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Showpiece APT plant rides the tungsten wave
Showpiece APT plant
rides the tungsten wave
China produces approximately 70 per cent of the world's tungsten raw materials and possesses nearly 45 per cent of the world's known tungsten ore reserves. Over the past five years the rapid growth in China's economy and increasing global demand for tungsten has driven up prices of high quality intermediate tungsten products such as ammonium paratungstate (APT) and tungsten oxides. In the second of two articles, Bernard Williams reports from a new 10 000 tonnes/year APT powder plant at Chenzhou in Hunan Province.
Figure 1. Bird's eye view of the Chenzhou APT powder plant.
metal-powder.net
October 2005 MPR
23
he recent and continuing boom in the Chinese economy has resulted in a surge in demand for tungsten raw materials. To meet increasing demand from both domestic producers and expanding export markets, production of tungsten concentrate grew in China from an estimated 31,100 metric tonnes (65 per cent WO3 content) in 1999 to a Government-controlled quota of 52,000 metric tonnes in 2004. At the same time some of the larger Chinese tungsten enterprises consolidated into vertically integrated groups involved in mining, ore processing, and production of downstream products such as cutting tools. One example is the Chenzhou Diamond Tungsten Products Co Ltd, now one of China's largest producers of
T
24
MPR October 2005
Figure 2. Hall showing part of the chemical purification process to produce APT powders.
ammonium paratungstate (APT) and tungsten oxide powders. Chenzhou Diamond Tungsten's 10 000 tonnes/year
capacity powder plant was set up in 2003 on an 110,000 square metre site some 12 km from Chenzhou City in Hunan Province. It is the result of a joint venture involving an investment of RMB 150 million (approximately $20 million) by carbide producer Zhuzhou Cemented Carbide Group (ZCC) and mining company Hunan Shi Zhu Yuan Non-ferrous Metals Ltd . ZCC has a 60 per cent controlling interest. In 2004 the plant, which employs just over 200 people, produced a total of 9000 tonnes of intermediate tungsten powders having a sales value of RMB 498 million. In 2005 the company expects sales to double to more than RMB 1 billion mainly as a result of increases in the selling price of APT over the past couple of years. According to Mr Zhengang Yao, deputy general manager at Chenzhou Diamond Tungsten, and Metal Powder Report's guide on the tour of the impressive facility, 70 per cent of current production is consumed by ZCC with some 20 per cent being directly
exported and 10 per cent sold to domestic producers. Mr Zhengang told Metal Powder Report that prices for APT powder have trebled over the past two years from RMB 50/kg to RMB 160/kg. He attributed the escalation in prices to three main factors: • A severe shortage of raw materials from China's tungsten mines resulting in higher tungsten ore concentrate prices; • China's surging domestic demand for tungsten from its producers of tungsten lamp filaments, carbide tools, etc; and • Growth in demand from export markets. Mr Zhengang said his company processes mainly two types of scheelite concentrates to produce its tungsten intermediate powders - one having 65 per cent WO3 content and another with 35 per cent WO3. Some wolframite is also processed, he said. While Hunan Province is well endowed with its own reserves of tungsten ore, Chenzhou Diamond Tungsten derives only around 30 per cent of its page 26
metal-powder.net
page 24
Figure 3. Mr Zhengang Yao demonstrates Chenzhou Diamond Tungsten's computer control system.
raw materials from local mines with the rest having to be purchased elsewhere in China. A tour of the plant included a well-equipped Analysis and Test Centre where the latest array of spectrometers and measuring instruments are in use. The chemical plant being relatively new also uses the latest equipment including a computer control centre which oversees the whole process.
Individual parts of the process are also computer controlled in the different workshops. The first stage of the chemical process involves ball milling the incoming tungsten (scheelite or wolframite) concentrate to a powder having less than 45 mesh particle size. This ball-milled powder is then charged under pressure of 10 bar into a tank containing a sodium hydroxide solution
Figure 4. Mr Zhengang (right) explains the chemical process to produce APT powder to Metal Powder Report representatives Bernard Williams, Xiao Yulin (left) and Tao Zhengji (second left).
maintained at around 200°C where the milled powder is decomposed. Impurities such as silica, arsenic and phosphorus are removed from this hot sodium tungstate solution by chemical purification to produce a pure sodium tungstate (Na2WO4) solution. The same basic process is used when wolframite ore concentrates are processed but the temperature during decomposition under pressure is lower at around 180°C. The next stage involves treating the pure sodium tungstate with hydrochloric acid to remove any molybdenum through filtration. A mineral of many colours The result is an ammonium wolframite solution which is finally evaporated at 90°C to produce insoluble a m m o n i u m paratungstate in a crystalline form with the complex chemical formula (NH4)10W12O41.5H2O that is also known as APT - the main tungsten raw material traded in the market. These crystals are washed, filtered, dried in continuous rotary furnaces at 200°C. The APT powder is then fed from the drying ovens onto vibrating screens to sieve out the required 100200 mesh size fraction and filled into 600 kg drums. A further stage beyond the APT grade is the production of tungsten oxides.
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MPR October 2005
Here the APT powder is calcined in rotary kilns in a reducing atmosphere at a temperature of 600°C - 700°C to convert it to WO3. The decomposition conditions in this heating step determine the type and quality of the oxide formed. For example, high oxygen content during calcining results in a yellow coloured WO3. With a slightly reducing atmosphere a blue tungsten oxide is formed, and in a hydrogen atmosphere WO2 is formed. The type of oxide determines the properties of the tungsten or tungsten carbide metal powder formed during the final stage of the process. Chenzhou Diamond Tungsten has, for example, developed its own proprietary process for producingb ”purple” WO3 for further processing into ultrafine W or WC powder.
Acknowledgements THE AUTHOR would like to extend his warmest thanks to Mr Yang Bohua, President of ZCC, and Vice-President Mr Gao Zairong and his colleagues at ZCC for their hospitality during his visit. In particular thanks are also due to Mr Xiao Yulin, and Mr Tao Zhengji for their efforts in arranging the visits, and for their input to the organisation of Metal Powder Report's PMAsia2005 Conference in Shanghai.
metal-powder.net
rides the tungsten wave
China produces approximately 70 per cent of the world's tungsten raw materials and possesses nearly 45 per cent of the world's known tungsten ore reserves. Over the past five years the rapid growth in China's economy and increasing global demand for tungsten has driven up prices of high quality intermediate tungsten products such as ammonium paratungstate (APT) and tungsten oxides. In the second of two articles, Bernard Williams reports from a new 10 000 tonnes/year APT powder plant at Chenzhou in Hunan Province.
Figure 1. Bird's eye view of the Chenzhou APT powder plant.
metal-powder.net
October 2005 MPR
23
he recent and continuing boom in the Chinese economy has resulted in a surge in demand for tungsten raw materials. To meet increasing demand from both domestic producers and expanding export markets, production of tungsten concentrate grew in China from an estimated 31,100 metric tonnes (65 per cent WO3 content) in 1999 to a Government-controlled quota of 52,000 metric tonnes in 2004. At the same time some of the larger Chinese tungsten enterprises consolidated into vertically integrated groups involved in mining, ore processing, and production of downstream products such as cutting tools. One example is the Chenzhou Diamond Tungsten Products Co Ltd, now one of China's largest producers of
T
24
MPR October 2005
Figure 2. Hall showing part of the chemical purification process to produce APT powders.
ammonium paratungstate (APT) and tungsten oxide powders. Chenzhou Diamond Tungsten's 10 000 tonnes/year
capacity powder plant was set up in 2003 on an 110,000 square metre site some 12 km from Chenzhou City in Hunan Province. It is the result of a joint venture involving an investment of RMB 150 million (approximately $20 million) by carbide producer Zhuzhou Cemented Carbide Group (ZCC) and mining company Hunan Shi Zhu Yuan Non-ferrous Metals Ltd . ZCC has a 60 per cent controlling interest. In 2004 the plant, which employs just over 200 people, produced a total of 9000 tonnes of intermediate tungsten powders having a sales value of RMB 498 million. In 2005 the company expects sales to double to more than RMB 1 billion mainly as a result of increases in the selling price of APT over the past couple of years. According to Mr Zhengang Yao, deputy general manager at Chenzhou Diamond Tungsten, and Metal Powder Report's guide on the tour of the impressive facility, 70 per cent of current production is consumed by ZCC with some 20 per cent being directly
exported and 10 per cent sold to domestic producers. Mr Zhengang told Metal Powder Report that prices for APT powder have trebled over the past two years from RMB 50/kg to RMB 160/kg. He attributed the escalation in prices to three main factors: • A severe shortage of raw materials from China's tungsten mines resulting in higher tungsten ore concentrate prices; • China's surging domestic demand for tungsten from its producers of tungsten lamp filaments, carbide tools, etc; and • Growth in demand from export markets. Mr Zhengang said his company processes mainly two types of scheelite concentrates to produce its tungsten intermediate powders - one having 65 per cent WO3 content and another with 35 per cent WO3. Some wolframite is also processed, he said. While Hunan Province is well endowed with its own reserves of tungsten ore, Chenzhou Diamond Tungsten derives only around 30 per cent of its page 26
metal-powder.net
page 24
Figure 3. Mr Zhengang Yao demonstrates Chenzhou Diamond Tungsten's computer control system.
raw materials from local mines with the rest having to be purchased elsewhere in China. A tour of the plant included a well-equipped Analysis and Test Centre where the latest array of spectrometers and measuring instruments are in use. The chemical plant being relatively new also uses the latest equipment including a computer control centre which oversees the whole process.
Individual parts of the process are also computer controlled in the different workshops. The first stage of the chemical process involves ball milling the incoming tungsten (scheelite or wolframite) concentrate to a powder having less than 45 mesh particle size. This ball-milled powder is then charged under pressure of 10 bar into a tank containing a sodium hydroxide solution
Figure 4. Mr Zhengang (right) explains the chemical process to produce APT powder to Metal Powder Report representatives Bernard Williams, Xiao Yulin (left) and Tao Zhengji (second left).
maintained at around 200°C where the milled powder is decomposed. Impurities such as silica, arsenic and phosphorus are removed from this hot sodium tungstate solution by chemical purification to produce a pure sodium tungstate (Na2WO4) solution. The same basic process is used when wolframite ore concentrates are processed but the temperature during decomposition under pressure is lower at around 180°C. The next stage involves treating the pure sodium tungstate with hydrochloric acid to remove any molybdenum through filtration. A mineral of many colours The result is an ammonium wolframite solution which is finally evaporated at 90°C to produce insoluble a m m o n i u m paratungstate in a crystalline form with the complex chemical formula (NH4)10W12O41.5H2O that is also known as APT - the main tungsten raw material traded in the market. These crystals are washed, filtered, dried in continuous rotary furnaces at 200°C. The APT powder is then fed from the drying ovens onto vibrating screens to sieve out the required 100200 mesh size fraction and filled into 600 kg drums. A further stage beyond the APT grade is the production of tungsten oxides.
26
MPR October 2005
Here the APT powder is calcined in rotary kilns in a reducing atmosphere at a temperature of 600°C - 700°C to convert it to WO3. The decomposition conditions in this heating step determine the type and quality of the oxide formed. For example, high oxygen content during calcining results in a yellow coloured WO3. With a slightly reducing atmosphere a blue tungsten oxide is formed, and in a hydrogen atmosphere WO2 is formed. The type of oxide determines the properties of the tungsten or tungsten carbide metal powder formed during the final stage of the process. Chenzhou Diamond Tungsten has, for example, developed its own proprietary process for producingb ”purple” WO3 for further processing into ultrafine W or WC powder.
Acknowledgements THE AUTHOR would like to extend his warmest thanks to Mr Yang Bohua, President of ZCC, and Vice-President Mr Gao Zairong and his colleagues at ZCC for their hospitality during his visit. In particular thanks are also due to Mr Xiao Yulin, and Mr Tao Zhengji for their efforts in arranging the visits, and for their input to the organisation of Metal Powder Report's PMAsia2005 Conference in Shanghai.
metal-powder.net