Removal of heavy metals from soil using low voltage electric current.Most economical and efficient method

1. Guide,
Dr. Vinish V. Nair
Associate Professor
Dept. Of Civil Engineering
VIJAI KRISHNAN V.
S7 CE
ROLL NO.: 58
Govt. RIT,Kottayam, KERALA

2. INTRODUCTION
 EKR is most efficient green technology to remove heavy metals
from soil by using low volt DC
 Heavy metals – group of metals or metalloids with atomic
density > 5 g/cm3
 Fe, Mn, Zn, Cu, Ni, Cd, Cr, Co, Hg, As etc…
 Non-biodegradable & persistent
 Affect quality of soil & water
 Stored by plants & crops
 Intake leads to health hazards - toxic, carcinogenic
 Use in US & Europe

3. How soil is contaminated?

4.  Rapid industrialization & urbanization
 Open dumping & landfills
 Mining, manufacture & use of synthetic products
 Waste-water & municipal sludge
 Change in life style
 Military & volcanic areas
 Pesticides & Fertilizers
Heavy metal
contamination at
Bagacay copper
mines, Philippines

5. Scenario in world & India
REF : European Environment Agency, 2015
Contaminants affecting soil matrix in Europe (2011)

6. Metal Surat
Pali,
Rajasthan Thane Chennai
Max limit in Soil
(mg/kg)
US-EPA Dutch
Standar
ds
Arsenic (As) - - - - 14 29
Selenium (Se) - - - - 1.6 0.7
Nickel (Ni) 79.0 - 183.6 78.8 32 35
Cobalt (Co) 51.3 - 68.7 - 20 9
Cadmium (Cd) - - - - 1.6 0.8
Chromium(Cr) 305.2 240.0 521.3 418.0 120 100
Copper (Cu) 137.5 298.0 104.6 372.0 100 36
Lead (Pb) - 293.0 - - 60 85
Mercury (Hg) - - - - 0.5 0.3
Zinc (Zn) 139.0 1,364.0 191.3 213.6 220 140
REF : Int. J. Electrochem. Sci. 2011, SPRINGER 2006, Researchgate 2005
Contamination in India

7. • Site Investigation
• Contaminants-type, depth,
concentration
Stages in Soil Remediation
Risk
assessment
Feasible
remediation
options
Verification
Design &
Implementation
Monitoring &
maintenance
• Solidification
• Soil washing
• Vitrification
• Isolation
•Bio-remediation
• Coagulation
• Flotation
• Electro-kinetic
remediation
• Type & Spacing of electrodes
• Electrolyte, Voltage gradient
•Period of operation
Lab test – removal
efficiency, economy

8. Why Electro-kinetic Remediation?
 Suitable for low permeability soils
 Faster remediation
 Efficient & applicable to wide range of heavy metals
 In-situ & ex-situ method
 Remove radio nucleotides, organic & inorganic contaminants
 Low cost

9. Electro-kinetic Remediation
 Consist of 4 parts
i). Electrode compartment - graphite, platinum
ii). Electrolytic solution reservoir
iii). Power supply unit – DC, Solar cell, Pulse current
iv). Soil cell
 Processes in EKR :-
i). Electro-osmosis
ii). Electro-migration
iii). Electrophoresis

10.  Electro-osmosis
 Movement of water molecules
 Flow towards cathode
 Electro-migration
 Transport of ions to opposite charged electrode
 Major transport of metal ions
 Electrophoresis
 Transport of charged colloidal particles
 Negligible in low permeable soil

11. Laboratory Setup – Chromium removal
 Sample is contaminated by Potassium Chromate solution
 Cr(VI) commonly exist in anionic form
 After 24hrs contaminated soil is compacted in HDPE container
 Electrodes – slotted graphite
 Electrolyte – potable water
 Voltage gradient – 1 Volt DC/cm
REF: Journal Of Environmental Engineering, ASCE 2004

12.  Electrolysis of water  At anode : 2H20 O2 + 4H+ + 4e-
At cathode : 4H2O + 4e-  2H2 + 4OH-
 H+ move from anode to cathode ( acidic front )
 OH- from cathode to anode ( basic front )
 Acidic front mobilize metal ions  Electro-migration occurs
 Cr(VI) migrate to anode ( + ) & precipitated
 Exhausted electrolyte stored in reservoir
 Concentration of Cr is determined by Atomic Absorption
Spectrometer
 Removal efficiency is low
 Enhancing agents are added & test is repeated

13. Enhancing Agent Removal Efficiency
EDTA 45 %
Acetic acid 57 %
Sulfuric acid 73 %
NaCl & EDTA 79 %
Citric acid 82 %
Enhancing Agents & Removal
Efficiency

14. Electrokinetic Remediation Field Setup
 Well is constructed
 Filling electrolyte
 Inserting Anode (+) &
Cathode ( - )
 Applying electric field
 Electro-osmosis &
Electrolysis of water
 Desorption of metal ion by acidic front
 Electro-migration & precipitation or dissolution of metal ion
 Pumping & storing of exhausted electrolyte

15.  Avg Spacing b/w anode & cathode – 14 ft
 Avg Spacing b/w anodes or Cathodes – 7 ft
 Vary depending on level of contamination & remediation time

16. How to improve removal efficiency?
 Use of enhancing agents :-
 EDTA, NTA, acetic acid, citric acid, NaOH, NaCl etc…
 Form complexes with metal ions  easy removal
 Ion selective membrane around electrodes Electrodialytic
remediation
 Use of pulse current
 Using combined EK technologies-EKR with Ultrasonics
 EKR remove metal
 Ultrasonic removes organic matter
 Removal efficiency for Pb increase up to 91%
 Making consistency of soil equal to liquid limit

17. Case Study
A. US Army Waterway Experiment Station, Louisiana
 Electrokinetics Inc.
 Electro-Klean Electrical Separation process
 Lead – avg removal efficiency -85%
B. Old TNX Basin, South Carolina
 Isotron Corporation
 Electrosorb process
 Mercury, Lead, Chrome
C. Sandia National Laboratories Chemical Waste Landfill
 Chromium
 Supported by US Dept of Energy
REF : US-EPA, 1995

18. Problems
 Insoluble organic matter & stable compound reduce removal
efficiency
 Polluting metal species is high  very slow remediation
 Buried metal objects  short circuiting, waste of current
 Careful design
 Success depends on :-
 Soil type
 Soil pH  high pH ( >10 ), lower removal efficiency
 Applied electric field
 Presence of carbonate
 Concentration of target metal ion

19. Installation of
electrode in site
Electrodes installed
at site

20. Conclusion
 Industrial effluent increase heavy metal contaminants
 Heavy metals cause several health hazards
 In-situ technique  minimum surface disturbance
 EKR - High removal efficiency upto 90%
 Suitable for any depth
 High level of sustainability, social acceptability & economic
performance
 Used commercially in Europe, USA
 Necessary to keep environment safe & healthy

21. References
1. US-EPA (1995), “Insitu remediation technology: Electrokinetics”
2. InterstateTechnology & Regulatory Council ( 2010 ), “Technology Overview-Electrokinetics”
3. Krishna R. Reddy & Supraja Chinthamreddy ( 2004 ), “Enhanced Electrokinetic Remediation
of Heavy Metals in Glacial Till Soil Using Different Electrolyte Solutions”, ASCE
4. Riffat Naseem Malik, Syed Zahoor Husain & Ishfaq Nazir ( 2015 ), “Heavy Metal
Contamination And Accumulation In Soil And Wild Plant Species From Industrial Area Of
Islamabad, Pakistan”, ResearchGate
5. P.K.Govil, J.E.Sorlie, N. N. Murthy, D. Sujatha, G.L.N.Reddy, Kim Rudolph-Lund,
A.K.Krishna & K.Rama Mohan (2007 ) “Soil contamination of heavy metals in the Katedan
Industrial Development Area, Hyderabad, India”, Springer
6. A.K.Krishna, P.K.Govil (2007), “Soil contamination due to heavy metals from an industrial
area of Surat, Gujarat”, Springer
7. A.K.Krishna, P.K.Govil (2004),“Heavy metal contamination of soil around Pali Industrial
Area,Rajasthan, India”,Springer
8. Burlakovs Juris, Stankevica Karina, Hassan Ikrema, Janovskis Reinis, Lacis Sandris,
“Removal Of Heavy Metals From Contaminated Soils By Elektrokinetic Remediation”
9. US Army Environmental Center ( 2000 ), “In-Situ Electrokinetic Remediation of Metal
Contaminated Soils Technology Status Report”

22. 10. European Environment Agency (2007,2015), “Progress in management of contaminated sites”
11. Shweta .S. Angadi, Rashma Shetty , Manjunath N.T. (2015), “Coagulation Study to Remove
Heavy Metals from Leachate”, IJIRSET
12. J.Aruna, Dr.B.Naga Malleswara Rao (2015), “Remediation of Heavy Metal Contaminated Soils”,
IJIRSET
13. Rageena S.S., Rani V. (2015), “Effect of Various Pore Fluids on Free Swell and Shrinkage
Cracking of Clays”, IJIRSET
14. Jaishree, T.I.Khan,(2015), “Assessment of Heavy Metals’ Risk on Human Health via Dietary
Intake of Cereals and Vegetables from Effluent Irrigated Land Jaipur District, Rajasthan”,
IJIRSET
15. Sruthy O A and S Jayalekshmi (2014), “Electrokinetic Remediation Of Heavy Metal
Contaminated Soil”, IJSCER
16. Okeke P. N. (2013), “Enhanced Electrokinetic Remediation of Cadmium Contaminated Soil “,
An Int. Journal of Sci. and Tech.

24.  Potassium chromate, Nickel chloride,Cadmium chloride
 Ion selective membrane-prevent entry of ions generated at electrode to soil
 Pulse current
A unidirectional surge of current of very short duration. It quickly rises to a maximum, then
drops to zero in a similar fashion
 EDTA – ethylene di amine tetra acetic acid-Form soluble complexes with Cr
 NTA – nitrilo tri acetic acid
 DTPA- di ethylene tri amine penta acetic acid
 Chelating agents – form several bonds to a single metal ion
 DC volt 20-30 V
 Diseases : - gastro intestinal disorders, diarrhoea , tremor, paralysis, vomiting,depression,
pneumonia
 Nuerotoxic,mutagenic
 Coagulation – alum + polyelectrolyte ( FeCl3)
 Electrode – carbon,platinum,graphite – cylindrical – inert –no residue
Pb Cd Cu Cr
* EDTA,DTPA •NTA (65-95%)
•H2SO4 soln (76 %)
* Battery &
electronics
* DTPA ( 60 %) * Citric acid>acetic
acid

25.  Cd – Ni-Cd battery, alloys, paints, ink catridge
 Zn- galvanizing
 Vitrification
 Soil is heated at high temp ~ 2000 C.Organic pollutants are volatalized, heavy metals are
retained in soil.Melted soil forms a solid block
 Dist b/w anode or cathode 7ft, b/w anode & cathode 14 ft ( US army
environment center)
 EKR field projects are funded & carried out in USA (by USEPA, ITRC, US army
Envt. Centre, Electropetroleum Inc., Terran Corporation, General electric) ,
Europe(Geokinetics International Inc.), Japan, Korea.
 Cost <100 $/cub m to >400 $/cub m ( site specific )
 Effect of pore fluid :-
 Increase in conc of NaCl, NH4Cl, Acetic acid to clay decrease free swell but
NaOH increases free swell.Affects crack behavoir
 Electrosorb process – contaminants are adsorbed to electrode
 Pesticides & fertilizer - Cd & Pb
 Micronutrients - Fe, Mn, Zn, Cu, Ni

26.  Fines & closure notice – India
 Potassium & sodium bichromate industry, gujarat
 Dyeing units, Tirupur,TN
 Steel industry, Kalmeshwar, Maharashtra
 Heavy metal contamination in Kerala –
 Kerala Minerals & Metals Ltd, Kollam – Lead & mercury ( perimeter of 500 m ) –
NDTV & KIMS
 Eloor & edayar industrial develpmt area- HIL,Grasim Indstrys, Merchem Limited
and FACT ( Zn,Pb,Cd,Hg,Cr ) closed all units (2004-05)
 KINFRA Textile Industries, Kannur – Zn,As,Pb
 Kerala Clay & Ceramics Ltd,Kannur – closed due > Fe in water

27. Enhancing agents
 EDTA Enhancement
 At Cathode – EDTA
 Form soluble complexes with Cr
 Removal efficiency 45%
 Acetic Acid Enhancement
 At Cathode – acetic acid
 Increase solubility of metal ion
 Removal efficiency 57%
 Citric Acid Enhancement
 Cathode – citric acid
 Electro-migration to anode is
more
 Chromium citrate complexes are
formed
 Removal efficiency 82%
 NaCl & EDTA Enhancement
 Anode – NaCl & Cathode – EDTA
 NaCl sustain high current &
electro-osmosis
 Removal efficiency 79%
 Sulfuric Acid Enhancement
 Greater electro-migration &
solubility
 Removal efficiency 73%