Hazardous waste hydrogen chloride

Hydrogen chloride and chlorine gases form when chlorinated organic compounds in hazardous wastes are burned. If uncontrolled, this chlorine can become a human health risk and is a large component in the formation of acid rain. U.S. EPA has developed different requirements to control the emissions of chlorine from the different classes of combustion units. 

Note that U.S. EPA regulations (under the RCRA) for hazardous waste incineration require that particulate emissions be no more than 180 mg/m3 and that hydrogen chloride removal efficiency from the exhaust gas can be no less than 99%. Therefore, trial bums to determine the maximum ash and chlorine content that a waste can handle are needed prior to issuance of a permit. 

Cyanides (reported as cyanide, hydrogen cyanide, sodium cyanide, potassium cyanide, calcium cyanide, or copper(I) cyanide) have been detected in air samples collected at 5 of the 406 hazardous waste sites where cyanides have been detected in some environmental medium (HazDat 1996). The HazDat information used includes data from both NPL and other Superfund sites. No information was found on detections of cyanogen, cyanogen chloride, or thiocyanates in air at any NPL or other Superfimd hazardous waste sites (HazDat 1996). 

Hydrogen selenide, a highly poisonous selenium compound, is a gas at room temperature, with a density much higher than air. Selenium oxychloride, also highly toxic, is more irritating and corrosive to the human respiratory tract than are other forms of selenium because the compound hydrolyzes to hydrogen chloride (HC1), which can then form hydrochloric acid in humid air and in the respiratory tract (Dudley 1938). Hydrogen selenide and selenium oxychloride are occupational exposure hazards that are not expected to be much of a concern at hazardous waste sites. 

In SMOBC processing, the metal-plated resist is removed to present a flat, clean copper surface for solder mask definition. Tin/lead alloys can be stripped in oxidizing fluoride solutions such as fluoboric acid and hydrogen peroxide or ammonium bifluoride with hydrogen peroxide or nitric acid. (Caution machine construction must be made compatible with fluorides by elimination of titanium and glass components.) Commercial formulations are available to be used inline after the etch machine rinses. Accumulations of spent solution or filtered lead-fluoride deposits must be treated as hazardous waste and have been accepted by solution vendors for treatment and disposal costs. Modern applications usually use lead-free tin plating resists, which can be fluoride containing as previously discussed, or compounds of ferric chloride... 

For the incineration of hazardous waste, three performance standards have been set Organic wastes must be destroyed with an efficiency of 99.99 percent gaseous hydrogen chloride (e.g., from the incineration of PVC scrap) must be reduced 99 percent or to less than 4 lbs per hour, and particulate matter emissions may not exceed ISOmg per dry cubic meter of stack gas. The EPA requires test bums on all incinerators to ensure that these conditions are met, a major expense costing companies up to 100,000 for each unit. 

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