1 Waste Treatment, Chemical ENVE 649

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

3 Typical Treatment Remove hazardous constituent from matrix Frequently a chemical from liquid –Solubility Main “chemical” techniques: –Precipitation –Neutralization –Coagulation and flocculation

4 Solubility Polar vs. Non-polar Water is polar -  - = Oxygen = Hydrogen +-+- -  - +-+-

5 N-Octane, non-polar = Hydrogen = Carbon

6 Like Dissolves Like Polar substances are hydrophilic –Ions are very hydrophilic Non-polar are hydrophobic and poorly soluble Some are both, ethanol

7 Ethanol

8 1-octanol

9 Hydrophobic in water Remove the hydrophobic layer In petroleum cleanups this is the “free product”

10 Neutralization Watery wastes May make non-hazardous directly Makes waste amenable to other processes pH = - log[H + ] pH = 7, neutral pH > 7, base or “alkaline” pH < 7, acid

11 Neutralizing Acid + Base = Salt +Water For acid water, use bases –soda ash Na 2 CO 3 –caustic soda NaOH –slaked lime Ca(OH) 2 For alkaline water, use acids –H 2 SO 4, HCL, CO 2

12 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-A weak in low pH (acid) solution A weak - (anion) in high pH (basic) solution

13 Oxidants Chlorine Cl 2 Ozone, O 3 Hydrogen Peroxide, H 2 O 2

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

15

16 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

17 Sulfide formation Add Na 2 S or NaHS -> S -- Metal, M ++ + S -- -> metal sulfide, MS Most metal sulfides are insoluble (at same pH where metal hydroxide is soluble)

18 Leaching Opposite of precipitation CN forms complexes Fe+++(CN - ) 6 But also gold (Au)

19 Size Scales

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

21 Colloids Very small typically charged and will not agglomerate

Stable Suspended Particles

Add Flocculent and mix rapidly

Micro-flocs

Flocs aggregate

26 Most common coagulants Inorganic Alum Al2(SO4)3 Ferric chloride FeCl3 Ferric sulfate Fe2(SO4)3

27 Organic polymers

28 Oil-water emulsion –emulsion breakers Stable Emulsion Flocculation Creaming Breaking

29 Ion Exchange Water softener “Zeolites” Remove low level metals recharge cycles Can’t use if suspended solids, organic material, oxidants