CLOSED-LOOP RINSE RECOVERY, USING ADVANCED REVERSE OSMOSIS, FOLLOWING COPPER CYANIDE PLATING

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1 CLOSED-LOOP RINSE RECOVERY, USING ADVANCED REVERSE OSMOSIS, FOLLOWING COPPER CYANIDE PLATING Thomas von Kuster, President. and Joel Malmberg, Vice President Water Technologies, Inc Washington Ave So Edina, MN Electroplaters and metal finishers are finding it difficult and costly to pretreat and dispose of contaminated rinse water. Cyanide rinses, and particularly copper cyanide rinses, are more difficult than most to treat effectively and economically. Technological advances in membranes, control technology and system design has lead to a unique method of rinse water recovery that conserveswater by cleaning and recycling rinses reduces hazardous waste generation eliminates prioritypollutantwaste discharge allows recycling of recovered cyanide plating solution case studv of comer cvanide rinse recoverv at a major lock kanufackker ;ill be discussed.?he ARO system cleans and controls the rinse to a plating specification. Further ARO offers concentrating capabilities not achievable with alternative methods which allows recycling of the copper cyanide bath dragout.

2 Summarv and Conclusions After an experimental evaluation to determine the feasibility of using an Advanced Reverse Osmosis (ARO) system, a major lock manufacturer installed two ARO systems to achieve closed-loop recovery of their copper cyanide plating rinses. The results of the evaluation and six months of data from the installed systems indicate that over 99% of the rinse water could be recovered and re-used when the systems have been operating. The recovered concentrate was concentrated to over 40% of bath strength on one plating line and to nearly 90% on a second line and plumbed directly to the bath for reuse. Currently the copper cyanide ARO systems are avoiding the treatment of about 2,000 gallons of rinse water per shift and recovered 20 to over 200 gallons per day of concentrate for reuse in the bath. Economic returns for the ARO units have not yet been calculated by the lock manufacturer because they are part of a larger recycling system (including electrowinning, evaporation and related solution storage); but the overall internal rate of return from the system is estimated to be 14%. The installations were not entirely trouble free and this paper also describes simple steps needed to insure the successful installation of any of the new recycling technologies which are becoming available. The steps include: 0 Controlfing process water quality and quantity 0 Establishing good housekeeping procedures 0 Designing the installation as a system, integrating process and waste treatment components together 0 Verifying design assumptions with real life 0 Meeting design requirements before turning on the equipment Introduction Copper cyanide plating is one of the most widely used plating solutions. Copper cyanide rinses are one of the most difficult and expensive to conventionally treat and discharge, because both cyanides and copper must be removed. Due to compliance costs and difficulty, many platers are moving away from all cyanide plating. Often however, the alternatives are more costly to operate and may result in plating difficulties in some applications. Rinse water treatment alternatives to conventional cyanide destruction and copper precipitation will certainly become essential for those platers wishing to continue to use cyanide based baths. An ideal alternative is total on-site recovery of rinse water and direct reuse of as much of the 224

3 recovered bath drag-out as possible. Other options include newer technologies combined with low sludge producing treatment. Advanced reverse osmosis (ARO) using specialized operating modes and membranes is an example of the ideal approach. From March through November, 1991, Master Lock Corporation and Water Technologies tested and subsequently installed ARO systems for recovery of copper cyanide rinses and plating bath for reuse. One system was installed in May, 1991 and a second in November, Master Lock CorDoration Master Lock is a major manufacturer of padlocks for commercial and consumer use. It currently performs copper, nickel, chrome and cadmium plating of component parts for its locks. It operates two large automated barrel plating lines for parts cleaning, copper plating and nickel plating of component parts. About one million parts per day are plated by these automated lines. Master Lock meets exacting quality requirements for its products. The most important requirements of Master Lock's rinse water treatment system in maintenance of rinse water quality as well as discharge compliance. Tightening of discharge requirements by the regional publicly owned treatment facility encouraged Master Lock to perform as much on-site recovery and recycling as possible. Further, proper rinsing performance is most critical to quality of the following nickel plating process. Insufficient rinsing can also affect the quality of the copper plate itself. Advance Reverse Osmosis WTI has adapted reverse osmosis (RO) for use in plating and corrosive applications. RO is a physical process'whereby contaminated water can be cleaned by applying pressure to the solution and squeezing clean water through a membrane barrier which selectively allows water to pass through the barrier. Larger molecules remain behind, becoming a concentrate. L., Reverse Osmosis Principles Mort

4 However, the ARO system design is very different from traditicnal reverse osmosis systems. System concentrations of 2,000 to 10,000 to 1 are achieved with single membranes. The ARO system can reconcentrate dilute solutions to at or near barn strength (typically a concentration of 40% to 70% of original bath strength is accomplished) without any evaporation or additional concentration technology. This concentration is often sufficient for direct return of the solution to the bath. Membrane materials and system components have been specially adapted to plating environments. Corrosion and heat resistant plastics and 316SS (or Hastalloy C) components give the System a long lifetime with almost all plating rinses and baths. Custom designed sensors and controls are required to manage the membranes. The degree of concentration, times of exposure, and pressures vary for every solution and membrane type. The variations are controlled by specialized software. Thus, in ARO, WTI uses the RO principle to both clean plating rinses and reconcentrate plating solution to at or near bath strength. The permeate (or cleaned water) is returned to plating rinses while the concentrate is held in the ARO system's internal storage tanks for further concentration passes through the membrane until the required concentrations are achieved. The schematic below (on the left) displays the nature of the ARO recovery and recycle System. The diagram (on the right) shows a schematic of the pumps, sensors, membrane and internal storage tanks inside the ARO system. Concentrate moves from the receiving tank to tank 3 and is recovered for reuse in the bath or for batch treatment with the existing or new systems. ARO System Conceptual Schematic Diagram of ARO Unit n t 226

5 In the ARO systems, internal microprocessors change operating parameters for each pass of feed or concentrate through the membrane. Pressures and process times are tightly controlled in order to achieve long membrane lifetimes and very high concentrations of dilute metal salts. In all applications, the plater can concentrate on plating production because the ARO system is self-controlled. There is a Service Switch with tlautott and tlservicetl positions. In "Autovt position, the ARO system microprocessor automatically monitors all remote rinse and internal sensors and initiates ARO processing whenever the final rinse exceeds the operator's preset rinse quality standard or whenever the volume of concentrate retained internally is sufficient for further concentration. In the tuservicett position, the ARO system flushes itself and depressurizes to allow the operator to service his/her rinse system or the ARO system. One of the most significant features of the ARO unit is its ability to be remotely monitored and controlled through a modem. This feature allows for rapid diagnosis and service response. The feature was used regularly during the project to gather operating data and monitor the ARO System. The picture below shows the interior of the ARO system and indicates its key components. The ARO system is in the foreground; other tanks, barrels and equipment are used to simulate customer applications prior to ARO installation. All operating components are located on the top of the system for easy repair or replacement. Membrane changes can be accomplished in 15 to 20 minutes. Interior of ARO System Showing Pressure Vessel (across front), Pressure Pump (at back), Recycle Pump, Valves and Plumbing.

6 Experimental Simulation of Copper Cyanide Rinse Recovery As the first step to a system design a study was undertaken to determine if the ARO system is capable of achieving closed loop operation on Master Lock's Copper cyanide rinse and bath with or without additional equipment. The first goal was to recover as much rinse water as possible in a permeate stream containing <5 ppm copper. The second goal was to increase the copper and cyanide levels in the concentrate stream to over 50% of those in the plating bath. Testing was performed using the system shown in below. This system contains a 4" membrane/pressure vessel and all the other components of an ARO system -- pressure pump, recycle pump, computer controller, motor speed controller, \ prefilters, conductivity sensors and pressure sensors. msfli)c VESSEL i J Testing was performed using a simulated rinse solution made by diluting a sample of Master Lock's plating bath. A sample provided by Master Lock fourteen months prior to installation contained an operating range of 2 to 3.5 ounces per gallon copper, 1 to 2 ounces per gallon sodium cyanide, and 0.5 to 1.25 ounces per gallon potassium hydroxide and had a conductivity of 89,000 ps. The solution strength used in testing was determined by measuring the copper concentration in Master Lock's rinse water during a typical daily period and simulating the best and worst cases. The analyses performed indicated that the copper concentration varied from approximately 5 to 200 ppm. Hence, simulated rinses containing approximately 5 and 200 ppm copper were prepared. Test Procedures -- Rinse Solution. Several runs were performed to determine the best operating pressures and cross flow rates to achieve the best steady state results. The goals were: 228 e

7 0 to develop the cleanest permeate from a single pass (Pass 1) through the ARO system. 0 to evaluate how the ARO system could achieve the highest/best level of concentration on subsequent passes (Passes 2 through 4). 0 to determine the highest possible level of concentration beyond which the ARO system could not concentrate the solution because of the limits of the membrane 0 to evaluate components of the system and operating strategies to insure that corrosion, precipitation or plate out of the solution would not occur within either the test system or the on site pilot plant unit Testing was performed at room temperature (68 to 87 degrees F). Individual passes (after the initial rinse tests) were simulated by mixing simulated operating batches of 10 ounces of bath per 50 gallons, 100 ounces and 1000 ounces per 50 gallons. Recovery of permeate for each batch processed was set at approximately 83% so that pressures and separation ratios could be uniformly evaluated. Recirculation rates in each pass exceeded 30 gpm. The conditions were chosen so that the software operating parameters could be chosen for the final system as well as verify the feasibility of the separation. Analytical Procedures. Permeate and concentrate streams were analyzed for copper, cyanide, hydroxide, ph and conductivity. The method used for copper was colorimetric using a Hach DR/3000. The method used for cyanide was titration with silver, and that for hydroxide, titration with hydrochloric acid. Conductivity was measured using an Orion 160 and ph using an Orion 720A. Simulation Test Results and Discussion. The concentrations measured in the two simulated rinses (Pass 1) described above were as follows: Feed umho Concentrate Permeate Copper PPm umho. UmhO in permeate 443 1, ,200 13, These tests indicated that the ARO system would be able to recover the rinse to a level required by the process (under 5 ppm copper). Simulated passes (Passes 2 through 4) also indicated that the ARO system could concentrate the recovered bath to over 60% of bath strength, 63,700 to 74,800 out of 89,000 umhos in the bath with contents as shown in the table below.

8 Sample Sample Copper Cyanide Hydroxide PH UmhO (oz/gal) (oz/gal) (oz/gal) Bath na 89, ARO Concentrate , The data indicated the ARO system could probably achieve bath strength using all four passes. However, the copper cyanide bath operates at a temperature of 140 degrees F and can accept the recovered solution given current daily water additions. So the ARO system did not need to achieve full bath strength. Nevertheless, WTI recommended that an evaporator be added to the system to assist evaporative losses during humid days. Furthermore, based upon experience with other plating solutions and rinse recovery applications, WTI recommended not exceeding 50% of bath strength because of the potentially high level of TDS/carbonates which can occur during summer months and the room temperature operation of the ARO system which might cause some precipitation to occur at higher operating passes/concentrations. In addition, WTI identified two other factors related to membrane performance/lifetime -- separation performance change and fouling (plugging) potential. There was no loss of separation performance on the membrane comparing standard test results before and after the tests. However, given past experience with caustic solution rinse recovery WTI expected ARO membrane life to be 3 to 4 months depending on dragout recovered and any cleanings required. WTI determined that occasional plugging of the membrane could occur if all hardness was not eliminated from incoming water or from aluminum in the zinc alloy being plated which could form a gelatinous precipitate on the membrane surface. Both could be cleaned with an dilute acid wash of the membrane. If these conditions were used for operating the ARO system, the copper levels in the permeate and concentrate as a function of recovery given above indicate that approximately 99% of the water can be reused while maintaining the average nickel concentration below a specified level of c40 ppm. Test Equipment Inspection. After completing the tests, WTI personnel disassembled critical components and segments of the ARO test bench system to check for any damage from the bath components. High temperatures and excessive concentration of bath components and breakdown products can cause corrosion, plate-out or precipitation of bath constituents and/or contaminants. The components and segments chosen were those which would most likely create plate-out or precipitation conditions. All the process storage tanks used were also inspected. 230 n

9 No corrosion, plate-out or precipitated constituents were found. These findings mean that the design and operating precautions taken to prevent precipitate were effective: 0 Keeping the concentrate less than 80% strength. 0 Maintaining temperatures less than 115 degrees F and preventing pressure build ups of more than 1050 psi by pre-cooling incoming rinses and shutting the pressure pump off when excess pressures would occur Results and Experience from Five Months of Operation Master Lock's Automated Barrel Line. The diagrams below show the automated barrel plating lines on which the ARO systems are installed at Master Lock in Milwaukee, Wisconsin. The lines contain cleaning, plating, and rinsing tanks. Cleaning and plating tanks have intervening rinses before the next process. The copper cyanide bath tanks each contain approximately 450 gallons of plating solution. The ARO system recovers and recycles the counterflow rinse system following the copper plating baths. (Separate ARO systems are installed on the nickel plating processes on the two lines.) Three or four stage counterflow rinses follow each bath and flowed at 2 gpm before the ARO systems were - installed. Diagrams were not complete and approved at the time of this submission. j A diagram of the ARO Installation at Master Lock. installation at Master Lock appears below. The diagram shows the configuration of the installation. Diagrams were not complete and approved at the time of this submission.

10 The connections required for system utilities, plumbing, electrical, and communications are simple. The installation required more modification of existing equipment than usual because of the integration of other recovery equipment for on-site treatment of the baths as well as the rinse -- evaporators and electrowinning systems. Master Lock had three main concerns in using WTI's equipment at its facility: 0 Quality of plating and rinsing 0 Reliability of the ARO system 0 Economics of the ARO system Plating Quality. With regards to quality of plating, Master Lock has noticed no loss of plating quality using the recovered concentrate for over 5 months at this time. There has been a build of carbonates in one of the baths, which occurs naturally in the ordinary operation of the bath. The recovery equipment accelerates this somewhat (by.9 to 1.6 gallons per hour recovered on Line #1) and Master Lock plans to chill this bath and decant the bath to remove the precipitated carbonates this winter. Chilling has been effective for carbonate removal from other ARO cyanide applications. Recovered Concentrate Quality and Quantity. The volume of solution recovered to date by the first system installed has been over 7,100 gallons. On a daily basis this has been between 13 gallons and 60 gallons per day or.9 to 1.6 gallons per hour of production. The amount recovered is as forecasted by drag-out studies. The content of the recovered concentrate versus the bath for both systems is shown below: Solution umho ph Copper Cyanide Hydroxide oz/gal oz/gal oz/gal Line #l 126, Concentrate 93, Percent of Bath 44% 37% 63% Line #2 148, Concentrate na na 3.4 na na Percent of Bath 89.5% Line #2 has recovered over 1,000 gallons of concentrate since its November installation at a rate of 16.2 to gallons per day. The rate of recovery has been up to 6 times that forecasted prior to installation. Rinse Standard and Quality. The ARO system is set to maintain the rinse at 1,500 umhos, which is approximately 2 232

11 to 25 ppm copper. The table below summarizes the quality of the recovered permeate from samples from both lines: Solution/ umho ph Copper Cyanide Hydroxide Line PPm PPm PPm Line #I na na Line # <lo 48 2, <lo 478 1, < ARO Economic Benefit. One ARO system avoids the cost of treating approximately 1,000 gallons per shift versus former practice of cyanide destruct and subsequent sludging. The avoided costs include water purchases and pretreatment costs, sewage discharges and surcharges for excess TDS, chemical treatment and sludge disposal expenses. Master Lock has not completed their economic analysis of individual components of their on-site recovery system at this point. Overall, they had forecasted an 18% internal rate of return and they are achieving a 14% return at the last review because of some cost overruns not related to the ARO systems. Creatincr Reliable Trouble Free Installations of Recovery Systems Common sense steps taken to install production equipment are frequently forgotten when installing recovery equipment. While the installation of most ARO equipment has gone relatively smoothly, the process could have been easier for the vendor, the engineering firm and Master Lock. Rather than highlight specific problems of this installation, we have listed the ingredients of successful installations of recovery technologies. There are five basic ingredients as noted earlier: 0 Designing the installation as a system, integrating process and waste treatment components together 0 Controlling process water quality and quantity 0 Establishing good housekeeping procedures 0 Verifying design assumptions with real life 0 Meeting design requirements before turning on the equipment System/Design Integration. Recovery technologies require that production and waste treatment personnel work together to solve waste, water and reuse issues. When technologies are installed without integrating inputs and outputs, sizing and operating problems cause failures or poor performance of the best equipment.

12 Water Quality and Quantity. Recovery systems need high quality water available upon demand. The water needs to be 2 to 10 umho in quality and can be provided by ion exchange or reverse osmosis. Poor water quality will cause ARO membranes to plug with hardness and require excessive cleaning. Not enough good water for make-up will starve ARO and other recycling systems and result in loss of rinse and product quality. Good Housekeeping. Rinse tanks should be thoroughly cleaned before any recovery technology is started because contaminants may damage the recovery system and/or the chemicals recovered. Bath filtration and carbon treatment to remove unwanted contaminants is inexpensive versus loss of parts, damage to resins, and premature failure of membranes. Some oils can cause permanent membrane damage. Establishing Real Life Operating Parameters. Many times how a bath or automated equipment is operated bears no resemblance to the original installation design or performance specification. There is no substitute for current laboratory analysis or process evaluation re dragout or system loading. Meeting design objectives for membrane separation, flow of clean/recovered rinse and concentration performance depends on knowing and designing for the content of the bath and volume of parts pushed through the plating line. Meeting Design Requirements. Frequently in the rush to get back into production, operators start up systems before installations are complete. Operators should not fool themselves or their vendors. System damage can set firms back even further. For this reason firms should always maintain backup systems to treat waste if schedules fall behind. Proper planning can avoid these problems which include loss of membranes when no cooling water is connected or no bath filter has arrived on site. 234