Recovery of chromium from F019 waste

Abstract

The United States EPA has defined the waste from aluminum extrusion industries (F019 waste) as hazardous due to chromium concentration above the allowable limit. The industrial process that produces F019 waste involves single state precipitation of both aluminum and chromium at about 8.5. This project studied a two stage precipitation process to recover chromium hydroxide precipitate at a pH of about 13.5 and aluminum hydroxide at a pH of about 7.0. The optimum pH ranges found from Experiment #1 and #1A were 5.5-8.5 for aluminum hydroxide. The range of chromium extended to 13.5 later by Experiment #3. Two separate stages of precipitation gave chromium hydroxide precipitate contaminated with about 10% of the total aluminum in the first stage and almost pure aluminum hydroxide precipitate in the second stage. The low concentration of chromium in the second-stage precipitate can decrease the cost of disposal, and the chromium in the first-stage precipitate can generate income if a market is found. Results of the TCLP test on original waste and the total test showed the aluminum precipitates in second stage with low chromium contamination so that it can be disposed in regular landfills (Experiment #2 results). Also, the chromium concentration in the wastewater after two-stage precipitation was found under the sage limit of disposal (i.e. less than 5 mg/l) and 55% of total waste could be recovered from hazardous F019 waste by two-stage precipitation.