# US 8,784,639 B2 · Electrochemical process for the recovery of metallic iron and chlorine values from iron-rich metal chloride wastes

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,784,639 B2
- Document ID: US8784639B2
- Status: Granted
- Kind: B2
- Application number: 12/933,653
- Filed: 2008-03-20
- Published: 2011-05-19
- Granted: 2014-07-22
- Earliest claimed: 2008-03-20
- Assignees: Rio Tinto fer et Titane Inc.
- Applicants: François Cardarelli; Sylvain Lefebvre; Claude Tousignant; Guillaume Hudon
- Inventors: François Cardarelli; Sylvain Lefebvre; Claude Tousignant; Guillaume Hudon
- Web page: https://patentgrep.com/patent/US8784639B2

## CPC

- C25C 1/06: or iron group metals, refractory metals or manganese
- C22B 7/007: {by acid leaching}
- C25B 1/26: Chlorine; Compounds thereof (by simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine C25B1/34)
- C25B 11/04: characterised by the material
- C25B 11/046: Alloys
- C25B 11/047: Ceramics
- C25C 7/02: Electrodes (consumable anodes for the refining the metals C25C1/00 - C25C5/00); Connections thereof
- C22B 3/045: {Leaching using electrochemical processes}
- Y02P 10/20: Recycling
- C25C: PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C22B: PRODUCTION AND REFINING OF METALS (electrolytic C25); PRETREATMENT OF RAW MATERIALS
- C25B: ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR (anodic or cathodic protection C23F13/00; single-crystal growth C30B)
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

An electrochemical process for the concurrent recovery of iron metal and chlorine gas from an iron-rich metal chloride solution, comprising electrolysing the iron-rich metal chloride solution in an electrolyser comprising a cathodic compartment equipped with a cathode having a hydrogen overpotential higher than that of iron and containing a catholyte having a pH below about 2, an anodic compartment equipped with an anode and containing an anolyte, and a separator allowing for anion passage, the electrolysing step comprising circulating the iron-rich metal chloride solution in a non-anodic compartment of the electrolyser, thereby causing iron to be electrodeposited at the cathode and chlorine gas to evolve at the anode, and leaving an iron-depleted solution, which is recirculated, at least in part, to the iron-rich metal chloride solution. The iron-rich metal chloride solution may originate from carbo-chlorination wastes, spent acid leaching liquors or pickling liquors.

## Claims

### Claim 1

An electrochemical process for the recovery of metallic iron and chlorine gas from an iron-rich metal chloride solution, which process comprises:
a) providing an iron-rich metal chloride solution;
b) electrolysing said iron-rich metal chloride solution in an electrolyser comprising a cathodic compartment equipped with a cathode having a hydrogen overpotential higher than that of iron and containing a catholyte having a pH below about 2, an anodic compartment equipped with an anode and containing an anolyte, and a separator allowing for anion passage, said electrolysing step comprising circulating said iron-rich metal chloride solution in a non-anodic compartment of said electrolyser, thereby causing iron to be electrodeposited at the cathode and chlorine gas to evolve at the anode, and leaving an iron-depleted solution;
c) separately recovering said electrodeposited iron and said chlorine gas; and
d) recirculating at least part of said iron-depleted solution into said iron-rich metal chloride solution in a).

### Claim 2 (depends on 1)

The electrochemical process of claim 1, wherein the catholyte contains mostly AlCl3 as a non-iron metal chloride and wherein the pH of the catholyte is periodically adjusted to a predetermined pH that ranges between about −1 and about 2.

### Claim 3 (depends on 1)

The electrochemical process of claim 1, wherein the catholyte contains mostly MgCl2 as a non-iron metal chloride and wherein the pH of the catholyte is periodically adjusted to a predetermined pH that ranges between about 0.3 and about 1.8.

### Claim 4 (depends on 3)

The electrochemical process of claim 3, wherein the pH of the catholyte is adjusted upstream of said electrolysing b).

### Claim 5 (depends on 1)

The electrochemical process of claim 1, wherein recirculating d) is made at a recirculation rate over about 60%.

### Claim 6 (depends on 1)

The electrochemical process of claim 1, wherein the cathode has an overvoltage, at 200 A·m−2, greater than about 425 mV in 0.5 mol·dm−3 HCl at 25° C.

### Claim 7 (depends on 6)

The electrochemical process of claim 6, wherein the cathode is constructed from or coated with a material being one of titanium, titanium alloy, zirconium, zirconium alloy, zinc, zinc alloy, cadmium, cadmium alloy, tin, tin alloy, copper, copper alloy, lead, lead alloy, niobium, niobium alloy, gold, gold alloy, mercury or metallic amalgam with mercury.

### Claim 8 (depends on 7)

The electrochemical process of claim 7, wherein the material consists of titanium or titanium alloy.

### Claim 9 (depends on 1)

The electrochemical process of claim 1, wherein the cathode is pretreated before the electrolysing step.

### Claim 10 (depends on 1)

The electrochemical process of claim 1, wherein said anolyte is circulated in loop within the anodic compartment of the electrolyser.

### Claim 11 (depends on 1)

The electrochemical process of claim 1, wherein said anolyte comprises HCl, a salt being at least one of MgCl2, NaCl, LiCl, KCl or CaCl2, and Fe(III) as a corrosion inhibitor.

### Claim 12 (depends on 1)

The electrochemical process of claim 1, wherein the anode is a dimensionally stable anode of the type [M/MxOy-AzOt], wherein M is a refractory metal or an alloy with a valve action property, including titanium, titanium alloy, zirconium, zirconium alloy, hafnium, hafnium alloy, vanadium, vanadium alloy, niobium, niobium alloy, tantalum or tantalum alloy, wherein MxOy is a metallic oxide of a valve metal forming a thin and impervious layer protecting the base metal, including TiO2, ZrO2, HfO2, NbO2, Nb2O5, TaO2, or Ta2Os, and wherein AzOt is an electrocatalytic metal oxide of a noble metal, an oxide of the platinum group metals including RuO2, IrO2 or PtOx, or a metallic oxide, including SnO2, Sb2O5 or Bi2O3.

### Claim 13 (depends on 1)

The electrochemical process of claim 1, wherein the anode is constructed from bulk electronically conductive ceramics, including sub-stoichiometric titanium oxides having as a general formula TiO2n-1, wherein n is an integer equal to or above 3; conductive oxides with a spinel structure AB2O4, wherein A is Fe(II), Mn(II) or Ni(II), and B is Al, Fe(III), Cr(III) or Co(III); or conductive oxides with a perovskite structure ABO3, wherein A is Fe(II), Mn(II), Co(II) or Ni(II), and B is Ti(IV), or with a pyrochlore structure AB2O7.

### Claim 14 (depends on 1)

The electrochemical process of claim 1, wherein the anode is constructed from carbon-based materials.

### Claim 15 (depends on 1)

The electrochemical process of claim 1, wherein the electrolysing step is performed in a two-compartment electrolyser in which the separator is an ion-exchange membrane, and wherein said iron-rich metal chloride solution is circulated in loop within the cathodic compartment of the electrolyser, acting as the catholyte.

### Claim 16 (depends on 1)

The electrochemical process of claim 1, wherein the electrolysing step is performed in a three-compartment electrolyser in which the anodic and cathodic compartments are separated from a central compartment by an anion and a cation exchange membranes, respectively, and wherein the iron-rich metal chloride solution is circulated within the central compartment of the electrolyser.

### Claim 17 (depends on 16)

The electrochemical process of claim 16, wherein said catholyte is circulated in loop within the cathodic compartment.

### Claim 18 (depends on 16)

The electrochemical process of claim 16, wherein the catholyte comprises about 1 to about 450 g/L of iron (II) chloride, about 1 to about 350 g/L MgCl2 or CaCl2 or a mixture thereof, optionally about 1 to about 350 g/L AlCl3, and 0 to about 10 g/L of free HCl.

### Claim 19 (depends on 1)

The electrochemical process of claim 1, wherein the electrolysing step is performed under constant current at a current density ranging from about 50 to about 5000 A/m2.

### Claim 20 (depends on 19)

The electrochemical process of claim 19, wherein the electrolysing step is performed under constant current at a current density ranging from about 50 to about 1000 A/m2, thereby obtaining an essentially dendrite-free smooth deposit of iron.

### Claim 21 (depends on 19)

The electrochemical process of claim 19, wherein the electrolysing step is performed under constant current at a current density ranging from about 3000 to about 5000 A/m2, thereby obtaining an essentially powdered iron.

### Claim 22 (depends on 1)

The electrochemical process of claim 1, wherein the electrolysing step is performed at an operating temperature ranging from about 40 to about 110° C.

### Claim 23 (depends on 1)

The electrochemical process of claim 1, wherein the iron-rich metal chloride solution originates from carbo-chlorination wastes, spent acid leaching liquors or pickling liquors.

### Claim 24 (depends on 23)

The electrochemical process of claim 23, wherein said providing of an iron-rich metal chloride solution a) includes:
a1) leaching a solid carbo-chlorination waste with a hot aqueous solution, thereby forming an aqueous slurry; and
a2) subjecting said aqueous slurry to a separation of solids, thereby forming an insoluble cake and isolating an iron-rich metal chloride solution.

### Claim 25 (depends on 24)

The process of claim 24, wherein said hot aqueous solution is hot process water, hot diluted hydrochloric acid, hot spent leaching acid or a spent pickling liquor.

### Claim 26 (depends on 24)

The process of claim 24, wherein the solid separation step is performed by physical separation method.

### Claim 27 (depends on 1)

The electrochemical process of claim 1, wherein the iron-rich metal chloride solution comprises vanadium, said process further comprising a vanadium separation step upstream, during or downstream of said electrolysing b).

### Claim 28 (depends on 27)

The electrochemical process of claim 27, wherein said vanadium separation step occurs upstream of said electrolysing b).

### Claim 29 (depends on 28)

The electrochemical process of claim 28, wherein said vanadium separation step consists in removing vanadium from the iron-rich metal chloride solution concurrently with chromium by co-precipitation at a pH ranging from about 0.5 to about 3.0.

### Claim 30 (depends on 27)

The electrochemical process of claim 27, wherein the pH of the catholyte ranges between about 0.3 and about 0.5, causing vanadium to precipitate at the cathode along with iron electrodeposition, and wherein the vanadium-separation step occurs downstream of said electrolysing b).

### Claim 31 (depends on 27)

The electrochemical process of claim 27, wherein the pH of the catholyte ranges between about 0.6 and about 1.8, causing vanadium to essentially remain within the circulating iron-rich metal chloride solution while iron is electrodeposited at the cathode, and wherein vanadium is thereafter recovered from the iron-depleted solution exiting the electrolyser, whereby the vanadium separation step occurs during said electrolysing b).

### Claim 32 (depends on 1)

An electrochemical process of claim 1 wherein said recovering of iron in c) is conducted by physically stripping said iron electrodeposited at the cathode and said recovering of chlorine is conducted by suctioning of chlorine gas above the anodic compartment.

### Claim 33 (depends on 1)

The electrochemical process of claim 1, wherein chlorine gas recovered from the anode is further dried and liquefied.

### Claim 34 (depends on 1)

The electrochemical process of claim 1, wherein the iron-depleted solution exiting the electrolyser is recovered and further treated in order to remove calcium and radioactivity by addition of sulphuric acid, thereby producing a magnesium- and aluminum-rich brine.

### Claim 35 (depends on 34)

The process of claim 34, further comprising a step of pyrohydrolysis of said magnesium- and aluminum-rich brine in a fluid-bed pyrohydrolyser, thereby producing azeotropic hydrochloric acid and spinel beads.

### Claim 36 (depends on 35)

The process of claim 35, further comprising recovery of said azeotropic hydrochloric acid for export.

### Claim 37 (depends on 1)

The process of claim 1, wherein a bleed solution formed during the process is electrolysed through a single-pass electrolyser, thereby recovering more iron and chlorine values.

### Claim 38

An electrochemical process for the recovery of metallic iron and chlorine gas from an iron-rich metal chloride solution, which process comprises:
a) providing an iron-rich metal chloride solution;
b) electrolysing said iron-rich metal chloride solution in a two-compartment electrolyser comprising a cathodic compartment equipped with a cathode having a hydrogen overpotential higher than that of iron, and an anodic compartment equipped with an anode and containing an anolyte, said cathodic and anodic compartments being separated by an anion-exchange membrane, said electrolysing step comprising circulating said iron-rich metal chloride solution, adjusted to a pH below about 2, as a catholyte in said cathodic compartment of said electrolyser, thereby causing iron to be electrodeposited at the cathode and chlorine gas to evolve at the anode, and leaving an iron-depleted solution;
c) separately recovering said electrodeposited iron and said chlorine gas; and
d) recirculating at least part of said iron-depleted solution into said iron-rich metal chloride solution in a).