Slags, nickel smelting

Endpoint summary

Additional information

Overview and Discussion of physico-chemical properties

Slag, nickel smeltingis a complex inorganic substance (a UVCB).It is co-produced out of the process to smelt and recover nickel from primary sources.

Characterization of representative sample obtained from the EU manufacture demonstratesrelatively uniform chemical and mineralogical composition.

Main constituents of the substance are iron silicate and silicates of aluminum and calcium that present in glass phase or crystalline phase. Metals contents are reduced to very low levels.

The studiedtypicalgranulated nickel slagsample contains 38.7% Fe, 32.4% SiO₂, 8.7% MgO, 2.6% Al₂O₃, 0.15% Ni and 0.13% Co.

Mineralogical composition is92.12% fayalite, 4.6% amorphous glass, 3.2% magnetite, 0.13% metallic nickel- iron alloys and 0.05% heazlewoodite –type nickel sulfide.

Nickel is carried mainly by fayalite (58.7%), metallic nickel (30%) and heazlewoodite (10%). The rest is carried by amorphous glass and magnetite. Other trace metals (Cu, Pb, As) are present in metallic, sulhide form orinclusion/isomorphic substitution in the silicates.

Trace metals are thus firmly built in or bonded into the glass/crystal structures of the silicate and other mineral phases, which are characterized by high bounding stability and low water-solubility. This determines the chemical-physical properties of the slag.

Slag, nickel smelting does not contain free crystalline silica.

Slag, nickel smelting is produced in the form of granules or stones (massive).

Typical slag sample was collected and tested as appropriate ( see attachment ECI sampling protocol).

Slags are thermally stable upon heating to very high temperature.

On that basis and consideration of mineralogical composition it is concluded that nickel slag has no self-ignition and no flammability hazardous properties. Examination of the mineralogical composition establishes that the there are no structural alerts with regard to oxidizing potential of the substance or explosive properties.

Tested slag sample was poorly soluble in water. Comprehensive solubility tests in environmental and biological media has been further performed.

The relevant physico-chemical properties of the nickel slag (tested as granules) are summarized below.

Table Overview of physico-chemical properties

 

Property	Results
Melting point	1404 °C
Physical state at 20°C and 1013 hPa	Solid Form:Granules or massive (stones) Colour: Black Odour: odourless
Boiling point	Not applicable
Density	3.77 g/m3
Granulometry	Particle size distribution was determined for granulated slags The measured D50 of particle size for the slag granules is measured of 1741 µm The slag stones are massive materials.
Vapour pressure	Not applicable
Partition coefficient n-octanol/water (log value)	Not applicable
Water solubility	Poorly soluble* Solubilization and agitation for 14 days (pH 7.4) resulted in dissolved Cu, Pb, As <0.2 mg/l , Ni<0.4 mg/l
Solubility in organic solvents	Not applicable
Surface tension	Not applicable
Flash point	Not applicable
Auto-flammability	No self - ignition
Flammability	Non flammable
Explosive	Non explosive
Oxidising properties	Non oxidizing
Stability in organic solvents and identity of relevant degradation products	Not applicable
Dissociation constant	Not applicable
Viscosity	Not applicable

*Transformation/dissolution (OECD, 2001) is more suitable for metals and sparingly soluble metal compounds (see IUCLID Section 5.6). The outcomes of the transformation/dissolution tests were used for aquatic classification.

 In vitro bio-accessibility tests were carried out to assess the solubility of metals in nickel slag in extraction solvent that resembles gastric fluid (using HCl 0.07N at pH 1.5) in accordance with the ASTM D 5517-07 standard(see IUCLID Section 7.1). The outcome of bio-elution test was used to support classification for human hazards.