China's Chromium Salt Industry Grows Steadily   

By Wang Peilin, China Inorganic Salt Industry Association

1.  Steady growth in production
Chromium compounds are important inorganic products. There are now about 30 types of inorganic chromium compounds commonly used in China. Sodium dichromate is the most basic chromium compound, because all other chromium compounds are derived from it. In recent years, China's chromium salt industry has made great progresses, but still lags behind developed countries. For example, China still cannot produce water-soluble chromated copper arsenate (CCA), which is a commonly used wood preservative in the USA.
   During the "Eleventh Five-Year Plan" period (2006-2010), China's chromium salt industrial structure had undergone great changes. From 2006 to 2009, China's total sodium dichromate production capacity increased from 364 000 t/a to 380 000 t/a, and the number of sodium dichromate producers dropped from 19 to 15, and their average production capacity rose from 19 000 t/a to 25 000 t/a.
   In recent years, China's chromium salt production has increased steadily, with an annual growth of 1.2% from 2005 to 2009. See Table 1 for details.
                        
Table 1  China's chromium salt output     (thousand tons)
Year    2005    2006    2007    2008    2009
Sodium dichromate    259    283    284    229    275
Chromic anhydride    106    112    118    93    91

   China is a net importer of chromium salts. In recent years, its annual net import volume of chromium salts (equivalent of sodium dichromate; the hereinafter the same) fluctuated dramatically, with the lowest level - only 1 100 tons in 2008 and the highest level - 27 000 tons in 2007. See Figure 1 for details.
   Chromite is one of major raw materials for the production of chromium salts. It is one of the most deficient minerals in China. In recent years, China's imports of chromite have increased year by year. India and South Africa are major exporters of chromite to China, and Vietnam, Pakistan and Philippines are also important exporters of chromite to China. China's chromium salt industry is highly dependent on imported chrome ore. Thus, international chromite price hikes and foreign policies on mineral resources have great impacts on the production costs of chromium compounds in China.
   In recent years, China's consumption of chromium salts has grown slowly. Its consumption of sodium dichromate increased from 267 000 tons in 2005 to 287 000 tons in 2009, with an annual growth rate of 1.44%, much lower than the 12.3% level during 2000 - 2005. Chromic anhydride is the most important consumer area for sodium dichromate. About 60.0% of sodium dichromate is used to produce chromic anhydride. The consumption of sodium dichromate by other chromium salt products, including chromium sulfate, chrome oxide, chromates and dichromates and organic chromium compounds, increased from 102 000 tons in 2005 to 135 000 tons in 2009, with an annual growth rate of 5.74%. China's consumption of chromium salts in recent years is shown in Table 2.
                 
Table 2 China's consumption of major chromium salts   (thousand tons)
Item    2005    2006    2007    2008    2009
Sodium dichromate    267    292    311    230    287
Chromic anhydride    103    108    124    89    95
(equivalent to sodium dichromate)    165    173    198    142    152
  Other chromium salts (equivalent to sodium dichromate)    102    119    113    87    135

    In the next five years, the consumption of sodium dichromate and chromic anhydride will grow moderately, and China will make breakthroughs in the application of trivalent chromium plating and water-soluble wood preservatives, which will become important potential consumer markets of chromium compounds. It is expected that in 2015, China's consumption of sodium dichromate will reach 350 000 - 360 000 tons, and its consumption of chromic anhydride will increase to 200 000 to 220 000 tons (equivalent to sodium dichromate).

2. Significant advance in cleaner production

1) Heat recovery from rotary kiln exhaust gas
In the production process of chromium salts, the kiln temperature can be up to more than 600 degree centigrade. To recover the heat from the kiln exhaust gas, waste heat boilers are installed in the tail of the rotary kiln. This can make the exhaust gas temperature drop below 150 degree centigrade, not only improving the utilization efficiency of waste heat, but also helping dust removal by electrostatic precipitators. The production of 1 ton of sodium dichromate can lead to more than 4 tons of byproduct steam, which can be used as the heat source of the waste heat boilers and reduce the coal consumption of the boilers by 40%. By electrostatic precipitators, the dust concentration of the exhaust gas can be reduced to less than 0.1 g per cubic meter.

2) Recycling of wastewater

Making 1 ton of sodium dichromate needs to consume more than 10 tons of water. The waste steam can be condensed into water, part of which can be used to wash aluminum slag and Glauber's salt. The remaining condensed water can be repeatedly used after being cooled down. This can reduce not only water consumption but also the cost of water softening. By taking these measures, the water consumption per ton of product drops to less than 4 tons. After wastewater is treated with ferrous sulfate, lime and pressure filters, its hexavalent chromium content, total chromium content, pH, COD and other indicators can meet the national emission standard.

3) Purification and absorption of chromic anhydride exhaust gas

The production of chromic anhydride can lead to a large amount of highly oxidative and corrosive exhaust gas. In the past, such exhaust gas was directly discharged into the air through high chimneys, causing great damages to surrounding equipment and factories, and heavily polluting the environment. Now, such exhaust gas is first cooled down by water washing and then absorbed and purified with caustic soda to meet the national emission standard.

4) Use of clean energy

In China, chromic anhydride producers generally use coal as fuel. Manufacturing 1 ton of product needs 0.28 tons of standard coal, and the resulting smoke is difficult to deal with, leading to serious pollution. In recent years, more than half of chromium salt producers in the country have begun to use clean energy like natural gas and water gas as fuel to replace coal. If natural gas is used as fuel, the production of 1 ton product can consume 100 - 110 cubic meters of natural gas, equivalent to 0.13 tons of standard coal. If water gas is used as fuel, the consumption of water gas in th