Although steel slags are classified as non-hazardous thermal waste according to the decree 2002-540 and “United States” (US) “Environmental Protection Agency” (EPA), it is well known that most metals they contain are quite toxic to living organisms and may pose serious environmental issues.
In France, the “Centre Technique de Promotion des Laitiers sidérurgiques” (CTPL) estimated that the total available stock of slags (including all slag families) was about 17 480 600 tons at the end of 2015. Thus, reusing steel slags appears the option of choice to ensure their sustainable management as well as to decrease their environmental concerns.
Consequently, the goal of the HYPASS project is to promote more consistent approaches for steel slag management. Particularly, HYPASS will focus on technological innovations for both an ecocompatible and cost-effective recovery of strategic metals. At its core is the development of a novel recovery process integrated within a policy of safeguarding the environment. HYPASS will be tested on a selected case study: the Industeel France ArcelorMittal site, situated at Châteauneuf (Loire), with an estimated stock of 500 000 tons of “Electric Arc Furnace” (EAF) slags, whose principal “Strategic Metals” (SMs) are: Cr2O3 (± 2,4 %), V (± 1500 ppm), Mo (± 500 ppm) and Zn (± 500 ppm). Notice: this slagheap belongs to the SAFIR network and, as such, is easily available for research programs.
The project will be essentially developed at two levels:
- technologically: research will be performed at a “laboratory scale” to develop a process based on physical (pre-concentration of the mineral matrix) and hydrometallurgical principles (under alkaline conditions) for extracting a significant fraction of strategic metals from slags. In the case the mineral matrix resulting from the hydrometallurgical process would not meet the environmental acceptability criteria for a safe re-use in the civil engineering field [defined by SETRA], HYPASS will promote the use of a phytomanagement approach to reduce the environmental risk of secondary waste;
- environmentally: through the application of multidisciplinary integrated methodologies, direct field techniques, and acquisition of preliminary informations, to reduce the geological uncertainty and evaluate the possibility of SMs (Cr, V, Mo, etc.) recovery at a large scale. The data analysis will allow understanding the geographical scenario (far and near-field analysis) of slag deposits at a national scale, collect the information of mineralogical association in terms of SMs recovery and incorporate the mineral related research to understand how this information can be used in exploitation and environmental impact assessment. To help identifying potential treatment methods and economically viable solutions for reuse, HYPASS will develop a tool enabling decision-makers and operators to simulate steel slag management and test the consequences of different treatment options in terms of financial costs (direct/indirect) and environmental impact.
The overall HYPASS objectives are related to SMs recovery and slagheap reclamation and rehabilitation. They can be splited into three categories, as listed below:
1. Technical objectives:
- to evaluate the twofold sustainable and cost-effective technologies (hydrometallurgy/phytostabilization) that HYPASS will promote for an eco-friendly recovery of valuable elements (SMs);
- to conduct “Life-Cycle Assessment” (LCA) for processing methods and assessing long-range sustainability;
- to develop a “Decision-Support Tool” (DST) to help identifying new waste treatment methods and economically viable solutions.
2. Social and societal objectives:
- to increase public awareness and to inform, advice and/or invite stakeholders, media, policy makers and experts through the channels of symposia, conferences, workshops;
- to assess the social impact of existing steel slag dumpsites on the local communities and their attitudes and interests related to the proposed valorization of these waste;
- to set up a “Project Advisory Board” (PAB) consisting of the HYPASS partners, the steelmaking industry and experts of research institutes;
- to reduce the dependence of import of SMs to European countries and increase industrial competitiveness;
- to create new jobs due to the possibility to economically operate the dumpsites.
3. Safety, health, environmental and quality objectives:
- to assess the environmental context in which the exploitation of old tailings will take place in terms of environmental impact, industrial viability and as a possible socio-economic resource;
- to monitor the environmental impact of the newly steel slag processing technology;
- to optimize the material cycle (minor use of natural resources for road construction and their substitution with recycled EAF slag, minor quantity of EAF slag dumped and costs of slag handling);
- to reduce the environmental impacts associated to steelmaking activities and waste disposal;
- to increase the efficient re-use of steel slags and hence reduce CO2 footprint;
- to identify and reduce the potential health hazards and sanitary risks for directly involved personal and urban environments.