Overview
Brine is the only realistic source of rubidium, and it already works — the old way: expensive and unprofitable. Rubidium comes out as a by-product of lithium mining, and the core technology there, DLE, targets one ion only. It needs costly membranes, chemicals and high-pressure reinjection, and it leaves a depleted brine with the rubidium still dissolved in it, which goes straight back into the formation.
The scale of that loss is the whole argument. World rubidium output is under 100 t/year — the French geological survey BRGM puts it below 8 t. A single average well stream of 1,000 m³/h at Salton Sea concentration carries about 970 t of rubidium a year. One well sends back underground roughly ten times more rubidium than the entire planet produces.
ARBOK ties a containerized module into the brine line after lithium extraction and separates the whole stream in one pass — clean water, salt, residual lithium, rubidium. There is more rubidium in the Earth's crust than copper. The shortage is not a shortage; it is the absence of the right technology.
> Core technology and architecture: see ARBOK-VC (Vacuum Cracking). Companion metals from the same stream: ARBOK-Cesium and ARBOK-Lithium.
Applications
Medicine. The isotope rubidium-82 is used in PET diagnostics of the heart for assessment of myocardial blood flow — the key niche.
Timing, quantum and electronics. Atomic clocks; neutral-atom quantum computers; photocells; electronics; 5G base stations.
Materials and optics. Specialty shock-resistant glass; fiber optics.
Feedstocks. Geothermal brines of Salton Sea type; the Upper Rhine Graben in France and Germany; the Qaidam basin and Tibet in China; oilfield brines of the Smackover Formation in Arkansas and East Texas; brines of the Middle East, the North Sea and Latin America; lepidolite tailings; pollucite and lepidolite ore as the route without lithium.
Scale: container-class units co-sited with brine, geothermal and oilfield operations, typically downstream of the lithium stage.
Operating Principle
Under deep vacuum the brine evaporates without heat being supplied — process temperature equals the temperature of the incoming stream, that is, of the feed and its surroundings. Where a specific site-climate temperature appears in the record, it describes the conditions at the location where units have run, not a setpoint or an operating window. Vapour condenses as clean water; every dissolved species remains as a dry cake at 10–15 % moisture, which is then separated by density. Rubidium, cesium, lithium and sodium differ noticeably in density, so one pass — rarely two — splits the dry salt stream into separate fractions.
The contrast with the incumbent route is structural. DLE, sorption and osmosis work inside the water, driving the whole stream through reagents, membranes, coagulants, inhibitors and filters for one target ion, and reject 60–70 % of flow as brine that must be reinjected under pressure. Rubidium is precisely what that rejected brine carries. ARBOK produces no brine, so no rubidium leaves the loop: water return is 100 %, with no reinjection at all.
Refining is a compact second, chemical stage that brings the rubidium fraction to commercial purity. Given the tonnages it is container-scale equipment, not a capital-intensive plant, and it can sit in any jurisdiction — which is what removes the refining dependence, not only the mining one.
In the conductivity ranking of aqueous alkali hydroxides — Li < Na < K < Rb < Cs — rubidium hydroxide stands second only to caesium hydroxide. ARBOK's electrolyte work is built on CsOH, documented in ARBOK-Cesium; no RbOH cell product exists in the portfolio, and this card covers rubidium recovery only.
Key Parameters
| Parameter | Value |
|—|—|
| Operating pressure | deep vacuum |
| Process temperature | ambient — equal to the temperature of the incoming stream and its surroundings; no heat supplied, no setpoint. Site climate varies by location and is not a setpoint |
| Specific electric energy | 0.72 kWh/m³ — the only cost item; renewable-compatible |
| Water return | 100 %; no reinjection. Platform water recovery 99.98 %, up to 99.9 % of volume returned clean in the article sources |
| Salt / dissolved-substance recovery | 85–90 % |
| Salt fraction moisture | 10–15 % |
| Throughput per module | 200 m³/day, standard containerized unit |
| Unit lifespan | 15–20 years — no corrosion, since there is no oxygen in vacuum |
| Consumables | none — no membranes, reagents, coagulants, inhibitors or filters |
| Rubidium, Salton Sea geothermal brine | 110 mg/l |
| Rubidium, Upper Rhine Graben | 25 mg/l |
| Rubidium in stream, 1,000 m³/h (~8.8 million m³/year) | ~970 t/year gross at Salton Sea concentration; ~770–820 t/year in the recovered-basis source estimates. Upper Rhine Graben at 25 mg/l: ~220 t/year |
| Rubidium in stream, 25 l/s (~405,000 m³/season) | ~45 t/season at 110 mg/l, per ARBOK-GEYSER; 70 % recovery assumed for the selective stage |
| Notional value per m³ of Salton Sea brine | ~$180 in rubidium — against ~$60 in cesium and ~$12 in lithium |
| Rubidium carbonate price | ~$1,200/kg |
| Metallic rubidium price | $36–130 per gram |
| Rubidium price used in basket economics | $560/kg — deliberately about 20 % below the market of the day |
Architecture and Components
Containerized vacuum separation module tied into the brine line, normally downstream of lithium extraction: deep-vacuum evaporation; vapour condensation to clean water; dry cake collection at 10–15 % moisture; density separation into rubidium, cesium, lithium and sodium fractions; clean-water return path.
Compact second-stage chemical refining brings the rubidium fraction to commercial purity — container-executable, deployable in any state.
Modular and scalable: 200 m³/day per module, combined into cascades as capacity requires.
Advantages
Technical. Whole-stream processing — rubidium is recovered because nothing is asked to pass a membrane and nothing is rejected as brine. Single-cycle removal of all dissolved salts with no chemical chain. The module bolts onto an existing lithium line rather than replacing it.
Economic. 0.72 kWh/m³ is the lowest reported extraction energy. Water and salt cover OPEX, so rubidium carries near-zero marginal feedstock cost — nobody will build a dedicated plant for rubidium from brine, and nobody has to: ARBOK takes it along the way. CAPEX comparable to DLE, OPEX orders of magnitude lower.
Environmental. Zero waste discharge; no depleted brine returned to the formation; reinjection cost and its energy penalty disappear; salts become a saleable product instead of a disposal liability.
Strategic. Breaks a 70 %+ single-group grip. The US has had no domestic primary rubidium production since 2019; one field is enough to end that. The EU has the Upper Rhine Graben; China has Qaidam and Tibet as an alternative to its own imports.
Integrations
ARBOK-VC (Vacuum Cracking) · ARBOK-GEYSER · ARBOK-CRYSTALLIZER · ARBOK-Cesium · ARBOK-Lithium · ARBOK-CHLORIDE · Arbok-BioLi · ARBOK-SODA · ARBOK LIGHT-SALT
Co-locates with lithium-brine, geothermal and lepidolite/pollucite operations and cascades on the platform with other metal recovery stages. On geothermal heat projects the rubidium fraction rides on the heat business described in ARBOK-GEYSER: the operator keeps wells, heat offtake and energy revenue, ARBOK processes the stream and takes the mineral basket.
Deployment & Operation
Deployment proceeds from brine or ore assay for rubidium and companion species, through recovery configuration, tie-in downstream of the lithium stage on the brine or geothermal line, commissioning, and handover. Container-class, automated, minimal operator involvement; installation typically 2–6 weeks depending on scale.
Commercial models. 15–20 year off-take paid per operation; franchise for brine operators with 5–7 year payback; global service network. Leasing and BOOM structures require no capital investment from the operator. Produced-water and existing lithium sites offer the shortest market entry — the wells exist and the brine is already at surface.
Ramp-up must be controlled: a market of under 100 t/year cannot absorb a sudden supply surge.
TRL
TRL 8 for the rubidium module as stated in the post source; TRL 9 confirmed for the integrated Li/Rb/Cs brine recovery case. Built on the industrially validated recovery platform, with selective recovery defined across both the brine and the pollucite/lepidolite routes.
Remaining steps: field reference site on a rubidium-bearing brine; validation of the selective-stage recovery assumption on the specific feed; offtake and grade qualification for the refined product.
Market Potential
Size and scarcity. World rubidium output is under 100 t/year; BRGM puts it below 8 t. The market is thinner than the cesium market.
Concentration. Sinomine holds over 70 % of global supply. Tanco in Canada and Bikita in Zimbabwe are 100 % its own. Even China imports over 66 % of its rubidium concentrate, two-thirds of it from Canada. Import reliance for the EU, Japan, India, the Gulf states and the USA is 100 %; about 85 % of world rubidium and cesium reserves sit in Canada, Zimbabwe and China, mined from rare granitic pegmatites — pollucite and lepidolite.
Resource. Salton Sea holds approximately 1.88 million t of dissolved rubidium — more, by mass, than its cesium resource. The Upper Rhine Graben holds approximately 900,000 t under Alsace and Baden. Smackover brines in Arkansas and East Texas are already pumped for lithium and bromine. Qaidam and Tibet are brines of the same class. There is more rubidium in the Earth's crust than copper.
Demand elasticity. Rarity here is a cause as much as a consequence: engineers do not design rubidium into products because supply is thin, priced high and controlled by one owner. Remove the shortage and applications appear that are not on drawing boards today. With growing supply the price falls moderately rather than collapsing, while industry revenue grows.
Typical Project Economics
Full-stream case, 1,000 m³/h (~8.8 million m³/year), at prices about 20 % below the market of the day:
| Item | Value |
|—|—|
| Rubidium, ~820 t × $560/kg | ~$460 million/year |
| Water, 8.7 million m³ × $1.2/m³ | ~$10 million/year |
| Salt, 880,000 t × $60/t | ~$53 million/year |
| Reinjection avoided | ~$5 million/year |
| Total, rubidium route | ~$530 million/year from one well |
Water and salt cover OPEX; rubidium sits on top. Where cesium and lithium are taken from the same stream the combined basket reaches approximately $980 million per year — see ARBOK-Cesium and ARBOK-Lithium.
Realizability caveat, stated in the sources. Roughly $180 per m³ in rubidium cannot actually be realized: the world market is under 100 t/year and any serious volume would saturate it instantly. The number is a notional, paper value at today's prices, and it proves one thing only — pumping rubidium back underground while chasing lithium is a strategic mistake. The real value of the recovered rubidium lies in strategic independence and in the volume the market will absorb, at practically zero marginal cost, because the brine is pumped for lithium anyway.
Geothermal co-production, per ARBOK-GEYSER. At Salton Sea chemistry (Rb 110 mg/l) the same hydraulics — 25 l/s, 405,000 m³ per season — carry approximately 45 t of rubidium through the module per season, on top of the heat business.
Risk Factors
Market thinness. Under 100 t/year of world output means volume and price move against each other; disciplined, staged offtake is mandatory, and a supply surge would collapse the price it is meant to escape.
Technology and scale-up. Selective-recovery scale-up and the compact refining stage require field validation; the 70 % recovery assumption for the selective stage must be proven on each specific feed — whole-stream retention in the dry cake is architectural, but finished-product yield is feed-dependent.
Feed variability. Rubidium concentrations differ between wells by orders of magnitude, from 110 mg/l at Salton Sea to 25 mg/l in the Upper Rhine Graben.
Commercial. Offtake and grade qualification; a field reference site is still required; conservative metals buyers and engineering inertia — products are designed to avoid rubidium and that must be actively reversed.
Strategic. Rubidium sits on critical-raw-materials lists and requires coordinated policy alongside private investment; decoupling from the incumbent supplier invites retaliatory restriction of technology or reagent exports.
Related Technologies
ARBOK-Cesium · ARBOK-Lithium · ARBOK-GEYSER · ARBOK-VC (Vacuum Cracking) · ARBOK-CRYSTALLIZER · ARBOK-CHLORIDE · Arbok-BioLi · ARBOK-SODA · ARBOK-Rubidium