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TRP Chapter 6.4 1
Chapter 6.4
Stabilisation and solidificationof hazardous wastes
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TRP Chapter 6.4 2
ImmobilisationImmobilisation 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
stabilisedS/S often used in combination
S/S feedstock is often the residue from other
treatment processes
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TRP Chapter 6.4 3
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
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TRP Chapter 6.4 4
Waste pre-treatmentAdjustment 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 constituentsdestruction of toxicity
reduction of toxicity
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TRP Chapter 6.4 5
StabilisationChemical reaction
Acid/alkali neutralisation
Chelation
Complexation
Oxidation/reduction
PrecipitationHydroxides
Silicates
Sulphides
ChemisorptionIon exchange
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TRP Chapter 6.4 6
SolidificationMay 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
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TRP Chapter 6.4 7
AdditivesActivated carbon
Emulsifiers and surfactants
Lime, fly ash & kiln dust
Oxidants
Reducing agents
Selected clays
Soluble silicates
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TRP Chapter 6.4 8
Key factorsCharacteristics of waste
chemical propertiescomposition and concentration
acidity/alkalinity
oxidation/reduction potential
solubility
Physical properties
state (liquid, sludge or solid)
particle size, shape & distribution
solid contentviscosity
Characteristics of binders
Mode of processing
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TRP Chapter 6.4 9
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
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TRP Chapter 6.4 10
Performance testsPhysical testsMoisture content
specific gravity
bulk density
permeabilityporosity
strength
durability
Chemical tests
pH
acid neutralisation capacity
oxidation/reduction potential
total organic carbonoil & grease
volatile organic compounds
metal analysis
Leaching/extraction tests
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TRP Chapter 6.4 11
Properties of S/S treated waste1. FORMULATION:
Waste type, % and composition
Binder composition
Water content
2. PROCESSING OF MIX
Mixing method
Hydration conditions
Age
Disposal conditions
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TRP Chapter 6.4 12
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
Compatibility with disposal environment shouldbe tested
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TRP Chapter 6.4 13
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
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TRP Chapter 6.4 14
Case study - UK
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TRP Chapter 6.4 15
Schematic of waste S/S plant
Part 1: Stabilisation
5000 tonnes
Alkali waste
pH > 12
9000 tonnes
acid waste
pH > 7-8
Inorganic
solids,liquids
and
sludge
TOC < 1000 mg/L
Stock
storagetank
pH 8.5-9.5
20-30%
solids
Vacuum
filtrationto
produce
filter
cake
Incoming waste storage blending stabilised
waste waste
Waste effluent
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TRP Chapter 6.4 16
Schematic of waste S/S plant
Part 2: Solidification
stabilised
wastefilter
cake
Output ~ 6Tper hour
15% Portland cement+ 15% Pulv. Fuel Ash
+ 70% filter cake
(~ 50% solids)
Landfill
disposalin clay
lined
cell
Stabilised High energy Mono-disposal
waste mixer
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TRP Chapter 6.4 17
Waste types treated by UK plant
Type of waste % of wholeSulphuric acid 4.7
Hydrochloric acid 4.6
Chromic acid 0.6
Mixed/other acids 6.6
Al-chloride solutions 16.6Fe-chloride solutions 0.9
Solid/liquid cyanides 2.7
Caustic solutions 30.5
Neutral sludges 10.4
Lime sludges 14.0
Other sludges 0.8
Filter cakes 1.1
Paint stripper washings 1.7
Ferrous sulphate 1.0
Others 3.1
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TRP Chapter 6.4 18
28 day strength from any 1 day of production willnot 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
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TRP Chapter 6.4 19
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 areavailable
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TRP Chapter 6.4 20
Chapter 6.4 SummaryStabilisation and solidification techniques
Reduce potential for hazardous waste leaching
Improve handling and physical characteristics
May require pre-treatment of wastes eg tochange particle size, pH
Stabilisation is usually followed by solidification
Should be considered as a pre-landfill treatment
process