Heavy metal stabilization in EAFD 22-26 June 2015 using magnesia - - PowerPoint PPT Presentation

Heavy metal stabilization in EAFD using magnesia and Sorel cements

• E. Ntinoudi1, H. Yiannoulakis2, Th. Zampetakis2, A.I.

Zouboulis1, E. Pantazopoulou1

1 Department of Chemistry, Aristotle University of Thessaloniki, Greece 2 R&D Center, Grecian Magnesite S.A., Thessaloniki, Greece

31st International Conference of Society for Environmental Geochemistry & Health 22-26 June 2015 Bratislava

Outline

Introduction

Industrial solid waste management in Greece Stabilization Magnesia – MgO Magnesia cements: MOC, MPC Electric arc furnace dust (EAFD)

Stabilization of EAFD

Method Results

Conclusions

31st SEGH 2015

Industrial solid waste management in Greece

Introduction

• Stabilization/solidification

aims to convert hazardous substances to more stable chemical forms that are much less soluble, mobile and toxic, using various additives, such as portland and magnesia cements.

• Stabilized wastes can be safely disposed

into the environment with minimal risk

• f

leaching toxic substances and polluting surface water or groundwater resources.

31st SEGH 2015

Magnesia – MgO

• MgO: A widest spectrum of applications, i.e. agricultural, industrial & chemical, construction,

steel & refractories & environmental

• Environmental applications: Flue gas treatment, soil decontamination and remediation, domestic

and industrial solid waste treatment

31st SEGH 2015

• MgO is a Grecian Magnesite S.A.

product: microcrystalline caustic calcined MgO

• Nominal purity 83.41% (grade 83 CG)
• Impurities: CaO, SiO2, Al2O3, Fe2O3,

SO3

• Specific surface area 32 m2/g, milled

below 200 μm

Magnesia cements

31st SEGH 2015

• Two types of magnesia cements:

(a) Magnesium Oxychloride Cement (MOC) or Sorel Cement: 5MgO + MgCl2 + 13H2O → 5Mg(OH)2.MgCl2.8H2O (phase 5) (b) Magnesium phosphate cement (MPC): MgO + phosphate + H2O → phosphate phase

• MOC, MPC: High strength, abrasion resistance & bonding
• MOC: lower water resistance than MPC

2.5 3.0 3.5 4.0 4.5 5.0 170 180 190 200 210 220 230 240 250

Setting Time (min) MgO/MgCl2

3.0 3.5 4.0 50 60 70 80 90 100

3d

• Comp. Strength (N/mm

2)

MgO/MgCl2

28d

5 10 15 20 25 30 50 55 60 65 70 75 80

• Comp. Strength (N/mm

2)

days

83CG/MgCl2 =2.8

• EAFD is a by-product of steel production
• It contains Zn, Fe, Pb & Ca among others
• 15–20 kg EAFD/t of steel is generated

Electric arc furnace dust

The current situation in Greece:

• Hydrometallurgical processes for heavy metal recovery from EAFD (Zn, Pb, Fe) have been

developed, but the annual produced volume is considered fragmentary for a profitable operation.

• Approximately 30,000–40,000 t/year is produced.
• Almost the entire quantity of EAFD is transported abroad.

31st SEGH 2015

Table 1. Typical composition of EAFD % wt. dry substance Al2O3 CaO Fe2O3 K2O MgO MnO PbO SiO2 ZnO LOI 0.9 4.6 33.9 1.4 0.7 3.3 6.2 4.1 34.9 7.8

mS/cm mV pH EC Redox EU Decision 2003/33/EC 12.3 18.0 +41 mg/kg of dry substance As Ba Cd Cr total Cu Hg Ni Pb Sb Se Zn F- Cl- DOC TDS 0.08 2.9 nd 4.4 nd 1.5 nd 650 0.03 1.2 nd 31 34000 21200 114 126500 nd: not detected

Characterization of EAFD

EAFD Deionized water L/S 10 L/kg 10 rpm 24 h EAFD cannot be accepted in hazardous waste landfills

31st SEGH 2015

Stabilization process

EN 12457-2 EAFD Determination of Pb, Se, Hg, Cl-, SO4

2- & TDS

Deionized water Deionized water MgO (5-25%) Phosphate

31st SEGH 2015

MgO (5-25%) 15 days aging MgCl2 1.5% H3PO4 Deionized water MgO (5-25%) MOC MPC

MgO/MgCl2 1.3 MgO/phosphate 0.3

Stabilization - Results

31st SEGH 2015

10 20 30 40 50 60 70 80 5 10 15 20 25

Pb (mg/kg)

MgO (% of EAFD) hazardous non-hazardous 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 5 10 15 20 25

Se (mg/kg)

MgO (% of EAFD) MgO only MOC MPC hazardous 7 mg/kg non-hazardous

• MgO only: pH ~12.0, MOC: pH 9.8-12.3, MPC: pH 11.4
• MOC, MPC: Hg nd, MgO only: Hg 0.01-0.06 < limit of inert waste
• MgO acts as a buffering agent
• MOC, MPC: very good bonding behavior, significantly decreased leaching of Pb, Se, Hg

Stabilization - Results

31st SEGH 2015

10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 5 10 15 20 25

Chloride (mg/kg)

MgO (% of EAFD) hazardous non-hazardous 10000 20000 30000 40000 50000 60000 5 10 15 20 25

Sulphate (mg/kg)

MgO (% of EAFD) MgO only MOC MPC hazardous non-hazardous

• MOC increases Cl- leaching
• MOC, MPC: poor water stability
• MPC: Dilution of EAFD with sand (1:1) resulted in a stabilized waste accepted in non-hazardous waste

landfills (Cl- 21,000 mg/kg)

• MOC, MPC: SO4

2- < limit of non-hazardous waste

Stabilization - Results

31st SEGH 2015

90000 95000 100000 105000 110000 115000 120000 125000 5 10 15 20 25

TDS (mg/kg)

MgO (% of EAFD) MgO only MOC MPC non-hazardous 60,000 mg/kg hazardous

• TDS

can be used alternatively to the values for SO4

2- and Cl-.

• MOC: TDS below the limit

value for waste acceptable in hazardous waste landfills above 10% MgO addition.

• MPC:

TDS < limit hazardous waste

• MPC: TDS 66,600 mg/kg

when EAFD is diluted with sand 1:1 ratio

• MgO only: TDS below the

limit value for waste acceptable in hazardous waste landfills above 20% MgO addition.

Conclusions

• EAFD may pose a risk to human health and the

environment, if not managed and disposed of safely.

• The proposed stabilization process, using magnesia

cements (MOC, MPC), is an effective method for heavy metal immobilization.

• Pb, Hg & Se are below the maximum limits for

non-hazardous waste landfills, when using MgO above 10% at magnesia cements.

• MOC increases Cl- leaching, while using MPC

does not increase the leached Cl-. Lower heavy metals leaching in the case of MPC than MOC.

• Using only MgO manages to reduce Pb leaching,

but not below the limit value for non-hazardous waste landfills.

31st SEGH 2015

Acknowledgements

This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Program "PAVET" – Project: Environmental applications of magnesia and utilization of produced by-products.

31st SEGH 2015

Thank you for your attention