In 2018, the Group chose to strengthen its efforts to better repurpose mineral resources through the formalization of a new circular economy action plan. The objective is to recover, through a range of innovative actions over the 2019-2023 period, more than 2 million tons of materials considered until that date as residues or waste rock. Four projects have been launched to contribute to this goal. Three of them have already produced results in terms of tons recovered.
Only the Comilog mine (Gabon) and the Tiébaghi and Népoui mining sites (New Caledonia) produce significant quantities of mine tailings resulting from concentration steps by mechanical means. These residues are chemically stable and do not constitute hazardous waste for the environment. In New Caledonia, the residues from treatment plants are also commercially repurposed as mining co-products. The characteristics of the small quantities of residues produced in Senegal allow for their return to the natural environment during the reconstitution of the dune. The question of the safety of tailings management structures therefore only arises for the Comilog mine in Gabon.
Among these improvement actions, the Group formalized a new dedicated procedure, "Management of waste storage facilities", in 2020. This procedure follows the fundamental requirements of the "Global Industry Standard on Tailings Management" published in 2020 by the United Nations Environment Programme (UNEP) and the International Council of Mines and Metals (ICMM). Beyond the governance requirements of this standard, the procedure also specifies a certain number of design criteria based on the ICOLD/ANCOLD standards. The aim of the procedure is to standardize, for all operations, the risk analysis and the associated minimum design criteria. Of course, regional regulatory specifications, if they are more restrictive, will be favored. Eramet is thus part of global initiatives aimed at strengthening the safety of tailings management structures through the mining industry. To this end, Eramet is also participating in the initiative launched by The Church of England Pension Board aimed at improving the transparency of reporting on this sensitive subject.
In New Caledonia, nickel extraction involves handling a large volume of waste material (i.e. natural materials that have no financial value). Being able to store these materials in appropriate structures and revegetate them is a long-standing challenge for the company. Over the decades, SLN has therefore developed various solutions to limit erosion as much as possible, as well as its impact on the ecosystem and landscapes. These include:
In New Caledonia, for example, SLN has built washeries (mineral processing plants) which allow the ore to be concentrated without adding any chemicals. These make it possible to repurpose ores initially considered to be marginal, and thus to significantly extend the life of the deposits while reducing the final environmental impact. The concentrated ore produced by these washeries is repurposed either at the Doniambo plant (New Caledonia) or for export to other customer plants, depending on its content.
A facility with new tri-optic technology has been set up at the Népoui mining site (New Caledonia). This makes it possible to more accurately sort residues previously considered as waste rock. Installed over the course of the year, this innovation made it possible to recover 33,000 tons of waste.
Thanks to their stability, these structures guarantee the long-term safety of stored tailings, even in the event of cyclonic rain. SLN's teams also carry out continuous monitoring and external experts regularly conduct audits to verify their condition. Operated directly or outsourced, all of the waste rock dumps meet identical construction and sizing conditions, which are compiled in a technical guide published by SLN, updated in 2012.
Constructed where technically possible, these facilities reduce clearing to a minimum and foster the restoration of sites.
Finally, within the framework of the expansion of low-grade ore exports, SLN (New Caledonia) was able to recover 660,000 tons of ore which had been stored "with due care" in waste rock piles awaiting their possible recovery. The recovery therefore takes place without any additional environmental impact linked to the extraction.
In Gabon, mine wastes are clay fractions of the ore, obtained through a physical separation process involving water scrubbing, without the addition of chemical products. The leaching tests showed that these are inert residues. These residues are stored in 11 ponds (of which 10 are inactive), made up of closed dikes with a maximum height of 16 meters, and a volume of between 1 and 1.5 million m3 inclusive. These structures are not raised: a new structure is built every 18 to 24 months.
The CIM enrichment plant (Gabon) also has a dike that can store the two types of non-hazardous waste associated with the plant: sand (particle size matter between 1 and 20 mm) and finer ore particles (< 1 mm) in the form of sludge. Coarse fractions are used to continuously reinforce its exterior walls (downstream method). The dike and reinforcement, with a combined width of 100 meters and 30 meters in height, contains 3.6 million m3 of sludge.
The Marietta metallurgical plant in the US also has a tailings dam. This is used to store tailings from industrial activities that are now discontinued, but still operated by Eramet. Measuring 35 meters high, the dam has a volume of 4.3 million m3. The structure is regularly inspected by the Ohio department of natural resources. The latest audit was conducted in 2018.
An ilmenite flow initially considered at GCO (Senegal) as a residue was able to be recovered by creating a new commercial product called Ilmenite 56. 61,000 tons of this product have been recovered since 2019.
Non-hazardous mine tailings
An important point is that the mine tailings produced in the mine ore milling facilities in Gabon or on the Népoui and Tiébaghi sites in New Caledonia are chemically stable. In other words, they are not hazardous waste as defined under French regulations. This natural sandy soil is separated from the larger ore using mechanical washing procedures without adding abrasive chemical products.
It should also be noted that every effort is made to recirculate the washing water where possible in order to minimize extractions and discharges into the environment.