Studies into the Formation of PBDEs and PBDD/Fs in the Iron Ore Sintering

ProcessDaniel Drage1, Stuart Harrad1 & Eric Aries2

1University of Birmingham, Geography, Earth and Environmental Sciences2Tata Steel, Group Environment, Environment Technology, Swinden Technology Centre, Moorgate, Rotherham, S60 3AR, UK

BFR - 08/04/13

Tata Steel

Second largest European steel manufacturers Two major steelmaking plants in the UK – each

producing 4 million tonnes of steel via integrated steel making (i.e. coke making, iron ore sintering, basic oxygen steelmaking, continuous casting).

All samples in this study provided by Tata Steel.

The Iron Ore Sintering Process

Anderson and Fisher, 2002, Chemosphere 46, 371-381

The Steel Industry as a potential source of PBDEs and PBDD/Fs to the Environment Buser (1986) showed that PBDEs can undergo thermolysis to form

key PBDD/Fs at temperatures of 510-630 ºC in the presence of air Weber & Kuch (2003) state that PBDEs in materials under

“thermal stress” can form high quantities of PBDD/Fs and mixed PXDD/Fs when undergoing incomplete combustion, but under “controlled combustion conditions” PBDEs and other BFRs can be destroyed

Odabasi et al. (2009) suggested that the steel industry, particularly scrap metal recycling (ie. Electronic Arc Furnace process) could be a significant source of PBDEs – 32% of steel worldwide is made from recycled ferrous scrap in EAFs

The Steel Industry as a potential source of PBDEs and PBDD/Fs to the Environment

It has been proposed by Wang et al. (2010) that PBDD/Fs and PBDEs could be formed by de novo synthesis in the iron ore sintering process & EAFs and emission factors were calculated.

They also suggest that sintering plants have the lowest PBDE and PBDD/F emission rates in steel-manufacturing with both potentially being destroyed in the process through debromination.

They also state that debromination of PBDEs could easily form PBDFs as well as converting the heavier PBDEs into those of a lower molecular weight (e.g. decaBDE tetraBDE).

EAF steelmaking and iron ore sintering are two thermal process that have been highlighted as potential sources of PBDEs and PBDD/Fs.

However, there is a lack of evidence to show that the iron ore sintering process causes de novo formation of PBDEs and the conversion of PBDEs to PBDD/Fs.

Aims & Objectives The aim of the project was to investigate the iron ore sintering

process, as a potential source of PBDEs and PBDD/Fs in the environment focussing on:– Characterisation of sinter plant emissions for PBDEs / PBDD/Fs

– Characterisation of raw material inputs for PBDEs / PBDD/Fs

– Test the hypothesis that PBDEs and/ or PBDD/Fs are formed in the iron ore sintering process using a laboratory pilot scale sintering unit (sinter pot)

– Test the hypothesis that PBDEs can act as pre-cursors for PBDD/F formation in the iron ore sintering process using the sinter pot

Raw Material Inputs & Outputs Analysis Measured PBDEs (-17. -28, -47, -49, -85, -99, -100, -153, -

154) in the following input and output materials from 6 sintering beds from a UK Tata Steel sinter plant:– 7 Raw Sinter Mix (INPUT)– 9 ESP Dust (OUTPUT)– 6 Sinter (OUTPUT)– 1 emission (OUTPUT)

Carried out total input/output mass balances for each sinter bed using tonnages / stack emission flow rates provided by Tata Steel.

Results Input/Output Mass Balance:

Note only bed 2272 had emission sample measured – all others include estimate

Input Components Analysis Measured PBDEs in components of Raw Mix:

– 29 Ores

– 20 Reverts

– 5 Fluxes

– 4 Fuels

Ores, reverts and fuels all contain PBDEs before they are processed in the sintering process, meaning that they are already contaminated before entering the sintering process

There is an noticeable reduction in PBDEs coming out of the process – is this destruction or conversion?

Component Mean Concentration (Range (ng/kg))

Iron Ores 5,900 (19-120,000)

Reverts 6,600 (110-32,000)

Fuels 12,000 (840-18,000)

Fluxes 440 (87-1,500)

Soil1 3,240 (9-100,000)

1Soil data taken from 4 studies across Spain, China, USA and SwedenEljarrat et al. 2008; Chen et al. 2012; Yun et al. 2008; Sellstrom et al. 2005

PBDD/F Emissions Measured PBDD/F and PCDD/F concentrations in 15 stack

emission samples

Presence of PBDD/F was confirmed in all cases, BUT the WHO-TEQ concentrations were 5-10 times lower than those of PCDD/Fs

Sinter Pot Study

Ooi et al., 2008 Minerals Engineering, 21, 167-177

Performs sintering process on a laboratory scale, whilst allowing the measurement of the TOTAL output

Sinterpot Study Experiment carried out at Tata Steel UK laboratories Set 5 conditions to test 3 hypotheses:

– The sintering process causes formation of PBDEs– The sintering process causes formation of PBDD/Fs– PBDEs act as pre-cursors for the formation of PBDD/Fs

5 conditions tested:– Base Case (Normal raw sinter mix used in full scale process)– Base Case + 74.5 mg/kg KBr– Base Case + 224 mg/kg KBr– Base Case + PBDE technical solutions (penta + deca)– Base Case + 224 mg/kg KBr + PBDE technical solutions (penta + Deca)

Measured the following samples:– Raw Mix input (PBDEs)– Sinter product (PBDEs)– Total emission (PBDEs + PBDD/Fs)

Results – PBDEs

Results – PBDEs

Results – PBDD/Fs

Conclusions Although PBDEs are present in the iron ore sintering process, they appear to be

already present in the raw materials before entering the process, mainly from iron ores, revert materials and fuels (ie. coke) (depending on the exact components and tonnages used in each bed). PBDEs in iron ores are found in similar concentrations as in soils.

Up to 95% of the total PBDE input is destroyed in the sintering process There is no increase in PBDE output when KBr input is increased, suggesting that

de novo synthesis of PBDEs does not occur in the sintering process. An increase in bromide input causes an exponential increase in PBDD/F output

indicating that de novo synthesis of PBDD/Fs does occur in iron ore sintering, however KBr is not added to the raw sinter mix and typical bromide concentrations in sintering are very low in practice.

Furthermore, the addition of PBDEs did not appear to increase PBDD/F formation suggesting that PBDEs do not act as precursors in the formation of PBDD/Fs in the iron ore sintering process.

Acknowledgements

Natural Environment Research Council Tata Steel

Thank you