Heavy metals in water presenc tủ tài liệu bách khoa

SharmaJaipur, India Heavy Metals in Water: Presence, Removal and Safety Edited by Sanjay K.. Dr Sharma is also associated, as an Editorial Board Member or a reviewer,with more than 15 in

11:25:17

11:25:17

Heavy Metals In Water

Presence, Removal and Safety

Print ISBN: 978-1-84973-885-9

PDF eISBN: 978-1-78262-017-4

A catalogue record for this book is available from the British Library

rThe Royal Society of Chemistry 2015

All rights reserved

Apart from fair dealing for the purposes of research for non-commercial purposes or forprivate study, criticism or review, as permitted under the Copyright, Designs and PatentsAct 1988 and the Copyright and Related Rights Regulations 2003, this publication may not

be reproduced, stored or transmitted, in any form or by any means, without the priorpermission in writing of The Royal Society of Chemistry or the copyright owner, or in thecase of reproduction in accordance with the terms of licences issued by the CopyrightLicensing Agency in the UK, or in accordance with the terms of the licences issued by theappropriate Reproduction Rights Organization outside the UK Enquiries concerning

reproduction outside the terms stated here should be sent to The Royal Society of

Chemistry at the address printed on this page

The RSC is not responsible for individual opinions expressed in this work

Published by The Royal Society of Chemistry,

Thomas Graham House, Science Park, Milton Road,

Cambridge CB4 0WF, UK

Registered Charity Number 207890

Visit our website at www.rsc.org/books

Agriculture and industrial developments are not possible without the dispensable element water All living and non-living things require water fortheir existence in one way or another So, if somebody says that ‘water is theliquid of life’, it is absolutely correct Nobody can live without water.The population explosion, increasing urbanization and industrializationare the major reasons for the depletion of water availability worldwide andthat’s why the water crisis has become a global challenge today Scientists,policy makers and academicians are continuously trying hard to address thisproblem to the best of their knowledge and abilities, but without completesuccess.

in-Besides the water crisis, the availability of ‘safe water’ is another ated challenge Because of various types of pollutants and impurities present

associ-in water, whatever water is available is not always ‘safe’ Unfortunatelydrinking such ‘unsafe’ water is the fate of billions of people around theworld and pure water is always a ‘dream’ for them

Dissolved solids, synthetic dyes, agriculture runoffs, industrial effluentsand microorganisms are a few of the things responsible for making waterunsafe The presence of heavy metals is an add-on to this list, and these are

so dangerous that they may actually lead to death Metals such as arsenic,cadmium, chromium, copper, lead, mercury, nickel and zinc are commonlyfound at contaminated sites and in aqueous systems For example, arsenicpoisoning claims thousands of deaths every year in Bangladesh and WestBengal in India, while lead is very toxic to living organisms, accumulating inthe bones, brain, kidney and muscles, and may be the cause of many seriousdisorders such as anaemia, kidney diseases, nervous disorders, sickness andeven death

The presence of heavy metals in water is due to both natural and thropogenic sources Natural sources may include parent rocks and metallic

an-Heavy Metals in Water: Presence, Removal and Safety

Edited by Sanjay K Sharma

r The Royal Society of Chemistry 2015

Published by the Royal Society of Chemistry, www.rsc.org

v

ores and, on the other hand, agriculture (fertilizers, animal manures,pesticides), metallurgy (mining, smelting, metal finishing), energy pro-duction (leaded gasoline, battery manufacture, power plants), micro-electronics, sewage sludge and scrap disposal can be included in theanthropogenic sources.

Removal of these heavy metals is a big problem for everyone Examples

of the many techniques being tried to achieve this include biosorption,bioremediation, phytoremediation, photocatalytic processes, use of func-tionalized magnetic nanoparticles and use of industrial and agriculturalwaste

This book is a sincere effort to showcase the latest research in the field ofheavy metals removal, written by leading scientists and researchers At thispoint in time I express my gratitude to all contributors who made this vol-ume possible I hope that the chapters presented will be a good source ofreference material for scientists in their further research and development.Also, I hope that this book provides an insightful text on the theme of

‘heavy metals removal’ and processes that are being studied, optimized anddeveloped to sustain both mankind and nature

I sincerely welcome feedback from all my valuable readers and critics.Happy reading!

Sanjay K SharmaJaipur, India

This is the opportunity to express my thanks and gratitude to my friends,colleagues, supporters and well wishers and to let them know that I am sograteful to have had them, and their valuable cooperation, along with meduring the journey of this book—Heavy Metals in Water: Presence, Removaland Safety.

First of all I express my special thanks to all the esteemed contributors,who deserve special mention for providing their writings, without which thisbook could not be possible

I sincerely acknowledge my parents Dr M.P Sharma and Mrs ParmeshwariDevi, my wife Dr Pratima Sharma and all other family members for theirnever-ending encouragement, moral support and patience during the course

My children Kunal and Kritika always deserve special mention as they are

my best companions, who energize me to work with refreshed mood andmotivation

Special thanks go to the team at the Royal Society of Chemistry behind thispublication, without whose painstaking efforts this work could not havebeen completed in a timely manner Thanks RSC!

I am also grateful to many others whose name I have not been able tomention but whose association and support has in no way been any less

Sanjay K SharmaJaipur, India

Heavy Metals in Water: Presence, Removal and Safety

Edited by Sanjay K Sharma

r The Royal Society of Chemistry 2015

Published by the Royal Society of Chemistry, www.rsc.org

vii

11:25:24

11:25:25

11:25:25

Prof (Dr) Sanjay K Sharma is a very well knownauthor and editor of many books, research journalsand hundreds of articles over the last 20 years.

At present Prof Sharma is working as Professor &Head, Department of Chemistry, JECRC University,Jaipur, India, where he is teaching engineeringchemistry and environmental chemistry to B TechStudents, green chemistry, spectroscopy and or-ganic chemistry to MS students and pursuing hisresearch interest in the domain area of greenchemistry

His research interests are green chemistry, heavy metals removal, polymers and green corrosion inhibition Dr Sharma has 15 books onchemistry from national–international publishers and over 52 researchpapers of national and international repute to his credit

bio-He has also been appointed as Series Editor by Springer, UK, for theirprestigious book series ‘Green Chemistry for Sustainability’, where he hasbeen involved in editing 12 different titles by various international con-tributors so far

He is a member of the American Chemical Society (USA), Royal Society ofChemistry (UK) and International Society for Environmental InformationSciences (ISEIS, Canada) and is also a life member of various internationalprofessional societies including the International Society of Analytical Sci-entists, Indian Council of Chemists, International Congress of Chemistryand Environment, Indian Chemical Society, etc

Dr Sharma is also associated, as an Editorial Board Member or a reviewer,with more than 15 international journals, including the prestigious Green

Heavy Metals in Water: Presence, Removal and Safety

Edited by Sanjay K Sharma

r The Royal Society of Chemistry 2015

Published by the Royal Society of Chemistry, www.rsc.org

xi

Chemistry, Green Chemistry Letters & Reviews, Ultrasonics and UltrasonicsSonochemistry, etc.

His recently published books are:

 Biosurfactants: Research Trends and Applications (CRC Taylor & Francis,USA)

 Waste Water Reuse and Management (Springer, UK)

 Advances in Water Treatment and Pollution Prevention (Springer, UK)

 Green Corrosion Chemistry and Engineering (Wiley, Germany)

 Handbook of Applied Biopolymer Technology: Synthesis, Degradation andApplications (Royal Society of Chemistry, UK)

 Handbook on Applications of Ultrasound: Sonochemistry and Sustainability(CRC Taylor & Francis, USA)

 Green Chemistry for Environmental Sustainability (CRC Taylor & Francis,USA)

Chapter 1 Contamination of Heavy Metals in Aquatic Media:

Transport, Toxicity and Technologies for Remediation 1Ravindra K Gautam, Sanjay K Sharma, Suresh Mahiya andMahesh C Chattopadhyaya

2.3 Basic Principle of Heterogeneous Photocatalysis 29

Heavy Metals in Water: Presence, Removal and Safety

Edited by Sanjay K Sharma

r The Royal Society of Chemistry 2015

Published by the Royal Society of Chemistry, www.rsc.org

xiii

2.4 Mechanism of Photocatalytic Reactions 292.5 Thermodynamics of Photoreduction of Different

2.6 Dependence of Photoreduction Kinetics on Different

2.6.1 Effect of Initial Metal Ion Concentration 31

2.6.3 Effect of Electron–Hole Scavenger 33

2.7 Recent Challenges in the Photocatalytic Process 34

2.8 Application of Photocatalysis for the Removal

2.8.2 Group 10 Metals (Nickel and Platinum) 372.8.3 Group 12 Metals (Zinc, Cadmium and Mercury) 37

Chapter 3 Removal of Dissolved Metals by Bioremediation 44

Subhajit Majumder, Suresh Gupta and Smita Raghuvanshi

3.3 Physico-Chemical Treatments of Heavy Metals 46

Chapter 4 Functionalized Magnetic Nanoparticles for Heavy Metals

Ravindra Kumar Gautam, Sanjay Kumar Sharma andMahesh Chandra Chattopadhyaya

4.2 Sources of Heavy Metals in the Environment 584.3 Toxicity to Human Health and on Ecosystems 62

4.7 Modeling of Adsorption: Kinetic and Isotherm

Maurizio Carotenuto, Giusy Lofrano and Sanjay K Sharma

5.3.6 Metabolisms and Toxicity of Arsenic 1025.3.7 Natural Groundwater Arsenic

Chapter 6 Removal of Iron and Manganese from Water—Chemistry

Keisuke Ikehata, Andrew T Komor and Yao Jin

6.2 Chemistry of Iron and Manganese Oxidation

6.2.1 Iron and Manganese Generation and

6.2.2 Chemistry of Iron Oxidation and Removal 1256.2.3 Chemistry of Manganese Oxidation and

6.3 Engineering Considerations for Iron and Manganese

6.3.2 Treatment Process Considerations 133

Chapter 7 Heavy Metal Pollution in Water Resources in

China—Occurrences and Public Health Implications 141Keisuke Ikehata, Yao Jin, Nima Maleky and Aijun Lin

7.2 Heavy Metals in Water: Definitions and Their Health

7.2.1 Brief Discussion on Heavy Metal Definitions 142

7.2.3 Toxicological Properties of Heavy Metals with

7.3 Heavy Metals in Chinese Water

7.3.1 China’s Recent Industrial Developments and

7.3.2 Current Water Quality Standards and

7.4.2 Impacts of Wastewater Irrigation on

7.4.3 Heavy Metal Pollution in Rivers and Drinking

7.4.4 Human Health Risk Assessment of HeavyMetals in Drinking Water Sources in China 1597.4.5 Heavy Metal Contamination in the

Chapter 8 Heavy Metals Distribution in Surface Water Samples

Hou-Qi Liu, Ying Liu, Guang Liu and Xue-Bin Yin

9.3 Nanosized Metal Oxides 180

Chapter 10 Modified and New Adsorbents for Removal of Heavy

M A Barakat and Rajeev Kumar

10.2 Heavy Metals in Industrial Wastewater and Toxicity 19410.3 Treatment Processes for Heavy Metals Removal 196

10.4.1 Adsorption of Heavy Metals on Modified

10.4.2 Adsorption of Heavy Metals on Industrial

10.4.3 Adsorption of Heavy Metals on Modified

Agriculture and Biological Wastes

10.4.4 Adsorption of Heavy Metals on Modified

Chapter 11 Natural Clays/Clay Minerals and Modified Forms for

Alfin Kurniawan, Suryadi Ismadji, Felycia Edi Soetaredjoand Aning Ayucitra

11.2 Structural Features of Clays and Clay Minerals as

11.3 Surface Modification Techniques of Clays and ClayMinerals for Enhanced Heavy Metals Sorption 222

11.3.2 Chemical Activation/Conditioning 22711.3.3 Pillaring, Grafting and Intercalation

Chapter 12 Heavy Metals in Tannery Wastewater and Sludge:

Environmental Concerns and Future Challenges 249Giusy Lofrano, Maurizio Carotenuto, Ravindra Kumar

Gautam and Mahesh Chandra Chattopadhyaya

Chapter 13 Fluorides in Different Types of Aquatic Systems and their

C Christophoridis, I Pasias, E Mitsika, S Veloutsou and

K Fytianos13.1 Heavy Metals and Fluorides in the Environment 261

13.1.2 Anthropogenic Sources of Fluorides 26313.1.3 Fluoride Content in Environmental

13.2 Relation Between Fluorides and Metals/Metalloids 26913.2.1 Role of Physico-chemical Parameters

13.2.2 Fluoride and Arsenic Correlation 272

Chapter 14 Use of Industrial and Agricultural Waste in Removal of

June Fang, Bin Gao, Yining Sun, Ming Zhang andSanjay K Sharma

14.5.1 Differences Between Materials in the

15.3 Biosorption Mechanisms: Physical

15.4.4 Competing Ions Present on Solution 30815.4.5 Initial Concentration of Metal Ions and of

Mariliz Gutterres and Bianca Mella

16.4 Unitary Operations in Tannery Effluents Treatment 327

11:25:28

Contamination of Heavy

Metals in Aquatic Media:

Transport, Toxicity and

Technologies for Remediation

RAVINDRA K GAUTAM,aSANJAY K SHARMA,*b

SURESH MAHIYAbAND MAHESH C CHATTOPADHYAYA*a

a

Environmental Chemistry Research Laboratory, Department of

Chemistry, University of Allahabad, Allahabad, 211 002, India;bGreenChemistry & Sustainability Research Group, Department of Chemistry,JECRC University, Jaipur, 303905, India

*Email: drsanjay1973@gmail.com; mcc46@rediffmail.com

in the metabolism of humans and animals in very trace amounts but theirhigher concentration may cause toxicity and health hazards The hazardous

Heavy Metals in Water: Presence, Removal and Safety

Edited by Sanjay K Sharma

r The Royal Society of Chemistry 2015

Published by the Royal Society of Chemistry, www.rsc.org

1

nature of heavy metals has been recognized because of their tive nature in biotic systems They can enter into the environment throughmining activities, industrial discharge and from household applications,into nearby bodies of water.

Heavy metals differ widely in their chemical properties, and are used tensively in electronics, machines and the artifacts of everyday life, as well as

ex-in high-tech applications As a result they are able to enter ex-into the aquaticand food chains of humans and animals from a variety of anthropogenicsources as well as from the natural geochemical weathering of soil androcks The main sources of contamination include mining wastes, landfillleaches, municipal wastewater, urban runoff and industrial wastewaters,particularly from the electroplating, electronic and metal-finishing indus-tries With increasing generation of metals from technologies activities, theproblem of waste disposal has become one of paramount importance Manyaquatic environments face metal concentrations that exceed water qualitycriteria designed to protect the environment, animals and humans Theproblems are exacerbated because metals have a tendency to be transportedwith sediments, are persistent in the environment and can bioaccumulate inthe food chain Some of the oldest cases of environmental pollution in theworld are due to heavy metal use, for example, Cu, Hg and Pb mining,smelting and utilization by ancient civilizations, such as the Romans and thePhoenicians

The heavy metals are among the most common pollutants found in tewater These metals pose a toxicity threat to human beings and animalseven at low concentration Lead is extremely toxic and shows toxicity to thenervous system, kidneys and reproductive system Exposure to lead causesirreversible brain damage and encephalopathic symptoms.2 Cadmium isused widely in electroplating industries, solders, batteries, television sets,ceramics, photography, insecticides, electronics, metal-finishing industriesand metallurgical activities It can be introduced into the environment bymetal-ore refining, cadmium containing pigments, alloys and electroniccompounds, cadmium containing phosphate fertilizers, detergents andrefined petroleum products Rechargeable batteries with nickel–cadmiumcompounds are also sources of cadmium.3–5 Cadmium exposure causesrenal dysfunction, bone degeneration, liver and blood damage It hasbeen reported that there is sufficient evidence for the carcinogenicity ofcadmium.3

was-Copper, as an essential trace element, is required by biological systems forthe activation of some enzymes during photosynthesis but at higher con-centrations it shows harmful effects on the human body High-level exposure

of copper dust causes nose, eyes and mouth irritation and may cause nauseaand diarrhea Continuous exposure may lead to kidney damage and evendeath Copper is also toxic to a variety of aquatic organisms even at very low

concentrations Mining, metallurgy and industrial applications are themajor sources of copper exposure in the environment.

Zinc is also an essential element in our diet Too much zinc, however, canalso be damaging to health Zinc toxicity in large amounts causes nauseaand vomiting in children A higher concentration of zinc may cause anemiaand cholesterol problems in human beings Mining and metallurgical pro-cessing of zinc ores and its industrial application are the major sources ofzinc in the air, soil and water It also comes from the burning of coal

Nickel occurs naturally in soils and volcanic rocks Nickel and its salts areused in several industrial applications such as in electroplating, automobileand aircraft parts, batteries, coins, spark plugs, cosmetics and stainlesssteel, and is used extensively in the production of nickel–cadmium batteries

on an industrial scale It enters into the water bodies naturally by weathering

of rocks and soils and through the leaching of the minerals.4 The watersoluble salts of nickel are the major problems of contamination in aquaticsystems.5 Paint formulation and enameling industries discharges nickelcontaining effluents to the nearby bodies of water.6Nickel is also found incigarettes, as a volatile compound commonly known as nickel carbonyl.7Arsenic is found naturally in the deposits of earth’s crust worldwide Theword arsenic is taken from Zarnikh in Persian literature, which means yelloworpiment.8It was first isolated as an element by Albert Magnus in 1250 AD.Arsenic exists in powdery amorphous and crystalline forms in the ores Incertain areas the concentration of arsenic may be higher than its normaldose and creates severe health hazards to human beings and animals Itenters the environment through the natural weathering of rocks and an-thropogenic activities, mining and smelting processes, pesticide use andcoal combustion The toxicity of arsenic as a result of the contamination ofgroundwater bodies and surface waters is of great concern Arsenic exists asarsenate, As(V), and arsenite, As(III), in most of the groundwater.9–12 Ad-sorption and solution pH commonly controls the mobility of arsenic in theaqueous environment.13–17Metal oxides of Fe, Al and Mn play a role in theadsorption of arsenic in aquatic bodies.18–20 Arsenic has been found nat-urally at high concentration in groundwater in countries such as India,Bangladesh, Taiwan, Brazil and Chile Its high concentration in drinkingwater causes toxic effects on humans and animals

The toxicity of mercury has been recognized worldwide, such as inMinamata Bay of Japan Mentally disturbed and physically deformed babieswere born to mothers who were exposed to toxic mercury due to con-sumption of contaminated fish The natural sources of mercury are volcaniceruption, weathering of rocks and soils, whereas anthropogenic mercurycomes from the extensive use of the metal in industrial applications, itsmining and processing, applications in batteries and mercury vapor lamps.Methyl mercury is more toxic than any other species of mercury

Extensive use of chromium compounds in industrial applications hasdischarged huge amounts of wastewater containing toxic chromium speciesinto water bodies Chromium enters into the environment by natural inputs

and anthropogenic sources Volcanic eruptions, geological weathering ofrocks, soils and sediments are the natural sources of chromium, whereasanthropogenic contributions of chromium come from the burning of fossilfuels, production of chromates, plastic manufacturing, electroplating ofmetals and extensive use in the leather and tannery industries.21Hexavalentchromium is more toxic than trivalent chromium.

Cadmium is the most toxic element, even at its low concentration in the foodchain and has been found to cause of itai-itai disease in Japan Unlike otherheavy metals, cadmium is not essential for biological systems Hence it has

no benefit to the ecosystem and only harmful effects have been reported It isused in the manufacturing of nickel–cadmium batteries, plastics and pig-ments Phosphate fertilizers and waste dumping are both routes for cad-mium transference into the environment Concern regarding the role andtoxicity of cadmium in the environment is on the increase, because it can behighly toxic to human beings and animals at very low concentrations Cad-mium toxicity causes renal dysfunction and lung cancer, and also osteo-malacia in the human population and animals, in addition to increasingblood pressure Smoking of cigarettes is one of the sources of cadmiumpoisoning in humans

Chromium is commonly used in the leather and tanning industries, paperand pulp and rubber manufacturing applications High levels of exposurecause liver and kidney damage, skin ulceration and also affects the centralnervous system With plant species it reduces the rate of photosynthesis It isalso associated with the toxic effects on hematological problems and im-mune response in freshwater fish Chromium(VI) causes greater toxicity thanchromium(III) in animal and human health

Copper has been used by man since prehistoric times It is used in theproduction of utensils, electrical wires, pipes and in the manufacture ofbrass and bronze It has a role as an essential element in human and animalbodies However, at a higher dose it shows toxic effects, such as kidney andstomach damage, vomiting, diarrhea and loss of strength

Human exposure to lead causes severe toxicity Higher doses may damagethe fetus and be toxic to the central nervous system Newborn babies aremore sensitive than the adults Lead toxicity may harm hemoglobin syn-thesis, the kidneys and reproductive systems Exposure to higher doses oflead may disrupt the function of the central nervous system and gastro-intestinal tract Airborne lead may cause the poisoning of agricultural food

by the deposition on fruits, soils and water.7

Mercury is a very toxic element in its organic form and has been the cause

of Minamata disease in Japan It shows toxicity to the physiology of animalsand human beings Mercury toxicity has been found to be associated withphysiological stress, abortion and tremors Methyl mercury is highly toxicand causes toxic effects on the central nervous system in the human

population Mercury can result from volcanic eruptions and degassing Theexposure to mercury causes toxicity to the brain, blindness, mental retar-dation and kidney damage.

Nickel plays an essential role in the synthesis of red blood cells; however,

it becomes toxic when taken in higher doses Trace amounts of nickel do notdamage biological cells, but exposure to a high dose for a longer time maydamage cells, decrease body weight and damage the liver and heart Nickelpoisoning may cause reduction in cell growth, cancer and nervous systemdamage.5–7

The undesirable presence of iron and manganese in drinking water maypose a toxicity threat to health However, iron and manganese are required

by the biological system as they play major roles in the hemoglobin synthesisand functioning of cells The presence of these metals in water may causestaining of cotton clothes and give a rusty taste to drinking water The majorconcerns focus on the dietary intake of iron because a higher dose may poseacute toxicity to newborn babies and young children The gastrointestinaltract rapidly absorbs iron that may pose a toxicity risk to the cells andcytoplasm The liver, kidneys and cardiovascular systems are the majortoxicity targets of iron Neurological disturbances and muscle functiondamage are the result of toxic effects of manganese in human bodies

Heavy metals are highly toxic to the fetus and newborn babies, wherehigher levels of exposure exist for human beings, mainly to industrialworkers Metal ions exposure to newborn babies may damage brain memory,disrupt the function of red blood cells, the central nervous system, physio-logical and behavioral problems Severe toxicity from these metals may causecancers Exposure of plants to heavy metals may lead to physiological andmorphological changes and damage to cell function and reduce photo-synthesis rates Mutagenic changes have also been observed in several plantspecies Metal ion toxicities may lead to chlorosis, bleaching, nutrient de-ficiencies and increased oxidation stress in plants Heavy metals obstruct thegrowth of microbes.22Table 1.1 shows the standards for metal concentration

in drinking water and the health effects

An arsenic presence in groundwater through the weathering of rocks andsediments and drinking of arsenic contaminated water causes poisoning tothe blood, central nervous system, lung and skin cancer, breathing prob-lems, vomiting and nausea Its presence in Third World countries is be-coming hazardous The countries that are suffering with the problems ofarsenic are India, Bangladesh, Taiwan, China, Brazil, Chile, South Korea,Thailand and Indonesia Arsenic is a geogenic problem worldwide but an-thropogenic sources, such as the processing of metals and manufacture ofpesticides and their byproducts, are contributing equally to the levels ofarsenic in the environment

Severe toxic effects and poisoning by heavy metal ions worldwide andstrict discharge regulations for wastewater effluents to aquatic bodiesrequires better treatment techniques Environmental scientists have de-veloped several procedures such as coprecipitation, membrane filtration,

Table 1.1 The standard metal concentration in drinking water and the health

effects

Lead  Toxic to humans, aquatic

fauna and livestock

 High doses causemetabolic poison

 Tiredness, irritability anemiaand behavioral changes ofchildren

 Hypertension andbrain damage

 Phytotoxic

 By the EnvironmentalProtection Agencymaximum concentration:0.1 mg L 1

 By European Community:0.5 mg L 1

 Regulation of water quality(India) 0.1 mg L 1

Nickel  High conc can cause

 By European Community:0.1 mg L 1

 Regulation of water quality(India) 0.1 mg L 1

Chromium  Necrosis nephritis and death

in man (10 mg kg 1of bodyweight as hexavalentchromium)

 Irritation of gastrointestinalmucosa

 By the EnvironmentalProtection Agencymaximum concentration:(hexavalent and trivalent)total 0.1 mg L 1

 By European Community:0.5 mg L 1

 Regulation of water quality(India) 0.1 mg L 1

Copper  Causes damage in a variety

 By the EnvironmentalProtection Agencymaximum concentration:1.0 mg L 1

 Abdominal pain etc

 By the EnvironmentalProtection Agencymaximum concentration:

Cadmium  Cause serious damage to

kidneys and bones in humans

 Bronchitis, emphysema,anemia

 Acute effects in children

 By the EnvironmentalProtection Agencymaximum concentration:0.005 mg L 1

 By European Community:0.2 mg L 1

 Regulation of water quality(India) 0.001 mg L 1

ion-exchange resins, photocatalytic reduction and adsorption for treatment

of wastewater effluents containing heavy metals

Bioaccumulation of heavy metals in food chains and their toxicity to logical systems due to increased concentration over time have led to tre-mendous pressure for their separation and purification Heavy metals canenter into water bodies through agricultural runoff, industrial effluents,household uses and from commercial applications We can remove heavymetals from drinking water very easily with reliable technology Severaltechnologies available in the market remove a huge range of metals com-monly found in drinking water and wastewater effluents There are variousremediation technologies that have been used for the removal of heavy metalsfrom water/wastewater These remediation technologies are summarized as:

bio- Precipitation and coagulation

 Causes mutagenic effects

 Disturbs the cholesterol

 By the EnvironmentalProtection Agencymaximum concentration:0.002 mg L 1

 By European Community:0.001 mg L 1

 Regulation of water quality(India) 0.004 mg L 1Arsenic  Causes toxicological and

 Immunotoxic

 Modulation of co-receptorexpression

 World Health Organizationguideline of 10 mg L 1

 By European Community:0.01 mg L 1

 Regulation of water quality(India): 0.05 mg L 1

homogeneous polymer thin films supported by a porous support structure.Partitioning water and dissolved salts between the membrane and the bulksolution, and transport of water and salts across the membrane, depend onthe chemical properties of the membrane as well as the physical structures

on nano- to microscales The nanometer length scale is defined as betweenthe scale of macroscopic particles suspended in water and dissolved atomicand molecular species From a filtration perspective, this intermediate rangecontains, for example, colloidal solids, large organic and biological mol-ecules, polymers and viruses It also corresponds to the dimensions at whichthat we recognize distinct modes of material transport across a membrane.For a larger dimension of porous membranes, transport is described interms of convective flow through pores On the other hand, transport in adense reverse osmosis membrane is typically described in terms of diffusiveflow through a homogeneous material

1.4.2 Phytoremediation

Bioremediation is the technological process whereby biological systems,plants and animals, including microorganisms, are harnessed to effect thecleanup of pollutants from environmental matrices.23During the past fewyears, microbe-assisted bioremediations have been widely applied for thetreatment of wastewater contaminated with heavy metals and metalloids.Here we will address the global problem of heavy metal pollution originatingfrom increased industrialization and urbanization and its amelioration byusing plants from various environmental conditions Conventional tech-nologies are not cost effective and may produce adverse impacts on aquaticecosystems Microbe-assisted bioremediation and phytoremediation ofheavy metals are cost-effective technologies and metal ion accumulatingplants have been successfully used for the treatment of wastewater.24Aquatic plants, especially ‘‘wetland ecosystems’’, have unique properties tosequester heavy metals and metalloids

Wetland ecosystems are much superior in comparison with other ventional methods, for example because of the low cost, frequent growth ofmicroorganisms, easy handling and low maintenance cost The rhizospheres

con-in wetlands provide an enhanced nutrients supply to the microbial systems of plants, which actively transform and sequester heavy metals

eco-in their biological functions Constructed wetlands have been actively usedfor the treatment of heavy metals from agricultural runoff, mine drainageand municipal wastes Many aquatic plants such as Phragmites, Lemna,Eichchornia, Azolla and Typha have been used for the treatment of wastewatercontaining heavy metals

Phytoremediation is a low-cost, low-tech and emerging cleanup ogy for contaminated soils, groundwater and wastewater.25Plants are verysensitive to metals but in phytoremediation wild and genetically modifiedplants, including grasses, herbs, forbs and woody species, are mainly used.The plants take up heavy metals and metalloids through the process of

phytostabilization, phytoextraction, phytofiltration or rhizoremediation.However, in contrast to organic compounds the heavy metals and metalloidscannot be metabolized but accumulate in the plant biomass.26The biomassgenerated by phytoremediation remains very limited in amount and persists,whereas all the biomass can be utilized in the form of fertilizer, forage,mulch or for the production of bio-gas.27Even though it is well known thatmetals are toxic to many plants, they have developed some internal mech-anisms that allow the uptake, tolerance and accumulation of high concen-trations of metals that would be toxic to other organisms Many researchershave reported that aquatic macrophytes viz Typha, Phragmites, Eichhornia,Azolla and Lemna are potential wetland plants for removal of heavy metaland metalloids due to their morphological change.24,28Being a cost-effectiveand easily applicable technique, phytoremediation can be implemented fortheir enhancement to metal accumulations and translocations In general,two strategies of phytoextraction have been developed, which are: (1) normalphytoremediation of heavy metals from aquatic bodies through the plants intheir entire growth cycle29–31 and (2) chemically induced phytoextractiontechniques to cleanup contaminated water by using metal-tolerant plants toremove heavy metals and metalloids.32The efficiency of phytoextraction can

be increased by using more biomass producing plant species and with theapplication of suitable chelates Hyperaccumulators or hyperaccumulatingplants are capable of accumulating large amounts of heavy metals andmetalloids, including Ni, As, Zn, Cd and Pb, in their aboveground tissueswithout any toxic symptoms.33

Metals uptake in relation to the external concentration of the toxic heavymetals may differ due to the different genotypes of plants Those plants thathave low uptake of metals at quite high metal concentrations are calledexcluders These plants have some kind of barrier to avoid uptake of heavymetals, however, when metal concentrations are at a high level this barrierlosses its function, probably due to the toxic action of the metals Someplants have certain detoxification mechanism within their tissue, whichallow the plant to accumulate high amounts of metals.34Several reports areavailable in the literature on the hyperaccumulator plants: Pteris vittata L.and Thlaspi caerulescens were found to hyperaccumulate As, Minuartia vernafor Pb, Aellanthus biformifolius for Co and Cu, Berkheya coddi for Ni,Macadamia neurophylla for Mn and Thlaspi caerulescens for Zn.34,35However,phytoremediation on a commercial scale is limited because of its low bio-mass production, limited growth rate and time consumption.35In order tocompensate for the low metal accumulation, much research has been con-ducted using synthetic chelators or ligands such as ethylenediaminetet-raacetic acid (EDTA); S,S-ethylenediaminedisuccinic acid (S,S-EDDS);nitrilotriacetate (NTA) and naturally occurring low molecular weight organicacids to enhance the availability of heavy metals and increase phytoextr-action efficiency.36,37

Phytoextraction is a publically appealing ‘‘green’’ remediation technique.However, phytoextraction can be effectively applied only for soils and

wetlands contaminated with specific potentially toxic metals and metalloids.Many researchers have reported that common crop plants with a high bio-mass can be triggered to accumulate large amounts of low bioavailabilitymetals when applied the phytochelates.38,39 In such chemically enhancedphytoextractions, chelating agents are used almost exclusively as the mo-bilizing agents.40However, EDTA was the most efficient chelate to increasemetal uptake by plants of Pb, but the slow degradation of chelating com-pounds in the root zone limits its application on an industrial scale.41Nevertheless, more biodegradable chelates, such as NTA, (S,S-EDDS) andother chelates are also recognized for metals removal Application of thesechelating agents with plants for the uptake of metal ions is gaining morepopularity and has become an interesting field of research Several studieshave been carried out using EDTA as a metal chelator for sequestration ofmetals.42The full-scale application for treating wastewater on an industrialscale should be based on optimization of several parameters such as solu-bilization of metals, chelates stability, plant roots and the capacity of metaltransport through the shoots of plants.43

1.4.3 Heterogeneous Catalysts and Catalysis

In 1972 Fujishima and Honda discovered the photocatalytic splitting ofwater on titanium dioxide (TiO2) electrodes.44,45Their discovery provided thefoundation stone for photocatalysis Since this remarkable discovery muchresearch has been carried out on the efficiency of TiO2 as a photo-catalyst.46–48 During the past few years, the applications of TiO2 for en-vironmental cleanups have been performed by several laboratories for thetreatment of industrial effluents.49,50

During the photocatalysis system, photo-induced reactions take place atthe surface of a catalyst Depending on where the initial excitation occurs,photocatalysis can be generally divided into two classes of processes Whenthe initial photo-excitation occurs in an adsorbate molecule, which theninteracts with the ground state catalyst substrate, the process is referred to as

a catalyzed photoreaction When the initial photo-excitation takes place inthe catalyst substrate and the photo-excited catalyst then transfers an elec-tron or energy into a ground state molecule, the process is referred to as asensitized photoreaction The initial excitation of the system is followed bysubsequent electron transfer and/or energy transfer It is the subsequent de-excitation process that leads to chemical reactions in the heterogeneousphotocatalysis process

1.4.4 Photocatalysts

Reduction of Cr(VI) using semiconductor heterogeneous photocatalystshas been carried out as an economical and simple method of wastewatertreatment.51,52Surface-catalyzed Cr(VI) reduction is a very slow reaction andhas been described as a feasible process in the presence of oxide surfaces

such as TiO2.53Furthermore, organic donors have a chelation capacity forthe TiO2surface, which accelerates the reduction of Cr(VI).54–57

Testa et al.58carried out the reduction of Cr(VI) over TiO2under near-UVradiation At pH 2, the addition of oxalate facilitated Cr(VI) reduction It hasbeen found that the oxalic acid accelerates the reduction of Cr(VI) over TiO2

particles Guo et al.59 have synthesized a plasmonic photocatalyst of Ag–AgCl@TiO2 by deposition–precipitation and photoreduction This photo-catalyst exhibited efficient photocatalytic activity for the photoreduction ofCr(VI) ion under irradiation with visible light

Photocatalytic reduction of Cr(VI) in an aqueous suspension of fluorinated anatase TiO2 nanosheets with exposed {001} facets has beenperformed by He et al.60The surface fluorination facilitated the adsorptionprocess by increasing the number of surface OH groups generated The re-duction of Cr(VI) occurred because of the oxidative dissolution of H2O on{001} facets and the Cr(VI) reductions that occurred on {101} facets weresimultaneous reactions

surface-1.4.5 Electrocoagulation

Electrocoagulation consists of electrodes that act as the anode and cathode,where oxidation and reduction takes place Many physicochemical processessuch as oxidation, reduction, coagulation and adsorption govern the elec-trocoagulation.61,62 Similarly to other treatment techniques, the electro-coagulation of heavy metals offers a cost-effective and easy-handlingtechnique on an industrial scale.63 This technique has been used for thetreatment of dyes, heavy metals, nitrates, fluorides and phenolic compoundsfrom wastewater.64–74 Recently, various workers have investigated electro-coagulation for the removal of heavy metals from wastewater.75–77

Removal of Cr31from aqueous solution by electrocoagulation using ironelectrodes is a feasible process Golder et al.78investigated the removal of

Cr31 from water by electrocoagulation methods It was found that the agulation and adsorption play very important roles in the removal of Cr31during electrocoagulation The removal of Cr31from aqueous solution washighest at a higher current density A multiple electrode was used in theelectrocoagulation system for the removal of Cr31 from aqueous solutionwith both bipolar and monopolar configurations.79 This technique can beused for the treatment of pollutants down to the ppb level, but the high cost

co-of resin makes the process costly for industrial scale applications.80,81 Gao

et al.82used a combined electrocoagulation and electroflotation system forthe removal of Cr61from aqueous solutions The performance of an elec-trocoagulation system with aluminium electrodes for removing heavy metalions on a laboratory scale was studied systematically by Heidmann andCalmano.83

Removal of heavy metal ions from wastewater by electrocoagulation withiron and aluminium electrodes with monopolar configurations was in-vestigated by Akbal and Camcı.84They explored the influence of electrode

material, current density, wastewater pH and conductivity on removal formance The results indicated that an electrocoagulation system with anFe–Al electrode was useful and 100% of the Cu, Cr and Ni were observedwithin 20 min with a current density of 10 mA cm 2 and a pH of 3.0 Theperformance of electrocoagulation, with an aluminium sacrificial anode, inthe treatment of wastewater containing metal ions has been investigated byAdhoum et al.85 Cu, Zn and Cr were removed successfully by using thistechnique The method was found to be highly efficient and relatively fastcompared with conventional existing techniques Direct electrochemicalreduction of Cr61 can be carried out at the cathode.86 The hydroxyl ionsproduced at the cathode induce the coprecipitation of Cu, Zn and Cr.87–89

per-1.4.6 Clays/Layered Double Hydroxides (LDHs)

Clays have been widely used for the removal of heavy metals from aqueoussolutions due to their outstanding properties.90,91 Heavy metals can be re-moved by ion exchange or a complexation reaction at the surface of clays.During the past few years, surface modifications of natural clays with re-agents containing metal binding groups have been explored.91–93 Severalmodification techniques such as intercalation of organic molecules into theinterlayer space and grafting of organic moieties have been applied.94,95Organic-modified clays based on montmorillonite were prepared by em-bedding ammonium organic derivatives with different chelating function-alities for heavy metal removal.96 Montmorillonite intercalated with poly-hydroxyl Fe(III) complexes was used for the sorption of Cd(II).97 Sodiumdodecyl sulfate modified iron pillared montmorillonite has been success-fully applied for the removal of aqueous Cu(II) and Co(II).98Smectite inter-calated with a non-ionic surfactant shows a good performance for theremoval of heavy metals.99 Through the grafting of inorganic and organiccomponents, natural clay can be functionalized to obtain a better sorptioncapacity.100,101 Heavy metals have been removed through the grafting ofamino or mercapto by reaction with the silanol groups onto the surface ofclays.102,103Synthesis of layered magnesium organosilicates for the removal

of heavy metals has been carried out with different organosiloxanes.104Sepiolite can be grafted with organic moieties due to its high content ofsilanol groups Liang et al.90 have functionalized the sepiolite by nano-texturization in aqueous sepiolite gel and surface grafting in toluene withmercaptopropyltrimethoxysilane The sorption of Pb(II) and Cd(II) werestudied and it was found that the surface modification can obviously in-crease the sorption capacities for Pb(II) and Cd(II)

LDH materials appear in nature and can be easily synthesized in the boratory In nature they are formed from the weathering of basalts or pre-cipitation in saline solution All natural LDH minerals have a structuresimilar to hydrotalcite, which has the formula [Mg6Al2(OH)16]CO3
4H2O.LDHs have been prepared using many combinations of divalent to trivalentcations including Mg, Al, Zn, Ni, Cr, Fe, Cu, Ga and Ca.105–118 A number of

synthetic techniques has been successfully employed in the preparation ofLDHs There are a number of methods used to synthesize LDHs includingcoprecipitation methods, hydrothermal synthesis, urea hydrolysis methods,sol–gel methods, ion-exchange methods and rehydration methods.

LDHs have been investigated intensively for anion-exchange propertiesdue to recent interest in developing the use of anionic clays for environ-mental remediation The main characteristic that has been studied is toclearly characterize the adsorption properties of the materials under vigor-ous solid–liquid interface conditions The effect of sorbent composition,surface and bulk adsorption and concentration of adsorption site have beenassessed The adsorption capacity is significantly affected by the nature ofthe counter anion of the LDHs layer LDHs can be used as precipitatingagents of heavy metal cations for the decontamination of wastewater Mn21,

Fe21 and Cu21 cations have been removed by synthetic hydrotalcite-likecompounds, with zaccagnaite and hydrotalcite thin films being used for theremediation of aqueous wastes containing hazardous metal ions.119

1.4.7 Biomass and Biosorption of Metal Ions

During the last few years numerous new processes have been tested cessfully, many of which have gone into operation and a great number ofpapers have been published on biosorption In this section we will discuss

suc-‘‘Biomass based biosorbents and biosorption of heavy metals’’ Biosorptionhas been defined as the ‘‘property of certain bio-molecules to sequestermetal ions or other molecules from aqueous solutions’’.120,121It differs frombioaccumulation, where active metabolic transport takes place, as biosorp-tion involves a passive process in which interaction between sorbent andsorbate occurs Biosorption of heavy metals has become a popular and activefield of research in environmental science.122–126

Rao et al.127 have studied the removal of Cr(VI) and Ni(II) from aqueoussolution using bagasse based biosorbents The bagasse was chemicallytreated with 0.1 N NaOH followed by 0.1 N CH3COOH The materials ad-sorption capacity in order of selectivity for Cr(VI) and Ni(II) was powderedactivated carbon 4 bagasse 4 fly ash and powdered activated carbon 4 flyash 4 bagasse, respectively Values for Langmuir and Freundlich isothermconstants for sorption of Cr(VI) ions onto powdered activated carbon,bagasse and fly ash were 0.03, 0.0005 and 0.001, and 0.12, 0.03 and 0.01,respectively A lower pH of 6.0 favors the uptake of Cr(VI) and pH 8.0 wassuitable for Ni(II) ions removal However, an increase in pH values of thesolution reduces the Cr(VI) adsorption because of the abundance of OHions, causing hindrance to the diffusion of dichromate.128,129However, theadsorption capacity was very low and their application for industrial effluenttreatment cannot be justified

Recently, pectin-rich fruit wastes have been investigated as biosorbentsfor heavy metal ion removal.130 It has been observed that biosorption ofcadmium by pectin-rich fruit materials and citrus peels were found to be

most suitable Equilibrium kinetics were achieved within 30–90 min, pending upon particle size A pseudo-second order model was found to bemore suitable than a first-order model to describe the kinetics Isothermstudies show that the data were well fitted to a Langmuir model It has alsobeen observed that the metal uptake decreased with decreasing pH, indi-cating competition of protons for binding to acidic sites Gurgel and Gil131have described the preparation of two new chelating materials, MMSCB 3and 5, derived from succinylated twice-mercerized sugarcane bagasse(MMSCB 1) MMSCB 3 and 5 were synthesized from MMSCB 1 using twodifferent methods In the first method, MMSCB 1 was activated with 1,3-diisopropylcarbodiimide and in the second with acetic anhydride, and laterboth were reacted with triethylenetetramine in order to obtain MMSCB 3 and

de-5 The capacity of MMSCB 3 and 5 to adsorb Cu21, Cd21 and Pb21 fromaqueous single metal ion solutions was evaluated at different contact times,

pH and initial metal ion concentrations Adsorption isotherms were wellfitted by a Langmuir model Maximum adsorption capacities of MMSCB 3and 5 for Cu21, Cd21and Pb21were found to be 59.5 and 69.4, 86.2 and106.4, 158.7 and 222.2 mg g 1, respectively

A few biosorbents have been reported for the adsorption of heavy metalsnot only in the form of metallic ions but also organometallic compounds.Saglam et al.132 have prepared the biosorbents from the biomass ofPhanerochaete chrysosporium, which adsorbed inorganic mercury and alkyl-mercury species with an affinity of CH3HgCl 4 C2H5HgCl 4 Hg21, withmaximum sorption capacities of 79, 67 and 61 mg g 1, respectively

The efficiency of Parthenium hysterophorous weed for the removal and covery of Cd(II) ions from wastewater has been studied by Ajmal et al.133These workers reported that the kinetics data for the adsorption processobeyed the second-order rate equation The adsorption process was found

re-to be endothermic and spontaneous in nature The maximum adsorptioncapacity of Cd(II) ions was 99.7% in the pH range 3–4 The desorption studiesconfirm 82% recovery of Cd(II) when 0.1 M HCl solution was used as theeffluent Coconut copra meal, a waste product of the coconut industry, wasused for the removal of cadmium from water.134 The biosorption processwas a spontaneous and exothermic process in nature

Rao et al.135 tested the biosorption potential of fennel biomass lum vulgari) for the removal of Cd(II) from water It was found that the bio-sorption of Cd(II) was a chemically controlled process Removal of Cd(II) wasconcentration dependent and increased with an increase in metal ion con-centration, which showed that the multilayer adsorption takes place at thesurface of the biosorbent and it was best described by a Freundlich isothermmodel and pseudo-second order rate kinetics El-Said et al.136 utilized ricehusk ash for the removal of Zn(II) and Se(IV) from water A higher removalcapacity of Zn(II) was found than for Se(IV) The removal capacity increaseswith an increase in biosorbent dose from 1 to 10 g L 1

(Foenicu-Recently, Schiewer and Iqbal137 investigated the role of pectin for theremoval of cadmium from water The carboxyl group plays an important role

in the surface charge and was responsible for the binding of cadmium ontothe biosorbent surface Typically, metal binding experiments were carriedout at an optimized pH of 5 A Langmuir isotherm model provided the bestfit Metal binding kinetics were better described by the first-order modelthan by the second-order model.

Removal of mercury from water was carried out using Carica papaya as abiosorbent.138Sulfuric acid treated almond husk based activated carbon wasprepared and used for the sorption of Ni(II) ions from water.139 The ad-sorption capacity was very high and 97.8% Ni(II) ions were removed by anadsorbent dose of 5 g L 1

1.4.8 Magnetic Nanoparticles as Nanosorbents

Magnetic nanomaterials are one of the recently highlighted branches ofmaterials science and technology that have been utilized in the removal ofpollutants from aqueous solutions Owing to their magnetic properties, highchemical stability, low toxicity, ease of synthesis and excellent recyclingcapability, magnetic nanoparticles have been studied to remove toxic metalions from water

Magnetic nanoparticles are of great interest for researchers from a widerange of disciplines, including magnetic fluids, catalysis, biomedicine,drug delivery, magnetic resonance imaging, data storage and environ-mental remediation.140,141 Although several suitable methods have beendeveloped for the synthesis of magnetic nanoparticles for a variety of dif-ferent compositions, successful application of such magnetic nano-particles in the areas listed here is particularly dependent on the stability ofthe particles under a range of different conditions In the majority of theenvisaged applications, the particles perform best when the size of thenanoparticles is below a critical value, which is dependent on the sourcematerial but is typically around 10–20 nm.142The design and fabrication ofnanoparticle-based adsorbents has generated great interest in a variety ofscientific communities ranging from chemical, biological and environ-mental science to engineering Magnetic nanoparticle-based adsorbentscan be used in the separation and purification of biologically as well

as environmentally relevant target species with high precision andaccuracy.143,144

1.4.9 Removal of Iron and Manganese from Water

The presence of iron and manganese gives an astringent and metallic taste

to drinking water, which causes problems in cooking and in the production

of beverages.145A simple method of iron and manganese removal consists ofoxidation and ion-exchange resins The oxidation of iron is dependent onthe solution’s pH, and organic matter and carbonate concentration Oxi-dation of iron and manganese can be achieved by introducing an oxidizingagent and it may be done through the application of methods that include

the addition of oxidants such as chlorine and potassium permanganate.Activated carbons have also been applied for the removal of iron and man-ganese from aqueous solutions.146 Klueh and Robinson147 investigatedthe sequestration of iron by polyphosphate addition while providing thenecessary disinfection through chlorine addition They observed that thepresence of calcium in the groundwater inhibited the removal of iron.The addition of polyphosphate to the groundwater first and the simul-taneous addition of polyphosphate and chlorine were both fairly successful

at removing the iron

1.4.9.1 Ion Exchange

Ion-exchange resins provide many advantages and are one of the mostwidely techniques used for treatment of wastewater effluents.148 Lee andNicol149 have used the Diphonix resin to remove ferric iron from a cobaltsulfate solution with various pH ranges A lower pH and higher dose of resingives a higher removal of iron from solution Elution of iron was observedwith an increase of Ti(III) in the sulfuric acid eluent These workers foundthat the iron elution enhancement with Ti(III) was due to the combined ef-fects of a reduction of Fe(III) and competitive adsorption of Ti(III) and Ti(IV)ions Lasanta et al.150studied the equilibrium diagrams for ionic exchange,which occurs between Fe31 in different solutions by a chelating ion ex-change resin A mathematical model was used to predict the equilibrium,which gave a good fit for the experimental data in various solutions It hadbeen observed that solvent type influences the adsorption capacity Khalil

et al.151 studied the removal of ferric ions by using crosslinked chitosanresins immobilized with diethylenetriamine and tetraethylenepentamine Ithad been found that the tetraethylenepentamine containing chitosan resinshowed a higher uptake capacity towards Fe(III) compared with diethylene-triamine containing chitosan resin Kinetic data showed that the adsorptionprocess followed the pseudo-second order kinetics Thermodynamic studiesindicated that the adsorption process was exothermic and spontaneous

in nature

1.4.9.2 Activated Carbons

Omri and Benzina152achieved the removal of Mn(II) ions from aqueous lutions by adsorption on activated carbons derived from Ziziphus spina-christi seeds The effects of process parameters such as solution pH, initialmetal ion concentration and temperature on the adsorption performance ofactivated carbons for Mn(II) ions removal were tested to optimize the system.Maximum adsorption was obtained at pH 4 Freundlich isotherms followedthe adsorption system and the higher adsorption capacity for a Langmuirisotherm was 172 mg g 1 Adsorption of iron and manganese ions fromaqueous solution by low-cost adsorbents of palm fruit bunch and maize cobswas carried out.153 Adsorption of iron ions on palm fruit bunch and maize

cobs was in the range of 80–57%, for initial concentrations ranging between

1.4.9.3 Other Treatment Methods

The effect of various organic acids, such as acetic, formic, citric, ascorbic,succinic, tartaric and oxalic acids, on the removal of iron has been studied byAmbikadevi and Lalithambika.156It was found that the oxalic acid gives thebest results, both at room temperature as well as at high temperatures, be-cause of its high acid strength, good complexing capacity and reducingpower The effects of several parameters such as time, temperature and re-agent concentration were studied for the optimization process The removal

of iron was found to beB80% by the authors

Ganesan et al.157used an electrocoagulation process for removal of Mn(II)from aqueous solutions using magnesium as the anode and galvanized iron

as the cathode Several removal parameters such as solution pH, currentdensity, electrode configuration, inter-electrode distance, effects of coexist-ing ions and temperature were studied The results obtained suggested thatthe highest removal of 97.2% at a pH of 7.0 was for a current density0.05 A dm 2with an energy consumption of 1.151 kWh m 3 Thermodynamicparameters indicated that the Mn(II) removal was feasible, spontaneous andendothermic in nature A Langmuir adsorption isotherm well fitted to theadsorption system The kinetic model was best described by a pseudo-secondorder rate at the various current densities Taffarel and Rubio158 appliedChilean zeolite as an adsorbent for removal of Mn(II) ions from aqueoussolutions The solution pH significantly influenced the adsorption of Mn(II)removal and the best results were been found at pH 6–6.8 The removalkinetics was best fitted with a pseudo-second order model The equilibriumisotherm data were best fitted to a Langmuir isotherm model It was foundthat the Chilean zeolite treated with NaCl, NaOH, Na2CO3 and NH4Cl in-creased its uptake ability in comparison with natural Chilean zeolite

1.5 Concluding Notes

The presence of heavy metals and their toxicity to the environment and tohuman beings is posing a serious challenge to environmental engineers withrespect to the treatment of wastewater effluents prior to discharge into thenearby water bodies Several removal techniques have been developed andapplied for the treatment of these wastes to remove the toxic metal ions.Technologies such as microbe-assisted phytoremediation, ion exchange,membrane filtration, photocatalytic oxidation and reduction and adsorptionhave their own advantages and disadvantages over metal ion sequestrationsfrom environmental matrices During recent years the developments in ad-sorption of heavy metals from aqueous solutions have gained tremendouspopularity among the scientific community as methods to treat industrialwastewater Several adsorbents such as clays, LDHs, zeolites, carbon nano-tubes and their composites, activated carbons, biomass derived biosorbents,inorganic nanomaterials, inorganic organic hybrid nanocomposites andmagnetic nanomaterials have been synthesized and investigated for theirability to sequester metal ions from water

Functionalized magnetic nanoparticles are very promising for cations in catalysis, biolabelling and bioseparation In liquid-phase ex-traction of heavy metals and dyes in particular, such small and magneticallyseparable particles may be useful as they combine the advantages of highdispersion, high reactivity, high stability under acidic conditions and easyseparation In this chapter we focused mainly on recent developments in thesynthesis of active adsorbents and nanoparticles Further, functionalizationand application of magnetic nanoparticles and their nanosorbents for theseparation and purification of hazardous metal ions from the environmentare discussed in detail in a separate chapter in this book

appli-Acknowledgements

R.K Gautam thanks the University Grants Commission for the award of aJunior Research Fellowship (JRF) Suresh Mahiya is grateful to the President,JECRC University, for the award of Scholarship for his PhD The authorsequally acknowledge the support and provision of the necessary facilities bythe University of Allahabad, Allahabad, India and JECRC University, Jaipur,India The support and encouragement of Prof V.S Tripathi from the De-partment of Chemistry, University of Allahabad, is also appreciated We alsothank the anonymous editors and reviewers for giving their kind criticismsand comments, which fuelled the zeal for the manuscript

References

1 J H Duffus, Pure Appl Chem., 2002, 74, 793

2 Agency for Toxic Substances and Disease Registry, Toxicological Profilefor Lead, U.S Department of Health and Human Services, Atlanta, 2007