electrokinetic remediation of heavy metal contaminated soil

Guide,Dr. Vinish V. NairAssociate ProfessorDept. Of Civil Engineering

VIJAI KRISHNAN V.S7 CE

ROLL NO.: 58Govt. RIT,Kottayam, KERALA

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

How soil is contaminated?

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

Scenario in world & India

REF : European Environment Agency, 2015

Contaminants affecting soil matrix in Europe (2011)

Metal SuratPali,

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

• Site Investigation• Contaminants-type, depth, concentration

Stages in Soil RemediationRisk

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

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

Electro-kinetic Remediation

Consist of 4 partsi). Electrode compartment - graphite, platinumii). Electrolytic solution reservoir

iii). Power supply unit – DC, Solar cell, Pulse currentiv). Soil cell

Processes in EKR :-i). Electro-osmosisii). Electro-migrationiii). Electrophoresis

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

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

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

Enhancing Agent Removal EfficiencyEDTA 45 %

Acetic acid 57 %

Sulfuric acid 73 %

NaCl & EDTA 79 %

Citric acid 82 %

Enhancing Agents & Removal Efficiency

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

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

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 Electrodialyticremediation

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

Case StudyA. 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

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

Installation of electrode in site

Electrodes installed at site

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

References1. US-EPA (1995), “Insitu remediation technology: Electrokinetics”2. Interstate Technology & 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”, ASCE4. 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 KatedanIndustrial 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”

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”, IJIRSET12. J.Aruna, Dr.B.Naga Malleswara Rao (2015), “Remediation of Heavy Metal Contaminated Soils”,

IJIRSET13. Rageena S.S., Rani V. (2015), “Effect of Various Pore Fluids on Free Swell and Shrinkage

Cracking of Clays”, IJIRSET14. 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.

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

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

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

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%