Analysis of pollution materials generated from electrolytic manganese industries in China

Analysis of pollution materials generated from electrolytic manganese industries in China

Resources, Conservation and Recycling 54 (2010) 506–511 Contents lists available at ScienceDirect Resources, Conservation and Recycling journal home...

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Resources, Conservation and Recycling 54 (2010) 506–511

Contents lists available at ScienceDirect

Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec

Analysis of pollution materials generated from electrolytic manganese industries in China Ning Duan a,∗ , Wang Fan a , Zhou Changbo a , Zhu Chunlei a , Yu Hongbing b a b

Chinese Research Academy of Environmental Sciences, 8 Dayangfang BeiYuan Road, Beijing, China Nankai University, Tianjin, China

a r t i c l e

i n f o

Article history: Received 8 September 2008 Received in revised form 9 October 2009 Accepted 13 October 2009 Keywords: Electrolytic manganese metal Manganese carbonate Material balance Substance balance

a b s t r a c t There are 202 electrolytic manganese metal (EMM) industries in China with a total capacity of 1.88 million tons in 2008. This accounts for 98.58% of the world’s overall capacity of EMM production. The industries generate a huge number of pollutants. To ascertain the factors causing these pollutants in the EMM industries in China, and cost-effective ways to reduce this pollution, a study was carried out at one of the largest Chinese EMM industries with the best operation practice from September 2005 to June 2007. Material and substance balances were established on the basis of gathering data through on-site measurement and auditing. Analyses of the pollution materials were subsequently conducted. The results showed: (1) for manganese, 71.9% enters the product, i.e. electrolytic manganese, 12.6% enters anode mud, 13.7% enters residues and 1.8% enters wastewater (before treatment); (2) for chromium, 2.4% enters the product and 97.6% enters wastewater; (3) for selenium, 60.7% enters the product, 22.3% enters anode mud and 17% enters residues; (4) for ammonia, 52.36% enters wastewater, 1.19% enters anode mud, 44.09% enters residues and 2.36% was evaporated and (5) for SO4 2− , 44.5% enters wastewater, 0.2% enters anode mud and 55.3% enters residues. Manganese residues are the largest and most dangerous waste stream of the EMM industry. Use of selenium in large quantities constitutes potentially severe environmental risks. The best way to curtail environmental pollution from the industry is to apply new and modern technologies to cut off the pollution before it is generated. © 2009 Elsevier B.V. All rights reserved.

1. Introduction The Chinese electrolytic manganese metal (EMM) industry has grown at a dramatic speed since the first EMM production facility was established in 1956 (Tan and Mei, 2005; Liu et al., 2007). After more than 50 years of development, China now has a dominant role in global EMM production, and accounted for 97.44% of the total world annual production and 98.58% of the total world annual production capacity in 2008 (Manganese Metal Company, 2009; Tan, 2009). With rapid development of the Chinese economy in recent years, the rise in EMM output in China maintained an average rate of 30% from 2000 to 2008 (Fig. 1) (Tan and Mei, 2005; Tan, 2009). As indicated in Fig. 1, the annual Chinese EMM production output in 2008 expanded 71-fold compared with that in 1990. It is remarkable that both the annual output and capacity in 2007 increased more than in previous years, and for the first time China’s annual output of EMM exceeded 1 million tons (Fig. 1). Although, much of the manganese output is used within China (Fig. 1), it should be pointed out that 2.134 million tons of EMM has been exported from the first exportation in 1984 up to the

∗ Corresponding author. E-mail address: [email protected] (N. Duan). 0921-3449/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2009.10.007

end of 2008 (Tao, 2002; Tan, 2003, 2007, 2009). A large portion of the Chinese output is used to produce the Stainless Steel 200 type series (SS200) to replace the traditional nickel-containing stainless steel. SS200 is a cheaper alternative stainless steel, which is used extensively in China and India and is gaining importance in other parts of the world, especially when nickel prices escalate sharply (Manganese Metal Company, 2008). The EMM industry as a whole is generally defined as an industry with a high level of resource consumption and large quantities of waste discharge. In China, on average, to produce 1 ton of EMM, 6–9 tons of solid waste and 1–3 tons of waste water are discharged into the environment. In addition 0.9–1.9 kg of selenium is consumed to produce 1 ton of EMM and selenium pollution is a worldwide concern (Lemly, 2004; Reilly, 2006). The situation has become worse as the grade of manganese ores gets lower due to depletion of mineral resources, which means more and more waste will be generated due to EMM production (Yu and Luo, 2006). The increased environmental and resource costs has resulted in closure of EMM production in France, Japan and the USA, leaving only two countries in the world (China and South Africa) to produce EMM from 2002 onwards (Manganese Metal Company, 2009). With a high-grade ore and selenium-free hydrometallurgical process, the Manganese Metal Company (MMC) in South Africa has been pro-

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Fig. 1. Chinese EMM output, exportation and capacity from 1990 to 2008. Note: The statistical data on capacity in 1992, 1994 and 1998 were not found.

Table 1 Indices of Chinese and South African EMM production industries. Index

South Africa

China

Unit

Mn ore content Product purity Ore consumption Solid waste generation H2 SO4 consumption Selenium consumption Chromium consumption Water consumption Electricity

44 99.9 2.67 1.67 0.25 None None 0.18 2100

16 99.7 8.68 7.68 1.96 0.8–1.2 0.1–0.3 2–4 6800

% % t/t EMM t/t EMM t/t EMM kg/t EMM kg/t EMM m3 /t EMM kW h/t EMM

Note: t represents ton; kg represents kilogram.

ducing pure electrolytic manganese (99.9%) since 1960 (Manganese Metal Company, 2009). Compared with the MMC Company, the Chinese EMM production industries exhibit three distinguishing features: low-grade manganese carbonate ores used as raw material (less than 20%); hazardous additives (selenium and chromium) used in the process; and backward automation level. Table 1 compares the differences in production indices between the Chinese and South African EMM industries (Karen, 2009). Altogether there are 202 EMM production industries in China, and these are mainly located in the provinces of Chongqing, Hunan, Guangxi and Guizhou (Tan, 2009). The raw material for EMM production in China is mainly ores of manganese carbonate (MnCO3 ) (roughly 95%) (Tan and Mei, 2005; Wang, 2004). After more than 50 years of development, the technological and managerial levels of the Chinese EMM industry have been greatly improved. Many

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advances have been made in the last 10 years as stricter laws and government regulations have been enforced (Yu and Luo, 2006). Urged by the mutual forces of government supervision and market competition, the Chinese EMM industry has made great efforts to improve production technology, especially in aspects such as energy conservation, raw materials (sulfuric acid, ores, and water) savings and pollution control. Moreover, it has been reported that a 20% energy saving, a 30% sulfuric acid saving as well as a 20% production cost reduction have been achieved in recent years (Tao, 2002; Zhang, 2007). The EMM industries are densely situated in the so-called “Manganese Triangle”, which is the border area between Huayan County in Hunan Province, Songtao County in Guizhou Province and Xiushan County in Chongqing. Due to the substantial quantity of pollution from the 42 EMM industries in the triangle, the local environment is severely polluted (Zeng, 2006). Founded in 2004, the Tianxiong Electrolytic Manganese Co., Ltd. is one of the EMM industries in the “Manganese Triangle”. This industry now has a production capacity of 30,000 tons of EMM per year and is the only industry that has process lines producing 10,000 tons of EMM per year. In 2007 and 2008, the EMM output of this industry was 29,000 tons and 28,000 tons, respectively. The industry is technologically and managerially advanced in China. As shown in Fig. 2, the production process of this industry, using manganese carbonate ore as raw material, is a traditional hydrometallurgical process (Zhang and Cheng, 2007). The EMM production process is described briefly as follows: Step 1: Sulfuric acid, MnO2 and ammonia are added to crushed ores to leach manganese ions from the ores, and to obtain the MnSO4 -contained slurry; Step 2: The slurry is filter pressed and purified to produce electrolyte; Step 3: The electrolyte is pumped into electrolytic cells and manganese is deposited on cathode plates; Step 4: The cathode plates are pulled out from the cells for passivation in potassium dichromate solution; Step 5: The cathode plates are washed and dried, manganese is stripped from the plates and final products are obtained. Currently, the solid wastes generated in Tianxiong Electrolytic Manganese Co., Ltd. are sent to stockyard for stacking and many environmental problems are generated due to seepage. The wastewater is treated by the end-of-pipe processes of reduction and neutralized sedimentation with scrap iron and lime slurry. It should be pointed out that all the MnCO3 -based EMM industries in China use the same production and end-of-pipe control technologies that are now used in Tianxiong. To conduct effective waste abatement and pollution prevention, a systematic investigation and analysis of waste generation during the whole process of EMM production is essential, which includes identification of pollutants, recognition of waste sources

Fig. 2. EMM production process in Tianxiong Electrolyzed Manganese Co., Ltd.

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Fig. 3. Material balance (per ton of EMM product) in Tianxiong Electrolytic Manganese Co., Ltd.

and determination of waste discharge routes. Accordingly, a 2-year investigation in more than 10 EMM industries in the “Manganese Triangle” was conducted to examine the status quo of the EMM industries, including manufacturing processes and operations, endof-pipe facilities, storehouse, the metering device and other related production units. Of these industries, three were selected to perform a material balance and a substance balance. This study presents details of the material and substance balances for one of the three industries (Tianxiong Electrolytic Manganese Co., Ltd.). It also presents extensive discussions based on the results of the material and substance balances. The objectives of this study were to: • Identify source, category, quantity and distribution of pollutants from a typical EMM production process; • Establish material and substance balances for water, manganese, chromium, selenium, ammonia and SO4 2− ; • Quantify actual utilization rates of manganese, chromium, selenium, ammonia and SO4 2− , and the volume of these substances discharged into the environment. 2. Data, material balance and substance balance 2.1. Data On-site measurements were conducted for each process from September 1st 2005 to January 31st 2006 in Tianxiong Elec-

trolytic Manganese Co., Ltd. to obtain consumption data for raw materials, which included consumption data on manganese ore, manganese dioxide, sulfuric acid, liquid ammonia, newly added water as well as quantity of rain water, reused anolyte, and recycled water. Quantitative data on the materials generated by the processes were also gathered for the same time period, which included anolyte, influent and effluent of the wastewater treatment workshop, recycled water, anode mud and manganese residues. A continuous monitoring scheme was conducted simultaneously during the same time interval, and samples of raw materials, pollutants, by-products and other materials were collected and sent to the laboratory for physico-chemical analysis. Analyses of Mn2+ , Cr2 O7 2− , Se4+ , total nitrogen, SO4 2+ and so on were carried out to determine their concentrations or contents in the material. The grades of manganese in the manganese carbonate ores, the manganese contents in manganese residues were measured in the laboratory after on-site sampling.

2.2. Material balance For the convenience of establishing the material and substance balances, the flow streams in Fig. 2 were redrawn in detail in Fig. 3. For the purposes of uniformity, all the data acquired were divided by the total production of EMM during the study period to obtain the amount of materials flowing in and out of each process per ton of EMM produced. Based on the results, the material

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Fig. 4. Substance balance of manganese (per ton of EMM product).

Fig. 5. Substance balance of chromium (per ton of EMM product).

Fig. 9. Distribution percentage (wt%) of manganese in product and waste.

3. Discussion 3.1. Analysis of processes that generate manganese pollutants Fig. 6. Substance balance of selenium (per ton of EMM product).

Based on the study of the material balance shown in Fig. 3, it can be concluded that manganese enters the environment by three main routes: manganese residues from the liquid preparation process, anode mud from the electrolysis process, as well as effluent and sludge from the wastewater treatment process. Fig. 9 summarizes the distribution of manganese in the product and waste streams (after wastewater treatment). Fig. 7. Substance balance of NH3 (per ton of EMM product).

Fig. 8. Substance balance of SO4 2− (per ton of EMM product).

balance for the whole EMM production process was then set up accordingly, as shown in Fig. 3.

2.3. Substance balance Analysis of substance flow for manganese, chromium, selenium, NH3 and SO4 2+ in each production process or department was conducted. Taking the manganese balance in the Liquid Preparation Department as an example: firstly, quantities of input materials such as manganese carbonate ores, manganese dioxide, returning anolyte, and seepage (sulfuric acid and ammonia were irrelevant and hence not included) and output materials (electrolyte and manganese residues) were determined. Secondly, the concentrations of manganese contained in each material flow were analyzed. Thirdly, the substance balance was established using substance concentration to multiply the quantity of relevant material flow (Bailey and Allen, 2004; Bailey and Bras, 2008). Using the quantity and concentration data obtained from the analysis of materials in and out of each process, the substance balances for the whole EMM production process were then established on the basis of the material balance (Fig. 3). Figs. 4–8 show the results of the substance balance of manganese, chromium, selenium, NH3 and SO4 2− for the whole EMM production process.

3.1.1. Manganese pollution generated by the liquid preparation process It can seen from Fig. 3, that in order to produce 1 ton of EMM, 7.5 tons of manganese carbonate ores with 16% manganese content, 0.76 ton of manganese dioxide with 25% manganese content, 53.87 tons of recycled anolyte with 1.2% manganese content and 1.71 tons of reused seepage with 0.132% manganese content entered the process. 55.94 tons of electrolytes with 3.3% manganese content, 9.97 tons of manganese residues with 30% electrolyte content containing 3.3% manganese content were discharged from the process. A further calculation revealed that, on average, to produce 1 ton of electrolytic manganese, 0.19 ton of manganese was lost in the 9.97 tons of manganese residues. This large quantity of manganese residues not only occupies substantial land areas but also poses a significant threat to the environment. The percentage distribution of manganese pollution generated in this process can be seen in Fig. 9, which shows that the liquid preparation process is the largest manganese pollution source due to the large number of manganese residues it generates. 3.1.2. Manganese pollution generated by the electrolysis process Fig. 3 also shows that in order to produce 1 ton of final product, the electrolysis process recycles 53.87 tons of anolyte with 1.2% manganese content, generates 0.35 ton of anode mud with 50% manganese content, and 0.72 ton of anolyte is evaporated in the process. The anode mud is also an environmental pollutant although sometimes it is used as a low value resource. The anode mud shown in Fig. 9 constitutes the 2nd largest manganese pollution stream generated by the electrolysis process (Fig. 3), hence the electrolysis process is ranked the second largest manganese pollution source due to the anode mud it generates. 3.1.3. Manganese pollution generated by the wastewater treatment process According to the data in Fig. 3, 0.57 ton of seepage with 0.132% manganese content, 1.14 tons of Mn-containing water with

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Fig. 10. Wastewater treatment process in the EMM production process.

1.15% manganese content from the washing and dying sector and 3.42 tons of Cr-containing water with 0.074% manganese content from the passivation sector are pumped into the wastewater treatment process. After this process, 1.14 tons of treated water which meets the required national standard (2 mg/L) is discharged into the ambient environment. Simultaneously, a huge amount of manganese is deposited into sludge from wastewater during the process (Fig. 10). Manganese in the sludge is much greater than that in the wastewater, as demonstrated in Fig. 9. Manganese leaching rate, resource utilizing rate and pollution generating rate can be used to further analyze the cause of pollution generated from EMM production. These parameters were calculated using the following formulas:

1.9 × 10−13 at room temperature. Therefore, to reduce the manganese in wastewater to a concentration below 2 mg/L, the pH value must be adjusted to 11 or higher. On the other hand, the effluent pH has to be below 9.0 as required by the environmental standard in China. Adjustment of the pH was required twice to completely treat the Mn-containing wastewater during the process, which was not only difficult to handle but also expensive. For economic reasons, some factories adjust the wastewater to pH 11 to remove manganese and discharge the effluent without readjusting the pH. The problem of ammonia in wastewater remains unsolved as current wastewater treatment technology is unable to remove any ammonia.

Manganese leaching rate

3.3. Analysis of the generation of chromium, selenium, ammonia and SO4 2−

=

Total amount of manganese leaching out Total amount of manganese added in

(1)

Resource utilizing rate =

Total amount of manganese metal produced Total amount of manganese added in

(2)

Fig. 11 shows an analysis of the results on the basis of the substance balance of chromium, selenium, ammonia and SO4 2− . It can be seen from the diagram that the majority of the substances were released into the environment. The distribution percentages are summarized as follows: (1) for chromium, 2.4% enters the product and 97.6% enters wastewater; (2) for selenium, 60.7% enters the product, 22.3% enters anode mud and 17% enters residues;

Pollution generating rate =

Total amount of manganese entering environment Total amount of manganese added in

(3)

It was calculated that the manganese leaching rate was 86.3% in the liquid preparation process and the resource utilization rate of manganese was 71.9% in the entire industry. The pollution generating rate of manganese was 28.1%. These results show that more than 10% of manganese was carried away by residues and hence lost, and nearly 30% of manganese was lost from the whole production process and released to the environment. For an EMM industry with an annual production capacity of 30,000 tons, 6,000 tons of EMM were lost directly. It was concluded that it was the low leaching rate of the leaching process and the filter pressing process that were mainly responsible for the low manganese utilization rate in the entire industry. 3.2. Further analysis of the wastewater treatment process The current treatment technology of manganese wastewater is depicted in Fig. 10. The solution product Ksp of Mn(OH)2 is

Fig. 11. Distribution percentage (wt%) of chromium, selenium, ammonia and SO4 2− in product and waste.

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Fig. 12. Percentage (wt%) of chromium, selenium, ammonia and SO4 2− entering pollution materials.

(3) for ammonia, 52.36% enters wastewater, 1.19% enters anode mud, 44.09% enters residues and 2.36% was evaporated and (4) for SO4 2− , 44.5% enters wastewater, 0.2% enters anode mud and 55.3% enters residues. The quantity released as environmental pollutants followed the order: SO4 2− (100%), ammonia (100%) > chromium (97.6%) > selenium (39.3%). Notably, China has now taken many measures to cut down the hazards caused by pollutants containing chromium. The hazards of pollutants containing selenium and ammonia have not been paid enough attention. Discharged selenium was reported to give rise to many problems concerning human health due to its toxicity (Karen, 2009). The analyses in this study showed that a large quantity of selenium and ammonia were released into the environment without proper treatment. Ammonia nitrogen released into the aquatic environment is also problematic as excessive ammonia can lead to eutrophication in water bodies. 3.4. Primary analysis of pollution generation in stockyard It can be seen from Fig. 3 that the manganese residues are the largest waste stream during the EMM production process. As Figs. 11 and 12 indicate, a large quantity of released pollutants containing manganese, chromium, selenium, ammonia and SO4 2− enter the manganese residues, which are all transported to the stockyard for stacking. Cadmium has also been tested in ores and residues, which undoubtedly constitutes another threat to the environment and ecosystem. So many pollutants have resulted in considerable environmental risk as auxiliary facilities such as the guide trench anti-seep system and others essential for safe stacking of residues have not yet been constructed. Hence, currently used stockyards have become the biggest pollution source in the surrounding environment and ecosystem. Consequently, a further investigation regarding a risk analysis and a reduction in stockyards is crucial to study pollution generation in the EMM industry. 4. Conclusion Tianxiong Electrolytic Manganese Co., Ltd. is a relatively advanced industry in terms of its technologies, equipment and management in China. Analyses for its material and substance

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balances indicate that the EMM industry is a heavily polluting industry. An EMM industry generates 9.97 tons of manganese residues for every ton of EMM produced (using 16% content ores). The manganese residues constitute the largest and most dangerous pollution stream in the industry, not only because they contain Mn2+ , Se and NH3 but also the dams used in landfills for manganese residues collapse occasionally and it is reported collapses of dam have killed people. Because of the high concentration of ammonia it contains and the large amount of chromium-contained sludge it generates wastewater is the second largest pollution stream from the EMM industry. Environmental impact of use of selenium in a large quantity (0.989 kg SeO2 /t EMM) should be assessed. Obviously reasons for the pollution problems generated by the EMM industry are the backward technologies it is using. It is because of its backward technologies its manganese leaching rate is just 86.3% leading to the low manganese utilization rate of 71.9% and the high manganese pollution generating rate of 28.1%. Also it is because of the backward technologies hazardous materials like selenium and chromium are employed in the industry. Its wastewater treatment technologies fail to remove ammonia at all. The best way to curtail pollutants for the EMM industry is to prevent its pollutants from generating and reuse the pollution materials that have to be generated. This means the priorities should be adoption of new technologies that increase manganese leaching rate. It is very important to develop technologies that reuse as resources the manganese residues to cut off completely the most dangerous waste stream from the industry and technologies that recover Cr6+ and Mn2+ from the wastewater. But the most important is to apply technologies that are selenium free and chromium free. References Bailey R, Allen JK. Applying ecological input–output flow analysis to material flows in industrial systems. Part I. Tracing flows. J Ind Ecol 2004;8(1):45– 68. Bailey R, Bras B. Measuring material cycling in industrial systems. Resour Conserv Recycl 2008;52:643–52. Karen H. Globally sustainable manganese metal production and use. J Environ Manage 2009;90(12):3736–40. Lemly AD. Aquatic selenium pollution is a global environmental safety issue. Ecotoxicol Environ Saf 2004;59:44–56. Liu TJ, Tan ZJ, Liao SH. An analysis of trend of EMM industry. China’s Manganese Ind 2007;24(1):9–12. Manganese Metal Company (MMC). Company Profile and Product Information, Nelspruit 1200, South Africa; 2009. Available from: http://www.mmc.co.za. Manganese Metal Company (MMC). IMnI Annual Review; 2008:9. Available from: http://www.mmc.co.za. Reilly C. Selenium in food and health. New York: Springer Science+Business Media; 2006. p. 20–36. Tan ZZ. How to develop China’s electrolytic manganese industry. China’s Manganese Ind 2003;21(4):1–5. Tan ZZ, Mei GG. Metallurgy of manganese. Changsha: Press of Central South University of Technology; 2005. Tan ZZ. A review and prospect of EMM in 2007. China’s Manganese Ind 2007;26(2):1–3. Tan ZZ. Retrospect of 2008 Chinese electrolytic manganese industry circumstances and responding measures in 2009. In: International forum on electrolytic Mn products; 2009. p. 44–52. Tao M. Past development and current status of Chinese EEM industry 2002. In: International manganese institute annual conference; 2002. Wang YM. Resources of Mn-ores and development of EMM. China’s Manganese Ind 2004;22(3):26–30. Yu Q, Luo J. Pollution and its treatment during EMM production. China’s Manganese Ind 2006;24(3):42–5. Zhang JS. Current challenge and chance in China’s Mn-industry. China’s Manganese Ind 2007;25(1):1–4. Zhang WS, Cheng CY. Manganese metallurgy review. Part II. Manganese separation and recovery from solution. Hydrometallurgy 2007;89:160–77. Zeng MY. Thinking on the developing of “Manganese Triangle” in Hunan, Chongqing and Guizhou Provinces. Coastal Enterprises Sci Technol 2006;9:81–3.