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TRP Chapter 6.4 1 Chapter 6.4 Stabilisation and solidification of hazardous wastes.

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Presentation on theme: "TRP Chapter 6.4 1 Chapter 6.4 Stabilisation and solidification of hazardous wastes."— Presentation transcript:

1 TRP Chapter Chapter 6.4 Stabilisation and solidification of hazardous wastes

2 TRP Chapter Immobilisation Immobilisation is a collective term for a range of treatment processes that primarily aim to make hazardous waste safe for disposal by reducing the potential for waste component leaching Stabilisation: techniques by which hazardous wastes are converted into a more stable form Solidification: techniques that create a solid mass of either the original waste, or waste that has been stabilised S/S often used in combination S/S feedstock is often the residue from other treatment processes

3 TRP Chapter Aims of S/S of hazardous waste Reduce potential for hazardous waste leaching Conversion of pollutants into less toxic form Decrease in waste surface area Reduction of pollutant mobility Formation of solid mass with no free liquid Improvement in handling and physical characteristics of waste Should normally be considered as a pre-landfill treatment process

4 TRP Chapter Waste pre-treatment Adjustment of physical characteristics particle size, shape and distribution by size screening and/or reduction moisture content homogeneity viscosity Adjustment of chemical characteristics pH toxicity removal of toxic constituents destruction of toxicity reduction of toxicity

5 TRP Chapter Stabilisation Chemical reaction Acid/alkali neutralisation Chelation Complexation Oxidation/reduction Precipitation Hydroxides Silicates Sulphides Chemisorption Ion exchange

6 TRP Chapter Solidification May be used to treat original or stabilised wastes Types of binders used: Cement-based Portland cement, cement kiln dust Lime/limestone/quicklime Lime/fly ash, lime kiln dust Lime/ other natural and artificial pozzolana based systems Thermoplastic materials Asphalt (Bitumen), Paraffin, polyethylene Thermosetting polymers Polybutadiene, (poly)urea-formaldehyde, polyvinylesterstyrene

7 TRP Chapter Additives Activated carbon Emulsifiers and surfactants Lime, fly ash & kiln dust Oxidants Reducing agents Selected clays Soluble silicates

8 TRP Chapter Key factors Characteristics of waste chemical properties composition and concentration acidity/alkalinity oxidation/reduction potential solubility Physical properties state (liquid, sludge or solid) particle size, shape & distribution solid content viscosity Characteristics of binders Mode of processing

9 TRP Chapter Waste assessment Waste sampling and characterisation to determine: type of contaminants levels of contamination spatial distribution of contaminants presence of possible interference effects S/S is best suited to largely inorganic wastes

10 TRP Chapter Performance tests Physical tests Moisture content specific gravity bulk density permeability porosity strength durability Chemical tests pH acid neutralisation capacity oxidation/reduction potential total organic carbon oil & grease volatile organic compounds metal analysis Leaching/extraction tests

11 TRP Chapter Properties of S/S treated waste 1.FORMULATION: Waste type, % and composition Binder composition Water content 2.PROCESSING OF MIX Mixing method Hydration conditions Age Disposal conditions

12 TRP Chapter Re-use applications for S/S waste Likely to be limited because of: Unreliable long term durability Poor mechanical properties Perception of risk May be possible to use as inert fill Should be seen as landfill pre-treatment method Disposal - should not be with mixed MSW Compatibility with disposal environment should be tested

13 TRP Chapter Wastes typically treated by S/S Air pollution control residues Metal sludge wastes Dredging sludge Filter press cake Tannery wastes Contaminated soils Lagoon sludge Plus other PREDOMINANTLY inorganic wastes - all are likely to contain some organics

14 TRP Chapter Case study - UK

15 TRP Chapter Schematic of waste S/S plant Part 1: Stabilisation 5000 tonnes Alkali waste pH > tonnes acid waste pH > 7-8 Inorganic solids, liquids and sludge TOC < 1000 mg/L Stock storage tank pH % solids Vacuum filtration to produce filter cake Incoming waste storage blending stabilised waste Waste effluent

16 TRP Chapter Schematic of waste S/S plant Part 2: Solidification stabilised waste filter cake Output ~ 6T per hour 15% OPC + 15% PFA + 70% filter cake (~ 50% solids) Landfill disposal in clay lined cell Stabilised High energy Mono-disposal waste mixer

17 TRP Chapter Waste types treated by UK plant Type of waste% of whole Sulphuric acid 4.7 Hydrochloric acid 4.6 Chromic acid 0.6 Mixed/other acids 6.6 Al-chloride solutions16.6 Fe-chloride solutions 0.9 Solid/liquid cyanides 2.7 Caustic solutions 30.5 Neutral sludges10.4 Lime sludges14.0 Other sludges 0.8 Filter cakes 1.1 Paint stripper washings 1.7 Ferrous sulphate 1.0 Others 3.1

18 TRP Chapter day strength from any 1 day of production will not be less than 700 kPa. No individual sample to have strength less than 350kPa Permeability at 28 days less than 1x10 -7 m/s No supernatant after S/S waste standing 24 hours Leaching properties: Depends on test but typically includes limits on pH, TOC, Total cyanide, total phenol, ammonia Heavy metals (Zn, Hg, Cr), total metal limit and total organic or organo-metallic pesticides Treated waste specification

19 TRP Chapter Key considerations Waste reduction and avoidance by generators should always be a priority Role of on-site vs off-site technologies Need to consider residues from treatment processes and their disposal Transitional technologies may be used until final high-quality installations are available

20 TRP Chapter Chapter 6.4 Summary Stabilisation and solidification techniques Reduce potential for hazardous waste leaching Improve handling and physical characteristics May require pre-treatment of wastes eg to change particle size, pH Stabilisation is usually followed by solidification Should be considered as a pre-landfill treatment process

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