slag, copper smelting

Endpoint summary

Additional information

Overview and Discussion of physico-chemical properties

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

Characterization of representative samples obtained from EU manufactures demonstrates relatively 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. The oxide mineral phase magnetite (Fe3O4) is also present. Metals contents are reduced to very low levels, Depending on the process: in slags from secondary copper production Cu, Pb and Zn are mainly present in alloy phase or inclusion/isomorphic substitution in the silicates where in slags from primary copper production Cu, Pb and Zn are mainly present in sulphide phase or inclusion/isomorphic substitution in the silicates. Furthermore data show that Ni is always present in metal/alloy phase and As is completely included in silicate phase.

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, copper smelting does not contain free crystalline silica.

Slag, copper smelting is produced in the form of granules, stones (massive) and powder.

Slag samples representative for all physical forms produced and different production processes , origin of raw material (primary or secondary) and slag cooling rate (rapid cooling /granulation or slow cooling) were collected and tested as appropriate ( see attachment ECI sampling protocol)

Slags are thermally stable upon heating to very high temperature. Due to differences in crystalization during slag cooling some properties (eg melting point, oxidation temperature) are slightly different.

On that basis and consideration of mineralogical composition it is concluded that copper 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

All tested slag samples were poorly soluble in water. Difference in particle size and surface area between slag in granules, massive and powder form slightly influence the solubility. Variations in solid phase speciation could also influence the solubility. Solubility tests in environmental and biological media have therefore been performed on all sample types and physical forms. 

The relevant physico-chemical properties of the copper slag are summarized below:

 

Table2. Overview of physico-chemical properties

 

Property	Results
Physical state at 20°C and 101.3 kPa	Solid Colour: Black , Reddish brown, Grey, Dark grey Odour: Odourless
Melting point	1027-1341 °C
Boiling point	Not applicable
Density	3.11 – 4.2 g/m3
Granulometry	Particle size distribution was determined for each of the three different forms of slag. The slag stones are massive materials. The measured D50 of particle size for the crushed slag stones is in the range of 1316 - 2029 µm The measured D50 of particle size for the slag granules is measured in the range of 741 - 2426 µm The measured D50s of particle size for the slag fines is in the range of 30 - 70 µm
Vapour pressure	Not applicable
Partition coefficient n-octanol/water (log value)	Not applicable
Water solubility	Poorly soluble* Solubilization and agitation for 14 days (pH 6.3 - 7.6) resulted in dissolved Cu, Ni, Pb <0.2 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 copper 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.