Olivine Weathering From the Lab to the Beach: Evaluation of data and deployment plan for the accelerated weathering reaction of olivine on beaches for carbon dioxide removal and ocean deacidification - AGU 2019 Poster

Plain Language Introduction and Contextual Discussion (unofficial):

Weathering rocks for planetary scale carbon dioxide removal is not a novel idea, in fact, the weathering of silicates and carbonates in the long-term carbonate silicate cycle is how more than 99.9% of carbon on Earth has come to be stored in rock. This weathering cycle is Earth’s natural carbon dioxide removal (CDR) process, however, it normally takes millions of years to occur, so methods of “enhancing” or accelerating the weathering rate have been proposed.

A majority of the proposals for large scale CDR with enhanced weathering have looked at distributing olivine (the fastest weathering silicate) on land or in the open ocean. These proposals have generally not been implemented for large scale CDR though because the weathering rate of stationary olivine on land may be too slow, and in the open ocean, the particle sizes required for the olivine to weather completely before reaching the seafloor is too energy-intensive to efficiently mill.

To overcome these issues, the coastal environment of high-energy tropical beaches has been proposed as an optimal place to weather olivine rapidly with low energy use. The strategy of using beaches to accelerate the olivine weathering rate overcomes the typical impediments to feasibility by avoiding a potentially prohibitive energy penalty. The strategy is further kept efficient by minimizing the transport distance of the olivine, utilizing only quarries within a limited distance of the beaches.

Considering olivine is highly abundant, making up over 50% of the upper mantle, and each 1 tonne of olivine can remove up to 1.25 tonnes of CO2 from the atmosphere, there is theoretically enough olivine to remove total current yearly and historical anthropogenic emissions from the atmosphere. There is great potential to utilizing the weathering process to meet the negative emissions requirements of the majority of IPCC models that keep global warming below 1.5°C (2.7°F). However, aspects of the process that have been proposed, have yet to be tested. If enhanced coastal weathering is to be implemented on a large scale in the coming decades, research needs to be carried out on the weathering rate, efficiency, and safety of the process.

Prior research has used mathematical models of weathering rates, table top shakers, and flumes to measure the weathering rate under continuous motion with encouraging results, yet no real-world pilot project has been carried out to test for speed or the environmental effects on wildlife that the addition of large quantities of olivine might have.

The most pressing task in this field is to carry such an experiment on a pilot beach in the real world. This experiment will need to determine the olivine weathering rate on a real beach, as well as safety and other metrics that would be necessary to quantify prior to the large scale deployment of coastal enhanced olivine weathering. This poster lays out aspects of the experimental design and other processes that would go into deploying a pilot project so that coastal olivine weathering can finally go “from the lab to the beach.”

The experimental design and need for implementation discussed in this poster are not just theoretical, as Project Vesta and our associated scientists plan to actually deploy the proposed pilot experiment in 2020.

This poster was presented at the 2019 AGU100 Conference in San Francisco, CA. It was featured in the poster session “Marine Based Management of Atmospheric Carbon Dioxide and Ocean Acidification” convened by Greg H Rau, Matthew Eisaman, and Phil Renforth.

This poster and Project Vesta were featured in the SF Chronicle article “Could putting pebbles on beaches help solve climate change?” and on local Bay Area CBS and Fox TV affiliates.

Abstract:

Ground olivine in large-scale coastal applications has been proposed as a low-tech, low-risk approach to remove CO2 and to counteract ocean acidification. With each 1 tonne of olivine weathered, equating to 1 tonnes of CO2 stored eventually stored in magnesium bi-carbonate. As a highly abundant mineral, there is sufficient olivine to remove significant quantities of CO2 from the atmosphere and oceans. Models and experimental studies have provided proof-of-principle, but lack a real-world, overall assessment covering costs, CO2 balance, weathering rate, optimal particle size, consequences to marine and beach life, behavior of heavy metals, legal, logistical, and practical concerns.

This paper reviews past attempts at this problem and sets forward a plan to take the science to the next step by putting the “olivine beach” concept to the test in real-world, tropical beach conditions. Amongst other topics, we will analyze and observe the real-world enhanced weathering rate of olivine on a tropical beach, provide an updated life cycle efficiency of the process from mine to beach, design and test a methodology to quantify impacts on marine life in the environment, and address other common criticisms that stand in the way of deployment of the concept on a large scale.

Enhanced weathering is a carbon dioxide removal (CDR) strategy that is inexpensive, modeled on nature’s natural long term carbon removal cycle, and requires no new or untested technologies in order to be deployed on a large scale. All that stands in the way is a scientific consensus on the details mentioned above and as such, this paper takes a detailed look at the entire process of mining, milling, transporting, weathering, and monitoring. There is a dire need to push this research forward and “move olivine weathering from the lab to the beach.”

Authors: Francesc Montserrat, Pol Knops, Eric Matzner

Why Green Sand Beaches?

The olivine weathering reaction consumes protons (H+) and in doing so, de-acidifies ocean water, thereby sequestering CO2 from the atmosphere (Fig. 1).


The weathering reaction is inherently slow, but can be sped up by grinding down the mineral rocks to sand-size grains and by introducing the mineral (sand) grains into high-energy environments, like coasts and estuaries.


Model, literature and laboratory studies have demonstrated the proof-of-principle and have indicated the potential for enhanced weathering in coastal environments by waves and biotic effects.

A large-scale pilot project is needed to demonstrate its feasibility, quantify the weathering rate and to investigate the environmental impacts in an integral manner. We plan to carry out such an experiment.

Proof of Principle

Mathematical Models

The olivine weathering reaction consumes protons (H+) and in doing so, de-acidifies ocean water, thereby sequestering CO2 from the atmosphere (Fig. 1).

The weathering reaction is inherently slow, but can be sped up by grinding down the mineral rocks to sand-size grains and by introducing the mineral (sand) grains into high-energy environments, like coasts and estuaries.

Model, literature and laboratory studies have demonstrated the proof-of-principle and have indicated the potential for enhanced weathering in coastal environments by waves and biotic effects.

A large-scale pilot project is needed to demonstrate its feasibility, quantify the weathering rate and to investigate the environmental impacts in an integral manner. We plan to carry out such an experiment.

Relationship between reaction time and percentage of olivine reacted for various particle diameters. For the calculation it is assumed that the olivine particle shrinks as it reacts with the (dissolved) CO 2 according to the shrinking particle model, see Appendix 1. The rate of dissolution is assumed to be 6.010 -8 moles m -2 *minute -1 and molar density is assumed to be 23245 mol/m 3 . This is the dissolution rate that corresponds to a pH found in soil and rainwater (Hangx and Spiers 2009). (via Joris Koornneef*, Evert Nieuwlaar)

Table Top Shaker

Natural processes enhancing dissolution include the surface abrasion by grain-grain collisions, creating minute slivers (with high surface-to-volume ratios) weathering an order of magnitude faster, and biotic activity such as microbial effects, and sediment processing by worms and other macrofauna.

Fine fraction olivine generated after 2 months on a table top rotary shaker from olivine originally sized with 75% 1.4-2.38 mm and 25% >2.38 mm (Schuiling 2011)

Desktop shaker experiments demonstrate the shortcomings of the mathematical models on taking into account the effect of grain-on-grain collisions. The collisions result in the creation of fine fraction that itself rapidly weathers and it causes abrasions on the surface that can remove the build-up of silica, which in stationary olivine slows the reaction down.

Flume Experiment

In prior studies, the proof of principle of enhanced olivine weathering has been established. Olivine in seawater increases pH, Total Alkalinity (= acid buffering capacity) and consequently increases the Dissolved Inorganic Carbon (DIC = total dissolved CO2 species) in the seawater. Water movement in experimental setups in the lab momentarily increases the pH, demonstrating instantaneous olivine weathering.

(de Boer & Schuiling 2015)

This experiment was carried out using a large recirculating flume filled with coarse sand made up approximately ~30% of olivine with all fine-grained sediments removed prior to the start.

The water was moved at a speed to model basic ocean currents of 40-60 cm/sec. When the water flows, the olivine is transported and tumbled as can be observed in the accompanying image.

Real-World Pilot Project Needed

In the large-scale pilot experiment proposed here, the olivine would be applied in a tropical marine coastal environment. This way, the weathering rate in a natural setting, as well as the environmental impacts, can be determined in an integral manner.

We propose beach characteristics and an experimental design required to carry out a safety study and initial costal enhanced weathering pilot experienment in the real world. Further this poster evaluates key processes & co-benefits, as well as logistics and costs related to potential upscaling. Common concerns, as well as the net impact on efficiency are also addressed through a life cycle assesment.

A real-world examination of the environmental factors of the "shelf milling engine" as well as safety and co-benefits to the local fauna is needed. (Image: Meysman & Montserrat 2017)

Weathering Reaction For CO2 Removal

We utilize Forsterite, the Magnesium rich form of olivine.
Carbon Dioxide (CO2) dissolves into the ocean at a higher rate as the atmosphere contains more CO2
The CO2 is transformed into bicarbonate, and will eventually turn to CaCO3, calcium carbonate, which is used by marine animals like corals for their shells.
Bicarbonate is alkaline and so its creation in the water raises the pH making the water less acidic.
Silicate is the limiting factor for diatoms. Diatoms are a type of plankton that makes up the base of many marine food chains. They are threatened by increasing ocean acidification and nutrient deficiencies. This silicate increases their numbers, and they in turn further sink carbon dioxide through photosynthesis.
Corals and other marine calcifying organisms use pull calcium ions and carbonate out of the ocean to build their skeletons.
Even at the proposed, full-scale yearly CO2 offsetting level for 100 years, it has been calculated that the magnesium level would only rise slightly from 1296 to 1296.6 ppm (and bicarbonate from 42 to 45 ppm), which is within normal global ocean water concentration ranges.
Over long time scales, as corals and diatoms die, their skeletons settle onto the seafloor, eventually turning to sediment and then limestone. The CO2 will be stored there for millions of years, until potentially being subducted through tectonic forces and then maybe released from a volcano in millions of years.

Beach Characteristics

A tropical climate ensures higher year-round temperatures, maintaining higher dissolution rates.

Corals are important key organisms both ecologically and for the purposes of this pilot experiment.

For practical monitoring and sampling purposes the embayment for the experimental beach should not be deeper than 15 m at its seaward end.

Median particle diameter 250-500 micrometer. Calcareous sand, or simple silicate sand, increases the measurability of olivine reaction products.

A semi-enclosed embayment with limited wave exposure, rather than an open-ocean beach face, increases seawater residence time, needed for the detection of reaction products.

Seawater exchange rate of the experimental embayment with the open ocean should be 24-72 hours.

Mahana Bay, a natural green sand olivine bay and beach found in Hawaii. (Image: courtesy of Francesc Montserrat, co-author of this paper, who took this photo while studying the corals and marine life found in this olivine-rich bay)

Experimental Setup

The experimental setup and monitoring scheme needs to adhere to a Before-After Control-Impact (BACI) design. In this manner, any measured effects can be unequivocally attributed to the olivine application.

Geochemical flux measurements are required to measure the olivine dissolution rate, to effectively convert it into carbon credits. The proxies for measuring olivine dissolution are:

  • Dissolved Silicate
  • Dissolved Nickel
  • Total Alkalinity (TA)
  • Dissolved Inorganic Carbon (DIC)

Floating, solar-powered pH monitor

Flux measurements of reaction products (above) over the sediment-water interface (SWI) are to be done both in situ and ex situ, by extracting sediment (with added olivine) from the system and incubating them in the lab.

The compartments of the ecosystem that need to be sampled are:

  • Overlying water
  • Sediment solid phase
  • Sediment pore water
  • Biota encountered in the ecosystem

Sediment core sample

Key Processes & Co-Benefits

Fluxes of reaction products from the sediment (with added olivine) to the overlying water will demonstrate the weathering rate, associated with sequestering a given amount of CO2.

Alkalinity (and pH) increase will create favourable conditions for calcifying organisms, like corals, shellfish and calcareous algae.

Release of Si from the weathering olivine may cause a fertilisation effect on siliceous organisms, like diatoms and radiolarians, but also sponges. Changes in environmental stoichiometry may cause shifts in community composition.

Release of (trace) metals, notably nickel (Ni), is monitored both in the seawater and throughout the trophic web. Tissue of organisms of different trophic levels (primary producers, primary consumers, secondary consumers, apex predators) is analyzed for potential accumulation.

Logistics

Minimize olivine transport to beach to less than 300 km (or 1000 km) for efficiency.

Open 30-50 large mines in the tropics, with > 100 million tonnes / year.

Less than 2 million people needed mining globally for total anthropogenic emission offsetting (~50 gt).

Dunite reserves with beaches within 300 km and 1000 km

Cost Model

Cost today at European mine €12.5 / tonne

Cost today with shipping €32 / tonne @ 8000 tonnes

Theoretical mining cost at @ 80,000 tonnes a day = €4 / tonne

Average mining, milling, and transport within < 300 km = €4-€5

Working cost for Phase III level olivine delivered to environment < €19 / tonne

Proposed future cost for 1 tonne of olivine to the beach Phase III-V < €10

Olivine prices go down as demand and supply increase.

Potential Upscaling

Common Concerns

Yes! Olivine is the most abundant mineral in the upper mantle, making up over 50% of it. There are large reserves near the surface (dunite), consisting of >90% olivine.

Yes! Annual mining of coal, oil equivalents, and construction minerals occurs in larger volumes than the volume of olivine needed for the removal of humanity’s yearly CO2 output

Yes! 6-8% of the Earth’s shores are the type of high-energy, shelf-seas necessary to adequately enhance the olivine weathering.

Life Cycle Assessment

Entire process can be 95% efficient with a net loss of < 5%, if transport is minimized, as well as grinding size and energy use.

Process can be made further efficient through the use of electric transport and milling techniques.

Transportation creates the majority of CO2 emissions.

(Olivine weathering LCA 2011)

Need for CDR Pilot Projects

The goals of the Paris Climate Agreement and a majority of the scenarios to stay below 1.5°C of change in global average tempeartures cannot be achived without significant levels of carbon dioxide removal (CDR) by 2100. Without the deployment of pilot experiments like this concept, that take the leap from the lab to the real world, policy makers may not have the data and tools available with enough time to make decisions that can stave off even the best case scenarios of climate change.