The project was divided into three main tasks:
Task 1 : The slags as such with regard to the regulations inside EC and leaching mechanisms.
Task 2 : Improvements of the slags by metallurgical parameters.
Task 3 : Valorization of the slags.
1. WITHIN TASK 1
The behaviour of slags was regarded as such, independently of any scenario of utilization.
It has been shown that total composition is irrelevant for evaluation of the environmental impact assessment, that the differences are due to the solubility control by mineral phases. The positive role of ageing has been confirmed. In fact, the pH which is developed within a specific scenario is the most relevant parameter.
Comparisons which have been made with current regulations (notably the Dutch Building Materials Decree) and with related materials (notably MSWI bottom ash) allow the identification of a potential scope for use.
2. WITHIN TASK 2
It has been looked at various ways of improving the slags by playing with metallurgical parameters : operation conditions in the furnaces, slag tapping at higher temperatures, remelting of the slag, alteration of the speed of cooling, annealing.
Some slight improvements can be pointed out, but they remain limited. Moreover, their implementation at an industrial scale would be unfeasible from an economic viewpoint compared to the stake.
3. WITHIN TASK 3
Different scenarios of utilization have been tested : concrete, bricks, breeze blocks, road construction, from laboratory to large pilot scale.
Technical performances have been measured following different recipes, that is different levels of substitution of slag in place of sand.
It has been shown that, through the use of slags, it is possible to prepare materials that meet the technical specifications without modifying the usual recipes.
The leaching behaviour of slag bearing materials has been measured in different conditions (notably conditions of pH). Thus the environmental impact of various scenarios has been assessed. The strong dependence on pH has been confirmed as well as the positive role of ageing.
Possible utilization of slag in typical scenarios has been pointed out :
- Cement based materials in open air conditions.
- It has been shown on a large scale pilot road using ISF slags that the levels of Zn and Pb release were very low even in extreme hydrological conditions, provided that the formula sand/slag/bitumen be preferred.
EC lead and zinc primary smelters produce and dump every year about 1 Mt of slag at increasing cost. Nearly all these producers together with major potential end users create a R & D consortium whose target is to develop uses of slag in civil engineering and building industry. Independent research institutes joined the consortium to bring their expertise on waste and end product characterization and evaluation, including leaching mechanism.
The major research tasks of the proposal are:
- Slag evaluation and characterization, focusing on heavy metal leachability:
- Comparison of the various leaching procedures in use.
- Investigation of the leaching phenomena in order to develop a leach model.
- Metallurgical optimization of the slags in order to reach the lowest heavy metal solubility, including optimal post treatment to improve particle size distribution, apparent density and such others characteristics needed to use them instead of raw materials.
-Test slags in all fields of application where they could replace significant amount of raw materials: end-products will be characterized and evaluated, leachability and durability will be examined.
The original approach of the proposers results from the wideness of their consortium, allowing a full coverage of all fields where slags could replace significant amounts of quarry or scarce raw materials, and the emphasis they put on the environmental impact of the applications. Successful completion should avoid damping of 1 Mt/y slags in the EC and save an equivalent amount of natural and functional characteristics and degradation resistance of construction materials.
Funding SchemeCSC - Cost-sharing contracts
BS11 8HT Bristol
30175 Porto Marghera Venezia