# US 2021/0277531 A1 · Selective sulfidation and desulfidation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0277531 A1 - Document ID: US20210277531A1 - Status: Published application - Kind: A1 - Application number: 17/134,429 - Filed: 2020-12-27 - Published: 2021-09-09 - Earliest claimed: 2020-02-27 - Assignees: Massachusetts Institute of Technology - Applicants: Massachusetts Institute of Technology - Inventors: Antoine Allanore; Caspar R. Stinn - Web page: https://patentgrep.com/patent/US20210277531A1 ## CPC - C25C 3/02: of alkali or alkaline earth metals - C22B 1/06: Sulfating roasting - C22B 1/11: Removing sulfur, phosphorus or arsenic other than by roasting - C22B 26/20: Obtaining alkaline earth metals or magnesium - C22B 59/00: Obtaining rare earth metals - C25C 3/34: of metals not provided for in groups C25C3/02 - C25C3/32 - 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 - Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS ## Abstract Various embodiments utilize selective sulfidation and/or desulfidation for such things as ore and concentrate cracking, metal separation, compound production, and recycling. Selective sulfidation can be used to selectively convert an oxide or other material in a feedstock to a sulfide or other sulfur-containing material, and selective desulfidation can be used to selectively convert a sulfide or other sulfur-containing material in a feedstock to an oxide or other material. In some cases, the material produced by such selective sulfidation/desulfidation of the feedstock can itself be novel and/or commercially valuable, while in other cases, such selective sulfidation/desulfidation can be followed by one or more processes to extract, isolate, or concentrate the converted material. ## Claims ### Claim 1 A process for selective sulfidation of a target metal compound of a feedstock material, the process comprising: introducing a feedstock material into a reactor, the feedstock material containing a target metal compound consisting of a metal oxide, oxysulfide, carbonate, sulfate, or sulfide; producing a flow of sulfur-containing gas within the reactor; and passing the flow of sulfur-containing gas through the feedstock material while controlling a roasting atmosphere in the reactor about the feedstock material including at least a process temperature and a ratio of sulfur to sulfur dioxide chosen for selective sulfidation of the target component to produce selectively sulfidized compound including a sulfate, oxysulfide, or sulfide of the target metal, the ratio of sulfur to sulfur dioxide being maintained above a predetermined critical ratio for such selective sulfidation of the target metal compound. ### Claim 2 (depends on 1) A process according to claim 1, wherein the selective sulfidation is run as a continuous or semi-continuous process. ### Claim 3 (depends on 1) A process according to claim 1, wherein the selective sulfidation includes high temperature selective sulfidation of an individual metal oxide, sulfate, carbonate, oxysulfide, or sulfide from a mixture of highly chemically-similar metal compounds in the feedstock material. ### Claim 4 (depends on 1) A process according to claim 1, wherein controlling the roasting atmosphere further includes implementation of a carbothermically-driven sulfur reflux system by back-reacting product sulfur dioxide to control sulfide product selectivity and valency. ### Claim 5 (depends on 4) A process according to claim 4, wherein implementing the carbothermically-driven sulfur reflux system comprises: introducing a carbon species into the reactor during selective sulfidation to remove sulfur dioxide from the reactor and reflux it back into sulfur while producing carbon monoxide or carbon dioxide. ### Claim 6 (depends on 1) A process according to claim 1, wherein the selective sulfidation includes at least one of: crystallization of the target metal compound from a mixed amorphous or semi-amorphous metal compound; or spontaneous separation of the selectively sulfidized compound upon sulfidation from a mixed metal compound due to differences in phase stability of the selectively sulfidized compound compared to the original target metal compound. ### Claim 7 (depends on 1) A process according to claim 1, further comprising: extracting the selectively sulfidized compound from the feedstock material. ### Claim 8 (depends on 1) A process according to claim 1, further comprising: using at least the selectively sulfidized compound in a subsequent molten sulfide electrolysis process. ### Claim 9 (depends on 8) A process according to claim 8, wherein the selectively sulfidized compound includes at least one of barium sulfide or a rare earth sulfide. ### Claim 10 (depends on 1) A process according to claim 1, wherein controlling the roasting atmosphere further includes controlling a ratio of carbon monoxide to carbon dioxide within the reactor to stabilize or react the target metal compound. ### Claim 11 (depends on 1) A process according to claim 1, wherein controlling the roasting atmosphere further includes controlling porosity change of the feedstock material within the reactor to stabilize or react the target metal compound. ### Claim 12 (depends on 1) A process according to claim 1, further comprising: pre-treating the feedstock material prior to introducing the feedstock material into the reactor including at least one of calcination, dehalogenation, dephosphorization, or sulfidative sintering. ### Claim 13 A reactor for selective sulfidation of a target metal compound of a feedstock material, the reactor comprising: a receptacle for receiving a feedstock material containing a target metal compound consisting of a metal oxide, oxysulfide, carbonate, sulfate, or sulfide; a source of sulfur-containing gas; and a process controller configured to control a roasting atmosphere in the reactor about the feedstock material while a flow of the sulfur-containing gas passes through the feedstock material including at least a process temperature and a ratio of sulfur to sulfur dioxide chosen for selective sulfidation of the target component to produce selectively sulfidized compound including a sulfate, oxysulfide, or sulfide of the target metal, the ratio of sulfur to sulfur dioxide being maintained above a predetermined critical ratio for such selective sulfidation of the target metal compound. ### Claim 14 (depends on 13) A reactor according to claim 13, wherein the reactor is configured to run selective sulfidation as a continuous or semi-continuous process. ### Claim 15 (depends on 13) A reactor according to claim 13, wherein the selective sulfidation includes high temperature selective sulfidation of an individual metal oxide, sulfate, carbonate, oxysulfide, or sulfide from a mixture of highly chemically-similar metal compounds in the feedstock material. ### Claim 16 (depends on 13) A reactor according to claim 13, wherein controlling the roasting atmosphere further includes implementation of a carbothermically-driven sulfur reflux system that back-reacts product sulfur dioxide to control sulfide product selectivity and valency. ### Claim 17 (depends on 16) A reactor according to claim 16, further comprising: a carbon source that introduces a carbon species into the reactor during selective sulfidation to remove sulfur dioxide from the reactor and reflux it back into sulfur while producing carbon monoxide or carbon dioxide. ### Claim 18 (depends on 13) A reactor according to claim 13, wherein the selective sulfidation includes at least one of: crystallization of the target metal compound from a mixed amorphous or semi-amorphous metal compound; or spontaneous separation of the selectively sulfidized compound upon sulfidation from a mixed metal compound due to differences in phase stability of the selectively sulfidized compound compared to the original target metal compound. ### Claim 19 (depends on 13) A reactor according to claim 13, wherein controlling the roasting atmosphere further includes controlling a ratio of carbon monoxide to carbon dioxide within the reactor to stabilize or react the target metal compound. ### Claim 20 (depends on 13) A reactor according to claim 13, wherein controlling the roasting atmosphere further includes controlling porosity change of the feedstock material within the reactor to stabilize or react the target metal compound.