分步沉淀法去除稀土废水中钙镁的研究黎新

、[1]。“”、-[2][3]。、[3]-。、。[4]。。11.11。1.21.2.1H2C2O4、NH4H2PO4、25%、HCl、、T、、EDTA、、EDTA、、、、。1.2.2BSA224SJB-3APB-10pHFG3Mseries(iCE3500)AASystemXRD。1.31Tab.1Maincompositionsoftheinvestigatedrareearthwastewater/(g·L-1)pH/(μS·cm-1)ρ/(mg·L-1)74.137.3060000＜41.895.5777236340.3012.254ρ/(mg·L-1)41.6311060.281380.640.0150.81119.12591221012112331.7100612.7100543.710077Ca2+、Mg2+pH、、。1.5‰pH=7.5nH2C2O4nCa2+=1.212hCa2+92.2%Mg2+MAPpH=7.5nNH4H2PO4nMg2+=0.912hCa2+81.8%Mg2+98.1%XCaC2O4MgNH4PO4·6H2O。MAPX703.1A1000-3770(2016)[e-mail][e-mail]42720167Vol.42No.7Jul.,2016DOI:10.16796/j.cnki.1000-3770.2016.07.02088。1.3.11pH300mLpH6.0、6.5、7.0、7.5、8.0、8.520min18hCa2+、Mg2+。2300mLn(H2C2O4):n(Ca2+)1.00:1、1.10:1、1.15:1、1.20:1、1.25:1、1.30:1、1.35:1pH7.520min18hCa2+、Mg2+。3300mL1.5‰n(H2C2O4):n(Ca2+)1.5:1pH7.51、2、4、6、8、22、26hCa2+、Mg2+。4300mL0‰、0.5‰、1.0‰、1.5‰、2.0‰、2.5‰、3.0‰n(H2C2O4):n(Ca2+)1.5:1pH7.52hCa2+、Mg2+。1.3.21pH300mLpH7.0、7.5、8.0、8.5、9.020min18hCa2+、Mg2+。2300mLn(NH4H2PO4):n(Mg2+)0.70:1、0.75:1、0.80:1、0.85:1、0.90:1、0.95:1、1.00:1pH7.520min18hCa2+、Mg2+。3300mL0‰、0.5‰、1.0‰、1.5‰、2.0‰、2.5‰、3.0‰n(H3PO4):n(Mg2+)0.91pH7.52hCa2+、Mg2+。22.12.1.1pHn(H2C2O4):n(Ca2+)=1:118hCa2+pH1。1n(H2C2O4):n(Ca2+)=1:1pHCa2+75%～82%pHCa2+。Mg2+。Ca2+C2O42-+Ca2+=CaC2O4↓。1Ksp(CaC2O4=[C2O42-]e[Ca2+]e=2.57×10-9。H2C2O4、HC2O4-C2O42-[5]Ca2+C2O42-。pH=6.0[5]99%C2O42-pHC2O42-Ca2+。7.5pH。2.1.2pH=7.518hCa2+Mg2+n(H2C2O4):n(Ca2+)2。2pH=7.5n(H2C2O4):n(Ca2+)Ca2+n(H2C2O4):n(Ca2+)＞1.20:1Ca2+92%～95%。C2O42-n(H2C2O4):n(Ca2+)1Ca2+5.56.06.57.07.58.08.59.0050100150200250300350400
Ca
CapH/%0102030405060708090100ρ(Ca2+)/(mg·L-1)1pHCa2+Fig.1EffectofpHontheremovalratioofCa2+1.001.051.101.151.201.251.301.35020406080100120140160180200
/%
5060708090100ρ(Ca2+)/(mg·L-1)n(H2C2O4):n(Ca2+)2n(H2C2O4):n(Ca2+)Ca2+Fig.2Effectofn(H2C2O4):n(Ca2+)ontheremovalratioofCa2+89。1.2:11000mL2.54g。2.1.31.5‰pH=7.5n(H2C2O4):n(Ca2+)=1.5:1Ca2+3。30～1hCa2+540mg/L154mg/L2～8hCa2+123mg/L69.2mg/L8～26hCa2+70mg/L0～1hCa2+540mg/L189mg/L2～22hCa2+171mg/L94.9mg/L22hCa2+94mg/L。。[6]、Ca2+。。[7]。2h。2.1.4n(H2C2O4):n(Ca2+)=1.5:1pH=7.52hCa2+4。4Ca2+。＜2.0‰Ca2+2.0‰Ca2+。[8][9]Ca2+。Ca2+2.0‰Ca2+。42.5‰1.5‰。2.2MAPMgNH4PO4·6H2O[10]2.2.1pHn(NH4H2PO4):n(Mg2+)=1:12hCa2+Mg2+pH5。5n(NH4H2PO4):n(Mg2+)=1:1ρ/(mg·L-1)5pHCa2+、Mg2+Fig.5EffectofpHontheremovalratioofCa2+andMg2+7.07.58.08.59.00102030405060pH
Ca
Mg0.00.51.01.52.02.53.00306090120150180210240
/%CaCa
0102030405060708090100ρ(Ca2+)/(mg·L-1)/%4Ca2+Fig.4Effectofthecrystalseed(calciumoxalate)amountontheremovalratioofCa2+0510152025300100200300400500600
/% ρ ρ

 ρ/h0102030405060708090100ρ(Ca2+)/(mg·L-1)3Ca2+Fig.3EffectofagingtimeontheremovalratioofCa2+42790pHCa2+pH7.0～7.5Mg2+pH＞7.5Mg2+99.6%。NH4H2PO4Mg2+3Ca2++2PO43-=Ca3(PO4)2↓。2Mg2++NH4++HPO42-+6H2O＝MgNH4H2PO·6H2O↓+H+。3Ksp[Ca3(PO4)2]=2.0×10-29Ksp(MgNH4PO4)=2.5×10-13Ksp[Ca3(PO4)2]＜＜KspMgNH4PO4。Ca2+Mg2+Ca2+10mg/L。MAP[11]pH[H+]MAPpH＜9.0MAPpH[12]MAPMg2+pH。7.5pH1000mL19.9g。2.2.2pH=7.52hCa2+Mg2+n(NH4H2PO4):n(Mg2+)6。pH=7.5n(NH4H2PO4):n(Mg2+)Mg2+n(NH4H2PO4):n(Mg2+)=0.90:10.95:1Mg2+97%。Ca2+n(NH4H2PO4):n(Mg2+)5～10mg/L。[11]n(NH4H2PO4):n(Mg2+)HPO42-Mg2+Ca2+。0.9:1。2.2.3n(H3PO4):n(Mg2+=0.9:1pH=7.52hMg2+7。7Mg2+。。2.3Ca(C2O4)·H2OC2H2CaO5。。311.5‰pH=7.5n(H2C2O4):n(Ca2+)=1.2:12hCa2+61.1mg/L92.2%Mg2+。2pH=7.5n(NH4H2PO4):n(Mg2+)=0.9:12hCa2+20.74mg/L81.8%Mg2+70.05mg/L98.1%。3XCaC2O4。7Mg2+Fig.7Effectofthecrystalseed(struvite)amountontheremovalratioofMg2+0.00.51.01.52.02.53.0200250300350400450500550600
/%
0102030405060708090100ρ(Mg2+)/(mg·L-1)/%0.700.750.800.850.900.951.000100200300400500600700800
Ca
Mgρ/(mg·L-1)n(NH4H2PO4):n(Mg2+)6n(NH4H2PO4):n(Mg2+)Mg2+Ca2+Fig.6Effectofn(NH4H2PO4):n(Mg2+)ontheremovalratioofMg2+andCa2+91StudyonRemovalofCalciumandMagnesiuminRareEarthWastewaterbyStepwisePrecipitationLiXin1,2,SunChangshun1,ZhaoJianjun1,2,JinXiaochun3,LuQiang3(1.ShaanxiProvincialAcademyofEnvironmentalScience,710061;2.Chang′anUniversity,710054;3.ShaanxiHualuGreenEnvironmentChemicalEngineeringCo.Ltd.,710077:Xi′an,China)Abstract:TherareearthwastewatercontainslargeamountsofCa2+andMg2+.Inordertoreducetheeffectofevaporationormembranefoulingtreatmentprocess,thisexperimentadoptsthemethodofstepwiseprecipitationforcalciumandmagnesiumremoval,namelyaddingoxalicacidandphosphatesuccessivelytothewastewater,producingcalciumoxalateandmagnesiumammoniumphosphateprecipitationrespectively,mainlystudiedpHvalue,dosageofprecipitationagent,agingtimeandseedamounthowtoaffecttheremovalefficiencyofthecalciumandmagnesium.Theresultsshowedthat,theoptimumconditionofCaC2O4precipitatewasseed(calciumoxalate)amount=1.5perthousand,pH=7.5,n(H2C2O4):n(Ca2+)=1.2:1,agingtimewas2hours,theremovalratioofCa2+reached92.2%,atthistime,theconcentrationofMg2+wasalmostunchanged;theoptimumconditionofMAPprecipitatewaspH=7.5,n(NH4H3PO4):n(Mg2+)=0.9:1,agingtimewas2hours,theremovalratioofCa2+reached81.8%,andtheremovalratioofMg2+reached98.1%;thesedimentswereCaC2O4a