31 st International Conference of Society for Environmental Geochemistry & Health Heavy metal stabilization in EAFD using magnesia and Sorel cements 22-26 June 2015 E. Ntinoudi 1, H. Yiannoulakis 2, Th. Zampetakis 2, A.I. Zouboulis 1, E. Pantazopoulou 1 Bratislava 1 Department of Chemistry, Aristotle University of Thessaloniki, Greece 2 R&D Center, Grecian Magnesite S.A., Thessaloniki, Greece
Outline 31 st SEGH 2015 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
Introduction 31 st SEGH 2015 Industrial solid waste management in Greece 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 of leaching toxic substances and polluting surface water or groundwater resources.
Magnesia MgO 31 st SEGH 2015 MgO is a Grecian Magnesite S.A. product: microcrystalline caustic calcined MgO Nominal purity 83.41% (grade 83 CG) Impurities: CaO, SiO 2, Al 2 O 3, Fe 2 O 3, SO 3 Specific surface area 32 m 2 /g, milled below 200 μm 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
Magnesia cements 31 st SEGH 2015 Two types of magnesia cements: (a) Magnesium Oxychloride Cement (MOC) or Sorel Cement: 5MgO + MgCl 2 + 13H 2 O 5Mg(OH) 2.MgCl 2.8H 2 O (phase 5) (b) Magnesium phosphate cement (MPC): MgO + phosphate + H 2 O phosphate phase MOC, MPC: High strength, abrasion resistance & bonding MOC: lower water resistance than MPC Setting Time (min) 250 240 230 220 210 200 190 180 170 Comp. Strength (N/mm 2 ) 100 28d 90 80 3d 70 60 50 2.5 3.0 3.5 4.0 4.5 5.0 3.0 3.5 4.0 MgO/MgCl 2 MgO/MgCl 2 Comp. Strength (N/mm 2 ) 80 75 70 65 60 55 83CG/MgCl 2 =2.8 50 0 5 10 15 20 25 30 days
Electric arc furnace dust 31 st SEGH 2015 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 Table 1. Typical composition of EAFD % wt. dry substance Al 2 O 3 CaO Fe 2 O 3 K 2 O MgO MnO PbO SiO 2 ZnO LOI 0.9 4.6 33.9 1.4 0.7 3.3 6.2 4.1 34.9 7.8 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.
Characterization of EAFD 31 st SEGH 2015 EAFD L/S 10 L/kg 10 rpm 24 h Deionized water ms/cm mv ph EC Redox 12.3 18.0 +41 EU Decision 2003/33/EC 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 EAFD cannot be accepted in hazardous waste landfills
Stabilization process 31 st SEGH 2015 MgO (5-25%) Deionized water EN 12457-2 MgO (5-25%) MOC Deionized water MgCl 2 EAFD MgO/MgCl 2 1.3 1.5% H 3 PO 4 15 days aging MgO/phosphate 0.3 MPC Phosphate Determination of Pb, Se, Hg, Cl -, SO 4 2- & TDS MgO (5-25%) Deionized water
Pb (mg/kg) Se (mg/kg) Stabilization - Results 31 st SEGH 2015 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 80 1,4 hazardous 7 mg/kg 70 1,2 60 50 40 hazardous 1,0 0,8 MgO only 30 0,6 non-hazardous MOC 20 0,4 MPC 10 non-hazardous 0,2 0 5 10 15 20 25 0,0 5 10 15 20 25 MgO (% of EAFD) MgO (% of EAFD)
Chloride (mg/kg) Sulphate (mg/kg) Stabilization - Results 31 st SEGH 2015 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: SO 4 2- < limit of non-hazardous waste 55000 60000 50000 45000 50000 hazardous 40000 40000 35000 30000 30000 MgO only MOC 25000 hazardous 20000 non-hazardous MPC 20000 15000 non-hazardous 10000 10000 5 10 15 20 25 0 5 10 15 20 25 MgO (% of EAFD) MgO (% of EAFD)
TDS (mg/kg) Stabilization - Results 31 st SEGH 2015 125000 120000 TDS can be used alternatively to the values for SO 4 2- and Cl -. 115000 110000 MgO only MOC: TDS below the limit value for waste acceptable in hazardous waste landfills above 10% MgO addition. 105000 100000 95000 90000 hazardous non-hazardous 60,000 mg/kg 5 10 15 20 25 MgO (% of EAFD) MOC MPC 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 31 st SEGH 2015 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.
31 st 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.
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