Slags, nickel smelting

Endpoint summary

Additional information

General discussion of environmental fate and pathways:

General summary of the information on environmental fate and pathways

Slag,nickelsmelting is a complex inorganic substance (UVCB). It mainly contains iron silicate and silicates of aluminum and calcium. Traces of metals exist in metal, mineral form or included in silicate phases. The physico-chemical characterization of the substance demonstrated that the trace metals are firmly built in and bonded into the glass/crystal structures of the silicate and other mineral phases. This resulted in limited release and low measured water-solubility of the trace metals present in the matrix.

Stability and Biodegradation

The classic standard testing protocols on hydrolysis, photo-transformation and biodegradation are not applicable to inorganic substance such as slag,nickelsmelting.

This was recognized in the Guidance to Regulation (EC) No 1272/2008 Classification, Labeling and Packaging of substances and mixtures (metal annex):“Environmental transformation of one species of a metal to another species of the same does not constitute degradation as applied to organic compounds and may increase or decrease the availability and bioavailability of the toxic species. However as a result of naturally occurring geochemical processes metal ions can partition from the water column. Data on water column residence time, the processes involved at the water – sediment interface (i. e. deposition and re-mobilisation) are fairly extensive, but have not been integrated into a meaningful database. Nevertheless, using the principles and assumptions discussed above in Section IV.1, it may be possible to incorporate this approach into classification. ”

Relevant fate aspects fornickelslag in the environment have therefore been included in the section “Additional information on fate and pathways”.

As outlined in the CLP guidance (2009), understanding of the rate and extent of transformation /dissolution of thenickelslag to soluble, potentially available metal species is relevant to the environmental hazard assessments and this is described below.

The uptake ofnickelslag by living organisms is related to the degree to which the metal mineral phases in the slag react with water / biological fluids and release soluble, potentially bio available ionic and other metal bearing species.

The release of metals from the slag is expected to involve transformation (eg oxidation of sulphide mineral phases) as well as dissolution of the original and transformed metal forms. Given the complex composition ofnickelslag, the solubility test data show that different metal transformation/dissolution processes occur simultaneously but at different rates.

Transformation/dissolution in standard medium

Standardized transformation/dissolution tests ofnickelslag were carried out to study its potential to release soluble available ionic and other metal-bearing species to the environment (Rodriguez et al.,2010). Transformation/dissolution test was performed on a typical granulated slag. Granules were tested in their original particle size as bulk material.

Considering the composition of this complex material, a 7days transformation / dissolution test at a loading of 100 mg/L was performed on one sample at pH 6 following the release of a broad range of metals. (Rodriguez et al.,2010).The results of the 7 days test demonstrate low release of Ni to the OECD media of 0.6μg/l .Releases below detection limit are recorded for the other metals.

Relative release rates (of Ni ) was calculated as dissolved metal at pH 6 during 7 days transformation/dissolution divided by total metal content in the slag. This resulted in the following relative release rate

-     Ni 0.4 % (ie 0.4% of the nickel present in a nickel slag sample is bio-available)

The observed dissolution rate is important to quantify the amount of metal release, which is further used for acute and chronic environmental hazard assessment. They also serve as an indication of the lability of the solid phase in both chemical and physical terms.

Transformation/dissolution in mesocosm pond water

7 days transformation/dissolution tests (several loadings, pH around 8) were also carried out for a range of copper slag analogue substance) , using, as test medium water of the mesocosm ecotoxicity study carried out on one of the slag materials (Schaefers et al, 2010).

Comparison between the 7 days transformation/dissolution tests in standard medium (Rodriguez et al., 2010) and mesocosm pond water (Schaefers et al., 2010) demonstrates, for all tested slag materials higher release rates in the classic T/D tests at pH6 . The observed metal release rates are related to differences in the test medium-specific characteristics (eg pH and DOC) as well as slag-specific characteristics (eg particle sizes and crystalline structure).

Attenuation of the released metal ions

Once released from the slag, the metal-ions will be sorbed to mineral and particulate organic matter surfaces in the water, sediment and soil and will bind to dissolved organic and sulphide materials present in water, soil and sediment compartments. Binding, precipitation and partitioning allows for a reduction of “bio-available metal species” and thus a potential reduction of the metal toxicity as a function of time.

The combination of metal release from the analogue substance copper slag materials and subsequent removal of the released metal ions was assessed during the mesocosm enclosures (data for >4 months) with varying concentration of slag introduced as stones or particulates (1-2 mm). The data with metal releases from particulates (1-2 mm) demonstrated initial short term increase in copper and lead concentrations followed by a decrease and equilibration of the soluble metal concentrations. The data on the metal releases from the stones indicated more gradual increases and stabilization of the soluble metal concentration thereafter (H. Rüdel, 2010, Mesocosm study Analytical report). The data from the particulates therefore demonstrate that the released metals are removed from the water column and the data from the stones indicate that the released metals are removed from the water column and /or the metal releases rates from the slag surfaces decrease as a function of time (passivation of the slag surfaces).

 

Transport and distribution

Assessing the transport and distribution of the slags substance has no meaning.

The mechanisms of distribution over liquid/solid phase (adsorption /desorption, precipitation and removal from water column) of the different metals contained in the slag have been assessed in details for each single metal in the respective risk assessments and/or Chemical Safety reports.

Partition coefficients for soil/water, sediment/water and suspended matter/water are available for different metals contained in the slag and further used for environmental exposure assessment. Cu, Pb, Ni, Zn, As and Cd are considered relevant. The data are summarized below.

 Table6.Overview of solid water partition coefficients (Kd) for the selected trace constituents of nickel slag and the fraction of emission directed to water by STP

 

	Unit	Cu	Pb	As	Ni	Cd	Zn
Suspended matter (freshwater)	L/Kg	30,246	295,121	10,000	26,303	130,000	110,000
Suspended matter (marine)	L/Kg	131,826	295,121	10,000	26,303	130,000	110,000
Sediment (freshwater)	L/Kg	24,409	154,882	6,607	7,079	130,000	73,000
Soil	L/Kg	2,120	6,400	191	724	280	158
Fraction of STP emission directed to surface water	%	20	16	26	60	40	74
Reference		Cu CSR	Pb CSR	Crommentuyn et al. (1997)	Ni CSR	Cd RAR	Zn RAR

Bioaccumulation and secondary poisoning

Nickel slag is a complex metal containing substance. It contains a range of trace metals which have a great variation in their physico-chemical and toxicological properties (Cu Pb, Zn, Ni). The assessment of bio-accumulation and secondary poisoning for the slag as a whole therefore has no meaning.

Accumulation data (BCF and BAF values) are available for all metal constituents in the slag. Metals like Cu, Zn are essential and well regulated in all living organisms and therefore the bio accumulative criterion is not applicable. Data for copper (Cu RA, 2008 and Cu CSR, 2010) demonstrate that copper is not biomagnified in the aquatic and terrestrial ecosystems and that there is no issue for secondary poisoning of copper.

Secondary poisoning is however considered relevant for lead, nickel and cadmium, based on their known bioaccumulation potential.

According to CLP Guidance for complex substances (SectionIII.3.2) it is not recommended to estimate an average or weighted BCF value but identify one or more constituents for further consideration.

Given the above, secondary poisoning of lead, nickel and cadmium contained in the nickel slag is further taken into account in the environmental exposure assessment.

The bioaccumulation/bio-concentration factors and PNECoral for lead, nickel and cadmium are as derived in the respective Risk assessments and/or Chemical Safety reports.

Other information on fate and pathways

Fiber-shaped particles might form during the use of analogue substancxe copper slag as an abrasive medium in high-pressure abrasive blasting. Research showed that high concentrations of fibers are generated in the air and in the used abrasive medium during high-pressure abrasive blasting. According to research of the Berufsgenossenschaftliches Institut für Arbeitsschutz (BIGA)[[Occupational Cooperative Institute of Work Protec-tion]], the detected fibers are not asbestos fibers but fragments of the amorphous mass of the abrasive medium or newly-formed crystalline phases.

It is assumed that such fiber shape particles are typically formed during use of nickel slag as weel as mineral abrasives in general.

Therefore a study has been conducted to assess the bio-persistence of fiber-shaped particles that are formed during use of analogue substance copper slag as abrasive medium and the potential health hazards arising from inhalation or ingestion (Professor Dr. Ewers, 2010, Investigation of the bio-persistence of respirable fiber-shaped particles in copper slag after use as an abrasive medium) See Section 7.12, Additional toxicological information