199 research outputs found
Recommended from our members
Homogeneous catalysis of the accelerated carbonation of Portland cement
A mechanism proposed for the accelerated carbonation of Portland cement has shown how the reaction proceeds through gaseous, liquid and solid phases in 9 distinct sequential steps. The overall speed of reaction is thus determined by the slowest step, and we have found that solvation and hydration of CO2 in water is commonly the rate-limiting step in the carbonation process. The literature suggests that the speed of this step might possibly be increased by three different classes of chemical 'enhancers' of CO2 hydration: (1) inorganic oxy-anions such as hypochlorite (ClO– ) or sulphite (SO32–) which act as Lewis bases to CO2; (2) organic solutes which form anions at alkaline pH, such as sugars and polyhydric alcohols; or (3) amines and alkanolamines, which may exert catalytic action by producing carbamates with CO2 by either zwitterion formation or charge-transfer. This paper explores these options in detail, supporting theoretical predictions with precise measurement of the rate of CO2 uptake in a 'eudiometer', to determine whether such rates might be beneficially enhanced in the carbonation of hydraulic binders and wastes, or in CO2 capture by mineral sequestration
Recommended from our members
Carbon8: Combined carbon capture and waste treatment – A commercial reality
Waste valorisation is essential to ensure future sustainability. However, often technologies are either undeveloped, remain uneconomical, or hindered by legislative barriers. Using technology developed by Carbon8 Systems Ltd, industrial thermal residues can be solidified and stabilised in a hardened pellet form that can be a direct substitute for natural aggregate e.g. for the production of concrete construction blocks. The route to commercialising the technology, which has required demonstrating the transition from hazardous waste feedstock to safe usable product, has been difficult and complex. The aggregates produced were rigorously tested and finally given ‘end-of-waste’ designation by the Environment Agency. In early 2012, a bespoke commercial plant was commissioned at Brandon in Suffolk, UK. In 2014, a second production line was added to the Brandon facility, increasing its capacity to 60,000 tonnes per year. The ACT-produced aggregate is carbon negative as it contains more imbibed carbon than is generated by its production. Consequently, concrete construction blocks produced can also be carbon negative, and are marketed under the name ‘Carbon Buster’. Plans are at an advanced stage for the construction of a second production facility in the UK. This is scheduled to be operational by late 2015
Recommended from our members
Carbon negative: First commercial application of accelerated carbonation technology
Carbon dioxide gas can be used as a resource to rapidly harden cementitious materials and manage the risks associated with hazardous waste and contaminated soil. The process is known as Accelerated Carbonation Technology or ACT. Carbon dioxide primarily combines with calcium and/or magnesium minerals present in many industrial thermal residues to form carbonates; this reaction can also be promoted by the addition of, for example, Portland cement. Carbon8 Systems Ltd. was formed in 2006 as spinout-company of the University of Greenwich to commercialise ACT. Carbon8 has applied ACT to hazardous wastes in the production of non-hazardous construction products.By using the Carbon8 process, industrial thermal residues are solidified and stabilised in a hardened pellet form. The pelleted product is a direct substitute for natural aggregate, and can be used in the production of concrete construction blocks. From 2009 to 2012, a series of pilot and full-scale demonstrations of the technology were carried out. The aggregates produced were rigorously tested and given ‘end-of-waste’ designation by the Environment Agency. In early 2012, a bespoke commercial plant was commissioned at Brandon in Suffolk, UK, operated by Carbon8 Aggregates Ltd. This plant, the first of its kind anywhere in the world, produced 24,000 tonnes of aggregate from municipal solid waste incineration (MSWI) air pollution control residues (APCr) in its first year. In 2014, a second production line was added to the Brandon facility, increasing its capacity to 50,000 tonnes per year. The aggregate is supplied to Lignacite, the UK’s largest independent concrete block manufacturer, and other companies. The ACT-produced aggregate is carbon negative as it contains more imbibed carbon than is generated by its production. Consequently, the concrete construction blocks produced by Lignacite are also carbon negative, and are marketed under the name: ‘Carbon Buster’. Plans are at an advanced stage for the construction of a second and third production facility in the UK. These are scheduled to be operational by mid-2015 and will increase aggregate production to 200,000 tonnes per year. The present work discusses the development of the Carbon8 process and describes the commercial application of accelerated carbonation technology for the production of sustainable carbon-negative construction materials
Recommended from our members
Global Environment Outlook GEO-6: Assessment for the Pan-European Region
Recommended from our members
Low cost urban wastewater infrastructure for environmental sustainability across Caribbean small island developing states (SIDS)
Effluent Dominated Hydrosystems (EDHs) across the Caribbean primarily consist of surface water systems affected by discharged treated and possibly untreated runoff from urban and agricultural zones in addition to wastewater catchments. These urban water bodies are precious and vital natural resources beneficial to the Caribbean’s economy, its environment and revitalisation. Human activities influence whether a hydrosystem consists of problems including excessive withdrawal for potable water supply, water quality, emerging contaminants from untreated stormwater runoff or wastewater. Land use patterns are one of the key driving forces behind changes in hydrology for EDHs. Runoff from agricultural land has also resulted in substances such as farm chemicals, petroleum products, nutrients and organic matter being washed into the surround EDHs. Historically, many industries across Trinidad and Tobago have been developed nearby natural hydrosystems with discharging pre-treated effluents directly into the water and transported away downstream. While such practices have been semi-regulated for several years by the Environmental Management Authority (EMA) for Trinidad and Tobago, several EDHs still consist of large amounts of pollutants present in sediments. This project evaluates the application of combined Biological and Photochemical (B-P) technologies as a low cost wastewater option for Small Island Developing States (SIDS) in the Caribbean. The application of B-P treatment for waste streams can significantly reduce industrial waste treatment cost, the water rates for farming and improve water quality in EDHs. The programme of research and implementation conducted by the University of Greenwich and the University of Trinidad and Tobago evaluates remediation technologies using two treatment processes (i) Biological and (ii) Photochemical. Although some organic contaminants can be degraded through biological process, many other composed synthetic compounds are non-biodegradable and hence the photochemical process will also be examined. The biological process is utilised like a pre-treatment step to enhance the photo-degradability and eliminate the toxicity of the effluents, whereby the total mineralization of contaminants would be completed in the photochemical process. The biological reactors are characterised by anaerobic respiration using pollutant-reducing bacteria as a terminal electron acceptor. These bacteria can thrive in human-impacted environments impacted by sewage or urban drainage. The photoreactor implements heterogeneous photocatalysts (readily available, cheap, non-toxic and inert semiconductors) such as Titanium Dioxide (TiO2). In this process TiO2 absorbs solar energy and transfers photonic energy to mobile toxic constituents. Various sources wastewater are being processed through the B-P reactors studying the kinetics of degradation
Recommended from our members
Novel permeable pavement systems utilising carbon-negative aggregate
The use of commercially produced Carbon-Negative aggregates from Carbon8 (a British company which applies patented Accelerated Carbonation Technology (ACT) to solidify waste residues producing useful eco-friendly aggregates) is being investigated in the Caribbean islands of Trinidad, Tobago and St. Lucia. Typical construction of the subbase layer of pavements in the Caribbean include layers of virgin aggregate material (gravel, pea gravel) on which the base course layer is located. These materials are usually unbound granular (crushed stone, crushed slag, crushed concrete, slate) or cement-bound. Permeable Pavement Systems (PPS) have emerged over the years using various quality of subbase materials including large pieces of rocks and concrete. For the first time in the Caribbean, the design, construction and implementation of such pavement systems is being carried out. The novel pavement systems consist of permeable or pervious concrete paving blocks and the Carbon-Negative aggregates in the sub-base as an innovative and effective method of providing structural pavements, whilst allowing urban stormwater runoff to infiltrate naturally into the pavements (mimicking the hydrologic cycle) into the base/sub-base reservoir for urban runoff attenuation and an overall reduction in stormwater discharge. These pavement systems are being considered to reduce the overall carbon footprint on the construction and implementation phase of pavements, in addition to reducing surface water flooding in several towns and cities across these Caribbean Small Island Developing States (SIDS). The project includes ongoing experimental assessment of the Permeable Pavement Systems (PPS) using Carbon-Negative aggregates versus conventional pervious pavements from a water quality, structural integrity and hydraulic perspective. Stormwater is being collected from various towns and cities across the islands and applied uniformly over the pilot scaled permeable pavements using a rainfall simulator. The permeable pavements stormwater treatment efficacies are being evaluated for the removal and retention of nutrients (total nitrogen and total phosphorus), heavy metals (zinc, lead, copper, cadmium), suspended solids and turbidity. The hydraulic performance, flow through and clogging patterns of these pavements are also being measured over a simulated 10-year period of sediment loading. Load bearing and deflection test are being carried out on the various pavement designs to assess its structural integrity and load bearing capacity. Static and dynamic loads applied representing the maximum contact pressure varying from 0.03 to 1.7 MPa over the cross-sectional area of 0.2 m2 (permeable pavement surface area). These contract pressures represent various loads from heavy vehicles, cars, pallets and handling equipment of industrial areas (ports)
Recommended from our members
Carbon Dioxide Sequestration in Wastes: The SAPICO2 Project
The SAPICO2 project is an INTERREG IVA cross channel collaboration established to develop new technologies utilising accelerated carbonation for the creation of eco-construction materials from solid wastes. Over three phases, the project has identified carbon dioxide reactivity of solid wastes, produced prototype-construction materials (from these wastes), and manufactured bulk samples of carbonated products. The project aims to introduce carbonated building products into continental Europe, by demonstrating the potential of this emerging technology to meet the EU sustainability agenda. By collaborating with the major bodies responsible for environmental matters, it is hoped that new policy and mechanisms can be developed that facilitate the full commercial valorisation of waste using gaseous CO2
Recommended from our members
Accelerated carbonation for the treatment of landfilled cement kiln dust
Accelerated Carbonation Technology (ACT) can be used to treat a wide range of alkaline wastes and metal-contaminated soils by exposing them to a carbon dioxide rich atmosphere in a way that promotes the massive precipitation of calcium carbonate. The material obtained has improved physical and chemical characteristics. This work presents the characterisation of historically deposited cement kiln dust (CKD) and its potential reactivity with carbon dioxide gas. The CKD investigated originated from a landfill, up to one hundred years old. The bulk chemical composition was determined by X-ray Fluorescence (XRF), the mineralogy of the untreated and carbonated CKD by X-ray Diffractometry (XRD) and the change in microstructure upon carbonation was examined by Scanning Electron Microscopy (SEM/EDS). Key characteristics of treated and untreated CKD such as carbon dioxide uptake, pH, and moisture content are presented and discussed
Recommended from our members
SAPICO2: Production of sustainable construction aggregates through cementation with carbon dioxide
The EU-funded project, Sustainable Aggregate Production with Imbibed Carbon Dioxide (SAPICO2) is an INTERREG IVa Channel Programme examining the development of eco-construction materials made from various carbonate-able wastes residues normally disposed to landfill. The partnership involves the University of Greenwich (UoG), the University of Picardie Jules Verne (UPJV), and Carbon8 Systems (a UoG spin-out company). The project applies accelerated carbonation technology (ACT) to facilitate waste valorisation in the production of manufactured carbonated materials that have re-use potential. SAPICO2 has investigated more than 100 wastes originating in NW France and the SE UK (Channel Region), with a view to explore new ways in which carbonation can be applied beneficially. Wastes have been collected and characterised for their chemical and physical properties, very importantly for their ability to react/combine with CO2 gas. It is shown that with careful control of a carbonation process reaction conditions it is possible to treat waste to give it value and re-use potential and thus, divert it from landfill into the materials supply chain. Such an outcome meets the needs of the developing European ‘circular economy’. The final part of the SAPICO2 project involved the production of bulk samples of carbonated materials for product testing/evaluation in France
- …