SolidâLiquid Equilibria for (NaNO3 + NaCl + H2O) and (NaNO3 +

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Solid−Liquid Equilibria for (NaNO3 + NaCl + H2O) and (NaNO3 + Na2CO3 + H2O) Systems at 313.15 K Jing Cao, Manxin Ding, and Yongsheng Ren*

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State Key Laboratory of High-Efficiency Coal Utilization and Green Chemical Engineering, School of Chemistry & Chemical Engineering, Ningxia University, Yinchuan 750021, P.R. China ABSTRACT: The salt mixture crystallized and buried underground, as hazardous waste, is not only harmful to the environment but also causes low pollution use resources. Thus, to research the gradual separation processes of pure salts crystallized from high salinity brine of MTO in coal-chemical industry is momentous. The thermodynamic equilibrium of Na+//Cl−, SO42−, NO3−, CO32− −H2O quinary system is essential to realize zero emissions for high salinity wastewater of MTO. Development of coal chemical industry in high salinity wastewater treatment technology includes the production of sodium sulfate, sodium chloride, nitrate sodium, sodium carbonate (refined industrial salt), and water recycling technology. The phase diagram of salt-water system plays a role in predicting and guiding the purification process, especially crystallization process. The phase equilibrium and physicochemical properties of NaNO3 + NaCl + H2O and NaNO3 + Na2CO3 + H2O systems at the temperature of 313.15 K were obtained by the method of isothermal solution saturation. The results showed that one invariant point, two univariant curves, and three crystallization fields are existed in both of systems. Each invariant point in the phase diagrams was analyzed. The physical properties (η, ρ, pH, nD) of the systems change regularly with composition change of liquid solution. The quaternary phase equilibrium in Na+//C1−, CO32−, NO3− −H2O system at 313.15 K was also researched by means of the thorough and intermediate translation techniques together. Thus, the research results, especially the crystalline regions, would be of great value in designing and optimizing the crystallization process of NaCl and other salts in high salinity brine treated of Methanol to Olefins (MTO) technology.

1. INTRODUCTION With the rapid development of the coal-chemistry industry, wastewater treatment has gradually become a hot spot.1 Typical moderncoalchemicalwastewatercanbedividedintotwocategories accordingtosaltcontent:oneisorganicwastewater,mainlyfromcoal gasificationprocesswastewateranddomesticsewage;itscharacteristicsarelowsaltcontentwiththemainpollutantbeingCOD,andthe other is high salinity water. It mainly comes from the production processofgaswashingwastewater,thedrainageofcirculatingwater system,thedrainageofdehydrationsystem,thereuseofconcentrated waterfromthesystem,andsometimesthebiochemicaltreatmentof organicwastewater,whichischaracterizedbyhighsalinitycontent. The60to70%ofthewastewatercontainsalargeamountofinorganic ions,suchasNa+,Cl−,SO42−,NO3−,CO32−.Ingeneral,thewastewater ismainlyconcentratedbymembranefiltrationtoimprovethetotal recoveryofindustrialwater.Theremaininghighsalinitywastewateris usuallytreatedwithevaporationprocess.2,3Asaresult,themixedsaltis crystallizedandburiedunderground.However,ashazardouswaste themixedsaltisharmfultotheenvironmentandcausedpollutionuse resources.4−6Thus,tostudythegradualseparationprocessesofpure salts crystallized from coal-chemical industry high salinity wastewaterismomentous.Thesalt-watersystemphasediagramplaysarole inpredictingandguidingthepurificationprocess. Atpresent,themultistageseparationmethodofNaClandNa2SO4 basedonthephaseequilibriuaofNa+//Cl−,SO42−−H2Osystemwas commonly investigated.7−9 However, due to the increase in the ©XXXXAmericanChemicalSociety

concentrationofnitrateandcarbonateionsduringtheconcentration process,itisalsonecessarytoconsidersodiumnitrate(NaNO3)and sodiumcarbonate(Na2CO3)inthesystem.Inotherwords,toachieve zerodischargeofcoal-chemicalindustrywastewater,thethermodynamicequilibriumofthequinarysystemofNa+//Cl−,SO42−,NO3−, CO32− −H2Oisnecessarytobestudied.10−12 Developmentofcoal chemicalindustryinhighsalinitywastewaterextractiontechnology includestheproductionofsodiumsulfate,sodiumchloride,nitrate sodium,sodiumcarbonate(refinedindustrialsalt)andcreateswater recyclingtechnology. The phase equilibria and diagram of solid−liquid system is theoreticalandofpracticalimportancetothecrystallizationprocess.9 Therefore,solid−liquidequilibriumof(NaNO3+NaCl+H2O)and (NaNO3+Na2CO3+H2O)atT=313.15Kisrequiredfordevelopment of coal chemical industry in high salinity wastewater extraction technology. Moreover, it is applicable to other crystallization processes involving the systems of our research. Therefore, it is essentialtoobtainandprovidemorephaseequilibriadatafor(NaNO3 +NaCl+H2O)and(NaNO3+Na2CO3+H2O)systemsatT=313.15K. TheaimofthisresearchistoobtainthephaseequilibriainNa+//Cl−, CO32−,NO3− −H2Oquinary systemat313.15Kbythe translation methodofpredictionofphaseequilibriaandconstructionofclosed Received: May 18, 2018 Accepted: January 9, 2019

A

DOI: 10.1021/acs.jced.8b00415 J.Chem.Eng.DataXXXX,XXX,XXX−XXX

JournalofChemical&EngineeringData

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phase diagrams for multicomponent systems.13,14 The method applied is derived from the compatibility principle15 of physicochemical analysis and obtains schematic phase equilibria diagrams.16−18 Inaddition,regardinghigh-salinitywastewater,wehavealsomadea numberofcommentsonothersectorswithhighsalinitywastewater, such as the shale gas production with different desalination proceduresandwiththephilosophyofzeroliquiddischargehaving beenstudied,suchasmultistageevaporationwithmechanicalvapor recompression,membranedistillation,andsoforth.

A constant temperature bath oscillator (SHZ-C, Shanghai Langgan Laboratory Equipment Co., Ltd.) with a temperature range from 293.15 to 373.15 K was used for the phase equilibria experiments. A super constant-temperature water bath (XMTD4000type,ZhengzhouYingYuYuhuaInstrumentCo.,Ltd.)wasused to keep 313.15 K temperature. The temperature of oscillator and constant-temperaturewaterbathcouldbecontrolledto±0.05K.An AutomaticKjeldahlAnalyzer(ShanghaiPeiouAnalysisInstrument Co.Ltd.,China)wasusedformeasuringtheNO3−concentrationofthe equilibratedsolution. 2.2. Experimental Method. The phase equilibria data was determined by isothermal solution saturation method19 and Schreinemaker’swetresiduemethod20−23 inthisstudy.Atacertain temperature,thesaturatedsolutionswereobtainedbyputtinginan excess ofNaNO3 orNaCltowateruntilNaNO3 or NaClcannotbe dissolved anymore. The solid−liquid phase equilibrium data in aqueous NaCl and NaNO3 solutions were obtained in this way. AlthoughNaNO3 andNaClarepresentinthesolution,onlyNaClor NaNO3issaturatedbeforethesolutionreachescosaturation.Thus,a series of points that represent the solubility of NaCl or NaNO3 in saturatedsolutionswereobtained.Thesolubilityof(NaCl+NaNO3+ H2O)systemcanalsobedeterminedbythesameway. To future study the NaNO3 (NaCl) saturated (solid + liquid) equilibrium of the NaCl−NaNO3−H2O system, an initial (solid + liquid)mixturewithwaterandNaNO3(NaCl)wasputinaconicalflask (250 mL). Then, the flask was sealed and placed in a constant temperaturewaterbathoscillator,whichwascontinuouslyvibrated and the temperature was controlled at 313.15 K. The actual temperature was controlled by a mercury thermometer (u(T) = ±0.05K).Whenthecomponentsofthesolutiondidnotchange,the solid−liquid equilibrium state was established in the system. Preliminary experimental results showed that 4 h was enough to reachequilibrium.Afterstirringfor4h,thesampleswerestoredinastop shakerfor16htoprecipitatetheremainingsolid.Thetemperaturewas maintainedaround313.15K(u=0.05K).Whentheoperationreached equilibrium,thesaturatedsolutionwastransferredtoabeaker(100

2. METHODOLOGY 2.1. Materials and Instruments. The chemicals used in this research are of analytical grade; Na2CO3 and NaNO3 are obtained fromSinopharmChemicalReagentCo.Ltd.andNaClispurchased fromTianjinKermelChemicalReagentCo.Ltd.,China.Allchemicals werewithoutfurtherpurification.Doublydeionizedwater(electrical conductivity≤10−4S·m−1)wasusedinthisresearch.Theinformation onallchemicalsusedintheresearcharelistedinTable1. Table1.InformationoftheMaterialsUsed chemicals

purity (mass fraction)

CASNo.

NaNO3

≥99.0%

7631−99−4

Na2CO3

≥99.8%

497−19−8

NaCl

≥99.5%

7647−14−5

analytical methoda potassium dichromate oxidation acid−base titration Volhard method

sources Sinopharm Chemicalreagent Co.Ltd. Sinopharm Chemicalreagent Co.Ltd. TianjinKermel ChemicalReagent Co.Ltd.,China

a Standard uncertainties u (mass fraction) are u(NaCl) = 0.005, u(NaNO3) = 0.004, u(Na2CO3) = 0.002.

Figure1.Typicalcoalchemicalwastewatertreatmentprocess. B



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Figure2.Evaporationcrystallizationsectionoftheexistingproblems.

synthesis is used to emphasize the participation of each entity in a multicomponentsystem.16−18

mL)atT=313.15K,thenaccuratelytransferredtothetotalmassofthe liquidphase.Acertainliquidphasemasswasplacedinavolumetricflask with a dropper and diluted with deionized water to the target for analysis.Moreover,remainderofliquidphaseswereusedtomeasure nD,η,ρ,andpHproperties.Thewetresiduesweretransferredtoabeaker withspoon.Similarly,theweightofthewetresidueswasmeasured, which was then dissolved in deionized water and the solution was transferredtoavolumetricflask(100mL)anddilutedwithdeionized water.Thebeakerwasrinsedfivetoseventimestoensurethatallwet residuesweretransferredintotheflask. Theabove-mentionedsampleswerequantitativelyanalyzed.The wetsolidphasewasseparatedanddriedat313.15Kandidentifiedby XRD (powder X-ray diffraction analyzer; D/MARX2200/PC, Japan).FortheNa2CO3−NaNO3−H2Osystem,theexperimental methodandprocessisthesameasNaCl−NaNO3−H2Osystem. 2.3.AnalyticalMethod.NO3− andCO32− concentrationwas determinedbythedichromateoxidationmethodwithuncertaintyof 0.006(massfraction)andneutralizationtitration24withuncertainty of0.002,respectively.Cl−andNa+concentrationwasdeterminedby Volhard method25,26 with uncertainty of 0.005 and ion balance methodwithuncertaintyof0.005,respectively.27Informationofthe above-mentionedanalyticalmethodsarelistedintheliterature.28,29 The physicochemical properties (nD, η, ρ, pH) of solution were measured.Density(ρ),pH,viscosity(η),andrefractiveindex(nD) weremeasuredwithaspecificweighingbottlemethod(anuncertainty 0.005g·cm−3),30 aPB-10pHmetersuppliedbySartoriusScientific Instruments(standarduncertaintyof0.1),anUbbelohdecapillary viscometer, which average relative deviation of the flow time measurements was 0.02 s, and an Abbe refractometer (WAY-2S) (standard uncertainty of 0.0002),31 respectively. All the measurementsweremaintainedataconstanttemperature.Physicalproperties oftheliquid-phaseweredeterminedforthedesignofthecrystallizer. 2.4.DeterminationofPhaseEquilibriaUsingTranslation Method.Theequilibriadataofn-componentsubsystemsareusedto predict the (n + 1)-component phase equilibria by the method of translationmethodasfollows.Todeterminetheinvariantpointsinthe entiresystemtogenerateadditional(curves,fields)geometryatthis level,thetheoreticalbasisofwhichweretheGibbs’phaseruleandstems from compatibility principle of physicochemical analysis. This methodiswelldescribedintheexistingliteratureandinvolvesthree techniques.Inthisresearch,thesamemethodwasusedtopredictof Na+//Cl−, CO32−, NO3− −H2O system phase diagrams and construction of comprehensive phase diagram at 313.15K, “thorough translation technique”, will be required. The word

3. RESULTSANDDISCUSSION 3.1. Source Analysis of High Salinity Brine. Typical coal chemicalwastewatertreatmentprogramisshowninFigure1.First,the Table2.EvaporationCrystallizationWaterQualityofaCoal ChemicalEnterpriseinNingxia no.

testitems

concentrateddesignpoint(mg·L−1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

pH TDS NH4+ +NH3 K+ Na+ Mg2+ Ca2+ Sr2+ Ba2+ CO32− HCO3− NO3− Cl− F− SO42− SiO2 CO2

7.58 42079.28 21.54 829.5 13292.14 140.06 320.66 9.62 0.41 15.98 356.7 841.26 8597.24 3.02 17554.29 97.03 5.1

organicwastewateristreatedbyacidification,biochemistry,filtration and the like to remove the sludge, and the qualified salt wastewater passesthestandard;thesaltywastewateristreatedbyclarified,filtered, ultrafiltered and reverse osmosis to become concentrated brine; treatment, filtration, reverse osmosis is performed to achieve the required high salinity brine. Finally, the high salt water curing is performed. High salinity wastewater curing treatment is generally divided into two parts: membrane reduction and evaporation crystallization. Our main research direction is to evaporate the crystalline part of the crystalline salt. Evaporation crystallization sectionmainlyshowsevaporationandcrystallizationastwoparts.As showninFigure2,therearestillsomeproblemsandsomescientific problems to be solved in the current evaporative crystallization section.Forexample,theevaporatingsectionplateheatexchangeris easytoscaleandthewaterdistributor/evaporatingchamberiseasyto corrode,scale,andsoforth.Weneedtobalancethecostandeconomic C



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Table3.SolubilityinWateratT=313.15KandP=88.35kPa ourwork

literature

substance

solubility/(wt%)

standarduncertainty/(wt%)

solubility/(wt%)

NaCl Na2CO3 NaNO3

26.88 32.82 51.61

0.005 0.002 0.006

26.9333 26.70134 26.8035 32.8036 51.2737

Table4.AComparisonofDensity,Solubility(S)inPureWater(wt%)forSaturatedSolutionsbetweenOurWork(atT=313.15KandP=88.35 kPa)andLiteratureData Na2CO3−H2O

NaCl−H2O no. 1 2 3 4 5 6 7

T/K 273.15 288.15 293.15 298.15 313.15 323.15 356.15

S/(wt%)

ρ/(g·cm−3)

NaNO3−H2O

ρ/(g·cm−3)

S/(wt%)

S/(wt%)

26.3 26.4038 26.537 26.88 26.938 27.638

ρ/(g·cm−3)

38

14.1 18.1 22.78 32.82 32.332

1.19840 1.1977831 1.1930 1.18540

42.2 45.637 46.7739 47.837 51.61 53.337 60.437

1.1515 1.1941 1.2416 1.3558 1.323532

1.39240 1.4179 1.42740

a Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.5 kPa, u(ρ) = 0.005 g·cm−3, u(S(NaCl)) = 0.005, u(S(NaNO3)) = 0.006, u(S(Na2CO3)) = 0.002.

Table5.Solid−LiquidEquilibriaandPhysicochemicalPropertiesofSaturatedSolutionsofNaCl+NaNO3+H2OatT=313.15KandP=88.35 kPa liquidphasecomposition(100w)

wetresiduecomposition(100w)

physicochemicalpropertiesofliquidphase

number

100w1b

100w2b

100w1

100w2

ρ/(g·cm−3)

η/10−3 Pa·s

equilibriumsolidphasea

1,E 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

51.61 49.28 47.18 45.84 44.27 42.98 41.40 41.16 38.67 38.68 37.64 36.21 34.16 32.33 29.36 26.43 23.99 21.57 18.87 16.06 13.23 9.72 6.66 3.42 0.00

0.00 1.26 2.45 3.81 4.95 6.36 7.78 8.81 10.90 10.80 11.30 12.22 12.82 13.50 14.46 15.13 16.14 17.25 18.36 18.89 20.13 22.54 23.64 25.09 26.88

NDc 82.96 86.89 84.30 84.50 81.18 77.60 84.37 73.35 21.74 13.91 11.95 10.85 10.67 9.45 8.80 8.85 7.49 6.41 5.65 5.34 4.17 3.14 1.96 ND

ND 0.54 1.02 1.47 1.97 2.57 2.55 2.81 5.54 58.13 68.93 71.94 71.33 71.66 74.18 72.43 72.20 74.07 69.97 70.03 64.77 71.27 72.01 71.31 ND

1.4179 1.4140 1.4100 1.4082 1.4048 1.4005 1.3985 1.3923 1.3913 1.3923 1.3848 1.3723 1.3626 1.3506 1.3364 1.3230 1.3092 1.2955 1.2814 1.2682 1.2550 1.2389 1.2227 1.2087 1.1930

2.1839 2.1990 2.2315 2.2325 2.2636 2.2734 2.3214 2.3236 2.3825 2.3876 2.3931 2.2224 2.1406 2.0460 2.0107 1.9073 1.7951 1.7035 1.6737 1.5719 1.5110 1.4090 1.3629 1.2896 1.2369

N N N N N N N N N+Cl N+Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl

Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.5 kPa, u(w1) = 0.006, u(w2) = 0.005, u(ρ) =0.005 g·cm−3, and ur(η) = 0.1. bw1, mass fraction of NaNO3, w2, mass fraction of NaCl. cND, not determined. dCl, NaCl; N, NaNO3 a

andHCO3−isconvertedtoCO2,thesetwoionsofthisprojectarenot expectedtoexist.Aftertheevaporation,crystallizationstillexists,for Na2CO3 and NaNO3 crystallization process, of the production of Na2CO3 andNaNO3. 3.2. Determination of Solid−Liquid Phase Equilibrium. 3.2.1.DataComparison.Agreatdealofresearchershaspreviously reportedsolubilitydataofbinarysystems(NaCl−H2O,Na2CO3−

benefitsoftheproblem.Therefore,itisparticularlyimportanttosolve theevaporationandcrystallizationpartofhighsaltwatertreatment. This research project aims to take the Ningxia coal chemical enterprises of high salinity brine processing technology as the background, seen in Table 2, from the main problems in the evaporationandcrystallizationbeforeNa+,SO42−,Cl−,NO3−,CO32− andHCO3−.However,afterevaporationcrystallizationafterCO32− D



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Figure3.Phasediagramfor(NaCl+NaNO3+H2O)systematT=313.15Kand P = 88.35 kPa. □, composition of moist solid phase; ●, composition of equilibriumliquidphase;100w1,NaNO3wt%;100w,NaClwt%;U,H2O;A, represents pure NaNO3 solid; W, represents NaCl; C, NaNO3 and NaCl invariantpoint;E,solubilityofNaNO3;F,solubilityofNaCl.

Figure 5. Phase diagram for (NaNO3 + NaCl+ H2O) system at T = (298.15,313.15 and 323.15) K.▼, literature data at T = 298.15 K;37 ■, literaturedataatT=323.15K37;●,ourexperimentdataatT=313.15K;100w1, NaNO3wt%;100w2,NaClwt%;U,H2O;A,NaNO3solid;W,NaClpuresolid; C,NaNO3 andNaClinvariantpointatT=313.15K;M,NaNO3 andNaCl invariantpointatT=298.15K.

Table6.InvariantPointCompositionof(NaNO3 +NaCl+H2O) SystemofDifferentTemperature thecompositionofinvariant point(100w) no. 38

273.15K 288.15K38 298.15K38 41 308.15K41 313.15K 323.15K38 356.15K38

NaCl

NaNO3

equibriumsolidphase

17.0 15.1 13.3 13.34 11.62 10.90 10.1 7.9

26.2 28.6 32.0 31.47 36.12 38.67 41.5 50.2

NaCl+NaNO3 NaCl+NaNO3 NaCl+NaNO3 NaCl+NaNO3 NaCl+NaNO3 NaCl+NaNO3 NaCl+NaNO3 NaCl+NaNO3

Figure6.DensityvstemperatureTforNaNO3−H2Osaturatedsolutions.■, literature;37 ●,Exp.

Toensurethedataquality,obtainedexperimentaldatainourresearch werealsolistedinTable3.Bycomparingwiththeliterature,itisfound thatexperimentalmethodsandthedataqualityinourwordisenough accuracy. As can be seen in Table 4, the measured data is consistent with literaturedataandisconsistentwiththetrend.Butthereareseveraldata thatdonotfitthistrend,especiallyρofNa2CO3−H2OatT=323.15Kin ref32andsolubilityinpurewaterdataofNa2CO3−H2OatT=323.15K. Accordingtotheliterature,Na2CO3solubilityincreasessharplywith thetemperatureincrease.Whentemperatureexceeds313.15K,the solubility decreases slowly. Maybe, the density changes with the solubility.AlthoughρofNa2CO3−H2Ois1.3235g·cm−3atT=323.15 K,32 itis1.3558g·cm−3 atT=313.15Kinthisstudy.Exceptforthese literaturedata,itisfoundthatdensityvalueandsolubilityofNa2CO3− H2O,NaCl−H2OandNaNO3−H2OatT=313.15Kcanbecompared withliteraturedata. 3.2.2. The Ternary System (NaNO3 + NaCl + H2O) at 313.15 K. Experimentaldataandphysicochemicalproperties(ρ,η)of(NaNO3

Figure4.Solid−liquidequilibriadatafor(NaNO3+NaCl+H2O)system.▼, ref38dataat323.15K; ■,ourexperimentaldataat313.15K; ▲,ref38dataat 298.15K; ●,literaturedata38 at288.15K.

H2O,NaNO3−H2O)atT=313.15K.Table3collectedthereported solubilityrelativetooursystems.AsshowninTable4,refractiveindex anddensitydataofseveralbinarysystemsinliteraturewerealsolisted. E



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+NaCl+H2O)systemat313.15KareshowninTable5andthephase diagramforthestudiedsystemisshowninFigure3. AsshowninFigure3,pointsA,U,andWrepresentNaNO3,H2O, NaCl,respectively.ThepointsE,FrepresentthesolubilityofNaNO3 andNaClatT=313.15K,correspondingto50.84and26.88(100w), respectively;Cisaninvariantpoint,whichindicatesthecosaturated solution of NaNO3 and NaCl. Composition of corresponding equilibratedsolutionatinvariantpointCisw(NaNO3)=38.67wt%, w(NaCl)=10.90wt%.Theresultsshowedthatoneinvariantpoint,two univariantcurves,threecrystallizedregionsinthissystemexisted.EC and FC are saturation curves and correspond to the solid phase of NaNO3 and NaCl, respectively. Connecting the points of the equilibrium liquid phase and wet solid phase along EC curve, the extended point of intersection of these tie-lines represent the solid phasecomponentforNaNO3.CurveECshowsthatNaClhasbeen saturatedinwaterandNaNO3hasbeenprecipitated.Linkingpointsin FCandcorrespondingpointsofwetresidue,thenextendingthem,the intersectionpointsofprolongedtie-linesareapproximatelythesolidphasecomponentofNaCl.Therefore,itcanbeconcludedthatthere aretherecrystallizationregionsandoneunsaturatedsolutionregion. ThreecrystallizationfieldscorrespondtoNaCl(I),NaNO3(II),and (NaCl+NaNO3)(III)mixedfield.FieldEUFC(IV)correspondsto unsaturatedsolution.Itcanbealsoseenthatcrystallizationregionof NaClismuchlargerthanregionofNaNO3 (II). HölzlandCrotogino38 reportedequilibriumdataatT=(273.15, 288.15, 298.15, 323.15, 356.15, 376.15) K for the ternary system (NaNO3+NaCl+H2O).Furthermore,Nikolajew41haddetermined this system at T = (288.15,298.15, 308.15) K. By comparison with literature values, quality of determined data can be examined. Reportedsolubilitydatainreferenceswereplottedbetween288.15 and 323.15 K in Table 6. From Figure 4, it can be seen that there is significantconsistencybetweenourexperimentalresultsandfromref 38at(288.15,298.15,323.15)Kfor(NaNO3+NaCl+H2O)system, though solubilities determined in our work are higher than the literaturevalues.Therefore,itispossibletoanalyzethereporteddatain ref38withotherdataforthestudiedsystem. Figure5showsthecomparisonofsolubilityvaluesfor(NaNO3 + NaCl+H2O)systematT=(298.15,323.15and313.15)K.InFigure5,a similar tendency is seen between references’ data and our experimentaldataofsaturatedsolutionfor(NaNO3 +NaCl+H2O) systematT=(293.15,323.15and313.15)K.ItcanbeseeninFigure5 thatsolubilityofNaClalwaysdecreasedwithNaNO3concentration increasing.DissolutionequilibriumofNaNO3andNaClisshownineq 1andeq2.

Figure7.Densityversusw(NaNO3)insaturatedsolutionsof(NaNO3+NaCl +H2O)systemat313.15K,88.35kPa.

Figure8.Viscosityversusw(NaNO3)insaturatedsolutionsof(NaNO3 + NaCl+H2O)systematT=313.15K,88.35kPa.

NaCl (s) ↔ Na + (aq) + Cl− (aq)

(1)

NaNO3 (s) ↔ Na + (aq) + NO3− (aq)

(2)

WhenNaNO3solidwasaddedintotheNaClsaturatedsolutionand dissolved, the Na+ concentration increased. Equilibrium in eq 1 movedtotheleftduetothecommonioneffect.Also, (a) NaClhasasignificantinhibitoryinfluencethedissolutionof NaNO3. (b) Withtemperatureincreasingfrom(298.15to313.15)K,the invariant point moves from point M to C; with temperature increasing from (313.15 to 323.15) K, the invariant point movesfrompointCtoP. c) NaCl and NaNO3 crystallization regions reduce a little with temperatureincreasing. d) NaClcrystallizationregionismuchlargerthanNaNO3region atT=(298.15,313.15,and323.15)K.Thisismainlybecausethe solubilityofNaClislow.

Figure9.PhasediagramforNaNO3+Na2CO3+H2Osystemat313.15KandP =88.35kPa. □,moistsolidphasecomposition; ●,equilibriumliquidphase composition;100w1,NaNO3wt%;100w2,Na2CO3wt%;U,H2O;A,NaNO3 solid;D,Na2CO3solid;S,Na2CO3andNaNO3invariantpoint;G,solubilityof NaNO3 at313.15K;H,solubilityofNa2CO3 at313.15K.

F



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Table7.EquilibriaandPhysicochemicalPropertiesofSaturatedSolutionsfor(Na2CO3+NaNO3+H2O)systematT=313.15K,P=88.35kPa liquidphasecomposition (100w)

wetresiduecompositionof (100w)

physicochemicalpropertiesofsolution

number

100w1b

100w2b

100w1

100w2

ρ/(g·cm−3)

η/10−3 Pa·s

nD

pH

equilibriumsolidphasea

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

51.61 49.60 44.05 42.43 42.27 40.45 39.11 36.21 33.93 32.89 27.22 22.92 19.27 14.64 10.02 5.02 0.00

0 2.44 7.37 8.89 9.05 9.14 9.62 11.38 12.53 13.73 15.82 18.26 20.60 23.11 26.11 29.34 32.82

NDc 92.48 89.44 79.78 69.82 19.29 18.91 18.53 16.04 13.31 11.81 8.46 6.73 5.12 3.59 2.11 ND

ND 0.68 2.32 4.49 11.75 55.86 49.97 48.82 56.14 56.03 61.87 63.33 70.34 68.02 66.39 67.36 ND

1.4179 1.4205 1.4351 1.4359 1.4341 1.4288 1.4258 1.4091 1.4024 1.3948 1.3868 1.3804 1.3704 1.3635 1.3566 1.3553 1.3558

2.1839 2.4819 3.3742 3.5463 3.5650 3.5023 3.5524 3.6567 3.7085 3.7767 3.9387 4.0211 4.3339 5.0941 5.5955 6.5902 7.9678

1.3888 1.3911 1.3945 1.3958 1.3960 1.3961 1.3960 1.3951 1.3946 1.3939 1.3938 1.3933 1.3945 1.3947 1.3958 1.3966 1.3977

8.051 10.828 11.154 11.224 11.304 11.113 11.148 11.149 11.173 11.204 11.266 11.321 11.371 11.434 11.479 11.553 11.678

N N N N N+C C C C C C C C C C C C C

Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.5 kPa, u(w1) = 0.006, u(w2) = 0.002, u(ρ) = 0.005 g·cm−3, ur(η) = 0.1, u(nD) = 0.0002, and u(pH) = 0.1. bw1, NaNO3 mass fraction; w2, Na2CO3 mass fraction. cND, not determined. dN, NaNO3; C, Na2CO3·H2O

a

Figure10.Densityversusw(NaNO3)insaturatedsolutionsof(NaNO3 + Na2CO3 +H2O)systematT=313.15K,88.35kPa.

Figure11.Viscosityversusw(NaNO3)inthesaturatedsolutionsof(NaNO3 +Na2CO3 +H2O)systemat313.15K,88.35kPa.

Experimental data of physicochemical properties (ρ, η) for (NaNO3+NaCl+H2O)systematT=313.15KwerelistedinTable5. DiagramsofmassconcentrationofNaNO3 andphysicalproperties areshowninFigures6−8.Asweknow,independentvariablesnumber for saturated solution is three, namely pressure, temperature and concentrationofNaNO3.Therefore,ourexperimentalsolutionsare saturated for this system. It can be seen that physicochemical propertiesofthissystemchangedregularlywiththeconcentrationof NaNO3.NaNO3hashighsolubilityandcommonioneffectonNaCl. Thus, NaNO 3 concentration is a main factor effecting on physicochemicalpropertiesvalues. Density for (NaNO3 + H2O) system can be found in literature studies.37−39Figure6isshownacomparisonofdensityfor(NaNO3+ H2O)system.Thereisaconsistencybetweenourdataandreported data in refs 37−39. Density has a positively relationship with the composition. The curves in Figure 7 and Figure 8 show a similar tendency. Viscosity and density increases with NaNO3 concentration

increasing. Physicochemical properties (ρ, η) at point C was the most remarkable singular points, which could be used to estimate approximatelytheNaNO3concentration.The(ρ,η)maximumvalue ofsolutionis1.3923g·cm−3,2.3876,respectively;NaNO3is38.68wt% atpointC. 3.2.3.TheTernarySystem(NaNO3+Na2CO3+H2O)at313.15K. Thesolubilityexperimentalresultsandtherelevantphysicochemical propertiesdeterminedfor(NaNO3 +Na2CO3 +H2O)systematT= 313.15KarelistedinTable7.Solutionwassaturated.Corresponding phasediagramfortheternary(NaNO3 +Na2CO3 +H2O)systemis showninFigure9. AswecanseefromFigure9,A,U,andDpointsrepresenttheNa2CO3, H2O, NaNO3, respectively. There is one invariant point, two univariantcurves,andthreecrystallizedfieldsinphasediagram.Point SistheinvariantpointofNa2CO3 andNaNO3.Thecompositionof correspondingequilibratedsolutionatpointSisw(Na2CO3)=9.05wt %,w(NaNO3)=42.27wt%.GS,SHcurveareunivariantcurves.Some G



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Figure15.Schematicphaseequilibriaof(Na+//C1−,CO32−,NO3−−H2O) systemconstructedbytranslationmethodatT=313.15K.

Figure 12. pH versus w(NaNO3) in the saturated solutions of (NaNO3 + Na2CO3 +H2O)systemat313.15K,88.35kPa.

Table8.EquilibriumSolidPhasesoftheTernaryInvariantPoints fortheNa+//C1−,CO32−,NO3− −H2Oquaternarysystemat 313.15K ternarysystem

invariantpoint

equilibriumsolidphase

NaCl+NaNO3 +H2O NaNO3 +Na2CO3 +H2O NaCl+Na2CO3 +H2O

E31 E32 E33

C1+N C+N Cl+C

lines can be prolonged to point H (solid phase component for Na2CO3).OtherlinescanalsobeprolongedtopointG(solidphase componentforNaNO3).IftheselinescouldbeextendedtolineHG, that indicates the solid phase components consist of NaNO3 and Na2CO3.Phasediagramconsistsofthreecrystallizationregions:(I) AGS corresponds to NaNO3 with saturated solution, (II) ASD correspondstothecoexistenceofNa2CO3andNaNO3withsaturated solution,(III)SHDcorrespondstoNa2CO3withsaturatedsolution. (IV)GUHScorrespondstounsaturatedsolution. Figures10−13showtherelationshipsbetweenphysicochemical propertiesandNaNO3 concentration.Inourwork,thepressureand temperature were constant and only one salt concentration was variable. Experimental solutions are saturated. Therefore, it can be easilyplotted(nD,η,ρ,pH)asafunctionofNaNO3weightpercentage forsaturatedsolutions. Aneffectofcommonioneffectwasexistedin(NaNO3+Na2CO3+ H2O).Thus,NaNO3concentrationistheprimaryfactoraffectingthe physicochemical properties values. Values of physicochemical propertiesoftheequilibriumsolutionarepositivelycorrelatedwith NaNO3 concentration and varied regularly with changes in liquid phaseconcentration,asshowninFigures10−13. Density versus composition diagram of saturated solutions is shown in Figure 10. In Figure 10, the density increases as the concentrationofNaNO3increases,andthenshowsadownwardtrend afterinvariantpointS.Themaximumvalueofdensityis1.4341g·cm−3 andNaNO3 is42.27wt%atinvariantpointS. TherelationshipbetweenviscosityandNaNO3 concentrationis showninFigure11.AsshowninFigure11,viscositydecreaserapidly withNaNO3concentrationincreasinganddescendingfrom7.9678× 10−3 Pa·sto3.5650×10−3 Pa·satinvariant pointS. Then,the value decreasesrapidlyandtheminimumvalueoftheviscosityis2.1839× 10−3 Pa·s. pH versus composition diagram of saturated solutions for the ternarysystemisshowninFigure12.ItcanbeseenthatpHvaluesrange

Figure 13. Refractive index versus w(NaNO3) in saturated solutions of (NaNO3 +Na2CO3 +H2O)systemat313.15K,88.35kPa.

Figure14.Expansionofthequaternary(Na+//C1−,CO32−,NO3−−H2O)at T=313.15Kontheternarylevel.

H



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research on salt crystallization by high salt wastewater treatment furthertheoreticalstudies.

from11.678to8.051becauseNa2CO3 andNaNO3 inthissystemare strongacidandstrongbasesalts.Asthesesaltsdissociate,thehydrogen ionconcentrationhardlychanges.ItcanbefoundthatpHvaluesof solutionaredecreasingslowlywithNaNO3concentrationincreasing andreachestotheturningpointatinvariantpointS.Then,itdecreases rapidly, approximately trending with density. When NaNO3 concentrationis42.27wt%atpointS,pHvalueis11.304. The relationship between refractive index and NaNO3 concentration is shown in Figure 13. Refractive index increases with an decreasesofNaNO3concentrationandreachtominimumvalueand then increases, reaching maximum at invariant point S. Then, it decreases.Refractiveindexmaximumvalueis1.3960atpointS. 3.3. Phase Equilibria in Na2CO3−NaCl−NaNO3−H2O Systemat313.15K.Thequaternarysystemiscomposedofthree ternary subsystems: NaCl−NaNO3−H2O, NaNO3−Na2CO3− H2O,andNaCl−Na2CO3−H2O.Thissystemhastheinvariantpoints showninTable8andtheircorrespondingequilibriumsolidphases. There are three equilibrium solid phases in the system at 313.15K: NaCl-halit rock salt (Cl); Na2CO3-soda (C); NaNO3-natratime saltier(N).16−18 Theternarylevelphaseequilibriadiagramoftheunfoldingprismis showninFigure14,whichisconstructedfromthedatainTable8. Allthreeternarysystempointsaretranslatedbythroughtranslation to quaternary composition. A monovariant curve formed by transformationofternarysysteminvariantpointsintoaquaternion curveproducesonequaternaryinvariantpointineq3 E13 + E32 → E14 = C1 + C + N

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AUTHORINFORMATION

CorrespondingAuthor

*E-mail:[email protected];[email protected]. ORCID

YongshengRen: 0000-0003-0599-6751 Notes

Theauthorsdeclarenocompetingfinancialinterest.

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ACKNOWLEDGMENTS ThisresearchwasfinanciallysupportedbyUndergraduateTraining ProgramsforInnovation(NXCX2018047),PostgraduateInnovative Projects of Ningxia University (GIP2018041), Key R&D Program (East-West Cooperation Project) (2017BY064), and National First-rate Discipline Construction Project of Ningxia (NXYLXK2017A04).

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REFERENCES

(1)Feng-Chen,Q.U.TheKeyTechnologiesandProblemsofWastewater ZeroDischargeinCoalChemicalIndustry.ChemicalIndustry2013,31(2), 18−24. (2)Turek,M.;Dydo,P.;Klimek,R.Saltproductionfromcoal-minebrinein ED-evaporation-crystallizationsystem.Desalination2005,184(1-3),439− 446. (3) Millar, G. J.; Couperthwaite, S. J.; Moodliar, C. D. Strategies for the management and treatment of coal seam gas associated water. Renewable SustainableEnergyRev.2016,57,669−691. (4)Dellantonio,A.;Fitz,W.J.;Custovic,H.;Repmann,F.;Schneider,B.U.; Grünewald, H.; Gruber, V.; Zgorelec, Z.; Zerem, N.; Carter, C.; et al. EnvironmentalrisksoffarmedandbarrenalkalinecoalashlandfillsinTuzla, BosniaandHerzegovina.Environ.Pollut.2008,153(3),677−686. (5) Zuberi, M. J. S.; Ali, S. F. Greenhouse effect reduction by recovering energy from waste landfills in Pakistan. Renewable Sustainable Energy Rev. 2015,44(44),117−131. (6)Bosmans,A.;Vanderreydt,I.;Geysen,D.;Helsen,L.Thecrucialroleof Waste-to-Energy technologies in enhanced landfill mining: a technology review.J.CleanerProd.2013,55(14),10−23. (7)Zhang,X.;Ren,Y.;Li,P.;Ma,H.;Ma,W.;Liu,C.;Wang,Y.N.;Kong,L.; Shen, W. Solid−Liquid Equilibrium for the Ternary Systems (Na2SO4 + NaH2PO4+H2O)and(Na2SO4+NaCl+H2O)at313.15KandAtmospheric Pressure.J.Chem.Eng.Data2014,59(12),3969−3974. (8)Lu,H.;Wang,J.;Yu,J.;Wu,Y.;Wang,T.;Bao,Y.;Ma,D.;Hao,H.Phase equilibria for the pseudo-ternary system (NaCl + Na2SO4 + H2O) of coal gasificationwastewateratT=(268.15to373.15)K.Chin.J.Chem.Eng.2017,25 (7),955−962. (9)Zhou,H.;Bao,Y.;Bai,X.;Ma,R.;Huangfu,L.;Zhang,C.Salt-forming regions of seawater type solution in the evaporation and fractional crystallizationprocess.FluidPhaseEquilib.2014,362(2),281−287. (10) Ericsson, B.; Hallmans, B. Treatment of saline wastewater for zero discharge at the Debiensko coal mines in Poland. Desalination 1996, 105, 115−123. (11)Turek,M.;Dydo,P.;Surma,A.Zerodischargeutilizationofsalinewaters from“Wesola”coal-mine.Desalination2005,185,275−280. (12)Yang,J.;etal.Solid-liquidequilibriumofNa//Cl,NO3,SO4 2‑ -H2O quaternarysystemat373.15K.FluidPhaseEquilib.2017,445,7−13. (13) Soliev, L. Prediction of Marine - Type Multicomponent System Phase EquilibriabyMeansofTranslationMethod;TGPU:Dushanbe,2000;BookI[in Russian]. (14) Tursunbadalov, S.; Soliev, L. Phase Equilibria in Multicomponent Water−SaltSystems.J.Chem.Eng.Data2016,61,2209−2220. (15)Goroshchenko,Y.G.TheCentroidMethodforImagingMulticomponent Systems;NaukovaDumka:Kiev,1982[inRussian]. (16)Soliev,L.Schematicphaseequilibriadiagramsformulticomponent systems.Zh.Neorg.Khim.1988,33,1305−1310.

(3)

Therefore, three quaternary monovariant curves with corresponding equilibrium solid phases in eq 3 extend between the determinedonequaternarypoint.Theimplementationofallthese phaseequilibriumresultsisshowninFigure15. Thus, it can be found that there was one invariant point, three univariant curves, three crystallized regions in Na+//C1−, CO32−, NO3−−H2Oquaternarysystemat313.15K,whichareinagreement withexperimentallyobtainedresults.

4. CONCLUSION 1.Therearestillsomeproblemsandsomescientificproblemstobe solvedinthecurrentevaporativecrystallizationsectionontreatment ofhighsalinitywastewaterofMTO. 2. Equilibrium experiments of (NaCl + NaNO3 + H2O) and (Na2CO3+NaNO3+H2O)systemswereinvestigatedat313.15K.It wasfoundthattherewasoneinvariantpoint,twouninvariantcurves, three crystallization regions in these phase diagrams. When w(NaNO3)=38.68wt%,w(NaCl)=10.90wt%,(NaCl+NaNO3 + H2O)systemreachedtosaturationat313.15K. 3. Composition of corresponding equilibrated solution: at invariantpointS,w(NaNO3)=42.27wt%,w(Na2CO3)=9.05wt%, which shows the two pure solids Na2CO3 and NaNO3 saturated in (Na2CO3 +NaNO3 +H2O)systematT=313.15K.Itindicatesthat there were all in one invariant point, two uninvariant curves, three crystallizationregionsinphasediagrams. 4.PhaseequilibriainNa+//C1−,CO32−,NO3−−H2Oquaternary system at 313.15 K were also investigated by thorough and intermediate translation techniques. There was one invariant point,threeunivariantcurves,threecrystallizedregions. 5.ItseemsthatthecrystallizationregionofNaClislargerthanthe NaNO3 and Na2CO3 in these two ternary systems. Thus, it can be concludedthatNaCliseasilysaturatedandcrystallizedfromthemixed solution.Allresultsobtainedinthisresearchcouldbeusedforbasic I



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