Mining Science and Technology( China)21(2011)599-603Contents lists available at Science DirectMining Science and Technology( China)ELSEVIERjournalhomepagewww.elseviercom/locate/mstcRole of Ni(NO3)2 in the preparation of a magnetic coal-based activated carbonZhang Jun, Xie Qiang", Liu Juan, Yang Mingshun, Yao XingSchool of Chemical and Environmental Engineering China University of Mining 6 Technology, Beiing 100083, ChinaARTICLE INFOABSTRACTThe role of Ni(NO,h in the preparation of a magnetic activated carbon is reported in this paper magnetic7 December 2010coal-based activated carbons(MCAC)were prepared from Taixi anthracite with low ash content in thein revised form 5 January 201126 January 2011presence of Ni(NO,]. The MCAC materials were characterized by a vibrating sample magnetometernline 16 July 2011(VSM), X-ray diffraction(XRD), a scanning electric microscope(SEM), and by N2 adsorption. the cylindrical precursors and derived char were also subjected to thermogravimetric analysis to compare theirbehavior of weight losses during carbonization. The results show that mCAc has a larger surface areaMagnetic coal-based activated carbon(1074 m"/g)and a higher pore volume (0.5792 cm /g)with enhanced mesopore ratio( by about 10%).ItNi(NO,hlso has a high saturation magnetization(1.6749 emu/g) and low coercivity(43 26 0e)l, which allowsMagnetic propertiesthe material to be magnetically separated. The MCAC is easily magnetized because the nickel salt is converted into Ni during carbonization and activation. Metallic Ni has a strong magnetism on account ofelectrostatic interaction. Added Ni(NOh catalyzes the carbonization and activation process by accelerat-ing bum off of the carbon, which contributes to the development of mesopores and macropores in theactivated carbon.e 2011 Published by Elsevier B V. on behalf of China University of Mining Technology1 Introductioncarbons. Moreover, the preparation of the magnetic activated carbon requires several steps and special chemicals. incorporation ofActivated carbon is among the important carbon based materi- the magnetic particles inside the pores of the activated carbon,als that find wider applications in almost every industrial field, while at the same time keeping a high surface area, is the key pointThey are employed in liquid phase adsorption to remove contam- for preparing magnetic activated carbons used as adsorbents.inants, recover products, and as catalysts, or catalytic supports,A simple one-step method for preparing magnetic activated car-due to the large internal surface area and specific pore structure. bon with a regulated pore size from coal in the presence of Fe3oHowever, difficulties encountered when separating spent activated has recently been published by our teams (9-11]. In the presentcarbon limit its application in many occasions. Filtration, the tradi- work the preparation of another new magnetic coal-based acti-tional method for separating activated carbon, may result in the vated carbon with a high surface area, appropriate pore size, andblockage of filters or the loss of carbon causing secondary pollu- magnetic separability is described. This carbon is prepared frotion Magnetic separation is considered a quick and effective tech- anthracite with a low ash content in the presence of Ni(NO 3h.nique for separating magnetic particles and has been used formany applications in biochemistry, analytical chemistry and ore 2. Experimentalmining [ 1-4. Therefore, magnetization of activated carbon is aneffective approach for separating and recovering spent activated2.1. Preparation of the magnetic coal based activated carbonSynthesis of magnetic activated carbon has recently become afocus in the activated carbon industry, and in metallurgy, environ-Synthesis of magnetic activated carbon from coal can be dividedinto three stages, ie. preparing cylindrical precursors, carbonizemental, chemical, and pharmaceutical areas (5-8). Usually, a mag- tion, and activation ( 12, 13). An anthracite coal(Taixi, China)con-netic activated carbon is prepared from a suspension ofcommercial activated carbon in a solution of an iron salt by adding taining 7 wt% volatile material and about 2. 52 wt x ash contentalkali to precipitate magnetic iron oxides.as crushed, ground, and sieved to particles sized smaller than0.074 mm. a blender was used to prepare a mixture of the anthraMost of these magnetic activated carbons have a small surface cite powder (68 wt%), coal tar (28 wt %) and Ni(NO3)2 9H20area and very poor porosity compared to common activated(4 wt %). in water. Then the thoroughly mixed feedstock was extruded in the form of 1 cm cylinders.nding author Tel +8610 62331014After 3 days ofE-mail address: dr-xieqcumtb educn(Q Xie)were put into a中國煤化工 nder a flow of N21674-5264/ssee front matter o 2011 Published by Elsevier B.V. on behalf of China University of Mining&TCNMHGdoi:10.1016mstc201101003. Zhang et al/Mining Science and Technology( China)21(2011)599-60380 mL/min )at a heating rate of 5C/ min to a final temperature of600C. The samples were carbonized at 600C for 45 min. Thensamples were heated to 880C at a heating rate of 10C min andwith a nitrogen flow of 80 mL/min. Steam activation at 880C withI NiOa steam flow of 0.77 mL H2o/(h g)was then carried out for 3 h. Theactivated carbon prepared in the presence of Ni(NO3h was labeledMCAC-Ni and the one without Ni(NO3h was labeled AC RM andCM represent the cylindrical precursor and the carbonized mate-rial, respectively.22. Characterization of the samples10203040506070The magnetic properties of the samples were measured using avibrating sample magnetometer(Lake Shore VSM-7307. USA). Thefield dependence of the magnetization was measured at room tem-2 x-ray diffraction patterns of AC, CM-Ni, and MCAC-Nperature. X-ray diffraction of the samples was performed with anX-ray diffractometer(Rigaku D/Max-RB, Japan)using Cu Ka radia- magnetization were very low suggesting that the MCAC-Ni couldtion at a scan speed of g /min The morphology of the activated car- not only rapidly respond to changes in external magnetic fieldbon was characterized with a scanning electron microscope (EoL but could also be easily demagnetizedJSM6700F, Japan).XRD patterns of AC, CM-Ni, and MCAC-Ni are shown in Fig. 2.The activated carbon was characterized by N2 adsorption/ The McAc-Ni contains nickel mainly in the form of metallic nickeldesorption at 77 K with a NoVA-1200 instrument from Quanta- (20-44.51%, 51.85. 76.37%). Diffraction peaks were also observedChrome(USA) The specific surface area(SBer)was derived from at 20-3725o and 43.28, suggesting the presence of smallthe N2 adsorption isotherms by the BET equation. The total pore amounts of NiO. These peaks were also observed weakly in thevolume was calculated from a single point on the nitrogen adsorp- XRD diffraction pattems of CM-Ni, which showed lower quantitiestion isotherm at a relative pressure of 0.99. The micropore volumes of nickel than the MCAc-Ni samplevere calculated using the t-plot method. The mesopore volumewere calculated from the volume of N2 adsorbed at a relative presThe magnetic properties of MCAC-Ni are attributed to ni that isformed by the thermal decomposition and reduction of the nickelsure of 0.99 minus the corresponding micropore volume. The BJHalt during the carbonization and activation process. the 3d elecmethod was employed to determine the mesopore distribution.trons of Ni are arranged in accordance with hunds rules and theThermogravimetric analysis(NETZSCH STA 409C, Germany) Pauli exclusion principles and these orbitals have unpaired elecwas conducted on the cylindrical precursors using these condi- trons. The electrons of the adjacent atoms have magnetictions:N2 flow of 80 mL/min; heating rate of 5C/ min; temperature moments. The unpaired electrons contribute to the magnetic mo-range from room temperature to 600C Thermogravimetric anal- ment of 0.6 on Ni. The direct exchange interaction of these elec-ysis(Versa Therm HS, USA)of the carbonized material was pertronic magnetic moments causes the atomic magnetic momentsformed under these conditions: N2 flow of 100 my min; heating to have planar alignment.te of 10oC min from room temperature to 880C: a hold temperIn previous studies added Fe304 was mostly converted into FeOature of 880C for 1 h under a flow of steam(0. 1 g/min). The flow during activation and residual Fe and Fe304 created the magnetismof steam was controlled by a trace constant-flow pump( Solvent in that magnetic activated carbon (10 11]. The non-magnetic nat-Delivery Module 501, USA).ure of Feo required a larger addition of Fe O4 in that case. The Niformed by thermal decomposition and reduction of the nickel sal3. Results and discussionis present in greater relative amounts. Further, if the content of Niwere to be increased the magnetic properties of the resulting acti-3. 1. Mechanism of magnetization of MCAc-Nivated carbon would be stronger.A characteristic hysteresis loop could be observed(Fig. 1)whichindicates the ferromagnetic character of the MCAC-Ni. The AC was 3. 2. Mechanism of pore size regulation in MCAC-Ninearly diamagnetic. Fig. 1 shows the saturation magnetizationvalue of the MCAC-Ni to be around 1. 6749 emu/g, which was high 32. 1. Pore characterizationenough to enable the samples to be manipulated with conven- Fig 3a shows a micrograph of AC without added Ni(NO3hThetional magnets. the values for both coercive force and residualAChas a surface morphology that shows deflected zonal or sheet-like graphite that affords a large number of micropores. Fig. 3bMCAC-NIshows the magnetic activated carbon at a magnification of 5000Observe that small aggregates of nickel, which appear brighterare present on the darker surface of the activated carbon. the fineCM-Ninickel particles tend to cover specific parts of the activated carboninstead of being dispersed evenly over the whole surface. The morphology of the MCAC-Ni, shown in Fig 3c, contains surface poros-ity that contributes to an increase in the surface area. there arealso some irregular macropores on the surface of the activated carbon. Nickel has a catalytic effect during carbonization and activa-tion that accelerates the burning off of the carbon wall and10000-5000Field (Oe)eton and the fo中國煤化工 g of the carbon skeFig. 4 showCN MH Gs for both AC andFig 1. Hysteresis loop of AC, CM-Ni, and MCAC-NiMCAC-Ni. The Samples snow type vi behavior, as defined by theJ Zhang et aL/Mining Science and Technology( ahina)21 (2011)599-603應(yīng)(aACb)MCAC-Ni(<5000)(c) MCAC-NI(×10000r玉 SEM photographs.activated carbon structure. Meanwhile, MCAC-Ni had an enhanced380number of mesopores as well as more macropores. Compared toadded Fe3O4, the ratio of mesopore increased significantly becauseMCAC-NIof the catalytic performance of the nickel, which is higher than thatof iron [11]3.2.2.E]ects of Ni(NO3)2 in the preparation of magnetic activatedcarbonThe mechanism of pore size development during the carboniza-240tion and activation of MCAc-Ni was studied by thermal analysis220under nitrogen and steam atmospheres. fig. 6 shows the thermo-gravimetric results Over the temperature range of 150-300C000204060.810the weight loss of RM-Ni was higher than that of RM becauseRelative pressure(p/po)nitrogen oxide from decomposition of the nickel nitrate(aboveFlk 4 N2 adsorption-desorption isotherms of AC and MCAC-Ni.110.C nickel nitrate decomposes) affords a more oxygen richatmosphere that accelerates the carbonization.Intemational Union of Pure and Applied Chemistry(IUPAC). TheFrom 400 to 600C RM-Ni has more weight loss comparedsample AC shows a small hysteresis loop in the adsorption-desorp- RM. This may be due to the catalysis of Ni in the carbonizationtion isotherm that indicates a microporous structure with a low and reductive decomposition of nickel oxide In the process of car-mesopore ratio and a fairly large surface area is present. The conization as the cylindrical precursors are heated the coal partiMCAC-Ni sample shows an obvious hysteresis loop that indicates cles undergo thermal decomposition and form solid semicoke orof the MCAc-Ni increase without reaching equilibrium temperatures of 450 and 700oC, and H2 and co are released atindicating the presence of small macroporesThe data shown in Table 1 suggest that the BET surface area, and reductant. Ni has a catalytic effect on anthracitepyrolysis duringe microporous and mesoporous volume werethe carbonization process and accelerates the rate of free radicalaffected by the added Ni(NO,h. An increase of surface area from generation [19, 20]. Ni in the carbonization process also hinders817.6m /g(for Ac) to 1074 mig(for the nickel doped carbon) the condensation of free radicals by absorbing electrons formedwas observed. The microporous volume changed from 0.3720 to during pyrolysis. This eventually leads to carbon having a crystal0.4421 cm lg and the mesoporous volume changed from 0.0575 structure with short range order but long range disorder, whichto 0. 1371 cm /g and the ratio of mesopore doubled because of the is beneficial to forming initial porosity in the activated carbon.added nickel. These results show that adding nickel salt helps config. 7 shows thermogravimetric analysis results from scans ontrol the pore structure in the coal-based activated carbon prepara- CM and CM-Ni: the curves have a distinctly different appearancetion [16-18]. Ac, without nickel salt, has a typical microporous After 60 min activation the burned off weight of CM-Ni was 15%lower than the weight of the burned off CM. Carbon gasificationunder H20 occurs at temperatures above 880C to produce COand H that may then reduce nickel oxides. Formation of carbonmonoxide and water is represented by0.04C+H20→H2+Co003Reduction of nickel oxides in a direct reduction occurs by theaction of gaseous reductants like Co and H2 rather than by the ac-0tion of solid carbon the present study shows that Nio undergoes00lstepwise reductions by Co and H2 which is repNio+C0冖Ni+C2No+H≠N+HoNiO reacts中國煤化工he pores accompa-nied by itsCNMHGNi has a catalyticPt 5 pore size distributions in activated carbons ac and MCAc-Ni.effect during Hiyu uall of the activatedJ. Zhang et aL/ Mining Science and Technology(China)21(2011)599-603Table 1Pore structure of AC and MCAC-NiSampleBET, surface area(m2/g)Pore volume(cmlg)817.60.429503720005751339MCAC-Ni107400.5792044210.1371105(2)The magnetic properties of the MCAC-Ni derive from free Ni,which is formed by thermal decomposition and reduction ofDTGthe nickel salt during the carbonization and activation pro-cess Electrostatic interaction gives Ni a strong magnetism095that enhances the magnetization of the coal based activatedcarbon(3)Nickel catalysis increased the rate of carbonization and acti-vation. the greatest effect was on the activation processwhere accelerated burn off of the carbon wall to form080numerous macropores and mesopores in the activated mate-rial was observed,」1100200300400500600Temperature()Acknowledgmentsgravimetric analyses in a nitrogen atmosphere: samples RM andThe authors are thankful for the financial support by theNational Natural Science Foundation of China(No. 20776150)the National Hi-Tech Research and Development Program of China(No. 2008AA05Z308)and the special Fund for Basic Scientific Re-search of Central Colleges(No. 2009QH15)[11 Rudge SR, Kurtz tL Vesely CR Catterall LG, williamson DL Preparation,particles for chemotherapy. 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Univ Sci Technol Beijingreacts with the reducing gases to enlarge the pore: (2)Metallic [101 Yang MS, Xie Q Zhang Jun, iuJ. wang Y,EfTects of coalnickel catalyzes the carbonization and activation process by accel-ank, Fe O4 amounts and activation teerating burn off of the carbon wall to enlarge the pores.characteristics of magnetic activated carbon. Mining Sci Technol010:206):872-6[111 Yang MS. Xie Q Xing w, Zhang ZH, Hang Jiang Y. Effect of Fe-containing4. Conclusionsm210:96901hMCAC-Ni having a large surface area(1074 m? /g)and a high (12) Gong Cz. xie Q Zheng YF Ye SF. Chen YF. Regulation of pore size distributioncoal-based activated carbon. New Carbon Mater 2009: 24(2): 141-6pore volume(0.5792 cm /g)with an enhanced ratio of mes- [131 Xie Q, Bian BX. Principles of control over coal carbonization and its applicationopores (about 10%),a high saturation magnetizationn preparation of activated carbon. 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