CO₂ Storage via Ex Situ Mineralization in Closed Engineered Systems

This Module details durability and monitoring requirements for storage of CO₂ removed from the atmosphere via engineered carbon removal technology (such as Direct Air Capture) and stored in the solid phase using engineered systems. Durability refers to the length of time for which carbon is removed from the Earth’s atmosphere and cannot contribute to further climate change.

CO₂ mineralization and storage in engineered systems refers to the addition of concentrated CO₂ to an engineered reactor containing crushed rock or mineral feedstock. The use of engineered systems accelerates the natural chemical reaction of mineral carbonation, which constitutes a durable (>1,000 years) CO₂ sink when storage site requirements are met. This is possible because parameters that drive the reaction rate (i.e. temperature, pressure, pCO₂) can be precisely controlled when operating in an engineered reactor. Additionally, because a reactor is a closed system, the amount of carbon stored can be precisely calculated with targeted measurements of the ingoing and outgoing CO₂ stream and feedstock. When implemented correctly, this provides high confidence in the amount of stored CO₂.

Mineralization of CO₂ as carbonate minerals, through reaction with silicate rocks, occurs naturally as part of the weathering process. The carbonation rate of silicate rock can be dramatically increased by increasing reactive surface area and/or the pressure and concentration of CO₂ in the fluid. Mineralization projects can occur at Earth’s surface (open system ex-situ mineralization), in the subsurface (in-situ mineralization), or in closed reactors (ex-situ mineralization in engineered systems). In engineered ex-situ mineralization, a concentrated CO₂ stream is introduced to rock or mineral feedstock, commonly waste materials from mining operations,^{1, 2 , 3} in a reactor to form carbonate minerals.^{4, 5} Because carbonation reactions are kinetically limited in typical surface environments, reactors may be held at elevated temperature and/or pressure and may use feedstock that has been pre-treated (i.e. crushed to a fine grain size, treated with acid or base, and/or heat treated (see Section 3) to increase reactivity⁶. Laboratory and pilot studies estimate that 65-85% of the total carbonation potential of a given feedstock can be achieved in 12 hours.^{6, 7} Given current global estimates of suitable feedstock, this represents a stable sink for carbon dioxide at the mega to gigatonne scale.

Reversal risks are considered to be minimal during the reaction of feedstock and concentrated CO₂. There are further reversal risks associated with storage of carbonated materials. These risks, as well as the monitoring requirements associated with them, are described in detail in the Carbonated Materials Storage and Monitoring Module.

This Module outlines the requirements for evaluating carbon storage in the solid phase via reaction of feedstock in engineered reactors for mineralization of rock or mineral feedstock, with an emphasis on in-line measurements of influent/effluent CO₂ and mineralogical change in post-reaction feedstock. Requirements for reactor design, calculation of carbon stored and CO₂ monitoring are given in Sections 2, 4 and 5 of this Module respectively. Requirements for feedstock characterization can be found in the Rock and Mineral Feedstock Characterization Module. Monitoring requirements for storage cases are detailed in the Carbonated Materials Storage and Monitoring Module.

This Module is applicable to any Project in which a rock or mineral feedstock is carbonated in an engineered system. This may include, but is not limited to:

• Direct gaseous mineral carbonation, in which CO₂ is introduced into the reactor in gaseous form
• Direct aqueous mineral carbonation, in which CO₂ is either:
  • dissolved in water and introduced into the reactor
  • bubbled through a reactor containing liquid
• Indirect mineral carbonation, in which metals are leached from rock or mineral feedstock and precipitated as carbonate minerals in a subsequent step. Project Proponents employing indirect mineral carbonation methods, such as a pH swing method (e.g. Azdarpour et al. 2015)⁸ are required to adhere to fluid monitoring requirements at each step of the process.

Details of the carbonation method employed must be described in the Project Design Document (PDD). This description should include:

• Whether the method is classified as direct gaseous mineral carbonation, direct aqueous mineral carbonation, or indirect mineral carbonation
• Any pre-treatment of the feedstock, as described in Section 3
• At which point CO₂ is introduced into the reactor
• Details of reactor design, as described in Section 2

To be eligible for carbon credits using this Module, CO₂ must be reacted with feedstock in an engineered reactor. This Section details the requirements for reactor design and maintenance. These requirements are applicable to any and all reactors used in the project. For example, if a project uses an indirect carbonation method (see Section 1.1), reactors used at each step of the process must adhere to the requirements outlined here.

Any type of engineered chemical reactor is eligible under the Module, provided that the reactor design requirements set out in Sections 2.2, 2.3, 2.4 and 2.5 below are satisfied. Acceptable reactor types include, but are not limited to, stirred tanks (batch, semi-batch or continuous) and tubular reactors (plug flow, fixed bed, fluidized bed, bubble bed or trickle bed). This list is meant to be comprehensive, but not exhaustive. A brief overview of common reactor types covered under this Module is provided in Table 1. Novel reactor designs not belonging to any of the categories listed here will be acceptable provided that the appropriate reactor design documentation according to Section 2.2 is supplied in the PDD. All reactor designs, including the reactor type, engineering design diagrams, reactor modeling calculations and materials selection must be described in the PDD.

An engineering design diagram of the chemical reactor must be included in the PDD. The design diagram must include details of the dimensions of the reactor, the locations of material inflows/outflows, the positioning of sensors for the monitoring of flow rate, reactant/product chemical composition, temperature and pressure, details of any internal equipment such as agitators or heating/cooling coils and details of any external heat transfer equipment (including heat exchange fluid entry/exit points and corresponding sensors for flow rate and temperature). A sufficient number of viewpoints must be included in the engineering design diagram to show the positioning of all of the key components listed above. Any other process equipment essential to the safe and effective operation of the reactor not listed above should be included and highlighted in the engineering design diagram.

The reactor design must include sensors necessary to quantify any loss of CO₂ from the feedstock during operation of the reactor to leakage. This should include, at a minimum, sensors to determine the inflow/outflow of carbon dioxide from the reactor, to be used in conjunction with a suitable reactor model to determine the amount of carbon dioxide reacted and to estimate any loss of carbon dioxide to leakage. Only carbon dioxide which has been determined by this calculation to have undergone complete chemical reaction into a solid mineral product is eligible for carbon credits issued under this Module.

In addition to loss of CO₂ from the reactor, Project Proponents should consider the possibility of rock or mineral feedstock loss from the reactor in applicable systems. For example, in a packed bed or fluidized bed reactor using CO₂ dissolved in liquid, it is necessary to set flow rates such that loss of solid feedstock particles from the system is minimized. Projects using reactors in which this is a risk are required to characterize solid feedstock loss; further detail is given in Section 5.1.3.

The chemical reactor model used to characterize reactor performance and estimate CO₂ and solid feedstock losses should consider all physical and chemical mechanisms relevant to operation of the chosen reactor type. The chemical reactor model should incorporate a chemical kinetics model which is based on the latest scientific understanding for the chosen chemical reaction pathway. Where chemical kinetics are derived from in-house experimental measurements, details of the experimental procedure used to perform these measurements should be included in the PDD.

Suitable mass/volume flow meters must be placed on all material inlets/outlets from the reactor to allow for characterization of reactor performance and to monitor any material losses to the environment. These sensors should be positioned immediately upstream/downstream of the reactor, as appropriate. Suitable sensors to measure pressure, temperature and pH (if applicable) should be implemented to allow for accurate characterisation of the reactor performance through a combination of measurements and modeling. For stirred tank reactor types, these sensors should be placed so that they accurately characterize the measured property in the bulk phase of the reactor. For tubular reactors, two (or more) measurements of each property at different locations may be necessary to accurately characterize the reactor performance. In this case, several sensors should be placed along the length of the reactor. Justification for the positioning of such sensors for characterization of reactor performance should be provided in the PDD.

It is anticipated that operation of the chemical reactor may occur at high temperature and pressure, and that the pH inside the reactor may be acidic. Appropriate considerations need to be made in the design of the reactor to mitigate these operational conditions to ensure operational loss prevention. Details must be provided in the PDD to describe the selection of materials for each component of the reactor, including suitable justification for these choices from the perspectives of heat and corrosion resistance. For reactors operating at high pressures, considerations should be made relating to the operating pressure, vessel shape/size, positioning of material inlets/outlets, and positioning of sensors to ensure mechanical integrity of the reaction vessel. Such considerations should be made in compliance with a suitable local standard which provides regulations for the design and fabrication of pressure vessels, such as 2014/68/EU (the “Pressure Equipment Directive”) or an appropriate regional equivalent standard in the region of operation. If no such regional standard exists in the area of operation, Project Proponents are required to use the 2014/68/EU standard.

Project Proponents are required to implement an appropriate reactor maintenance plan should be in place, and must be detailed in the PDD. The maintenance plan should outline how the Project Proponent will ensure the structural integrity of the reactor vessel to mitigate against potential material loss events. This includes suitable monitoring and mitigation for mechanical, thermal and corrosive events which may lead to failure of the vessel and subsequent release of reaction materials into the environment. All maintenance plans should be in compliance with a suitable local standard which provides regulations for the maintenance of pressure vessels, such as 2014/68/EU or an appropriate regional equivalent standard in the region of operation.

Table 1. Reactor type overview

All feedstocks must be characterized according to the Rock and Mineral Feedstock Characterization Module prior to commencement of project activities.

Note that Project Proponents are required to perform a full suite of geotechnical characterization measurements for all feedstocks used in ex-situ mineralization projects. Ex-situ mineralization projects are additionally required to characterize carbonated feedstocks according to the Rock and Mineral Feedstock Characterization Module prior to storage in accordance with the Carbonated Materials Storage and Monitoring Module.

Some Project Proponents may choose to pre-treat their feedstock to increase reactivity.

Methods of pre-treatment may include, but are not limited to:

• Additional crushing or grinding after obtaining feedstock material but prior to the onset of project activities
• Thermal activation, particularly if using serpentinite minerals⁹
• Chemical activation using reagents, which may include (but is not limited to):
  • NaOH⁹
  • H₂SO₄⁹
  • Oxalate¹⁰
  • HCl¹¹
  • Citrate¹²

Any pre-treatment must be fully described in the PDD, including:

• Rationale for pre-treatment
• Method used
• Physical and chemical characteristics of the feedstock after pre-treatment, if employing thermal or chemical activation methods
  • Particle Size Distribution (PSD)
  • Surface area
  • Total Inorganic Carbon (TIC)

Project Proponents using a thermal activation method for feedstock pre-treatment must demonstrate that there were no carbonate minerals in the feedstock prior to heating. If carbonate minerals are present in the feedstock prior to pre-treating, Project Proponents are required to characterize the mass of carbon lost during heating and include this in calculations of Greenhouse Gas Emissions (GHG) emissions related to project activities.

This section details the calculation of net CO₂ storage for ex-situ mineralization projects. The monitoring requirements are described in detail in Section 5. Ex-situ mineralization projects are subject to some additional monitoring requirements associated with pre-treated and carbonated feedstocks, including the geochemical and physical characteristics of carbonated feedstocks (see Section 3, Section 5.3 and the Rock and Mineral Feedstock Characterization Module) and reversal risk monitoring associated with the storage conditions of carbonate materials (see Carbonated Materials Storage and Monitoring Module).

The quantity of net CO₂ removal for each Reporting Period, RP, can be calculated as follows:

$CO_2e_{Removal, RP} = CO_2e_{Stored, RP} - CO_2e_{Counterfactual, RP} - CO_2e_{Emissions, RP}$

Equation 1

Where:

$CO_2e_{Removal, RP}$ is the net quantity of CO₂e removed as a result of project activities during a reporting period, in tonnes of CO₂e.

$CO_2e_{Stored, RP}$ is the total quantity of inorganic carbon stored in the solid form during a reporting period, in tonnes of CO₂e.

$CO_2e_{Counterfactual, RP}$ the total CO₂ removed from the atmosphere and permanently stored in baseline scenario for a given RP, presented in tonnes CO₂e. This is the amount of inorganic carbon that would have been stored via carbonation regardless of the CO₂ storage process, over the lifetime of the Credit, either in a given feedstock as a result of natural weathering

$CO_2e_{Emissions, RP}$ is the total quantity of greenhouse gase (GHG) emissions from project activities for a reporting period, in tonnes of CO₂e.

$CO_2e_{Stored, RP}= CO_2e_{Mineralized, T2-T1, MP} - CO_2e_{Losses, MP}$

Equation 2

Where:

• $CO_2e_{Mineralized, T2 - T1, MP}$ is the difference in total inorganic carbon (TIC) present as carbonate minerals in the feedstock before and after reaction, summed across a measurement period. Measurement periods can either be equal to a reporting period, or divided into small time intervals which are then summed across the length of the reporting period. $CO_2e_{Mineralized, T2 - T1, MP}$ should be calculated from direct measurements of the influent and effluent CO₂ stream using sensors. These measurements must be validated by regular analyses of TIC in the feedstock following carbonation. Feedstock characterization is required to include quantification of pre-existing carbonate minerals; these analyses must be conducted for every batch of feedstock, as defined in the Rock and Mineral Feedstock Characterization Module. Feedstock sampling plans must be described in detail in the PDD, paying specific attention to ensuring that samples are representative of any heterogeneity in the feedstock. Project Proponents may choose to use TIC in feedstock prior to and following carbonation as the primary quantification metric in consultation with Isometric.
• $CO_2e_{Losses, MP}$ is calculated as:

$CO_2e_{Losses, MP} = CO_2e_{Leakage, MP} + CO_2e_{Pore Space, MP}$ Equation 2

Where:

• $CO_2e_{Leakage, MP}$ is the sum of CO₂ reversals across a measurement period. Measurement periods can either be equal to a reporting period, or divided into small time intervals which are then summed across the length of the reporting period. Details on calculation of $CO_2e_{Losses, MP}$ are given in the Carbonated Materials Storage and Monitoring Module.

• $CO_2e_{Pore Space,MP}$ is the amount of CO₂ that is accumulated in the pores of the feedstock in tonnes CO₂. As carbonates form from reaction of the feedstock with CO₂, permeability is reduced, trapping CO₂ within the pore volume. This trapped CO₂ may then be released upon removal of the materials from the reactor. The volume of CO₂ trapped in pore space can be conservatively estimated based on the density and bulk density of the feedstock and the measured concentration of CO₂:

$$CO_2e_{Pore Space} = \rho_{CO_2} \left( \frac{m_{\text{feedstock}}}{\rho_{\text{bulk}}} \cdot \epsilon_{\text{feedstock}} \right)$$

Equation 3

Where:

• $ρ_{CO_2}$ is the density of CO₂ in the gas phase in tnCO₂/m³;

• m_feedstock is the mass of feedstock in the reactor in tn;

• $ρ_{Bulk}$ is the bulk density of the feedstock in tn/m^3_feedstock};

• $\epsilon_{feedstock}$ is the porosity of the feedstock in m³_pores/m³_feedstock

$CO_2e_{Counterfactual, RP}$ is defined as the amount of inorganic carbon that would have been stored in the aqueous or solid phase as a result of passive weathering of the feedstock used, without project intervention, across a credit lifetime (in this case, 1,000 years). In calculating $CO_2e_{Counterfactual}$, this is the default assumption if no additional information regarding the storage conditions and duration of the feedstock at the mine/quarry site can be provided. If additional information on the conditions and duration of feedstock storage at the feedstock supplier are available, Project Proponents may justify calculating the counterfactual across a time period relevant to the specific mine or quarry from which the feedstock is sourced in the PDD. For example, projects operating in conjunction with active mines may find it appropriate to use the time of mine closure and provide details of the closure plan in the PDD; alternatively, if sufficient documentation exists suggesting that piles of waste materials generated by the feedstock will not be exposed to ambient environmental conditions for a period exceeding a set number of years, the counterfactual may be considered across that time span.

Additionally, it is important to note that studies have shown that the vast majority of weathering in tailings piles occurs in the surface layer that is exposed to the atmosphere, provided that there is no mechanical overturn^{13 ,14 ,15}. For this reason, counterfactual weathering needs to be accounted for in the top meter of the tailings pile.

$CO_2e_{Counterfactual, RP}$ must be calculated by a combination of direct measurements and modeling of the expected weathering rate of feedstock under storage conditions relevant to the source site for either 1,000 years or a time period justified in the PDD as described above. Models must be justified by empirical data from subsamples of the feedstock; guidelines for sampling procedures that adequately capture feedstock heterogeneity are described in the Rock and Mineral Feedstock Characterization Module. Models must take into account:

• Feedstock mineralogy (direct measurement)
• Feedstock surface area (direct measurement)
• Baseline carbonation of the tailings pile (direct measurement)
• Carbon Dioxide Removal (CDR) potential of the tailings pile in the top meter (calculated from direct measurements)
• Environmental conditions of the source site (direct measurement or publicly available data), including:
  • Temperature
  • Average yearly precipitation
  • Rainwater pH
  • Groundwater pH
  • Carbonate saturation
• Permeability (direct measurement or calculated from direct measurement)
• Water saturation (direct measurement or calculated from direct measurement)
• Microbial activity (direct measurement)

The measurements and model used to calculate $CO_2e_{Counterfactual}$ must be provided to Isometric and the VVB. Project Proponents may choose to either assume the total counterfactual as a one-time deduction or to spread the counterfactual deduction across a project lifetime.

$CO_2e_{Emissions}$ is the total greenhouse gas emissions associated with a given Reporting Period, RP.

Equations and emissions calculation requirements for $CO_2e_{Emissions}$, including emissions associated with reactor operations and reaction monitoring, are set out in the relevant Protocol and are not included in this Module.

This Module requires that fluids are characterized at the point of fluid introduction (influent) and at the point of fluid exit from the system (effluent). Where applicable, analytical methods must be cross-referenced with an appropriate standard (e.g. ISO, EN, BSI, ASTM, EPA) or standard operating procedure. Where a Project utilizes a non-standardized methodology or SOP for the determination of a listed parameter, the Project Proponent is required to outline the relevant method within the project design document (PDD) submitted to the Validation and Verification Bodies (VVB). Note that this Module does not prescribe specific measurement methods, though suggested methods are included. Novel measurement methods may be considered on a case-by-case basis. Further detail is given in Section 5.4.

Project Proponents are required to characterize the amount of non-carbonic acid present in the water source used prior to commencement of project activities. This is to determine the potential risk of non-carbonic acid for dissolution of precipitated carbonates in ex-situ mineralization projects. This must be measured as major anions in the water source, including NO_3^-, Cl^-, PO_4^3-, SO_4^2-, and any other anions relevant to the specific fluid and feedstock used. Measurement methods should comply with ISO 10304-1:2007 or an equivalent national standard. If anion measurements are made on the influent by a partner facility (e.g. wastewater treatment plant, industrial facility), these values may be substituted for direct measurements. To conservatively calculate weathering that occurs as a result of non-carbonic acid, Project Proponents choosing to substitute this data for measurements must assume that all non-carbonic acid present in the fluid will react with feedstock:

$$CO_2e_{Non-carbonic acid} = \sum_i  c_i n_i$$

Equation 4

Where:

• $c_i$ is the charge of the anion
• $n_i$ is the concentration of the anion in solution in ppm

The concentration of non-carbonic acid in the source fluid must be reported in the PDD. Project Proponents are strongly encouraged to calculate the expected losses related to non-carbonic acid and compare this value to expected CO₂ storage based on feedstock characteristics to ensure that the water source is suitable for the project.

Depending on the source of the fluid, the concentration of anions may be highly temporally variable. Project Proponents using direct measurements must provide details of their baseline sampling plan and describe how the chosen sampling frequency is appropriate for capturing any significant variation in concentration in the water source.

This Module requires direct monitoring of the carbonic acid system to verify storage via ex-situ mineralization. To adequately constrain the carbonic acid system within the engineered reactor, Project Proponents are required to measure at least two of the following parameters in both the influent and effluent fluids:

• pH (via direct measurement -- [ISO 10523:2008])
• Alkalinity (via titration -- [ISO 9963-1:1994])
• Dissolved Inorganic Carbon (DIC; via acid titration or infrared detection)
• pCO2 (via in-line sensor or headspace equilibration and gas chromatography)

To reduce uncertainty in carbonic acid system calculations, it is highly recommended to measure all four of these parameters where possible. Bicarbonate (HCO3^-) and carbonate (CO3^2-) can then be calculated using the two-for-six method¹⁶, which is commonly accomplished using PHREEQC (typically used for freshwater) software. Project proponents are required to submit data for all parameters of the carbonic acid system, both measured and calculated; where calculations were performed using methods other than PHREEQC, Project Proponents are required to submit the script or spreadsheet where the calculations were made.

Due to the high CO₂ concentrations in reactor streams, it is critical that samples are stored properly and analyzed as soon after collection as possible to mitigate any potential re-equilibration of the carbonic acid system. Samples must be stored in refrigerated conditions without headspace in sealed vials. Sample collection procedures and sample storage conditions must be described in the PDD. Where possible, measurement via in-line sensors is highly recommended. Where in-line sensors are installed, Project Proponents are required to report calibration data and frequency, fluid flow paths through the sensor and measurement error (as determined by measurement of standards).

As part of reporting carbonic acid system measurements, Project Proponents must describe in detail the point at which concentrated CO₂ is introduced to the system, whether it is dissolved in water prior to introduction into the reactor or if it is introduced into the reactor directly via bubbling or similar. Where possible, the CO₂ concentration of the influent must be measured directly. Where this is not possible (e.g. in instances where CO₂ is introduced to the reactor directly), Project Proponents must calculate a conservative estimate of CO₂ concentration using the concentration of the CO₂ stream, the reactor volume, and the partial pressure of CO₂ in the reactor. All calculations must be described and reported in the PDD.

In engineered systems where feedstock may be lost, such as fluidized bed reactors, Project Proponents are required to monitor feedstock loss from the system. This should be monitored using turbidity/total suspended solids sensors installed at the influent and effluent points. Alternate methods of quantifying feedstock loss may be appropriate and must be described and justified in the PDD.

This Module requires a full suite of elemental analyses in influent and effluent samples. Fluid samples must be analyzed by either inductively coupled plasma mass spectrometry (ICP-MS; [ISO 17294-1:2004]) or inductively coupled plasma optical emission spectroscopy (ICP-OES; [ISO 11885:2007]) as the primary determination method. Project proponents should take analytical precision and detection limits into account when determining their measurement method. Project proponents are required to describe their measurement methods in the PDD. When reporting data from ICP-MS/OES, project proponents must include information on calibration standards, blanks, and geostandards; requirements for data reports are described in the Rock and Mineral Feedstock Characterization Module.

For Projects employing a direct carbonation method, in which concentrated CO₂ is introduced directly into the reactor without being dissolved in water, Project Proponents are exempt from liquid-phase measurements; instead, influent CO₂ concentration must be reported. Reactors must be closely monitored for any potential leakage of CO₂ and this monitoring plan must be provided in the PDD.

As outlined in Section 2.4, measurements of temperature, pressure, flow rate and/or pH inside the reactor at one or more locations (depending on the reactor type) may be required for (i) characterization of loss of CO₂ due to leakage from the reactor, and/or (ii) as part of a maintenance plan to ensure reactor integrity in terms of thermal, mechanical, or corrosive containment failures. Measurement methods to determine temperature should comply with the ASTM Temperature Measurement Standards, or an equivalent standard in the region of operation. Measurement methods to determine pressure should comply with ASME 19.2-2010, or an equivalent standard in the region of operation. Measurement methods to determine pH should comply with ASTM E70-19, or an equivalent standard in the region of operation. Reactor modeling conducted for quantification of CO₂ loss due to leakage from the reactor should follow best practice reactor modeling principles. Owing to the variety of valid approaches which could be used to accurately model the performance of a given chemical reactor, justification of the chosen reactor model formulation should be supplied in the PDD.

In addition to feedstock characterization prior to introduction to the reactor, ex-situ mineralization projects are required to characterize their materials post-carbonation, following the requirements in the Rock and Mineral Feedstock Characterization Module. This is required for all ex-situ mineralization projects, including those choosing to quantify carbon removal based on aqueous phase measurements, as the physical and geochemical characteristics of carbonated materials are critical for determining appropriate storage conditions and reversal risk monitoring (detailed further in the Carbonated Materials Storage and Monitoring Module).

Project Proponents must describe their sampling plan in detail in the PDD, paying particular attention to how it addresses heterogeneity in the carbonated feedstock. This includes variation associated with the degree of carbonation, grain sorting based on particle size, geochemical variability inherent to the source material, or any other feedstock characteristics that may introduce bias into the quantification scheme.

Novel measurement methods may be permissible for quantification of any parameter and will be examined on a case-by-case basis. To be eligible, Project Proponents must demonstrate that the novel measurement technique performs within error of conventional methods for all system variation that can be expected under normal operational conditions. Where system variability is well-characterized, Project Proponents may choose to perform this comparison at intervals that reflect the full variability of the system. If this is not possible, due to high variability or lack of system characterization, this comparison must be performed across a full reporting cycle. System variability characterization must include the following parameters:

• The parameter targeted by the novel measurement method
• Operational temperature
• Operational pressure
• Flow rate
• pH

The final storage reservoir for ex-situ mineralization projects is in the carbonated materials removed from the reactor. Modeling and monitoring requirements associated with storage of carbonated materials are given in the following modules:

In accordance with Section 3.8 of the Isometric Standard, it is a requirement of this Module that all data associated with quantification of $CO_2e_{Stored}$ is hosted publicly on the Isometric Registry. This includes all measurements that directly feed into the equation terms listed in Section 4. While it is required to measure and report redundant data that is collected to resolve the mass balance of a system to Isometric, it is not a requirement to make this data public. Further clarity on which measurements will be publicly shared is given in Appendix 1.

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