1)
http://www.testmasters.com/assets/docs/limesoftening.pdf, accessed 11/18/2013
An example of a water softening bar chart is above. This chart can be used to determine the
amount of lime and soda ash to add to water to soften (remove metal ions). The recipe is: 1
equivalent of lime per equivalent CO2, 1 equivalent lime per equivalent calcium hardness, 2
equivalents of lime per equivalent of magnesium carbonate hardness, 1 equivalent of lime per
magnesium non-hardness, and one 1 equivalent of soda ash (sodium carbonate) per equivalent
of non-carbonate hardness. In the bar graph above, the lime requirements would be = 12.9(1) +
179(1) + 14(2) + 77(1) = 296.9 mg/L as CaCO3 (assuming no excess lime), and 77(1) = 77 mg/L as
CaCO3
2) Cyanide detox of water – oxidative treatments. Compare three different methods
Cyanides can be used in many chemical and metallurgical processes as simple salts or cyanide
complexes. Cyanide is highly toxic, and has tight compliance limits in wastewater.
Alkaline chlorination
Alkaline chlorination is used by most electroplating shops that generate dilute cyanide bearing
wastewater. Alkaline chlorination can be achieved by either directly adding chlorine gas and
sodium dioxide to the water, or by direct addition of sodium hypochlorite. The gaseous chlorine
has been estimated to be about half as costly, but is perceived to be more dangerous due to
the handling of chlorine gas. Assuming the use of sodium cyanide, the first stage reaction using
sodium hypochlorite is
NaCN + NaOCl  NaCNO + NaCl,
and the second stage is
2NaCNO + 3NaOCl + H2O  3NaCL + N2 + 2NaHCO3
Stable cyanide complexes (ferrocyanides) are typically unaffected by chlorinates and cannot use
this method of destruction. Cyanides complexed with copper, nickel, and precious metals react
more slowly than free cyanide and requires excess chlorine. Concentrated wastes (such as
spent plating solutions) cannot use alkaline chlorination due to the potential for chlorine gas.
http://www.nmfrc.org/bluebook/sec623.htm
Ozone Oxidation
Ozone oxidation can be used for cyanide destruction. The operating costs are less than alkaline
chlorination, but the equipment is more expensive due to the expense of an ozone generator.
An advantage to ozone over chlorine is that while chlorine can combine with organics to
produce toxic compounds, ozone will not. Ozone can also destroy zinc, copper, and cyanide
complexes.
Chemical Precipitation
Ferrocyanide (Fe(CN)6 4- is a less-toxic cyanide because it tends not to release free cyanide.
Ferrous sulfate can be used to precipitate cyanide, which can be removed in a subsequent
sedimentation process.
3) Reductive treatments for cr(vi) detoxification of water, compare at least three different
methods
Hexavalent chromium is frequently used in industrial processes, but is highly toxic and has tight
compliance discharge limits.
Ion Exchange
Ion exchange removes chromium ions from the aqueous phase by replacing them with the
anion present in the ion exchange resin such as chlorides or hydroxides. Ion exchange units
typically require pretreatment to remove organics, suspended solids, and other contaminants
that can foul the resin. Ion exchange units minimize the need for handling and on-site storage
of chemicals and wastes.
Conversion to Trivalent Chromium and Precipitation
To convert hex chrome to trivalent chrome, acid (usually sulfuric) is added to wastewater to
produce a low pH (between 1 and 2). Then, reducing agents such as sulfur dioxide, sodium
bisulfate, or sodium metabisulfate are added. For example:
3SO2 + 2H2CRO4 + 3 H2O <-> Cr2(SO4)3 + 5H2O.
When the reaction is complete, a sudden drop in ORP will occur. Once the reaction is complete,
lime is added to increase and maintain a pH of 8 or higher and to precipitate chromium
hydroxide. The precipitate chromium hydroxide is non-toxic and can be easily removed and
disposed.
Cr2(SO4)3 +3Ca(OH)2 <-> 2Cr(OH)3 + 3CaSO4)
Bioabsorbtion
Some biological materials have the ability to accumulate heavy metals. Algae, bacteria, and
fungi have shown to be potential metal bioabsorbents. Biological materials have benefits of
Low cost, high versatility, high uptake, high tolerance of organics, and regeneration. In a paper
by Sukumar “reduction of hexavalent chromium by rhizopus oryza”, the reduction ability of a
specific organism was tested at a laboratory scale. At optimum conditions, there was a 91.15%
conversion of hex chromium to trivalent chromium. Based on the high removal chromate
removal, bioabsorbtion may be a feasible, economical technique for chromate removal.
Sukumar, M. Reduction of hexavalent chromium by Rhizopus Oryza. African Journal of Environmental Science and Technology. Vol 4(7)( pp 412418, July 2010.
http://www.water.siemens.com/en/applications/wastewater_treatment/chrome-removal/Pages/default.aspx
http://www.hubbardhall.com/chemical-apps-wastewater-chrome-reduction.htm
http://www.sensorex.com/docs/AppNoteChromeWaste.pdf
4) 1000 word essay summarizing progress on project
Paper mostly done at this point. Needs to be reviewed for punctuation/grammar/readability.