無機(jī)高分子聚合鐵鹽類混凝劑制備方法評述

無機(jī)高分子聚合鐵鹽類混凝劑制備方法評述

摘要：綜述了無機(jī)高分子聚合鐵鹽類混凝劑的幾種生產(chǎn)制備方法。對用硫酸亞鐵經(jīng)催化氧化法和直接氧化法制備聚合硫酸鐵，用各種含鐵工業(yè)廢渣制備復(fù)合聚鐵，以及采用生物和電化學(xué)方法制備聚鐵類混凝劑等方法的優(yōu)缺點(diǎn)等作了較全面評述。還對固體聚合鐵的生產(chǎn)及液體聚合鐵混凝劑的穩(wěn)定性進(jìn)行了討論，對目前聚合鐵生產(chǎn)中存在的問題及發(fā)展方向提出了建議。

關(guān)鍵字：聚合硫酸鐵

硫酸亞鐵

混凝劑

硫鐵礦燒渣ProgressonManufacturingMethodofInorganicPolymerCoagulantPolyferricsaltcategoryAbstract:Thispapergivesareviewofthemanufacturingmethodofinorganichighpolymercoagulantpolymerizedferricsulfate.ThepresentsituationofthestudiesandtheproductionofPFSisdiscussed.ItpointsoutthemeritandtheshortcomingofthemanufacturingmethodsofPFSwithferroussulfate,pyritecinderandotherslagscontainingiron.SomesuggestionsaboutpresentproblemsanddevelopmentdirectionintheproductionofPFShavebeenputforward.Keywords

Polyferricsulfate,ferroussulfate,coagulant,pyritecinder油I扶n層t拌r尤o迫d豐u惡c列t瞞i鳴o快n

Polymerizedferricsulfate(PFS)isanewinorganichighpolymercoagulant.ItsmolecularformulaisFe2(OH)n(SO4)3-n/2]m,(n>2,m=f(n)).Itcanbeusedinwastewatertreatmentandthepurificationofdrinkingwater[1]鳴.武團(tuán)C秀o點(diǎn)m振p晨a泄r翁e冤d腥竊w猴i修t其h心嫌g駱e餐n紫e希r擇a余l(xiāng)易追i姓n荒o鎮(zhèn)r不g具a模n骨i銹c錄灑c侍o通a錯(cuò)g鍵u姑l宿a郵n頁t啊s掀,低慚f陶o謙r偏垃e默x遣a煤m山p觸l接e番,死些f躁e棟r浩r綢o刪u哲s鏈?zhǔn)舠朵u負(fù)l董f材a恒t肆e黃,島抗f震e衣r離r朝i革c宜堵c幼h守l勸o積r躁i匙d襖e故,奴建a療l挺u帝m昆i勇n樓u滾m爛鞏c伶h卷l擋o向r演i獅d丈e斃,杜言a吩l裁u系m濫i爭n刑u尊m封距s寧u評l經(jīng)f產(chǎn)a娛t匙e雅,她庫a牌l燈u柄m腰院f彩l規(guī)o搖c醫(yī)馬a俗n拐d閃籍p辯o槳l廈y掃m節(jié)e旅r喝i旬z清e(cuò)拐d輝由a緞l壺u兵m理i燈n持u道m(xù)寫顧c壞h嘉l手o慈r壟i冠d鏡e牢(捆P婚A俗C興)光么,封具P躲F克S比肺i波s底垂t貌h帶e左蒙b港e煉s逐t何懲c完o師a蹦g右u塵l門a尾n能t池.株劃I掘t停s洗弊c封o代a戒g董u票l澇a郊t章i級n繳g產(chǎn)撇a料b墳i仿l跨i銅t挖y抗得i未s草總s絞t被r貌o推n椅g吃,暈些s訊i呢n償k叮i瓣n沫g妙啦s片p廣e壽e拴d暈懸i堵s嚴(yán)忠q劈u館i粒c長k普,意離a疫n叫d秧史p沫r菊o泳d翠u烘c校i簡n礎(chǔ)g跨蓮c百o鉆s榮t鈔丹i倚s瞇薯l稱o沖w惕.茄貨I訪n們吩a漆d顫d醉i轎t宴i機(jī)o廣n隱,訪白t膠h摧e學(xué)貢l錘e練a絕v庸i偽n釋g臂邀o魯f登求a決l走u航m裕i緊n棵u仆m擺刊i喂s超天m掛o青r詞e艱拾i砍n照殘t演h網(wǎng)e善幅w逐a敲t延e求r撕奉t著r綿e贈(zèng)a切t鏡e限d擋買w悟i顏t匆h瑞盞t介h授e云科c意o盲a趨g阻u符l哥a脾n坐t乓s站甘c今o秀n驚t成a懸i腦n疏i茫n兇g膏撫a梯l階u惜m決i厚n快u弄m駁,削鑒a疲n興d嘉例i濤t慧核i貢s夫膛h池a圾r資m醋f愉u線l脹引t跟o獎(jiǎng)架t案h掉e鎖煮h視e員a忌l賭t強(qiáng)h杏奇o款f患魔h甩u充m姜a綢n胖羅b億o患d筆y也[戰(zhàn)2債]魔.咬希T奪h挎i浮s兩惡r癥e悶s他t煌r憐i榮c聰t把s湊晉t纖h原e每槽d頂e救v閥e修l濁o寇p死m(xù)局e顏n漠t誼湖o常f吧歷a挨l篩u退m明i糊n蕉u誠m蜂月c傭o仆a孕g(shù)同u夕l真a模n軌t革s輛,廊初a梨n釘d紅殊p退a哥r輔t薯i撐c通u復(fù)l末a侍r淹l伙y寺猛i啄n涉認(rèn)d鐮r醫(yī)i寇n章k壟i接n躲g誰輸w借a胞t階e責(zé)r育者t邀r諒e禾a娛t哨m冒e睛n汪t門.葬歪N渣e滔v吹e惠r謎t蝶h源e風(fēng)l梅e內(nèi)s杜s愚,排扭t字h色e褲村l著e角a送v約i畜n怕g障骨o扇f孩讓f掘e刪r戴r氧i歷c墻歸i謝s鏟緩l階i省t窗t罷l熟e狐挽i哲n或丟t晉h繞e綁嚷w朋a矩t淹e磨r叢侮t峰r偉e季a騰t尿e士d躬革w每i統(tǒng)t廁h彈炒P輩F探S寬,衛(wèi)增a息n膽d法白i艇t嗽蠢i繁s迎鉗n隊(duì)o沙t顯居h晃a圣r資m籌f協(xié)u鵲l院配t漠o澡袍h傷u北m荷a誦n溫峰b拼o散d抓y卷.梢秘A呀t仆皇t懼h搏e礎(chǔ)帝s細(xì)a賺m鴿e該槍t槽i般m究e讓,賞后P木F歡S豐構(gòu)i想s刷惜a遍l碑s權(quán)o怎扶s陰u裙p漫e撲r返i慶o勵(lì)r酒偶t秘o立土o丈r云g俗a取n兔i盛c廊漆c瞧o宗a曠g餓u掩l貿(mào)a均n著t卷s捆馳s徒u紹c貌h情需a祥s棗拌p不o介l朝y真a肚c滋r雀y緣l號a仰m豈i學(xué)d厲e宿(鍛P軌A撐M綠)圓沿i原n約忘s駛o局m籌e漂瞇i攜n討d容u咽s鏈t裁r鋼i想a場l羅億w來a仙s寧t弦e開w溫a盟t儀e駱r軌棵t擺r檔e因a吊t處m餅e嫁n辟t慧[應(yīng)3東]輝.影逃W關(guān)h鞠e懷n伙青P示F蜻S喘妻s密u架b蘿s偷t字i杰t噸u血t義e貸d稍租f隔o牽r用歉P帽A籮M月血i國n翻粉w晶a當(dāng)t壞e危r吉禿t換r高e較a輕t艱m稱e時(shí)n岡t拔,溫題t永h高e甘封h慣a濤r府m休泳o詢f腹聾m度o鄰n惹o牧m踐e彩r手云A災(zāi)M國,蛛由w旗h絞i位c縣h徒很w國a夢s途素l駝e有f詠t拾施i閉n豆耍w胃a戶t悅e捎r休貓a陶f勵(lì)t婆e狐r廣樹P親A客M提艱w鍵a卵s湖逢d息e舅g趴r晝a龜d通e霸d帶,圓襖c糾o丹u哪l篩d濾捕b怨e傍溉a樂v跨o郵i狗d港e曠d慈.呈駐S桐o摩糠t疲h杏e您應(yīng)a的p般p雜l昏i顫c饞a既t峽i劃o扭n兵明p綿r籃o虜s府p鄙e摔c巧t腎灘o身f立銜P宵F誼S然三i仙s教臥v純e窗r恐y路裳g碧o菌o惕d份芳a回n浪d瘦糊t壘h誓e何株m心a娘r辯k室e駱t攤釘c誤o電m叮p漁e繁t葛i衰t量i休o卻n蔑娘p兩o歉w蕩e說r廉鉗i慕s頸跡s煩t鑄r清o宗n篩g葛e彩r品促i活n隨崗i加n勤d羅u來s閱t博r光i墻a各l桂裁w遲a撥s右t巖e森w遷a思t軋e抽r記垂t沫r挑e拍a昏t隨m裳e祖n額t粗,籍赤i寸n納d君u豆s匙t版r掉a求i雹l簽火u聽s示i銷n捏g聾免w薦a殲t澆e嘴r利,隸傳a曬n熊d女荒l征i朝f隊(duì)e準(zhǔn)夫d敗r存i羞n雙k為i圓n悠g鉆證w販a雄t絡(luò)e爪r皂.

In1972,JapanputforwardPFSasoneofcoagulants,andappliedforthefirstpatent[4]ofPFSmadefromferroussulfate.Thenindustrialscopeproductionandapplicationinwatertreatmentwereformed.ChinastartedthestudiesofPFSin80'searly.ThemanufactureofPFSmadefromferroussulfatewasdevelopedsuccessfullybyTianjinResearchAcademiesofChemicalIndustryunderMinistryofChemicalIndustryofChinain1982.TheproductionofPFSwasindustrialized[5]in1984.Hereafter,popularizingapplicationstepbystepinWuhanironandsteelcompany,etc.Now,PFShasbeenuniversalconcernedandappliedinChinaasanewinorganichighpolymercoagulant[6].Atpresent,themajormanufacturingmethodofPFSistheoxidationmethodofferroussulfate.Ferroussulfateandsulfuricacidareimportantrawmaterialsinthismethod.PFScanbemadebytheoxidationofferroussulfateandthehydrolysisandthepolymerizationofferricsulfate.Anothermethodisthatsomeironoredregs(orwasteresidue)andsulfuricacidareusedastherawmaterialsofPFS.Ironoredregsaredissolvedinsulfuricacid,thenhydrolysis,polymerization.1ManufactureofPFSwithferroussulfate

Ingeneral,ferroussulfate,whichisaby-productproducedintheproductionprocessoftitaniumwhite(titaniumdioxide),andsulfuricacidareusedastherawmaterialsofPFS.Besides,acidwashingwasteliquids,scrap-iron,andsulfuricacidcanalsobeused.Inthemanufacturing

processofPFS,thereactionsofoxidation,hydrolysis,andpolymerizationareallexistentialatthesametime.Becauseofthecauseofdynamics,theoxidizingreactionofferroussulfateisslowerunderaciditycondition.Sotheratecontrollingstepofthereactionsystemistheoxidizingreaction.Thisreactionmaybedirectedoxidationorcatalyzedoxidationaccordingtodifferentoxidizingprocess.1.1Methodofdirectedoxidation

Themethodofdirectedoxidationisthatferroussulfatewasoxidizeddirectlyintoferricsulfatebyoxidizer.Theoxidizerusedherewashydrogenperoxide[7],manganesedioxide,potassiumchlorate[8],sodiumpersulfate,sodiumhypochloriteornitricacidandsoon.Theoxidizingreactioncanbecompletedwithintwohoursundertheconditionofroomtemperaturewhenhydrogenperoxideisusedasoxidizer:

2FeSO4+H2O2+H2SO4=Fe2(SO4)3+2H2O（1）Then,hydrolysisandpolymerization:

Fe2(SO4)3+nH2O=Fe2(OH)n(SO4)3-n/2+n/2H2SO4

（2）

m[Fe2(OH)n(SO4)3-n/2]=[Fe2(OH)n(SO4)3-n/2]m（3）Thetimeoftheoxidizingreactionmaybeshortenedfurtherundertheconditionof50℃.

Themethodofdirectedoxidationhassomemerits,suchassimpleprocess,easyoperation,andshorterreactiontime,buttheconsumptionofoxidizersishighandthepriceisexpensive.SoPFSmadebythemethoddoesnothavemarketcompetitionpower.

Inthemethodofdirectedoxidation,literatures[9]putforwardanotherwaywhichwaseasytooperateandpopularize.Thewaywasbasedonsomefeaturesoftheinstabilityofferroushydroxideandbeingeasytobeoxidizeintoferrichydroxide.Firstly,ferroussulfatewaschangedintoferroushydroxidebyaddingalkaliinthesolutionofferroussulfate:

FeSO4＋2NH3·H2O＝Fe(OH)2＋(NH4)2SO4

(4)Secondly,ferroushydroxideforminginthereactionabovewasoxidizedintoferrichydroxideafterbeingplacedinair:

4Fe(OH)2＋O2＋2H2O＝4Fe(OH)3

(5)Then,oxidizersolutionwasobtainedthoughthereactionbetweenhydrogenperoxideandferroussulfateaccordingtotheequation(1).Finally,PFSwasmadebymixingtheferrichydroxidesuspensionandtheoxidizersolutionwithin2hoursunderthestirredcondition.

2Fe(OH)3＋H2SO4＋Fe2(SO4)3?[Fe2(OH)n(SO4)3-n/2]m＋H2O(6)

Thesereactionsmentionedabovecantakeplaceinroomtemperature.TheprocessingequipmentofthemethodaresimpleanditiseasytooperateandthecostofPFSislowtoo.

Literature[9]reportedthatthestabilityofPFSmadeinthiswaywaspoorer.Infact,theinstabilityofPFSmadeinothermethodsmentionedinfollowingisexistenttoo.ThecriticalfactorsaffectingthestabilityarepH,Fe3+/SO42-oraddingstabilizerinPFS.1.2Methodofcatalyzingoxidation

Themethodofcatalyzingoxidationisthatferroussulfateisoxidizedintoferricsulfatebyoxidizerundertheeffectofcatalyst.ItisamajormethodofmanufacturingPFSwithferroussulfate.Manystudies[10-15]havebeenmadeinthisaspect.Undertheconditionsofhavingoxidativecatalyst

andsuitabletemperature,PFScanbemadethroughtheoxidationofferroussulfate,hydrolysis,andpolymerization.Thecatalystsusedinthereactionofcatalyzingoxidationweresodiumnitrite,manganesedioxideorchloride.Atpresent,themostproductioncompaniesofPFSusethismethod.

ThemanufactureofPFSwithferroussulfateandsulfuricacidwasreportedfirstlybyJapanpatent[4].Whensodiumnitriteandairwereusedascatalystandoxidizerrespectively,themechanismofcatalyzingoxidationcanbeshowedasfollows:

2FeSO4+H2SO4+2NaNO2＝2Fe(OH)SO4+Na2SO4+2NO

(7)

FeSO4+NO＝Fe(NO)SO4

(8)

2Fe(NO)SO4+1/2O2+H2SO4＝Fe2(SO4)3+2NO+H2O(9)

2NO+O2＝2NO2(10)

2NO+1/2O2＝N2O3

(11)

2FeSO4+N2O3+H2O＝2Fe(OH)SO4+2NO(12)or

2FeSO4+N2O3+H2SO4＝Fe2(SO4)3+2NO+H2O(13)

2FeSO4+NO2+H2O＝2Fe(OH)SO4+NO

(14)or

2FeSO4+NO2+H2SO4＝Fe2(SO4)3+NO+H2O(15)

Ferricsaltsproducedinthesereactionswerehydrolyzedandpolymerized:

2mFe(OH)SO4+(1-n/2)mH2SO4＝[Fe2(OH)n(SO4)3-n/2]m+(2-n)mH2O

(16)or

Fe2(SO4)3+m×nH2O＝[Fe2(OH)n(SO4)3-n/2]m+nm/2H2SO4(17)

ItcanbeseenfromthereactionsabovethatthemechanismoftheoxidizingreactionofferroussulfatehadbeenchangedowingtotheparticipationofNOwhichmadetheoxidizingreactioneasy.Thecatalyzingoxidationtimewasshortenedto4~5hoursfromoriginal17hours.Evenso,thetimewasstilllongerandtheconsumptionquantityofcatalystwasalsomore.Meanwhile,nitrogenoxidesweredischargedintoairinthemanufacturingprocessofPFSandthisresultedintheenvironmentalpollution.

Forthesakeofshorteningthereactiontime,somemeasuressuchasheatingandhighpressureandstrongstirring,wereoftenadoptedinthemanufacturingprocess.Amongthem,themethodoftwostepsoxidationcouldshortenthetime.Firstly,ferroussulfatewasoxidizedintoferricsulfateundertheheatingcondition.Secondly,bothferroussulfateandhydrogenperoxidewereaddedinthesolutionofferricsulfatemadeaboveaccordingtoproportion.Then,PFSwasobtainedafteronehourreactionunderthestirredcondition.

Inordertoavoidpollution,Shortenfurtherreactiontime,andreduceenergyconsumption,themanufacturingtechnologyandthemanufacturingmethodofPFShadbeeninvestigatedthoroughly.Someprogresseshadbeenmade[16],forexample,thecatalysisoxidizingreactiontakenplaceinahermeticcontainerandtheproportionofSO42-/Fe3+wascontrolledinthereactionsystem.Inaddition,takingtheplaceofair,oxygenwasusedasoxidizer.Insuchsituation,PFSwasobtainingundertheconditionofstirringstronglywithin1.5~2hoursand55~90℃and29.4-147′104Pa.Neverthelesstheseconditionsofhightemperatureandhighpressureandstrongstirringwillincreasethedifficultyoftechnologyandtheinvestmentofequipments.Furtherimprovementwasthatthespeedofaddingsulfuricacidwascontrolledandsodiumnitritecatalystwasaddedinbatchesintheoxidizingprocessofferroussulfate.Undertheconditionsofnormalpressureandabove40℃,theoxidizingreactioncouldachievedwithin2-3hourswhenoxygenwasusedasoxidizer[13].Thisreportthoughtthatthemethodofaddingsulfuricacid,thatisthePHofreactionsystemwascontrolledincertainscope,wasthekeyofshorteningthereactiontime.BecausetheoxidizingreactionofferroussulfatewasverydifficultintheconditionoflowerPH,butitcouldtakeplaceeasilywhenthePHwashigherthan2.

Inaddition,literature[17]developedanewmanufacturingtechnologyofPFSwithanatomizationmethod,thatis,undertheconditionsofnormalpressureandheating,theatomizationdripofferroussulfatewascontactedwithnitrogendioxideincirculationstate.Theaimofthisprocesswastoraisethecontactareabetweennitrogendioxideandferroussulfatesolution,quickenreactionvelocity,andshortenproductioncycle.TheprocesspioneeredanewwayfortheproductionofPFS.Ofcourse,thiswillalsoincreasethedifficultyoftechnologyandtheinvestmentofequipment.

Moreover,itwasreportedthatthebestkindofcatalysthadbeenfound[18]alreadyuptonow.Thiscatalystwasnotonlyhigheffectivebutnonpoisonous.Whenitwasusedintheoxidizingreactionofferroussulfate,thereactioncouldbecompletedintwohours.WehopeitcanbeusedintheindustrialproductionofPFSearly.

InthemanufacturingprocessofPFSabove-mentioned,thereactionofferrousandnitrogenoxidesbelongstoareactionbetweenliquidandgas.Inordertoincreasetheircontactareaandquickenthereactionspeed,somemeasures,suchasheating,high-pressure,strongstirring,andspraying,wereoftenused.So,thetechnologyofthemethodiscomplicatedandtheinvestmentcostofequipmentisalsohigher.

Besides,inotherreport,potassiumchlorateorhydrogenperoxidewereusedasasubstituteforairoroxygeninthesystemofsodiumnitrite.Althoughthiscanquickenthespeedofcatalysisoxidizingreaction,itincreasestheproductcost,too.1.3Effectofcatalystpromoteronthereactionofcatalyzedoxidation

BecausetheoxidizingreactionisaratecontrollingstepinthemanufacturingprocessofPFS,shorteningthereactiontimehasalreadybecomeafocalpointconcerned.Sopeoplehadmadethoroughstudies[3,6,18]attheaspectsofoxidizer,catalyst,andcatalystpromoter.Literature[3]hadmadesomedetailedstudiesonthekindandtheadditionofcatalysts,theselectionofcatalystpromoters,thetemperatureandtheacidityofreactionsystem.Thisliteraturethoughtthatsodiumiodideasacatalystpromotercouldquickenthereactionspeed.Atthesametime,italsothoughtthatcontrollingthePHofthereactionsystemwasakeytoquickenthespeedofoxidizingreaction.Itdiscussedhowsodiumiodidequickensthespeedoftheoxidizingreaction,too.

Onthebasisofinspectingtheeffectofcatalystsandoxidizersonthespeedofcatalysisoxidizingreaction,literature[6]reportedthatthetracecatalystpromoterofHG-1,HG-2,orHG-3couldnotablyraisethespeedinthereactionsystemofoxygenandsodiumnitrite.Thismadenotonlytheconsumptionofcatalystdecreasesoneathirdbutthereactiontimesshortentwothirds.Inaword,sodiumnitritewasgenerallyusedasthecatalystintheprocessofcatalysisoxidizingreaction.Itshoudbepointedoutthatsodiumnitriteisacarcinogen,andsomenitricoxideswereletintheprocess.Thisresultsinenvironmentalpollution.Inordertosimplifytechnology,cutdownthecostofproductanddecreasepollution,thedevelopmentdirectionofPFSmadewiththecatalysisoxidizingmethodshouldbestudyingandimprovingfurtherthemanufacturingtechnology,anddevelopingnewcatalystsandcatalystpromoterswhicharehigheffectiveandnonpoisonous.2ManufactureofPFSwithslagorwasteresidue

ItisagoodmethodofturningwasteintousefulproducttomanufacturePFSfromslagorwasteresiduecontainingoxidecompoundofiron.Itcannotonlysolvethethree-wasteproblem,andalsocutdownthecostofPFS,simplifymanufacturingtechnology,havebettereconomicbenefit.2.1ManufactureofPFSwithpyritecinder

PyritecindercanbeasarawmaterialofPFS.ThisisoneofmajormethodspreparingPFSwithslagorwasteresidue.Avastamountofpyritecinderisproducedintheproducingcourseofsulfuricacid.Itsmaincomponentsareferricoxideandferriferrousoxide.Attheaspectofthecomprehensiveutilizationofpyritecinder,thegreaterpartofpyridecinderwasusedasanassistantintheproductionofcement.

Ingeneralsituation,totalironcontentisabout65~65%inpyritecinderandferriccontentis96.5%intotaliron.Afterpyritecinderisdissolvedinsulfuricacid,thefiltratingcandirectlybeusedinthemanufactureofPFS.Thishasdevelopedanotherbetterwayforthecomprehensiveutilizationofpyritecinder.ThemanufacturingmethodofPFSusingpyritecinderiseconomical,anditscostisalsolower.Atpresent,manyprogresseshadbeenmadeinthisaspect[19-22].

ThemanufacturingprocessofPFSusingpyritecindermaybedividedintotwosteps.Thefirststepisthatpyritecinderisdissolvedinsulfuricacid:

Fe3O4+4H2SO4=Fe2(SO4)3+FeSO4+4H2O

(18)

Fe2O3+3H2SO4=Fe2(SO4)3+3H2O(19)Thesecondisoxidation,hydrolysisandpolymerization:

FeSO4＋2H2SO4＋O2＝2Fe2(SO4)3＋2H2O(20)

Fe2(SO4)3+nH2O＝Fe2(OH)n(SO4)3-n/2+(n-2)H2SO4

(21)

mFe2(OH)n(SO4)3-n/2＝[Fe2(OH)n(SO4)3-n/2]m(22)

Inthesecondstep,ferroussulfatemaybeoxidizedwithdifferentmethods.Oneisdirectedoxidation[19].Anotheriscatalysisoxidation[41].Moreover,whenthecontentofferroussulfateisverylowinthefiltrating,theoxidationmaybeleftoutandboththehydrolysisandpolymerizationcantakeplacedirectly[21,22].Inthemanufacturingprocess,itisimportanttoimprovethedissolvingrateofpyritecinderfurtherlyinsulfuricacid.Author'sstudiesindicated[23,24]thatthedissolvingrateisconcernedwithsulfuricacidconcentration,temperature,andtheratiobetweensolidandliquid.Becausethedissolvingcourseofpyritecinderisanexothermicreaction,thedissolvingratemayachieve95%undertheeffectofthereactionheat.Thecontentofferrousonlyoccupies3%ofthetotalironcontentinthefiltrating.PFScanbeobtainedthroughthehydrolyzingandthepolymerizingofferricsulfateundercertaincondition.Oxidizerisnotneededinthemanufacturingprocess.Thishasnotonlyeliminatedthepollutionofnitricoxides,andalsosavedspendingandcutdownfurtherthecostofproduct.

WhenPFSmadebyourselveswasusedinthetreatmentofpapermakingwastewater(CODCr=1000mg/L),theremovalrateofCODCrwasmorethan90%astheadditionofPFSwas150mg/L(thatis,[Fe3+]=150mg/L).Inaddition,theremovalrateofCODCrwasmorethan60%inthetreatmentofsaccharinsodiumslatwastewater(CODCr=15000mg/l)astheadditionofthePFSwas800mg/L.

Inordertoraisethedissolvingratefurtherly,pyritecindermaybepreprocessed.First,

ferricoxideinpyritecinderwasreducedasferrousoxideundertheeffectsofbothhightemperatureandreducer.Pyritecinderwaschangedintoreductiondregs.Second,thereductiondregswasdissolvedinsulfuricacid,obtainingmid-productferroussulfate.Final,PFSwasmadethroughoxidationandhydrolysisandpolymerizationasmentionedin1.2.

Itwassaidthatthismethodcanraisetheutilizationratioofpyritecinder,neverthelesstherewasnotonlyoxidizingreactionbutalsoreducingreactioninthemanufacturingprocessofPFS.Soitwillresultinlongerproducingperiodandhigherconsumption,anditspopularizationandapplicationwillbeverydifficult,too.

2.2ManufactureofPFSwithotherslagscontainingiron

Siderite,magnetiteore,ironmud,naturalironsandandopen-hearthfurnacedust[25-28]arealsotherawmaterialsofPFSbesidespyritecinder.Thecontentsofferriferrousoxideandferricoxidearehighinthem,too.

Literature[26]hadobtainedbetterresultinthemanufactureofPFSusingironmud.Ironmudisthewasteproducedintheproducingprocessofdyemediums.Itsmaincomponentareferriferrousoxideandalittleferricoxide,ferrousoxide,andironbesides.InChina,thetreatmentmethodofironmudisgenerallytostoreuportobury.Thiscauseseasilyenvironmentalpollutionagain,andtheusefulresourceinironmudisalsowasted.ItisagoodwayofwastecomprehensiveutilizationforironmudtobeusedastherawmaterialofPFS.

NaturalironsandisakindofrichmineralresourcesoftheDabieshanMountainsarea.Totalironcontentis59.6%init,andferriccontentis41.1%.ItisagoodrawmaterialofpreparingPFS.Literature[27]reported,usingnaturalironsandandsulfuricacidastherawmaterials,highconcentrationPFS(220g/L)couldbemadethroughpickling,oxidizing,andpolymerizing.Then,theliquidPFSwasconcentratedintosolidbyspray-dryingprocess.

Open-hearthfurnacedustisanotherwasteusedalsotomanufacturePFS.Itisthesmokeanddirtintheopen-hearthfurnacesteelmakingwastegas.Thecontentofferricoxideismorethan90%init.Literature[28]reportedthatthedustcouldbeusedastherawmaterialofPFS:Firstly,thedustwasdissolvedinalkalisolutionforremovingsomeimpurityinit.Thecontentofferricoxidewasmorethan99.5%inthedustpurified.ThenPFScouldbemadethroughaciddissolving,hydrolysisandpolymerization.WhenthePFSwasusedtotreatwashingwastewaterofblastfurnacegas,thetreatedefficiencywasverygood.Moreover,becausethereisnototherharmfulioninthePFS,itisverysuitableforthePFStotreatdrinkingwater.

Inotherreports,wasteresiduecontainingferricoxidewasusedtomanufacturingPFS,too.Undercertaintemperatureandpressure,PFScouldbeobtainedbydissolving,hydrolysis,polymerizationwithoutoxidizer.

Onthewhole,themanufactureofPFSbyslagsorwasteresidueisaneconomicalmethod.Thismethodissimplerthanthecatalysisoxidationmethodmentionedabove.Certainly,therearestillsomeproblemsthatshouldbesolvedfurtherlyinthemanufacturingprocessofPFS.Forexample,thedissolvingrateofslagsshouldberaisedagain,soastoraisetheutilizationrateofrawmaterial.Inaddition,thereisexcessiveacidgenerallyinthesolutionofferricsulfateobtainedbydissolvingslagsinsulfuricacid.Thiswillincreasetheconsumptionquantityofotherassistantsinthecourseofhydrolysisandpolymerization.Iftherearesomeharmfulheavymetalsinslagsandwasteresidue,therewillbesomeheavymetalionsinPFS.Thiswillrestrictitsapplicationindrinkingwatertreatment.3ManufactureofPFSwithothermethods3.1Methodofbiologicoxidation

Usingpyrite,coal,sulfur,andhydrogensulfideasrawmaterials,PFScanbemadewiththemethodofbiologiccatalyzingoxidationundertheinfluenceofiron-sulphurbacteria,suchasthiobacillusferrooxidansandthiobacillusthiooxidans.Literature[29]investigatedsomefactorswhichaffectingthemanufacturingofPFSwithbiologicoxidation.ItreportedthatthesefactorswerepH,theadditionofpyrite,temperature,stirring,andreactiontime.UndertheconditionsofpH2.0~2.3,2.8gpyrite/L,30℃,and300r.p.m.,amid-productwasobtainedin10hoursreaction.ThenPXTcoagulant(thatisPFS)wasmadethroughacidification,concentration,andaging.WhenthePXTwasusedtotreatthehighSSashwaterofpowerplant,itcoulddecreasenotonlySSbutpHandF-.

Intheprocessofbiologicoxidation,boththiobacillusferrooxidansandthiobacillusthiooxidansplayanimportantrole.Theyarethepeculiarmicro-organismswhichcanobtaincarbonresourcesfromCO2inairandliveininorganicenvironment.Theycanoxidizeironandreducesulphurintoferricandsulfuricacid,respectively.

ThepreparationofPFSwithbiologicoxidationisaverygoodway.ThewaydoesnotneedanyotherrawmaterialsbesidespyriteandalittledilutesulfuricacidusedtoadjustthepHofreactionsystem.Itischaracterizedbysimpleproces,savingenergy.Nevertheless,manystudiesshouldbedoneifthemethodofbiologicoxidationisusedinindustrialproductionofPFS.Atpresent,thismethodisstillintheinitialstageofstudyanddevelopment.3.2MethodofelectrolyticoxidationItshouldbepointedoutthattheelectrolyticoxidationofferroussulfateisalsoapreparingmethodsofPFS.First,ferroussulfatewasoxidizedintoferricsulfatewithD.C.electricityinelectrolyticbath.Then,PFSwasobtainedthroughthehydrolysisandthepolymerizationofsulfateferric.However,theelectrolyticoxidationexpendsenormouselectricenergy.Itcannotbespreadedandappliedinindustry.4ManufactureofsolidPFS

Ingeneral,theproductofPFSisliquidstate.Thisproducthasthemeritofbeingeasytouseinwastewatertreatmentprocess,butitsshortcomingisthatthecostoftransportationishigherthansolidstatebecauseofitsvalidcomponentlowerthansolid.SosomestudiesaboutthemanufactureofsolidPFShadbeenmade.

SolidproducthadbeendevelopedthoughconcentratingliquidPFS[9,12,15,27],suchasheatingevaporization,stoving,andvacuumevaporationanddrying.Wecallthesemethodsthetwo-stepprocessasitincludesboththepreparationofliquidPFSandtheconcentration.KreplkaJ[30,31]reportedthatsolidPFScouldbemanufacturedbyoxidizingthesolutionofferroussulfatewithairundertheconditionsof120~180℃and0.3~2.5MPa.Inaddition,PrasakTP[32]developedasimplemethodofmanufacturingsolidPFS:firstly,preparingsolidbasicferricsulfatebyoxidatingferroussulfatewithairinarevolvingblastfurnaceundertheconditionsof200℃and3hours,andthenobtainingsolidPFSbymakingthesolidbasicferricsulfatereactswithsulfuricacid.Theshortcomingofthemethodisthattheoxidationofferroussulfateisnotcompleteinthefirststep.Usingsolidrawmaterials,LiKechang[33]alsosucceededinmanufacturingsolidPFSthroughsolidphasereaction.

Recently,WangDuoren[34]reportedthatsolidPFScouldalsobemadebyone-stepprocess.First,mixturingthesolutionofpotassiumchlorateandthesuspensionofferroussulfate.Then,obtainingsolidgranulatedPFSundertheconditionsof100℃andpH2-3after1hourreaction.

AlthoughhavingovercometheshortcomingofthehightransportationcostofliquidPFS,solidPFSconsumesenormousheatenergyinmanufactureprocess,andithavetobedissolvedagainbeforebeingusedinflocculationprocess.SothesuitablemethodofmanufacturingPFSshouldbetomakehighconcentrationliquidPFS.

5StabilityofPFS

IfliquidPFSislong-termstored,Fe(OH)SO4sedimentwillbeproducedinPFSsolution,thatis,liquidPFSisunstable.ThestabilityofPFSisaveryuniversalandveryimportantproblem,anditmustbeconsideredinthemanufactureandtheapplicationofPFS,butthisproblemisreportedseldominmostliteraturesaboutPFS.

LiuChangrangetal.[9]hadstudiedthestabilityofPFSandpointedoutthatliquidPFS,whichwasmadefromferroussulfatewithcatalysisoxidationmethod,wasunstable.OnestabilizerwasaddedinliquidPFSinordertostrengthenthestabilityofPFS.Inaddition,ShuWangenetal.[35]andWangShicaietal.[36]hadstudiedthestabilityofpolymerizedferricchlorideandpolymerizedaluminumsulfate,re