Carbonation of

alkaline residues in

the manufacture of

lightweight aggregate

Dr Paula Carey

Chief Technical Officer,

Carbon8 Systems
 

 

 

 

 

Contents

• Carbonation and mineralisation

• History of Carbon8 Systems

• Products from carbonation

• CO2 capture capacity

• Value generation

© Carbon8 Systems Ltd, 2022
 

 

 

 

 

 

 

 

 

 

Carbonation & Mineralisation

• Carbonation can be accelerated by using increased concentration of CO2

• Calcium and Magnesium silicates, oxides and hydroxides can react with CO2 to

form carbonates

• These minerals can be found in

• Basic and ultrabasic rocks (basalts, serpentinites, dunites)

• Industrial thermal residues (steel slags, ashes from EfWs, cement and concrete residues etc)

• Reaction is exothermic

• Does not require large amounts of energy for the transformation of the CO2

molecule

• Permanent capture of CO2

• Can use pure CO2 or CO2 directly captured from flue stacks or the air (DAC)

© Carbon8 Systems Ltd, 2022
 

 

 

 

 

 

 

 

 

 

 

Conditions of Carbonation

Two main conditions of carbonation

1. Wet water: solid ratios > 1:1 alkaline water leading

to precipitation of carbonate in the water.

2. Semi-dry or thin film: Carbonate nucleates on the

grains or replaces the grains of the residue and

can help bind the grains together.

• The reaction can be performed at atmospheric

temperatures and pressures or at a range of elevated

temperatures and pressures up to super critical CO2

conditions

© Carbon8 Systems Ltd, 2022
 

 

 

 

 

 

 

 

 

 

Carbon8 Systems

• Formed in 2006 after +10 years research into carbonation

• Particularly, treatment of contaminated soils with UK EA and USEPA

• Early patent using a modification of cement stabilization to treat hazardous wastes

• Use semi-dry carbonation, at atmospheric temperature and pressure conditions

• Commercialised the technology in 2010 via a license for the treatment of APCr from EfW

• Currently, three plants treating APCr in the UK using pure CO2 delivered in a tanker

• From 2018, developed technology to use CO2 directly from flue gas

• Two demonstration deployments in Ontario 2018 and UK 2019

• First commercial deployment with Vicat Cement Group in France 2021

© Carbon8 Systems Ltd, 2022
 

 

 

 

 

 

 

 

Contaminated Land Remediation

• ACT can be applied to contaminated soils – through the addition of a carbonatable binder

• Modified form of cement stabilisation/solidification (S/S)

• Reduced pH

• Final granular product generated in minutes rather than hours for traditional S/S

0.25 0.1 0.03 16

14

0.025 0.08

12

0.2

Nickel leached (mg/l)

Lead leached (mg/l)

Zinc leached (mg/l)

0.02

Cu leached (mg/l)

10 0.15 0.06

0.015 8

0.1 0.04 6

0.01

4

0.05 0.02

0.005

2

0 0 0

Cu Ni Pb Zn

0

Metals leached during TCLP testing from treated Untreated ACT

and untreated soil from an ex-pyrotechnics site

Treatment of heavy metal contaminated soil. © Carbon8 Systems Ltd, 2022 Treatment of soil washing residues, Olympic Park
Applicable residues
 

 

 

 

 

 

 

Carbon Sequestration Potential

The total amount of CO2 that could be sequestered globally through C8S

Accelerated Carbonation Technology processes is theoretically 1,045Mt per

year but 500 Mt per year more realistic

Coal Cement CDW Biomass Steel Oil shale EfW Paper & pulp

411Mt 192Mt 178Mt 174Mt 79Mt 5Mt 4Mt 1Mt

All figures based on annual production of residues, excluding legacy wastes

This information is based on external academic papers as well as internal know how

© Carbon8 Systems Ltd, 2022
 

 

 

Air Pollution Control Residues

• Thermal residues from Energy from Waste

Plants: Air Pollution Control residues (APCr)

• APCr treated using Accelerated Carbonation

Technology

• Treated APCr mixed with binders and fillers

and then pelletised with further carbonation.

• 3 plants in the UK treating APCr under licence

• Use pure CO2delivered in tanker

• Treating 40,000 t APCr /year

• End of Waste acceptance by Environment Agency

• Demonstration of CO2ntainer for treatment of

APCr in 2020 at AVRin Netherlands
 

 

 

 

 

 

 

 

Use of Flue Gas derived CO2

• Work with UCL in 2006 showed that higher

concentrations of CO2 resulted in lower

conversion rates

• Thus, there were benefits to using flue gas

derived CO2 directly

• This was supported by our work in 2010 using

landfill derived CO2

• Pure CO2 is expensive and can be in short

supply

• In 2018, returned to using point sources of CO2
 

© Carbon8 Systems 

Early deployments of the CO2ntainer

14 90

12

10

8

CO2 conc. by volume

6

4

2

0

Weight

%

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0

80

70

60

50

40

30

20

10

0

0 30 50 60

Reaction time

Time (minutes)

CaCO3 Ca2SiO4 Ca(OH)2 Ca2SiO4 IN OUT Absorption

Ltd, 2022
 

 

 

 

 

 

 

 

 

 

The CO2ntainer – Carbon Capture in a Box

Introducing the Plug ‘n Play CCUS solution: retrofittable into any existing industry plants

CO2 

capture Direct capture solution,

1,500tonnes– 4,000tonnes CO2 per annum

12,000 tonnes Waste treated per annum

100% automation Manual or automatic operation

Seamless integration No interference with production

CO2ntainer at Vicat Group in Montalieu, France

© Carbon8 Systems Ltd, 2022
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

© Carbon8 Systems Ltd 2021

Cement By Pass Dust

Exhaust Gas • By-pass dust produced primarily as a result of Cement Kiln Dust 

change to alternative fuels

Raw Meal 

• Chlorides etc in the refuse derived fuel need to be

prevented from getting into the clinker

• Can cause clogging in the kiln

• Annual global cement production is 4100 Mt (2020)

Bypass Dust • Production of CKD and CBD between 250 and 400 Calciner 

Mt per year.

• >40 Mt of CO2 could be captured per year. Potential Clogging Rotary Kiln Kiln Burner • Assuming an average of 15% CO2 reactivity

Condensation of sulfur • Compared with using natural aggregate the use and chlorine Vaporisation of chlorine 

CBD aggregate in concrete can lower its the overall Partial vaporisation of sulfur Cement Clinker 

carbon footprint by >10%.

,
Properties of By-pass Dust

min max average 

CO2 uptake (wt%) 7 33 18

Loose bulk density (kg/m3) 276 910 625

Chloride content (wt%) 2 23 10

 

 

 

 

 

 

 

 

• By-pass dust variable between plants and within a plant

• Variable composition of fuel and amount burnt

• Undertake “mix design development” project for each new plant

• Assessment of technological and economic viability of CO2ntainer deployment

© Carbon8 Systems Ltd, 2022
Properties of Aggregate

Vicat ACT 

aggregate 

Leca 

CO2 uptake (weight %) 10-15% -

Strength (Mpa) >1.0 O.9

Los Angeles Abrasion (%) <40 Not tested

Loose Bulk Density (kg/m3) <1100 350

Water absorption (%) <25 <30

Water soluble chloride (%) <2.0 <0.04

Acid soluble sulfate (%) <0.5 <0.5

 

 

 

 

 

 

 

 

© Carbon8 Systems Ltd, 2022
 

 

 

 

Applications in Construction

Concrete blocks

Ready-mix Concrete

Asphalt

Pipe bedding

Floor screeds

© Carbon8 Systems Ltd, 2022
 

 

 

 

 

 

 

 

 

 

 

Benefits – Economic sustainability

A circular solution to industrial waste and CO2 capture

Carbon footprint reduction 

Permanently and safely store CO2 from point

source

2

© Carbon8 Systems Ltd, 2022

Direct cost savings 

Divert residues from landfill with sustainable

waste management and offset associated

costs

1

High-value manufactured products 

Enable circularity through implementing

sustainable alternative building materials in

production or market them for a profit

3
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