1-s2.0-S0921344913002590-main

F

Rs

Ga

Cb

a

ARR2A

KCWMB

1

iiT12pcmsFCewoL

n

0h

Resources, Conservation and Recycling 83 (2014) 24 33

Contents lists available at ScienceDirect

Resources, Conservation and Recycling

journa l h om epa ge: www.elsev ier .com/ locate / resconrec

ull length Article

eduction and utilization of coal mine waste rock in China: A casetudy in Tiefa coalfield

angwei Fana,, Dongsheng Zhanga,b, Xufeng Wanga

School of Mines, Key Laboratory of Deep Coal Resource Mining, Ministry of Education of China, China University of Mining & Technology, Xuzhou 221116,hinaCollege of Geology and Mineral Engineering, Xinjiang University, Urumchi 830046, China

r t i c l e i n f o

rticle history:eceived 1 April 2013eceived in revised form7 November 2013ccepted 2 December 2013

eywords:oal mineaste rockine design

a b s t r a c t

In China, coal mine waste rock (CMWR) produced during coal mining and processing is still increas-ing significantly as a result of coal production which has huge environmental impact. CMWR reductionand utilization is a major issue for coal enterprises and government to reduce the surface footprint andthe public environmental impact. Tiefa coalfield, an old coalfield with 60 years of coal exploitation, wasselected as a case to study the methods to minimize the environmental impacts of CMWR piles in a shortperiod. We argue that a systematic design on CMWR utilization is needed on the basis of a usage evalu-ation which takes consideration of CMWR source, compositions, and proximate analysis. Mine design iscrucial and the base for reducing the CMWR generation at the headstream. Placing roadway into coal seamrather than rock, panel optimization, and parametric analysis for mining technique were conducted in

ackfill Tiefa coalfield. A promising technology of CMWR backfill under the ground was employed with a resul-tant increase of coal recovery rate. The surface CMWR recycling depends on brick making, electricitygenerating, and rehabilitation of subsided land. The practice of the presented methods indicates that theCMWR piles on Tiefa coalfield may disappear in 3 years, which could significantly reduce the environ-mental impacts of CMWR dumps. The technologies conducted in Tiefa coalfield developed a model ofCMWR reduction and utilization for Chinese coal mines.

. Introduction

In China, coal mine waste rock (CMWR) produced in coal min-ng and processing is the greatest source of industrial solid wasten terms of production, accumulation volume, and occupied area.here are about 4.5 billion tons of CMWR stockpiled into more than700 waste dumps which occupied 150 km2of land (Bian et al.,009; Zhao et al., 2008). Furthermore, it is estimated that the annualroduction of CMWR is more than 315 million tons for undergroundoal mining (Liu and Liu, 2010). The traditional CMWR manage-ent by dumping in cone-shaped heaps may leave environmental,

ocial and economic impact for thousands of years (Bell et al., 2000;ranks et al., 2011; Glauser et al., 2005; Szczepanska, 1999). TheMWR dumps may cause environmental problems in many differ-nt ways, such as poison releasing into soil, groundwater, or surface

r nuclear pollution (Hao et al., 2009; Lambert et al., 2004; Liu andiu, 2010; Martinez et al., 2007; Meck et al., 2006; Querol et al.,

Corresponding author at: School of Mines, China University of Mining and Tech-ology, Xuzhou, Jiangsu 221116, China. Tel.: +86 516 83103893.

E-mail address: [email protected] (G. Fan).

921-3449/$ see front matter 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.resconrec.2013.12.001

2013 Elsevier B.V. All rights reserved.

2008; Ribeiro et al., 2010; Tiwary, 2001). More seriously, land-slides or even explosions sometimes occur in the dumps, whichmay directly injure or kill people. Fig. 1 shows an explosion acci-dent occurred in a CMWR dump in China in 2005 with 8 personsdead and 122 persons injured (Wang et al., 2008).

Tiefa coalfield was selected as a case to study the CMWRreduction and utilization in China. Tiefa coalfield is an old min-ing area with over 60 years of coal exploitation. In 2008, 16CMWR stockpiles stood in 8 coal mines and about 1.23 km2 of landwere resultantly occupied. The CMWR inventory had been up to31.76 Mm3 by 2006 with an average increase of 5.50 million m3

per year. A new stockpile will appear in 810 years and 20 millionYuan (about 6.13 Yuan per US dollar) will be spent. The local resi-dents had suffered the environmental impacts of CMWR in a longterm. Therefore, a systematic study on how to reduce the CMWRgeneration and dispose the accumulated stockpiles should be con-ducted to avoid underground CMWR discharged to surface dumpsor new ones.

CMWR reduction and utilization is a systematic engineering,

G. Fan et al. / Resources, Conservation and Recycling 83 (2014) 24 33 25

fsrw(2onltlrmtb

2

2

wtPcc

TT

Fig. 1. An explosion accident occurred in a CMWR dump.

rom underground or ground surface should be disposed in theubsequent processing. Many approaches had been practiced toeuse the CMWR in recent years, for instance, high carbon CMWRas used for power generation, for building material, and so on

Canibano, 1995; Kwolek, 1999; Liu and Liu, 2010; Lottermoser,003). However, not every approach can be used to dispose all kindsf CMWR. Most of the existing papers focused on a specific tech-ology or a certain coal mine. Seldom research made a design for a

arge whole coalfield for CMWR deduction and treatment. Besideshe technologies evaluation on the basis of proximate analysis, theocations, the CMWR source, the market, the policy, and the envi-onment effect should be taken into considerations. Reusing soany CMWR piles and avoiding the continuous generation in a

ime period of 35 years is still a great challenge, which shoulde systematically designed on the basis of a scientific evaluation.

. CMWR usage evaluations

.1. CMWR piles distribution in Tiefa coalfield

In 2008, 12 CMWR piles were still growing and the other 4 pilesere abandoned. The abandoned piles, 8.03 Mm3 accumulated in

otal were Daming No. 2 Pile, Xiaoming No. 1 Pile, Xiaonan No. 1ile, and Daxing No. 1 Pile. The total CMWR accumulation in Tiefaoalfield is listed in Table 1. Fig. 2 shows the locations for all theoal mines in Tiefa coalfield.

able 1he CMWR piles in Tiefa coalfield.

Coal mine No. Occupiedarea (km2)

Height/m Accumulatedvolume (Mm3)

Daming(DM) 1 0.09 98 2.882 0.02 42.5 0.4253 0.01 40.5 0.1817

Xiaoming(XM) 1 0.11 116.7 4.162 0.02 44.2 0.2358

Dalong(DL) 1 0.12 103.8 4.2552 0.13 101.8 4.339

Xiaonan(XN) 1 0.07 55.1 1.3622 0.07 97.8 2.233

Xiaoqing(XQ) 1 0.16 85 1.742 83. 4 1.668

Daxing(DX) 1 0.15 85.2 2.0182 0.11 98.31 3.3483 0.07 52.8 0.528

Xiaokang(XK) 1 0.06 81 1.652Daping(DP) 1 0.04 65.5 0.737Total 16 1.23 31.7625

Fig. 2. Locations for all the mines in Tiefa coalfield.

The CMWR is produced by the following three ways: under-ground roadway driving, underground roadway maintenance, andsurface coal washing. The sources of CMWR in Tiefa coalfield in2009 are shown in Table 2. The CMWR discharged from coal wash-ing took about 80% of the total, which is a great challenge fordisposal.

2.2. CMWR compositions and proximate analysis

CMWR is a mixture of many kinds of rock. Generally, CMWRis comprised of inorganic matter and little organic matter. Theinorganic matter mainly contains SiO2, Al2O3, Fe2O3, and someimpurities (see Table 3). The result of proximate analysis forCMWRs from different coal mines is shown in Table 4, which isthe basic data for CMWR usage evaluation (Li and Han, 2006).

2.3. CMWR usage evaluation

Researchers present many methods for classifying CMWR usage.In China, CMWR is commonly classified into four sorts by theirsources, coal roadway driving, rock roadway driving, coal wash-ing, and post-self-combusted (Wang and Sun, 2004). However, thecommon classification system, which ignores the essential factor ofcomposition, is still over-simplified and insufficient for usage eval-uation. The criterions for CMWR usages based on the compositionsare drawn in Table 5, which can be used for evaluating the potentialusages of CMWR (Li and Han, 2006).

Based on Tables 35, the potential approaches to utilize the

26 G. Fan et al. / Resources, Conservation and Recycling 83 (2014) 24 33

Table 2Sources of CMWR in Tiefa coalfield.

Coal mine CMWR fromsurface coalwashing 104 m3

CMWR from underground 104 m3 Total 104 m3

Roadway driving Roadway maintenance

DM 12 4.6561 0.4280 17.084XM 16.8 1.3397 2.1729 20.3126DL 35 4.4 3.6 43XN 6.021 5.677 2.024 13.722XQ 18 5.5357 1.28 24.8175DX 30 3.73 0.11 37.68XK 19.184 2.858 1.5 23.542DP 36 5.04 8.59 49.63Total 210.585 34.8365 21.1049 266.9281

Table 3Chemical compositions of CMWR from different coal mines.

Coal mine Pd SiO2 Al2O3 Fe2O3 TiO2 CaO MgO SO3 K2O Na2O P2O5% % % % % % % % % % %

DM 0.01 60.48 21.2 7.12 0.89 1.22 0.78 0.78 1.22 1.09 0.05XM 0.011 55.88 23.70 6.46 0.97 1.63 1.16 0.40 1.37 1.05 0.07DL 0.013 53.69 22.26 12.33 1.51 1.77 1.63 0.30 1.22 0.84 0.14XN 0.029 58.97 23.15 6.48 1.19 1.77 1.32 0.45 1.37 0.65 0.07XQ 0.016 62.74 20.52 5.46 1.03 1.5 1.09 0.12 1.41 0.95 0.05DX 0.02 55.41 23.24 12.23 1.03 2.17 1.32 0.22 1.33 1.20 0.12XK 0.036 59.54 22.27 7.7 1.07 2.17 1.17 1.15 0.80 0.65 0.14DP 0.03 56.94 22.52 7.82 0.88 2.3 0.93 2.10 0.61 0.4 0.17

Table 4Proximate analysis of CMWR from different coal mines.

Coal mine Moisture Ash content Volatile Fixed carbon Total sulfur True relative densityMad Ad Vdaf (FC)ad St,d (TRD)d% % % % % %

DM 1.13 80.28 61.59 7.48 0.37 2.19XM 1.36 82.71 60.47 6.75 0.13 2.2DL 1.96 79.36 65.91 6.89 0.09 2.18XN 1.06 82.19 65.27 6.12 0.2 2.22XQ 1.39 85.64 66.31 4.77 0.15 2.2DX 1.12 84.30 77.00 3.57 0.06 2.22

a

2

ta

TT

a

XK 3.09 74.40 62.15 DP 1.80 76.85 72.94

d = air-dried; d = dry; daf = dry ash-free; t, d = total, dry.

.4. CMWR usage decision

Although the potential usage for CMWR could be evaluatedhrough the above analysis, the final decision on CMWR deductionnd treatment should be made up according to the local conditions

able 5he criterions for CMWR usage.

Concentration Criterion Potential usage orproduct

Fixed carbon content (FCad) >15% Fuel in combustion boiler6%15% Mixed with other fuel in

combustion boilerSulfur content (St,d) >6% Sulfur can be recovered

through gravityseparation process

Ratio of Al2O3 content to SiO2 content >0.7 Top-grade ceramicproducts, synthesizingseries molecular sieve,farm fertilizer

>0.3 Al series cleansing agentTotal content of CaO and MgO

vation and Recycling 83 (2014) 24 33 27

wdbitCauC

sbao7abii8tTiawGD

awpi

oa(fiba

3

frr

3

wisbii

omrs

Direction of minin g

fault

Coalface

2-New setup gateroad

1-Equipments withdrawing gateroad

TailgateHeadgate

G. Fan et al. / Resources, Conser

CMWR making baking-free brick is a promising technologyhich wins the support from Chinese government. In Tieling, aeveloping and expanding city, where Tiefa coalfield locates in,rick demand is pretty high. In addition, an economic benefit is

mportant for this technology application. According to statistics,he net profit for 1 t of CMWR making brick is about 35.9 Yuan. TwoMWR brick plants were decided to be built nearby XK Coal Minend DX Coal Mine. Each plant produces 1.6 billion bricks per yearsing 255 thousand m3 of CMWR, by which the costs for piling theMWR will reduce.

The biggest blocks to using CMWR as fuel admixture are theubsequent residual cinder, ashes, and sulfur dioxide with the com-ustion of CMWR. Electrostatic precipitator was tested to solve thesh issue, which proved that the dust collection efficiency reachedver 98% for the CMWR from the Tiefa. The residual cinder, about0% of original CMWR in weight, could be crushed and used asdditions of concrete for roadway grouting. Circulating fluidizeded (CFB) technology provides an effective method for desulphur-

zation. It was proved that if the CMWR mixed with CaO are putnto CFB combustor, the desulfurization degree could reach over5%. On the other hand, the sulfur content of the CMWRs from allhe coal mines of Tiefa coalfield is low, say no greater than 1.2.herefore, CMWR using as fuel admixture is technically feasiblen Tiefa coalfield. The net profit for 1 t CMWR generating power isbout 9.0 Yuan. Liaoning Diaobingshan Coal Gangue Power Co., Ltd.ith capacity of 2 330 MW, a joint venture of Tiefa Coal Industryroup and Liaoning Energy Investment Group was so built nearbyiaobingshan in 2008.

CMWR making Al series cleansing agent is not a sophisticatednd scalable technique, especially for the CMWR from the Tiefa,here the Al content is almost on the boundary. Therefore, inresent conditions, the CMWR making Al series cleansing agent

s not suggested.For an old coalfield, rehabilitation of subsidence land by use

f CMWR is practical and economical (Bian et al., 2009; Wangnd Wang, 2012). An investigation conducted by Wang and Wang2012) revealed that the effect of land rehabilitation by CMWRlling on groundwater is slight in Tiefa coalfield. The cost for reha-ilitation of subsidence land by 1 m3 of CMWR is about 24.2 Yuannd the profit of 1 m2 rehabilitation land is about 200 Yuan in Tiefa.

. CMWR reduction at source

Coal mining is the original source of CMWR, which mainly comesrom rock roadway driving, the rock cavern excavating, and coalecovery mixed with rock. Therefore, mine design is crucial toeduce the CMWR generation at the headstream.

.1. Roadway in coal seam instead of rock

As the rock roadway could be supported easily, coal mine road-ays, especially for main roadways, were always in rock in China

n the 20th century. However, with the development of roadwayupport technology, roadway located in coal seam is not hard toe supported under many conditions. The roadways in coal seam

nstead of rock will not only reduce the CMWR production, but alsoncrease the advance rate of roadway.

For example, in multi-seam mining, mine design should focus

oadways in rock can be eliminated. The production system in eacheam is independent.

Fig. 3. Coalface passing fault through pre-driving gateroads.

3.2. Panel design optimization

A coalfield is always divided into several panels. All the min-ing operations take place in the panels. Therefore, the panel designdirectly affects underground CMWR generation. In panel design,the following works were conducted to reduce the CMWR genera-tion:

(a) Geologic structures such as faults were selected as the natureboundaries between panels. Resultantly, the coalface passingthe structures with CMWR generation was avoided.

(b) The dimensions of coalface should be reasonably determined.Taking thin coal seam for example, a small part of rock roofis always cut during the roadway driving in order to provideenough room for man working and machine running, which willgenerate CMWR. In this case, increasing the length and width ofcoalface may reduce CMWR generation from roadways drivingdue to the reduction of the number of gateroads in a given panel.

(c) Bleeder roadway with retaining wall along gob. A bleeder road-way protected by the retaining wall along gob that will be stillused for next coalface, was used widely in Tiefa coalfield, whichreduced coal resource loss and the number of entries.

(d) Passing geological fault through pre-driving roadway was con-ducted to avoid CMWR generating. When the mining operationencounters a geological fault, rock cutting is unavoidable ifcoalface directly passes the fault. In order to produce the rockgangue as few as possible, two roadways along the fault weredriven in advance (see No.1 in Fig. 3), in which the miningequipments could be withdrawn. Another roadway was devel-oped on the opposite side of fault (see No.2 in Fig. 3), in whichthe mining equipments could be reinstalled. When the workingface is right positioned at No.1 roadway, the mining equipmentswere hauled out of the working face and transported to No.2roadway for installing. By means of this method, the coalfaceskipped the fault without gangue generating.

3.3. Parametric analysis for mining technique

Long wall top coal caving (LTCC) is an important method forthick coal seam mining, which is widely used in China. LTCC iscost effective because only the lower part of a coal seam is cutby shearer and the upper part is allowed to cave under gravity,provided the ground conditions are appropriate (Alehossein andPoulsen, 2010; Unver and Yasitli, 2006; Yasitli and Unver, 2005).For the LTCC method, two crucial parameters, namely the ratio ofmining height to caving height (MC ratio) and top coal caving inter-

28 G. Fan et al. / Resources, Conservation and Recycling 83 (2014) 24 33

Fi

ImttarOliaed

lMtlstmwfs

Table 7Six groups of possible MC ratios and TCCIs.

No. MC ratio TCCI

1 1:0.8 0.82 1:0.8 1.63 1:1 0.84 1:1 1.65 1:1.2 0.8

ig. 4. The influence of TCCI on the CMWR content and coal recovery rate. (a) TCCIs too great; (b) TCCI is reasonable; (c) TCCI is too small.

f the TCCI is too great (see Fig. 4a), the CMWR above the caving coalay arrive at the coal drawing chute earlier than the caved coal in

he gob, leading to a low coal resource recovery or high CMWR con-ent; If the TCCI is too small (see Fig. 4c), the CMWR in the gob mayrrive at the coal drawing chute earlier than the caving coal, alsoesulting in a low coal resource recovery and high CMWR content.nly when the TCCI is correctly selected, the CMWR content is the

east and the coal recovery rate is the highest (Xu, 2003). Therefore,t is impossible to carry out top coal caving with low CMWR contentnd high resource recovery unless the mining parameters are sci-ntifically determined. However, there is no existing function forirect calculation of the best values.

Physical simulation in laboratory, a scale modeling using simu-ated materials, provides a qualitative indication on the influence of

C ratio and TCCI on CMWR content and coal recovery rate. In LTCC,he top coal and the roof in certain area is well fractured after theower coal is excavated. The principles of top coal caving can be con-idered as similar to granular material flow, which indicates thathe coal and the roof can be similarly simulated by some granular

aterials like gravel stone and sand. Several physical simulationsere conducted to determine the reasonable MC ratios and TCCIs

or the LTCC coalfaces of Tiefa coalfield. A case for panel S2S7 waselected to show the method in this paper.

6 1:1.2 1.6

The panel, which is 1288 m long and 230 m wide, lies in an aver-age 6.8 m thick coal seam. There is a kerogen shale stratum with anaverage thickness of 47.5 m in the roof of the coal seam. Generally,TCCI is 1 or 2 times the cutting web which is depended on the coal-face equipments. In this case, the cutting web is 0.8 m. Thus, thepossible TCCIs are 0.8 and 1.6 m. MC ratio always ranges 1:31:1 inLTCC (Xu, 2003). The engineering practice on LTCC showed that theharder the coal, the greater MC ratio should be. The uniaxial com-pressive strength of coal sample in this case is about 25 MPa, whichmeans that the coal is hard for LTCC. Hereby, the scenarios underMC ratios of 1:0.8, 1:1, and 1:1.2 were compared through physicalsimulations. Six models were built to analyze six groups of possibleparameters as shown in Table 7. In the model, fine black stone of lessthan 0.5 cm in diameter was selected to simulate the coal, mediumwhite stone of 0.51 cm in diameter was used for simulating theimmediate roof, and large black stone of more than 1 cm in diam-eter was used for simulating the overlying main roof. The modelframe is 130 cm long and 12 cm wide. The MC ratios and TCCIs canbe evaluated by weighing the caved stones. The simulation resultsfor Model #1, taken as an example, are shown in Fig. 5. Initially, allthe simulation materials and shield were placed into the frame; seeFig. 5(a). After the bottom was excavated out, the top coal was cavedand drawn through opening the coal drawing chute, see Fig. 5(b).The CMWR content and the coal recovery rate were analyzed afterseparating the collected mixture of coal and CMWR, see Fig. 5(c)and (d). All the six modelings were conducted following the sameprocedures. The collected CMWR contents and coal recovery ratesfor the models are shown in Fig. 6. It can be concluded that the TCCI1.6 m is not reasonable due to the high CMWR content and the lowcoal recovery rate. The results for Model #3, as Fig. 7 shows, revealthat the coal recovery rate is 79.3% and the CMWR content is 4.29%,which means that the recovery rate is high and the CMWR contentis low. The parameters in Model #3 of MC ratio being 1:1 and TCCIbeing 0.8 m were selected to attain reasonable CMWR content andcoal recovery rate.

4. CMWR disposals under the ground

CMWR disposed under the ground contributes to reducing theCMWR transportation to surface and avoiding the environmentalinfluence of CMWR stockpiling.

4.1. CMWR backfilling

A simple method to dispose CMWR is filling them into someunderground space, which includes underground roadway and gob.As for an old coalfield, there are many abandoned spaces suitablefor the storage of CMWR. Moreover, new openings or coalface couldbe developed into some permanent pillars left for protecting thesurface buildings, and the main roadway, which means the coal

G. Fan et al. / Resources, Conservation and Recycling 83 (2014) 24 33 29

Fig. 5. Results for Model #1. (a) The initial model; (b) The top coal was caved; (c) The coseparated.

Fig. 6. The modeling results.

llected coal from the coal drawing window; (d) The caved coal and the rock were

4.1.1. CMWR filling in roadwayAll the methods of CMWR filling in gateroad are similar in pro-

cedure. Take the practice in DL Coal Mine as an example, see Fig. 8,after the CMWR car carrying the CMWR arrives at the dumper, theCMWR is unloaded onto the scraper conveyor by rolling the dumperand transported to the working place through scraper conveyor andbelt conveyor. The CMWR is then filled into the opening by CMWRfeeder.

This system is workable under many conditions as long asthere is enough room for CMWR storage. As coal exploita-tion scale increases significantly year by year, especially in

30 G. Fan et al. / Resources, Conservation and Recycling 83 (2014) 24 33

F The cos

4

ftr1r

ig. 7. Results for Model #3. (a) The initial model; (b) The top coal was caved; (c) eparated.

.1.2. CMWR backfilling in gobFor a coal mine, gob is another great place which could be used

or storing CMWR. CMWR filling in gob could free the coal resourcerapped under buildings, water bodies, and railways due to the

Fig. 8. CMWR filling pro

llected coal from the coal drawing window; (d) The caved coal and the rock were

In recent years, Chinese scholars developed two methods to fill theCMWR into the gob, paste backfill, and dry backfill (Chang et al.,2008; Zhang et al., 2011). Paste backfill method refers to the mate-rials of coal CMWR, fly ash made into paste. Dry backfill means that

cess in roadway.

G. Fan et al. / Resources, Conservation and Recycling 83 (2014) 24 33 31

ateTpttCrtfih

Ntpatiwcfi

shows.

Fig. 9. Sketch on the process of CMWR paste filling.

In DM Coal Mine, the total remaining reserve is only 7.01 Mtfter over 60 years of exploitation. However, 4.87 Mt of coal israpped under the surface buildings. In order to increase the recov-ry rate, paste backfill is used for mining the trapped coal seams.here are four components in this technology, namely CMWRrocessing, material storage and transportation, paste prepara-ion, and filling (see Fig. 9). The CMWR processing system iso prepare the appropriate aggregation through step-crushing ofMWR. Materials such as additions, aggregations, fly ash, watereducer, and so on, are prepared and transported to paste prepara-ion plant in the material storage and transportation system. Thelling system is to fill the paste into gob through pipes or bore-oles.

Dry backfill of CMWR is conducted at many coalfaces, such asos. E1-404 and E1-406 of XQ Coal Mine. The crushed CMWR is

ransported to working face by conveyor. A special hydraulic sup-ort which adds a rear beam, a rear armoured face conveyor (AFC)nd a CMWR presser was used to fill the gob, see Fig. 10. Underhe protection of rear beam, the rear AFC, running for transport-ng the CMWR and filling the gob, is modified by traditional AFC

ith some bed opening, see Fig. 11. The CMWR presser working forompressing the loose CMWR in the gob is applied to increase thelling ratio.

Front AFC

Fig. 10. The special hydraulic s

Fig. 11. The function of rear AFC in CMWR filling.

4.2. Grout aggregations

According to the usage evaluation of CMWR, the CMWR of theTiefa could be used as grout aggregations instead of sands whichcould reduce the cost of roadway developing.

In order to develop a proper proportioning of grout aggrega-tion, field trials were conducted in XN Coal Mine. In the scenarioof the concrete to CMWR ratio of being 1:3, the strength reached10 MPa or more and the rebound ratio was less than 15%, whichwere suitable for roadway shotcreting. The grain size was selectedas 0.510 mm in consideration of the presetting time, the reboundand the strength.

5. CMWR utilizations on surface

CMWR is also regarded as a kind of resource which could bemade into building materials, fuel, and other materials depend-ing on its physical and chemical components. According to theevaluation on the CMWR usage and the actual situation of Tiefacoalfield, brick making, electricity generating, and rehabilitation ofsubsided land are applicable to utilize the surface CMWR on a grandscale.

5.1. CMWR brick making

CMWR could be used as not only the aggregation but alsothe internal fuel in brick making. As the heating value of CMWRfrom the Tiefa reaches 3.5 MJ kg1, the drying and the roast-ing during brick making are finished by the internal combustionof CMWR without any additional fuel. At least, 1 t of stan-dard coal could be saved for making 10 thousand pieces ofbricks. The CMWR made into brick experiences crushing, grind-ing, stirring, compacting, shaping, drying, and roasting, as Fig. 12

As the technology of CMWR brick making was widely applied, alarge amount of accumulated CMWR and new output CMWR wasutilized and the traditional clay brick fell into disuse. Resultantly,

Rear beam

Rear AFC

CMWR pre sser

upport for CMWR filling.

32 G. Fan et al. / Resources, Conservation

tstaob

5

cwfcCincwas

5

sgt5ismtlirs2

aeCacof

Fig. 12. CMWR brick shaping.

he pollution from CMWR was reduced, the coal resource wasaved, and the clay delivered from lands was eliminated. Takinghe CMWR brick plant at XK Coal Mine as an example, under thennual production of 160 million pieces of brick, 255 thousand m3

f CMWR was utilized with 2.67 ha of land free of being occupiedy CMWR.

.2. Power generating by burning CMWR

According to the proximate analysis, the CMWR in Tiefaoalfield is classified into the type of medium-carbon CMWRhich can be used in combustion boiler as a component of

uel. In Liaoning Diaobingshan Coal Gangue Power Co., Ltd. withapacity of 2 330 MW was so built in Tiefa coalfield in 2008.irculating fluidized bed (CFB) technology was introduced to

ncrease the combustion efficiency and air cooling (AC) tech-ology was used to recycle and save water resource. The fuel,omprised of CMWR, coal slurry with the mixture ratio of 6:4,as transported into the CFB combustor through belt conveyor

fter being crushed into the pieces of less than 8 mm in grainize.

.3. Rehabilitation of subsidence land by CMWR filling

In underground mining, when the gob exceeds a certain size,urface subsidence basin will appear above the gob which involveseneral public issues, such as surface subsidence, farmland destruc-ion, and surface water loss and pollution (Peng, 2008). In the past

decades, 76 km2 of surface farmland in Tiefa coalfield turnednto subsidence basin due to underground coal mining; moreeriously, the farmland was flooded and then got salinized. Theaximum subsidence reached 10.15 m in DL Coal Mine. Therefore,

here are strong demands by local farmers to reclaim subsidenceands, which is a great issue for a coal mining group. CMWR fill-ng provides a good chance to fill up the subsidence trough andeclaim subsidence lands into farmland, which has been provedafe for surface water and the environment (Wang and Wang,012).

The steps for rehabilitation of subsidence land by CMWR fillingre: striping the top soil by 0.5 to 1.5 m in thickness and deliv-ring them to the adjacent area; filling the subsidence area with

f CMWR was used as fills and 0.63 km2 of lands were reclaimed asarmlands.

and Recycling 83 (2014) 24 33

6. Economic, social and environmental benefits

6.1. Economic benefits

There are two major economic benefits for CMWR disposal, onefrom underground disposal, one from the surface utilization.

The underground CMWR is not necessary to be transported outand piled on surface when underground disposal is adopted. Thebenefits of underground disposal are from the reduction of CMWRtransportation and surface storage and the increase of coal recov-ery. According to the statistics in Tiefa coalfield, the expenditurefor lifting 1 t of underground CMWR to surface is about 62 Yuan;the total charge for land occupation and eco fee of 1 t of CMWRis about 61 Yuan; the cost for disposing 1 t of CMWR under theground is about 28.2 Yuan. Therefore, 94.8 Yuan is saved due to 1 tof CMWR is disposed underground. On the other hand, if the coalresource that should stay permanently is replaced by the backfilledCMWR, the revenue will increase. According to the statistics, 88.7Yuan could be earned by filling 1 t of CMWR for replacing coal. It isestimated that 684 thousand tons of underground CMWR per yearis avoided to be lifted out and 2.34 million tons of CMWR per yearis backfilled into underground for replacing coal. The total benefitfor underground disposal is about 272.40 million Yuan.

The economic benefits for surface utilization of CMWR are con-tributed by the productions of CMWR. There are two CMWR brickplants located in Tiefa coalfield, each of which has an annual pro-duction of 1.6 billion bricks. 1.377 million tons of CMWR is used formaking brick per year. Therefore, the net profit reaches 49.43 mil-lion Yuan per year. The net profit for 1 t CMWR generating power isabout 9.0 Yuan. In Liaoning Diaobingshan Coal Gangue Power Co.,Ltd., 2.17 Mt of CMWR is used as fuel admixture with the profit of19.53 million Yuan per year. 2.0714 million m3 of CMWR could beused for reclaiming 0.63 thousand m2 of subsided land per year.The revenue for the rehabilitation of subsided land by CMWR fill-ing reaches 76.69 million Yuan. In total, the benefit for surfaceutilizations of CMWR is about 145.65 million Yuan.

6.2. Social and environmental benefit

The negative environmental effects of CMWR piling on surfaceare being diluted due to the reduction of CMWR. The land occupa-tion area of CMWR is reduced and the emissions of H2S, SO2 due tothe spontaneous combustion of CMWR are lowered.

7. Discussion

By applying the technology of CMWR reduction at source, theunderground CMWR production from Tiefa coalfield in 2009 isreduced by 37.3% in comparison with that in 2007. The surfaceCMWR dumps would disappear in 3 years as a result of the wideuse of CMWR disposal and utilization at underground and on sur-face, which could significantly reduce the CMWR environmentalimpacts.

CMWR reduction and utilization related to coal mining has hugepotentials but a long way to go, especially in China. Although somestate-owned coal groups like Tiefa Energy Co. Ltd. have taken somemeasures to reduce and utilize the CMWR, most of coal groups stillignore the environmental effect of CMWR accumulating on sur-face, both because some technologies need to be improved andthe industrial chains for CMWR process have not been establishedcompletely.

The existing technologies offer some helps but are not enoughto solve the CMWR issues. As the mining depth becomes deeper,roadways in coal seam are difficult to support due to high groundstress. The traditional supporting technologies have encountered

vation

mafpdtTetC

cssaotbee

8

iuCbus

osa

iTwsstCdtuta

CpCcimah

opBnfpe

G. Fan et al. / Resources, Conser

any challenges and need to be improved. CMWR filling in gob is promising technology for utilizing the accumulating CMWR andreeing the trapped coal resources. However, increasing the com-action rate of CMWR filled into gob is still a great problem whichirectly limits the application of this technology. Secondary pollu-ion in CMWR utilization is a major concern for utilizing the CMWR.here are more or less secondary pollution issues appearing in thexisting CMWR utilization technologies. More technologies neededo be developed to dilute the influences of secondary pollution inMWR utilization.

A complete industrial chain for CMWR process is not only cru-ial for large-scale use of accumulated CMWR, but also helpful forustainable development of a coal mining group. However, a sub-tantial initial investment for building the chain is difficult to befforded by most of minor enterprises. Collaboration with somether enterprises such as brick plant, power plant, etc., is essen-ial to make the best use of CMWR and to obtain a great economicenefit. In addition, the government must make more efforts toncourage the enterprise to pursue the energy conservation andmission reduction, and to punish the environment polluters.

. Conclusions

To eliminate the environmental effect of CMWR in coal min-ng and processing, a conceptual design on CMWR reduction andtilization should be first conducted systematically on basis ofMWR evaluation. The potential industrial usages of CMWR shoulde evaluated through proximate analysis. The applicable meas-res could then be arranged over the coalfield. Tiefa coalfield waselected to conduct the present studies.

The base is to reduce the CMWR production at source throughptimizing the mine design, such as placing the roadway into coaleam instead of rock, panel design optimization, and parametricnalysis for mining technique.

If the CMWR is inevitably produced during underground min-ng, the best method is to dispose the CMWR under the ground.he CMWR could be filled into some underground rooms like road-ays, gobs, and used as grout aggregations. The space for CMWR

torage can be some abandoned workings, but there also can beome new roadways developed in some coal pillars to replace therapped coal resources. Gob provides an ideal room for storing theMWR, which may be used for reducing the ground subsidenceue to coal mining. CMWR filling in gob could free the coal resourcerapped under buildings, water bodies and railways, which is highlyseful in China. The CMWR could also be used as grout aggrega-ions instead of sands in roadways. A proper proportioning of groutggregation was developed through field trials in XN Coal Mine.

As for the previous CMWR accumulated in dumps and theMWR produced in coal processing, the CMWR should be trans-orted to brick plants, power plants or subsidence area. The coalMWR with a proper heating value, ranging from 2.1 to 4.2 MJ kg1,ould be used as not only the aggregation but also the internal fueln brick making. In the present case, the medium-carbon CMWR

ixed with coal or coal slurry was used in combustion boiler. Ton extent, rehabilitation of subsidence land by CMWR filling couldeal the land damage due to underground mining.

The technologies conducted in Tiefa coalfield developed a modelf CMWR reduction and utilization. The underground CMWRroduction from Tiefa coalfield has been reduced year by year.enefited from the systematic design and application in the Tiefa,

ace CMWR was dumped onto the stockpiles. The previous CMWRiles may disappear in 3 years, which could significantly reduce thenvironmental impacts of CMWR dumps.

and Recycling 83 (2014) 24 33 33

Acknowledgements

The authors would like to thank the Fundamental ResearchFunds for the Central Universities(Grant No. 2012QNA35) and theNational Natural Science Foundation of China (Grant No. 51264035)for their financial support. The authors are also grateful for thehelpful comments provided by the anonymous reviewers.

References

Alehossein H, Poulsen BA. Stress analysis of longwall top coal caving. Int J Rock MechMin Sci 2010;47:3041.

Bell F, Stacey T, et al. Mining subsidence and its effect on the environment: somediffering examples. Environ Geol 2000;40:13552.

Bian Z, Dong J, Lei S, Leng H, Mu S, Wang H. The impact of disposal and treat-ment of coal mining wastes on environment and farmland. Environ Geol2009;58:62534.

Chang Q, Zhou H, Hou C. Using particle swarm optimization algorithm in an artificialneural network to forecast the strength of paste filling material. J China Uni MinTechnol 2008;18:5515.

Canibano JG. Latest developments in the utilization of coal mining wastes. Coal SciTechnol 1995;24:162932.

Franks DM, Boger DV, Cte CM, Mulligan DR. Sustainable development princi-ples for the disposal of mining and mineral processing wastes. Resour Policy2011;36:11422.

Glauser S, McAllister ML, Milioli G. The challenges of sustainability in mining regions:the coal mining region of Santa Catarina, Brazil. Nat Resour Forum 2005;29:111.

Hao J, Wang C, Han Z, Zhou G. Heavy metals distribution pattern in coal gangue. In:3rd International Conference on Bioinformatics and Biomedical Engineering;2009.

Kwolek JK. Aspects of geo-legal mitigation of environmental impact frommining and associated waste in the UK. J Geochem Explor 1999;66:32732.

Lambert DC, McDonough KM, et al. Long-term changes in quality of dischargewater from abandoned underground coal mines in Uniontown Syncline: FayetteCounty, PA, USA. Water Res 2004;38(2):27788.

Li N, Han B. Chinese research into utilisation of coal waste in ceramics, refractoriesand cements. Adv Appl Ceramics 2006;105:648.

Liu H, Liu Z. Recycling utilization patterns of coal mining waste in China. Resou,Conserv Recy 2010;54:133140.

Lottermoser B. Mine wastes: characterization, treatment and environmentalimpacts. Berlin, Heidelberg, New York: Springer; 2003.

Martinez RC, Belen FS, Philip DP, Maria JFG. Natural and man-induced revegetationon mining wastes: changes in the floristic composition during early succession.Ecol Eng 2007;30:28694.

Meck M, Love D, Mapani B. Zimbabwean mine dumps and their impacts onriver water qualitya reconnaissance study. Phys Chem Earth 2006;31:797803.

Peng SS. Coal mine ground control. 3rd Edition Morgantown: Syd S. Peng; 2008.Querol X, Izquierdo M, Monfort E, Alvarez E, Font O, Moreno T, et al. Environmen-

tal characterization of burnt coal gangue banks at Yangquan, Shanxi Province,China. Int J Coal Geol 2008;75:93104.

Ribeiro J, Flores D, Ward CR, Silva LFO. Identification of nanominerals andnanoparticles in burning coal waste piles from Portugal. Sci Total Environ2010;408:603241.

Szczepanska J. Distribution and environmental impact of coal-mining wastes inUpper Silesia, Poland. Environ Geol 1999;38(3):24958.

Tiwary RK. Environmental impact of coal mining on water regime and its manage-ment. Water Air Soil Pollut 2001;132:18599.

Unver B, Yasitli N. Modelling of strata movement with a special reference tocaving mechanism in thick seam coal mining. Int J Coal Geol 2006;66:22752.

Wang G, Sun C. Recovery pathway for coal gangue. China min Magazine2004;13:403.

Wang H, Wang L. The environmental effects of subsided land rehabitation by coalgangue filling in Tiefa coalfield. Mod Agr 2012;11:768 (In Chinese).

Wang Y, Sheng Y, Gu Q, Sun Y, Wei X, Zhang Z. Infrared thermography monitor-ing and early warning of spontaneous combustion of coal gangue pile. Beijing:The International Archives of the Photogrammetry, Remote Sensing and SpatialInformation Sciences; 2008.

Xu Y. Mining science. Xuzhou: China University of Mining and Technology Press;2003 (In Chinese).

Yasitli N, Unver B. 3D numerical modeling of longwall mining with top-coal caving.Int J Rock Mech Min Sci 2005;42:21935.

Zhang J, Zhou N, Huang Y, Zhang Q. Impact law of the bulk ratio of backfilling body

Zhao Y, Zhang J, Chou C, Li Y, Wang Z, Ge Y, et al. Trace element emissions fromspontaneous combustion of gob piles in coal mines, Shanxi, China. Int J CoalGeol 2008;73:5262.