Recovery of chromium in high purity state from waste materials of etching operations
US5171547A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 19, 1990 |
| Grant date | Dec 15, 1992 |
| Priority date | — |
| Expiry date | Sep 19, 2010 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S423/02
- WIPO fieldMaterials, metallurgy
- WIPO sectorChemistry
Abstract
The present invention is directed to a method for treating a sludge containing substantial amounts of chromium, aluminum, calcium, iron, and phosphorous. The method comprises forming a slurry of the sludge; reacting the slurry with an acid to dissolve substantially all the aluminum and chromium and provide a solids residue comprising mostly calcium sulfate; separating the chromium/aluminum-containing solution from the solids residue; raising the pH of the chromium/aluminum solution to precipitate chromium as chromium hydroxide; and separating the chromium hydroxide from the remaining aluminum-containing solution. The chromium hydroxide is then enriched with an alkali or earth alkali compound and calcined in an oxidizing atmosphere to convert the chromium to a chromate. The calcine is leached in an aqueous medium at a controlled pH to yield a high concentration, high purity chromate solution suitable for producing metallic chromium or a variety of chromium chemicals.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.