Grantee Research Project Results
Final Report: Processes for Recovery and Recycling of Chromium From Spent Chromium Oxide Fluorination Catalysts
EPA Contract Number: 68D99038Title: Processes for Recovery and Recycling of Chromium From Spent Chromium Oxide Fluorination Catalysts
Investigators: Coons, Darrell E.
Small Business: Chemical and Metal Industries Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1999 through March 1, 2000
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1999) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)
Description:
The purpose of this Phase I project was to develop a process for recovery of chromium from spent chromium(III) oxide fluorination catalysts and similar waste or byproduct streams. The spent catalysts contain 40-64% chromium, primarily in the forms of chromium(III) oxide, Cr2O3, and chromium(III) fluoride, CrF3. They are hazardous solid wastes, for which no known processes for chromium recovery had previously existed. Little has been reported on the chemistry of chromium(III) fluoride. Work in our laboratories has shown that the spent catalysts are extremely inert to chemical attack by acidic, basic, and oxidizing solutions.We proposed three methods for chromium recovery from spent chromium fluorination catalysts. In the first method, mixtures of the spent catalyst and sodium peroxide are fused. The chromium compounds in the spent catalyst are oxidized to form sodium chromate, which is subsequently leached from the fusion product. The second method is a high-temperature chlorination process. Chlorination of chromium(III) oxide with carbon tetrachloride is a known method for the preparation of chromium(III) chloride. Chlorination of chromium(III) fluoride has not been previously reported. We proposed chlorination of the chromium compounds in the spent catalyst by high-temperature reactions with carbon tetrachloride or carbon and chlorine and by halogen exchange with calcium chloride. In the third method, mixtures of spent catalyst, sodium carbonate, and calcium oxide are roasted in air. The chromium compounds in the spent catalyst are oxidized to form sodium chromate, while fluoride is converted to calcium fluoride, which is nearly insoluble in water. The roasted solid is leached with water to give an aqueous sodium chromate solution and a leached solid containing the calcium fluoride.
Summary/Accomplishments (Outputs/Outcomes):
All three of the proposed processes were found to be technically feasible methods for recovery of chromium from the spent fluorination catalysts. The fusion process was investigated in a series of experiments using spent catalyst-to-sodium peroxide ratios ranging from 1:100 to 1:2. Whereas high chromium recoveries as aqueous sodium chromate are achieved at ratios of 1:100 to 1:10, lower recoveries and less-consistent results are obtained at ratios of 1:5 to 1:2. This process is extremely useful for solubilizing these rather inert materials for analysis. However, because of the high cost of sodium peroxide and the severe materials of construction requirements, this process appears to be the least attractive of the three options economically.High-temperature chlorinations of chromium(III) oxide, chromium(III) fluoride, and spent chromium fluorination catalyst to generate anhydrous chromium(III) chloride were successfully carried out in good yield. Four different chlorination methods were found to be effective. The chlorination reactions of chromium(III) fluoride using carbon tetrachloride, carbon and chlorine, calcium chloride, or magnesium chloride and chlorine are all new reactions, which were discovered in the course of this project. Each of these reactions can be used to recover the chromium in the spent catalyst as chromium(III) chloride. These processes are technically feasible and could potentially be developed into commercially viable processes. Because of the extremely promising results in the air roast process and the larger market for its products, we have opted not to pursue further development and commercialization of the chlorination process at this time.
The air roast process consists of roasting mixtures of the spent catalyst, sodium carbonate, and calcium oxide followed by leaching the roasted solid with water to give an aqueous sodium chromate solution. Although the oxidation of chromium(III) oxide by this method to generate sodium chromate is a known process, oxidation of chromium(III) fluoride to sodium chromate is new chemistry that has led to the development of a technically feasible process. An extensive series of experiments was carried out to define and optimize the important parameters in the air roast process. Excellent results were obtained over a substantial range of conditions and reactant ratios. Nearly quantitative chromium recovery is achieved using the air roast/water leach steps. The fluoride from the spent catalyst reacts to form calcium fluoride. This effectively sequesters the fluoride in a form that is nearly water-insoluble and remains unleached in the solid. Crystalline sodium chromate can be produced by concentration of the leach solution. Sodium dichromate and other chromium chemicals can be produced from the leach solution using standard processing steps.
Conclusions:
In this Phase I project, six technically feasible methods were developed for recovery of chromium from a currently-wasted, secondary resource. An air roast process has been selected for further development and commercialization. It is based on newly discovered chemistry from this project and has been demonstrated to be an extremely effective process for near-quantitative recovery of chromium from spent fluorination catalysts. Based on our preliminary economic analysis, it is also commercially viable. The major U.S. producers of fluorocarbons are highly interested in this process as a means of eliminating this material as a waste and recycling the contained chromium. Processing of the spent catalyst from these producers would eliminate an estimated 450,000-600,000 pounds per year of hazardous solid waste. It will also result in recovery of 700,000-930,000 pounds of sodium chromate or other chromium chemicals containing 220,000-300,000 pounds of chromium. The chromium products from this process would be marketable to users of chromium chemicals in a variety of industries, including catalyst production, metal plating, and pigments.Supplemental Keywords:
Chromium recovery, chromium recycling, chromium(III) oxide, sodium chromate, sodium dichromate, spent catalyst processing, waste elimination., Scientific Discipline, Toxics, Waste, Sustainable Industry/Business, National Recommended Water Quality, cleaner production/pollution prevention, Chemistry, Technology for Sustainable Environment, Engineering, 33/50, Hazardous, waste minimization, chromium & chromium compounds, Chromium, recovery, catalysts, hazardous waste, metal recovery , metal recoveryThe 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.