# US 4,377,410 A · Chromium recovery from superalloy scrap by selective chlorine leaching

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- Number: US 4,377,410 A
- Document ID: US4377410A
- Status: Granted
- Kind: A
- Application number: 06/156,131
- Filed: 1980-06-03
- Granted: 1983-03-22
- Earliest claimed: 1980-06-03
- Assignees: The United States of America as represented by the Secretary of the Interior
- Inventors: John A. Thomas; David L. Jones; Victor A. Ettel
- Web page: https://patentgrep.com/patent/US4377410A

## CPC

- C22B 7/002: {by treating with halogens, sulfur or compounds thereof; by carburising, by treating with hydrogen (hydriding)}
- C22B 7/007: {by acid leaching}
- C22B 34/32: Obtaining chromium
- Y02P 10/20: Recycling
- C22B: PRODUCTION AND REFINING OF METALS (electrolytic C25); PRETREATMENT OF RAW MATERIALS
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

To recover chromium and other metals from scrap such as superalloy scrap, the scrap is sulfided to provide a molten matte which is cooled and fragmented, the fragments are leached selectively in an aqueous solution with chlorine at a controlled temperature and with agitation while controlling chlorine flow by redox potential to provide the major portion of the chromium in the leach residue and dissolving other valuable metals present as chlorides and thereafter recovering the chromium from the solid.

## Claims

### Claim 1

In a process for separating chromium from other metals in superalloy scrap consisting essentially of chromium alloyed with at least one other metal selected from the group consisting of nickel, cobalt and iron, said scrap being sulfidized with a sulfidizing agent selected from the group consisting of elemental sulfur, nickel sulfide, cobalt sulfide, copper sulfide and mixtures thereof, and melting to form a sulfidized matte, the improvement comprising:
(i) forming said matte into solid fragments,
(ii) subjecting said fragments to an aqueous leaching medium,
(iii) feeding chlorine into said aqueous leaching medium in the presence of a redox couple with agitation at an elevated temperature, said chlorine being fed at a rate to maintain the redox potential below about 600 mV,
(iv) recovering the undissolved sulfidized chromium from said leach medium,
(v) recovering chromium metal from said undissolved sulfidized chromium, and
(vi) recovering the dissolved nickel, cobalt or iron from said leach medium.

### Claim 2 (depends on 1)

A process according to claim 1 wherein said redox coupled is a cuprous-cupric redox couple.

### Claim 3 (depends on 1)

A process in accordance with claim 1 wherein said steps of fragmenting comprises comminution to particles not greater than about 500 microns in diameter.

### Claim 4 (depends on 1)

A process in accordance with claim 1 wherein said elevated temperature is in the range of about 70.degree. C. to just below the boiling point of said aqueous leaching medium.

### Claim 5 (depends on 4)

A process in accordance with claim 4 wherein said elevated temperature is in the range of about 85.degree. C. and 105.degree. C.

### Claim 6 (depends on 5)

A process in accordance with claim 5 wherein the redox potential is controlled to remain in the range of about 250 mV and 550 mV.

### Claim 7 (depends on 5)

A process in accordance with claim 5 wherein the redox potential is controlled at about 400 mV and the copper content of the leach solution is about 10 grams/liter.

### Claim 8 (depends on 1)

A process according to claim 1 wherein said molten matte is granulated by pouring a stream of matte into water.

### Claim 9 (depends on 1)

A process according to claim 1 wherein the molten matte is solidified and then ground to fragments.

### Claim 10 (depends on 1)

A process according to claim 1 wherein the molten matte is slowly cooled at a rate effective to produce chromium sulfide crystals in the solidified matte, and the matte is leached with or without physical separation of individual phases therein.