Element geochemistry and cleaning potential of the No. 11 coal seam from Antaibao mining district

2142Science in China ser. D Earth Sciences 2005 Vol 48 No 12 2142--2154Element geochemistry and cleaning potential ofthe No. 1l coal seam from Antaibao mining districtWANG Wenfeng, QIN Yong, SONG Dangyu, SANG Shuxun, JIANG BoZHU Yanming& FU Xuehai1. College of Resources Geosciences, China University of Mining and Technology, Xuzhou 221008, China2. State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, ChinaCorrespondenceshouldbeaddressedtoWangWenfeng(email:wenfwang@vip.163.com)Received November 3. 2003Abstract Based on the analyses of sulfur and 41 other elements in 8 channel samples of theNo. 11 coal seam from Antaibao surface mine, Shanxi, China and 4 samples from the coalpreparation plant of this mine, the distribution of the elements in the seam profile, their geochemical partitioning behavior during the coal cleaning and the genetic relationships between theboth are studied. The conclusions are drawn as follows. The coal-forming environment wasprobably invaded by sea water during the post-stage of peatification, which results in the fact thatthe contents of As, Fe, S, etc. associated closely with sea water tend to increase toward the topof the seam, and that the kaolinite changes into illite and montmorillonite in the coal-sublayernear the roof. These elements studied are dominantly associated with kaolinite, pyrite, illitemontmorillonite, etc, of which the As, Pb, Mn, Cs, Co, Ni, etc. are mainly associated with sulfidesthe Mo, V, Nb, Hf, REEs, Ta etc. mainly with kaolintie, the Mg, Al etc. mainly with epigeneticmontmorillonite, and the Rb, Cr, Ba, Cu, K, Hg, etc. mainly with epigenetic illite. The physical coalcleaning is not only effective in the removal of ash and sulfur, but also in reducing the concentration of most major and trace elements. The elements Be, U, Sb, W, Br, Se, P, etc are largely orpartly organically bound showing a relatively low removability, while the removability of the otherelements studied is more than 20%, of which the Mg, Mn, Hg, Fe, AS, K, Al, Cs, and Cr associ-ated mostly with the coarser or epigenetic minerals show a higher removability than that of ashThe distribution of the elements in the seam profile controls their partitioning behavior to a greatdegree during the coal cleaning processesKeywords: Antaibao mining district, No 11 coal seam, element geochemistry, cleaning.DOI:10.1360/03vd0506It has aroused great attention that the mobilization Unfortunately, there are fairly few studies on the parti-of potential toxic substance during coal mining, pro- tioning behavior of trace elements during the coalcessing and using has serious negative influence on cleaning/->. Moreover, studies on geochemistry ofenvironment. Clearly, the coal cleaning can be prop trace elemerhacic work for understanderly applied to removing hazardous elements or re- ing their en中国煤化工 hat is thducing their concentrations prior to combustion, which ternal relatioCNMHalso is considered as an economical and effective elements in coal and their partitioning behavior duringtechnique in minimizing some of these problemshe coal cleaning? Studies on this will be emphasizeCopyright by Science in China Press 2005Element geochemistry and cleaning potential of the No. 1 l coal seam from Antaibao mining districtin this paper.I Geological setting and samplesThe Antaibao surface mine. Pingshuo. ShanxiThe Antaibao mining district is located in theProvince, as a super-huge coal enterprise, is one of the southwestPingshuo mining district, northerlargest five surface coal mines in China, and its affili- Shanxi Province, China. The coal-bearing strata in theated coal preparation plant is the largest steam one in mining district occur in the Taiyuan Formation of UpChina.The NoS 4. 9 and 11 coal seams are major per Carboniferous age and the Shanxi Formation ofproductive ones in the mine. The geochemistry of ele- Lower Permian age(Fig. 1). The coal-bearing strata ofnents in the Nos 4 and 9 coal seams was studied by Taiyuan Formation were mainly accumulated in tidalsome researchers,". Currently, the No. ll coal seandelta, tidal-flat and lagoon environments. The Taiyis being mined, the geological exploration data and the Formation, with an average thickness of 90 m, con-findings of previous study indicate that sea water had atains eight coal seams, of which NoS 9 and 1 l are migreater effect on the no. ll coal seam than on the nonable throughout the whole district. The No. ll coal9 coal seam. Consequently, the distribution characseam,a paralic sedimentation environment, was ac-teristics of trace elements in the two seams shouldcumulated in a peat swamp developed on tidal-flat andsandbank, and it has been obviously influenced by seahave an obvious difference, and it is necessary thatwater during the coal accumulation 6 The seam is gasfurther studies on the enrichment genesis of trace coal, with marlstone at the roof and silty mudstone orelements in the No Il coal seam be conducted Based fine sandstone at the bottom. and its thickness rangeson the analyses of sulfur and 4l other major and trace from 0 to 9.30 m throughout the whole district. onelements in 8 channel samples of the No. 11 coal seam average 3.74 m. In the sampling locality, the thicknessfrom the Antaibao surface mine and 4 samples from of the seam is 4.99 m. and the incremental channelthe affiliated coal preparation plant, the present paper samples were collected according to the macrolitho-is to discuss the distribution of these elements in the type of coal seam(Fig. 1), of which PA2 coal-sublayerseam profile, their geochemical partitioning behavior contains a thin layer of carbonaceous mudstone part-during the coal cleaning and the genetic relationships ings. At the meantime, the four samples of the feedbetween both, in hopes of providing scientific infor- coal, cleaned coal, middlings and coal slime are alsomation for the rational exploitation of the seam and collected from the affiliated coal preparation plant ofenvironmental protectionsthis mineTable 1 Fundamental data for 12 samples from the Antaibao mining distriProximateSample type Thickness/m analysis(%)Sulfur analysis (%o)Some major and trace elements/ug.gTI Pfeed coaNd23.2428.510.720.040.811.57971839019505100408001678280.89930.222.4AB2 middlings3980Nd0.450.030.240.721570570017702400931005032341.222844.246.AB3 cleaned coal Nd13.31Nd0.260020.690.9741728403653300212001188267.56821483AB4 coal slime5739Nd2.050.030.032,128202290038002900818004446278622093.585.,1PAo marlstoneNdNd4.650.110.585.3482905340020209700285006653181.876941.0718.70.1411.2945.461430.071773.27680152004307670559036061745916.1727.5,4738.341.050.060.691.80730110004002670378003109134,49419854.5PA3 bright coa0.4821.5042480.800.061.392.257138520140638010900160569.05012472.6dull coal1.95308838660.230.030.891.1584128303703510256003947104.210415.7629PA5 semibright coal 0.6134.3842,440.580.021,191.7965066804102250314001706155,65811.682PA6 bri0.3519.5839380.400.031.41.87952中国煤化工5633023PA7 silty mudstoneNdNd0.330.020070.421420a) ABl-AB4 are respecthe feed coal. middlings. cleaned coal and coal slime froHCNMHG69273443934ant of this mine: PAO-PA7 are respectively the roof, 5 coal-sublayers, bottom of the No. Il coal seam, as seen from Fig. 1. Ad, ash content, dry basis; Vdaf, volatile matter,dry ash-free basis, Sp, d, pyritic sulfur; Ss, d, sulfate sulfur; Sod, organic sulfur; S,d, total sulfur Nd, no dataScience in China ser D Earth Sciencesls巴sCoarseMudstoneFineQSiltstoneCoal seamPebbled coarsePAORoofNo 6 coal0.14mNo. 7 coal0.48 m PANo 9 coal1.95【氯0.61 m PA5No. 12 coal0.35 m PA6BottomStratigraphic column of Carboniferous-Permian coal-bearing strata in Antaibao mining district(modified from ref. [7])and sampling locais and volatile matter) for coal sam-2 Analytical methodsples were中国煤化工 Provincial coalFundamental data of the samples studied are given Research In CNMHGinese standardin Tables 1,2 and 3. The total sulfur and sulfur form method(GB/T214-96, Gb/T215-96 and GB/T212-9analyses for all samples and a partial proximate respectively). The concentrations of 41 major andElement geochemistry and cleaning potential of the No. 1 l coal seam from Antaibao mining districtTable 2 Concentrations of some major and trace elements in the 12 samples(ug g)as Sb Ba rb Se Th Cr Hf CsTa Co Br w Mo Zn Pb Ni Mn Nb Hg BeABI1.200.30545.15.09.715.13.80.365.00.512.906.81.004.8017.1018.985.2737.2636.188.920.1941.50AB20910.35736.38,224.722,48,20.3710.41.501.902.42.008.3065016.1668l16.8182.0821.630.2302.56AB30.470.33383.04.27.58.42.40.203.90.391.70590.833.3010.1015014.1510.9924.126920.0671.72AB44.000.561331988.519.038.28.21.2010.11404.401.71908.5024.5037.1312.9628.3679.2221.250.6941.8PA054.200.225639.811223.36607.03.7012.91.7012.302.62.8020.6661.43520358.33389579.7629.500.0972.83PAl3.200.45966.43.61413.3140.239.80.1819018.32606.1043.97260149077.6818935.120.0862.49PA21.800.44864.28,412,915.7640.5110.50970.695.7240116827.6724.4840922.2766.5923930.073340PA31200.27673.97.369563.70.254.80.590.929.32.104.56294813943.46379320.279310.165094PA40.430.2164.34.016.312.1560.309,11.000.69791.708.7834.1415.074.2520.1047.9220.170.135171PA50.970.22443.64.28.55.2500.295.00.922.70761.2099027.65219411.18114649,8519620.095196PA60.870.331978.74.89.019.03.30.478.40.473.20761.406.5133.50214626.1013.6737.8311810.2022.87PA72.000.30316078.27.312.856.84.70.8413.01.206404.12.9023.5160.732248384339.21133.648.800.0352.12Table 3 Anaylses of REEs and relevant parametersSampleREEs/μg·gRelevant parametersCe Pr Nd Sm Eu Gdy Ho Er Tm Yb L∑REEδEuδCeTh/UAB33.460.054716.43.70.662.980.512920.631.650.231.20.20129960.680.93404AB241.87947.5624.9601.104910.834.871.082.920432.30.41178.500.690.934.12AB325,643.84.0812.82.90.473.140.693.780.771.890.241.10.181014AB451.192410.1042.06.91.105.030.875.331.243.520.553.10.45223.680.640.853.73PA67.8118011.1135.88,01.l6.701.407861.664.210.572.80.53267.55,490.821.2PAl17843.04.8921.55.70.894.770.935.591.283.550.540.57114010.05PA259.7130.012.50420941.308.031.709872.175.770.84440.74288420.490.95287PA315,229029110.62.70.553.030.603.660.852,400.372.10.3574.320.650.862.65PA410.124.22.721l.83.40.713.740.724.220.942.540.37200.3067.760.670.955.62PA542.18798.2626.56.51.205.370.915.171.102.860.40200.25PA641,290.08.7129.7691.606.45,451.142840.381.80.21193.350.790.95391PA786.9103.09.3427.76.01.305.585.171.102.860402.00.36252.620.740.633.76trace elements were also determined by the instru- Research, NaUniversity, and cold vapor atomicnental neutron activation analysis(As, Ba, Br, Ce, Co, absorption spectrometry(Hg, error 5%)at the InstCr Cs. eu Fe HfK. la lu. mo na nd rb Sb. stute of Environmental Health of Chinese Academy ofSe, Sm, Ta. Tb, Th,U.V.w and Yb, standard devia- Prevention Medicine. It should be noted that in Tabletion: +2%-+7%)at the Institute of High Energy 3, the contents of some rare-earth elements(REes)Physics of the Chinese Academy Sciences, inductively such as Pr,中国煤化工 alculated by incoupled plasma atomic emission spectroscopy(Al, Be, terpolationchondrite-nor.Ca Cu Mg Mn Nb. Ni. P. Pb. Ti and Zn error malized diaCNMHGwutuautng methods of10%)at the State Key Laboratory of Mineral Deposits relevant parameters are described in ref. [9]. Addi2146Science in China ser. d Earth sciencestionally, X-ray powder diffraction(XRD, model some coal-sublayersD/Max-3B) analysis was applied to identifying main4 Enrichment mechanism of trace elementsminerals for three channel samples and two samples offeed and cleaned coal at the center of Forecasting andThere are many geological factors that control theAnalysis of China University of Mining and Technol- distribution and enrichment of trace elements in coalogyBased on the analydrite-normalized ree patterns, and XRD, together3 Distribution of the elements in the No 11 coal with correlation analysis and factor analysis, the au-seam profilethors in this paper discuss the enrichment mechanismFig. 2 exhibits the vertical distribution of sulfur and of trace elements in the seam41 major and trace elements in the No. 11 coal seam 4.1 Facies element analysisprofile. The concentrations of a number of elementssuch as U. as sb. Br. Ca. W.P. Mn. s. Pb Fe and ZnIt is generally agreed that the Th/U ratio of contiin the coal-sublayers near the roof tend to increase nental sediments is over 7 but that of marine sedimentsupward, which thus implies that there is a genetic rela- below 710, 1. As regards the channel samples from thetionship between the distribution of these elements andNo. 1l coal seam, their Th/u ratio all is below 7(Ta-the deposition of the roof. Expect U, Sb, Br, P and Hgble 3), and it is, therefore, inferred that the seam wasthe rest 37 of the elements studied show that the high- accumulated in coastal peat swamp environmentest concentration in the roof, bottom or partings(PA2 Moreover, the Th/U ratio, as an indictor of the sedi-contains a thin layer of carbon mudstone), implyingment environment, decreases overall toward the top othat the 37 elements prefer to enrich in the inorganicthe seam, suggesting that the salinity of water mediumconstituents rather man the organic constituents of in the peat swamp increases gradually upwardcoal. However. the elements u. sb. Br. P and hg haveIn the samples of the roof(PAO)and first coalthe highest concentration in coal-sublayer, of which sublayer(PAl), total sulfur contents are respectivelythe Br concentration is significantly higher in each 5.34% and 4.65%, and pyritic sulfur contents areoal-sublayer than in the roof and bottom, which re- respectively 3. 27% and 1.43%. In addition, in the verflects to a certain degree that the 5 elements show a tical direction of the seam, the total, pyritic and sulfatecloser association with the organic constituents thaisulfur contents tend to decrease overall toward thewith the inorganic constituents of coal, and indicates bottom, and the organic sulfur contents do not de-that the Br has a stronger organic affinity, whereas the crease distinctly but its content is higher in the roofU, Sb, P and Hg have a certain organic affinity in and the coal-sublayers near the roof than in the bottomRoof La Ce Nd Sm Eu Tb Yb Lu U As Sb Cr Co Br Ca WB00o0101o0101140101001010100112060015010Roof Hf Be Cu Se Th Na TaB〓中国煤化工Bottom I0o021o0no1030010101001010010(0o0CNMHGIO.Fig.2. Vertical variation of sulfur and 41 other elements in the No. 1 l coal seam(Al, Ca, Fe, Mg, K, S, Ti: % the others: ug.g)Element geochemistry and cleaning potential of the No. 1l coal seam from Antaibao mining districtand the coal-sublayers near the bottom respectively strates that the rees in PAl underwent the modifica(Table 1). High pyritic sulfur and sulfate sulfurtion of post-stage geological action and were depletedTaiyuan coals from North China were mainly derived which is possibly attributed to the loss of clay mineralsfrom sea water 213. Thus, the change tendency in-(the carriers of REEs)in the coal-sublayer because ofvolving total sulfur and sulfur forms observed above the influence of marine transgressindicates that. from the bottom to the roof. an associa-tion of the coal-forming peat swamp with sea water(2)The 8 Ce values of the channel samples varyincreases gradually, and that the reducibility, salinityfrom 0.63 to 0.95(Table 3), with slightly negativeanomalies which reflects that the seam was once af-and ph of water medium also increase gradually. Thisis in agreement with the analysis results above. In fact,fected by sea water. The negative Ce anomaly is arit is because the influence of the sea water on the topindicator of the marine facies environment 9. The 8Eupart of the No. 1l coal seam was greater than on its values(0.49-0.79)of all channel samples are smallerbottom part, while the elements U, As, sb, Br, Ca, Fehan unity, showing negative Eu anomalies. From theMn, sulfur, etc. have a relatively higher content in roof to the bottom, the 8 Eu values increase as a wholeweak alkaline and reducing sea water that these ele- in the coal samples, which is possibly related to thenents are enriched in the top part of the seamdecreasing influence of sea water on the seam 14)4.2 Ree analysis3) The different sublayers of the same coal seamformed in identical depositional environment shorThe rEEs in coal bear much geology-geochemistrhave basically similar REE patterns, while the abnor-information and also are important indicators of themal ree patterns possibly indicate that the seam wasenrichment characteristics of the associated trace eleaffected by post-stage geological actions". It isents in coal. The REEs in the No Il coal seam were clearly seen from Fig. 3(a)that the REE distributionnormalized based on the REE concentrations of com- curve of the roof, bottom and other coal-sublayersbination sample of chondrites determined by with the exception of the first coal-sublayer(PAl),Herrmann in 1970 and the chondrite-normalizedprimarily similar in shape, while the slope coefficientree distribution patterns in the seam were establishedof light rare-earth elements(LrEEs) distribution curveThe distribution characteristics of REEs areof pal is lower than that of other sublayers and be.as followslongs to the type of LREE-depleted distributie(1)The REe contents are obviously lower in the terns. Obviously, this was associated with the enfirst coal-sublayer(PAl)near the roof of the seam croachment of sea water after the forming of thethan in the second coal-sublayer(PA2), and are also coal-sublayer. The distribution curve of REES relatedlower than that in the sixth coal-sublayer(PA6)near to sea water is markedly characterized by slight deplethe bottom and the feed coal (Table 3 ) This demon- tion of LREEs, distinct negative Ce anomalies and10001000PAOPAlFeed coalMiddingsCoal slime#样好中国煤化工La Ce Pr Nd Sm EuGd Tb DyHo Er TmYb LCNMHGFig 3. REE distribution patterns in the 12 samples from the Antaibao mining district2148Science in China ser D Earth Sciencesobscure Eu anomalies! 151mostly attributable to pyrite, and that other elements(4)With respect to the feed coal and preparation related positively with pyritic sulfur are greatly distributed in the mineral. Additionally, a close relationproducts, the distribution curve of REEs is basically ship between Na. Ca and pyritic sulfur probably re-similar (Fig. 3(b), and has a good succession as aflects their identical source, namely sea waterwhole. In other words, the Ree contents graduallydecrease in the order of coal slime middlings, feed Although U is not a sulphophile element, reducingcoal and cleaned coal, while their ree patterns almost environment is favorable for the accumulation of sulremain the same. Hence it is reasonable to infer that fur, also for the enrichment of U. due to the invasionthe physical cleaning only can change REE contents of sea water, pH, Eh value and hydrogen sulfide conbut cant change its distribution patternstents in peat swamp were changed and formed a par-4.3 Correlation analysisticular geochemistry environment that benefited theenrichment of U. For example, humic acid and ulricAccording to the whole sample data, pyritic sulfur acid can complex U and other metal ions stronglyhas significant positive correlations with Fe, As, Pb, forming uranyl organic complex in the environment! 6)Mn, Cs, Co and Na at the 99% confidence level and In addition, alkali reducing environment affected bycritical positive correlations with Ni, Cr, Se and U at sea water made some elements activate out from de-the 95% confidence level. Of them, the correlations trital material of terrigenous origin, and played a rolebetween pyritic sulfur and Fe as well as as are shown in the establishment of the new chemistry equilibriumin Fig. 4(a)based on the analyses of the 10 coal sam- On the other hand, the environis favorableples. Here, the regression equation for Fe vs. pyritic for the accumulation of a large quantity of metal elesulfur is very close to the theoretical line for pyments in the water medium by bacterial biologenAnd it is therefore concluded that the variation in Fe is agency. The sulfates in the water are reduced to form20y=20286x-0.1118=0.984y=6.8547x+1.0661.076x+00309=0.862r=0.998A.. theoretical line for pyrite(a)(b)0.52.0Pyritic sulfur (%)Organic sulfur(%)1.00.608=90266x+0.0501040.2fc0.040.12中国煤化工6Sulfate sulfur(%)CNMHGFig. 4. Correlation analyses between Fe, As, Br, Ca and sulfur formElement geochemistry and cleaning potential of the No. 1l coal seam from Antaibao mining districtsulfides by the action of plenty of sulfate-reducing siderite and calcite. Liu et al. pointed out that whenbacteria, and compose amino-acids. Of these amino- Fe contents in water solution attain a certain density,acids, cystines react readily with metals ions Fe, Mn, the replacement might take place between carbonatiteAs, Pb, Zn, Cd, etc as well as salts to form pyrite and and Fe under supergenesis conditionother sulfides[ 1714.4 Factor analysisThe Br is significantly positively correlated withFactor analysis is used for the volatile matter (vdat)organic sulfur(Fig. 4(b)), suggesting that they bothash yield(Ad), total sulfur(SL. d), pyritic sulphur (Spd),originate from sea water, and that the br has a strongorganic affinity. Additionally, the volatile matter hasulfate sulfur (Ss.d), organic sulfur(S d), 2REE andrelatively high correlations with Br, W and U, andthe 33 other elements in order to obtaincritical positive correlation with Zn, demonstratingtive factors, the original component was rotated usingthat these elements are partly bound to the organicthe varimax method. In the analysis, Approximatelymatter. Except the second coal-sublayer sample(Pa2)95 of the cumulative variance is attributed to thea significant positive correlation is recorded between first five principal factors(Table 4). As seen from Tand sulfate sulfur(Fig. 4(c)), and it is theble 4, the factors are interpreted as followsinferred that there are some gypsums occurring in part(1) Factor 1(Fl) has higher positive correlationsof these samples studied. Similarly, if the roof and first with Fe. As. Sb, U. P Mn, W. Pb. Br. Ca, Sc. Be andcoal-sublayers samples (i.e. PAO and Pal respectively) total sulfur. These elements loaded on fl are almostare not taken into consideration and if the contents of identical to the chFe present in pyrite and that of Ca present in gypsum tration increase upward in the coal-sublayers near theare cut out, the rest of Fe and Ca contents in the other roof or are highest in the coal-sublayers )mentionedsamples show a certain negative correlation(Fig 4(d), above in analyzing the distribution of elements in thecorrelation coefficient: -0. 414).The Ca in coal is No. 11 coal seam profile. The F1 correlates positivelymostly associated with carbonates(principally cal- with Br and Ca as characteristic elements in sea watercite)+ 8, thereby the rest of Ca in the coal occurs also with pyritic sulfur and sulfate sulfur to a certainchiefly in calcite. Consequently, this correlation im- degree, but negatively with lithophile elements such asplies that siderite occurs in some of these samples and Hf, Ta, Ti, K, Th, etc, which suggests that the elethat the replacement possibly takes place betweenments loaded on Fl are greatly associated with seaTable 4 Rotated component matrixariable Factorl Factor 2 Factor 3 Variable Factor I Factor 2 Factor 3 Factor 4 Factor 5 Variable Factor 1 Factor 2 Factor 3 Factor 4 Factor 5Fe0.972W0.6710.5520.3880.444-0.696Br0.653-0.50417Hg-0.584-0.5980.3800.3650.7460.962U0.8250.5630.6970.3576230.6760.823Ti-0.4500.5490.6590.811Mn0.787-0.573Th-0.6010.5320.536Se0.0900.290-0.026-0.0510.075Pb0.7310.4010.393Rb0.904A:-0.1960.901-0212-0.1370.127a0.557-0.7710.234-0.019-0.1540.946-0.1470.969-0.0970.9470.828-0.530Sd0.788-0.2800.1580.2500.9100.3950.432Sad0.268-0.5890.624-0.352Hf-0.410.78Be0.4010.6110.657CREE0.597-0.591中国煤化工0480259Ta-0.4830.7600.350Sc0.4180.602CNMHGindicates loadings with an absolute value < 0.352150Science in China ser. d Earth scienceswater in origin. Meanwhile, a number of no-sulpho- as those in any other sample, and the concentrations ofphile elements(e. g. U, P, W, Br, Ca, Sc, Be, etc. ) as a Fe, As and Sb are higher in the pyrite sample than inpart of the elements loaded on Fl, are possibly partly any of the other samples. This conclusion is nearly inassociated with the organic matter because of the fac- accordance with the present studytor correlated positively with the volatile matter and(4)The combination of Mg, Al and Na implies thatorganic sulfur but negatively with the ash. In addition, the Mg, Al, Na, K, Cu and Hg negatively correlatedne organic sulfur contents also are fairly high in each with factor 4(F4) are possibly associated with montcoal-sublayer(Table 1), indicating that the organic morillonite. Of them Mg also is possibly associatedmatter in the seam still maintains active when the with carbonates. In addition, the F4 has a higher posiseam(peat swamp) was invaded by sea water, so thattive correlation with the volatile matter and organicthese elements(mentioned above) enriched insea water could combine with the organic matter. It is, theresulfur, suggesting that the Zn, W and Br, with a posifore, inferred that the invasion of sea water possiblytive loading on the factor, have a certain organic affinaceord, the elements loaded on F1 mainly originate (5) The elements Na, Ti, Th, Sc and w loaded onfrom sea water, of which the majority(mainly sul- factor 5(F5) are possibly associated with feldspar(So-phophile elements) occur in pyrite and part(mainly dium feldspar). Additionally, Se shows a weak posino-sulphophile elements)are possibly associated with tive correlation only with F2, little with other factorthe organic matter, but the possibility that the minority implying its other origins and possibly organicallyof them(e.g. Fe and Ca)are associated with sulfates bound. There is an extensive literature on the occuand/or carbonates cannot be ruled outrence of se in coal. which shows that the bulk of the(2)The Mo, V, Nb, Hf, REEs, Ta, Al, Cs, Be, T1,Se in most coals is associated with the organic conTh and Na show a considerably high positive correla- stituents and that a small of the Se is associated withtion with factor 2(F2), and the majority of them arepyrite and, to a lesser extent, with galena as well asclay minerals. 21. It should be noted that some elelithophile elements. Additionally, F2 correlates nega- ments studied(e.g. Al, Be, Cs, Cu, Na, Pb, REES, Th,tively with Ca, Br, total sulfur and sulfur forms, inTi, W, Sc, Sb, etc.) have close correlations with two ordicative of their terrigenous origin. A stronger positivecorrelation is recorded between f2 and al. but themore than two principal factors, reflecting the comcorrelation involving K and Mg is not observed, and it plexity of their modes of occurrence and a mixture ofis. therefore. concluded that the elements loaded ontheir origins. The ash shows a higher positive correlathe factor are possibly mainly associated with kaolinite.tion with F2 but poorly with F3, F4 and F5, whichFurthermore, the F2 correlates positively with ash inindicates that kaolinite dominates in the great majorityof the coals, while illite, montmorillonite and feldspardicating the kaolinite, as a main mineral, occurring inas accessory minerals, are present in the minority ofcoal samples(3)The Rb, Ba, Cr, Cu, Ni, Cs, Be, K, Sc, Co, SIREEs, Pb and Hg have higher positive correlations4.5 XRD analysiswith factor 3(F3)and they are possibly associatedIn order to confirm the above analytical results, fivewith illite. On the basis of the determination of 29 samples (PAl, PA2, PA6, ABland AB3) of theelements concentrations from four samples (i.e. kao- coal-sublayers, feed coal and cleaned coal were stud-linite, illite, pyrite and quartz, the four most abundant ied by X-ray diffraction analysis(Fig. 5). The Xrdminerals in coal)) isolated from the coal, Palmer et data display凵中国煤化工ial.o discovered that Hf. Ta. Th etc are lower con- and minorICNMHGitedominate incentrations in illite than in kaolinite and the concenthese samples ana there aIso exist a small amount ofations of k, Rb and Cs are about ten times as much pyrite, calcite, siderite, dolomite, quartz, feldspar,Element geochemistry and cleaning potential of the No. 1l coal seam from Antaibao mining districtnot affect the other coal-sublayers. This is in accor-KK: Kaolinitedance with the above conclusion drawn from the reeM: MontmonlloniteP: Pyranalysis. The presence of gypsum in the coalrectly confirm that the peat was once invaded by seaer 22l. Illite andfrom the transformation of kaolinite; because the topD: Dolomitepart of the seam has a close association with sea water,C: caleita great deal of Na, K and Mgand alkaline environments are favorable for the trans-PA2formationThe Xrd diffractogram of the cleaned coal is basically the same as that of the feed coal, but what differsis that the various mineral peaks shown on the formerQ: Quhave a somewhat low intensity, especially for illite peakGK O: OthersThis suggests that these mineral are removed to differentPA6degrees during the coal cleaning, and illite is relativelyto be removed due to its epigeneticKK.K5 Partitioning behavior of the elements duringthCleaned coalWhen comparing the element concentrations listedin TablesI and 2, it is easily found that the Be, U andKconcentrations are higher in the cleaFeed coalin the feed coal. In other words, the removability ofthe three elements is of negative value(removabilityelement concentration in the feed coal). Additionally,the removability of w, Br, Se and P are also considably low(<20%, Fig. 6), while that of the other ele-ig. 5. X-ray diffractograms of some samples(PAl, PA2, PA6.cleaned coal and feed coal)ments studied and ash are relatively high(>20%). It isncluded from the above that the physical coalgypsum,etc.This is in agreement with the above inter- cleaning is not only a mature technology as applied topretations of factor analysis and correlation analysisthe removal of ash and sulfur but also effective in reThere exists a great difference comparing the Xrd ducing the concentration of most major and tracediffractogram of the first coal-sublayer(PAl)with that ments. Usually, elements primarily associated with theof the two other coal-sublayers(PA2 and PA6), feed organic constituents will not be effectively reduced bycoal and cleaned coal(Fig. 5). It is seen from the figphysical coal cleaning and they may still be enrichedure that a certain montmorillonite, illite and gypsum asin the cleaned coal 24 As a result of this. their rerell as kaolinite peak with low intensities are shown movability may even show a negative value. However,on the XRd diffractogram of PAl, whereas the three the elements associated with mineral phases offer theminerals are not shown and kaolinite peak with high potential for中国煤化工 ing proceduresintensities is shown on the xrd diffractograms of during thee-Size minerCNMHPA2 and PA6, indicating that PAl underwent the are separatend can be effec.modification of post-stage geological actions which do tively removed from the coal, and some of finer2152Science in China ser. d earth Sciences806040IMIInnnng Mn Fe Hg SpaAs K Al Cs Cr Ad Co Rb Zo Sud Hf Ca V Na Mo Ba Ti Cu Ta Nb Th Se 2R-Ni Pb w Se BiFig. 6. Removabity of ash, pyritic sulfur, total sulfur, ZREE and 32 other elements in the cleaned coal from the Antaibao coal preparation plant(removability =I-an element concentration in the cleaned coal/ the element concentration in the feed coal)grained minerals can also be liberated by furtherIn general, during coal cleaning process, the or-crushing of the coal; finest-dispersed minerals are dif- ganically bound elements and the fine-grained minerficult to separate from the parent coals and still stay in als encapsulated in organic coaly constituent report topreparation products (mainly the middlings and the cleaned coal, the minerals closely associated orcleaned coal)because they are closely associated or- ganic coaly constituent to the middlings, and theganIc cofine-Size minerals dissociated and precipitations of theAccording to the above analyses, the Br is pre- fine coal particles to the coal slime. Hence, the ele-dominantly bound to the organic matter, the w, U and ments Fe, Mg, Ca, As, Co, Br, Zn, Pb and Mn with and the P. Sb. Be and lower concentration in the middlings than in the feedHg only in some few samples to the organic matteral. and the ca. p. br and mn with a loyConsequently, the majority(Br, Be, U, Sb, W, P, etc.) tration in the slime than in the feed coal, either occurof these elements cannot be effectively removed dur- in large-size minerals reporting mainly to the washerying the coal cleaning. The Se is possibly associated rejects or occur in the organic matter reporting mainlywith fine-size pyrite(has a critical positive correlation to the cleaned coal. In addition, because some minerwith pyritic sulfur based on correlation analysis)and als(e.g. carbonates) are dissolved in process waters(pH<7) during coal cleaning, the Ca shows a lowerity during the coal cleaning. Demir et al. 4 believed concentration in the cleaned coal, middlings and coalthat the elements with a reduction more than that of slime than in the feed coal. The above-mentioned eleash are enriched in the coarse minerals, such as epige- ments with a lower concentration in the middlings andnetic pyrite and calcite, and that coarse minerals are coal slime are basically the same as those loaded onrelatively easily removed by conventional coal clean- the factor 1 and the characteristic elements of the ver-ing. Thus, the Fe, As, Pb, Mn, CS, Co, etc. mainly as- tical distribution analysis. So, it is reasonably con-sociated with sulfides, the Mg, Al, etc. mainly with cluded that the distribution of the elements in the seamepigenetic montmorillonite, and the Rb, Cr, Ba, Cu, K, profile and their partitioning behavior during the coalHg, etc. mainly with epigenetic illite, should have a cleaning processes are greatly controlled by the genehigher removability. Consequently, during the coal sis of these elementspractical cleaning, most (Mg, Mn, Hg, Fe, As, K, Al6 ConclusionsCs and Cr) of these elements and pyritic sulfur have aremovability over that(42. 7%)of ash. Mo, V, Nb, Hf,(1) The coal-forming environments of the No 11REEs, Ta, etc. are mainly associated with kaolintie, coal seam from Antaibao mining district were invadedshowing a moderate removability(20%0-40%), which by中国煤化ratification andthere is much kaolinite and little illite retained in the was greaterCNMHGis led to the factthat some kaolinite changes into illite and montmorilElement geochemistry and cleaning potential of the No. 1l coal seam from Antaibao mining districtlonite in the coal-sublayer near the roof, and that the 2. Wang Wenfeng, Qin Yong, Song Dangyu et al, Cleaning potentialcontents of total sulfur, pyritic sulfur, sulfate sulfurof hazardous elements during coal washing, Journal of Fueland the elements u. As. Sb. Br. Ca. W. P Mn. s. PbChemistry and Technology (in Chinese with English abstract)Fe, Zn, etc, closely associated with sea water in the2003,31(4):195-299coal-sublayers near the roof tend to increase upward3. Qin Yong, Wang Wenfeng, Song Dangyu, Migrating behaviand mechanism of deleterious elements in Taixi coals during(2) Kaolinite dominates in the No. ll coal seam,cleaning process, Journal of Fuel Chemistry and Technology (ind the accessory minerals consist of pyrite, illiteChinese with English abstract), 2002, 30(2): 147-150montmorillonite, calcite, siderite, dolomite, quartz4. Demir, I, Ruch, R. R, Damberger H. H. et al., Environmentallycritical elements in channel and cleaned samples of illinois coalsfeldspar, gypsum, etc. In addition, that the top part ofFuel,1998,77(1-2:95-107the seam was invaded by sea water resulted in th5. Luttrell, G. H, Kohmuench, J N. 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