Grantee Research Project Results
Final Report: Excess Etchant Reduction and Copper Recovery Process for Cupric Chloride Recovery
EPA Contract Number: 68D98143Title: Excess Etchant Reduction and Copper Recovery Process for Cupric Chloride Recovery
Investigators: Oxley, James E.
Small Business: Oxley Research Inc.
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)
Summary/Accomplishments (Outputs/Outcomes):
The overall reaction during etching of copper by acid cupric chloride (CuCl2/HCl) is:Cu + CuCl2 ==> 2 CuCl (1)
Most users of acid cupric chloride currently employ continuous chemical regeneration, using oxidizers such as Cl2 or H2O2 to reverse the above reaction and thus maintain solution etching power. This results inevitably in generation of excess etchant, which must be disposed of. Growth of unwanted etchant can be quite rapid. Thus, an industry standard spray etch machine, etching copper at a rate of 6 kg/hr will typically generate 3-4 gallons of surplus etchant per day, per gallon of initial etchant sump inventory.
Acid cupric chloride etchant is being increasingly employed by, (a) printed circuit (PC) board manufacturers, (b) leadframe etchers that utilize copper alloy 7025 containing 4% nickel, and (c) a variety of specialty copper and copper alloy etchers covering a broad range of electronic and other specialty applications. In PC board production, which represents the major use of acid cupric chloride, manufacturers etch over 25 million pounds of board-mounted copper foil per year in the U.S., producing 15-20 million gallons of surplus etchant that has to be transported over-the-road to treaters for disposal and/or reclamation of the copper values. The rate of copper foil use, and thus production of waste excess etchant, has been growing in the U.S at 12-15%/year in recent years.
This SBIR program is aimed at developing a new electrolytic recovery process for use with acid cupric chloride. Successful development of this new process would mean that users could, (a) cut excess etchant shipments by more than 50%, (b) capture 91% of the value of the etched away copper, that they are now in many cases paying haulers and treaters to take away, (c) reduce HCl requirements for conventional chemical regeneration by 57%. Additionally, the environmental impact of excess etchant would be reduced beyond the value of the lowered excess etch shipment rate due to the out-of-proportion reduction in the copper and HCl load. Leadframe fabricators would have an additional revenue producing stream, i.e. the high Ni, low Cu, excess etchant from that process.
The new process which the present SBIR program addresses, is partly modeled on an on-line electrolytic regeneration and copper recovery process developed earlier at Oxley Research which maintains an etchant bath whose volume and CuCl/CuCl2 concentrations stay constant. The new process is instead aimed specifically at copper etchers who wish to continue chemically regenerating their CuCl2/HCl etchant, chiefly because they don't want to have a build-up of some undesirable species in their etchant bath. By using chemical regeneration and shipping away the resultant excess etchant, leadframe producers keep nickel at very low levels, while PC board producers get rid of undesirable organic contaminants such as etch resists. However, this is a "sledgehammer" approach, and significantly lower purge rates could also remove all their "undesirables". By electrolytically capturing much of the etched copper and HCl used, and reducing the generation of excess etchant, the new process gives many of the benefits of continuous, on-line electrolytic regeneration to those copper etchers who still prefer to operate with chemical regeneration. In our earlier process, the necessary reduction of Cu2+ to Cu+ and Cu+ to copper metal are carried out at the cathodes of separate electrochemical cells, referred to as the "knockdown" and "plating" cells, respectively, while the oxidation of Cu+ to Cu2+ is common to the anodic side of each cell. The new process employs the same 2 cell approach with the same cathodic reactions but requires an alternate anodic reaction since there is no longer a supply of cuprous ions from etching.
The anodic reaction that the process requires is enabled by using a novel, proton permeable membrane to separate anode and cathode compartments. In these cells the anodic reaction is O2 evolution, from e.g. H2SO4 at, for example, an inert Pt-clad niobium electrode, according to the reaction,
H2O ==> 1/2 O2 + 2 H+ + 2e (2)
Key to successful operation of such a cell is a family of "electropermeable" membranes (EPMs) developed by T & G Corporation in Lebanon, Connecticut. These materials display the highly desirable property of being selectively permeable to the protons produced by reaction 2. Most importantly water does not pass through these membranes, thereby avoiding any dilution effects associated with use of the membrane to separate electrolytes of differing composition.
EPM membranes consist basically of long chain hydrogel molecules dispersed and bound within a chemically resistant plastic matrix. They are both non-porous and non-diffusive due to the fact that the hydrogel, in "plugging" the pores of the supporting structure, are thus prevented from forming water-logged gels, as hydrogels normally do in aqueous media. EPMs have many similarities to biological membranes: The fact that they are both non-porous and non-diffusive differentiates them from other, commercial non-porous polymeric membranes such as the cellulosics which transport material through their "free" volume. They thus function more like semiconductor material, relying upon thermally facilitated ion transport along hydrogel backbones. Permeation is not dependent upon hydraulic pressure or concentration differences as with diffusive membranes.
The main activity of the Phase I program was demonstration of a membrane with optimum electrochemical performance in small bench-scale flow cells, operating with minimal ohmic losses, low sulfate migration from anolyte to etchant, and of zero water crossover. The duration of each test was typically 1 week. A total of 12 membranes were tested in the program, 9 of these were EPMs of various proprietary formulations provided by T&G, and 3 were from two other suppliers (2 from Pall Corp and 1 from Aqualytics Inc) of proton selective membranes. All of the EPM membranes were found to be resistant to water transport. However, not unexpectedly, the Pall and Aqualytics membranes, although exhibiting several other desirable properties, detailed in the body of the report, allowed water transport and were therefore eliminated from further consideration. Among the EPM membranes, one family in particular, designated 14118 by T&G, was found to be preferable to the others in terms of the above criteria; of these, 14118C appeared to have the best combination of properties for the application and was chosen for the "system" test (see below).
The effect of dissolved Ni on copper etching rates was measured in a small bench-top stirred tank reactor. Etchant ORP was held approximately constant at 495-505 mV by periodic addition of H2O2 which oxidized the cuprous ions formed by the etching of a copper rod during its timed immersion at about 50oC. In these tests nickel was added up to a level of 14 g/l; that is the maximum level our material balance shows would be produced by etching 7025 leadframe and employing the new process. No decrease in etching rate was indicated by these tests, actually if anything the rate increased somewhat.
Finally, overall feasibility of the concept was demonstrated by operating a small bench-top, 2-cell (plating and knockdown cell) recovery system. Here the purpose was to simulate operation of a fully integrated recovery system employing our preferred EPM 14118C as separator in both knockdown and plating cells. At the end of this test, the plating cell was opened up and the plated copper "harvested" as a single peelable sheet. In preparation for the plating operation, it was necessary to run the system for several days in order to prepare a cuprous-rich solution (from the starting, predominantly cupric solution) needed as feed for the cathodes of both cells. During this "knockdown period" it was noted that the cells' voltage, although it did fluctuate somewhat, remained below 3 volts.
Supplemental Keywords:
Scientific Discipline, Toxics, Waste, Sustainable Industry/Business, National Recommended Water Quality, Chemical Engineering, cleaner production/pollution prevention, Chemistry, Technology for Sustainable Environment, New/Innovative technologies, Hazardous, chemical use efficiency, cleaner production, printed circuit boards, electrochemical techniques, industrial process, production processes, electrochemical, innovative technology, integrated energy, environment, and manufacturing method, copper, pollution prevention, source reduction, innovative technologies, cadmiumThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.