Stabilization(1)

7/28/2019 Stabilization(1)

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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

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Stabilization(1)