1. ON THE POTENTIAL TOXICITY OF “PROMISING” CHROMIUM EXTRACTANTS G
ON THE POTENTIAL TOXICITY OF “PROMISING” CHROMIUM EXTRACTANTS G. Lytras, G. Malavetas, C. Lytras, G. Lyberatos ICEHT/FORTH and NTUA

2. Approximately 4.500 kg/d chromium are discharged into the environment.

3. Chromium in water & wastewater
Two stable oxidation states:
Hexavalent [Cr(VI)]
Trivalent [Cr(III)].
Hexavalent chromium is highly toxic and can cause serious damage to the environment and human beings.
Trivalent chromium is less toxic and can be readily precipitated out of solution in the form of Cr(OH)3.
Hexavalent [Cr(VI)]
Hexavalent chromium is highly toxic and can cause serious damage to the environment and human beings.

4. Presence of Cr(VI) in the Environment
Chromium from the anthropogenic sources is discharged into the environment mainly as hexavalent chromium.
Recent studies have shown that Cr(VI) can be formed naturally in the environment.

5. Legislation for Chromium and Cr(VI)
Potable water:
Both in U.S.A. and E.U. the maximum Cr (VI) concentration in potable water is 0.05 ppm.
Wastewater:
In E.U. the maximum daily effluent concentration for industrial wastewater should not exceed 3 ppm.

6. Ways for Cr(VI) removal
Chemical reduction to Cr(III) which can be precipitated as hydroxides.
Ion Exchange
Adsorption
Reverse Osmosis
Biological removal of Cr(VI)
Liquid-Liquid Extraction

7. Liquid-Liquid Extraction
During Liquid- Liquid Extraction (LLE) Cr(VI)  contained in an aqueous phase  is transferred to another organic phase which is water immiscible.
Cr(VI) ions
Cr(VI) ions
Organic Phase
Aqueous Phase

8. Advantages of LLE
LLE can selectively extract a desired metallic ion from a feed solution containing a significant amount of metallic impurities.
LLE can concentrate the desired ion in final aqueous solution so that it can be treated by methods inappropriate for the initial dilute feed.
LLE is well suited for process automation and efficient metal recovery from a mixed-metal hydroxide slurry.
(Knocke et al., 1978; Petersen et al., 1981)

9. Organic & Aqueous Phase
Organic phase:
Organic solvent
Extractant
(Modifier or stabilizer)
Aqueous phase:
Wastewater containing 1000 ppm Cr(VI)

10. Organic Solvent The organic solvent must be: Bio-compatible
Non- biodegradable
Non- volatile
Water-immiscible

11. Organic Solvents The following organic solvents were screened:
Hexane [C6H14]
Heptane [C7H16]
Chloroform [CHCl3]
Ethyl acetate [C4H8O2]
Kerosene

12. Extractants The following extractants were used:
N-Methyl-N,N-dioctyloctan-1-ammonium chloride (Aliquat 336) [C25H54CIN]
 Tri-n-octylphosphine oxide (TOPO) [C24H51OP]
Tri-n-butyl phosphate (TBP) [C12H27O4P]

13. Experimental procedure
Stir at 25oC at 35rpm for 24 hours
Transfer to a separation funnel and leave it for 45 minutes
Organic phase
Aqueous phase with Cr(VI)
Separation of organic and aqueous phase

15. Toxicity of organic solvents
Growth
Hexane, C6H14 -
Heptane, C7H16 +
Chloroform, CHCl3
­­-
Ethyl acetate,C4H8O2
Kerosene ++
Microorganisms derived from anaerobic sludge of the Municipal Wastewater Treatment Plant of Lycovrisi, Attica, Greece
24 hours at 35rpm
25oC

16. Stabilizer
The kerosene/Aliquat 336 forms an intense interphase. So, we used 1-hexanol as a stabilizer.
+10% v/v 1-Hexanol
Organic phase:
5% v/v Aliquat 336
Kerosene
Aqueous phase:
1000ppm Cr(VI)
20 ml organic phase: 20 ml aqueous phase

17. Optimization of conditions during Cr(VI) extraction from aqueous solutions with kerosene/Aliquat 336/1-hexanol mixture

18. Effect of pH on the Cr(VI) extraction efficiency
Initial Cr(VI) concentration: 1000 ppm
Shaking time: 24 hours
Organic: Aqueous phase: 1:1
Temperature: 25 oC

19. Effect of organic:aqueous phase ratio on the Cr(VI) extraction efficiency
Initial Cr(VI) concentration: 1000 ppm
Shaking time: 24 hours
Temperature: 25 oC

20. Effect of the initial Cr(VI) concentration on the Cr(VI) extraction efficiency
Shaking time: 24 hours
Organic: Aqueous phase: 1:1
Temperature: 25 oC
pH: 7

21. Effect of shaking time on the Cr(VI) extraction efficiency
Initial Cr(VI) concentration (ppm)
Final Cr(VI) concentration (ppm)
Standard Deviation
(SD)
% Extraction of Cr(VI)
0 min
1000
69,8
4,51
93,0
5 min
66,1
7,11
93,4
10 min
78,8
2,03
92,1
20 min
75,8
6,71
92,4
40 min
66,4
5,18
2 h
79,4
7,28
4 h
82,5
1,53
91,8
24 h
66,3
6,73
Organic:Aqueous phase: 1:1
Temperature: 25 oC
pH: 7

22. Toxicity of Organic Phase
Microorganisms derived from the anaerobic sludge of a Municipal Wastewater Treatment Plant, grown either in YPD or in a Basal Medium, were incubated with the organic phase.
100% mortality of both cultures during the second day of incubation.
YPD: 20 g/L Glucose, 10 g/L Yeast Extract, 20 g/L Bactopeptone
Basal Medium: 4 g/L Glucose, 1 g/L NH4Cl, 1.75 g/L KH2PO4, 0.25 K2HPO4, 7 ml/L trace elements’ solution

23. Toxicity of Organic Phase
Incubation:
2 days
Temperature:
25oC
17 ml Kerosene + 2ml 1-Hexanol +1ml Aliquat 336
20 ml of mixed culture+ 20 ml sterile H2O
18 ml Kerosene + 2ml 1-Hexanol
20 ml of
mixed culture
20 ml of
mixed culture
Aliquat 336 is the toxic ingredient of the organic phase
YPD
Basal Medium

24. Toxicity of Aliquat 336
Addition of 200 μl of Aliquat 336 in 20 ml of the mixed culture growing in Basal Medium led to 100% mortality during the second day of the incubation.
The mixtures Aliquat 336/Heptane, Aliquat 336/Kerosene, Aliquat 336/Olive pomace oil were also toxic.

25. Toxicity of Aliquat 336
The addition of 200 ml Organic Phase in a 2L anaerobic bioreactor led to 100% mortality during the first days of the operation.
The bioreactor was inoculated with an acclimated mixed culture with high Cr(VI) reduction rate (15ppm/day) and tolerance to the organic solvents.

26. Aliquat 336

27. Uses of Aliquat 336 Extraction of Chromium Vanadium extraction
Arsenic extraction
Separation of platinum group metals
Copper extraction
Saeed et al., 2009

28. Concerns about the use of Aliquat 336 as Extractant

29. Safety information Acute toxicity (oral, dermal, inhalation)
Hazardous to the aquatic environment
Acute hazard
Chronic hazard
Corrosive to metals
Skin corrosion
Serious eye damage

30. Concerns
Aliquat 336 has high water solubility (Torma and Itzkovitch, 1976).
Aliquat 336 is an inhibitor of growth of intact algal cells. Ιt also inhibits the photosynthesis in intact plant cells and in isolated spinach chloroplasts (Egneus et al, 1977).
Aliquat 336 is toxic to Lactobacillus delbrueckii (Roffler et al., 1984).
Aliquat 336 is toxic to Activated sludge (Quijano et al., 2011).
Aliquat 336 is toxic to anaerobic sludge (this study).

31. Thank you very much for your attention!
Acknowledgements
This research has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: THALIS. Investing in knowledge society through the European Social Fund.