5 Treatment of Metal Finishing Wastes Olcay Tu¨nay and Is¸ık Kabdas¸lı I ˙ stanbul Technical University, _ IIstanbul, Turkey Yung-Tse Hung Cleveland State University, Cleveland, Ohio, U.S.A. 5.1 INDUSTRY OVERVIEW In the metal finishing industry, metals or alloys are used as starting materials to manufacture a wide range of metal components. The metal finishing and metal fabricating industry is identified as SIC (Standard Industrial Class ification) code 34. SIC code 34 is further divided into nine classes: SIC 341 to SCI 349. These subclasses indicate product groups [1]. Metal finishing involves the forming and shaping of metals and the altering of surface properties to enhance corrosion resistance, electrical conductivity or resistance, wear resistance, chemical and tarnish resistance, solderability, torque tolerance, ability to bond rubber and adhesives or organic coatings, hardness, reflectivity, and decorat ive appearance. A broad range of processes is employed in the metal finishing industry. Met al fabrication covers mostly mechanical operations such as cutting and forming. Surface treatment involves plating, conversion coating, anodi zing, painting, heat treating, and many other operations. Degreasing, cleaning, pick ling, and etching are supporting processes. The industry manufactures a wide range of metal components such as cans, hand tools, hardware, cutlery, and structural metal products. Many industries use metal finishing in their manufacturing processes. Metal finishing is an essential part of a number of industries including automotive, electronics, defense, aerospace, hardware, heavy equipment, appliances, telecommunication and jewelry. With this profile, the metal finishing industry is among the most common industrial activities in the United States and in man y other countries as well. While production methods and applications are similar in all metal finishing plants, capacities vary widely. Metal finishing facilities are grouped into two major categories: captives and job shops. Captive facilities are part of a larger operation and perform metal finishing processes on in-house manufactured parts. The plants in this category tend to be larger in capacity than job shops. Job shops are independently owned small plants that rely on a variety of customers and work on the parts manufactured by others. Job shops may also be used as subcontractors by the captive facilities. This application tends to be more common [2]. Captive facilities are more specialized in their operations, while job shops are more flexible in operations to respond to the varying demands of customers. 203 Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. Metal finishing industries use a variety of chemicals including solvents, acids, bases, surfactants, complex organic substances, and metal salts such as cadm ium, nickel, and chromium. The industry is one of the largest users of toxic chemicals in the United States [3] and is a significant source of pollutants that are discharged to virtually all receiving media, including air, surface water, land and publicly owned treatment works (POTWs). A considerable part of the wastes is sent offsite for treatment or recycle. This profile makes the metal finishing industry the focus of environmental pollution control and prevention applications and subject to many limitations and standards. Thus, the metal finishing industry uses a greater variety of treatment technologies compared to other industries. Increased cost and sophistication of treatment methods have led to development of in-plant controls, as well as limitations as to chemicals for which control and treatment are considered to be inadequate and/or unreliable. Many of the chemicals, particularly solvents used in the metal finishing industry, have been phased out. A great variety of means and technologies has been employed for pollution prevention. Captive plants, being a part of greater enterprises, tend to be more proactive in their approach to environmental management. However, job shops having the ability to adapt themselves to varying conditions can be quite successful in implementing pollution prevention measures and may even develop original solutions for pollution control. Pollution prevention measures and applications in the metal finishing industry are mostly associated with production methods and recovery options. Therefore, an evaluation of pollution prevention applications in the industry requires an acquaintance with the unit operations of production. 5.2 PROCESS AND OPERATIONS OF THE INDUSTRY 5.2.1 Overview of Processes Metal finishing and other related manufacturing categories employ some 50 unit processes and operations. These operations are applied in many variations depend ing on production demands; however, the main characteristics of the operations or processes remain unchanged. Forty-five unit operations and processes of metal finishing and metal fabricating are listed in Table 1 [3]. Some processes or operations are important in terms of waste generation but are not included in the table because they either employ a group of unit processes to produce a specified product Table 1 Unit Operations of Metal Finishing Industry [3] † Electroplating † Thermal cutting † Hot dip coating † Electroless plating † Welding † Sputtering † Anodizing † Brazing † Vapor plating † Conversion coating † Soldering † Thermal infusion † Etching (chemical milling) † Flame spraying † Salt bath descaling † Cleaning † Sand blasting † Solvent degreasing † Machining † Other abrasive jet machining † Paint stripping † Grinding † Electrical discharge machining † Painting † Polishing † Electrochemical machining † Electrostatic painting † Tumbling (barrel finishing) † Electron beam machining † Electropainting † Burnishing † Laser beam machining † Vacuum metalizing † Impact deformation † Plasma arc machining † Assembly † Pressure deformation † Ultrasonic machining † Calibration † Shearing † Sintering † Testing † Heat treating † Laminating † Mechanical plating 204 Tu ¨ nay et al. Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. such as printed circuit boards (PCB), or constitute integral parts of some processes such as rinsing. Therefore, rinsing, cooling and lubrication, and PCB manufacturing are also briefly explained. One additional process that is not a production process and therefore not shown in the table is fume and exhaust scrubbing. This process has been widely used in metal finishing plants and constitutes a significant source of pollution. Brief information about these processes and operations is given below [1 –5]. After a short definition of the process, emphasis is placed on the chemicals used in the processes. A general scheme of the metal finishing processes indicating the sequence of application is given in Figure 1 [2]. 5.2.2 Description of Processes and Operations Electroplating Electroplating is defined as coating a metal surface with another metal by applying electric current (electrolysis). Electroplating baths contain metal ions that are reduced to a metallic state on the metal being plated. The metal being plated serves as the cathode. The anode is mostly the metal providing plating by dissolution in the bath solution. If an inert metal serves as the anode, the bath solution is replenished by the addition of a salt of the metal as it is consumed by plating. Electroplating baths contain metal salts, complexing agents, pH buffers, as well as organic and organometallic additives. Table 2 presents the major constituents of commonly used electroplating baths [4]. A great variety of metals or alloys is used for plating; those that are commonly used include cadmium, copper, chromium, nickel, zinc, and precious metals. Electroless Plating Electroless plating, as the name implies, does not utilize an electric current for plating. Electroless plating can be carried out as autocatalytic and immersion plating. Autocatalytic plating is the process in which the metal ion in the solution is forced to convert into the metallic state and deposit onto the object to be plated by the use of reducing agents. The process is started by the catalytic action of the surface being plated. For this purpose the surface is pretreated, usually by the application of metal plating. Electroless plating can be applied to metal and nonmetal substrates. The process requires the use of specific chemicals in addition to reducing agents, such as complexing agents and stabilizers. Specific conditions such as pH and temperature also need to be satisfied. Hydrazine, dimethylamine borane (DMAB), hypophosphite, and formaldehyde are common reducing agents. Many types of complexing agents such as EDTA, Rochelle salt, tartrates, and citrates are used. Thiodiglycolic acid, mercaptobenzotiazone (MBT), thiourea, fluoride salts, heavy metals, thioorganic compounds, and cyanides are among the stabil izers used. HCl, H 2 SO 4 , NaOH, and ammonium hydroxide are used for pH adjustment. Copper and nickel electroless plating is commonly used for PCBs. Electroless plating of precious metals is also common. Immersion plating is also carried out without the application of electric current. However, in this case the metal ion in solution is plated onto the base metal, not by forcing with reducing Figure 1 Sequence of the metal finishing operations. (From Ref. 2.) Treatment of Metal Finishing Wastes 205 Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. agents, but spontaneously and as a thin film only, by the difference of electrode potential of the metal in solution and base metal. The metal in solution has a higher electrode potential, that is, it has a higher tendency to be reduced. Immersion plating baths contain alkalis and complexing agents. Sometimes nonalkaline heated bath s are used, as in the case of copper plating on steel, or aluminum. Complex agents commonly used are lactic, glycolic, and malic acid salts, ammonia, and cyanide. Sulfuric and hydrofluoric acids are used for nonalkaline applications. Aluminum, copper alloys, zinc, and steel are plated by immersion plating. Commonly used metals for plating are cadmium, copper, nickel, tin, zinc, and precious metals. Table 2 Common Electroplating Bath Compositions [4] Electroplating baths Composition Brass and bronze Copper cyanide Zinc cyanide Sodium cyanide Sodium carbonate Ammonia Rochelle salt Cadmium cyanide Cadmium cyanide Cadmium oxide Sodium cyanide Sodium hydroxide Cadmium fluoroborate Cadmium fluoroborate Fluoroboric acid Boric acid Ammonium fluoroborate Licorice Copper cyanide Copper cyanide Sodium cyanide Sodium carbonate Sodium hydroxide Rochelle salt Copper fluoroborate Copper fluoroborate Fluoroboric acid Acid copper sulfate Copper sulfate Sulfuric acid Copper pyrophosphate Copper pyrophosphate Potassium hydroxide Ammonia Fluoride-modified copper cyanide Copper cyanide Potassium cyanide Potassium fluoride Chromium Chromic acid Sulfuric acid Chromium with fluoride catalyst Chromic acid Sulfate Fluoride 206 Tu ¨ nay et al. Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. Conversion Coatings Conversion coating is one of the main categories of coating and it is widely applied in metal finishing processes. The purpose of conversion coating is to form a film of a substance that is bonded by the metal coating. This film converts the characteristics of the metal surface into a structure that is more resistant to external effects or amenable to further processing. Chromating, phosphating, passivation, metal coloring, and anodizing are among the common applications of the process. Chromating or chromate conversion coating is realized through a chemical or electrochemical reaction of hexavalent chromium with the metal surf ace. Mineral acids and activators such as acetate, formate, phosphate, nitrate, and chloride are used in the process. Chromate coating provides corrosion resistance. It is widely applied to aluminum, copper, cadmium, and zinc. Among the precious metals, silver is often chromated. Anodizing is a process in which the metal is covered by an insoluble metal oxide. Anodizing particularly refers to oxide coating to aluminum; however, the process is applied to other metals, particularly to zinc, magnesium, and titanium. It is an electrochemical process in which the metal being coated with an oxide layer constitutes the anode. A thin nonporous oxide layer forms on the metal. This layer provides corrosion and wear resistance as well as facilitating further coating operations. The electrolyte in the bath is an acid. Aluminum anodizing includes the use of chromic acid anodizing, sulfuric or boric-sulfuric acid anodizing. Magnesium anodizing solutions are mixtures of fluoride, phosphate, and chromic acids, or of potassium hydroxide, aluminum hydroxide, and potassium fluoride. Phosphoric and oxalic acids are also used for anodizing. Anodized metals are generally sealed. Nickel/cobalt acetate is widely used to seal anodic coatings. Dichromate seal is also very effective. Passivation is a process by which protective films on the metal surface are formed by immersing the metal in an acid solution for oxidation. Strong oxidizing solutions like nitric acid and/or sodium dichromate are used. The oxide layer provides corrosion resistance. Passivation can be accomplished through anodizing or chromating. Phosphating is a conversion coating by which nonmetallic, nonconductive surfaces composed of insoluble metal phosphate crystals are obtained. The main function of phosphating is to impart absorptivity to the surface and to provide a base for adhesion of paints, lacquers, and plastic coating. Phosphating is carried out by immersing the metal into a phosphoric acid solution. The phosphates of zinc, iron, and manganese are commonly used for phosphating. Strontium, cadmium, aluminum, chromium, as well as fluorine, boron, and silicon are common constituents. Nitrate, nitrite, chlorate, and peroxides are used as accelerators. Phosphating is performed on aluminum, cadmium, iron, magnesium, and zinc. Coloring is a chemical conversion of a metal surface into an oxide or other metallic compound to produce a decorative finish. Coloring is commonly applied to copper, zinc, steel, and cadmium. A wide variety of solutions is used for coloring. Examples of coloring solutions are ammonium molybdate, ammonium polysulfide, copper carbonate, ferric chloride and potassium ferricyanide, potassium dichromate and nitric acid, potassium chlorate, and nickel sulfate. Chemical Milling and Etching Chemical milling is used for shaping or blanking the metal parts. Highly concentrated sodium hydroxide solutions are used in chemical milling. Chemical etching is used to remove relatively small amounts of metal from the surface of metals for surface conditioning or producing a Treatment of Metal Finishing Wastes 207 Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. pattern as in PCB manufacturing. Highly acidic solutions containing ferric chloride, ammonium persulfate, cupric chloride, sodium persulfate, and chromic acid can be used for the process. Cleaning Cleaning soil (oil and dirt) from metal surfaces is an essential step preceding many of the unit operations involved in metal finishing. Oil and dirt may be organic or inorganic in nature. Organic materials include saponifiable oils of animal and vegetable origin, mineral oils and waxes, and other organic contaminants such as inhibitors. Metal oxides, residues from the operations such as polishing, abrading, fluxing, and dust are the main inorganic materials. Cleaning operations consume large amounts of water and involve the use of a variety of chemicals. Some processes such as electroplating and electroless plating require a high degree of cleanliness, while others may not require the same degree of cleanliness. On the other hand, the composition and physical prope rties of the material being cleaned are important for the cleaning processes. As a result of these varying requirements, many types of cleaning processes have been developed. However, considering the basic character of the cleaning solution, four main cleaning groups can be defined: solvent cleaning, alkaline cleaning, electrocleaning, and acid cleaning. Solvent cleaning is described under solvent degreasing. Alkaline cleaning involves the use of builders such as sodium or potassium sal ts of phosphates, carbonates, silicates and hydroxides, surfactants, and, sometimes, antioxidants or inhibitors, complex formers, stabilizers, and small amount of solvents. Newly introduced nonemulsifying surfactants are very effective in separating the soil from surfaces. Strong alkaline cleaners may also contain cyanide. Alkaline cleaning is more effective for removing soil from surfaces. Electrocleaning uses a strong alkaline with an electric current either reverse, peri odic reverse, or direct, to remove soils and activate the surface. It is applied, generally, as a last step of cleaning. An electric current electrolyzes the water, evolving hydrogen and oxygen gases. Oxygen exerts a scrubbing effect on the surfaces. In reverse cleaning, the workpiece functions as the anode and the evolved oxygen assists in the removal of soil. In direct cleaning, the workpiece is the cathode and liberated hydrogen at the surface facilitates the scrubbing action. In the periodic reverse system, the workpiece is made alternately anodic and cathodic. The three most common application modes of aqueous cleaning are immersion with mechanical agitation, immersion with ultrasonic agitation, and spray washing. Ultrasonic cleaning is a highly effective method. The method uses high-frequency sound waves, which locally exert high pressure and temperatures to loosen and remove the contaminants. Sometimes semi-aqueous methods of cleaning can be used. Emulsion cleaning uses common organic solvents such as kerosene, mineral oil, and benzene, dispersed in an aqueous medium. Diphase cleaning is a two-layer system of water-soluble and water-insoluble organic solvents. Machining and Grinding Machining and grinding are the mechanical operations to shape and condi tion metals and their surfaces. These operations involve the use of natural and synthetic oils for cooling and lubrication. Polishing, Tumbling, and Burnishing Polishing is used to smooth out surface defects using polishing and buffing compounds. Metallic soaps, mineral oils, dispersing agents, and waxes are among the chemicals used. 208 Tu ¨ nay et al. Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. Barrel finishing (tumbling) is used to remove burrs and scales. Several chemicals in addition to abrasives are used in the process. Oils, soaps, organic acids such as citric and maleic acids, sodium dichromat e, as well as sodium cyanide are among the chemicals used. Burnishing is a smooth finishing by displacement of small surface irregularities. Lubricants and soap solutions are used for cooling of burnishing tools. Light spindle oil, sodium cyanide (as a wetting agent), and rust inhibitors are used. Impact Deformation, Pressure Deformation, and Shearing Impact deformation, pressure deformation, and shearing are all mechanical operations. Oils, light greases, and pigmented lubricants are used for the deformation and shearing equipment. Heat Treating Heat treating aims to modify the physical properties of workpieces through the application of controlled heating and cooling cycles. Case-hardening produces a hard surface over a metal core. The surface is wear-resistant and durable. Quenching is realized using several types of solutions. Brine solu tions contain sodium and calcium chloride and mineral acids. Water/oil emulsions contain soaps, alcohols, oils, emulsifiers, in addition to dissolved salts. Liquid carburizing and carbonitriding solutions contain sodium cyanide, detergents, and dissolved salts. High- temperature quenching baths contain sodium cyanide, boron oxide, sodium fluoride, dissolved salts, as well as manganese dioxide and silicon carbide. Molten lead is used for heat treatment of steel. Thermal Cutting, Weld ing, Brazing, Soldering and Flame Spraying Thermal cutting is accomplished using oxyacetylene oxygen, or electric arc tools. A rinsing step may follow the operations. Welding, brazing, and soldering operations are used to join metal parts, applying heat and pressure to melt the metal or filling material. The operations can be followed by quenching, cooling, or annealing in solutions or emulsified oils. Flame spraying is the process of applying a metallic coating to a workpiece u sing powdered metal together with fluxes. This process is also followed by quenching, cooling, or annealing in a solution, or emulsified oils. Sand Blasting Sand blasting involves the use of abrasive grains pneumatically directed against workpieces to mechanically clean the surfaces. Rinsing may follow the operation. Other Abrasive Jet Machining Abrasive jet machining is a mechanical operation similar to sand blasting. Abrasive materials such as aluminum oxide, silicon carbide, and dolomite are used in alkaline or emulsified solutions. Electrical Discharge Machining and Electrochemical Machining Electrical discharge machining is applied to conductive materials using an electrode that creates an electrical spark. Dielectric fluids such as hydrocarbon-petroleum oils, kerosene, silicone oils, and ethylene glycol are used in the operation. Electrochemical machining is an electrolysis process in which the metal to be treated is the anode. Both aqueous and organic solvents are used as electrolytes. Treatment of Metal Finishing Wastes 209 Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. Electron Beam Machining, Laser Beam Machining, Plasma Arc Machining, and Ultrasonic Machining Electron beam machining and laser beam machining are thermoelectric processes. Plasma arc machining involves the use of high-temperature ionized gas at high velocity. Ultrasonic machining is the use of ultrasonic energy to machine hard and brittle material in a liquid. Sintering and Laminating Sintering is a process of forming a metal coating from powdered metal under pressure and heat. Laminating is bonding layers of metal, plastic, or wood by adhesives. A rinsing or cooling may follow the process. Hot Dip Coating Hot dip coating is achieved by coating a metal with another metal by immersion in a molten metal bath. The molten metal coats the part by forming an alloy at the interface of the two metals. Aluminum, lead, and tin can be used for hot dip coating; however, the most common application is zinc coating (galvanizing). Cleaning operations and fluxing precede the hot dip coating. In galvanizing, a zinc ammonium chloride flux is used. Sometimes coated pieces are quenched. Sputtering, Vapor Plating, and Thermal Infusion Sputtering is coating by bombarding metal ions in a gas discharging tube. Vapor plating is coating by decomposition of a metal compound on the heated surface of the base material. Thermal infusion is the application of a fused metal on heated ferrous material. Salt Bath Descaling There are several types of baths such as oxidizing, reducing, and electrolytic, for removing surface oxides and scale, in which workpieces are immersed. Salt baths are followed by quenching and acid dipping. The baths contain molten salts, sodium hydroxide, sodium hydride, and other chemical additives. Solvent Degreasing Solvent cleaning aims to remove oil and oily contaminants. Cold cleaning, diphase cleaning, and vapor phase cleaning are the three main methods applied. Cold cleaning is the application of unheated solvents of nonhalogenated type by wipe cleani ng, soak cleaning, ultrasonic cleaning or steam gun stripping. Diphase cleaning systems use both water and solvent. After a water bath, solvent spra y is applied to remove oil. Vapor phase cleaning is carried out in a tank where a halogenated solvent is heated to its boiling point. The parts to be cleaned are placed in the vapor zone. Solvent vapors condensed on the parts dissolve the oil and drip down the liquid phase. Air pollution devices such as coolers and condensators are placed above the vapor zone to minimize solvent emissions. Vapor degreasing involves the use of chlorinated solvents such as trichloroethylene, and perchloroethylene. Paint Stripping Paint stripping is the removal of an organic coating from a workpiece. Stripping solutions may contain caustic soda, wetting agents, detergents, emulsifiers, foam soaps, alcohol amines, 210 Tu ¨ nay et al. Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. ammonia, or solvents. Chlorinated solvents, polar solvents like acetone, methyl ethyl ketone, benzene, and toluene are commonly used. A rinsing step follows the process. Painting, Electropainting, and Electrostatic Painting Painting is the application of an organic coating such as paint, varnish, lacquer, shellac, and plastics. Spray painting is the most common method of painting; however, a variety of other methods such as dipping, brushing, and roll coating are used. Electrostatic painting is the application of electrostatically charged paint particles to an oppositely charged surface of the workpiece. It is followed by thermal fusing. Electropainting is carried out in a bath of aqueous emulsion of the paint, and the workpiece to be painted is made anodic or cathodic to collect the paint. Paint and other coating ingredients include a wide range of chemicals: pigments, resins, solvents, and other additives. Vacuum Metalizing and Mechanical Plating Vacuum metalizing is the process of coating a workpiece with a metal by flash heating the metal vapor in a high vacuum and condensing it on the workpiece surface. Mechanical plating is a process where cadmium, zinc, and tin powders are used for coating in barrels immersed in an acid solution by inert impact media. The plated parts are then rinsed. Assembly, Calibration, and Testing Assembly is the fitting together of previously manufactured parts or components. Calibration is the application of thermal, electrical, or mechanical energy to set or establish a reference point for a component or assembly. Testing is used to control the suitability or functionality of a finished or semi-finished product by the application of thermal, electrical, or mechanical means. Oils and fuels are used in nondestructive testing. Oily penetrants are used in dye-penetrant testing. Kerosene, ethylene glycol, and lubricating oils are among common penetrants. Rinsing Rinsing is the most common operation that follows many unit operations in metal finishing. Plating, cleaning, degreasing, and heat treating are the operations for which rinsing is an integral part of the operation. Rinsing may also be used after dry processes such as sand blasting. Rinsing is the major water-using process – a significant part of plant wastewater originates from rinsing. Many rinsing operations are continuous, which determines the bulk of continuous wastewater. The aim of rinsing is to remove contaminants of the preceding process. These contaminants may be oily, solid, but mostly aqueous. The drops or particles of contaminants that have the same or similar character of the solution or bath content on the workpiece are termed “dragout,” which is mostly valuable. Therefore, rinsing is required to completely remove the contaminants, to achieve this with a minimum amount of water, and to enable recovery of dragout in a most efficient way. Of course, there is no ideal way to combine all these purposes, but what is applied is to select an optimum system depending on the process, that is, the value of the dragout, flow conditions, quality requirements of the subsequent processes, or of the finished product. Sever al rinsing systems may serve as an optimum in terms of general applications. Rinsing systems are based on several types of rinsin g techniques: single running, countercurrent, in series, spray, dead, or economical. Single running rinse is the simplest and is an efficient method, but it consumes the largest amount of water. Countercurrent rinsing makes use of several tanks, but only the last tank receives fresh water, while preceding tanks are fed with the overflow of the following tank. Series or multistage static rinse is made up of several tanks in series, each having Treatment of Metal Finishing Wastes 211 Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. a separate feed. The conditions of each tank can be set up independently. Spray or fog rinse is the most efficient mode of continuous dilution rinsing. Dead or economy rinse follows the bath, receiving the most concentrated dragout, and is used to make up the preceding bath, or for recovery. Several methods of rinsing systems have been developed by combining these techniques. Cooling and Lubrication Cooling and lubrication is a common applica tion employed in many operations such as machining operations, grinding, burnishing, and testing. Metalworking fluids are used for cooling and lubrication. Metalworking fluids are applied to the workpiece or cutting tool in order to cool the workpiece and/or tool, lubricate, wash away chips, to inhibit corrosion or surface oxidation, and to provide a good finish. Metalworking fluids can be air-blasted, sprayed, or applied by suction. Aqueous solutions contain an alkali such as borax, sodium carbonate, or trisodium phosphate. Emulsions are suspension of oil or paste in water. Oil–water or synthetic emulsions can be used. Some operations use a high oil to water ratio, for example, greater than 1/20, while others that require primarily lubrication rather than cooling, use oil. In addition to synthetic or petroleum-based oil content, metalworking fluids may contain chlorine, sulfur and phosphorus compounds, phenols, creosols, and alkalis. Printed Circuit Board Manufacturing Printed circuit board manufacturing is widely used in many fields, from electronics to transportation. The processes employed throughout the manufacturing are, to a great extent, metal finishing unit processes such as plating and etching. Wastewaters originating from PCB manufacturing also have a very similar character to those of metal finishing plants. Printed circuit board manufacturing is based on creating a circuit by sandwiching a conductive metal, usually copper, on or between layers of plastic or glass boards. There are three main production methods: subtractive process, additive process, and semi-additive process. Cleaning and surface preparation is the first step common to all processes. Cleaning and surface preparation includes the processes of scrubbing, alkaline cleaning, etching, and acid cleaning. Catalyst application involving the use of palladium and tin is essential for additive and semi- additive processes. Electroless copper plating in different patterns is common to all methods. Electroless copper plating uses copper salts, mostly copper sulfate, formaldehyde as the reducing agent, chelating compounds, mostly EDTA or tartrates, various polymers and amines, and sodium hydroxide. Copper electroplating used in subtractive and semi-additive processes can be carried out using a cyanide copper bath or other copper baths such as fluoroborate, pyrophosphate, and sulfate copper baths. Other processes employed in the manufacturing include solder plating, solder brightening, nickel and gold plating, and immersion plating. Fume and Exhaust Scrubbing Air pollution is a common problem in the metal finishing industry. Solvent wastes, metal ion bearing mists, metal fumes, acid mists and fumes are primary pollutant sources. Air pollution control is, in many cases, a mandatory application. Control of water-soluble contaminants and gases is usually carried out using wet collectors. Wet collectors can be simple spray chambers or packed-bed scrubbers. Scrubber blowdown contains the same pollutants as those of the sources and contributes to wastewater flow in varying propor tions depending on plant characteristics. 212 Tu ¨ nay et al. Copyright #2004 by Marcel Dekker, Inc. All Rights Reserved. [...]... ( 2- Chloroethyl) ether 2- Chloroethyl vinyl ether 2- Chloronaphthalene 2, 4,6-Trichlorophenol Parachlorometa cresol Chloroform 2- Chlorophenol 1 , 2- Dichlorobenzene 1,3-Dichlorobenzene 1,4-Dichlorobenzene 3,3-Dichlorobenzidine 1,1-Dichloroethylene 1 , 2- trans-Dichloroethylene 2, 4-Dichlorophenol 1 , 2- Dichloropropane 1,3-Dichloropropylene 2, 4-Dimethylphenol 2, 4-Dinitrotoluene 2, 6-Dinitrotoluene 1 , 2- Diphenylhydrazine... biphenyls) PCB- 124 2 (Arochlor 124 2) PCB- 125 4 (Arochlor 125 4) PCB- 122 1 (Arochlor 122 1) PCB- 123 2 (Arochlor 123 2) PCB- 124 8 (Arochlor 124 8) PCB- 126 0 (Arochlor 126 0) PCB-1016 (Arochlor 1016) Toxaphene 2, 3,7,8-Tetrachlorodibenzo-p-dioxin 21 8 ¨ Tunay et al The above discussion indicates that segregation of wastewater is the basic approach for management, control, and treatment of the metal finishing wastewaters... Indeno(1 ,2, 3-cd) pyrene 2, 3-Phylene pyrene Pyrene Tetrachloroethylene Toluene Trichloroethylene Vinyl chloride Aldrin Dieldrin Chlordane 4,4-DDT 4,4-DDE (p,p-DDX) 4,4-DDD ( p,p-TDE) Alpha-endosulfan Beta-endosulfan Endosulfan sulfate Endrin Endrin aldehyde Heptachlor Heptachlor epoxide (BHC-hexachloro-cyclohexane) Alpha-BHC Beta-BHC Gamma-BHC Delta-BHC (PCB-polychlorinated biphenyls) PCB- 124 2 (Arochlor 124 2)... N-nitrosodi-n-propylamine Pentachlorophenol Phenol bis ( 2- Ethylhexyl) phthalate Butyl benzyl phthalate Di-n-butyl phthalate Di-n-octyl phthalate Diethyl phthalate Dimethyl phthalate 1 , 2- Benzanthracene Benzo(a)pyrene 3,4-Benzofluoranthene 11, 1 2- Benzofluoranthene Chrysene Acenaphthylene Anthracene 1, 1 2- Benzoperylene Copyright #20 04 by Marcel Dekker, Inc All Rights Reserved Fluorene Phenanthrene 1 ,2, 5,6-Dibenzanthracene... Fluoranthene 4-Chlorophenyl phenyl ether 4-Bromophenyl phenyl ether bis ( 2- Chloroisopropyl) ether bis ( 2- Chloroethoxy) methane Methylene chloride Methyl chloride Methyl bromide Bromoform Dichlorobromomethane Chlorodibromomethane Hexachlorobutadiene Hexachlorocyclopentadiene Isophorone Naphthalene Nitrobenzene 2- Nitrophenol 4-Nitrophenol 2, 4-Dinitrophenol 4,6-Dinitro-o-cresol N-nitrosodimethylamine N-nitrosodiphenylamine... 10 mg/L lead, 1 022 M sulfate, and 3 Â 1 025 to 1.5 Â 1 022 M carbonate between pH 3.9 and 11.3 have indicated that PbSO4(s), PbCO3(s), and Pb3(CO3 )2( OH )2( s) precipitates formed, while no Pb(OH )2( s) was detected [25 ] Carbonate precipitation applied to battery manufacturing wastewaters yielded residual lead values of less than 0 .2 mg/L [26 ] Lead precipitation with carbonate in the presence of Fe3þ resulted... for ligand sharing action has been investigated [34] Calcium, ferrous and ferric ions, Mn2þ and Mg2þ were theoretically Copyright #20 04 by Marcel Dekker, Inc All Rights Reserved Treatment of Metal Finishing Wastes Figure 7 Cadmium – succinic acid and NTA (From Ref 33.) Figure 8 Nickel – EDTA and NTA (From Ref 33.) Copyright #20 04 by Marcel Dekker, Inc All Rights Reserved 23 1 23 2 ¨ Tunay et al and experimentally... list of significant organic parameters is presented in Table 4 [6] Table 4 Toxic Organics in Metal Finishing Wastewaters [6] Acenaphthene Acrolein Acrylonitrile Benzene Benzidine Carbon tetrachloride Chlorobenzene 1 ,2, 4-Trichlorobenzene Hexachlorobenzene 1 , 2- Dichloroethane 1,1,1-Trichloroethane Hexachloroethane 1,1-Dichloroethane 1,1 , 2- Trichloroethane 1,1 ,2, 2-Tetrachloroethane Chloroethane bis ( 2- Chloroethyl)... calcium Alkalinity removal is quite high, particularly if pH is over 10 Formation of calcium carbonate may help the removal of some Copyright #20 04 by Marcel Dekker, Inc All Rights Reserved Treatment of Metal Finishing Wastes 22 9 pollutants; however, it results in loss of buffer capacity and an increase in the amount of sludge Solubility of calcium sulfate is higher and its removal depends on ionic strength,... however, Copyright #20 04 by Marcel Dekker, Inc All Rights Reserved Treatment of Metal Finishing Wastes 23 5 pressure filters may be preferred when the flow is pumped for further treatment because they permit higher loadings Addition of polyelectrolytes improves filter performance Volumetric loads used for gravity sand and high-rate mixed media filters are 40– 50 L/min.m2 and 80– 120 L/min.m2, respectively . (Arochlor 125 4) 1,3-Dichloropropylene Benzo(a)pyrene PCB- 122 1 (Arochlor 122 1) 2, 4-Dimethylphenol 3,4-Benzofluoranthene PCB- 123 2 (Arochlor 123 2) 2, 4-Dinitrotoluene 11, 1 2- Benzofluoranthene PCB- 124 8 (Arochlor. Delta-BHC 1 , 2- trans-Dichloroethylene Diethyl phthalate (PCB-polychlorinated biphenyls) 2, 4-Dichlorophenol Dimethyl phthalate PCB- 124 2 (Arochlor 124 2) 1 , 2- Dichloropropane 1 , 2- Benzanthracene PCB- 125 4. Chlordane 1,1 , 2- Trichloroethane Naphthalene 4,4-DDT 1,1 ,2, 2-Tetrachloroethane Nitrobenzene 4,4-DDE (p,p-DDX) Chloroethane 2- Nitrophenol 4,4-DDD (p,p-TDE) bis ( 2- Chloroethyl) ether 4-Nitrophenol Alpha-endosulfan 2- Chloroethyl