Research Article Influence of Hydrothermal Temperature on

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 451984 6 pageshttpdxdoiorg1011552013451984

Research ArticleInfluence of Hydrothermal Temperature on PhosphorusRecovery Efficiency of Porous Calcium Silicate Hydrate

Wei Guan Fangying Ji Qingkong Chen Peng Yan and Weiwei Zhou

Key Laboratory of Three Gorges Reservoir Regionrsquos Eco-Environment of Ministry of Education Chongqing UniversityChongqing 400045 China

Correspondence should be addressed to Fangying Ji jfycqueducn

Received 2 November 2012 Revised 20 December 2012 Accepted 3 January 2013

Academic Editor Wen Zeng

Copyright copy 2013 Wei Guan et alThis is an open access article distributed under theCreativeCommonsAttributionLicensewhichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Porous calcium silicate hydrate (PCSH) was synthesized by carbide residue and white carbon blackThe influence of hydrothermaltemperature on phosphorus recovery efficiency was investigated by Field Emission Scanning Electron Microscopy (FESEM)Brunauer-Emmett-Teller (BET) and X-Ray Diffraction (XRD) Hydrothermal temperature exerted significant influence onphosphorus recovery performance of PCSH Hydrothermal temperature 170∘C for PCSH was more proper to recover phosphorusPCSH could recover phosphorus with content of 1851 The law of Ca2+ and OHminus release was the key of phosphorus recoveryefficiency and this law depended upon the microstructure of PCSH When the temperature of synthesis reached to 170∘C thereactions between CaO and amorphous SiO

2

were more efficient Solubility of SiO2

was a limiting factor

1 Introduction

Phosphorus recovery fromwastewater in the form of hydrox-yapatite is an effective method [1] However the optimal pHvalue for the formation of hydroxyapatite is in the range of105sim125 [2] But this pH value is too high to biochemicaltreatment system where the pH value is located between 60and 90 [3]

Phosphorus recovery on the condition of alkalescencynot only decreased the significant competition between car-bonate and calcium but also decreased the cost of chemicaltreatment and increased the effective phosphorus composi-tion of the final products [4] To address these issues calciumsilicate hydrate was introduced [5] The existing researchesshowed that calcium silicate hydrate could be considered as avery attractive and promisingmaterial to remove phosphorusfrom wastewater when compared with the common naturalmaterials [6] Because calcium silicate hydrate could releaseCa2+ and OHminus [7] Ca2+ OHminus and PO

4

3minus in the solutionform a condition locally for the growth of HAP which couldgrow with pH = 80-90 In order to achieve this goal itis necessary to find a process condition to prepare calciumsilicate hydrate

From a theoretical and practical point of view thesynthesis properties and structure of calcium silicate hydrate

have been analyzed in detail [8ndash11] Dynamic hydrothermalsynthesis is a common method to prepare calcium silicatehydrate [12 13] Hydrothermal temperature is one of themostimportant factors which determine the microstructure ofcalcium silicate hydrate [14] Prophase researches showed thatthe difference of microstructure has an effect on the phos-phorus recovery performance of calcium silicate hydrateHowever the bottleneck problem was that it was hard todetermine the appropriate hydrothermal temperature for thepreparation of the calcium silicate hydrate which possessesthe phosphorus recovery performance

The main aim of the research is to find a properhydrothermal temperature for calcium silicate hydrate torecover phosphorus The originality and importance of thispaper are highlighted by the following three points

(1) PCSH was synthesized by carbide residue and whitecarbon black with a dynamic hydrothermal methodThe influence of hydrothermal temperature on phos-phorus recovery performance was investigated

(2) The relationship between pore structure and the lawof Ca2+ and OHminus release was established by Avramikinetic model

2 Journal of Nanomaterials

Table 1 Chemical components of carbide residue and white carbon black

Chemical components (contents)CaO SiO2 Al2O3 SO2 MgO Fe2O3 SrO NaOH CuO H2O

Carbide residue 7934 357 214 122 062 021 026 mdash mdash 1264White carbon black 008 9746 016 182 mdash 003 mdash 029 002 014

(3) The mechanism of phosphorus recovery was studiedby FESEM BET and XRD on the basis of an in-depthcritical investigation

2 Materials and Methods

21 Preparation of PCSH PCSH was synthesized with car-bide residue (providing Ca) and white carbon black (pro-viding Si) Carbide residue (calcareous hoar and powdery)was obtained from Chongqing Changshou Chemical CoLtd and calcined at 700∘C for 2 h White carbon black(particles present spherical with homogeneous diameter)was purchased from Chongqing Jianfeng chemical Co LtdChemical constituents of carbide residue and white carbonblack are shown in Table 1 The phosphorus solution wasadjusted by adding KH

2PO4(Analytical reagent Chongqing

Boyi Chemical reagent Co Ltd) to prepare solution withinitial phosphorus concentration of 100mgL The abovematerials and chemicals were placed into sealed bottles forstorage

Carbide residue and white carbon black were mixedand the CaSi molar ratios were controlled at 16 1 Themixture was then added to prepared slurries The slurry washydrothermally reacted at 110∘C 140∘C 170∘C and 200∘Crespectively and the reaction time was 6 h The samples weretaken out when the temperature was reduced to the naturalcondition The hydrothermal reaction was carried out witha liquidsolid ratio of 30 The obtained products were driedat 105∘C for 2 h and then were ground through a sieve of200 meshes The prepared samples that were hydrothermallyreacted at 110∘C 140∘C 170∘C and 200∘C were denoted asPCSH 110∘C PCSH 140∘C PCSH 170∘C and PCSH 200∘Crespectively

22 Evaluation of Phosphorus Recovery Performance Firstlysynthetic solution (1 L) was added into several bottles 4 g ofsamples were added to these bottles respectively and shakenat 40 rmin under controlled temperature conditions (20∘C)Phosphorus concentration of supernatant was measuredaccording to themolybdenumblue ascorbic acidmethod (therelative error of data is 03) with a Unico spectrophotome-ter (UV-2012PCS Shanghai Unico Instruments Co LtdChina) The solid samples were then separated from theremoved synthetic solution with the addition of samplesafter reaction Finally the produced sedimentswere separatedfrom removed synthetic solution dried and weighted Phos-phorus was contented by

119875 =

(119862

0minus 119862

119905) times 119907

119908

times 100 (1)

where 119862119905is the restrained phosphorus concentration in

synthetic solution (mgL) 119907 is the volume of the solution(L) 119908 is the mass of produced sediment after phosphorusrecovery (mg) and119862

0is the initial phosphorus concentration

(mgL)4 g of samples (PCSH 110∘C PCSH 140∘C PCSH 170∘C

and PCSH 200∘C) were immersed in 1 L of demonized waterrespectively contained in a glass bottle generating sampleswith a solution concentration of 4 gL The bottle was placedon an agitation table and shaken at 40 rmin under controlledtemperature conditions (20∘C) Samples of solution weretaken after 5 10 15 20 40 60 and 80mins of agitationCa2+ concentration of the samples was determined by EDTAtitration (the relative error of data is 005)

23 Characterization Methods XRD patterns were collectedin an XD-2 instrument (Persee China) using Cu K120572 radi-ation FESEM images were collected on an S-4800 fieldemission scanning electron microscope (Hitachi Japan)BET surface areas were measured by nitrogen adsorption at7735 K on an ASAP-2010 adsorption apparatus (Micromerit-ics USA)

3 Results and Discussion

31 Phosphorus Recovery Performance of PCSH The PCSHsamples were separated from the removed synthetic solutionafter phosphorus removal and these samples were addedinto synthetic solution with initial phosphorus concentration100mgL again This process was repeated for several timesin order to explore the phosphorus recovery performanceof PCSH Changes of restrained phosphorus concentrationare shown in Figure 1 There were great differences amongthe phosphorus recovery performance of these samplesPhosphorus content of PCSH 110∘C was only 649 after 7times of phosphorus removal Phosphorus content of PCSH140∘Cwas 907 after 9 times of phosphorus removal PCSH170∘C could remove phosphorus repeated for 15 times andphosphorus content of this sample reached 1851 Phospho-rus content of PCSH 200∘C was 1292 after 11 times ofphosphorus removal Generally speaking the material couldbe used as a high grade phosphorus ore when the phosphoruscontent of this material exceeds 15 [15] Therefore thehydrothermal temperature 170∘Cwas beneficial for the PCSHto phosphorus removal As seen in Figure 2 these samplesreflected good phosphorus removal efficiency when pHvalues maintained 80sim90 But with the times of phosphorusremoval increased pH values and the phosphorus removalefficiency of PCSH samples declined The concentrationof restrained phosphorus kept unchanged when pH values

Journal of Nanomaterials 3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 150

20

40

60

80

100co

ncen

trat

ion

(mgmiddot

Lminus1 )

Restr

aine

d ph

osph

orus

porous calcium silicate hydrate samplesNumber of times of phosphorus removal by

PCSH CPCSH C

PCSH CPCSH C

Figure 1 Changes of restrained phosphorus concentration bycirculation of phosphorus removal

declined to 70 This phenomenon showed that these sampleshad no phosphorus recovery performance on the condition ofneutral In contrast PCSH 170∘C could maintain pH valuesat a range of 80sim90 more effectively

32 The Pore Structure and Ca2+ Release of PCSH Specificsurface area and pore size distributionwere calculated byBETequation and Barrett-Joyner-Halenda method respectively(Figure 3) The nitrogen sorption analysis was conducted toreveal the pore structure of calcium silicate hydrate All threesamples showed similar adsorption-desorption isothermswhich could be classified as type IV according to IUPACnomenclature [16] The results suggested the phenomenon ofadsorption hysteresis loop That mean mesopore or narrowgap pore existed on sample Adsorption in mespore occurredmainly in medium pressure region (04 lt 119875119875

0lt 09)

When the hydrothermal temperature was lower than 170∘Cwith the increase of hydrothermal temperature the phe-nomenon of adsorption hysteresis loop became obvious andthe adsorption curve increased While the adsorption curveof PCSH 200∘C declined slightly specific surface areas ofPCSH 110∘C PCSH 140∘C PCSH 170∘C and PCSH 200∘Cwere 1191 4985 11336 and 5967m2g respectively Porevolumes of these sampleswere 007 015 053 and 030 cm3grespectively

The morphology of PCSH 110∘C PCSH 140∘C PCSH170∘C and PCSH 200∘C was examined by FESEM observa-tions (Figure 4) It could be indicated from the photographsthat the surface structure of PCSH 110∘C seems dense withpore size inhomogeneous distribution The surface structureof PCSH 140∘C and PCSH 200∘C seems dense with poresize homogeneous distribution In contrast PCSH 170∘Cpossesses obverse fibrous-network structure with a largenumber of mesopores and the particle size of sphericalparticle distributed from 25 to 30 120583m uniformly

7

75

8

85

9

95

pH

val

ues

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

porous calcium silicate hydrate samples

Number of times of phosphorus removal by

PCSH 110∘CPCSH 140∘C


Figure 2 Changes of pH values by circulation of phosphorusremoval

0

50

100

150

200

250

300

350

0 04 08 12

Volu

me (

cm3 middotg

minus1)



Relative pressure 1198751198750

Figure 3 Nitrogen adsorption-adsorption isotherms on samples

The experiments showed that Ca2+ concentration dis-solved from PCSH 110∘C PCSH 140∘C PCSH 170∘C andPCSH 200∘C was 270 311 491 and 376mgg respectively(Figure 5) This result showed that PCSH 170∘C reflectedbetter performance of Ca2+ release The experimental capac-ities of Ca2+ release were potted according to Avrami kineticmodel as follows [17]

minus ln (1 minus 119909) = 119896119905119899 (2)

where 119896 is the kinetic constant 119899 is the characteristic constantof solid 119905 is the reaction time (min) and 119909 (119909 = 119862

119905119862max 119862119905

is concentration of time 119905 (mgL) and 119862max is concentrationof the maximum (mgL) is the fraction conversion Thecharacteristic constant 119899 was 0947 The kinetic constants


(a) (b)

(c) (d)

Figure 4 FESEM photographs of samples (a) PCSH 110∘C (b) PCSH 140∘C (c) PCSH 170∘C (d) PCSH 200∘C

were determined by fitting the Avrami kinetic model to theexperimental data obtained from Table 2 The high correla-tion coefficients (1198772 gt 09) indicated that this model coulddescribe the law of Ca2+ release well Combined with specificsurface area (119878) of samples a relationship between 119896 and 119878could be established as follows

119896 = 0018119878

0315

(3)

According to (3) specific surface area of samples and therate of Ca2+ release were in good agreement with each otherThe relationship between specific surface area and dissolvedconcentration of Ca2+ was obtained by substituting (3) into(2) as follows

minus ln (1 minus 119909) = 001811987803151199050947 (4)

According to (4) concentration of Ca2+ release wasrelated to specific surface area This result demonstratedthe influence of hydrothermal temperature on phosphorusrecovery performance Hydrothermal temperature affectedthe pore structure and the performance of Ca2+ release Ca2+was released faster due to the larger specific surface areaComparatively speaking PCSH 170∘C possesses larger spe-cific surface area Porous structure provided a local conditionto maintain a high concentration of Ca2+ release PCSH

170∘C could release a suitable concentration of Ca2+ andOHminusto maintain the pH values during 80sim90 Phosphate existedin the form of HPO

4

2minus in the range of these pH values [18]Ca2+ OHminus and HPO

4

2minus formed a local condition with highconcentrationThis condition was beneficial to the formationof hydroxyapatite with pH = 80sim90 The major reaction ofthe hydroxyapatite crystallization on PCSH crystal seed wasas follows

5Ca2+ +OHminus + 3HPO4

2minus

997888rarr Ca5(PO4)

3

(OH) darr +3H+(5)

33 Mechanism of Hydrothermal Temperature Effect on Phos-phorus Recovery Performance Themechanism of hydrother-mal temperature effect on phosphorus recovery performancecould be further investigated by XRD The XRD patterns ofPCSH samples were compared (Figure 6) The main phaseof PCSH 110∘C was SiO

2(PDF card 18-1169) and this result

indicated that carbide residue and white carbon black hadnot reacted completely When the hydrothermal temperatureincreased to 140∘C the main phase included Jennite (PDFcard 18-1206 chemical formula Ca

9Si6O18(OH)6sdot8H2O) and

SiO2 but the principal peaks of Jennite were not obvious

In this stage a part of SiO2had involved in the forma-

tion of Jennite but the reaction was not completely so


Table 2 Correlation equations and rate constants for the Avrami kinetic model describing Ca2+ release

Samples Avrami kinetic equations Kinetic constant (119896) Correlation coefficient (1198772)PCSH 110∘C minus ln(1 minus 119909) = 00391199050947 0039 0973PCSH 140∘C minus ln(1 minus 119909) = 00521199050947 0052 0985PCSH 170∘C minus ln(1 minus 119909) = 00851199050947 0085 0998PCSH 200∘C minus ln(1 minus 119909) = 00661199050947 0066 0988

0

1

2

3

4

5

6

Reaction time (min)0 20 40 60 80

Con

cent

rate

of d

issol

ved

Ca2+

(mgmiddot

gminus1)



Figure 5 Concentrate of Ca2+ dissolved from samples

the content of Jennite was low When the hydrothermaltemperature reached to 170∘C the principal peaks of Jenniteappeared instead of the principal peaks of SiO

2in the XRD

patterns This result indicated that the main component ofPCSH 170∘C was Jennite As the hydrothermal temperatureheated to 200∘C the production included jennite xonotlite(PDF card 23-0125 chemical formula Ca

6Si6O17(OH)2) and

Ca3Si2O7(PDF card 11-0317)

As the siliceous material white carbon black exhibitedhigh activity [19] Therefore the hydrothermal reaction inthe high-pressure reactor belonged to controlling solutionreaction The reaction process depended on the dissolutionof SiO

2 and the dissolution rate depended on the solubility

of SiO2in the white carbon black Based on the above

analysis when the hydrothermal reaction was too low SiO2

was difficult to dissolute and formed a layer of rich siliconon the surface of samples This condition made the porestructure of samples became dense Rising the hydrother-mal temperature could increase the solubility of SiO

2 The

solubility of white carbon black was low at atmospherictemperature and pressure but the solubility increased withthe increasing of hydrothermal temperature Jennite formedwhen the hydrothermal temperature reached to 170∘C andthis material could dissolve a proper concentration of Ca2+and OHminus due to loose and porous structure So PCSH 170∘Chas better phosphorus recovery performance The systemof PCSH became instable due to a too high hydrother-mal temperature and multiple impurities appeared in this

0

100

200

300

400

500

600

CD DA

D

B

BB

BB

A

A

A

AA

AA A

Inte

nsity

(au

)

AC

10 20 30 40 50 60 70

D Ca3Si2O7B SiO2

C XonotliteA Jennite

PCSH 110∘C

PCSH 140∘C

PCSH 170∘C

PCSH 200∘C

2120579 (degrees)

Figure 6 XRD patterns of samples

systemThe phosphorus recovery performance of the sampledeclined because the efficiency of Ca2+ and OHminus release ofthe impurities was too low

4 Conclusions

Porous calcium silicate hydrate was synthesized by carbideresidue andwhite carbon black with a dynamic hydrothermalmethodThis material could be considered a tenable materialfor phosphorus removal and recovery from wastewaterHydrothermal temperature showed significant influence onphosphorus recovery performance of PCSH Hydrothermaltemperature 170∘C for PCSH was more proper to recoverphosphorus PCSH could recover phosphorus with contentof 1851

The law of Ca2+ and OHminus release was the key ofphosphorus recovery efficiency Changes of hydrothermaltemperature led to the different pore structures The increaseof specific surface area and the increase in concentration ofCa2+ release were in good agreement with each other

Further analysis by XRD indicated that hydrothermalreaction process depended on the dissolution of SiO

2 And

hydrothermal temperature affected the solubility of SiO2

References

[1] E H Kim S B Yim H C Jung and E J Lee ldquoHydroxyapatitecrystallization from a highly concentrated phosphate solution


using powdered converter slag as a seed materialrdquo Journal ofHazardous Materials B vol 136 no 3 pp 690ndash697 2006

[2] J Z Zhou L L Feng J Zhao et al ldquoEfficient and controllablephosphate removal on hydrocalumite by multi-step treatmentbased on pH-dependent precipitationrdquo Chemical EngineeringJournal vol 185 pp 219ndash225 2012

[3] P Battistoni P Pavan M Prisciandaro and F Cecchi ldquoStruvitecrystallization a feasible and reliable way to fix phosphorusin anaerobic supernatantsrdquo Water Research vol 34 no 11 pp3033ndash3041 2000

[4] P Battistoni A de Angelis P Pavan M Prisciandaro and FCecchi ldquoPhosphorus removal froma real anaerobic supernatantby struvite crystallizationrdquo Water Research vol 35 no 9 pp2167ndash2178 2001

[5] D Sugiyama and T Fujita ldquoA thermodynamicmodel of dissolu-tion and precipitation of calcium silicate hydratesrdquo Cement andConcrete Research vol 36 no 2 pp 227ndash237 2006

[6] X C Chen H N Kong D Y Wu X Z Wang and YLin ldquoPhosphate removal and recovery through crystallizationof hydroxyapatite using xonotlite as seed crystalrdquo Journal ofEnvironmental Sciences vol 21 no 5 pp 575ndash580 2009

[7] J J Chen J J Thomas H F W Taylor and H M JenningsldquoSolubility and structure of calcium silicate hydraterdquo Cementand Concrete Research vol 34 no 9 pp 1499ndash1519 2004

[8] F Tariq R Haswell P D Lee and D W McComb ldquoChar-acterization of hierarchical pore structures in ceramics usingmultiscale tomographyrdquoActaMaterialia vol 59 no 5 pp 2109ndash2120 2011

[9] S Sanchez-Salcedo JWerner andMVallet-Regı ldquoHierarchicalpore structure of calcium phosphate scaffolds by a combinationof gel-casting and multiple tape-casting methodsrdquo Acta Bioma-terialia vol 4 no 4 pp 913ndash922 2008

[10] R Siauciunas and K Baltakys ldquoFormation of gyrolite duringhydrothermal synthesis in the mixtures of CaO and amorphousSiO2

or quartzrdquo Cement and Concrete Research vol 34 no 11pp 2029ndash2036 2004

[11] S Shaw S M Clark and C M B Henderson ldquoHydrother-mal formation of the calcium silicate hydrates tobermorite(Ca5

Si6

O16

(OH)2

sdot 4H2

O) and xonotlite (Ca6

Si6

O17

(OH)2

) anin situ synchrotron studyrdquo Chemical Geology vol 167 no 1-2pp 129ndash140 2000

[12] M Li and H Liang ldquoFormation of micro-porous spherical par-ticles of Calcium Silicate (Xonotlite) in dynamic hydrothermalpocessrdquo China Particuology vol 2 no 3 pp 124ndash127 2004

[13] A A P Mansur and H S Mansur ldquoPreparation characteri-zation and cytocompatibility of bioactive coatings on porouscalcium-silicate-hydrate scaffoldsrdquo Materials Science and Engi-neering C vol 30 no 2 pp 288ndash294 2010

[14] T T H Bach C Cau Dit Coumes I Pochard C MerciercB Reveld and A Nonatb ldquoInfluence of temperature on thehydration products of low pH cementsrdquo Cement and ConcreteResearch vol 42 pp 805ndash817 2012

[15] M Sinirkaya A K Ozer and M S Gulaboglu ldquoInvestigationof the changes of P

2

O5

content of phosphate rock duringsimultaneous calcinationsulfationrdquo Powder Technology vol211 no 1 pp 72ndash76 2011

[16] Y Geng X Wang W Chen Q Cai C Nan and H Li ldquoSyn-thesis characterization and application of novel bicontinuousmesoporous silica with hierarchical pore structurerdquo MaterialsChemistry and Physics vol 116 no 1 pp 254ndash260 2009

[17] N Demirkiran and A Kunkul ldquoDissolution kinetics of ulexitein perchloric acid solutionsrdquo International Journal of MineralProcessing vol 83 no 1-2 pp 76ndash80 2007

[18] Y Liu X Sheng Y H Dong and Y J Ma ldquoRemoval of high-concentration phosphate by calcite effect of sulfate and pHrdquoDesalination vol 289 pp 66ndash71 2012

[19] M Felipe-sese D Eliche-Quesada and F A Corpas-lglesiasldquoThe use of solid residues derived from different industrialactivities to obtain calcium silicates for use as insulatingconstruction materialsrdquo Ceramics International vol 37 no 8pp 3019ndash3028 2011

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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Table 1 Chemical components of carbide residue and white carbon black

Chemical components (contents)CaO SiO2 Al2O3 SO2 MgO Fe2O3 SrO NaOH CuO H2O

Carbide residue 7934 357 214 122 062 021 026 mdash mdash 1264White carbon black 008 9746 016 182 mdash 003 mdash 029 002 014

(3) The mechanism of phosphorus recovery was studiedby FESEM BET and XRD on the basis of an in-depthcritical investigation

2 Materials and Methods

21 Preparation of PCSH PCSH was synthesized with car-bide residue (providing Ca) and white carbon black (pro-viding Si) Carbide residue (calcareous hoar and powdery)was obtained from Chongqing Changshou Chemical CoLtd and calcined at 700∘C for 2 h White carbon black(particles present spherical with homogeneous diameter)was purchased from Chongqing Jianfeng chemical Co LtdChemical constituents of carbide residue and white carbonblack are shown in Table 1 The phosphorus solution wasadjusted by adding KH

2PO4(Analytical reagent Chongqing

Boyi Chemical reagent Co Ltd) to prepare solution withinitial phosphorus concentration of 100mgL The abovematerials and chemicals were placed into sealed bottles forstorage

Carbide residue and white carbon black were mixedand the CaSi molar ratios were controlled at 16 1 Themixture was then added to prepared slurries The slurry washydrothermally reacted at 110∘C 140∘C 170∘C and 200∘Crespectively and the reaction time was 6 h The samples weretaken out when the temperature was reduced to the naturalcondition The hydrothermal reaction was carried out witha liquidsolid ratio of 30 The obtained products were driedat 105∘C for 2 h and then were ground through a sieve of200 meshes The prepared samples that were hydrothermallyreacted at 110∘C 140∘C 170∘C and 200∘C were denoted asPCSH 110∘C PCSH 140∘C PCSH 170∘C and PCSH 200∘Crespectively

22 Evaluation of Phosphorus Recovery Performance Firstlysynthetic solution (1 L) was added into several bottles 4 g ofsamples were added to these bottles respectively and shakenat 40 rmin under controlled temperature conditions (20∘C)Phosphorus concentration of supernatant was measuredaccording to themolybdenumblue ascorbic acidmethod (therelative error of data is 03) with a Unico spectrophotome-ter (UV-2012PCS Shanghai Unico Instruments Co LtdChina) The solid samples were then separated from theremoved synthetic solution with the addition of samplesafter reaction Finally the produced sedimentswere separatedfrom removed synthetic solution dried and weighted Phos-phorus was contented by

119875 =

(119862

0minus 119862

119905) times 119907

119908

times 100 (1)

where 119862119905is the restrained phosphorus concentration in

synthetic solution (mgL) 119907 is the volume of the solution(L) 119908 is the mass of produced sediment after phosphorusrecovery (mg) and119862

0is the initial phosphorus concentration

(mgL)4 g of samples (PCSH 110∘C PCSH 140∘C PCSH 170∘C

and PCSH 200∘C) were immersed in 1 L of demonized waterrespectively contained in a glass bottle generating sampleswith a solution concentration of 4 gL The bottle was placedon an agitation table and shaken at 40 rmin under controlledtemperature conditions (20∘C) Samples of solution weretaken after 5 10 15 20 40 60 and 80mins of agitationCa2+ concentration of the samples was determined by EDTAtitration (the relative error of data is 005)

23 Characterization Methods XRD patterns were collectedin an XD-2 instrument (Persee China) using Cu K120572 radi-ation FESEM images were collected on an S-4800 fieldemission scanning electron microscope (Hitachi Japan)BET surface areas were measured by nitrogen adsorption at7735 K on an ASAP-2010 adsorption apparatus (Micromerit-ics USA)

3 Results and Discussion

31 Phosphorus Recovery Performance of PCSH The PCSHsamples were separated from the removed synthetic solutionafter phosphorus removal and these samples were addedinto synthetic solution with initial phosphorus concentration100mgL again This process was repeated for several timesin order to explore the phosphorus recovery performanceof PCSH Changes of restrained phosphorus concentrationare shown in Figure 1 There were great differences amongthe phosphorus recovery performance of these samplesPhosphorus content of PCSH 110∘C was only 649 after 7times of phosphorus removal Phosphorus content of PCSH140∘Cwas 907 after 9 times of phosphorus removal PCSH170∘C could remove phosphorus repeated for 15 times andphosphorus content of this sample reached 1851 Phospho-rus content of PCSH 200∘C was 1292 after 11 times ofphosphorus removal Generally speaking the material couldbe used as a high grade phosphorus ore when the phosphoruscontent of this material exceeds 15 [15] Therefore thehydrothermal temperature 170∘Cwas beneficial for the PCSHto phosphorus removal As seen in Figure 2 these samplesreflected good phosphorus removal efficiency when pHvalues maintained 80sim90 But with the times of phosphorusremoval increased pH values and the phosphorus removalefficiency of PCSH samples declined The concentrationof restrained phosphorus kept unchanged when pH values


1 2 3 4 5 6 7 8 9 10 11 12 13 14 150

20

40

60

80

100co

ncen

trat

ion

(mgmiddot

Lminus1 )

Restr

aine

d ph

osph

orus


PCSH CPCSH C

PCSH CPCSH C




0lt 09)



7

75

8

85

9

95

pH

val

ues

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






0

50

100

150

200

250

300

350

0 04 08 12

Volu

me (

cm3 middotg

minus1)






minus ln (1 minus 119909) = 119896119905119899 (2)


119905119862max 119862119905



(a) (b)

(c) (d)



119896 = 0018119878

0315

(3)


minus ln (1 minus 119909) = 001811987803151199050947 (4)



4


4



2minus

997888rarr Ca5(PO4)

3

(OH) darr +3H+(5)











0

1

2

3

4

5

6


Con

cent

rate

of d

issol

ved

Ca2+

(mgmiddot

gminus1)





2in the XRD


6Si6O17(OH)2) and







2 The


0

100

200

300

400

500

600

CD DA

D

B

BB

BB

A

A

A

AA

AA A

Inte

nsity

(au

)

AC

10 20 30 40 50 60 70

D Ca3Si2O7B SiO2


PCSH 110∘C

PCSH 140∘C

PCSH 170∘C

PCSH 200∘C

2120579 (degrees)



4 Conclusions




2 And


References















Si6

O16

(OH)2

sdot 4H2


Si6

O17

(OH)2






2

O5













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




1 2 3 4 5 6 7 8 9 10 11 12 13 14 150

20

40

60

80

100co

ncen

trat

ion

(mgmiddot

Lminus1 )

Restr

aine

d ph

osph

orus


PCSH CPCSH C

PCSH CPCSH C




0lt 09)



7

75

8

85

9

95

pH

val

ues

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






0

50

100

150

200

250

300

350

0 04 08 12

Volu

me (

cm3 middotg

minus1)






minus ln (1 minus 119909) = 119896119905119899 (2)


119905119862max 119862119905



(a) (b)

(c) (d)



119896 = 0018119878

0315

(3)


minus ln (1 minus 119909) = 001811987803151199050947 (4)



4


4



2minus

997888rarr Ca5(PO4)

3

(OH) darr +3H+(5)











0

1

2

3

4

5

6


Con

cent

rate

of d

issol

ved

Ca2+

(mgmiddot

gminus1)





2in the XRD


6Si6O17(OH)2) and







2 The


0

100

200

300

400

500

600

CD DA

D

B

BB

BB

A

A

A

AA

AA A

Inte

nsity

(au

)

AC

10 20 30 40 50 60 70

D Ca3Si2O7B SiO2


PCSH 110∘C

PCSH 140∘C

PCSH 170∘C

PCSH 200∘C

2120579 (degrees)



4 Conclusions




2 And


References















Si6

O16

(OH)2

sdot 4H2


Si6

O17

(OH)2






2

O5













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)



119896 = 0018119878

0315

(3)


minus ln (1 minus 119909) = 001811987803151199050947 (4)



4


4



2minus

997888rarr Ca5(PO4)

3

(OH) darr +3H+(5)











0

1

2

3

4

5

6


Con

cent

rate

of d

issol

ved

Ca2+

(mgmiddot

gminus1)





2in the XRD


6Si6O17(OH)2) and







2 The


0

100

200

300

400

500

600

CD DA

D

B

BB

BB

A

A

A

AA

AA A

Inte

nsity

(au

)

AC

10 20 30 40 50 60 70

D Ca3Si2O7B SiO2


PCSH 110∘C

PCSH 140∘C

PCSH 170∘C

PCSH 200∘C

2120579 (degrees)



4 Conclusions




2 And


References















Si6

O16

(OH)2

sdot 4H2


Si6

O17

(OH)2






2

O5













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






0

1

2

3

4

5

6


Con

cent

rate

of d

issol

ved

Ca2+

(mgmiddot

gminus1)





2in the XRD


6Si6O17(OH)2) and







2 The


0

100

200

300

400

500

600

CD DA

D

B

BB

BB

A

A

A

AA

AA A

Inte

nsity

(au

)

AC

10 20 30 40 50 60 70

D Ca3Si2O7B SiO2


PCSH 110∘C

PCSH 140∘C

PCSH 170∘C

PCSH 200∘C

2120579 (degrees)



4 Conclusions




2 And


References















Si6

O16

(OH)2

sdot 4H2


Si6

O17

(OH)2






2

O5













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















Si6

O16

(OH)2

sdot 4H2


Si6

O17

(OH)2






2

O5













CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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