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Thermal Decomposition AND ACID/BASE ABSORPTION of MAGNESIUM CARBONATES

Thermal Decomposition AND ACID/BASE ABSORPTION of MAGNESIUM CARBONATES. Rafael Snell- Feikema , Neil Mehta, and Dr. Thomas DeVore. Introduction.

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Thermal Decomposition AND ACID/BASE ABSORPTION of MAGNESIUM CARBONATES

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  1. Thermal Decomposition AND ACID/BASE ABSORPTION of MAGNESIUM CARBONATES Rafael Snell-Feikema, Neil Mehta, and Dr. Thomas DeVore

  2. Introduction • The ternary system MgCO3-Mg(OH)2-H2O encompasses a great many magnesium carbonate and magnesium hydrate minerals, most of which are naturally produced in caves ( W.B. White; Environmental Geology (1997) 30: 46-58 )

  3. Introduction • Specifically, we are interested in: • Hydromagnesite: Mg5(CO3)4(OH)2-4H2O. • Nesquehonite: MgCO3-3H2O • Brucite: Mg(OH)2 ( W.B. White; Environmental Geology (1997) 30: 46-58 )

  4. Applications • Thermal and chemical stability leads to widespread use in industrial and commercial applications including perfume retainers, fire retardants, rubber reenforcers, and antacids. • Of more immediate focus is a possible method of carbon sequestration through use of brucite. Here, nesquehonite and hydromagnesite are possible intermediates or end products† †V. Vágvölgyi; M. Hales; R.L. Frost; A. Locke; J. Kristóf; E. Horváth; J Therm Anal Calorim (2008) 94:523-528

  5. Samples studied - hydromagnesite • Acros “MgCO3” • Fisher “MgCO3” • Synthesized Mg5(CO3)4(OH)2 † • Dissolved 0.01 moles magnesium sulfate in 50 mL of water. • Dissolved 0.01 moles sodium hydrogen carbonate in 50 mL of water. • Heated to boiling and mixed. • Vacuum filtered the precipitate. • Air dried for twenty-four hours. †Z. Zhang; Y. Zheng; Y. Ni; Z. Liu; J. Chen; X. Liang; J. Phys. Chem. B 2006, 110, 12969-12973

  6. Samples studied - nesquehonite • While attempting to create MgCO3, we accidentally made a very good sample of nesquehonite • Used the same process as the one which produced hydromagnesite†, but changed the temperature via use of ice water – replicating the change in conditions that occurs in caves • Dissolved 0.01 moles magnesium sulfate in 50 mL of water. • Dissolved 0.01 moles sodium hydrogen carbonate in 50 mL of water. • Heated to boiling and mixed. • Vacuum filtered the precipitate. • Air dried for twenty-four hours. †Z. Zhang; Y. Zheng; Y. Ni; Z. Liu; J. Chen; X. Liang; J. Phys. Chem. B 2006, 110, 12969-12973

  7. Samples studied - brucite • Fisher Mg(OH)2 • Actually competent commercial sample

  8. Which means we went from this:

  9. To this:

  10. Background information • Fourier Transform Infrared Spectroscopy (FTIR) • Shoot some light at some stuff • Said stuff does certain unique things in the way it absorbs light • Gives us a fingerprint of each piece of a sample

  11. Raf’s Job

  12. Neil’s Job

  13. Simple FTIR apparatus

  14. HYDROMAGNESITE

  15. IRs

  16. IRs †N. Koga; Y. Yamane; J Therm Anal Calorim (2008) 93:963-971 ‡J. Lanas; J.I. Alvarez; ThermochimicaActa(2004) 421:123-132

  17. XRD - hydromagnesite

  18. Experimental TGA • Analysis was done using a MettlerToledo TGA /SDTG 851e • N2 flow rates: purge = 150 ml/ min; protect = 50 ml/ min • Capped and uncapped 70 ml alumina cells

  19. TGA/DTG – all samples uncapped

  20. Experimental EGA • EGA-FTIR was done on a Thermo Nicolet 6700

  21. EGA – Synthesized

  22. IRs – Fisher decomposition Temperature (K) 425 575 625 675 725 925

  23. Open cell mass loss • Step 1 matches in both cases and is fairly slight, low temperature – it’s surface drying • Accounting for this addition to the mass, we can approximate the other steps Mg5(CO3)4(OH)2-4H2O <=> Mg5(CO3)4(OH)2 +4H2O Mg5(CO3)4(OH)2 <=> 2Mg(CO3)+ 3MgO + 2CO2 + H2O (overlapping step #2) Mg(CO3) <=> MgO + CO2

  24. TGA/DTG – all samples capped

  25. SDTA – all samples capped

  26. TGA – effect of sample size

  27. TGA – effect of heating rate

  28. Kinetics Theory • DTG data can be used to find activation energy via the Kissinger equation† : • Where β is the heating rate and T is the temperature at the maximum reaction rate • Graphing ln(β/T2) vs 1000/T gives -E/R as the slope in kJ/mol †X.W. Liu; L. Feng; H.R. Li; P. Zhang; P. Wang ; J Therm Anal Calorim (2012) 107:407-412

  29. Kinetics - dehydroxylation

  30. Kinetics - decarbonation †X.W. Liu; L. Feng; H.R. Li; P. Zhang; P. Wang ; J Therm Anal Calorim (2012) 107:407-412

  31. Observations • MgCO3 (s) <=> MgO(s) + CO2 (g) • As the pressure of CO2 rises, it drives the equilibrium to the left, causing the apparent decomposition to occur at a higher temperature. • Amorphous MgCO3 turns to crystalline MgCO3 at 808 K, which then decomposes rapidly, giving the observed “new” transition. • Fisher and Acros vary due to differing apparent densities • Fisher and our synthesized sample vary due to differing morphologies† †D. Bhattacharjya; T. Selvamani; I. Mukhopadhyay; J Therm Anal Calorim (2012) 107:439-445; “Thermal decomposition of hydromagnesite: Effect of morphology on the kinetic parameters”

  32. Nesquehonite desorption

  33. Acetic acid Absorption

  34. Introduction, part II • Aside from carbon sequestration, magnesium minerals (again due to their high thermal and chemical stability) can be used to neutralize harmful VOCs such as industrial gasses, paint fumes, and agricultural waste • As such, it is useful to study absorption of an acid onto essential forms of the ternary system as well as desorption afterwards • Chemicals studied: • Hydromagnesite(Mg5(CO3)4(OH)2-4H2O) • Nesquehonite (MgCO3-3H2O) • Brucite (Mg(OH)2) • Magnesia (MgO)

  35. Absorption apparatus

  36. Absorption of HOAC by MgO

  37. Absorption of HOAC by Mg(OH)2

  38. Absorption of HOAC by Hydromagnesite

  39. Absorption of HOAC by Nesquehonite

  40. Desorption, Nesquehonite-HOAC

  41. Desorption, Mg(OH)2-HOAC

  42. Desorption, MgO-HOAC

  43. Desorption, Hydromagnesite-HOAC • Ran out of time • Desorption products can be assumed through the other compounds and through what we already know • INSERT PRODUCTS

  44. Conclusions • MgCO3 is a conspiracy made up by the chemistry illuminati • Ternary systems found in caves are kinda complex • Carbon sequestration on to Mg(OH)2 with the possible product of nesquehonite and the possible intermediate of hydromagnesite is actually very practical • Acetic acid absorbs to varying degrees on to each compound (although fairly easily on all of them) • RANK HERE

  45. Acknowledgements • Dr. Reisner (X-ray diffraction lab) Research Corporation Departmental Development Grant #7957 NSF: MRI 0340245 (TGA-MS) NSF: DMR 0315345 (XRD) NSF: REU - 1062629

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