor k.Toachi evethepr operfragmentation,aser iesofblasthol esi s general lyshotinacar ef ull ycontrol ledsequence. Theobj ectofbl astingi st of ragmentt her ockandt hendi splacei tintoapi l et hat willf acilit ateitsloadi ng and t ranspor t.Inl arge open pi tst he mai nimplement sf or l oadi ngar eelectric,diesel-el ect r ic,orhy dr aul i cshov els,whileel ectr icormechani cal - driv et rucksar eusedf ortranspor t.Thesi zeoft heshov elsisgener al lyspeci f iedby dipper,orbucket ,size;thosei ncommonusehav edippercapaci t iesrangingf rom 15t o 50cubi cmet r es( 20t o65cubi cy ards).Thismeanst hat30t o100t onscanbedugi na si ngle“ bite”oft heshov el.Thesi zeoft het rucksismat chedt othatoft heshov el,a commonr uleoft humbbei ngt hatt het ruckshoul dbef il l edi nf ourtosi xswi ngsoft he shovel.Thus, forashov elof15- cubic- metrecapaci ty ,at ruckhav ingacapaci tyof120t o 180t ons( fourtosi xswi ngs)shoul dbeassi gned.Thel argesttruckshav ecapaci tiesof mor ethan350t ons( about12swi ngs)andar eequi ppedwi thengi nesthatpr oduce mor ethan3, 500hor sepower ; theirt i r ediamet ersareof tenmor ethan3met res( 10f eet). Becauseoft heirhighmobi li ty,veryl arge-capaci t ywheell oaders( fr ont - endloader s)ar e al sousedi nopen- pitmi nes. Aspi tsbecamedeeper —t hedeepestpi tsint hewor ld exceed 800 met res( 2,600 feet) —alt ernate modes oft ransport ing br oken or e and waster ock became mor e common.Oneoft heseist hebeltconveyor,butingeneralthismet hodr equiresin-pit crushi ngoft herun-of- minemat eri alpri ortotransport.Formostmat erial samaxi mum angleof18°ispossible.Tot r ansportdir ectl yupt hesidesofpitwall s, specialconvey i ng techni quesar eunderdevelopment. Afterl oadi ng,wast er ocki stransportedtospeci aldumps,whileoreisgeneral lyhauled toami ner al- processingpl antf orfur thertr eatment.( Insomecasesor eisofsuffi cientl y highquali tyfordirectshi pmentwi t houtinter mediat eprocessing. )Insomeoper ations separat edumpsar ecr eat edf orthev ar iousgradesofsub- orematerial ,andt hese dumpsmayber e- mi nedl aterandpr ocessedinthemill.Cert aindumpscanbet reated by vari ous soluti ons t o extractt he contai ned metal s( a process known asheap l eachingordumpl eachi ng). 2.Quar ryi ng: Themet hodofr emov al ofstonesf r om t heirnatural bedbyusi ngdi f ferentoper at ionsi s call edquar r y i ng.Quar r yingisat ypeofopen- pitmi neinwhi chdi mensi on stone,rock, const r uctionaggr egate,sand, gravel,slateisexcav atedf rom thegr ound. Typesofr ockext ractedf r om quar ri esinclude: Chal k,Chinaclay , Coal , Constructi on aggregat e(sandandgr avel) ,Granite,Gypsum, Limest one,Mar ble, Phosphat erock, Quartz,Sandst one,Slateetc.Ther earetwot ypesofquar ry ing.Firstt heext r actionof ornament al stonebl ocksofspeci ficcolor,size,shape, andqual it y.Thisoper ation requi ringspeci alandexpensi vepr oductionpr ocedur es.Second, thet erm quar ryi nghas beenappl iedt ot herecov er yofsand, gr av el,andcr ushedst onef ort hepr oduction ofroadbase, cement ,concreteetc. Met hodsofquar ryi ngi ncl ude: a)Di ggi ng–Thi smet hodi susedwhent hequar ryconsi stsofsmal l&sof tpi ecesof st ones. b)Heating–Thi smet hodi susedwhent henat ural rockbedi shor izont alandsmal li n thi ckness. c)Wedging–Thi smethodisusedwhenthehardr ockconsi stsofnatural fissur e.When nat ural fissur esar eabsentt henart if ici alf issur esarepr epar edbydr i l lingholes. d)Bl asting–Itistheprocessofremoval ofstoneswiththehelpofcontrol l ed expl osi vesisfil l edi nt hehol esofthestones.Lineofleastr esist anceplaysvery i mportantrol eintheblasti ngprocess.Followi ngst epsareusedintheblast ingprocess;  i. Dr il li nghol es–Bl asthol esar edr il ledbyusi ngdr il li ngmachi nes. i i. Char ging–Expl osi vepowder sar efedi ntot hecl eaned&dr iedbl asthol es. i ii. Tamping–Ther emai ningpor ti onoft hebl asthol esar efi l ledbycl ay, ash, fuse& wir ings. i v. Fi ri ng–Thef usesofbl ast inghol esar efi redbyusi ngel ect ri cal powersuppl yor matchst icks. 3.St ri pmi ning: Str ipminingisconsi stsofstrippingsurfacelayer sof ftorevealore/seamsunder neat h. Str ipmining"ist hepracti ceofmi ningaseam ofmi ner al,byfir str emov ingalongstri p ofov er lyi ng soiland rock ( theoverburden) ;t hi s activi tyi s also r ef err ed to as "ov erburdenremoval ".Iti smostcommonl yusedt ominecoal andl igni te(browncoal). Str ipminingisonlypract icalwhent heorebodyt obeexcav atedi srel at i vel ynearthe surf ace.Thi stype of mi ning uses some of t he lar gest machi nes on earth, i ncludi ngbucket- wheelexcav atorswhichcanmov easmuchas12, 000cubi cmetresof eart hperhour. Therearetwoformsofst r ipmining. Thecy cl eofoperat ionsf orbothtechniques consi stsofveget ati oncleari ng,soilremoval,dri l li ngandblasti ngofov er burden( i f needed) ,st ri ppi ng,r emovalofthecoalorothermineral commodit y,andrecl amat i on. A.Areami ning-Themor ecommonmet hodi s"ar eastrippi ng"or“ areami ning”,whi ch i susedonf air lyfl atterr ain,toextractdepositsoveral ar gear ea.Aseachl ongstri p i sexcav at ed,theov erbur deni spl acedint heexcavationproducedbyt hepr evi ous st rip.Areami ningisappr opri atef ortheex t racti onofnear - surface,relati velyfl at- l yi ng, andt hindeposit sofcoal ,phosphat e, andsimi l armi ner als.Ar eaminingusuall y pr ogr essesinaser iesofpar al leldeept r enchesreferr edt oasf urrowsorst ri ps.The l engthoft hesest r ipsmaybehundr edsofmet er s. B.Contourmi ning -Contourmi ning i nvol vesr emov i ng theover bur den abovethe mineralseam neart heoutcropinhil lyterr ain,wheret heminer alout cropusuall y fol lowst hecontouroftheland.Contourst rippingisoft enfol lowedbyaugermini ng i ntot hehill side,toremovemor eoft hemi neral.Thismethodcommonl yl eaves behindterr acesinmount ai nsides.  4.Mount aint opr emov almi ning: Mountaintopr emov alminingcommonl yassociatedwi t hcoal mi ni ng,whi chinvol v es t akingthet opofamount ainof ft or eachor edepositsatdept h.USEPAdi agram of mountaintopmi ningisasf ollows: " Step1.Lay ersofrockanddi rtabovet hecoal(call edov erburden)areremoved." " Step2.Theupperseamsofcoal areremov edwi thspoil spl acedinanadjacentvall ey. " " Step3.Dr agl i nesexcav atelowerl ayersofcoal withspoil spl acedinspoi l pi l es." " Step4.Regr adingbeginsascoal excav at ioncont i nues." " Step5.Oncecoal remov aliscompl eted,fi nalregardingtakespl aceandtheareais r evegetated." Thepr act iceofmount aintopremov almini nghasbeencont rov ersi al.Thecoal i ndustr y ci teseconomi cbenefitsandcl ai mst hatmount aint opremov ali ssaferthan undergroundmining.Publ i shedscientif icst udieshav efoundthatmount ai ntopmining hasser i ousenvi ronment ali mpactst hatmit igationpract icescannotsuccessful ly address.Ahighpotential f orhumanheal thi mpact shasalsobeenreported.  5.Landf il lmi ning: Wastecont ainsmanyresour ceswithhighvalue,forexampl enon-ferr ousmetalssuch asalumi num cansandscrapmetal.Theconcentrati onofal uminum inmanylandfi ll si s hi ghert hant heconcentr ati onofaluminum inbauxitefrom whicht hemetali sderived. Landfi llmi ningisaprocesswhichexcavatesandpr ocessessolidwasteswhichhav e prev iouslybeenl andfil l ed.Landfi l lmi ni nginvolv essi teswherel andfi ll sareexcav ated andprocessed. Mechani sm ofLandf il lmi ning: i.Anexcavat oruncover sthel andfi ll edmat eri alsandpl acest hem onaconv eyorbel tto bet akentothesort ingmachi ner y. i i.Thenseparat edthemateri alsbysize.First , l argemateri alsl i keappliancesandf abri cs areseparat es.Thensmall ermat er ial slikebi odegradedsoi lfr acti onar eall owspassi ng thr oughleavi ngnon-bi odegr adable.Ther ecyclablemater ial sarecol lected. i ii.Anelect romagneti susedtoremov ethef err ousmat eri alf rom t hewast emassasi t passesal ongtheconv eyorbel t. i v.Thesor tedmat eri alsar emov edt oforf urt herpr ocessi ng. v.Thesmel li sreducedf rom exposedwast es. vi.Dependingont helevelofresourcerecover y,materi alsar esepar atesfr om li ght or ganicmat eri altoheavyorganicmateri al.Thesepar atesaret henl oadedontot rucks ei therf orfurtherpr ocessi ngorf orsal e. I I. Dr edgi ngmi ning: Dredgingmi ningisusedtorecovervaluablemi neral depositsormar iner esourcesf r om waterbodi es.Dredgi ngistheunderwat eroperationofexcavat ingmat erial.Exceptf r om mining,dredgingisusedforotherpurposeslikei mprovingexi sti ngwat erfeatures, reshapinglandandwat erfeat urestoal terdr ainage,constructdams, dikes, andother control sf orstreamsandshoreli nes,andt or ecov ermarineli f ehav i ngcommer ci alvalue. Dredgingsy stemsareclassi fi edasmechani cal orhydr auli c, dependingont hemet hod ofmat eri al t ransport. 1.Mechani calsy stem: a.Thebucket -ladder , orbucket- li ne,dredgehasbeent hetradit ionalmi ningtool.Itis stil lthemostf lexi bl emethodfordredgingundervaryi ngcondi t ions.Itconsist sofa singlehullsupportinganexcavati ngandl i ft ingmechanism, benefici ati onci rcuits, and wast e- disposal systems.Theexcavati onequi pmentconsistsofanendl esschai nof openbucket st hattravel aroundaladder.Thelowerendofthel adderrest sont hemine face—thatis,thebot tom oft hepondwher eexcavati ontakespl ace.Andt het opendis l ocat ednearthecent r eoft hedredge, atthef eedhopperoft hetreatmentplant.The chainofbucket spassesar oundtheupperendoft heladderatadr i vesprocket(cal l ed theuppert umbler)andloopsdownwar dtoani dl ersprocket(t hel owertumbler)att he bottom.Thef il l edbucket s,support edbyrollers,arepull edupt heladderanddumpt hei r l oadi ntothehopper.Aft erthev al uabl emat erialhasbeenr emovedbyt hetreatment plant,wasteisdumpedof fthebackendoft hedr edge. b.Theclamshelldredge,anothermechanicalsy stem,ischaracteri zedbyalargesi ngle bucketoperat ingattheendofcabl es.Alt houghitcanoperateindeeperwaterthan othersyst emsandhandl esl ar geparti clesandtrashwell.Ithasthedisadv antageof beingadisconti nuous,batch-t ypesystem,andtakingappr oximat el yonebiteperminut e. 2.Hydr aul icsy stem: Inpurehydraul i cdr edgingsystems,thediggingandl i ft ingforceiseitherpuresuction, sucti onwi t hhydrojetassist ance,orenti relyhydroj et.Theyarebestsui tedtodigging rel ati vel ysmal l -si zedloosemat er ial suchassandandgr avel ,mar i neshel l deposits,mil l tai li ngs,andunconsolidatedoverbur den.Hy draul icdredginghasalsobeenappl i edt o themini ngofdeposi tscontaini ngdiamonds, ti n,tungsten,ni obium-tantal um, t itanium, monazite,andrar eear ths. I II. Subsur facemi ning: Subsurf aceminingr efer stovar iousundergr oundminingtechni quesusedtoexcav ate mineral sfr om rockl ayer.Ther earemainlytwotypesofsubsurf acemining 1.Under groundhar drockmi ning: Undergroundhardrockmi ningrefer stov ari ousundergroundminingtechniquesused toexcavatehar dmi neralsfr om igneousormet amorphicrocks, usuall yt hose contai ningmetals, suchasor econt ai ning gol d,si lver,ir on,copper,zinc, nickel ,ti nandlead.Italsoinvol vesusingt hesametechniquesforexcavati ngor es ofgemssuchasdi amondsorr ubi es. Met hodf orUnder groundhar drockmi ning: a.Cutandf illmini ngi samet hodofshort- holemini ngusedinst eepl ydippi ngor i rregularorezones, i npar ti cularwherethehangingwalll imi tst heuseoflong-hol e met hods.Theor eismi nedinhor i zontalorsl i ghtlyi ncl inedsli ces,andthenfil ledwith wast erock,sandortailings.Eit herfi llopti onmaybeconsolidatedwithconcreteor l eftunconsol idat ed.Cutandf il lmini ngisanexpensivebutselecti vemethod,withthe advantagesofl owor elossanddi lut ion. b.Driftandf il lissi milartocutandf i ll ,exceptthati tisusedinor ezones, whi chare widert hanthemet hodofdr i fti ngwi l lal lowtobemi ned.Inthiscase,thef irstdrif tis developedi ntheore,andi sbackf il ledusingconsoli datedfi ll.Theseconddr i ftisdri ven adjacenttot hefir stdrif t.Thiscar ri esonunt i ltheor ezonei smi nedouttoitsfullwi dth, atwhi chtimet hesecondcuti sst artedatopoft hefi rstcut. c.Shri nkagest opingisashor t -holemi ni ngmet hodwhi chissui tableforsteeplydipping orebodies.Thi smet hodissimilartocutandf i l l miningwitht heexcept i ont hataf t er beingbl asted,br okenoreisl eftint hestopewher eitisusedtosupportthesur rounding rockandasapl atfor mfrom whi cht owork.Onl yenoughor ei sremov edf r om t hest ope toall owf ordri l lingandbl ast ingt henextsli ce.Thest opeisemptiedwhenal l oft heor e hasbeenbl ast ed. d.VRM/VCR: Vert icalr etreatmi ning(VRM)al soknownasVerti calcr aterretr eat(VCR) i samet hodwheremi neisdividedi nvert icalzoneswit hdepthofabout50met ers. Large- diameterholesaredril ledv erti cal lyint ot heor ebodyfrom t hetopusi ngdri ll s,and thenblasti nghori zontalsl icesoft heor ebodyi nt oanundercut.Oreblast edi nret ri eval takeni nphase. 2.Undergroundsof trockmi ni ngisagroupofundergr oundmi ni ngtechni quesusedt o extr actcoal,oilshal e,potashandotherminer alsorgeol ogicalmater ial sfrom sedi ment aryrocks.Becausedeposi tsinsedimentar yrocksarecommonl ylay ered andrelat ivel ylesshar d. Met hodf orUnder groundsof trockmi ning: a.Longwallmini ng–Longwallminingi sgri ndingalongoresur faceunder ground. Longwall mi ner sext ract" panel s"-rect angul arblocksofcoal aswideasthefacethe equi pmenti sinst all edi n,andasl ongassev eral kil omet ers. b.Room-and-pi ll armi ningorconti nuousmi ni ng–Room andpi l larminingi scommonl y doneinfl atorgentlydippingbeddedores.Pill arsarelef tinplacei nar egularpatter n whil etheroomsar emi nedout.Inmanyr oom andpill armi nes,thepill arsar etakenout, star ti ngatthefart hestpoi ntf rom theminehaul ageexit ,retr eating,andl et tingtheroof comedownupont hef l oor.Room andpil larmet hodsarewel ladaptedt omechani zati on, andareusedindeposi t ssuchascoal , pot ash,phosphate,sal t,oilshal e, and beddedurani um ores. c.Blastmini ng–Anol derpract iceofcoalmini ngthatusesexpl osivessuch asdy nami tetobreakupthecoal seam.Aft erwhicht hecoal i sgatheredandloaded ontoshutt lecar sorconv ey orsforr emoval toacentr alloadi ngarea. d.Shortwal lmining–Acoal mi ningmethodt hataccountsforl essthan1%ofdeep coalproduction,shor twal l involv estheuseofacont inuousmini ngmachi newith mov eabl er oofsupports,si mi l art olongwall.Thecont i nuousminershearscoalpanel s 150–200f eetwideandmor et hanahal f- milelong,dependingonotherthi ngsli kethe str ataoftheEar thandt hetransv ersewaves. e.Coalskimming–Whi lenolongeringener aluse,becauseoft hemassiveamountof waterneededandalsoasar esultoftheenv i ronmentaldamagecausedbycoal ski mmi ng.Themethodwasmuchf asterandlesslabour-i ntensivet hanpr evi ous methodstoseparat et heli ghtercoalfrom theminingrefuse(e.g.sl ate)call ed"coal ski mmi ng"orthe" sinkandf l oatmet hod"