Waste Treatment, Chemical

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Waste Treatment, Chemical

• ENVE 649

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Why Treat Waste

• Have a RCRA Waste
• TSDS
• Treat instead of disposal, landfill
• Treat before disposal
• Or treat in process stream
• eliminate waste

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Typical Treatment

• Remove hazardous constituent from matrix
• Frequently a chemical from liquid
• Solubility
• Main chemical techniques
• Precipitation
• Neutralization
• Coagulation and flocculation

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Solubility

• Polar vs. Non-polar
• Water is polar

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Oxygen
Hydrogen
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N-Octane, non-polar
Carbon
Hydrogen
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Like Dissolves Like

• Polar substances are hydrophilic
• Ions are very hydrophilic
• Non-polar are hydrophobic and poorly soluble
• Some are both, ethanol

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Ethanol
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1-octanol
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Hydrophobic in water

• Remove the hydrophobic layer
• In petroleum cleanups this is the free product

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Neutralization

• Watery wastes
• May make non-hazardous directly
• Makes waste amenable to other processes
• pH -logH
• pH 7, neutral
• pH gt 7, base or alkaline
• pH lt 7, acid

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Neutralizing

• Acid Base Salt Water
• For acid water, use bases
• soda ash Na2CO3
• caustic soda NaOH
• slaked lime Ca(OH)2
• For alkaline water, use acids
• H2SO4, HCL, CO2

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Weak Acids and Bases

• Chemistry of weak acids
• Strong acids are 100 ionized
• The ionization of weak acids depends on pH
• Most organic acids are weak
• Changes in pH may change solubility
• H-Aweak in low pH (acid) solution
• Aweak- (anion) in high pH (basic) solution

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Oxidants

• Chlorine Cl2
• Ozone, O3
• Hydrogen Peroxide, H2 O 2

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Precipitation

• Not all salts are soluble
• Some metals (Pb) form insoluble hydroxides as
  high pH (alkaline)

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Precipitation

• Temperature is important
• Oxygen content
• Valence state of metal
• Example
• Raw well water has Fe (II) or ( Fe or
  Ferrous)in water as Fe(OH)2 which is soluble
• But at surface Fe goes to Fe or Ferric)which
  forms Fe(OH)3 which is insoluble

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Sulfide formation

• Add Na2S or NaHS -gt S--
• Metal, M S-- -gt metal sulfide, MS
• Most metal sulfides are insoluble
• (at same pH where metal hydroxide is soluble)

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Leaching

• Opposite of precipitation
• CN forms complexes Fe(CN-)6
• But also gold (Au)

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Size Scales
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• Solids
• Evaporate water and get
• Total Solids
• Filter for Suspended Solids
• Define, 1 micron filter typically
• Also, Imhoff cone
• What settles in 60 minutes

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Colloids

• Very small
• typically charged and will not agglomerate

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Stable Suspended Particles
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Add Flocculent and mix rapidly
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Micro-flocs
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Flocs aggregate
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Most common coagulants

• Inorganic
• Alum Al2(SO4)3
• Ferric chloride FeCl3
• Ferric sulfate Fe2(SO4)3

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Organic polymers
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• Oil-water emulsion
• emulsion breakers

Creaming
Breaking
Stable Emulsion
Flocculation
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Ion Exchange

• Water softener
• Zeolites
• Remove low level metals
• recharge cycles
• Cant use if suspended solids, organic material,
  oxidants