Slag as feedstock to extract high added value metals

Slag as feedstock to extract high added value metals

Securing reliable and unhindered access to raw materials is important for the EU. In the EU, there are at least 30 million jobs depending on the availability of raw materials. The European Commission’s actions to ensure a sustainable supply of these materials can be divided into two interlinked parts: the Raw Materials Initiative and the European Innovation Partnership on Raw Materials.

In 2008, the Commission adopted the Raw Materials Initiative, which set out a strategy for tackling the issue of access to raw materials in the EU. This strategy has three pillars which aim to ensure:

  • Fair and sustainable supply of raw materials from global markets
  • Sustainable supply of raw materials within the EU
  • Resource efficiency and supply of “secondary raw materials” through recycling

The strategy covers all raw materials used by European industry except materials from agricultural production and materials used as fuel. Ensuring sustainable access to these raw materials is crucial to the competitiveness and growth of the EU economy and to the objectives of the Europe 2020 strategy.

The Commission has also published a list of 54 critical raw materials in the EU.

In this ambition, the pilot 1 of RESLAG project aims at extracting critical metals from a used slag by combining mechanical and physical technologies developed by Optimum Cement and CEA Tech.

In the frame of the Pilot 1 demonstration, a slag containing about 10 wt.% REEs from spent NiMH batteries by smelting is supplied graciously by the French batteries recycler SNAM. Indeed such way of valorization is economically relevant only for rich critical metals content slag (>1-2 wt.%) or other wastes.

The whole process of Pilot 1 is a multistep treatment of slag by mechanical crushing and milling to achieve a fine slag powder fraction below 500 µm and by a chemical treatment based on a selective leaching and a chemical separation from a Sequential Simulated Moving Bed Chromatography (SSMB) equipment.

The mechanical operation is carried out from industrial scale Optimum Cement facilities and the chemical treatment by CEA Tech mostly from SSMB equipment developed through the RESLAG project in collaboration with the French SME SEPROSYS.

The collaborative work between SEPROSYS and CEA Tech is firstly focused on the identification and the selection of the best media to separate REEs from other low value metals (Al, Fe, Ca, K, Na…) of the slag leached by an acid, then on the design and the setting of equipment to perform a good separation with a high purity (>99.5%) and a low reactant and water consumption and a high treatment capacity (1 L/H).

SSMB technology is a continuous process optimally used in food ingredient and bio-industrial applications for the separation of two compounds, or for the binary fractionation of complex mixtures. Such technology is also relevant for the chemical separation of metal species in a solution.

SSMB is achieved by the use of a multiplicity of columns in series and a complex valve arrangement, which provides for flow of the feed mixture and solvent, and “eluent” or “desorbent” feed at any column. The valving and piping arrangements and the predetermined control of these allow switching at regular intervals the sample entry in one direction. The solvent entry in the same direction but at a different location in the continuous loop, whilst changing the fast product and slow product takeoff positions to also move in the same direction, but at different relative locations within the loop.

The 6 columns SSMB equipment located at Grenoble CEA Tech center is designed to be flexible, able to address various chemical systems by changing separative media made of ionic exchange resin and the parameters setting from a lab scale study. Such pilot could be relevant for most slags containing critical metals or other spent technologies containing critical metals in a significant amount.

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