Grantee Research Project Results
Final Report: The Recovery of Pure Chromium Metal From Hazardous Plating Sludge
EPA Contract Number: 68D99039Title: The Recovery of Pure Chromium Metal From Hazardous Plating Sludge
Investigators: Whelan, Edward P.
Small Business: Climax Research Services
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 chromium values in low-purity chromium plating sludge have been extracted and converted into pure chromic oxide and then into pure chromium metal by means of a combination of conventional hydrometallurgical mineral processing operations and a pyrometallurgical aluminothermic reaction. The metallic and non-metallic impurities in the sludge have been reduced to low levels during processing. The pure chromic oxide that results from this processing is well suited to conversion by the aluminothermic process to pure chromium metal that meets ASTM Specification A 481-97.Summary/Accomplishments (Outputs/Outcomes):
The process developed involves a reaction in the solid state between damp plating sludge and sodium carbonate at 500C. Leaching of the products of this reaction in water removes sodium chromate from the reacted material. Extraction of chromium from the sludge with efficiencies in excess of 97% is possible using the processes developed here. Many of the characteristic metallic and non-metallic impurities that are present in the as-received sludge do not transfer over with the reaction products into the leached sodium chromate. Elements such as phosphorus that are carried over to the chromate solution are removed subsequently by precipitation from the solution.By utilizing the metastable nature of the hydrous oxides in the sludge, reaction with sodium carbonate can be conducted at relatively low temperatures, in the vicinity of 500C, that are below the melting point of the carbonate. These reactions are solid state reactions, and are have not been used previously in the metals' recovery industry for the treatment of chromium plating sludge. This low temperature solid state behavior contrasts with the elevated temperatures of 900-1000C, above the melting point of 851C of the carbonate, that are necessary for the extraction of chromium from chromite ore.
Pure chromic oxide was precipitated from the purified sodium chromate solution using a variety of reductants, including ammonia gas, ammonium chloride, hydrazine, methanol and sodium sulfite. The dried filter cake that remained after leaching operations was blended with soda glass and vitrified. The vitrified material passed an EPA TCPL test for leachable chromium. Solid waste in the form of an alumina-based slag resulted from the aluminothermic reaction. This slag also exhibited chromium leaching behavior in a TCLP test within the limits established by the EPA for leachable chromium. The filtrate that resulted from filtering operations has been treated with a cation resin followed by activated alumina. The residue stripped from the ion exchange resin would be returned to the process in a pilot plant operation.
The chemical composition data presented in the report show that chromic oxide of excellent purity can be produced from chromium plating sludge, using the processing treatments described here.
These composition data clearly establish the feasibility of extracting the chromium values from chromium-containing plating wastes and converting them readily to a pure chromic oxide. This chromic oxide acts as the precursor to aluminothermic chromium metal.
The chemical composition data for chromium metal presented in the report show that high purity metallic chromium can be produced from the purified chromic oxide. The metallic impurities in the plating sludge can be reduced to the levels specified by ASTM for aluminothermic chromium when contamination of the chromium oxide charge during the aluminothermic reduction process is avoided.
Conclusions:
a) A process has been developed for extracting and recovering the chromium values from contaminated chromium plating wastes and converting them into pure chromic oxide and subsequently to pure aluminothermic chromium metal.
b) The metallic impurities from the plating sludge can be reduced to extremely low levels during the conversion of the sludge to purified chromic oxide.
c) This purified chromic oxide is well suited to reduction by the aluminothermic process to produce pure chromium metal that meets ASTM Specification A 481-97.
d) The goal of producing aluminothermic chromium metal that meets the ASTM specification for Grade A metal was essentially achieved in this feasibility study.
e) The processing used involves an initial reaction in the solid state between the sludge and sodium carbonate and subsequent leaching of sodium chromate from the reaction product. More than 97% of the available chromium could be extracted by this processing in one pass.
f) Subsequent treatment of the filtrate by magnesium chloride removes a phosphorus impurity as a phosphate.
g) Treatment of the filtrate with a reductant causes the precipitation of a high purity chromic oxide.
h) The reductants ammonia gas, ammonium chloride, hydrazine, methanol and sodium sulfite have been demonstrated to be candidates for the conversion of sodium chromate to chromic oxide.
I) Solid waste in the form of filter cake was vitrified by melting with soda glass cullet. This vitrified waste exhibits leaching behavior in a TCLP test within the limits established for chromium.
j) Solid waste in the form of alumina-based slag that results from the aluminothermic reduction of chromic oxide exhibits leaching behavior in a TCLP test within the limits established for chromium.
k) Following precipitation of chromic oxide, the filtrate liquid can be treated by ion exchange using the Dow cation resin IRC-718 followed by treatment with activated alumina. This resin will remove chromium from the filtrate liquor to 0.5ppm, and phosphorus to 2ppm on a single pass over the resin. The filtrate liquid can then be returned to the process.
A commercialization assessment performed independently by Foresight Science & Technology Inc. found that there was agreement among potential industrial partners and users that the technology developed here will produce a valuable chromium metal product for use in the domestic foundry industry. Since there is no U.S. production of aluminothermic chromium, all chromium metal that is used in the foundry industry is imported. Thus, the commercialization of the process developed here will both provide a domestic source of chromium metal and remove a valuable resource from hazardous landfill sites. It was concluded that the chromium produced by this process could capture at least 25% of the domestic market for aluminothermic chromium, currently estimated at 5000-8000 metric tons.
Supplemental Keywords:
Chromium recovery; chromium recycling; aluminothermic chromium metal; ASTM Specification A 481-97; pure chromic oxide., Scientific Discipline, Toxics, Waste, Water, Sustainable Industry/Business, National Recommended Water Quality, cleaner production/pollution prevention, Wastewater, Chemistry, Technology for Sustainable Environment, New/Innovative technologies, Engineering, 33/50, Hazardous, Engineering, Chemistry, & Physics, plating sludge, plating bath chemistry, chromium & chromium compounds, Chromium, hazardous plating sludge, hazardous waste, metal plating industry, metal recovery , metal recovery, hazardous waste generation, chemical processing, innovative technology, chromium plating sludge, contaminant removal, industrial innovations, innovative technologies, chromium recycling, metal removal, chromium electroplating bathsThe 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.