Transcript Hazardous Wastes Introduction

Chapter 6.4
Stabilisation and solidification
of hazardous wastes
TRP Chapter 6.4 1
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
TRP Chapter 6.4 2
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
TRP Chapter 6.4 3
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
TRP Chapter 6.4 4
Stabilisation
Chemical reaction
•Acid/alkali neutralisation
•Chelation
•Complexation
•Oxidation/reduction
•Precipitation
•Hydroxides
•Silicates
•Sulphides
Chemisorption
Ion exchange
TRP Chapter 6.4 5
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
TRP Chapter 6.4 6
Additives
•Activated carbon
•Emulsifiers and surfactants
•Lime, fly ash & kiln dust
•Oxidants
•Reducing agents
•Selected clays
•Soluble silicates
TRP Chapter 6.4 7
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
TRP Chapter 6.4 8
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
TRP Chapter 6.4 9
Performance tests
Physical tests
Chemical tests
•Moisture content
•pH
•specific gravity
•acid neutralisation capacity
•bulk density
•oxidation/reduction potential
•permeability
•total organic carbon
•porosity
•oil & grease
•strength
•volatile organic compounds
•durability
•metal analysis
Leaching/extraction tests
TRP Chapter 6.4 10
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
TRP Chapter 6.4 11
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
TRP Chapter 6.4 12
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
TRP Chapter 6.4 13
Case study - UK
TRP Chapter 6.4 14
Schematic of waste S/S plant
Part 1: Stabilisation
Inorganic
solids,
liquids
and
sludge
TOC < 1000 mg/L
Waste effluent
5000 tonnes
Alkali waste
pH > 12
Stock
storage
tank
pH 8.5-9.5
20-30%
solids
9000 tonnes
acid waste
pH > 7-8
Incoming
waste
waste storage
blending
Vacuum
filtration
to
produce
filter
cake
stabilised
waste
TRP Chapter 6.4 15
Schematic of waste S/S plant
Part 2: Solidification
stabilised
waste
filter
cake
Stabilised
waste
Output ~ 6T
per hour
15% OPC + 15% PFA
+ 70% filter cake
(~ 50% solids)
High energy
mixer
Landfill
disposal
in clay
lined
cell
Mono-disposal
TRP Chapter 6.4 16
Waste types treated by UK plant
Type of waste
Sulphuric acid
Hydrochloric acid
Chromic acid
Mixed/other acids
Al-chloride solutions
Fe-chloride solutions
Solid/liquid cyanides
Caustic solutions
Neutral sludges
Lime sludges
Other sludges
Filter cakes
Paint stripper washings
Ferrous sulphate
Others
% of whole
4.7
4.6
0.6
6.6
16.6
0.9
2.7
30.5
10.4
14.0
0.8
1.1
1.7
1.0
3.1
TRP Chapter 6.4 17
Treated waste specification
• 28 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
TRP Chapter 6.4 18
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
TRP Chapter 6.4 19
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
TRP Chapter 6.4 20