Environmental assessment of foundry sand based brick in different steps of its life-cycle using leaching tests
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Engineering - Poster (CPD&E - P)
Keywords: foundry sand, brick, leaching tests, sustainable process, recycling
The incorporation of waste materials into the production cycles is an interesting alternative in the modern industry, which leads to an economical profit and considerable reduction in environmental impact. The aim of this work is the study of the reutilisation of waste materials as foundry sands, in order to replace raw materials partially and for preventing possible pathological behaviour. The used waste are often landfilled, despite having relatively high levels of some heavy metals of potential environmental concern; therefore there is now increasing incentive to develop economically viable reuse and recycling options.
The utilisation of heavy metal contaminated waste as additives in brick manufacturing has become more and more established. Waste materials such as, tannery sludge, electric insulators, steel dusts, sewage sludge incinerator ash, dredged harbour sediments, petroleum sludge, coal fly ash and slag are used as substitutes for natural clay in the brick industry. Since, even natural clays contain quantities of metals, which form compounds during brick burning processes. It is important to note one advantage of this process, thermal treatment, is that organic compounds are completely destroyed in the course of brick production, and most inorganic contaminants become immobilised in the silicate matrix of the bricks. This gives the opportunity to admix waste materials containing various organic or inorganic contaminants into the common raw material to overcome environmental problem.
Foundry Sands (FS) generated from casting of ferrous pieces in the process of manufacturing of cores and moulds are reused in 90-95% depending on of the recycling system used. But, finally the sands lost their chemical-physical characteristics and are disposal as waste materials in landfill. In Spain their great volume is an important problem. The composition of the FS is silica, chromite, cement and resins, mainly. However, it is a material of silica of high fineness and homogeneity, which incentives reuse options. If the current practice of the depositing solidified/stabilised steel dusts and foundry sands in landfills is maintained, landfill capacity is limited. Alternative strategies of waste management should be investigated to avoid the construction of new landfill. Producing bricks using waste materials could be a technically feasible alternative.
The absence of common specific legislation in European Union, related to environmental requirements for secondary construction products, is an important disadvantage. The environmental assessment of new construction materials should not be based on the total concentration of the metals, since many studies have found that is not systematic correlation between the total concentration of elements and the release to the environment. Since the release into the environment is controlled by transport through the water phase, leaching tests are suitable to assess the environmental impact of this type of products. The CEN (European Committee for Standardisation) started a harmonisation project in which new EU leaching tests are being developed. These tests can be classified in practise as characterisation, compliance and on-site verification tests. From a technical point of view leaching tests are classified as tests aimed at equilibrium conditions during leaching, e.g. TCLP and EN12457; or tests aimed at the dynamic aspect of leaching, e.g. NEN 7345 and prEN14405.
The aim of the present work has been the study of the leaching behaviour of mixtures clay/waste sands, in different steps of its life-cycle. The long-term leaching test NEN 7345, proposed as a Dutch regulatory test, has been used to analyse the behaviour in its service-life, as monoliths samples. The leaching test for granular materials EN 12457, proposed by Landfill of Waste Directive, has been used to analyse the behaviour in the so-called “end of step” as demolition material. The release mechanisms have been studied allowing the material environmental evaluation and providing information about long-term effects.
Presented Wednesday 19, 13:30 to 15:00, in session Chemical Product Design & Engineering - Poster (CPD&E - P).
