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Zinc and Chromium removal mechanisms from industrial wastewater by using water hyacinth, eicchonia crassipes

( Télécharger le fichier original )
par John Gakwavu Rugigana
National University of Rwanda - Master's in WREM (water resources and environmental management) 2007
  

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Appendix XV: Synthetic wastewater and Nutrient solutions

A) Heavy metals concentration in synthetic wastewater

Substances

Concentration (mg / L)

Zn (mg/l)

5

Cu (mg/l)

0,4

Pb (mg/l)

1

Cr (mg/l)

6

B) Heavy metals concentration in synthetic wastewater

Substances

Concentration (mg / L)

Zn (mg/l)

5

Cu (mg/l)

0,4

Pb (mg/l)

1

Cr (mg/l)

6

SO42- (mg/l)

200 - 2000

OC (mg/l)

50 - 500

C) Hutner solution (Leman, 2000)

Substances

Concentration (mg / L)

NH4Cl

20

K2HPO4

40

Ca(NO3)2 4H2O

20

MgSO4 4H2O

50

FeSO4 7H2O

2,5

MnCl2 4H2O

1,5

ZnSO4 7H2O

6,5

H3BO3

1,5

Na2MoO4 2H2O

2,5

CuSO4 7H2O

0,4

CoSO4 7H2O

0,1

EDTA (Na)2

50

Appendix XVI: Protocol used in laboratory experiments

The destruction of plants and fish tissue for the determination of Cd, Cr, Cu, Pb, Mn,

Fe and Zn with the atomic absorption technique

2.2.1 Apparatus

a) Destruction-bloc with destruction tubes made of borosilicate glass

b) Nichiryo pipet model 3100 with removable tips

2.2.2 Reagents, all with a low metal content

a) Nitric acid, 65% HNO3

b) Hydrogen peroxide, 30% H2O2

c) Pumice

2.2.3 Glassware

All rinsed with 1 + 1 HNO3

Measuring cylinder, 50 mL

Funnels with a diameter of 6 cm Volumetric flasks of 250 mL

2.2.4 Procedure

1. Transfer not more than 1.250 g dried sample (24 hours at 103°C) to the destruction tube, add 25 mL HNO3, three boiling chips and place a funnel on

top of the destruction tube.

2. a) Heat the tube to 100°C and maintain for 1 hour b) Heat to 125°C and maintain for 15 minutes

c) Heat to 150°C and maintain for 15 minutes

d) Heat to 175°C and maintain for 15 minutes

e) Heat to 200°C and add, if necessary (if no volume is left), 5 mL HNO3

3. Concentrate to about 5 mL

4. Add, after cooling, 1 mL 30% H2O2 and destruct for 10 minutes, repeat 1 x

5. Add, after cooling, 3 mL 30% H2O2 and destruct again for 10 minutes

6. Add 25 mL water, mix and heat till boiling

7. Cool and transfer the whole sample to a 250 mL volumetric flask, fill up to the mark, mix and let settle during at least 15 hours

8. Measure the absorbance of the clear supernatant.

Note: 1. Duration of procedure steps 1-7 at least 7 hours 2. Determine two blancs

2.3 The destruction of soil and sludge for the determination of Cd, Cr, Cu, Pb,

Mn, Fe and Zn with the atomic absorption technique

2.3.1 Apparatus

a) Destruction-bloc with destruction tubes made of borosilicate glass

b) Nichiryo pipet model 3100 with removable tips

2.3.2 Reagents

All reagents with a low percentage of heavy metals

a) Hydrochloric acid, 37% HCl

b) Nitric acid, 65% HNO3

c) Hydrogen peroxide, 30% H2O2

d) Pumice

2.3.3 Glassware

All rinsed with 1 + 1 HNO3

Measuring cylinder, 500 mL Measuring cylinder, 50 mL Funnels with a diameter of 6 cm

1 L flask for the acid-mixure, see note

Volumetric flasks of 250 mL

2.3.4 Procedure

1. Transfer not more than 1.250 g of a ground air-dried sample to the destruction tube, add 50 mL H2O and three boiling chips

2. Add 50 mL HCl/HNO3 3:1, mix, and place a funnel on top of the destruction

tube

3. a) Heat the tube to 100°C and maintain for 1 hour b) Heat to 125°C and maintain for 15 minutes

c) Heat to 150°C and maintain for 15 minutes

d) Heat to 175°C and maintain for 15 minutes

e) Heat to 200°C and add, if necessary (if no volume is left), 5 mL HNO3

4. Concentrate to about 5 mL

5. Add, after cooling, 1 mL 30% H2O2 and destruct for 10 minutes. Repeat 1 x

6. Add, after cooling, 3 mL 30% H2O2 and destruct again for 10 minutes

7. Add 50 mL water and 25 mL HCl, mix and heat till boiling

8. Cool and transfer the whole sample to a 250 mL volumetric flask, fill up to the mark, mix, and let settle during at least 15 hours

9. Measure the absorbance of the clear supernatant.

Note: 1. Prepare a fresh acid-mixture and do not close the container!!

2. Duration of procedure steps 1-7 at least 7 hours

3. Determine two blancs

4. Sludge samples will decompose almost completely

2.4 Preliminary Digestion for Metals in water

To reduce interference by organic matter and to convert metal associated with particulates to a form (usually the free metal) that can be determined by atomic absorption spectrometry or inductively-coupled plasma spectroscopy, use one of the digestion techniques presented below. Use the least rigorous digestion method required to provide complete and consistent recovery compatible with the analytical method and the metal being analyzed.

Nitric acid will digest most samples adequately. Nitrate is an acceptable matrix for both flame and electrothermal atomic absorption. Some samples may require addition of perchloric, hydrochloric, or sulfuric acid for complete digestion. These acids may interfere in the analysis of some metals and all provide a poorer matrix for electrothermal analysis. Confirm metal recovery for each digestion and analytical procedure used. As a general rule, HNO3 alone is

adequate for clean samples or easily oxidized materials: HNO3-H2SO4 or
HNO3-HCl digestion is adequate for readily oxidizable organic matter; HNO3-
HClO4 or HNO3-HClO4-HF digestion is necessary for difficult-to-oxidize organic

matter or minerals. Dry ashing is helpful if large amounts of organic matter are present, but yields highly variable precision and bias, depending on sample type and metal being analyzed. Dry-ash only samples that have been shown to yield acceptable precision and bias.

2.4.1 Dry ashing procedure, use only if necessary

Mix sample and tranfser a suitable volume into a platinum or high-silica glass evaporating dish. Evaporate to dryness on a steam bath. Transfer dish to a muffle furnace and heat sample to a white ash. If volatile elements are to be determined, keep temperature at 400 to 450°C. If sodium only is to be determined, ash sample at a temperature up to 600°C. Dissolve ash in a minimum quantity of conc HNO3 and warm water. Filter diluted sample and

adjust to a known volume, preferably so that the final HNO3 concentration is about 1%. Take portions of this solution for metals determination.

2.4.2 Nitric acid digestion procedure

Apparatus

a) Hot plate

b) Conical flasks, 100 mL, acid-washed and rinsed with water

Reagents

Nitric acid, HNO3, conc. Procedure

Mix sample and transfer a suitable volume (50 to 100 mL) to a 100 mL conical
flask or beaker. Add 5 mL conc. HNO3 and a few boiling chips. Bring to a slow

boil and evaporate on a hot plate to the lowest volume possible (about 10 to 20

mL) before precipitation occurs. Continue heating and adding conc HNO3 as

necessary until digestion is complete as shown by a light-colored, clear solution. Do not let sample dry during digestion.

Wash down flask or beaker walls with water and then filter if necessary. Transfer filtrate to a 100 mL volumetric flask with two 5 mL portions of water, adding these rinsings to the volumetric flask. Cool. dilute to mark, and mix thoroughly. Take portions of this solution for required metal determinations.

2.4.3 Nitric Acid-Hydrochloric Acid Digestion Apparatus see 2.4.2

Reagents

a) Nitric acid, HNO3, conc.

b) Hydrochloric acid, 1 + 1

Procedure

a) Total HNO3/HCl: Transfer a measured volume of wellmixed, acid-preserved

sample appropriate for the expected metals concentrations to a flask or
beaker. Add 3 mL conc HNO3. Place flask or beaker on a hot plate and

cautiously evaporate to less than 5 mL , making certain that sample does not
boil and that no area of the bottom of the container is allowed to go dry. Cool
and add 5 mL conc HNO3. Cover container with a watch glass and return to

hot plate. Increase temperature of hot plate so that a gentle reflux action occurs. Continue heating, adding additional acid as necessary, until digestion is complete (generally indicated when the digestate is light in color or does not change in appearance with continued refluxing). Evaporate to less than 5 mL and cool. Add 10 mL 1 + 1 HCl and 15 mL water per 100 mL anticipated final volume. Heat for an additional 15 min to dissolve any precipitate or residue. Cool, wash down beaker walls and watch glass with water, and adjust to a predetermined volume based on the expected metals concentrations. If necessary (when particles are present), let settle overnight.

b) Recoverable HNO3/HCl: For this less rigorous digestion procedure, transfer

a measured volume of well-mixed, acid-preserved sample to a flask or
beaker. Add 2 mL 1 + 1 HNO3 and 10 mL 1 + 1 HCl and heat on a steam

bath or hot plate until volume has been reduced to near 25 mL, making certain sample does not boil. Cool and let settle overnight. Adjust volume to 100 mL and mix.

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