UTAR - Zinc Adsorption from Waste: Literature Review & Treatment Tech

This literature review provides an overview of zinc adsorption as a method for treating waste containing heavy metals. It discusses the sources of zinc pollution, its environmental and health effects, and various technologies for its removal from wastewater, with a focus on adsorption techniques. The review covers the mechanisms of adsorption, factors affecting the process, and the use of materials like nano zinc oxide (ZnO) as adsorbents. It also touches on the importance of zinc oxide in industries like rubber manufacturing and the economic aspects of zinc recovery. The review highlights the advantages and disadvantages of different treatment technologies, including oxidation, ion exchange, and electrochemical methods, and emphasizes adsorption's effectiveness, flexibility, and reusability. This document is available on Desklib, a platform providing study tools and resources for students.

Zinc adsorption from waste1
ZINC ADSORPTION FROM WASTE
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Zinc adsorption from waste

Zinc adsorption from waste 2
Literature review
Large quantities of heavy metals are released into the water masses such as streams and lakes
on a day to day basis from huge industrial processes, for instances car production, mining and
electroplating. Heavy substances are nonbiodegradable and toxic. They will collect in the
human body, food web and cause an environmental difficulties and considerable health
concerns (Al-Malack and Basaleh 2016). Many negative effects of heavy materials exists, for
examples the hypertension, renal damage and malformation of skeletal in foetuses
(Pourbeyram 2016). For example, cadmium ions, Cd2+ are sixth most dangerous substances
and very toxic to human beings (Khan, Rahman, Marwani, Asiri and Alamry 2013). Cd2+ can
discharged into the water bodies from many sources such as pigments, smelting, metal plating,
sewage sludge, alloy industries and phosphate fertilizers. The negative impacts of huge amount
of cadmium are chronic and severe ailment such as abdominal pain, vomiting, testicular atrophy
and diarrhoea (Almamoori, Hassan and Kassim 2012).
Many procedures for the use of heavy metal such as oxidation, electrochemical, adsorption, ion
exchanges and irradiation exists as shown below. Adsorption is well-known to be effective and
economic method for use in the removal of the heavy materials. The process comprises a mass
transfer routine and components are attached by the physical and chemical bonds to the
surface of the solid. The methods is normally utilised due to its easiness to perform, flexible in
structure and design, insensitive to dangerous materials, and the adsorbents could be
reprocessed by suitable desorption routine (Pourbeyram 2016).
Of recent, the Nano-adsorbents have become a centre for research due to their high interfacial
routine and large surface are to volume. Nano zinc oxide (ZnO) is a crucial inorganic function

Zinc adsorption from waste 3
substances in which are demonstrates a huge adsorption bulk for the carbon monoxide, carbon
dioxide and hydrogen. Therefore, Nano ZnO is more cost friendly compared to other Nano-
particles such as (Zhang et al. 2014).
The enticing aspects of Zn have focused concentration of many researchers from diverse
industries. ZnO have a high electron bonding power at room temperature, helping it to create
devices that work precisely at room temperature (Ahmed et al. 2013). Moreover, zinc oxide has a
perfect photoconductivity aspects and it is so utilised for photocopying. The rubber industry is
releasing a huge amount of wastewater and it contains physical, chemical and biological
pollutants. The main focus is to remove zinc that can be recovered from this wastewater and
produce zinc oxide from the recovered zinc (Moaref, Sekhavatjou and Hosseini 2014). Currently,
there are three methods in the rubber industry to remove the heavy metals which is adsorption,
membrane separation, and precipitation. Precipitation is not suitable due to highly organic
polluted wastewater, the excessive residue of precipitate and more odours while membrane
separation require high permeate flux with trans membrane pressure and flow rate which leads to
cost (Mohammadi et al. 2010). However, adsorption actions are normally applied by many
experts for the heavy metals eradication from the waste rivers and activated carbon has been
frequently utilised as an adsorbent (Hang, Li, Gao and Shang 2012).
Furthermore, 50 % of ZnO is utilised in the rubber business, attending as a vulcanizing promoter
to improve the efficiency of vulcanization procedure over the creation of three dimensional
cross-linking amid sequence of rubber particles to advance rubber bounciness (Mussatto et al.
2010).

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Figure 1: (Statista 2015)
It has been noted that ZnO is to have an enormous marketplace viewpoint in Malaysia resultant
from the universal rubber quest. The nation is one of the top three rubber exporters 2013. In
2013, the country exported around $ 2,230,998,000 of natural rubber in terms of dollar
establishing a 9.6 % of the whole rubber (Yap 2016). With such an enormous
search for natural rubber, the study works on ZnO in the surface.
Country Value of natural rubber ($) Total export (%)
Thailand 82335100 35.4
Indonesia 69106630 29.7
Malaysia 22309980 9.6
Vietnam 18102160 7.8
Côte d'Ivoire 9425180 4.0
Germany 3368160 1.4
Belgium 296,0080 1.3
Guatemala 2388430 1.0
Liberia 2019980 0.9
Myanmar 199,6190 0.9
Figure 2: (Yap 2016).
Even though the existence of heavy metals is common in the surrounding and in the food chain
that is important for survival for a sustainable ecosystem, an excess of any quantity of these
metals in the chain may cause chronic or acute poisoning (Yang et al. 2014). Heavy metal toxicity

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interferes with a nervous system, minimises the energy levels, disrupts the blood content and
subsequently affects the liver, kidney, lungs and all vital organs. Long exposure of the heavy
metals may cause neurological and muscular degenerative illness, including Alzheimer’s disease,
Parkinson’s disease, muscular dystrophy and multiple sclerosis. Frequent exposure to high
levels of heavy metals may also cause cancer (Wang and Chen 2015).
Sources of Heavy metal pollution
In the last few years, the speedy industrialization has facilitated the current level of
environmental pollution, particularly water contamination. The effluents created from the various
businesses such as electroplating, paper, excavating, metal melting are reported to have a huge
quantity of dangerous pollutants such as heavy metals. Heavy metals are categorised as
hazardous effluents owing to their hostile ecological and well-being impacts even at a small
concentration (Dermentzis, Christoforidis and Valsamidou 2011). Heavy metals are
carcinogenic, poisonous and biodegradable to human bodies as well as to the vegetation and
animals. Heavy metals incline to bio accumulate in living creatures. Copper is necessary for
plants (Hu and Shipley 2013).
Heavy metals are nonbiodegradable, tenacious and get accrued in nature and therefore are the
main sources of environmental contamination. Numerous anthropogenic sources such as
wastewater disposal and industrial effluents, agricultural water flows and cosmetics sewage
discharge heavy substances into the marine surrounding (Motsi 2010). Heavy metals are
widespread effluences and contaminate the surrounding such as air and water. The existence of
such metals in the surrounding are currently a grave subject of concern, to reduce the health peril
and for the control of surround degradation, strict rules were imposed for the effluent discharge

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and drinking water. Compliances with the above strict guidelines are currently major challenges
for the drinking water providers, industries, and expertise (Kordialik-Bogacka 2011).
Environmental and health effects
Heavy metals are typically termed as metals which have a specific density exceeding 5g/cm3 and
severely affect the ecology and living micro-organism (Hu and Shipley 2012). The metals are
archetypal to uphold numerous physiological and biochemical processes in living being when
they are in low levels. But, they can become noxious when they go beyond certain threshold
level. Heavy metals are biggest environmental contaminates and their toxicity is a concern of
rising significant for nutritional, evolutionary, and ecological reasons. The most common type of
heavy metals is copper, cadmium, nickel, chromium and zinc, of which all of them can be
dangerous for environmental and human health (Kim et al. 2013). Heavy metals can goes to the
atmosphere through the human actions or natural means. Many sources of heavy metals include
mining, urban runoff, soil erosion, industrial effluents, sewage discharge, and natural
weathering of the earth’s crust. Even though these substances have important biological roles in
animals and plants, occasionally their oxidation-reduction and chemical coordination features
have given them an extra advantage so that they can avoid regulations mechanism such as
compartmentalization, homeostasis, transport and joining to required cell components. The
metals join with the sites of protein by substituting the original metals from their natural joining
locations resulting to the cells malfunction and eventually toxicity. Previous study has
established that oxidative deterioration of biochemical macromolecules is due to the heavy
metals binding to the nuclear proteins and DNA (Fu and Wang 2011).

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Many communal health controls have been done to regulate, avert and treat metal toxicity
happening at numerous levels such as environmental aspects, occupation exposures and
accidents. It is worth noting that toxicity of metals relies on the exposure route, absorbed
dosage, and time of exposure. As earlier discussed, metal exposure can led to many disorders
and an result to extreme harm as a result of oxidation stress due to the free radical generation
(Grassi, Kaykioglu, Belgiorno and Lofrano 2012).
Despite its harmful impacts on human beings, Zn is one of the most utilised materials with plenty
of real usages. Zn is important for biological purposes in many metabolism paths such as gene
expression, human cell reproduction and cell replication in plants. About 40% of Zn has been
used to electrify iron and other materials for averting weathering. Another significant use of Zn
is the production of ZnO (Tong, Li, Yuan and Xu 2011).
Technologies to remove heavy metals from wastewater
There are numerous courses for the use of heavy metals eliminations such as oxidation, ion
interchange, irradiation, electrochemical treatment, photochemical and adsorption. Among the
above method, adsorption is well-known as an effective and economical method for the use of
heavy substance removal (Choo 2018). Adsorption is normally utilised because it is easy to do,
elastic in dimension and operation, not sensitive to deadly materials, revisable and the adsorbents
could be reprocessed by suitable desorption action (Pourbeyram, 2016). Among above-
mentioned treatment knowhow, adsorption is one of the frequently utilised purification and
separation techniques due to its high selectivity, great effectiveness and cheaply. It is controlled
by numerous crucial parameters predominantly the temperature, pH and contact period.

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Figure 3: (Choo 2018).
Treatment technologies advantages Disadvantages
Oxidation Fast process High energy cost and generation
of by-product
Adsorption Insensitive to toxic contaminants
and flexibility and simplicity of
design
Adsorbent need regeneration
Ion exchange Broad range of heavy metals can
be eradicated
Expensive
Ozonation Can be used in gaseous states Half life is short
Flocculation/coagulation Cost effective Big particle size and generation
of sludge
Electrochemical treatment Routine is quick and is good for
specific metal ions
Cost ineffective and big particle
size
Fenton’s reagent Energy inputs is not important
for the activation of H2O2
Sludge is generated
Photochemical No production of sludge Generation of by-product
Irradiation Excellent is large scale A lot of dissolved oxygen is
needed
Electro kinetic coagulation Economically viable Production of sludge
Adsorption of Zinc

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The adsorption application was on18th century so as to avert the nasty smell employing the
dusted wound with crushed charcoal acting as an adsorbent. Currently, adsorption is a well-
initiated expertise for the eradication of heavy substance due to low cost and high efficacy.
Adsorption is controlled by Van der Waals forces (physical adsorption) or chemical action
(chemisorption) reliant on the type of energy reliant on the nature of forces. Physical adsorption
is a flexible routine from the intermolecular forces between the adsorbent and adsorbate
molecules. Chemisorption occurs due to the bondage between the adsorbate and solid.
Numerous crucial factors have to be taken care before adsorption processes such as temperature,
contact time, pH, and type, dosage, and concentration of adsorbate (Xu, Cao and Zhao 2013). The
above parameters affect the three major process of adsorption mechanism.
Chemisorption Physisorption
Attracted by chemical bonding Vander Waal’s forces
Preferred at high temperature Low temperature
High energy is needed for adsorption Lower energy is needed
Irreversible processes Reversible processes
Activation energy is needed for the routine No need for activation energy
Creates a mono-molecular layers Generates a multi-molecular layers
Figure 4: (Choo 2018).
Mechanism of adsorption
Adsorption refers to the phenomenon of which the accumulation of one substance on
the surface of other substance in a solution. The initiation of adsorption is mainly due to the
existence of unstable forces in the solution or surface of solid substances. These physical or
chemical forces have a tendency to attract the substances nearby and interact with the absorbents

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surface. However, adsorption is a term which is totally different from the absorption. In general,
absorption is defined as the dispersion of substance throughout the bulk.
Sorption process is known as both of the adsorption and adsorption processes occurs
simultaneously. In the adsorption system, both adsorbent and adsorbate are involved in the
solution. Adsorbent will have the tendency to attract adsorbate in the bulk solution.
The adsorption performance will depend on many factors including surface charge,
presence of functional groups and solution pH.
Figure 5: (Khoo 2018).
Factors affecting adsorption
The PH of the solution takes an essential part in the metal ions adsorption in outlook of
speciation of metal ions. At pH of below of 2, removals of zinc ions are negligible. At advanced
pH, an exchange of hydrogen ion amongst the surface of the carbon with Zn ions results in an
improvement in Zn ions uptake. This reveals significance of pH in upsetting the uptake of Zn
ions (Özçimen and Ersoy-Meriçboyu 2010).

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The influence of adsorbent amount en route for the elimination of heavy substances from
aqueous solution employing natural bentonite has been described. They established that an
upsurge in the adsorbent dosage in a range of 0 to 1.2 gram in one liter of adsorbate improved the
portion of Zn ion detached. The situation happened due to an upsurge of active places offered by
bentonite for more Zn ions to join onto its surface.
The change in temperature affects the whole thermodynamics process of the adsorption course.
It is established that the adsorption volume reduces with rise in temperature. The above is due to
the reduced surface action, showing that the adsorption system shows the exothermic action. An
upsurge in temperature also reduces the attraction forces between the zinc ions and clay
adsorbent, producing a reduction in sorption routine. The impact of contact interval towards the
adsorption bulk of the adsorbent is modest. Each adsorbent process has a distinct equilibrium
contact period attributed to the different chemical and physical properties of the adsorbent.
An appropriate adsorbent takes part an important part as it defines the affinity of the metal ion
eradication. The primary requirement of adsorbent is capacity, long lifespan and high selectivity.
Therefore, with a longer span, higher capacity, then there will be more Zn being adsorbed and
the adsorbent can be reprocessed for a long duration.
The attention of the study exertions in the previous decades focused on the application of
numerous wastes to create activated carbon. Carrot residues, castor seed hull, bagasse, coconut
shell, chestnut, palm kernel shell and tea are instances of agrarian wastes that have been
researched in regarding Zn removal volumes. The parameters require to be controlled to get the
quality adsorption outcome before the succeeding process. Then, there will be a huge quantity of

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Zn being desorbed in the advanced portion of the trial due to the larger quantity of Zn ions
overloaded on the adsorbent surface.
Adsorbent Adsorption
capacity (mg/g)
Optimum conditions
PH Time (hours) Temperature (OC)
Bagasse fly ash 13.21 4 6-8 30
Banana peel 5.80 - - -
Carrot residues 29.61 - 1.1 -
Castor seed hull 6.72 5.8 - -
Chestnut shell
(acid treated)
2.41 - - 25
Cocoa pod husk 100.93 - 2 -
Coconut shell 9.43 - 0.8 -
Coffee husk 5.56 5.4 - -
Mango seed 28.21 5 1 25
Palm shell
activated carbon
15.6 6 -- --
Risk husk ash
(treated with
H2SO4
39.17 6 - -
Sawdust 6.93 5 - -
Shell carbon 50.93 6 3 25
Tea waste 8.90 4.2 0.5 60
Wheat 16.40 6.5 24 -