Chemical Cleaning Wastes

Snow has reviewed (53 references) a number of different methods for reducing the volume of nuclear steam generator wastes. Disposal methods that are mostly mechanical that were considered include direct solidification, thermal degradation, incineration, and evaporation. Direct solidification methods include addition of a cement binder and solidification with a vinyl ester binder. The latter method was used to solidify the NS-1 waste from the decontamination of Dresden-1 after partial evaporation to reduce the volume. Thermal degradation and incineration methods require a large amount of equipment to ensure destruction of the very stable EDTA molecule, which must be subjected to temperature 200°C (392°F) to cause rapid degradation. 

Most of the chemical waste treatment methods use some form of precipitation technology to remove the heavy metals, which are the primary problem species. After precipitation, the slurry is allowed to settle, and the thickened solids are dewatered by using mechanical devices such as filter presses or centrifuges. Bell has reviewed treatment methods for treating many types of wastes. Spent mineral 

Hydrochloric acid solutions may contain thiourea if this solvent is being used to remove copper and iron from a boiler. Since thiourea is a known animal carcinogen, treatment methods must include a step to reduce the concentration of this chemical. McConnell has developed an oxidation method for removing thiourea from acid solutions. Alkaline solutions can be oxidized to carbon dioxide and nitrogen in a two-step procedure. 

Treatment of more concentrated chelant wastes requires the use of a more aggressive chemistry. Kennedy demonstrated that iron and copper could be removed from EDTA by a combination of lime, NaOH, and diethyidithiocarbamate. By this process, 99.9% of the iron and copper was removed. However, only 82% of the nickel was precipitated. Samuelson described the use of this technology to treat several waste streams from operational cleaning of utility power boilers. 

A very different approach to disposal of chelated iron boiler wastes made use of these materials to oxidize hydrogen sulfide at the Geysers Power Plant in California. The spent EDTA-iron waste was used to oxidize the sulfide gasses produced with the geothermal steam. The chemical reaction is as follows  

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Evans, D.W. et al., Treatment of steam generator chemical cleaning wastes Development and operation of the Bruce spent solvent treatment facility, in Proc. 5th Int. Symp. Nashville, TN, 1995, International Oxidation Application, 1995. 

Snow, A. L. "Chemical Cleaning Waste Disposal," Rep. NP-4954, Electric Power Research Institute Palo Alto, CA, 1986. 

Metal cleaning wastes include wastewater from chemical cleaning of boiler tubes, air preheater washwater, and boiler fireside washwater. 

EDTA has been determined in a wide variety of sample matrices by HPLC. These matrices include waste waters, natural waters, sediments, fertilizers, chemical cleaning solutions, radioactive waste solutions, and pharmaceutical preparations. Chinnick reported the separation and identification of EDTA and other aminopolycarboxylic acid sequestrants by a high performance liquid chromatographic (HPLC) method [57]. 

Expert service More effective cleanings Documented results Higher cost Requires second set of membranes Membranes cleaned in situ—no need for replacement membranes Faster cleaning Less expensive Less efficient Capital outlay for cleaning skid Storage and handling of chemicals and waste... 

In the same vein, certain waste-handling procedures, even those performed intermittently, can result in very serious contaminant exposure without proper precautions. Workers need to be instructed in the proper procedures for cleaning up spills and accumulated debris. Spilled materials can become airborne and pose an inhalation hazard. Spills and chemical process wastes may end up in the waste-water treatment facilities where they again can be volatilized into the air and result in unexpected worker exposure. 

One of the most serious forms of membrane fouling is bacterial adhesion and growth [11]. Once they form, biofilms can be very difficult to remove, either through disinfection or chemical cleaning. This wastes energy, degrades salt rejection, and leads to shortened membrane life. This is one area, for example, where further research is required. 

Wastes from chemical cleaning of steam generator... 

Research at Los Alamos National Laboratory into the environmental chemistry of coal wastes has demonstrated the quantitative chemical relationships between the composition of a waste and the contaminants found in water that has been in contact with the waste. We have examined several alternative environmental control technologies (ECTs) aimed at reducing contaminants to an acceptable level before surface or ground waters leave a coal mining/cleaning operation. Preliminary cost comparisons of some of these ECTs for coal-cleaning wastes are reported elsewhere [1,2 ]. 

Chemical and mineralogical analyses of feed coal, clean coal, and refuse (coal-cleaning waste) are essential to the conceptual design of ECTs and therefore to the calculation of the costs of alternative ECTs. Because the major pollution factor is the contamination of water run-off from refuse piles, information on the acidity and chemical content of water leachates also is needed for cost calculations. 

Ten alternatives for correcting or preventing water pollution from acid drainage produced by piles of coal-cleaning wastes are compared. Options 1, 2 and 10 involve pretreatments of the waste before it is disposed to the pile. Options 3 to 6 refer to treatments undertaken as the pile is being formed. Options 7 to 9 refer to chemical treatment of the pile effluent. All costs are based on 1985 dollars. 

Except in special cases, chemical recychng involves the input of clean waste which has been sorted and well characterized. To make the process profitable, we need to work with large qnantities, which are difficult to handle. As a result, chemical recycling currently appears to be rather a marginal sector. 

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