The construction and demolition wastes (C&DW) frequently are abandoned in private properties, roads, and landfills or collected by non-licensed companies. In Portugal they are few recycling plants operating with this residue, and this work makes the bridge between the mechanical recycling process developed on semi-industrial scale, and the recycling products characterization process developed on laboratorial scale. The main goal of the present work is the quality improvement of the recycled aggregates produced by a construction and demolition waste recycling pilot plant with 50 ton/h located in Montemor-o-Novo. Process operations are the hammer mill comminution, magnetic separation and sieving (bar sieves: 0-4mm, 4-8mm and 8-12mm; and square sieves: 12-22mm, 22-31mm and above 31mm). In order to improve the magnetic separation process, several tests with different distances between the magnet and the conveyor belt were made (21-31cm). On the other hand, to improve the quality of the produced aggregates, the bar screen size fractions were analyzed, according to the Portuguese Standard (NP EN 933-1 2000). The most efficient distances for the magnetic separation process were identified as between 21 and 27cm, with efficiency between 85% and 90% respectively. According to the histograms, the more frequent red aggregate from 0-4mm size fraction are +0.425-0.850; +0.850-1.7 and +1.7-3.35. From the 4-8mm red aggregates, the more frequent size fractions are +4.75-6.7 and +6.7-9.95. Finally, from the 8-12mm red aggregates, the more frequent new size fractions are +6.7-9.50 and +9.50-13.20. Sieving results obtained from cumulative curves for red aggregate showed an decrease in the mass % amount for the size fractions: 0-4mm: 97%, 4-8mm:76% and 8-12mm: 56%. The results from cumulative curves for grey aggregate showed a light decreased in the amount mass % for the size fractions: 0-4mm: 90%, 4-8mm:56% and 8-12mm: 60%.
In this study chemical leaching with sulphuric acid has been performed on 10 selected
oxidic by-products in order to determine their neutralising capacity. The ultimate aim with this work
is to replace the lime or limestone normally used in bioleaching operations to maintain pH at 1.5,
the optimum pH-level for bioleaching microorganisms, with oxidic by-products. The investigated
by-products includes three ashes from combustion for energy production, five slag samples from
ore and scrap based steelmaking, an EAF dust and mesa lime from a paper and pulp industry, slaked
lime (Ca(OH)2) was used as reference material. The neutralising potential of the by-products were
evaluated by leaching them with sulphuric acid and comparing the amount of acid needed to that of
the reference. Most of the by-products examined had good neutralisation potential and some had
even higher capacities than Ca(OH)2. Neutralisation kinetics were lower for some slag products due
to slow dissolution of some of the silicates present, but kinetics are considered good enough since
stirred tank bioleaching is a relatively slow process. Zinc recoveries from the zinc containing
materials were high, which thus is an additional benefit if these materials were to be used for
neutralisation in a bioleaching process for zinc recovery.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.