An article by Eugene Parks, about a process called "source reduction" and how many jewelry manufacturers would be bettter served by exploring today's source-reduction alternatives.
Are you missing out on a chance to save money? Old-fashioned end-of-pipe waste treatments can be costly and of limited benefit. Many jewelry manufacturers would be better served by exploring today's source-reduction alternatives.
By Eugene Park
What do a $10 drip bar and a $10,000 ion-exchange system have in common? Both are effective systems jewelry manufacturers can use to reduce hazardous waste as the source. More importantly, from a bottom-line perspective, both are systems that have the potential to pay for themselves in a short period of time.
The process called "source reduction" is rapidly replacing old-fashioned end-of-pipe treatments as the preferred way of confronting hazardous waste issues. The reason for this preference is obvious: With environmental regulation becoming increasing stringent, and hazardous waste disposal becoming increasingly expensive, it is far more cost-effective to reduce at the source the amount of waste that must be disposed.
In addition, because upstream process modification can be used to minimize the company's dependence on costly end-of-pipe chemical treatment, many source reduction modifications can pay for themselves in a short period of time.
Wastewater discharges and the sludge generated through end-of-pipe chemical treatment of wastewater are the main hazardous discharges from jewelry facilities. The first steps toward upstream process modification involve improved housekeeping and product substitution. Many of these techniques are easy to implement, and provide immediate results in terms of reduced end-product waste. These techniques also lay the groundwork for the more sophisticated in-process recycling technologies that we will discuss later in this article.
Simple housekeeping changes may significantly reduce the amount of metals discharged, the amount of water used, or both. Proper rinsing techniques, drip bars, and dragout reduction steps will prolong the life of baths, reduce the amount of waste used in the process, and reduce the dependence on chemical treatment.
Thanks to this ultrafiltration system, J&L Finishing President Edward Lavoie (left) has dramatically reduced his hazardous sludge disposal costs. Dr. Eugene Park (right) of the University of Rhode Island assisted J&L in implementing the system.
Drip Bars
The largest source of contamination in the rinse water, and therefore in the waste stream, comes from solution that clings to parts as they are passed from tank to tank, typically referred to as "dragout." Many companies have found that reducing dragout is an inexpensive, easy way to implement pollution prevention in their facility.
Drip bars are simple rack structures installed over tanks, from which the plating racks are suspended after removal. This allows the bulk of the dragout solution to drain back into the tank of origin. The use drip bars not only prolongs fluid life by reducing cross-tank contamination, but it also reduces the contaminants entering rinse streams.
Drip bar structures can be built easily and inexpensively from materially readily available to any jewelry facility. However, there are operational issues that have to be considered, such as monitoring the drip time so as not to allow product spotting, and adjusting worker and facility tank patterns to allow for easy implementation of new practices. Each jewelry company should carry out simple tests to determine the optimum drip time and tank layout. (Figure 1 illustrates the use of a drip bar). In some cases the plated parts can be blown with air while suspended over the tank, to further minimize the amount of dragout.
Figure 1; Drip Bars
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Dragout Recovery Tanks
Most plating operations use a standard, non-flowing rinse tank ("dragout tank") to capture dragout before it enters their running rinse streams. A rule of thumb is that each extra dragout tank added to the system will reduce metal concentrations in the running rinse by up to 50 percent. When the concentration in the dragout tank approaches that of the plating tank, the fluid is usually returned to the plating tank to help replenish lost metal salt solution and evaporated water.
Counter-Current Rinsing
Rinse water can be used several times before discharge. Rinse water tanks can be set up in series with the water flowing opposite to that of the work flow (see figure 2). Fresh water is fed into the rinse tank farthest from the plating tank. Water from this tank feeds the next tank closer to the plating tank, etc. Studies have shown that two counter current rinse tanks can reduce water use by to 95 percent.
Figure 2: Counter-Current Rinsing
The jewelry industry has traditionally used a number of compounds that are considered toxic and hazardous. With pollution prevention becoming the more accepted approach to reducing waste, many less hazardous substitutes have been developed.
Aqueous Cleaning
Part surfaces must be free of organic materials, oils, etc., to ensure proper plating. Traditionally, solvents like trichloroethylene and 1,11-trichloroethane were used in open-top vapor degreasers to remove these materials. This process worked quite well since the parts were cleaned quickly and no rinsing was required.
With the advent of the Clean Air Act and Resource Conservation and Recovery Act, at the use and disposal of these compounds have become more and more expensive; eventually, the use of these chemicals will be banned altogether. Many companies are switching to water-based (aqueous) cleaning and have modified their operations to produce satisfactorily clean parts. The rising costs and liabilities of using organic solvent cleaners means most companies can realize a very quick pay-back when converting to aqueous cleaning (typically less than one year).
A number of vendors offer free testing to help determine the best replacement cleaning process. The operational changes include the addition to a rinse tank and increased cleaning times in some cases. Also, what was previously an air emissions concern in now essentially converted into wastewater and treatment concerns. However, this shift in waste form should result in fewer liabilities and lower costs. (Later in this article we will discuss how technologies such as ultrafiltration can be used to recycle these cleaners and rinses to minimize sewer discharges and overall waste.)
Plating Bath Reformulation
Cyanide baths are commonly used in the industry because of their "forgiving" nature. However, treating cyanide-containing wastes requires an extra treatment step to oxidize and thereby destroy the cyanide. The Rhode Island Department of Environmental Management (DEM) Pollution Prevention Program has funded projects to determine the feasibility of replacing cyanide baths can be replaced with either acid baths or newer proprietary non-cyanide baths.
The main drawbacks of these replacement baths include the increased monitoring required, especially in the area of pre-plate part cleanliness. Present studies all point to the importance of a clean part surface for non-cyanide plating. Although the results indicate that there are little significant cost savings, companies that have switched over to the non-cyanide solutions report improved working conditions. Both environmental and safety liabilities have been reduced dramatically.
Another plating reformulation technique involves operating baths at lore metal concentrations. Often this can be done without affecting plat quality. Many platers are more comfortable with overdosing the plating tank to ensure proper plating, but this can cause unnecessarily high dragout concentrations, and thus more waste to be dealt with.
Present plating baths, whether it be acid copper or nickel, should be analyzed for optimum metal concentrations. For example, one copper plating bath may run well at concentrations ranging from 27 up to 32 ounces per gallon. By running at the minimum of 27 oz/gal, overall cooper discharges from dragouts and rinses can be reduced by 13 percent over the 23 oz/gal tank concentration.
After these basic source reduction measures have been investigated, jewelry manufacturers can look at implementing in-process separation and recycling processes that can further reduce pollution loads to the company's pretreatment system. While these in-process methods are generally more com-lex and costly to implement, we'll look at several real life examples where they have paid for themselves in a short period of time.
Before proceeding, it's important to note that cleaning and recycling can only occur when waste streams are not mixed. As soon as waste streams are mixed, the probability that these fluids can be reused is greatly diminished.
Many water-based process streams found in the jewelry industry become waste due to contamination by oils and suspended solids. Aqueous cleaners and their rinses fall into this category. So does wastewater from mass-finishing processes (tubbing and vibratory machines), which can be contained suspended solids, soap, oils, and metals.
Technologies commonly used for in-process recycling in the jewelry industry are membrane filtration (microfiltration, ultrafiltration, reverse osmosis) and ion-exchange. Each can be used in different scenarios to recover water, dissolved metals, and sometimes over fluids such as soaps and plating fluids.
Figure 3: Membrane Recycling System
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Membrane Filtration
Separating contaminants from the water stream makes it possible to continuously reuse process water, and thereby reduce loading to the pretreatment system. This is best performed in two stages. Many companies already have the first stage for cleaning used solutions, which is coarse filtration. Coarse filtration can be defined as removing particles in the 30 to 200 micron range, and is performed with either cartridge or bag filters.
The next stage is membrane filtration. Membrane filters are available in configurations that can filter micro-sized particles (microfiltration), particles less than 0.1 microns (ultrafiltration), and small molecules and metal ions (nonfiltration and reverse osmosis). Because these filters are available in closely defined ranges, they are the best means of mechanically separating different constituents for recycling.
For the most part, companies have relied on microfiltration and ultrafiltration for cleaning and reusing aqueous cleaner and mass finishing waste streams. As is illustrated in our first case study below, one of the benefits of using these technologies is the potential for recovery of the water and the original soaps, thereby reducing soap and water costs. (A typical process schematic for a recycling system is presented in Figure 3.)
At J&L Finishing in Providence, jewelry parts are mass-finished prior to in-house and outside plating. The parts are mixed with ceramic or plastic media in vibrating basins. During the process, soap and water are used to clean and lubricate parts-in-process. The dirty, gray wastewater was originally sent to the company's waste treatment system where chemicals were used to treat the water before discharge to the sewer.
Based on recommendations made by the Rhode Island Pollution Prevention Program, the company implemented pollution prevention measures that included the reduction of the number of different soaps to one type of soap, and the replacement of the chemical treatment system with a 500 gallon-per-day ultrafiltration system cleans the water by removing the impurities while allowing the slap to be recycle.
J&L Finishing has minimized liabilities by not discharging water from their operation for more than two years. Tangible savings include the elimination of treatment chemical costs, the reduction of soap purchase costs (because of soap recycling), and the lowering of hazardous sludge disposal costs by 50 percent. The system paid for itself in less than two years.
Ion-Exchange
Dissolved metals dragged out into rinses can be recovered through adsorption onto ion exchange resins. Resins produce high purity water for recycling back into the rinse tanks. Two different columns, one containing cation resin, the other containing anion resin, can be installed for any plating line. Cation resins remove metals while anion resins remove salt counterpart such as chloride or sulfate ions. An activated carbon bed is usually installed upstream in the process to pre-filter organic materials that an potentially damage resins.
When resin columns are saturated, they can either be sent off-site for refining, or they can be regenerated on-site by using acid (cation resins) or caustic (anion resins) to flush out the captured material. With careful monitoring, it is possible to regenerate usable metal solutions from cation columns with the same composition and purity as plating bath make-up. (This materials recycling process can be seen in Figure 4). Anion resins are typically regenerated and sent to the company's pretreatment system. Spent carbon material is usually shipped off-site as non-hazardous waste.
Figure 4: Ion Exchange for Rinsewater and Plating Fluid Recovery
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Whether a small job shop or a large production facility, businesses that use electroplating and mass-finishing processes generate hazardous waste.
The well-known Environmental Protection Agency regulations under the Resource Conservation and Recovery Act govern the treatment and disposal of hazardous materials, making the practice of generating these materials very costly to manage. These costs are rising and will continue to rise in the coming years.
Electroplating in particular relies on heavy metals, acids, and alkaline compounds. Bath fluids, cleaners, and rinse water are usually mixed, and all end up in the wastewater . In addition, chemical coagulants, flocculents, and pH-adjustment chemicals are used in the end-of-pipe treatment process.
EPA defines any sludge resulting from chemical treatment (pretreatment) in a plating facility as a hazardous waste, and regulates its handling and disposal accordingly. Local sewage treatment facilities also regulate the concentration of contaminants such as dissolved metals, suspended solids, pH, and oils. Typically, they will require companies to pretreat before sewer discharge.
This is while "pollution prevention" becomes important. While the term "pollution prevention" may sound very general, it actually has a very specific definition. Pollution prevention is defined by EPA as "any practice which reduces the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise release into the environment (water, air, solid waste) prior to recycling, treatment, or disposal."
This article deals with "source reduction" which the fast becoming the preferred method in the pollution prevention hierarchy.
Process modifications to eliminate or reduce pollutants at the source (e.g., solvent elimination, better housekeeping, and in-process recycling of spent materials).
Off-site processing of waste materials for reuse (e.g. sludge reclamation for metal recovery).
End-of-pipe treatment of waste prior to disposal (e.g., chemical treatment system that several waste streams prior to sewer discharge with hazardous sludge generation).
Tri-Jay Plating of Johnson, RI, recently installed an ion-exchange system to reclaim nickel plating solution and rinse water from their operation. Prior to this, the final rinse was sent to the end-of-pipe waste treatment system, where the nickel metal became part of the hazardous waste sludge that was treated off-site. The firm now pumps its nickel rinses through resin beds as a final polishing step (as shown in Figure 5).
Figure 5: Implementation of Reverse Osmosis for Closed-loop Plating
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Having properly engineered the size of the columns and the regeneration frequency, Tri-Jay Plating is now able to return the regeneration, which is rich in nickel salts, back to the plating tank. The system has been successfully operating for almost a year. Capital costs for the nickel ion-exchange system were under $10,000, and a quick pay-back is expected.
Reverse Osmosis
Through a process called reverse osmosis, membranes can be used to remove metal ions from plating rinse waters while recovering useful plating solutions. Reverse osmosis is similar to micro and ultrafiltration in that impurities are removed by a physical barrier. The pores are much smaller to remove contaminations at the molecular level, and therefore higher pressures are needed (up to 500 psi).
The implementation of pollution prevention techniques can incur a wide range or costs, ranging from minimal labor costs for simple process modifications to tens of thousands of dollars for sophisticated separation equipment.
Any investment to change the jewelry operation as a result of pollution prevention assessments is commonly evaluated using the concept of annual pay-back. For example, if it is determined that a company must spend $5,000 for process modifications or equipment purchases to reduce waste in its process, then the company would want to see a savings of $5,000 over the next year for a two-year pay-back.
Let's use mass-finishing as an example. The costs associated with equipment purchases or process modifications described in this article are commonly offset by savings achieved in the following areas:
A major factor that many companies are willing to add to their economic evaluation is the reduced environmental and health liabilities associated with the successful implementation of pollution prevention. While no exact cost figure can be equated to reduced liabilities, each company has its own "break-even" equivalent value relative to reduce liabilities.
Quaker Plating in Johnson, RI, is currently installing a reverse osmosis system on their "bright" and "dull" nickel plating lines. While other processes exist to deal with metal waste solutions, it is believed that reverse osmosis has the potential to be the most effective pollution prevention methodology for the recovery of nickel solution and rinse waters.
The advantage of using reverse osmosis over existing facilities are multi-fold. The amount of sludge waste can be significantly reduced, it not totally eliminated. And while some technologies like ion-exchange require hazardous chemicals like acids and caustics for regeneration. (Figure 5 demonstrates the use of the process.)
The concentrate (indicated in Figure 5 as the plating solution recycle stream) from the reverse osmosis process is essentially dragout solution that has been de-watered. It should be returned to the plating bath to make up evaporative losses. In the past, companies have been reluctant to return ion exchange regenerate to the plating bath for purity reasons. Reverse osmosis eliminates these concerns, and may allow Quaker Plating to completely reuse materials in two of their plating lines.
Diffusion Dialysis
Concentrated acid solutions are commonly used in the jewelry industry to etch parts before plating, and to strip plates from unfinished surfaces. These acid solutions become saturated with dissolved metals, rendering them unusable. Diffusion dialysis technology removes these metals and reclaims the acid solution.
Diffusion dialysis is currently being studied at Allied Metal Finishing in Providence. The company hopes to eliminate its costly batch discharge and treatment of the corrosive solution. Also, the metal removed from the acidic solution is potentially reclaimable.
Substituting for Brite Dip Solutions
Use of brite dip (concentrated acid) solutions can be reduced in some applications through process replacement with mass-finishing.
The correct combination of soaps and operating conditions is currently being studies at Liberty Plating in Central Falls, RI. Preliminary results have indicated that the success of this process depends on part configuration, operating times, finishing media, and soaps.
These examples show how jewelry manufacturers are using technology to effectively limit waste at the source. With the costs associated with generating these wastes guaranteed to rise in coming years, now is the time to explore cost-effective alternatives. Those firms which run most efficiently, by disposing the least while recovering the most from their processes, will continue to be profitable by reducing both costs and associated liabilities.
Eugene Park is assistant research professor in the University of Rhode Island's Chemical Engineering Department, Center for Pollution Prevention. The work presented in this article was performed under grants funds provided by the Rhode Island Department of Environmental Management's Pollution Prevention Program. The author would like to acknowledge the contribution of Richard Girasole, Jr., Environmental Engineer, RI DEM Pollution Prevention Section.
The author welcomes comments and questions, and can be contacted at (402) 277-3434, ext. 4415.
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Last Updated: October 17, 1995