Industria De Cloro Soda

Multilateral Investment Guarantee Agency

Environmental Guidelines for

Chlor-Alkali Industry
Industry Description and Practices
There are three basic processes for the manufacture of chlorine and caustic soda from brine: the mercury cell, the diaphragm cell, and the membrane cell. The membrane cell is the most modern and has economic and environmental advantages. The two other processesgenerate hazardous wastes (containing mercury or asbestos). In the membrane process, the chlorine (at the anode) and the hydrogen (at the cathode) are kept apart by a selective polymer membrane that allows the sodium ions to pass into the cathodic compartment and react with the hydroxyl ions to form caustic soda. The depleted brine is dechlorinated and recycled to the input stage. The membrane cellprocess is the preferred process for new plants. Diaphragm processes may be acceptable, in some circumstances if non-asbestos diaphragms are used. The energy consumption in a membrane cell process is of the order of 2,200-2,500 kiloWatt tons per metric ton compared to 2,4002,700 kiloWatt tons per metric ton (kWh/t) of chlorine for a diaphragm cell process. The World Bank Group does not financemercury cell technology, which would preclude MIGA guarantees. filtered or settled, the supernatant is then recycled and the mud is dried and landfilled. Chlorine is a highly toxic gas, and strict precautions are necessary to minimize risk to workers and possible releases during its handling. Major sources of fugitive air emissions of chlorine and hydrogen are vents, seals, and transfer operations.Acid and caustic wastewaters are generated in both the process and the materials recovery stages.

Pollution Prevention and Control
The following pollution prevention measures should be considered: • Use metal rather than graphite anodes to reduce lead and chlorinated organics. • Resaturate brine in closed vessels to reduce the generation of salt sprays. • Use noncontact condensers to reduceprocess wastewater quantities. • Scrub chlorine tail gases to reduce chlorine discharges and to produce hypochlorite. • Recycle condensates and waste process water to the brine system, if possible. • Recycle brine wastes, if possible. For the chlor-alkali industry, an Emergency Preparedness and Response Plan is required for potential uncontrolled chlorine and other releases. Carbon tetrachloride issometimes used to scrub nitrogen trichloride (formed in the process) and maintain its levels below 4 percent to avoid explosion. However, substitutes for carbon tetrachloride may have to be used as the use of carbon tetrachloride may be banned globally.

Waste Characteristics
The major waste stream from the process is the "brine muds," which are the sludges from the brine purification step andwhich may contain magnesium, calcium, iron, and other metal hydroxides, depending on the source and purity of the brines. The muds are normally

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Chlor-Alkali Industry

Target Pollution Loads
Implementation of cleaner production processes and pollution prevention measures can provide both economic and environmental benefits. The following production-related targets can beachieved by measures such as those detailed in the previous section. The numbers relate to the production processes before the addition of pollution control measures. Target Levels Per Unit of Production Diaphragm process (maximum load/t chlorine) 0.04 kilograms 1.6 cubic meters Membrane process (maximum load/t chlorine) N/A 0.1 cubic meters

The following guidelines present emission levels normallyacceptable to the World Bank Group in making decisions regarding provision of World Bank Group assistance, including MIGA guarantees; any deviations from these levels must be described in the project documentation. The guidelines are expressed as concentrations to facilitate monitoring. Dilution of air emissions or effluents to achieve these guidelines is unacceptable. All of the maximum levels...