minerals

Article Fabrication and Thermal Properties of Capric Acid/Calcinated Iron Tailings/Carbon Nanotubes Composite as Form-Stable Phase Change Materials for Thermal Energy Storage

1,2,3, 4, 5 1, 2 2 Peng Liu †, Xiaobin Gu †, Zhikai Zhang , Jianping Shi *, Jun Rao and Liang Bian 1 School of Electronic & Communication Engineering, Guiyang University, Guiyang 550005, China; [email protected] 2 School of Gemology and Materials Technology, Hebei GEO University, Shijiazhuang 050031, China; [email protected] (J.R.); [email protected] (L.B.) 3 Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, South West University of Science and Technology, Mianyang 621010, China 4 Materials Interfaces Center, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518005, China; [email protected] 5 School of Water Resources and Environment, Hebei GEO University, Shijiazhuang 050031, China; [email protected] * Correspondence: [email protected] These co-first authors contributed equally to this work. †


Received: 16 September 2019; Accepted: 15 October 2019; Published: 23 October 2019


Abstract: In this study, a novel form-stable phase change material (FSPCM) consisting of calcination iron tailings (CIT), capric acid (CA), and carbon nanotubes (CNT) was prepared using a simple direct melt impregnation method, and a series of tests have been carried out to investigate its properties. The leakage tests showed that CA can be retained in CIT with a mass fraction of about 20 wt.% without liquid leakage during the phase change process. Moreover, the morphology, chemical structure, and thermal properties of the fabricated composite samples were investigated. Scanning electron microscope (SEM) micrographs confirmed that CIT had a certain porous structure to confine CA in composites. According to the Fourier transformation infrared spectroscope (FTIR) results, the CA/CIT/CNT FSPCM had good chemical compatibility. The melting temperature and latent heat of CA/CIT/CNT by differential scanning calorimeter (DSC) were determined as 29.70 ◦C and 22.69 J/g, respectively, in which the mass fraction of CIT and CNT was about 80 wt.% and 5 wt.%, respectively. The thermal gravity analysis (TGA) revealed that the CA/CIT/CNT FSPCM showed excellent thermal stability above its working temperature. Furthermore, the melting and freezing time of CA/CIT/CNT FSPCM doped with 5 wt.% CNT reduced by 42.86% and 54.55% than those of pure CA, and it showed better heat transfer efficiency. Therefore, based on the above analyses, the prepared CA/CIT/CNT FSPCM is not only a promising candidate material for the application of thermal energy storage in buildings, but it also provides a new approach for recycling utilization of iron tailings.

Keywords: capric acid; calcinated iron tailings; carbon nanotubes; FSPCM; thermal energy storage

1. Introduction In recent years, the environmental issue and the energy crisis are driving people to develop renewable energy. However, low utilization efficiency and poor stability hinder the large-scale applications of renewable energy [1]. In addition, the sharp unbalance contradiction of energy supply and demand makes it urgent to develop energy storage technology to store the renewable energy [1,2].

Minerals 2019, 9, 648; doi:10.3390/min9110648 www.mdpi.com/journal/minerals Minerals 2019, 9, 648 2 of 16

Thermal energy storage (TES) as an efficient and clean method can improve energy utilization efficiency and ease the contradiction between energy supply and demand [2]. In the TES technologies, the latent heat storage using phase change materials (PCMs) was considered to be one of the promising solutions due to their many advantages such as high energy storage density, nearly constant temperature during thermal energy storage, etc. [3]. Therefore, PCMs are widely researched and applied in many fields, including air-conditioning [4,5], electronic devices [6–10], waste heat recovery [11,12], building energy [13,14], smart textile [15,16], and solar energy storage [17,18]. According to the phase change process, PCMs can be divided into solid-liquid, solid-solid, solid-gas, and liquid-gas categories [19]. Moreover, the solid-liquid PCMs can be divided into inorganic and organic ones. Presently, intensive studies have been conducted on organic PCMs, for fatty acids have many useful characteristic properties such as appropriate suitable phase change temperature, high heat latent value, almost no super-cooling, nontoxic, etc. [20,21]. Although fatty acids exhibit excellent properties, leakage issue and low thermal conductivity seriously impede their practical applications. Hence, it is very necessary to overcome the two shortcomings mentioned above. In order to hold back the leakage of fatty acids during the working process, the syntheses of form-stable PCMs (FSPCMs) by adsorbing fatty acids into different supporting materials have been widely researched in the past few years [22]. In practice, there are two main methods to be usually used to prepare the FSPCMs: (1) Encapsulation of fatty acids into a macro or micro dimension microcapsule structure, namely, microcapsule technology [23]; (2) simply impregnated fatty acids into various porous materials. Obviously, the second one has remarkable advantages of low cost, simple operation, unique pore structure, and easily available materials [22]. As a result, different porous materials were employed to prepare FSPCMS, thereinto, clay mineral-based FSPCMs were extensively studied such as expanded graphite [24,25], perlite [26], kaolinite [27,28], diatomite [29,30], and meteorite [31]. A large number of research results demonstrated that by adsorbing PCM into porous material to fabricate FSPCMs, the liquid leakage problems can be effectively solved [32,33]. However, the fabrication of FSPCMs is relatively costly by these natural porous mineral clay materials compared with the preparation of solid waste-based FSPCM. Moreover, the reserves of natural porous mineral clay materials are exhaustible. Fortunately, iron tailings (ITs) are a kind of solid waste produced from iron ore separation, and they are very cheap and quite easily available. Meanwhile, the treatment and recycling utilization of iron tailings have always been a problem. The comprehensive utilization is becoming one of the hot social topics all over the world [34–37]. It is worth noting that the main chemical components of typical iron tailings are similar to several natural mineral materials reported in the literature [38]. The chemical components such as SiO2, Al2O3, and MgO can be used as porous materials. Moreover, some of the chemical components in IT such as Na2O and K2O have a fluxing effect, which make ITs possible to be used as a supporting material of PCM. Therefore, the iron tailings were calcinated to prepare porous mineral materials in this study. To overcome poor thermal conductivity of fatty acids, a lot of efforts have been made to synthesize composite PCMs by adding additives with high thermal conductivity. The introduction of thermal conductivity enhancers has been proven to be a superior way to effectively improve the thermal conductivity of fatty acids. Therefore, many researchers attempt to add thermal conductivity enhancers into PCMs, mainly including carbon nanofibers (CNF) [39], activated carbon (AC) [40], expanded graphite (EG) [41], graphene [42], and carbon nanotubes (CNT) [43,44]. Among the investigated thermal conductivity enhancers, CNT was considered to be a promising enhancer of thermal conductivity in future practical applications and has been a research hotspot in recent years. The feasibility and effectiveness have also been verified by the above-mentioned literatures [43,44]. Therefore, CNT was employed to be as the thermal conductivity enhancer in this work. This study aims to fabricate an FSPCM with an appropriate phase change temperature, good thermal conductivity, and high heat latent, which could be used in the intelligent temperature control of buildings. In the FSPCM composite, capric acid (CA) is one of the promising fatty acids used for building energy conservation because of its suitable phase change temperature and high phase Minerals 2019, 9, 648 3 of 16 change latent heat. Particularly, the phase change temperature of CA is within the human body comfortable temperatures. Hence, CA was chosen as the PCM in this research. Considering the cost, simple preparation, and practical utility, the iron tailings were pretreated firstly by calcination. Then, the obtained calcination iron tailings (CIT) were acted as the supporting material to prevent the liquid CA leakage. Additionally, CNT was used as the thermal conductivity enhancer to improve the thermal conductivity of CA. The composite PCMs were prepared through the facile direct impregnation method. The prepared CA/CIT/CNT FSPCM has great potential for TES application in buildings. Simultaneously, it creates an innovative approach for recycling utilization of iron tailings.

2. Experiment

2.1. Material The CA was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). The iron tailings were obtained from the Hanxing Mining Bureau (Handan, China). The iron tailings were firstly screened into 60 mesh. Additionally, the sample was mixed with a montmorillonite binder − additive (provided from Yipusheng Tianjin Pharmaceutical Co., Ltd.). Then, the mixture was roasted in a high-frequency furnace at about 300 ◦C for 30 min. After that, the mixture was heated at 600 ◦C for 120 min. The cooled residual ash sample became CIT to package PCM. As seen from Table1, CIT has similar chemical components as some typical minerals and this indicates that it can be used as carrier matrix to prepare mineral-based composite phase change materials in theory. The CNT was supplied by Suzhou Tanfeng Tech, Inc. (Suzhou, China). The main properties of the CA and CNT were given in Table2.

Table 1. Comparison of chemical constituent of iron tailings, calcination iron tailings (CIT), and some typical natural minerals [45,46].

Material SiO2 Al2O3 Fe2O3 CaO MgO K2O + Na2O Others Iron tailings 31.98 6.49 10.23 30.77 13.84 1.64 5.05 CIT 33.97 7.23 10.59 31.14 13.91 1.66 1.50 Diatomite 97.91 1.04 0.65 - 0.05 0.12 0. 23 Perlite 74.6 13.1 0.83 0.83 0.19 7.87 2.58

Table 2. Main properties of capric acid (CA) and carbon nanotubes (CNT).

Properties CA CNT CAS number 334-48-5 308068-56-6 Chemical formula C10H20O2 - Molecular weight 172.26 - Purity (%) 98.5 91% Melting point (◦C) 31.4 ◦C 3550 ◦C Solidifying point ( C) 29.0 C- ◦ ≥ ◦ Thermal conductivity (w/(m k)) - 2860 ·

2.2. Preparation of FSPCM As shown in Figure1, the FSPCM was fabricated according to the following two steps. First of all, the different mass ratio of CA and CIT were put into different beakers and evenly mixed, respectively. Then, the mixtures were heated and evenly stirred on the water bath at 60 ◦C for 30 min. After they were cooled down to room temperature for 2 h, the composites were formed. Then, the leakage tests were carried out though the simple and effective method reported by the literature 47–50 [47–50]. Secondly, the CA/CIT sample without leakage and maximum adsorption capacity of CA was mixed with 1 wt.%, 3 wt.%, 3 wt.%, and 7 wt.% CNT in 25 mL beakers, respectively. Moreover, the preparation procedures of the sample composites in the first step were repeated. Thus, the CA/CIT/CNT FSPCMs can be obtained. Minerals 2019, 9, x FOR PEER REVIEW 4 of 15

MineralsMoreover,2019 , the9, 648 preparation procedures of the sample composites in the first step were repeated.4 of 16 Thus, the CA/CIT/CNT FSPCMs can be obtained.

Figure 1. Preparation process of CACA/CIT/CNT/CIT/CNT composites.composites. 2.3. Characterization of FSPCM 2.3. Characterization of FSPCM The leakage tests were conducted on the constant magnetic stirrer by taking advantage of the The leakage tests were conducted on the constant magnetic stirrer by taking advantage of the diffusion-oozing testing method. Before testing, 3 g CA/CIT composites consisting of different mass diffusion-oozing testing method. Before testing, 3 g CA/CIT composites consisting of different mass fractions of CA and CIT were separately pressed at 12 MPa for 3 min in the mould with the diameter of fractions of CA and CIT were separately pressed at 12 MPa for 3 min in the mould with the 3 cm. The made-up samples similar to small round flakes were put on the medium speed filter papers, diameter of 3 cm. The made-up samples similar to small round flakes were put on the medium respectively. Then, the samples along with the corresponding filter paper were placed in the constant speed filter papers, respectively. Then, the samples along with the corresponding filter paper were humidity magnetic stirrer to be heated at 60 C for 10 min. The leakage phenomenon and the result placed in the constant humidity magnetic ◦ stirrer to be heated at 60 °C for 10 min. The leakage of the samples can be observed during the heating process. The leakage stain of every sample was phenomenon and the result of the samples can be observed during the heating process. The leakage measured by a ruler with a test error of 0.5 mm. The amounts of the samples were weighed by digital stain of every sample was measured ±by a ruler with a test error of ±0.5 mm. The amounts of the electronic precision balance with one-thousandth precision. The microstructure of CA, CIT, CNT, samples were weighed by digital electronic precision balance with one-thousandth precision. The CA/CIT, and CA/CIT/CNT FSPCM were characterized by scanning electron microscope (SEM). The microstructure of CA, CIT, CNT, CA/CIT, and CA/CIT/CNT FSPCM were characterized by scanning chemical characterization of the constituents of FSPCM was evaluated by using Fourier transformation electron microscope (SEM). The chemical characterization of the constituents of FSPCM was infrared spectroscope (FTIR) at a wavenumber range of 400–4000 cm 1. The melting temperature and evaluated by using Fourier transformation infrared spectroscope (FTIR)− at a wavenumber range of latent heat of CA/CIT and CA/CIT/CNT FSPCM were measured by differential scanning calorimeter 400–4000 cm−1. The melting temperature and latent heat of CA/CIT and CA/CIT/CNT FSPCM were (DSC) at the heating/cooling rate of 10 C/min under N gas atmosphere. The thermal gravity analyses measured by differential scanning calorimeter◦ (DSC) 2at the heating/cooling rate of 10 °C /min under (TGA, from 20–600 ◦C) of CA, CA/CIT, and CA/CIT/CNT were used to investigate the thermal stability N2 gas atmosphere. The thermal gravity analyses (TGA, from 20–600 °C) of CA, CA/CIT, and of FSPCM. The thermal storage and release performance were conducted by using an intelligent CA/CIT/CNT were used to investigate the thermal stability of FSPCM. The thermal storage and paperless recorder. For this purpose, the same amount of CA, CA/CIT FSPCM, and CA/CIT/CNT release performance were conducted by using an intelligent paperless recorder. For this purpose, FSPCM were put into centrifuge tubes, respectively. Then, the thermocouple was embedded into the same amount of CA, CA/CIT FSPCM, and CA/CIT/CNT FSPCM were put into centrifuge tubes, the centrifuge tube, while the other was connected to the intelligent paperless recorder. After that, respectively. Then, the thermocouple was embedded into the centrifuge tube, while the other was all the centrifuge tubes were placed into the refrigerator at 10 C to maintain the same starting connected to the intelligent paperless recorder. After that, all− the ◦centrifuge tubes were placed into temperature. When the experiments were started, they were placed into the water bath at room the refrigerator at −10 °C to maintain the same starting temperature. When the experiments were temperature. The temperature range of the sample was 10 to 60 C for the heating process, while 60 started, they were placed into the water bath at room− temperature.◦ The temperature range of the to 10 C for the freezing process, respectively. When the temperature of the water bath rose up to 60 sample− ◦ was −10 to 60 °C for the heating process, while 60 to −10 °C for the freezing process, C, it was kept for half an hour during the heating process. The temperature data during the whole ◦respectively. When the temperature of the water bath rose up to 60 °C , it was kept for half an hour process of heat storage/release were continuously recorded by the intelligent paperless recorder. during the heating process. The temperature data during the whole process of heat storage/release 3.were Results continuously and Discussion recorded by the intelligent paperless recorder.

3.1.3. Results The Leakage and Discussion Tests of CA/ CIT/CNT Composites The sample tablets of CA/CIT composites used in the leakage tests were given in Figure2. 3.1. The Leakage Tests of CA/CIT/CNT Composites The testing results were shown in Figure3. Obviously, the leakage is more and more serious from FigureThe3d sample to Figure tablet3a, whiles of CA/CIT the leakage composites of CAliquid used in cannot the leakage be observed tests were in Figure given3e,f. in Figure Usually, 2. noThe leakagetesting results of PCM were is the shown basic in criterion Figure to3. evaluateObviously, the the package leakage effi isciency more and of FSPCM. more serious Hence, from the sample Figure Minerals 2019, 9, x FOR PEER REVIEW 5 of 15 Minerals 2019, 9, 648 5 of 16 3d to Figure 3a, while the leakage of CA liquid cannot be observed in Figure 3e,f. Usually, no leakage of PCM is the basic criterion to evaluate the package efficiency of FSPCM. Hence, the sample S1-5 S1-5can be can considered be considered to be to t behe theFSPCM FSPCM without without liquid liquid leakage. leakage. Sometimes, Sometimes, the the sample sample without without any liquid stains of of CA CA o onn filter filter paper paper after after heating heating can can also also be be used used to to evaluate evaluate the the package package efficiency efficiency of ofFSPCM FSPCM.. There Therefore,fore, the the liquid liquid stains stains of ofCA CA in inCA/CIT CA/CIT on onthe the filter filter paper paper were were further furthermoremore shown shown in inFigure Figure 4. 4As. Asseen seen from from Figure Figure 4, sample4, sample S1-6 S1-6 indicates indicates no liquid no liquid leakage leakage form formeded in the in F theSPCM FSPCM while whilethere wa theres a wassmall a smallliquidliquid stain of stain the ofsample the sample S1-5 on S1-5 the on filter the filterpaper paper.. To quantify To quantify the leakage the leakage of CA, of CA,the leakage the leakage ratio ratio was wasintroduced, introduced, which which is the is theweight weight of leaked of leaked CACA divided divided by bythe the total total weight weight of ofCA CA in in the the corresponding corresponding composites composites [32 [32]. ].As As seen seen in in Table Table 3,3 , the the leakage leakage ratios of S1-5S1-5 andand S1-6 S1-6 were quitequite smallersmaller than than the the others others so so that that their their leakage leakage could could be negligible.be negligible Furthermore,. Furthermore the, CNTthe CNT can alsocan also be employed be employed to act to as act the as supporting the support material.ing material. When CNTWhen was CNT added was intoadded the into CA/ CIT the FSPCM,CA/CIT theFSPCM leakage, the ratioleakage of FSPCMratio of wouldFSPCM be would much be lower much than lower without than without CNT at CNT the mass at the fraction mass fraction of S1-5. Therefore,of S1-5. Therefore to be a comprehensive, to be a comprehensive consideration, consideration the sample, the S1-5 sample in the firstS1-5 step in the can firstbe considered step can be to beconsidered the FSPCM to be used the inFSPCM the second used step.in the In second the same step. way, In the when same the way CA, /whenCIT FSPCM the CA/CIT was fabricated FSPCM was by mixingfabricated the by specified mixingamount the specified of CNT amount during of the CNT second during step, the the second thermal step, conductivity the thermal enhancer conductivity CNT wasenhancer added CNT into was the CAadded/CIT into FSPCM the CA/CIT to fabricate FSPCM CA /toCIT fabricate/FSPCM. CA/CIT/FSPCM.

Figure 2.2. SampleSample tabletstablets of of CA CA/CIT/CIT composites composites used used in leakagein leakage tests. test (as). S1-1,(a) S1 (-b1), S1-2,(b) S1 (c-)2 S1-3,, (c) S1 (d-)3 S1-4,, (d) (S1e)- S1-5,4, (e) (S1f)- S1-6.5, (f) S1-6.

Figure 3. LeakageLeakage test test results results obtained obtained at at 60 60 °C◦ Cof ofCA/CIT CA/CIT composites composites.. (a) (S1a)- S1-1,1, (b) (S1b)-2 S1-2,, (c) S1 (c)-3 S1-3,, (d) (S1d)-4 S1-4,, (e) S1 (e)-5 S1-5,, (f) S1 (f)-6. S1-6. Minerals 2019, 9, 648 6 of 16 Minerals 2019, 9, x FOR PEER REVIEW 6 of 15

Figure 4. LLiquidiquid stains of CA in CA/CIT CA/CIT composites on the filter filter paper after heating at 60 °C◦C.. ( (aa)) S1 S1-1,-1, (b) S1-2,S1-2, (c) S1-3,S1-3, (d)) S1-4,S1-4, ((e)) S1-5,S1-5, ((ff)) S1-6.S1-6.

Table 3. Basic proportion and leakage results of CA/CIT composites. Table 3. Basic proportion and leakage results of CA/CIT composites.

The CompositionThe Composition Ratio of Ratio of Leakage Area of StepStep Sample Sample Leakage RatioLeakage (%) Leakage Ratio (%) Area of the Sample (cm2 2) the CA/CITthe Composites CA/CIT Composites the Sample (cm ) 1 1S1-1 S1-1Pure CA Pure CA46.07 46.0772.35 72.35 1 1S1-2 S1-250% CA + 50% CIT CA + 50% CIT21.80 21.8039.57 39.57 1 1S1-3 S1-340% CA + 60% 40% CI CAT + 60% CIT15.43 15.4326.41 26.41 1 1S1-4 S1-430% CA + 70% 30% CI CAT + 70% CIT12.89 12.8918.85 18.85 1 S1-5 20% CA + 80% CIT 0.50 (negligible) (Missing) 1 S1-5 20% CA + 80% CIT 0.50 (negligible) (Missing) 1 S1-6 10% CA + 90% CIT 0.33 (negligible) 0 1 S1-6 10% CA + 90% CIT 0.33 (negligible) 0

ToTo quantitativelyquantitatively evaluate the leakage results, the leakage area and leakage ratio ratioss of CA/CIT CA/CIT composites werewere calculatedcalculated and and shown shown in in Figures Figure5s and 5 and6. From 6. Fro Figuresm Figure5 ands 56 ,and it can 6, beit can clearly be clearly seen thatseen boththat both the leakage the leakage area andarea theand leakage the leakage ratio ofratio CA of/CIT CA/CIT composites composites increase increase monotonously monotonously with thewith increasing the increas ofing the of mass the mass fraction fraction of CIT. of Moreover, CIT. Moreover, the linear the linear relationships relationships can be can described be described as the followingas the follow formulations,ing formulations, respectively. respectively.

Y1= −0.5931X1 + 48.8259, R2 = 0.9773 Y = 0.5931X + 48.8259, R2 = 0.9773 1 − 1 Where Y1 represents the leakage ratio of sample, %. X1 represents the mass fraction of sample, %. where Y1 represents the leakage ratio of sample, %. X1 represents the mass fraction of sample, %. Y2= −0.9539X2 + 73.9642, R2 = 0.9757 Y = 0.9539X + 73.9642, R2 = 0.9757 Where Y2 represents the leakage area2 − of sample,2 cm2. X2 represents the mass fraction of sample, %. Obviously, when the mass fraction of CIT is about 80%, the leakage area and the leakage ratio of where Y represents the leakage area of sample, cm2. X represents the mass fraction of sample, %. CA/CIT 2composites are very small and negligible. Furthermore,2 the mentioned relationships may Obviously, when the mass fraction of CIT is about 80%, the leakage area and the leakage ratio provide a relatively feasible quantitative method to evaluate and judge the leakage of PCM of CA/CIT composites are very small and negligible. Furthermore, the mentioned relationships may composites. provide a relatively feasible quantitative method to evaluate and judge the leakage of PCM composites. Minerals 2019, 9, 648 7 of 16 MineralsMinerals 20192019,, 99,, xx FORFOR PEERPEER REVIEWREVIEW 77 ofof 1515

FigureFigure 5. 5. LeakageLeakage areaarea ofof CA/CITCA/CIT CA/CIT composites composites with with different didifferentfferent mass mass fraction fractionsfractionss of of CIT.CITCIT..

FigureFigure 6. 6. LeakageLeakage ratiosratios ofof CA/CITCA/CIT CA/CIT compositescomposites with with different didifferentfferent mass mass fraction fractionsfractionss of of CIT CIT.CIT.. 3.2. Morphology of the CA, CIT, CNT, CA/CIT, and CA/CIT/CNT Composites 3.2.3.2. MMorphologyorphology ofof thethe CA,CA, CIT,CIT, CNT,CNT, CA/CITCA/CIT,, andand CA/CA/CITCIT//CNTCNT CompositesComposites Figure7 shows the SEM images of CA, CIT, CA /CIT FSPCM, and CA/CIT/CNT FSPCM. As shown FigFigureure 77 showsshows thethe SEMSEM imagesimages ofof CA,CA, CIT,CIT, CA/CITCA/CIT FSPCMFSPCM,, andand CA/CIT/CA/CIT/CNTCNT FSPCM.FSPCM. AAss in Figure7a, the CA displayed the viscous paste liquid. From Figure7b, it can be seen that the CIT had shownshown inin FigFigureure 77aa,, thethe CACA displaydisplayeded thethe vviscousiscous ppasteaste liquid.liquid. FromFrom FigFigureure 77bb,, itit cancan bebe seenseen thatthat thethe a porous microstructure. As seen from Figure7c, the CNT looked like an expanded cotton floc with CITCIT hadhad aa porousporous microstructuremicrostructure.. AsAs sseeenen fromfrom FigFigureure 77cc,, thethe CNTCNT looklookeded llikeike anan eexpandedxpanded cottoncotton various pore network structures. As observed from Figure7d, the surface of CIT was covered by the flfloocc withwith variousvarious pore pore nnetworketwork structures structures.. AAss observedobserved fromfrom FigFigureure 77dd,, thethe surface surface of of CIT CIT was was impregnated CA. Simultaneously, most of the porous hole of CIT were completely covered and the coveredcovered byby thethe impregnatedimpregnated CA.CA. SSimultaneouslyimultaneously,, mostmost ofof thethe porousporous holehole ofof CITCIT wwereere completelycompletely porous holes were reduced. This indicated that the suitable amount of CA could be absorbed into coveredcovered anandd thethe porousporous holeholess werewere reduced.reduced. ThisThis indicatedindicated thatthat thethe suitablesuitable amountamount ofof CACA couldcould bebe porous holes of CIT due to capillary and surface tension forces among the components. As clearly absorbedabsorbed into into porous porous holes holes of of CIT CIT duedue to to capillary capillary and and surface surface tension tension forces forces among among the the noticed from Figure7e,f, some CNT was covered on the surface porous hole of CIT, which confirmed componentscomponents.. AAss clearclearlyly noticednoticed fromfrom FigFigureure 77ee,f,f,, somesome CNTCNT waswas coveredcovered onon thethe sursurfaceface porousporous holehole that the CNT was successfully impregnated into the synthesized FSPCM, while most of the CNT was ofof CIT,CIT, whichwhich confirmconfirmeded thatthat thethe CNTCNT waswas successfullysuccessfully impregnatedimpregnated intointo thethe synthesynthesizedsized FSPCMFSPCM,, filled into CIT particles. This is the reason why CNT can enhance the heat transfer efficiency of CA by whilewhile mostmost ofof thethe CNTCNT waswas filledfilled intointo CITCIT particlesparticles.. ThisThis isis thethe reasonreason whywhy CNTCNT cancan enhanceenhance thethe constructing path channels for CA successfully. heatheat transfertransfer efficiencyefficiency ofof CACA byby cconstructonstructinging papathth channelchannelss forfor CACA successfullysuccessfully.. Minerals 2019, 9, 648 8 of 16

Minerals1 20193.2., M9, orphologyx FOR PEER of REVIEW the CA, CIT, CNT, CA/CIT and CA/CIT/CNT composites 8 of 15

(a) (b)

8μm

μ 100 m 20μm 2

(c) (d)

3μm CIT

CA

10μm 20μm 3 (e) (f) CA CA CIT

3μm

CIT

CNT CNT 100μm 20μm 4 Figure 7. SEMSEM photographs photographs of of CA CA ( (aa),), CIT CIT ( (bb),), CNT CNT ( (cc),), CA/ CA/CIT ( d), CA/CIT/CNT CA/CIT/CNT,, ((ee)) andand ((ff).).

3.3. Chemical Compatibility of the CA/ CA/CIT//CNTCNT CompositesComposites TheThe FTIR spectrums spectrums of of the the CA, CA, CIT, CIT, CA/CIT CA/CIT FSPCM FSPCM,, and and CA/CIT/ CA/CITCNT/CNT FSPCM FSPCM we werere given given in inFig Figureure 8. 8It. can It canbe seen be seenthat in that the in spectrum the spectrum of pure of CA, pure the CA, absorption the absorption peaks at peaks 939, 1410, at 939, and 1410, 1710 1 andcm−1 1710corresponded cm− corresponded to the stretching to the stretching vibration vibrationss of –OH of, C=O –OH,, and C=O, COO and– COO–,, respectively. respectively. The 1 Thecharacteristic characteristic peaks peaks at 2850 at 2850 and and2930 2930 cm− cm1 represent− representeded symmetric symmetric stretching stretching vibration vibrationss of –CH of –CH3 and3 –CH2, respectively [51,52]. In the spectrum of CIT, the bands at 476, 695, and 882 cm−1 can be ascribed to the stretching of the Si–O–Si group. Additionally, the stretching vibrations of the Si–O group Minerals 2019, 9, 648 9 of 16 and –CH , respectively [51,52]. In the spectrum of CIT, the bands at 476, 695, and 882 cm 1 can be Minerals 20192 , 9, x FOR PEER REVIEW − 9 of 15 ascribed to the stretching of the Si–O–Si group. Additionally, the stretching vibrations of the Si–O group 1 appearedappeared in 1090 andand 11701170 cmcm−−1.. T Thehe spectrums spectrums of of CA/CIT CA/CIT and CA/CIT/ CA/CIT/CNT show showeded the primary peakspeaks ofof CACAand and CIT, CIT and, and CNT CNT had ha nod no eff ecteffect on theon the spectrum spectrum peaks peaks of composites. of composites Moreover,. Moreover, no other no additionalother additional peaks peaks occurred occurred in the fabricatedin the fabricated FSPCMs FSPCMs except forexcept slight for changes slight changes in the intensity in the intensity of some peaksof some because peaks ofbecause weak of physical weak physical interaction interaction such as, such hydrogen as, hydrogen bonding bonding interactions, interactions, surface tensionsurface force,tension and force capillary, and capillary force. These force findings. These indicated findings thatindicate thered wasthat onlythere physical was only interaction physical amonginteraction CA, CIT,among and CA, CNT CIT in, compositesand CNT in without composite anyskind without of chemical any kind action. of chemical Hence, action FTIR results. Hence confirmed, FTIR results that FSPCMconfirmed had that good FSPCM chemical ha compatibilityd good chemical among compati the constituentsbility among in FSPCM. the constituents Moreover, thein physical FSPCM. interactionMoreover, the largely physical contributed interaction to the largely shape-stabilization contributed to ofthe CA shape/CIT- becausestabilization the CAof CA/CIT molecules because were firmlythe CA tied molecules to CIT poreswere firmly by the tied confinement to CIT pores effect. by the confinement effect.

Figure 8. FTIRFTIR spectra spectra of of C CA,A, C CIT,IT, C CAA//CITCIT,, and CACA//CIT//CNTCNT samples.samples.

3.4. T Thermalhermal Properties of the CA/ CA/CITCIT//CNTCNT FSPCMsFSPCMs TheThe thermal properties including latent heat value and phase change temperature of CACA/CIT/CIT FSPCM andand CA CA/CIT//CIT/CNTCNT FSPCM FSPCM were were examined examined by DSC. by DSC. The DSCThe curves DSC curves and data and of data CA/CIT of CA/CIT FSPCM andFSPCM CA /andCIT /CNTCA/CIT/ FSPCMCNT areFSPCM shown are in shown Figure 9in and Fig Tableure 94 and. As Table seen from 4. As Figure seen 9from and TableFigure4, 9 the and meltingTable 4, temperaturethe melting temperature and freezing and temperature freezing of temperature CA/CIT FSPCM of CA/CIT and CAFSPCM/CIT/ CNTand CA/CIT/FSPCM wereCNT determinedFSPCM were as determined 35.89 and 26.8 as ◦3C5. for89 and CA, as26.8 30.73 °C for and CA 26.77, as◦ C30.73 for CAand/CIT 26.77 FSPCM, °C for as CA/CIT 29.70 and FSPCM 26.09, ◦asC for29.70 CA and/CIT 2/6CNT.09 °C FSPCM, for CA/CIT/CNT respectively. FSPCM In comparison, respectively. with I puren comparison CA, the melting with pure temperatures CA, the melting of the compositestemperatures were of the diminished composites by 5.16 were and diminished 6.19 ◦C, respectively. by 5.16 and Compared6.19 °C , respectively. to pure CA, Compared the freezing to temperaturespure CA, the freezing of composites temperature were reduceds of composites by 0.03 were and 0.71reduc◦C,ed respectively.by 0.03 and 0 In.71 addition, °C , respectively there was. In aaddition, difference there between was a thedifference freezing between temperature the freezing and melting temperature temperature. and melting The reason temperature. may be T thehe physicalreason may interaction be the physical among theinteraction components among in composites.the components Fortunately, in composites. the phase Fortunately, change temperature the phase ofchange composites temperature is closed of composite to the comfortables is closed roomto the temperature comfortable ofroom 20–26 temperature◦C, so the of prepared 20–26 °C CA, so/CIT the FSPCMprepared is CA/CIT suitable forFSPCM application is suitable in buildings. for application Moreover, in buildings. the thermal Moreover enthalpy, the of CA,thermal CA/ CITenthalpy FSPCM, of andCA, CACA/CIT/CIT/ CNTFSPCM FSPCM, and CA/CIT/ are 169.5,CNT 25.14, FSPCM and 22.69are 169.5 J/g during, 25.14, theand melting22.69 J/g process, during respectively.the melting Theproc comparisonsess, respectively. of thermal The comparisons properties between of thermal this work properties and some between other this literatures work and were some also listed other inliterature Table4.s Althoughwere also the listed thermal in Table enthalpy 4. Although of CA /CIT the/CNT thermal FSPCM enthalpy is slightly of CA/CIT/CNT lower than that FSPCM of some is literatures,slightly lower it has than many that advantages of some literature over others, it materials has many in advantages building applications over other suchmaterial as lows in cost, building wide source,application larges insuch quantity, as low easy cost, to w use,ide andsource, simple large process. in quantity In short,, easy we canto use conclude, and s thatimple the process fabricated. In CAshort/CIT, we/CNT can FSPCMconclude has that TES the potential fabricated in buildings CA/CIT/CNT as energy-saving FSPCM has materials.TES potential in buildings as energy-saving materials. Minerals 2019, 9, 648 10 of 16 Minerals 2019, 9, x FOR PEER REVIEW 10 of 15

FigureFigure 9. 9. DSCDSC curves curves of CA, of CA/ CA,CIT CA form/CIT-stable form-stable phase change phase material change (FSPCM material), and (FSPCM), CA/CIT/CNT and CAFSPCM/CIT/.CNT FSPCM.

Table 4. Thermal properties and results comparison with some literatures. Table 4. Thermal properties and results comparison with some literatures. Melting Solidifying Latent Heat of Latent Heat of Item TemperatureMelting TemperatureSolidifying LatentSolidifying Heat LatentReferences Heat Melting (J/g) Item Temperature(◦C) (◦C)Temperature of Melting(J/g) of Solidifying References Capric-myristic acid (20 wt.%)/VMT 19.8(°C ) 17.1(°C ) 27.46(J/g) 31.42(J/g) [53 ] Capric-myristic acid (20 wt.%)/VMT 19.7 17.1 26.9 (Missing) [53] Capric-myristic acid+ EG (20 (2 wt.%)wt.%)/VMT 19.8 17.1 27.46 31.42 [53] Capric-myristic acidCapric-lauric (20 wt.%) acid/VMT (26 + EG (2 19.1119.7 (Missing)17.1 35.2426.9 (Missing) (Missing [54] ) [53] wtwt.%).%) /gypsum Dodecanol (25–30 wt.%)/gypsum 20.0 21.0 17.0 (Missing) [55,56] Capric-lauric acidPropyl (26 palmitate wt.%)/gypsum (25–30 19.11 (Missing) 35.24 (Missing) [54] 19.0 16.0 40.0 [55,56] Dodecanol (25–30wt.%) wt/.gypsun%)/gypsum 20.0 21.0 17.0 (Missing) [55,56] Capric-lauric acid (25–30 wt.%) + Propyl palmitate (25–30 wt.%)/gypsun 17.019.0 21.016.0 28.040.0 (Missing) [57] [55,56] fire retardant/gypsum Capric-lauric acidParaffi (25n (18–30 wt.%) wt/.kaolin%) + fire 23.9 26.3 27.9 (Missing) [58] Xylitol pentalaurate (19 17.0 21.0 28.0 (Missing) [57] retardant/gypsum 44.07 41.08 31.09 27.36 [59] wt.%)/cement Paraffin Xylitol(18 wt pentalaurate.%)/kaolin (20 23.9 26.3 27.9 (Missing) [58] 40.44 39.53 31.77 29.47 [59] Xylitol pentalauratewt.%) (19/gypsum wt.%)/cement 44.07 41.08 31.09 27.36 [59] Capric-palmitic acid (25 Xylitol pentalaurate (20 wt.%)/gypsum 21.1240.44 21.4639.53 36.2331.77 38.2829.47 [60 ] [59] wt.%)/gypsum wallboard Capric-palmitic acid (25 wt.%)/gypsum Emerest 2326 (25.7 wt.%)/gypsum 16.3221.12 19.721.46 34.7736.23 33.9738.28 [61 ] [60] PA (25 wt.%)/active aluminum wallboard 74.13 59.57 28.56 17.53 [62] Emerest 2326 (25.7 woxidet.%)/gypsum 16.32 19.7 34.77 33.97 [61] S1-5 (CA 20 wt.% + CIT 80 wt.%) 30.73 28.98 25.14 23.05 This study PA (25 wtCA.%)/active/CIT/CNT aluminum (CA20 wt.% +oxideCIT 80 74.13 59.57 28.56 17.53 [62] 29.70 28.09 22.69 21.17 This study S1-5 (CA 20 wtwt.%.% +/CNT CIT 5 80 wt.%) wt.%) 30.73 28.98 25.14 23.05 This study CA/CIT/CNT (CA20 wt.% + CIT 80 29.70 28.09 22.69 21.17 This study 3.5. Thermalwt.%/CNT Stability 5 wt.%) of the CA/CIT/CNT FSPCMs The thermal stability of CA, CA/CIT FSPCM, and CA/CIT/CNT FSPCM were examined by TGA, 3.5. Thermal Stability of the CA/CIT/CNT FSPCMs and the TGA curves were presented in Figure 10. As seen from Figure 10, the weight loss percentage of CA, CAThe/CIT thermal FSPCM, stability and CA of/CIT CA,/CNT CA/CIT FSPCM FSPCM were 99.92%,, and CA/CIT/ 20%, andCNT 18.90%, FSPCM respectively. were examined The results by indicatedTGA, and that the theTGA mass curves fractions were presented of CA confined in Figure into 10 CIT. As andseen CIT from/CNT Fig wereure 10 20%, the and weight 18.90%, loss respectively.percentage of In CA,addition, CA/CIT CIT wasFSPCM still, thermallyand CA/CIT/ stableCNT over FSPCM 440 ◦C. were It demonstrated 99.92%, 20% that, and the CIT18.90% was, quiterespectively. feasible toThe act results as supporting indicate materiald that the of CAmass PCM. fraction Moreover,s of CA the confined onset degradation into CIT and temperatures CIT/CNT ofwere CA, 20% CA/ CITandFSPCM, 18.90%,and respectively CA/CIT/CNT. In addition FSPCM were, CIT 220 wa◦sC, still 380 thermally◦C, and 440 stable◦C, respectively. over 440 °C The. It temperaturedemonstrated limit that for the thermal CIT wa degradations quite feasible of CAto act/CIT as FSPCMsupporting and material CA/CIT /CNTof CA was PCM. much Moreover, higher thanthe onset that ofdegradation the working temperatures temperatures of (16–26 CA, CA/CIT◦C). These FSPCM results, and confirm CA/CIT/ thatCNT the FSPCM CA/CIT were FSPCM 220 and °C , 380 °C, and 440 °C , respectively. The temperature limit for thermal degradation of CA/CIT FSPCM and CA/CIT/CNT was much higher than that of the working temperatures (16–26 °C ). These results Minerals 2019, 9, 648 11 of 16 Minerals 2019, 9, x FOR PEER REVIEW 11 of 15

CAconfirm/CIT/ CNT that FSPCM the CA/CIT have good FSPCM thermal and stability, CA/CIT/ whichCNT FSPCM makes them have more good suitable thermal for stability, TES application which inmakes buildings. them more suitable for TES application in buildings.

FigureFigure 10. TGA curves of C CA,A, C CAA//CIT FSPCM,FSPCM, and CACA//CIT//CNTCNT FSPCM.FSPCM.

3.6. T Thermalhermal Storage/ReleaseRelease PerformancePerformance ofof thethe CACA//CITCIT/CNT/CNT FSPCMs FSPCMs ToTo further further evaluate evaluate the the improvement improvement eefficiencyfficiency of heat heat transfer, transfer, the the thermalthermal storagestorage//releaserelease performanceperformance waswas also examinedexamined throughthrough thethe coolingcooling curvecurve method.method. The test method and storagestorage eefficiencyfficiency definitiondefinition of of the the melting melting and and cooling cooling curve curve in in this this study study was wa thes the same same asthe as the condition condition in our in previousour previous work work [63]. Moreover,[63]. More theover, evaluation the evaluation method method of heat of transfer heat transfer of the prepared of the prepared FSPCMs FSPCMs was also aswas the also conditions as the conditions in our previous in our previous work [63 ].work The [ melting63]. The andmelting cooling and curves cooling of curves CA, CA of/ CITCA, PSPCM,CA/CIT andPSPCM CA/,CIT and/CNT CA/CIT/ FSPCMCNT with FSPCM different with mass different fraction mass CNT fraction were CNT shown were in Figure shown 11 in. FromFigure the 11 curves. From of Figure 11, for a 40 C increase in temperature (from 12 to 30 C) during the melting process, the the curves of Figure ◦11, for a 40 °C increase in temperature− (from◦ −12 to 30 °C ) during the melting requiredprocess, the time required was about time 21, was 18, about 15, 13, 2 12,1, 18 and, 15, 11 13 min, 12 for, and CA, 11 CAmin/CIT for FSPCM,CA, CA/CIT and CAFSPCM/CIT/,CNT and FSPCM,CA/CIT/CNT respectively. FSPCM, Compared respectively with. Compared the melting with time the ofmelting CA and time CA of/CIT CA FSPCM, and CA/CIT the melting FSPCM time, the wasmelting reduced time bywas 47.62% reduced and by 38.89%, 47.62% respectively and 38.89%, for respectively CA/CIT/CNT for (7 CA/CIT/CNT wt.%) whereas (7 itwt was.%) reducedwhereas by it 42.86%was reduced and 33.33% by 42.86 for% CA and/CIT 33.33/CNT% for (5 CA/CIT/CNT wt.%). In a similar (5 wt. way,%). In for a similar a 40 ◦C way, decrease for a in40 temperature °C decrease (from 30 to 12 C) during the solidifying process, the passed time was about 22, 20, 13, 12, 10, and 8 in temperature− ◦(from 30 to −12 °C ) during the solidifying process, the passed time was about 22, 20, min,13, 12 respectively,, 10, and for8 min CA,, CA respectively/CIT FSPCM,, for and CA, CA / CA/CITCIT/CNT FSPCM FSPCMs., and In comparison CA/CIT/CNT with FSPCMs the freezing. In timecomparison of CA and with CA the/CIT freezing FSPCM, time it was of CA reduced and CA/CIT by 63.64% FSPCM and 60.00%,, it was reduced respectively by 63.64 for CA% /andCIT /60.00CNT%, (7 wt.%)respectively whereas for it wasCA/CIT/CNT reduced by (54.55%7 wt.% and) whereas 50.00% forit CA was/CIT reduced/CNT (5 by wt.%). 54.55 Moreover,% and 5 the0.00% time for of maintainingCA/CIT/CNT an (5 equilibrium wt.%). Moreover, temperature the time platform of maintaining for CA, CA an/CIT equilibrium FSPCM, and temperature CA/CIT/CNT platform FSPCMs for withCA, CA/CIT different FSPCM mass fractions, and CA/CIT/CNT CNT in the meltingFSPCMs process with different was 12, 9,mass 5, 2.5, fractions 2, and 1.8CNT min, in respectively.the melting Additionally,process was 12, the 9,time 5, of2.5, maintaining 2, and 1.8 themin equilibrium, respectively temperature. Additionally, platform the time for CA, of CAmaintaining/CIT FSPCM, the andequilibrium CA/CIT /temperatureCNT FSPCMs platform during thefor freezingCA, CA/CIT process FSPCM was, 14,and 7, CA/CIT/CNT 4, 2.5, 2, and 1.8FSPCMs min, respectively. during the Thefreezing time of process maintaining was 14, the 7, equilibrium 4, 2.5, 2, temperatureand 1.8 min platform, respectively. of CA/CIT The/CNT time FSPCMs of maintain was lessing than the thatequilibrium of CA and temperature CA/CIT FSPCM platform during of CA/CIT/CNT the melting FSPCMs or freezing wa process.s less than The that CA of/CIT CA/CNT and FSPCMCA/CIT exhibitsFSPCM aduring greater the heat melting storage or/ release freezing rate process than CA. The/CIT CA/CIT/CNT and pure CA. FSPCM These exhibits results meana greater that heat the CNTstorage/release additive in rate PSPCM than CA/CIT can evidently and pure reduce CA. These the thermal resultsstorage mean that/release the CNT time additive and improve in PSPCM heat transfercan evidently efficiency. reduce the thermal storage/release time and improve heat transfer efficiency. Minerals 2019, 9, 648 12 of 16 Minerals 2019, 9, x FOR PEER REVIEW 12 of 15

Figure 11. Storage and release curves of C CA,A, C CAA//CIT FSPCM,FSPCM, and CACA//CIT//CNTCNT FSPCM.FSPCM. 4. Conclusions 4. Conclusions In this study, CIT was used as the supporting material to prevent the liquid leakage of CA and In this study, CIT was used as the supporting material to prevent the liquid leakage of CA and fabricate the FSPCM. A novel CA/CIT/CNT FSPCM was developed to be used in a building TES fabricate the FSPCM. A novel CA/CIT/CNT FSPCM was developed to be used in a building TES by a by a facile direct impregnation method. The leakage tests reveal that both the leakage area and the facile direct impregnation method. The leakage tests reveal that both the leakage area and the leakage ratio of CA/CIT composites decrease monotonously with the increase of the mass fraction of leakage ratio of CA/CIT composites2 decrease monotonously with the increase2 of the mass fraction of CIT (Y1 = 0.5931X1 + 48.8259, R = 0.9773. Y2 = 0.9539X2 + 73.9642, R = 0.9757). The absorption CIT (Y1 = −−0.5931X1 + 48.8259, R2 = 0.9773. Y2 = −0.9539− X2 + 73.9642, R2 = 0.9757). The absorption of CA of CA in CIT is about 20 wt.% without liquid leakage. The good chemical compatibility among CA, in CIT is about 20 wt.% without liquid leakage. The good chemical compatibility among CA, CIT, CIT, and CNT were confirmed by SEM and FTIR tests. When the mass fraction of CIT is about 80 and CNT were confirmed by SEM and FTIR tests. When the mass fraction of CIT is about 80 wt.% in wt.% in CA/CIT/CNT FSPCM including 5 wt.% CNT, the DSC results indicate that the fabricated CA/CIT/CNT FSPCM including 5 wt.% CNT, the DSC results indicate that the fabricated CA/CIT/CNT FSPCM melts at 29.70 ◦C with a latent heat of 22.69 J/g and solidifies at 28.09 ◦C with the CA/CIT/CNT FSPCM melts at 29.70 °C with a latent heat of 22.69 J/g and solidifies at 28.09 °C with enthalpy of 21.17 J/g, respectively. The fabricated CA/CIT/CNT FSPCM has a suitable phase change the enthalpy of 21.17 J/g, respectively. The fabricated CA/CIT/CNT FSPCM has a suitable phase temperature, which is close to the suitable room temperature range of 20–26 ◦C. The TGA analysis change temperature, which is close to the suitable room temperature range of 20–26 °C . The TGA confirms that the CA/CIT/CNT FSPCM has good thermal stability above its working temperature. analysis confirms that the CA/CIT/CNT FSPCM has good thermal stability above its working Moreover, the melting and solidifying time of the prepared CA/CIT/CNT (5 wt.%) FSPCM are 42.86% temperature. Moreover, the melting and solidifying time of the prepared CA/CIT/CNT (5 wt.%) and 54.55% less than those of pure CA, respectively. The introduction of CNT can increase the thermal FSPCM are 42.86% and 54.55% less than those of pure CA, respectively. The introduction of CNT conductivity of CA/CIT composites and improve the storage/release performance of CA/CIT and pure can increase the thermal conductivity of CA/CIT composites and improve the storage/release CA. In conclusion, the produced CA/CIT/CNT FSPCM presents a potential choice for TES in buildings performance of CA/CIT and pure CA. In conclusion, the produced CA/CIT/CNT FSPCM presents a as ingredients material. Moreover, it may provide a novel path for recycling utilization of iron tailings. potential choice for TES in buildings as ingredients material. Moreover, it may provide a novel path Authorfor recyc Contributions:ling utilizationConceptualization, of iron tailings. P.L. and X.G.; methodology, P.L. and X.G.; literature review, P.L. and X.G.; investigation, P.L. and X.G.; Resources: J.R., and Z.Z.; writing—original draft preparation, P.L. and X.G.; writing—reviewAuthor Contributions: and editing, Conceptualization, P.L. and X.G. and P.L Z.Z.;. and supervision, X.G.; methodology, L.B. and J.S.; P.L project. and X. administration,G.; literature review, L.B. and P J.S.;.L. Funding Acquisition: J.S. and X.G.; investigation, P.L. and X.G.; Resources: J.R., and Z.Z.; writing—original draft preparation, P.L. and Funding:X.G.; writingThis—review work wasand editing, financially P.L. supported and X.G. and by Z the.Z.; special supervision, funding L.B of. and Guiyang J.S.; project science administration, and technology L.B. bureau and Guiyang University (GYU-KYZ(2019~2020)DT-13), the National Natural Science Foundation of China (41872039),and J.S.; Funding the Opening Acquisition: Project J.S of. Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education (18zxk03), Hebei Key Technology R&D Program of the Agency of Hebei province (17214016), Science andFunding technology: This research work wa Youths financially Fund Project supported of Hebei by Province the special Higher funding Education of Guiyang (QN2018124), science and and Hebei technology Province Naturalbureau andScience Guiyang Foundation University Youth (GYU Fund- (E2019403135).KYZ(2019~2020)DT-13), the National Natural Science Foundation of Acknowledgments:China (41872039), theThe Opening authors would Projectlike of Keyto express Laboratory their gratitude of Solid to Waste the Instrument Treatment Chemical and Resource Analysis Recycle, Center ofMinistry Peking of University Education (Beijing, (18zxk03) China), Hebei for thermal Key Technology properties R&D analysis. Program Hebei of GEO the University Agency of Gemsbase Hebei province is also warmly acknowledged for FTIR analysis. (17214016), Science and technology research Youth Fund Project of Hebei Province Higher Education Conflicts(QN2018124 of Interest:), and HebeiThe Provinc authorse declareNatural no Science conflict Foundation of interest. Youth Fund (E2019403135). Minerals 2019, 9, 648 13 of 16

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