The Distribution of Arsenate and Arsenite in Shoots and Roots of Holcus lanatus is Influenced by Arsenic Tolerance and Arsenate and Phosphate Supply

The recent discovery that phytochelatins are important for arsenic (As) detoxification in terrestrial plants results in the necessity to understand As speciation and metabolism in plant material. A hydroponic study was therefore conducted to examine the effects of different levels of phosphate and arsenate [As(V)] on As speciation and distribution in tolerant and non-tolerant clones of Holcus lanatus. Speciation of As in tissue (using high-performance liquid chromatography-inductively coupled plasma mass spectrometry) revealed that the predominant species present were the inorganic As species (As(V) and arsenite [As(III)]), although small levels (<1%) of organic As species (dimethylarsinic acid and monomethylarsonic acid) were detected in shoot material. In roots, the proportion of total As present as As(III) generally increased with increasing levels of As(V) in the nutrient solution, whereas in shoots, the proportion of total As present as As(III) generally decreased with increasing levels of As(V). H. lanatus plants growing in the high-phosphorus (P) (100 μm) solution contained a higher proportion of As(V) (with regard to total As) in both roots and shoots than plants supplied with low P (10 μm); in addition, tolerant clones generally contained a higher proportion of As(V) with regard to total As than non-tolerant clones. The study further revealed that As(V) can be reduced to As(III) in both roots and shoots. Although the reduction capacity was limited, the reduction was closely regulated by As influx for all treatments. The results therefore provide a new understanding about As metabolism in H. lanatus

In situ monitoring of mineral waste carbonation under high CO₂ pressure

The treatment of fine grained steel slags with CO2 at elevated pressure and temperature conditions is a process that allows to produce high quality building materials. In this process the mineral waste is stabilized and CO2 is permanently sequestered in the form of carbonates. However, in order to enhance the sequestration potential and further improve the quality of the building materials, it is essential to understand the carbonate formation and the impact of this process on the pore network in the building material. A better understanding of the process will translate in improved building materials and enhanced CO2 sequestration. In this study, the process of carbonate formation stainless steel slags is investigated. The carbonate formation in the pore network of the fine grained steel slags is monitored during CO2 exposure in a specially designed mini reactor using high resolution X-ray tomography (HRXCT). The use of this non-destructive technique allows to visualize and quantify the amount carbonate that is precipitated inside the building material. The technique also provides a 3D representation of the pore network from which the porosity and permeability reduction through time is deducted. This new approach using HRXCT provides new insights in the carbonation process and provides better input parameters for modelling of carbonation models

Carbonate-bonded construction materials from alkaline residues

Accelerated carbonation is a rapidly developing technology that is attracting attention as it uses CO2 as a binder to make construction materials. Originally stemming from geochemical and environmental research into CO2 sequestration or waste remediation, accelerated carbonation has been developed into a technology that enables to transform alkaline precursors into products that meet technical requirements for use as aggregates or shaped blocks. Alkaline precursors can be manufactured from primary resources or derived from industrial residues: a.o. metallurgical slags, incineration ashes and concrete recycling residues are prone to carbonate under controlled conditions. Moist carbonation of shaped Ca-silicate rich precursors at elevated curing temperature and CO2 concentration or pressure has delivered the most promising results so far. This letter presents an overview of current accelerated carbonation approaches to make carbonate bonded construction materials from alkaline residues. The general carbonation mechanism is explained and two application routes are exemplified: i.e. production of lightweight aggregates and compact blocks by accelerated moist carbonation

Environmental assessment of CO2 mineralisation for sustainable construction materials

peer reviewedMineral carbonation is a carbon utilisation technology in which an alkaline material reacts with carbon dioxide forming stable carbonates that can have different further uses, for instance as construction material. The alkaline material can be a residue from industrial activities (e.g. metallurgic slags) while CO2 can be recovered from industrial flue gasses. Mineral carbonation presents several potential environmental advantages: (i) industrial residues valorisation, (ii) CO2 sequestration and (iii) substitution of conventional concrete based on Portland cement (PC). However, both the carbonation and the CO2 recovery processes require energy. To understand the trade-off between the environmental benefits and drawbacks of CO2 recovery and mineral carbonation, this study presents a life cycle assessment (LCA) of carbonated construction blocks from mineral carbonation of stainless steel slags. The carbonated blocks are compared to traditional PC-based concrete blocks with similar properties. The results of the LCA analysis show that the carbonated blocks present lower environmental impacts in most of the analysed impact categories. The key finding is that the carbonated blocks present a negative carbon footprint. Nonetheless, the energy required represents the main environmental hotspot. An increase in the energy efficiency of the mineral carbonation process and a CO2 valorisation network are among the suggestions to further lower the environmental impacts of carbonated blocks production. Finally, the LCA results can promote the development of policy recommendations to support the implementation of mineral carbonation technology. Further research should enable the use of mineral carbonation on a broader range and large volume of alkaline residues

Environmental assessment of CO2 mineralisation for sustainable construction materials

status: Published onlin

Artificial intelligence for waste characterisation and real-time mass balances

Urban mining is defined as the process of reclaiming raw materials from spent products, buildings and waste and is often put forward as one of the solutions to fulfill our ever increasing demand for materials in highly urbanized areas. The strong temporal, seasonal and regional variations of this waste and its intrinsic heterogeneity are a source of high insecurity and risk for the waste processing industry and puts high pressure on the applied processing technologies. Processing plants should therefore continuously adapt to changing input variations to warrant optimal material valorisation. However, due to the lack of suitable (continuous and fast) characterisation methods this is often not possible. As a consequence, the input variability translates directly to the output streams. The variable quality of secondary materials strongly decreases market interest in these materials and hampers the transition to a circular economy. Quality assessment is traditionally performed by superficial visual inspection or manual separation of too small and possibly non-representative samples, and is therefore often not reliable. In addition the task is tedious, time-intensive, subjective and rather unpleasant. To meet this need for a rapid, continuous, automatic, objective and reliable characterisation technology, a device, combining different sensor types, was built. The technology will allow to optimize existing and to develop new recycling processes, and assess secondary raw material quality, based on accurate, representative and objective data. Current sensor techniques in waste characterization mainly focus on surface properties, e.g. near-infrared, colour, hyperspectral or X-ray fluorescence. However waste material is often dirty and the surface properties are not representative for the bulk of the material. To overcome this limitation, a technology that sees “through” the material was adopted: X-ray Transmission (XRT). By measuring at two energy levels, called Dual Energy (DE-XRT), it is possible to determine material properties such as the average atom number and density. To accurately interpret the information gathered by DE-XRT, extra information such as the 3D shape and volume of the object is employed. This is measured by 3D laser triangulation (3DLT). 3DLT is a well-known technology in the industry that can measure the geometry of object at high resolution (sub-mm) using a laser and a camera. The combination of these technologies allows to fully characterise a waste stream on the level of individual particles with respect to volume, mass, shape and composition. Using this information, accurate mass balances can be measured. In addition, the material and shape measurement is complemented by an RGB detector, bringing in additional information which can be used to better differentiate the materials using image processing and machine learning algorithms. The development of methods to extract the relevant information from the sensor data is the topic of ongoing research. The technology will allow to optimise existing and to develop new recycling processes, and assess secondary raw material quality, based on accurate, representative and objective data. During the conference, a real demo case will be presented based on mixed construction and demolition waste typically collected by SUEZ in Belgium