1492Ch18

Manahan,StanleyE.INDUSTRIALECOLOGY,RESOURCES,ANDENERGYEnvironmentalChemistryBocaRaton:CRCPressLLC,200018INDUSTRIALECOLOGY,RESOURCES,ANDENERGY____________________________________________________18.1.INTRODUCTIONModerncivilizationdependsuponawidevarietyofresourcesconsistinglargelyofmineralsthatareprocessedtorecoverthematerialsneededforindustrialactivities.Themostcommontypeofmineralmaterialsoused,andonethatallpeopledependuponfortheirexistence,issoil,usedtogrowplantsforfood.Alsoofcrucialimportancearemetalores.Someofthesemetalsourcesarecommonandabundant,suchasironore;others,suchassourcesofchromium,arerareandwillnotlastlongatcurrentratesofconsumption.Therearealsosomecrucialsourcesofnonmetals.Sulfur,forexample,isabundantandextractedinlargequantitiesasaby-productofsulfur-richfuels.Phosphorus,akeyfertilizerelement,willlastonlyforseveralgenerationsatcurrentratesofconsumption.Thematerialsneededformodernsocietiescanbeprovidedfromeitherextractive(nonrenewable)orrenewablesources.Extractiveindustriesremoveirreplaceablemineralresourcesfromtheearth’scrust.Theutilizationofmineralresourcesisstronglytiedwithtechnology,energy,andtheenvironment.Perturbationsinoneusuallycauseperturbationsintheothers.Forexample,reductionsinautomotiveexhaustpollutantlevelstoreduceairpollutionhavemadeuseofcatalyticdevicesthatrequireplatinum-groupmetals,avaluableandirreplaceablenaturalresource.Furthermore,automotivepollutioncontroldevicesresultingreatergasolineconsumptionthanwouldbethecaseifexhaustemissionswerenotaconsideration(aparticularlypronouncedeffectintheearlieryearsofemissionscontrol).Theavailabilityofmanymetalsdependsuponthequantityofenergyusedandtheamountofenvironmentaldamagetoleratedintheextractionoflow-gradeores.Manyothersuchexamplescouldbecited.Becauseoftheseintimateinterrelationships,technology,resources,andenergymustallbeconsideredtogether.Thepracticeofindustrialecologyhasasignificantpotentialtoimproveenvironmentalqualitywithreducedconsumptionofnonrenewableresourcesandenergy.Indiscussingnonrenewablesourcesofmineralsandenergy,itisusefultodefine©2000CRCPressLLCtwotermsrelatedtoavailablequantities.Thefirstoftheseisresources,definedasquantitiesthatareestimatedtobeultimatelyavailable.Thesecondtermisreserves,whichreferstowell-identifiedresourcesthatcanbeprofitablyutilizedwithexistingtechnology.18.2.MINERALSINTHEGEOSPHERETherearenumerouskindsofmineraldepositsthatareusedinvariousways.Theseare,forthemostpart,sourcesofmetalswhichoccurinbatholithscomposedofmassesofigneousrockthathavebeenextrudedinasolidormoltenstateintothesurroundingrockstrata.Inadditiontodepositsformeddirectlyfromsolidifyingmagma,associateddepositsareproducedbywaterinteractingwithmagma.Hotaqueoussolutionsassociatedwithmagmacanformrichhydrothermaldepositsofminerals.Severalimportantmetals,includinglead,zinc,andcopper,areoftenassociatedwithhydrothermaldeposits.Someusefulmineraldepositsareformedassedimentarydepositsalongwiththeformationofsedimentaryrocks.Evaporitesareproducedwhenseawaterisevaporated.Commonmineralevaporitesarehalite(NaCl),sodiumcarbonates,potassiumchloride,gypsum(CaSO4•2H2O),andmagnesiumsalts.Manysignificantirondepositsconsistingofhematite(Fe2O3)andmagnetite(Fe3O4)wereformedassedimentarybandswhenearth’satmospherewaschangedfromreducingtooxidizingasphotosyntheticorganismsproducedoxygen,precipitatingtheoxidesfromtheoxidationofsolubleFe2+ion.Depositionofsuspendedrocksolidsbyflowingwatercancausesegregationoftherocksaccordingtodifferencesinsizeanddensity.Thiscanresultintheformationofusefulplacerdepositsthatareenrichedindesiredminerals.Gravel,sand,andsomeotherminerals,suchasgold,oftenoccurinplacerdeposits.Somemineraldepositsareformedbytheenrichmentofdesiredconstituentswhenotherfractionsareweatheredorleachedaway.Themostcommonexampleofsuchadepositisbauxite,Al2O3,remainingaftersilicatesandothermoresolubleconstituentshavebeendissolvedbytheweatheringactionofwaterunderthesevereconditionsofhottropicalclimateswithveryhighlevelsofrainfall.Thiskindofmaterialiscalledalaterite.EvaluationofMineralResourcesInordertomakeitsextractionworthwhile,amineralmustbeenrichedataparticularlocationinearth’scrustrelativetotheaveragecrustalabundance.Normallyappliedtometals,suchanenricheddepositiscalledanore.Thevalueofanoreisexpressedintermsofaconcentrationfactor:Concentrationfactor=Concentrationofmaterialinore(18.2.1)AveragecrustalconcentrationObviously,higherconcentrationfactorsarealwaysdesirable.Requiredconcentrationfactorsdecreasewithaveragecrustalconcentrationsandwiththevalueofthecommodityextracted.Aconcentrationfactorof4mightbeadequateforiron,whichmakesuparelativelyhighpercentageofearth’scrust.Concentrationfactorsmustbe©2000CRCPressLLCseveralhundredorevenseveralthousandforlessexpensivemetalsthatarenotpresentatveryhighpercentagesinearth’scrust.However,foranextremelyvaluablemetal,suchasplatinum,arelativelylowconcentrationfactorisacceptablebecauseofthehighfinancialreturnobtainedfromextractingthemetal.Acceptableconcentrationfactorsareasensitivefunctionofthepriceofametal.Shiftsinpricecancausesignifican