Mercury in the Chlor-Alkali Industry

Global Hg production increased markedly in the 20th century, due to industrial use other than for gold and silver mining. One of the main consumers was and still is the chlor-alkali industry, where Hg cells are used for production of chlorine, hydrogen, and sodium (in a few plants potassium) hydroxides by electrolysis of a brine solution. In 1996, approximately 1 344 t Hg, 40% of all Hg produced, was consumed by the world's chlor-alkali industry and has recently decreased to an estimated 30% or lower, since West European and North American chlor-alkali industry reported 173 t consumed in 2000, corresponding to 9.4% of Hg produced. Quantities of Hg consumed by chlor-alkali industries in other parts of the world remain to be reported. (reference)

While 53% of the chlorine and alkali production in Europe is still done with Hg cells, the corresponding figure for the USA is about 10%, while Japan has produced all chlorine and alkali with Hg-free technologies for more than 15 years already. Measured direct emissions to air and water from chlor-alkali plants have decreased substantially during the past years, especially in Western Europe and North America, but are still amounting to about 10 tons a year in Western Europe. In addition, large amounts of Hg-containing sludge are produced, which may explain much of the Hg consumption of 135 t per year by West European chlor-alkali plants. Only about 10% of the reported Hg consumption was accounted for as emitted or entering the products. Mercury in the sludge was reported as unaccounted until a few years ago, when a new routine was introduced for reporting to the national and regional authorities. Potential releases of Hg from these wastes are of concern. If wastes are deposited in landfills instead of recycling the Hg, the waste producers should reserve funds for the costs of future generations to maintain these sites.

Using Hg cells is not the economically most favorable technology for production of chlorine and sodium hydroxide any longer. The alternative membrane technology does not use or emit any Hg and in addition has lower energy consumption. It is regarded socially as well as economically feasible to convert all chlor-alkali plants in the EU to Hg-free technology already by 2007. While several companies have infrastructure with Hg cells still operable, Euro Chlor presently advocates a delay of the final phase-out date. Nevertheless, the two remaining Swedish chlor-alkali plants with Hg cells are due to conversion before 2010, and it is expected that Hg cells, the main consumer and polluter for a century, will worldwide be entirely replaced within a few decades.