31 st International Conference of Society for Environmental Geochemistry & Health Heavy metal stabilization in EAFD 22-26 June 2015 using magnesia and Sorel cements E. Ntinoudi 1 , H. Yiannoulakis 2 , Th. Zampetakis 2 , A.I. Bratislava Zouboulis 1 , E. Pantazopoulou 1 1 Department of Chemistry, Aristotle University of Thessaloniki, Greece 2 R&D Center, Grecian Magnesite S.A., Thessaloniki, Greece
31 st SEGH 2015 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
31 st SEGH 2015 Introduction 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
31 st SEGH 2015 Magnesia cements 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 100 80 250 240 75 28d 90 2 ) 2 ) Comp. Strength (N/mm Comp. Strength (N/mm 230 Setting Time (min) 70 220 80 210 3d 65 70 200 60 190 60 180 55 83CG/MgCl 2 =2.8 170 50 50 0 5 10 15 20 25 30 2.5 3.0 3.5 4.0 4.5 5.0 3.0 3.5 4.0 days MgO/MgCl 2 MgO/MgCl 2
31 st SEGH 2015 Electric arc furnace dust 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 7.8 0.9 4.6 33.9 1.4 0.7 3.3 6.2 4.1 34.9 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.
31 st SEGH 2015 Characterization of EAFD EAFD L/S 10 L/kg 10 rpm 24 h Deionized water EAFD cannot be mS/cm mV accepted in hazardous pH EC Redox waste landfills EU Decision 2003/33/EC 12.3 18.0 +41 mg/kg of dry substance F - Cl - As Ba Cd Cr total Cu Hg Ni Pb Sb Se Zn 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
31 st SEGH 2015 Stabilization process MgO (5-25%) Deionized water EN 12457-2 MOC MgO (5-25%) Deionized water MgCl 2 15 days 1.5% H 3 PO 4 aging MgO/MgCl 2 1.3 EAFD MPC MgO/phosphate 0.3 Determination of Pb, Se, Hg, Cl - , Phosphate 2- & TDS SO 4 MgO (5-25%) Deionized water
31 st SEGH 2015 Stabilization - Results 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 1,0 hazardous Se (mg/kg) 50 Pb (mg/kg) 0,8 MgO only 40 0,6 MOC 30 non-hazardous MPC 0,4 20 non-hazardous 10 0,2 0 0,0 5 10 15 20 25 5 10 15 20 25 MgO (% of EAFD) MgO (% of EAFD)
31 st SEGH 2015 Stabilization - Results 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) 2- < limit of non-hazardous waste MOC, MPC: SO 4 55000 60000 50000 hazardous 50000 45000 Sulphate (mg/kg) Chloride (mg/kg) 40000 40000 35000 MgO only 30000 30000 MOC hazardous MPC 25000 20000 non-hazardous 20000 10000 non-hazardous 15000 0 10000 5 10 15 20 25 5 10 15 20 25 MgO (% of EAFD) MgO (% of EAFD)
31 st SEGH 2015 Stabilization - Results 125000 TDS can be used alternatively to the values 120000 2- and Cl - . for SO 4 MOC: TDS below the limit 115000 TDS (mg/kg) value for waste acceptable in hazardous waste landfills 110000 MgO only above 10% MgO addition. MPC: TDS < limit MOC 105000 hazardous waste MPC MPC: TDS 66,600 mg/kg hazardous 100000 when EAFD is diluted with sand 1:1 ratio 95000 MgO only: TDS below the limit value for waste non-hazardous 60,000 mg/kg 90000 acceptable in hazardous 5 10 15 20 25 waste landfills above 20% MgO addition. MgO (% of EAFD)
31 st SEGH 2015 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.
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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