BY STEVE SUSLIK, EDITOR

Transcription

1 As times change, platers must reevaluate their systems to make certain efficiency is maintained. Years ago a single waste treatment plant for treating all the wastes in a shop was all that was needed. Today that may not be enough to keep a shop in compliance with government regulations and keep costs at a manageable level. The first question to be asked when evaluating needs for waste treatment is, Can the production of waste be avoided in the first place? Recovering chemicals for reuse reduces the cost of materials and the cost of waste treatment. A number of recovery systems are available, and it is possible that a different system for each of the processes in a shop may be economically feasible. A system for cadmium, another for zinc and a third for nickel may result in lower overall costs when compared with a single waste treatment plant. There s one set of figures to look at if disposal is all that s being considered-and quite a different set of figures to evaluate when considering recovery. When is it worthwhile to recover materials? lt s easy to understand the economics of recovering precious metals, but it s a bit more difficult to see the value in reclaiming nonprecious materials. The value can be seen when the cost of the bath makeup chemicals and disposal are considered. Methods of recovery include evaporation (heat and atmospheric), electrodialysis, ion exchange, electrochemical, reverse osmosis and ultrafiltration. Industrial Finishing has contacted manufacturers of recovery systems for an analysis of the various systems. Their responses give a better understanding of the recovery process. Evaporation Evaporation is the most widely used and understood method of recovering plating chemicals, and its key benefit is its adaptability to various solutions. Corning Process Systems supplies evaporative recovery systems. Its original equipment was manufactured to recover chromic acids and nickel solutions, but the Corning evaporator has been modified to recover cyanides, lead-tin fluoborates, precious metals and mixed industrial waste acids. Reliability makes evaporative recovery attractive, and because the technology is simple, nearly anyone can mas- BY STEVE SUSLIK, EDITOR ter the operation. Recovery equipment must function with as little downtime as possible; even the smallest of maintenance crews is capable of keeping evaporative recovery systems onstream. Corning has developed a gold recovery unit specifically for printed circuit and connector manufacturers; it is called the GoldminerTM and can consolidate gold rinse waters (to reduce shipping and refining costs) or recover and recycle baths directly. The new evaporators feature a horizontal boiler design with a 7.6- to 15.2-cm (3- to 6-in.) low static and dynamic head and a large surface area-to-volume ratio. This design results in a gentle boiling action with low vapor velocities that minimize or eliminate entrainment losses. Systems Engineering Research Facilities (SERF) also provides evaporative recovery and recycle equipment. The Vapor-Phase recovery systems evaporate, concentrate and recycle solutions containing cyanide rinse waste, radioactive wash water, toxic wastewater, acid or basic by-products, organic waste, salt and brine water and photographic wash water. The unique features of this equipment are its ability to control nominal bath concentrations with a minimum of personnel attention and its ability to modulate capacity with the metal finisher s plating production throughput. Through a joint contract with the Department of Energy (DOE) and the U.S. Navy, Licon, Inc. has developed two evaporators-the Aquavap (vapor compression) and Fridgevap (freon heat pump). The company s standard waste heat evaporator and the Aquavap are installed on hard chrome plating lines at the Naval air rework facility in Pensacola, FL. Both units have been operating approximately 18 months. The Fridgevap is installed on a cadmium cyanide plating operation in Forrestville, CT and has been operational for a little more than two months. The waste heat evaporator is designed to run off waste heat that is available from heated plating tanks, condensate drains or existing chillers. It has a low operating temperature gradient, and energy requirements seldom exceed 3.7 kw (5 hp) if waste heat is available. The Aquavap vapor recompression evaporator has all the features of the company s standard evaporator but is only available in sizes larger than 189.9L/hr (50 gph) distillate capacity. By recycling the latent heat contained in the vapor, the Aquavap is 10 to 20 times more energy efficient than singleeffect, steam-fired evaporators. The larger they are, the more energy efficient they are. The Fridgevap evaporator is identical in arrangement to the waste heat evaporator except that the heat pump package is coupled with the evaporator in the event that no waste heat is available in the plant. The Fridgevap pack- age eliminates the need for boilers or cooling towers to run the evaporator. The energy efficiency of freon heat pumps is four to eight times greater than steam-fired, single-effect evaporators. These units operate at boiling temperatures as low as 30C (86F), allowing recovery of cadmium cyanide or heat-sensitive brighteners. Nickel and chrome recovery are available with the evaporation process from Industrial Filter & Pump Manufacturing Co. The atmospheric evaporator consists of a reservoir, a feed pump and a heat-transfer device. A packed tower-type unit is available in various sizes up to 91 O-Uhr (240-gph) evaporative capacity. Separating efficiency is 99.7%; options include a cation purifier. The Cosmos Mineral Miser is another evaporation unit; it returns reusable electroplating chemicals and a continuous flow of distilled water that is independent of solution processing. The tower portion is the heart of the unit; its patented internal design separates plating solution from the vapor and returns it to the evaporator. This design assures that the vapor going over through the transfer pipe is clear and free of any carryover. The condenser

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3 . and flow best suited to an individual plating line. Most concentrates can be returned as is to the plating tanks. The Baker Bros. ElectrocoveryTM module is a completely self-contained unit with membrane stack, filter, rinse water recirculation pump, electrode rinse reservoir and pump, conductivity meter for rinse solution, flow meters, control valves and a single power supply for all electrical requirements. The cell-pair is the heart of the system; it is composed of one cation and one anion exchange membrane with internal flow directing spacers. The spacers between membranes create concentration and rinse compartments. Incoming flow is directed into each rinse compartment. When a dc current is imposed, cations pass through the cation membrane and are trapped in a concentration compartment. The anions travel through the anion membrane, are rejected by the adjacent cation membrane and are trapped in another concentration compartment. The solutions in the concentration compartments combine in the concentrate line for return to the plating tank. The partially deionized rinse stream returns to the reclaim rinse tank. The ERC/Lancy electrodialysis unit is a standardized product for the recovery of metal salts (copper, nickel, tin, zinc and others). A multi-cell membrane assembly is housed in a cabinet with a control panel and gauges for monitoring pressure, solution temperature and conductivity. It has a separate filter and strainer and its own tanks and pumps for electrode rinse and product recircu- lation. The heart of the system is the membrane assembly, which contains an arrangement of anion and cation permeable membranes. In operation, the first rinse stream in a typical metal finishing operation that contains removable metal salts is pumped through every other cell of the membrane assembly. With the application of a direct electrical current, the anions are made to migrate through the membranes into the next cell where they concentrate and are trapped by the next membrane. The result is two streams emerging from the cell-a demineralized rinse water stream that is returned to the rinse tank and a concentrated solution of metal salts that generally is suitable for direct return to the plating bath. The system typically allows 90 to 95% recovery of reusable metal salts based on dragout; automatic functions eliminate the need for continuous operator attention. In a typical application the system reduces plating chemical consumption in the range of 75 to 95%. The system occupies approximately 0.74 m2 (8 ft*) of floor space, but the actual size depends on volume and quality of rinse water, rate and type of work being processed, quantity of metal salts in the bath, dragout volume and rinse tank capacities. Lea Manufacturing has installed many recovery systems in the plating field for recovery of gold, silver, cadmium and nickel. The electrodialysis process can be integrated with other recovery and closed-loop systems. ERCILANCY Ion transfer lnnova Technology, Inc. offers a wellknown ion-transfer membrane system that recovers chromic acid from the dilute end of a countercurrent dragout rinse system and concentrates the acid for return to the hex-chrome plating bath. The recovered chromic acid contains all of the valuable bath chemicals but not the undesirable metallic cation impurities. In conjunction with the countercurrent rinsing techniques, the ChromenapperTM provides a totally closed-loop rinsing system and recovers virtually all of the chromic acid that would have been lost in the dragout. In a typical decorative plating operation that presently uses no recovery methods, this system could reduce chrome consumption by up to 95% and water consumption by up to 99%. A study performed by the EPA in 1971 gave a capital and operating cost comparison between the Chromenapper and a conventional treatment system. The parameters on which the comparison was based: a programmed hoist and four rinse tanks; bath temperatures of 46C (1 15F); tank dimensions of 3 by 1.2 by 1.5 m (10 by4 by 5 ft); a 16-hr operating day with dragout of 3.8 L/hr (1 gph); a rinse water flow rate for the conventional treatment system of 37.9 L/min (IO gpm). The installed cost of a Chromenapper sized for such an operation would be $21,200. Gopper and nickel recovery is made simple by a technological breakthrough by Enthone. The company has developed a method for removing the metals completely in the presence of complexing agents. The ion-exchange process uses an ion-specific resin called compound WT-118 that is capable of removing copper from electroless copper rinse water; copper from ammoniacal etchant rinse water; and nickel from electroless nickel rinse water. In all cases, 0.03 m3 (1 ft ) of material removes 0.45 kg (1 Ib) of copper or nickel. The metal is removed from solution, leaving the effluent suitable for sewer discharge (ph adjustment may be required). Realizing that countercurrent dragout rinse techniques are popular, and that impurities that may be returned to the bath could create problems, lnnova has developed a way to remove those impurities. The CatnapperTM uses a specially designed membrane in conjunction with the principle of electromigration to remove metallic cation impurities, such as iron, trivalent chrome,

4 HSA REACTORS copper, zinc and aluminum. The system removes the impurities at the rate of buildup, thereby stabilizing the bath and preventing its loss of effectiveness. A two-column, packaged ion-exchange system is also available from Industrial Filter & Pump Manufacturing Co. Its patented distribution and collection devices promote effective ion-exchange resin regeneration. Individual cation and anion units may be supplied for special applications and mixed-bed systems for applications requiring extreme purity. Eco-Tec nickel salt recovery systems are based on short bed, rapid cycling reciprocating flow ion-exchange (RE- COFLO) technology. Over 50 systems have been put into operation since The system removes nickel from plating rinse waters and produces a concentrated nickel salt solution that is free of organics for return to the plating bath. The equipment consists of a nickel salt decationizer (DCN) and a deacidification unit (DAU). The DCN includes a cartridge-type prefilter to remove solids and a RECOFLO column of special sorption resin. The unit automatically recycles between onstream (nickel removal from rinsewater) and offstream (production of concentrated nickel salt solution). The offstream I CATHODE FRAME phase lasts approximately two min- Utes; then the system returns onstream. The concentrated nickel salt solution leaving the DCN cation exchanger contains residual acid from the regeneration procedure. This excess acid is removed as the solution flows through the column of special sorption resin on the deacidification unit to bring the ph to about 3.5. After each volume of solution passes through the DAU, only water is used to regenerate the resin. The entire sequence is automated, and the final nickel salt solution is ready for \ FRP COATED TUBULAR STEEL FRAME RFLOW NOZZLE THERMOPLASTIC NOZZLE recycling to any nickel-sulfate-based plating bath. With little variation, the same type of system may be used to recover other metal salt baths, such as acid copper, acid tin and aiuminum electrolytic coloring baths. An ion-exchange gold reclaimer is available from Camac for operating temperatures up to 82.2C (1800. Solutions are pumped through a monofilament, polypropylene sleeve filled with resin. When the resins have absorbed metals to their capacity, the sleeve is

5 I 1 removed for shipment to a refinery. Electrochemical recovery The HSA metal recovery system can reclaim in excess of 99% of the metal normally dragged out of the plating bath. The use of patented high-surfacearea electrodes permits the efficient electrochemical recovery of metals at low concentration; only metal is returned to the plating bath, so the plating bath quality is not affected. HSA systems are currently recovering cadmium, copper, zinc and silver in a number of captive and job shops. Of particular interest to users in the printed circuit board industry is the system s ability to recover copper from solutions without destroying costly additives like EDTA. The modular system is totally automated and takes up approximately 1.9 m2 (20 ft2) of floor space. The ERC/Lancy electrolytic metal recovery cell recovers silver, gold, copper, tin and other metals. The system provides high agitation, which in turn provides more efficient and better quality metal recovery, lower labor and maintenance requirements and the utilization of smaller, less expensive units with fewer cathodes to replace and maintain. Agitation velocities as high as 0.6 to 0.9 m (2 to 3 ft) per second make it possible for the unit to operate at higher current densities, thus directly increasing the metal recovery capability per square foot of cathode area. The unit is normally installed in a closed-loop recirculation system in conjunction with a process or rinse tank. The metal removal rate is controlled electrolytically to maintain a specified S RFILCO metal concentration in the stream being treated. The metal is continuously deposited on easily removable cathode plates until the deposits are approximately 1.27-cm (0.5-in.) thick. Then the cathodes are manually removed and rinsed with water; the slabs of recovered metal are easily peeled off by hand. Cathode removal usually is staggered so the metal recovery cell does not have to be taken out of service. An electrolytic gold recovery system is available from Serfilco. The unit is compact and completely ready for use following either acid or alkaline electroplating baths. Included with the system is an electrolytic chamber; magnetically coupled, leakproof pump; and a variable dc power supply. A prefilter is available as an option; to insure that all of the precious metal has been removed prior to dumping of the water in the dragout rinse, a resin chamber is also available. The gold is plated onto a stainless steel plate for easy recovery. Reverse osmosis Several years ago a field test was conducted by the EPA at a job shop to demonstrate closed-loop recovery of zinc cyanide rinse water. A zinc cyanide bath operating at room temperature had an evaporation unit attached to it in addition to a reverse osmosis (RO) treatment system. The permeate from the RO unit was recycled to the first rinse after plating, while the distillate from the evaporator was recycled to the second rinse after plating. Continuous, unattended operation of the system had no adverse effects on plating quality. An Abcor reverse osmosis system and a Wastesaver evaporator were used in the test, which showed that the total operating costs of a combined RO and evaporation system (including amortization) was somewhat less than for evaporation alone. The field test, conducted several years ago, is available from National Technical Information Service, 5285 Port Royal Road, Springfield, VA Many advances have been made since this report, but it is worthwhile reading for anyone interested in this specific method of recovery. Ultrafiltration Ultrafiltration is a pressure-driven process for separating high molecular weight solutes or colloids from water solutions by means of a membrane that is permeable to the colloids but impermeable to the solutes. The separation process is performed by flowing solution past a membrane surface under an applied pressure. Rejected solutes, which leave the flowing stream, do not accumulate on the membrane surface. Ultrafiltration technology is well suited for alkaline cleaner baths; it concentrates the dilute oily waste and recycles cleaning chemicals. Because ultrafiltration membranes allow only low molecular weight solutes and water to pass through, emulsified oil and particulates are held back and concentrated. The alkali and builders are generally low molecular weight solutes. These materials pass through the membrane freely and are returned to the cleaner bath. Except for those surfactants that are oil soluble or remain with the emulsified oil, surfactants are also recycled. Abcor furnishes two standard-sized ultrafiltration systems for cleaner bath pretreatment. Each system employs tubular membranes that consist of noncellulosic membrane polymer supported on an epoxy-impregnated fiberglass backing, a process tank, cleaning tank, circulating pump, heat exchanger and controls. The information contained in this article is not meant to be an exhaustive listing of recovery methods and equipment. It is offered to better acquaint the reader with some of the more popular methods and available equipment. Recovery is and will continue to be a major concern of platers as the regulatory powers are tightening up, and enforcement of compliance dates is coming closer to reality. Ea