Wastes and by-products: most residues can become products, but the hazardous dust needs a secure route before start-up

6.1 What an EAF works leaves behind

Steelmaking is efficient in its use of materials. worldsteel’s indicators put the industry’s material efficiency, the share of solid materials converted to products and co-products, at 92.8% in 2024, against 97.6% in 2022 [T01]. On average, each tonne of steel made in an EAF yields about 200 kg of co-products, and slags make up about 90% of the industry’s solid co-products by mass [T02]. The IFC EHS Guidelines give a benchmark of 110 to 180 kg of solid waste per tonne of EAF steel [G03]; most of it is slag.

Our planning model applies these benchmarks to the planned capacities. It assumes 140 kg of EAF slag per tonne of liquid steel (within the IFC solid-waste range of 110 to 180), 15 kg of EAF dust (planning range 10 to 20; the European reference document reports 10 to 30 [G17]) and 20 kg of mill scale per tonne of product (range 15 to 25) [X03][G03]. Figure 6.1 shows the result by phase. For comparison, the Malaysian EAF works reviewed by the IFC in 2026 reports about 6,000 t of EAF dust a year from 600,000 t of steelmaking capacity, or about 10 kg per tonne. It reports about 70,000 t of EAF slag (about 117 kg per tonne) and 18,000 t of ladle slag [T08]. Our planning values are deliberately conservative.

Source: Cameroon Steel planning model, 10 October 2026 [X03]; IFC solid-waste benchmark [G03]; dust planning range [X03][G17]. Indicative values; ladle slag, refractories and minor wastes not shown.

Beyond the three main streams, an EAF long-products works generates several smaller ones:

• ladle-furnace slag;
• spent refractory linings from furnaces and ladles;
• sludges from the water-treatment circuits;
• used oils and greases;
• electrode stubs;
• packaging;
• workshop and office waste;
• during construction, cleared vegetation, spoil and building waste.

Table 6.1 lists each stream with its nature, first-choice outlet and fallback. The assessment will quantify the minor streams once the design is fixed.

Table 6.1 Residue register: nature, first-choice outlet and fallback (planned)

Source: IFC EHS Guidelines [G03]; worldsteel co-products [T02]; Décret 2012/2809/PM [L06]; Cameroon Steel planning model [X03]. Quantities indicative and rounded.

6.2 Slag: from residue to aggregate

EAF slag forms when lime and other fluxes combine with the oxides of the metallic charge. Once cooled and crushed it is a hard, dense, angular stone. Around the world it is used as road base, in asphalt wearing courses, as railway ballast and in hydraulic structures. The IFC guidelines note the sale of steel slags for civil engineering, road building and cement making [G03]. worldsteel describes the same uses and notes that, in some uses, physical properties rather than chemistry determine suitability [T02].

Two technical conditions must be met before slag leaves a site as a product. First, the slag must be volume-stable. Steel slags can contain free lime and magnesia, which expand slowly when they react with water. If laid too early they can crack roads. The standard remedy is ageing in weathered stockpiles for several months, with regular wetting and turning, followed by expansion testing. Second, the slag must not leach harmful substances. worldsteel’s position is that leachate criteria for slags in road construction should match those applied to natural aggregates [T02]. We will test every production batch with a recognised leaching test, such as EN 12457, before release (Table 6.2).

The market exists. The road and motorway network around Kribi is expanding. An international tender to reconstruct the 110 km Édéa to Kribi road was signed in February 2025 [K09]. The industrial zone will itself need large volumes of fill and pavement for internal roads and platforms [K02]. A cement plant has operated in the zone since 2024 [K10]. A locally produced aggregate that meets specification can substitute for quarried stone, reducing quarrying elsewhere in the coastal strip.

One regulatory point needs early attention. We found no Cameroonian framework that defines when a processed residue ceases to be waste and becomes a product. Without one, a road contractor buying slag aggregate could be treated as receiving waste. We will ask MINEPDED, as part of scoping, to agree product criteria for processed slag, including stability and leaching limits and traceability by batch. The criteria would be written into the environmental certificate, giving buyers and regulators the same reference.

6.3 EAF dust: the hazardous fraction

EAF dust is the fine material caught by the melt shop’s bag filters. Its composition depends on the charge. Galvanised scrap brings zinc, coated scrap brings lead and cadmium, and plastics and salts bring chlorides. Dust from a charge rich in galvanised scrap carries enough zinc to make it both a hazard and a resource. Cameroonian law treats it as industrial hazardous waste [L06]. Only approved operators may handle it. The generator needs an environmental permit, must keep a register and must track every consignment with a manifest [L06].

Three management routes exist:

• Zinc recovery. In a Waelz kiln, EAF dust is heated with a reducing agent. The zinc volatilises, re-oxidises and is collected as a concentrate for zinc smelters, while the residue can be used in construction [T02]. Waelz kilns need large feed volumes, and none is known to operate in Central Africa. Recovery would therefore mean export. The Basel Convention governs transboundary movements of hazardous wastes. Within Africa, the Bamako Convention bans imports of hazardous wastes into the continent and controls movements between African states [G15]. Export to a recovery facility requires prior informed consent from the importing and transit countries, and documentation from start to finish.
• Recirculation and enrichment. Part of the dust can be injected back into the EAF. This raises the zinc content of the remaining dust and makes recovery more economic. It reduces the volume but does not remove the need for an outlet.
• Stabilisation and secure disposal. Dust can be mixed with binders to immobilise metals, tested for leaching, and placed in an engineered cell with liners, leachate collection and groundwater monitoring. It is the fallback, not the preferred route, because it locks away zinc that could be recovered.

The Malaysian works reviewed by the IFC collects its EAF dust in silos for zinc extraction or reuse [T08]. That is the practice we intend to follow. The decisive point is timing. A melt shop produces dust from its first heat. If no outlet is ready, dust accumulates in temporary storage, and temporary storage of hazardous dust in an equatorial climate is exactly where problems begin.

We will therefore treat a signed contract with a licensed recovery facility, or a permitted secure cell on site, as a condition of starting the furnace. Until dust leaves the site, it will be held in sealed silos or closed bags inside a roofed, bunded store, with a maximum storage period set in the waste management plan. The register and manifests will be open to inspection by MINEPDED and to the independent monitor described in Chapter 10.

6.4 Mill scale, sludges, refractories and the rest

Mill scale is the iron oxide that forms on hot steel and flakes off during casting and rolling. It is collected in the scale pits of the direct-contact water circuits. It is one of the most valuable residues of a steelworks, a rich source of iron units. Once de-oiled, it can be briquetted with a binder and recharged to the EAF, or sold to cement producers who use iron oxide to correct their raw-material chemistry. Water-treatment sludges can follow the same route after de-oiling.

Spent refractories are mostly inert ceramic. Suppliers increasingly take them back for recycling, and some magnesia-based materials can replace part of the lime used to condition slag. Used oils will go to an approved recycler. Electrode stubs are reused in the furnace. General waste will be segregated at source, with recyclables separated. Nothing will be burned in the open, on site or by contractors.

6.5 The register, the tests and the zone

Good residue management is mostly a matter of records and discipline. Our waste management plan will rest on four elements:

• a register that tracks every stream from generation to final outlet;
• segregated, labelled and roofed storage, with bunding for liquids and hazardous materials;
• testing before any residue leaves as a product (Table 6.2);
• audits of every contractor and receiving facility before first use and at least once a year thereafter.

Table 6.2 Tests before a residue leaves the site as a product (planned)

Source: IFC EHS Guidelines [G03]; worldsteel co-products [T02]; Décret 2012/2809/PM [L06]; Cameroon Steel objectives (planned).

Source: IFC EHS Guidelines [G03]; worldsteel [T02]; Décret 2012/2809/PM [L06]; Basel and Bamako Conventions [G15].

A wider problem lies beyond any single tenant. We found no information on a shared hazardous-waste facility, engineered landfill or slag processing area planned for the industrial zone. As heavy industry arrives in Kribi, each tenant building its own small secure cell would be costly and hard to supervise. We will propose to the zone’s management that the tenants and the authorities jointly assess shared facilities, from slag processing and a licensed hazardous-waste transfer station to an engineered landfill. We will contribute our data and a share of the study’s cost.

6.6 Construction waste and cleared vegetation

The construction phase brings its own residues: vegetation from clearing, topsoil, excavated spoil, concrete and steel offcuts, packaging and workers’ camp waste. Clearing will follow the forest law, including the salvage and declaration of any merchantable timber [L15]. Topsoil will be stripped and stockpiled for later landscaping and for the green belt. Spoil will be balanced across the site wherever the earthworks design allows, to limit haulage. Contractors will be bound by a construction waste plan with the same register, segregation and no-burning rules as the operating plant. Compliance will be checked by the site environmental team and reported in the half-yearly reports to MINEPDED.