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Chromium Remediation:

Removal of Hexavalent Chromium from the Environment

What is Chromium?Hexavalent Chromium Cr (VI) Trivalent Chromium Cr (III)

K2Cr2O7CrO3

CrCl3Cr2(SO4)3

The Good The Bad The Ugly

Chromium in the Environment

1. Cr (VI) detected in 3342/5477 wells tested

2. Los Angeles [Cr6+] > 10 g/L

3. 2104 CA to limit Cr6+ to 10 ppb

4. Hinkley, CA had Cr6+ levels of 31.8 ppb

Where Does Chromium Come From

Fate of Chromium in Environment

ChromiumRemediation

Batch ReactorBiochemicalNanotechnologyPrecipitationFiltration

Ion exchange

Chromium Filtration Devices

Biological Treatment

Batch Reactor

Methods:1) Packets of walnut shells, corncob, saw dust (mix of various types of wood), woodshavings and activated charcoal powder were made using coffee filter paper and placed into a container Above media known to adsorb chromium2) Chromium solution was diluted by a factor of 10^6 in order to use UV vis throughout entire sample range (the UV Vis test kit used only measured accurate values 300ppb and below),it was then added to reactor for single batch3) Samples of the solution were collected every 5 minutes for an hour4) Samples were analyzed using UV Vis and titration

Precipitation

Methods:1) Packets of walnut shells, corncob, saw dust (mix of various types of wood), woodshavings and activated charcoal powder were made using coffee filter paper and placed into a container Above media known to adsorb chromium2) Chromium solution was diluted by a factor of 10^6 in order to use UV vis throughout entire sample range (the UV Vis test kit used only measured accurate values 300ppb and below),it was then added to reactor for single batch3) Samples of the solution were collected every 5 minutes for an hour4) Samples were analyzed using UV Vis and titration

Organic Reagents

Back Titration

Colorimetric Analysis: UV-VisAnalysis of Chromium

Organic Analysis of Chromium

Dipehenylcarbazide

Method is use only for low concentration of Cr -- 1.0 ppm or 0.1 mg/L or lessmust dilute sample before using testmachine measures the absorbance of green light and gives reading in ppbOnly measures Cr(VI); if want to measure Cr(III) in sample, must convert to Cr(VI) first.1,5-Diphenylcarbazide reacts with Cr(VI) ions under acidic condition to create a pink solutionDiphenylcarbazide is oxidized to Diphenylcarbazone, while Cr(VI) is reduced to Cr (III)the intensity of color is dependent on the concentration of Cr

Source: google bookformula

Sulfamic acid, Iodide, Dichromate reaction6I-(aq) + Cr2O72-(aq) +14H+(aq) 3I2(aq) +2Cr3+(aq) + 7H2O (l)Dichromate

Diluted Chromium SampleSulfamic Acidand Potassium Iodide

Titration Analysis

Describe what Titration is Redox reactionDichromate reacts with iodide in acidic solution to form elemental iodineSolution becomes more yellow after reaction

sulfamicacid, KI, Dichromate: https://answers.yahoo.com/question/index?qid=20080815061454AAF0vsrAlso see Production and Use section of : http://www.britannica.com/science/iodineCompared to clock experiment reaction

Formation of TriiodideI-(aq) + I2(aq) I3-(aq) triiodide

Black-blue complexI3-(aq) + StarchBlack-Blue Complex

Starch IndicatorIodine Oxidation-Reduction

The iodine from the previous reaction reacts with excess iodide ions to form triiodide2 drops of starch indicator is added to the mixtureA black-blue complex is formed from triiodide and the starch indicator

https://en.wikipedia.org/wiki/Starch_indicatorhttps://en.wikipedia.org/wiki/Iodine_test

Titration with thiosulfateI3-(aq) + 2 S2O32-(aq) 3 I-(aq) +S4O62-(aq) thiosulfatetetrathionate

After TitrationBack Titration

A thiosulfate solution is added drop by dropThe thiosulfate reacts with the triiodide in the black-blue complex to form the iodide ionThere is no more triiode to create the black-blue complex, making the mixture clearThe amount of Chromium is figured in relation to the amount of triiode, which is figured out by the known amount of thiosulfate added.

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch19/oxred_2.php

Colorimetric Analysis of Chromium

UV-Vis instructions: https://www.bioassaysys.com/Datasheet/DCRM.pdf

Purified Chromium Solutions

FiltrationFiltrationPrecipitationE.ColiBatchBeforeDPA: 139,000,000 ppb

Titration: 10 g/L

UV-VIS: >1000 g/L27,800,000

10 g/L

139,000,000 ppb

10 g/L

>1000 g/L139,000,000 ppb

10 g/L

>1000 g/L100 ppb

1000 g/L

AfterDPA: 780,000 ppb

Titration: 5 g/L

UV-VIS: >1000 g/L

37,700 ppb

0.60 g/L13 ppb

0 g/L

Not Measured25,000 ppb

0.6 g/L

Not Measured56 ppb*

1000 g/L

*10 minutes

Analysis of Chromium

Summary of Results

AcknowledgementsCal Poly Pomona

Dr. Monica PalomoDr. Ali SharbatLucas TownsendKahao LimSHINE

Dr. Graciela MatrajitBrian RucciKristine Schroeder

Pasadena City College

Dr. Veronica JaramilloRafik NazarpoorPhu Nguyen