Grantee Research Project Results
Final Report: In-Process Recycling of Spent Hexavalent Chromium Plating Bath
EPA Contract Number: 68D98140Title: In-Process Recycling of Spent Hexavalent Chromium Plating Bath
Investigators: Renz, Robert P.
Small Business: Faraday Technology, Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $69,428
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)
Description:
Purpose
The overall objective of the program was to develop and commercialize a novel in-process recycling process to decontaminate a spent hexavalent chromium plating bath for in-process recycling and eliminate the hazardous waste associated with chromium plating operations. Since hexavalent chromium plating will continue to be used due to unique performance characteristics, and the toxic mist associated with hard chrome plating processes can be contained, the only remaining issue is to develop a technology to cost-effectively decontaminate a spent hexavalent chromium plating bath. The novel in-process recycling process will integrate electrodialysis and ion-exchange into one system to simultaneously remove all the contaminants from the spent chromium plating bath. The process makes in-process recycling of a spent chromium plating bath possible and will save millions of dollars in both materials costs through recycling, and the costs of sludge disposal in a hazardous waste landfill.
Research Work Carried Out
The Phase I work successfully demonstrated the technical and economical feasibility of decontaminating spent chromium bath for in-process recycle of the bath. Specifically, we demonstrated that 1) Metal cations are efficiently transported through the membrane and removed by the cation exchange resin, 2) metal cation impurities, such as Cu2+, Fe2+, and Ni2+ can be removed from the spent chromium bath without decreasing CrO42- concentration; and therefore, the purified bath can be recycled to the plating operation; 3) the optimal modulated current can provide a higher metal impurity removal rate than DC; and 4) the process is cost effective. The in-process recycling system is schematically shown in Figure 1.
Figure 1: Schematic of the In-Process Recycling System Cell.
Regeneration of the IIX cathode is accomplished by reversing the polarity with the dummy loop of H2SO4 still being pumped through the cathode. By reversing the polarity of the cell, the IIX electrode containing cation exchange resin becomes an anode during regeneration. The oxygen evolution reaction at the anode will generate high concentration of H+. The local high H+ concentration on the electrode will regenerate the cation exchange resins and release the metal cations from the cation exchange resin. This acid solution mixes with the ionic metal constituents creating a highly concentrated solution appropriate for traditional flat plate electrowinning. The metallic foil is collected and sent for off-site recycling.
Figure 2: Regeneration of the Cell.
The key technical challenges associated with our system were 1) efficient transport of metal cations across the membrane instead of protons, and 2) efficient collection of the diluted metal cations at the IIX cathode. To achieve high transport rate (high mass transfer rate), modulated electric field (MEF) was used.
Results
Nine experiments were run including a DC baseline test. The following operating parameters were used for the treatment phase: flow rate - 0.8 and 2.4 L/min; frequency - 10 and 100 Hz; average current - 4 and 25 A; duty cycle - 20 and 80%. During the treatment phase, 16 L of 0.1% H2SO4 was recirculated between the catholyte holding tank and the cathode compartment of the cell. The spent chromium bath (16 L) was recirculated between the anolyte holding tank and the anode compartment of the cell. Each experiment was run for four hours with samples taken from the catholyte loop at 20, 40, 60, 120, and 240 minutes. A 30-minute regeneration cycle was run soon after the 4-hour treatment run was complete using the same modulated current parameters as used for the treatment phase but with the current direction reversed. Specifically, during regeneration the IIX electrode containing cation exchange resins became the anode and the anode in treatment mode became the cathode. Sulfuric acid (16 L, 0.1%) was recirculated between the anode compartment and the anolyte tank. Chromic acid (16 L) was recirculated between the cathode compartment of the cell and the catholyte holding tank. Samples were taken from the catholyte tank (cathode compartment in regeneration mode) at 10, 20, and 30 minutes. These samples were sent to Bowser-Morner Inc. for analysis of Cu, Fe, and Ni. Additionally, the final sample was also analyzed for Cr concentration. In summary, experiments were conducted with a 4-hr treatment followed by a 30-minute regeneration.
Potential Commercialization
Commercialization will occur in conjunction with a shop floor validation at a job shop plating facility. One such shop participated in the Phase I effort by supplying contaminated hexavalent chromium plating chemistry for our experiments. Commercialization of an emerging technology requires the developer to focus, not on increasing sales volume from, say 50 to 100 units (the market share mentality), but to generate sufficient data and experience from actual Beta testing to affect an initial sale. The vendor community, who will ultimately distribute our in-process recycling system, is risk averse. In other words, they are not necessarily interested in risking the addition of another product line (e.g. our in-process recycling system) until it has been fully validated (Beta tested) and installed on several full production plating lines. For this purpose, Faraday Technology, Inc. and our Phase I partner have executed a mutual non-disclosure agreement and are planning to work closely in the Phase II program.
Beta Testing and Technical Marketing - As referenced above, it is anticipated that during a Phase II program we will complete a field demonstration in conjunction with a job shop plater, or another company of interest to our USEPA program officer. Additionally, we have most recently presented and published the results of our Phase I effort at the AESF Week 99 conference and exhibition. This presentation has resulted in an interest from more than 30 plating shops, vendors, and regulators. Finally, Faraday Technology, Inc. has agreed to collaborate a rectifier manufacturer via a joint tradeshow booth display registered for the upcoming IPC 99 (electronics industry) tradeshow to be held in Long Beach, Ca. during March, 1999. This collaboration is a key component of utilization of our technology, because, although the rectifier manufacturer fully understands the electronic and circuitry requirements for implementing modulated and modulated reverse electric fields, they need an electrochemical engineering expertise (Faraday Technology, Inc.) to assist their customers in optimizing the appropriate waveform for the required output.
Supplemental Keywords:
Economic, Social, & Behavioral Science Research Program, Scientific Discipline, Air, Waste, Water, Sustainable Industry/Business, hexavalent chromium, cleaner production/pollution prevention, Chemistry, Technology for Sustainable Environment, Engineering, Hazardous, Engineering, Chemistry, & Physics, Market mechanisms, in-process recycling, recovery, in process recycling, electroplating, electrodialysis, electrochemical techniques, electrochemical, reuse, chromium plating sludge, cost effective, pollution prevention, contaminant removalThe 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.