Feasibility Studies of Utilizing Domestic Waste to Refill a Discarded Open Iron Mine

Ecosystems and Sustainable Development V 519

Feasibility studies of utilizing domestic waste to refill a discarded open iron mine

W. Wu1, 2, K.-H. Lux1, Z. Hou1 & Q. Feng3 1Institute for Waste Disposal and Geomechanics, Technical University of Clausthal, Erzstrasse 20, 38678 Claustha—Zellerfeld 2Institute of Rock & Soil Mechanics, the Chinese Academy of Sciences, 430071 Wuhan, People’s Republic of China 3Institute of Environmental and Sanitary Design, 430022 Wuhan, People’s Republic of China

Abstract

The feasibility of utilizing Wuhan’s domestic waste to refill the discarded Daye open iron mine is stated in the paper as follows: (1) the situation and existent of primary problems of municipal solid domestic waste (MSW) are analyzed; (2) the characteristics of the open iron mine and primary problems are investigated; (3) the feasibility of utilizing domestic waste to refill a more or less stable open mine and aspects of reconstruction of the landscape are presented in general; (4) the primary economic evaluations are performed. The results indicate that much money will be saved in the long term by cutting expenditure on Wuhan’s domestic waste disposal and by recultivating land for the mine. In addition, environment surrounding the mine and Wuhan city will be improved and much land for landfills will be saved. Keywords: waste disposal, discarded open mine reconstruction.

1 Introduction

In China, municipal solid domestic waste (MSW) amounted to 150.0 million tons in 2002. In the past few years, MSW has been dumped in the cities’ surroundings, which has now resulted in more than 2/3 of the cities in China being besieged by MSW. The soil, water and atmosphere near the dumps of

MSW have been severely polluted and people’s health has been also harmed. The situation is the same in Wuhan [1, 2]. On the other hand, a lot of discarded pits and shafts exist from the many years of mining in China. They will result in subsidence of the ground or sliding of slopes. All of these processes will have negative impacts on the environment and the safety of people living next to the mines; furthermore, the economic and social development in these areas will also be affected if the discarded mines or pits are not stabilized and reconstructed in time [5]. Daye open iron mine is one of the largest open mines in China and it is located next to Daye town in Hubei Province, 80 km from Wuhan, which is the capital of Hubei Province. The mined iron ores supply the Wuhan Steel Company with raw materials. The mine has been operated for more than 50 years up till now and will be closed in 2005. The volume of the mine is estimated to amount to more than 200 million m3. The huge pit will give birth to many new negative impacts on the environment if it is not treated after closure. In Wuhan, domestic waste generation amounts to annually 2.25 millions tons (in 2003), which has to be dumped in five uncontrolled landfills at present. Much land surrounding the city is taken up by the five landfills and the environment surrounding the landfills is also being polluted. Therefore, it may be an excellent idea to use Wuhan’s domestic waste, after they have been treated, to refill the discarded Daye open mine. It has been calculated that the pit can be used to refill Wuhan’s domestic for 87 years, taking into account an increase of 10% annually. It will be a good chance not only to dispose of Wuhan’s domestic waste, but also to stabilize and reconstruct the discarded open mine. This general idea has been the basis of some pre-investigation, the results of which are presented in this paper, titled “Feasibility of utilizing municipal solid domestic waste in Wuhan to refill open discarded iron ore mine of Daye with 200 million m3 volume in China” [1].

2 Situation of MSW and the Mine

2.1 Situation of MSW in Wuhan

2.1.1 Waste management Organizations of waste management are addressed as follows: Bureau of construction management of the city Bureau of the DistrictLandfills (environmental and sanitary departments of the streets or companies). (1) MSW Sources Knowledge of the sources and the types of solid waste, along with data on the composition and rates of generation, is basic to the design and operation of the functional elements associated with the management of solid waste. There are, in general, five sources of MSW in Wuhan city, including industrial waste, commercial waste, institutional waste, hospital waste, and residential waste. In 2002, the highest fraction of MSW sources has been residential waste (56%), the second-highest, industrial waste (23%), and from the remaining 2% to 10% was

WIT Transactions on Ecology and the Environment, Vol 81, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) Ecosystems and Sustainable Development V 521 constituted by hospital, commercial and institutional waste, respectively. Apart from hospital waste, the other types of waste are disposed in dumps or landfills. (2) MSW Generation From 1950 to 2003, MSW generation continued to increase sharply as an unfortunate concomitant result of several decades with development of sprawling urban area, the increase of its population and improvement of living standards in Wuhan City. For instance, in 1950, the population was about 1.08 million and MSW generated only 0.104 million tons of waste, but MSW generation has amounted to approximately 2.25 million tons and Wuhan’s population was more than 7.0 million in 2003. MSW generation has been increased 16.5 times in 50 years. (3) Components of MSW In the 1970s, coal ashes and residual waste of households such as vegetables and skins of fruit constituted the largest portion of components of MSW at 60%, whereas residual foods of canteens, restaurants and hotels etc. were the second- largest portion (about 30%) and others such as waste paper, waste glass, porcelain and a small quantity of metals amounted to 10%. The food waste increased sharply from 12.94% in 1984 to 37.43% in 2003, and the coal ashes declined sharply from 74.70% in 1984 to 14.78% in 2003. The inorganic component reached at a level of 70% in 1984. But with improved living standards, such as the utilization of gas and electricity power for kitchens, the inorganic portion decreased drastically in MSW; meanwhile, the organic portion increased. It was determined that the inorganic portion took up 78.78%, 49.27%, 27.91% and 21.78% in 1984, 1994, 1996, and 2003 respectively; on the other hand, the organic portion took up 21.22%, 50.73%, 72.09% and 78.22% in 1984, 1994, 1996, and 2003, respectively. (4) Collection and transportation of MSW There are three principal collection modes for MSW in Wuhan (see Figure 1): (a) corridor collection. Corridors for MSW are installed along the aisles of some apartments; (b) container collection. Containers for MSW are installed some of the resident districts; (c) worker collection. In areas which have not corridors and containers, waste is collected by workers.

corridor

(a) (b) (c)

Figure 1: Collection modes for MSW. (a) corridor collection, (b) container collection and (c) worker collection.

Transportation of MSW has also three modes: (a) direct transportation - Waste are transported to the dump or the landfill from collecting places by vehicles; (b) indirect transportation - waste are first transported to the transferring station, then they are transported to the dump or landfill; (c) direct disposal - A small quantity of waste is disposed of directly onto sites. It was investigated that amounts of waste for indirect transportation took up the largest portion, comprising of 86.5% and the portion of direct transportation and others occupied 7.2 % and 6.3%, respectively in 1997.

(a) (b)

Figure 2: Some photographs of landfills in Wuhan city. (a) Baiyangqiao dump, (b) Liufang dump, (c) Daishan dump and (d) Jinkou sanitary landfill.

(5) Disposal In Wuhan, the treatment method of MSW is only by depositing in landfills. MSW is not separated, and commingled MSW is also not pre-treated before they are transported to the dumps or landfills. There are now 4 uncontrolled landfills (dumps) and 1 simple sanitary landfill (see Figure 2). The facilities including the infrastructures of these landfills are at a very low technical level. This means that they don’t have any facilities for leachate and gas collection, neither do they have good sealing systems. The dumps and the landfill were located next to the boundary of the city when they were built, but with the development of sprawling urban areas, the sites of the dumps are now situated in the residential

WIT Transactions on Ecology and the Environment, Vol 81, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) Ecosystems and Sustainable Development V 523 center of districts. For instance, the international congress center and large resident apartment blocks were built surrounding the Jinkou landfill; other sites of the dumps will also become municipal development regions in the next future. The estimated available life span of the five landfill sites is only 1 to 3 years.

2.1.2 Problems of MSW disposal in Wuhan The principal aspects of the problems associated with dumps are as follows: Dumps take up a lot of land, which takes up 275,000 m2 annually if the total amount of WSM meets 2.25 million tons and the height of dumps comes up to 10 m. At present, 60-70% of the buildings in Hankou have been constructed on the old dumps. Facilities of waste disposal associated with infrastructures on the sites are at the very low technical level, particularly the collection and transportation system of waste and facilities of these dumps. The environment, especially the atmosphere, surrounding these dumps has been terribly polluted. Surveying results showed that the content of ammonia, sulphur hydrogen and small grains reached at 234—518mg/ m3, 4.1—6.6 mg/ m3 and 550-4640 mg/m3 respectively in the atmosphere around the Guozikou dump in Hanyang district in 1997. All values exceeded limit values [2]. Without good performance of the sealing systems and the leachate collection systems, the soil and water have been also severely polluted. Results indicated that the contents of heavy metals such as copper, lead, cadmium, chromium, arsenic and mercury as well as other hazardous substances exceeded limit values in the water and soil. [2] The facilities for the indirect transport systems of waste result in new polluting problems. Leachate and gas are produced during the process of transportation from waste collecting spots to the transferring stations because of poor performance of facilities associated with vehicles and transferring stations. At present, the remaining life span of Wuhan city’s 5 dumps amounts to only 1 to 3 years. New landfills must be sited and built in the near future.

2.2 Daye open iron mine

2.2.1 Introduction to Daye open iron mine Daye open iron mine was designed in 1952 and its mining capacity has been 2.0 Mt/a; the ores of the mine are supplied to the Steel Corporation of Wuhan. They are still transported from the mine to Wuhan by train. The railway, the road down to the bottom of the open mine and the drainage facilities at the bottom of the mine have been operating well. (1) Mining parameters of the pit The main mining parameters of the pit are indicated as follows: The length is 2.2km, the width, 1.1 km and the maximum and minimum depth reach, 520m and 100m; the estimated volume amounts to about 200 million m3 and the inclinations of the working slopes reach at 41- 45o, as shown in Figure 3.

(2) The stratum and classification of rock mass The stratum belongs to primary Triassic diorite which is a series of different rock formations; its lithology is classified commonly into diorite, tint diorite, strong corrode diorite with diopside, infirm diorite with diopside. The rock mass of the mine belongs to class I of the Chinese classification. This class contains hard and intact rock mass according to “the classification criteria of engineering rock mass” (GB50218-94 Chinese). The permeability of these rocks is very low. (3) Structure properties of rock mass (a) Large faults. The rock mass is crossed by few large faults, but they have enough load bearing capacity and good mechanical performance. There are six groups of faults, with an orientation in NNE, NE, NNW, NW, nearly SN, and NNW directions respectively. The dip of these faults range from 50O to 85 O. These faults are, normally, not harmful to slope stability of the mine. (b) Little faults. There are 7 relatively small developed little fault systems. The principal direction is NNE, the others are NNW, SW, SN, and NWW, and the succession are NE and NW. Faults with azimuth/dip as N76°W/SW∠60°, N40°E/SE. NW∠75° and N51°W/SW∠82° are harmful to slope stability as shown in Figure 4. (c) Joints and cracks. There are 7 or 8 joint groups in the district. Most of them are NE and NWW developed; NNE and NW are the second. In addition, many of the cracks were generated during operation, as shown in Figures 5 and 6.

Figure 3: The open mine. Figure 4: The little faults.

Figure 5: The cracks. Figure 6: The joints.

(4) Slope disaster—deformation and fracturing of the slopes. The collapse of slopes has occurred twice in the open mine. Before sliding, that is before April 30, 1990, the displacement velocities of observation points in the parallel direction in neighbor rock bodies above ∇84m were lower than 1 mm/d, mostly 0.4 mm/d, from March 29 to April 27. After sliding, their displacement velocities increased sharply; the velocities of some points near to the sliding area even surpassed 15 mm/d, and this deformation process with its high deformation rates lasted for about 10 days. After this, the velocities decreased evidently to only 0.1 mm/d. The reason for this decrease is perhaps the unloading after sliding and the reduction of rainfall. From June 4 to June 16, the velocities increased to 3.5 mm/d with the increase of rainfall. Finally, the displacement velocities of the sliding bodies tended to be zero even after rainy season by reinforcement measures. [3,4] The other sliding body called A1# started to slide in March 1991, and the displacement was up to 500 mm in a month. At that time, the stretching displacement of tensile cracks at ∇+72m platform in the east of this sliding body increased to 10 mm.

2.2.2 Main problems of the pit Daye open mine will be closed in 2005. Up to now, the mine has not been reconstructed. The following problems may arise in general:

Possibility of the large-scale collapse of slopes, which means severe threats to the life and estates of the people and to the environment surrounding the mine. No reuse of land in the order of a magnitude of 2.5 km2 in the future.

3 Feasibility of utilizing domestic waste to refill the open mine

3.1 General remark

The pit will be boosted with enormous economic and social value if the MSW from Wuhan including Daye and Huangshi city near the mine is refilled into the mine. The operation time will exceed 87 years if a refilling amount of MSW of 2.0-3.0 Mt/a is taken into account. The main advantages by utilizing domestic waste to refill the open mine, which could be a new method for MSW utilization are as follows:

Reduction of occupied land for landfills in Wuhan including Daye and Huangshi; Creating a new industry of MSW treatment and stabilization of the discarded mine. Renewing of lands at the surface of the refilled open mine; Improvement of environment around the city and the mine. Increasing chances of employment.

3.2 Feasibility of separated collection of MSW

MSW needs be separated in order to carry out the proposed treating method. In this context, the primary tasks for government, institutions and citizens at present are listed as follows:

Constituting new regulations of integrated waste management including source reduction, recycling and disposal. At present, special items for integrated waste management are being investigated by some institutions of the government in Hubei Province; Public education for waste management such as newspaper releases, speeches, community calendar announcements, radios and TV. Citizens will understand that integrated waste management is essentially useful and significant; Techniques and criteria for a separated collection of MSW are being investigated by some institutions; Separated collection of MSW is being adopted in practice for some communities such as ShuiguoHu Community in Wuhan.

3.3 Feasibility of waste transferring and the transportation of the MSW to the mine

The MSW will at first be transported by vehicles from collecting waste containers to the transferring station. In order to transport the MSW to the mine, a waste pre-treatment at the transferring station will be necessary. This transferring station has to be set up in the Qingshan district near the Wuhan Steel Corporation. At the transferring station, the MSW will be separated, recycled, dehydrated, composted and packed. After pre-treatment in the transferring station, the waste will be transported to Daye open mine by train of a special railway. A special railway already exists from Wuhan Steel Corporation to the mine, and iron ores of several mines including some underground mines are transported by train from Daye region to the steel plant in Wuhan. But the trains have no loads to transport from Wuhan to Daye open mine. If MSW could be transported by the trains from Wuhan to Daye, the transporting income for Wuhan Steel Corporation will be increased; this means that the cost of transportation will be decreased.

3.4 Feasibility of reconstruction of the open mine.

3.4.1 Stability of the slopes in the mine Daye open iron mine has been in operation for many decades. The slopes have been investigated and stabilization methods have been designed and constructed by the Institute of Rock Mechanics in Wuhan, Institute of Mining and Metallurgy in Changsha and Wuhan Steel Corporation. The research reports are listed in the references, [3, 4] and the conclusions have indicated that the main slopes are stable. One example for the existing main slopes in the Daye open mine is shown in Figure 7. The angle of the slopes are between 41o and 45o, the

WIT Transactions on Ecology and the Environment, Vol 81, © 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) Ecosystems and Sustainable Development V 527 heights of the slopes are 60m, 72m, 91m, and the safety coefficients of the slopes are equal to 1.235 , 1.169 and 1.014 as respectively calculated by the Bishop’s method for proof of slope stability. The slopes are stable at the moment because the calculated safety coefficients are more than 1.0.

Figure 3: A typical calculation cross-section in Daye open mine.

However, long-term safety seems to be questionable with reference to the relatively low safety margins. It is possible that small-scale slopes will not be stable in the long term, taking into account effects such as rock corroding and weathering. A possible loss of stabilization could be monitored and prevented by appropriate reinforcement techniques such as anchors or anchor-ropes, resisting slide-piles, as well as injection and concrete etc. These measures were attested to be effective by deformation measurements during many years of mining.

3.4.2 Permeability of rock mass Seepage is possible because of a great number of little faults and cracks around the bottom and the slopes in the pit. However, the problem of seepage can be overcome by technical measures. Concerned measures toward the permeable problems will focus on:

Classification of the faults according to their permeability; Injection techniques to reduce permeability using clay or concrete that will be injected into the crashed rock mass in faults and cracks; Clay liners to be installed at the bottom and along the slopes; A synthetic liner to be installed at the bottom and along the slopes.

3.4.3 Drainage of leachate There exists (1) a drainage tunnel with the dimensions of 2.0m*3.0m, length of 3.0km for transportation of waste water at the bottom of the mine to the outside of the mine and (2) a treatment facility for waste water, which has been operated well for many years shown in Figure 8. After the mine is closed, these facilities will be able to be used additionally for the transportation and treatment of seepage water from the deposited waste.

Drainage tunnel

(a) (b)

Figure 8: The drainage tunnel in the open pit mine. (a) the position of the drainage tunnel and (b) the cross-section of the drainage tunnel.

3.4.4 Refilling techniques The principles of the refilling techniques will be taken as follows: The pit will be divided into different districts according to different waste types; The thickness of a layer of waste will be limited to 0.5—1.0m and every layer of waste will be compacted by a compactor in order to reduce the settlement of the waste. One must not forget that the organic waste will be pre-composted in the transferring station. The open pit volume has to be divided into sub-blocks and every sub- block should be handled like an individual landfill (monitoring, documentation); Leachate and gas production rates, as well as organic content, can be minimized by additional pre-treatment (offsite and site, and disposal techniques); A leachate collecting system will be integrated into the existing drainage system of the open mine; The pipes for gas collecting and transportation will be designed with a consideration of the deformation properties of the waste.

4 Economic analysis

Economic analyses are based on two scenarios as follows: (1) waste refilling into the open pit mine and (2) construction of a new landfill near Wuhan city. A description of the two scenarios is as follows: (1) Scenario I utilizes Daye open mine for the disposal of waste: The distance between Wuhan and the mine is about 80 km, the area takes up 2.5 km2 and its capacity will add up to about 150 million tons of waste. This means that the operation time will come to 87 years. Waste in Wuhan will be first transported to the transferring station by trucks with a compacting facility and afterwards, pre-treatment waste transported from the transferring station to the mine by train. (2) Scenario II is siting and constructing a few new landfills near Wuhan city: The loaded waste distance is about 20—40 km from the city to the new landfills and the area of landfills (about 5 landfills) will take up 12.5 km2

for 150 million tons of waste to disposed of (the height of the deposited waste amounts to about 20 m). The investment calculation is based on the correlation data of the Erfeishan landfill which is a new landfill constructed next to Wuhan and financed by The Dutch and Chinese Government. Construction investment The construction investment adds up to 41 million Renmenbi Yuan (RMB) to scenario I, whereas scenario II reaches to 70 million RMB； Equipment and materials investment The equipment and materials investment of scenario I add up to 94 million RMB； ; that of scenario II will reach to 76 million RMB； Other investments (a) Land compensating cost: Land compensating cost will be zero to scenario I and will add up to 42 million RMB (3.4236 million RMB/km2) in scenario II. (b) Other costs: These costs include managing cost, designing cost training cost and engineering insurance cost, etc. These costs are 11.3 million RMB for scenario I more than that for scenario II. (c) Transportation cost: The transportation cost of scenario I is 16 RMB/ton more than that of scenario II because there is train transportation which has to be taken into consideration in scenario I. In summary, the total investment of scenario I will amount to 1.7 billion RMB and that of scenario II will amount to 3.0 billion RMB; this means that the investment of scenario I is in the order of a magnitude 1.3 billion RMB less than that of scenario II. Utilizing Wuhan’s domestic waste to refill the discarded Daye open mine, will not only save much money and the landscape, but more jobs will also be created; furthermore, the environments of Wuhan and Daye city will be much improved.

5 Conclusion

Utilizing Wuhan’s domestic waste to refill the discarded Daye open pit mine in the future will result in the fact that valuable lands occupied for landfills to date will be significantly reduced in Wuhan, including, in particular, Daye and Huangshi. The new landfills have to be built in the next few years because of the small number of years left for operation of Wuhan’s landfills today. As part of the further consequences of the proposed waste management concept, the environment in Wuhan will be able to be significantly improved. By renewing the lands in the area of the open mine with waste backfill, the environment surrounding the mine will also be improved. Last but not least, the proposed method will reduce unemployment. The main conclusions are as follows: There are many problems associated with waste disposal in Wuhan and the discarded Daye open iron mine at present, which, essentially, have to be solved in the near future in order to improve the environment; It is feasible to utilize the waste from Wuhan to refill the discarded Daye open iron mine due to economy and environment factors, especially: (1) the

feasibility of classification and collection of MSW by constituting new laws, information of the public, education and making experiments; (2) the feasibility of waste transportation by vehicles to a transferring station with pre-treatment and then the transportation of pre-treated waste by trains to the open mine; (3) the feasibility of improving the stability of the open mine and the environment, as well as to use the existing facilities of the mine, especially the drainage tunnel and the waste water treatment plant; Investment for new landfills in Wuhan and for reconstruction measures in the mine will be saved. Of course, many correlative items will essentially have to be researched in the near future because utilizing Wuhan’s domestic waste to refill the discarded Daye open iron mine is a complex and highly disciplinary project.

Acknowledgements

The authors of the paper would like to express their sincere thanks to the sponsors of this pre-investigation, namely (1) the Bureau of Science and Technology of Hubei Province, and the Bureau of Construction of Wuhan City in China; (2) the Lower Saxony Government in Germany.

References

[1] Wen Wu et al (2002, in Chinese): Investigation report: environment integrated treatment by utilizing MSW in Wuhan to refill Daye open mine. Institute of Rock & Soil Mechanics, the Chinese Academy of Sciences, Wuhan. [2] Wen Wu, Qiling Feng & Chunhe Yang (2003, in Chinese): New method for waste disposal and renewing land of discarded mines. Publishing House of Science and technology of Hubei. [3] Xiurun Ge et al (1998. in Chinese): Investigation report: Analysis on stabilities of slopes for Daye open mine. Institute of Rock & Soil Mechanics, the Chinese Academy of Sciences, Wuhan. [4] Xiurun Ge et al (1992, in Chinese): Investigation report: Analysis on stabilities of slopes for Daye open mine and measures reinforcement of slopes in Daye iron open mine. Institute of Rock & Soil Mechanics, the Chinese Academy of Sciences, Wuhan. [5] Zhimeng Gu, Shiwei Bai (2000, in Chinese): Suggestions of environment integrated treatment by utilizing MSW to fill discarded mines. Technological progress and countermeasure, No.1, pp.1—4.