Using ikaite and other hydrated carbonate minerals to increase ocean alkalinity for carbon dioxide removal and environmental remediation

Removing large volumes of CO2 from the atmosphere, as well rapid and deep emission reductions, may be required to meet goals Paris Agreement. This has catalyzed recent attention on carbon dioxide removal (CDR) approaches that can remove more atmosphere than they emit. The oceans absorb approximately 25% is emitted which causes acidification adds stress experienced by some shell-forming organisms. Some proposals have been put forward additional increasing ocean alkalinity, also help ameliorate impact converting bicarbonate (HCO3−) ions remain in >105 years (often termed “ocean alkalinity enhancement” or OAE1Renforth P. Henderson G. Assessing for sequestration.Rev. Geophys. 2017; 55: 636-674https://doi.org/10.1002/2016RG000533Crossref Scopus (149) Google Scholar). first OAE proposal involved calcining limestone create lime (Equation 1) then dissolving it 2).2Kheshgi H.S. Sequestering atmospheric alkalinity.Energy. 1995; 20: 915-922https://doi.org/10.1016/0360-5442(95)00035-FCrossref (134) Scholar process consumes thermal energy chemical transformation material would only negative if emissions were captured stored.3Renforth Jenkins B. Kruger T. Engineering challenges liming.Energy. 2013; 60: 442-452https://doi.org/10.1016/j.energy.2013.08.006Crossref (61) released during carbonation 2) impossible recover. As such, technoeconomic assessments suggest an penalty 1–7 GJprimary a cost $70–$160 per net tonne removed (enthalpy used Equations 1 2 reflect requirements; although given inefficiencies within processing equipment, actually requirements are usually much greater).3Renforth ScholarCaCO3→CaO+CO2ΔHr = 179 kJ mol−1(Equation CaO+2CO2+H2O→Ca2++2HCO3−ΔHr −215 Given surface supersaturated with respect calcium carbonate minerals (e.g., calcite), not possible sequester spreading these directly into ocean. Increasing partial pressure (>1,000 ppmv at atm) seawater/limestone reactor induce mineral dissolution,4Caldeira K. Rau G.H. Accelerating dissolution ocean: Geochemical implications.Geophys. Res. Lett. 2000; 27: 225-228https://doi.org/10.1029/1999gl002364Crossref but this require (and 2.5 GJ electricity gross CO25Xing L. Pullin H. Bullock Renforth Darton R.C. Yang A. Potential enhanced weathering calcite packed bubble columns seawater removal.Chem. Eng. J. 2022; 431: 134096https://doi.org/10.1016/j.cej.2021.134096Crossref (8) Scholar) direct air capture systems removal. hydrated will spontaneously dissolve ambient pressures (Figure S1; Note S1). These rare thus cannot extracted natural deposits sufficient quantity make meaningful climate impact. However, them specifically addition One promising candidate ikaite (CaCO3.6H2O), naturally occurring, metastable mineral6Bischoff J.L. Fitzpatrick J.A. Rosenbauer R.J. solubility stabilization (CaCO3· 6H2O) 0 25 C: Environmental paleoclimatic implications thinolite tufa.J. Geol. 1993; 101: 21-33https://doi.org/10.1086/648194Crossref (161) forms cold (<15°C), alkaline, nutrient-rich waters.7Schultz Thibault N. Huggett its pseudomorph glendonite: Historical perspective legacies Douglas Shearman Alec Smith.PGA (Proc. Assoc.). https://doi.org/10.1016/j.pgeola.2022.02.003Crossref (5) In conditions, precipitation favored over anhydrous eventually dehydrates dissolves upon changes solution chemistry, pressure, temperature.6Bischoff precipitate synthetic ikaite.8Hu Y.-B. Dieckmann G.S. Wolf-Gladrow D.A. Nehrke Laboratory study coprecipitation phosphate sea ice.J. Res.: Oceans. 2014; 119: 7007-7015https://doi.org/10.1002/2014JC010079Crossref (11) enthalpy reaction exothermic 3), spontaneous most earth temperature/pressures due change entropy (ΔSr −0.14 mol−1 K−1). Subsequently, “lost” through lower when using 4).CaCO3+6H2O→CaCO3.6H2OΔHr −32 3) CaCO3.6H2O+CO2→Ca2++2HCO3−+5H2OΔHr −4 4) feasibility ikaite, other minerals, requires produced remains stable time added dissolve. If transform before addition, no effect possibly cause reduction seeding precipitation.9Moras C.A. Bach L.T. Cyronak Joannes-Boyau R. Schulz K.G. Ocean Alkalinity Enhancement - Avoiding runaway CaCO3 quick dissolution.Biogeosciences Discuss. 2021; 2021: 1-31https://doi.org/10.5194/bg-2021-330Crossref Experimental work suggests (Figures 1A 1B ) days low temperature (sufficient ocean; Figure 1C) stoichiometrically increases 1D). ephemeral environments, we discuss potential multi-step system mass production 2). uses high-pressure pure contact water calcite-bearing (which abundant occurring); product passed reactors degassed. become ikaite. was inhibited under temperatures, solid formed important environmental function, behavior described focus sustained research decades. sufficiently constrain operation reactor. Work examined postulated similar rate calcite-seeded solutions.11Papadimitriou S. Kennedy Thomas D.N. Kinetics seawater-derived brines sub-zero temperatures 265K.Geochem. Cosmochim. Acta. 140: 199-211https://doi.org/10.1016/j.gca.2014.05.031Crossref (19) Therefore, estimates made size their capital cost. swing depend ratio (PR) between Maximizing precipitated smallest desirable, reduce relative amount recirculation pumping/compression costs. ikaite6Bischoff evaluate concentration gas-phase PR, results (∼2 bar) total (∼0.02 bar), larger concentrations mol kg−1) PR 3B–3D). To assess costs approach, developed bespoke model dissolution, gas transfer, processes simulated geochemical modeling software PHREEQC (v3.4) conjunction supplied phreeqc.dat thermodynamic database. nested balance coded Python (Anaconda v3.9), evaluates “first-of-a-kind” (FOAK) pilot (103 metric tonnes [t] year) industrial scale (1011 t processes. Learning rates applied consider mega-tonne (∼106 “nth-of-a-kind” (NOAK) See Notes S3–S6 supplemental references details modeling. For base case (temperature 3°C), bar (pure CO2) occurred ∼8 min (for reach 95% equilibrium), controlled transfer hydration kinetics. relatively reaction, volume (12 m3 kt yr−1 FOAK system; 1201 plant). degassing (at 0.5 takes longer (16 min) requiring (11 min), similar-sized (20 2080 will, partly, increased deviation absolute desired extent. predicts levelized (LCOC) $3,800 tCO2−1 pilot-scale process, $650 tCO2 <$310 NOAK systems, fixed running costs—which include labor, maintenance, supervision, administration, company overheads, taxes, insurance, distribution—dominate (20%–50%). These, together expenditure, offer largest economies component selection reductions technology development. million scaled could drive down <$90 tCO2−1. compares favourably projected future ($90–$200 12) liming ($70–$160 atmosphere. Energy 850 kWh 54 MJ fuel systems. 140–554 5 6 270–1,400 3–6 methods OAE.1Renforth LCOC sensitive input parameters 3A), particularly uptake (“sequestration efficiency”; see S7). A full list presented Table S5 represents reasonable present-day values. decreases -pressures 3E), apparent favorable conditions being <0.05 precipitator >1 there limited applicability beyond maximum compression (35–70 compressors, 100 pumps, 50 reactors) below minimum vacuum (1 mbar 6–12 vaporization water), constraints selected equipment. 0.02 choices further optimised. consequences uncertain. targeted effects moderate absorption capacity ocean.1Renforth increase stimulate threshold saturation levels (>12 Ωaragonite) exceeded carbonate-producing organisms.12Bach Gill S.J. Rickaby R.E.M. Gore Removal With Enhanced Weathering Enhancement: Risks Co-benefits Marine Pelagic Ecosystems.Frontiers Climate. 2019; 1https://doi.org/10.3389/fclim.2019.00007Crossref (66) avoids co-addition bioactive elements Si, Fe, Ni), limits approaches.12Bach Limestone purposes typically up ∼97% carbonate,13Harrison D.J. High-purity limestones England Wales.QJEGH. 26: 293-303https://doi.org/10.1144/gsl.qjegh.1993.026.004.05Crossref (9) remaining primarily composed Mg (incorporated phase) silica considerably less soluble retained reactor). Results (over <15°C), such loaded onto dedicated vessels dispersed back ship. considering ocean3Renforth 3 4 needed unload 300 vessel; while smaller shorten time, use potentially expensive. There spare existing shipping fleet transport distribute billions materials,14Caserini Pagano D. Campo F. Abbà De Marco Righi Grosso M. Maritime Transport Liming Atmospheric Removal.Frontiers 3: 1-18https://doi.org/10.3389/fclim.2021.575900Crossref (17) associated production, delivery appropriate. base-case here, distribution method3Renforth accounts <6% around 40% Ikaite crystals <300 μm mixed layer, contribute (see S4). waters <15°C, approach applicable coasts Northern Europe, Alaska, Maine Northwestern United States, Canada, Chile, Argentina, Southern Peru, Western South Africa, Australia, New Zealand, Russia, Japan S5). Large sedimentary present regions, nations collectively extract Gt annually, aggregate cement S6). order ∼100 Mt waste rock dust generation (5%–20% bulk production), raw (Table Much extractive created last years, global extraction growing population. facilitate hundreds MtCO2 next 20–30 subsequently >Gt thereafter. investigate relationship resource locations, suitability resources purity), appropriate siting facilities nation socioeconomic regulatory context, logistics facilities, optimum sites. Here, describe removing mineral. meta-stable solutions <15°C transforms unhydrated polymorphs calcite) days. proposed here synthesizes elevated (>1 bar). resulting alkaline series vent (0.5 bar, respectively), causing precipitates solid. Experiments show adding alkalinity. (850 fuel) ($650 FOAK; NOAK) comparable to, than, alternative permanently scale. materials scalable potential, yr−1. (Si, social acceptability approaches. All supporting data code freely available Heriot-Watt University’s publication portal (https://doi.org/10.17861/082667ec-1eba-45e4-989e-8d114f58e9d9) obtained request corresponding authors. authors like thank Reece Crawford assistance preliminary versions techno-economic assessment. P.R. K.P. acknowledge philanthropic funding ClimateWorks Foundation Climate Pathfinders Foundation. Nico Lahajnar thanked collecting experiments M153 equatorial Atlantic cruise. anonymous reviewers helpful comments. concept initiated J.H. scope design, S.B.; sample collection analysis, S.B. B.D.M.; P.R., S.B., K.P., B.D.M., J.H.; assessment development, P.R.; manuscript writing editing, inventors patent (GB2206475.2) Method producing metal hydrate. Download .pdf (3.75 MB) Help pdf files Document S1. Figures S1–S7, Tables S1–S5, S1–S6,