Waste Treatment, Chemical

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 = Carbon = Hydrogen

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 Na2CO3 • caustic soda NaOH • slaked lime Ca(OH)2 • For alkaline water, use acids • H2SO4, HCL, CO2

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-Aweak in low pH (acid) solution • Aweak- (anion) in high pH (basic) solution

13. Oxidants • Chlorine Cl2 • Ozone, O3 • Hydrogen Peroxide, H2 O 2

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

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 Na2S 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

22. + + + + + + + + + + + + + + + + + + + + + + Stable Suspended Particles

23. - - - - - - - - + - + + - - + - + + + + + + + + + + + + + + - + - + + - - + Add Flocculent and mix rapidly

24. - - + - - - + + + + - - + + + + - - - - - + + - - + + - - + + + Micro-flocs

25. - + + - - - + - + + + - - - + + - + - - + + - - - + - + + + + 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 Creaming Breaking Stable Emulsion Flocculation

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