Due to fast generation and industrialization in many countries, the levels of industrial pollution have been steadily rising.

As a result, the pollution problem of industrial wastewater is becoming more and more serious in the world.

Consequently, the treatment of polluted industrial wastewater remains a topic of global concern since wastewater

"heavy metal ions" is used for elements, whose atomic masses are in the range of 63.5 to 200.6 with a specific gravity

being higher than 5 g/cm

. Some cases of heavy metals involve cadmium, zinc, copper, nickel, lead, mercury and

chromium. These are mainly present in processes involving metal plating, mining, battery manufacturing, petroleum

refining and paint manufacturing (Alatabe & Hussein, 2017), (Faisal & Hussein, 2013).

Lead (II) ions are non-biodegradable impurities that are not only hard to remove from the ecological system but are

also extremely poisonous if concentrations exceed the permissible limits. Increased concentrations of these Lead (II)

ions may also accumulate in human bodies if they enter the food chain. Consequently, these may also lead to serious

health issues. Lead also has an impact on the environment because of its harmfulness, which occurs due to its presence

in industrial wastes produced from manufacturing sites. These include storage-battery manufacturing, printing, fuel

combustion cookware, some Mexican pottery glazes and also photographic materials (Ab Latif Wani & Usmani,

2015)(Faisal & Hussein, 2015). Besides, lead appears to be one of the major risk factors for several deadly diseases if the

concentrations of lead go above the permissible limits, as recommended by the World Health Organization (WHO). To

elaborate, concentrations greater than 3-10 μg/l in drinking water can lead to serious harmful effects on human bodies.

Also, lead is a harmful metal that can also have serious health effects on humans including children. Children are more

of miscarriages and neonatal deaths (Alatabe & Hussein, 2017) (Ab Latif Wani & Usmani, 2015); (Hussein, 2018).

Lead exists naturally in an insoluble form and other harmless forms as well (Carson et al., 1986). Several processes are

used for treating wastes produced from industries that consist of Lead (II)ions. Chemical precipitation, ion-exchange,

electrodialysis, and carbon adsorption are a few vital processes that have been employed for treating wastewater.

Furthermore, other progressive practices are also used for removing Pb

which may not be reasonable for the small-scale productions that discharge lower amounts of wastewaters. Many

treatments for wastewater polluted with lead ions have been proposed, including an adsorption process, which does not

have high effectiveness, unless the adsorbent material shows certain physicochemical and mechanical properties. In

recent years, some physical, chemical, and biological treatments on natural raw minerals have been performed to modify

on the results of these studies, it appears that the elimination of Pb

ions with the use of low-cost adsorbents is

increasingly favorable, especially in the long term (Siti et al., 2013). This is because several materials are (natural,

sustainably, economically, viable and environmental friendly for Lead ions removal) readily available, i.e. these exist

naturally or are found in agricultural waste and manufacturing by-products, and can be used as low-cost adsorbents.

Previous researches show that there is a growing interest in searching for a variety of materials, which can serve as low-

cost adsorbents. These include: sawdust (Ansari & Raofie, 2006), cocoa shell (Candelaria et al., 2018), rice husk ash

(Feng et al., 2004), modified sawdust of walnut (Bulut & Tez, 2003), cane papyrus (Alatabe & Hussein, 2017), papaya

wood (Saeed, Akhter, et al., 2005), maize leaf (Babarinde et al., 2006), rice husk (Cruz-Olivares, 2015), water hyacinth

(Eichhornia Crassipes), (Anzeze et al., 2014), Gamma Irradiated Minerals (Cruz-Olivares et al., 2016), tree fern ( Ho et

(Yadla et al., 2012), (Chitradevi & Mothil, 2015), tea waste (Liu et al., 2009), dried olive stones (Siti et al., 2013), thorns

(Alatabe & Obaid, 2019), sunflower husks (Hussein, 2019), pine cone activated carbon (Momčilović et al., 2011),

activated carbon from militia ferruginea plant leaves (Mengistie et al., 2008), granular activated carbon (Dwivedi et al.,

2008), pomegranate peel (El-Ashtoukhy et al., 2008), maize stalks (Jagung, 2011), activated carbon derived from waste

biomass (E rdem et al., 2013), chemically modified orange peel (Lasheen et al., 2012), modified orange peel (FENG &

GUO, 2012), maize (Zea mays) stalk sponge (García-Rosales & Colín-Cruz, 2010), olive mill solid residue (Hawari et

al., 2014), petiole and fiber of palm tree (Hikmat et al., 2014), cladophora rivularis (Linnaeus) Hoek (Jafari & Senobari,

2012), flamboyant flower (Delonix Regia), (Jimoh et al., 2012), common edible fruit wastes (Okoro & Ejike, 2005),

watermelon rind: agrowaste or superior biosorbent (Liu et al., 2012), shewanella oneidensis (Jaafar et al., 2016),

chemically modified moringa oleifera tree leaves (Reddy et al., 2010), zeolite A4 supported on natural carbon (Makki,

2014), rosa bourbonia (Manzoor et al., 2013), grape stalk waste (Martinez et al., 2006), spirodela polyrhiza (Meitei &

Prasad, 2013), crop milling waste (black gram husk) (Saeed, Iqbal, et al., 2005), arborvitae leaves (Shi et al., 2016), African

breadfruit (treculia africana) seed hulls (Sonde & Odoemelam, 2012), potato peels (Taha et al., 2011), acid modified and

unmodified gmelina arborea (verbenaceae) leaves (Jimoh et al., 2011), waste chestnut shell (Vázquez et al., 2012),

ailanthus excelsa tree bark (Curr, 2013), lemon peel (Tovar et al., 2018), EDTA-modified cocoa (the obroma cacao) pod

husk residue, Iranica (Yahaya & Akinlabi, 2016) and biological activated dates stems (Yazid & Maachi, 2008).

Therefore, the utilization of these materials as low-cost adsorbents is acknowledged as a possible and economical

application for wastewater treatment. This is reflected in the increasing numbers of periodicals, which have appeared in

the literature on the usage of low-cost adsorbents (Shafaghat et al., 2012). These mainly conclude the immense interest

in finding appropriate adsorbents for the process of adsorption (Gupta et al., 2009),(Alslaibi et al., 2014).

Lead (II) ions are commonly found on earth and are well known for their characteristics which include perseverance,

increased harmfulness along with their ability to serve as non-biodegradable impurities if gathered in the ecological

system. Several industries are still making use of lead. These include the autonomous, battery, recycling, refining,

smelting and various more manufacturing industries. Lead is known to be a toxic metal, which can affect organs in a

human body (Baby et al., 2010),(Gonick, 2011). It is also known to have the most severe effect on the nervous system

in humans of all ages. However, lead is more harmful in children as children tend to have softer internal and external

tissues as compared to adults. Thus, they are more prone to being severely impacted by lead toxicity (Nordberg et al.,

2014),(Jentschke & Godbold, 2000). In terms of the negative effects of lead poisoning in adults, it has been found that

long term exposure to lead can cause a decrease in cognitive ability, which means that the nervous system is mainly

pregnant couples, exposures to lead may cause miscarriages in women while leading to decreased fertility in males (Ezzati

et al., 2004). Table 1 presents a summary of the different sources which may produce Lead (II) ions, which exist in the

environment (Basso et al., 2002),(Al-atabe & Hussein, 2018), along with providing the limit of the concentration of

these ions that can be present in wastewaters in MCL (Maximum Contaminant Level), as recommended by USEPA

(Babalola et al., 2010),(Hussein & Alatabe, 2019),(Ab Latif Wani &Usmani, 2015).

Table 1. Various Sources of Lead (II) Ions in the Environment.

and also underground waterways (Gidlow, 2004). This can result in pollution of soil while enhancing the overall pollution

rate, especially when ores from mining processes are disposed of in landfill sites. Besides, agricultural wastes in soils can

consist of metals, which would then be consumed by plants thus resulting in the accumulation of such harmful

ions involves the chemical precipitation (Kavak, 2013)(Matlock et al., 2002), membrane filtration (Bisheh et al., 2020);

(Kumar et al., 2016); (Al-Rashdi et al., 2011), ion exchange (Bezzina et al., 2019)(Hubicki & Kołodyńska, 2012), reverse

osmosis (Mikulášek & Cuhorka, 2016)(Bessbousse et al., 2008), electro-dialysis (Sadyrbaeva, 2018) (Mohammadi et al.,

2004), solvent-extraction (Konczyk et al., 2013)(Baba & Adekola, 2013), evaporation (El-Naggar et al., 2019); (Şölener

et al., 2008), oxidation (Saleh & Gupta, 2012) (Wang et al., 2015) and activated carbon adsorption (Denizli et al., 2000);

(Eliassen & Bennett, 1967). Chemical precipitation is the commonly used process for Lead (II) ions removal from

inorganic effluents depending on the pH alteration in a basic solution (Pang et al., 2011). Nevertheless, the disadvantages

of chemical precipitation are manifold. To elaborate, the discharge of too much sludge produced needs additional

treatments, which slows the metal precipitation, leads to inadequate settling and the aggregation of metal precipitates.

Also, there are several long term ecological concerns with the disposal of sludge (Gunatilake, 2015),(Alatabe, 2018).

concentrations, involve the enhancement of the application of adsorption as a useful and practical approach. The

effectiveness of the adsorption processes is mainly categorized depending on the nature of the solution in which the

pollutants are spread, the molecule sizes and the polarity of the contaminant along with the type of adsorbent used.

Adsorption also occurs based on the interactions between surfaces and species being adsorbed at certain molecular

levels (Barka et al., 2013),(Worch, 2012).

Adsorption can be categorized into two methods; physical adsorption and chemisorption. Physical adsorption is a

reversible phenomenon that results due to intermolecular forces of attraction that take place in molecules of the

adsorbent and the adsorbate. Meanwhile, chemisorption occurs because of the chemical interactions amongst solid and

adsorbed substances. Chemi-sorption is an irreversible method, which is also known by activated adsorption. Increased

physical adsorption occurs at a temperature in the range of the critical temperature of a known gas while chemisorption

along with no interactions existing between adsorbed molecules (Langmuir, 1916). For the Langmuir equation, it is

written as Eqs. 1 and 2.

Table 4. Adsorption Models of the Lead(II) Ions System.

a) Adsorption

Isotherm

i)Langmuir

K

b) Adsorption

Kinetics

i)Pseudo first-order

q

equilibrium and at time t, k

is the rate

constant

(Lagergren

, 1898)

ii)Pseudo-second-

order

(Ho and

Freundlich isotherm models are used for the interpretation of the adsorption on heterogeneous surfaces with

interactions taking place among the adsorbed molecules. This process is not limited to the production of a mono-layer

this isotherm is usually utilized to define the adsorption of organic and inorganic compounds on a wide diversity of

Where K

is the adsorption equilibrium constant, 1/n is the heterogeneity factor, which is associated with the capacity

and intensity of the adsorption and C is the equilibrium concentration (mg/l). This model makes use of the assumption

that with an increase in the adsorbate concentration, the concentration of adsorbate on the adsorbent surface also

increases and, consistently, the sorption energy reduces exponentially with the achievement of the adsorbent's sorption

center. Langmuir and Freundlich isotherm models are usually employed to define the short term and mono component

adsorption of metal ions through varying materials (Redlich & Peterson, 1959).

Temperature is a significant factor for the sorption of metal ions related to the thermodynamics of the adsorption

procedure. Usually, two general types, which exist are endo-thermal and exothermal sorption processes. These are

determined depending on the rise or reduction in the temperature during the process of adsorption. The term endo-

thermal is applicable when the sorption rate increases due to the rise in temperatures. On the contrary, the term

exothermal refers to the decrease in sorption as the temperature increases. The equilibrium constant achieved from the

Langmuir equation at several different temperatures can be used to control the various thermodynamic variables. These

conditions, ionic strength, and experimental circumstances.

The contact time based on the experimental parameters can be considered for studying the rate-limiting step in the

adsorption process, relating to the kinetic energy.

The overall adsorption processes can be regulated through steps such as pore diffusion, surface diffusion or a mix of

more steps. Lagergen's first-order equation (Lagergren, 1898) and Ho’s second-order equation (Ho & McKay, 1998)

(Ho, 1998) are instances of kinetic models, which are often used to describe these adsorption kinetic models. The

pseudo-first-order kinetic equation of Lagergen's model (Lagergren, 1898) is given as Eq. 7.

equation refers to the assumption of the rate of change of solute's uptake with time which is in direct relation to the

change in the saturation concentration and the amounts of solid uptake over time (Ho & McKay, 1998). The pseudo-

second-order kinetic is given as Eq. 8.

concentrations, adsorbent doses, the solution's pH and particle sizes. It was revealed that the ratio of adsorbent to the

solution along with the metal ion concentration can have an effect on the quality of the metal ions removed.

The most adsorption of Pb

per 200 ml at various concentrations of the ions, i.e., 200 mg/l and 100 mg/l. An increase in the adsorption takes place

with an increase in the electrolyte concentration. It was noticed that the most metal uptake in tea waste took place at 48

mg/g and 65 mg/g for Pb

data achieved at 22°C demonstrated that the equilibrium data for Pb

rise in the overall adsorption rate and capacity of Pb

Besides, investigative research was performed with varying pH (i.e. pH of 2.5, 6.6 and 7.2), varying temperatures (i.e.

30°C, 40°C, 50°C and 60°C) and adsorbent doses (i.e. 1 to 10g). The outcomes of this investigative study showed that

adsorption capacities of clays for removing lead increase with a rise in the solution's temperature. It was also revealed

that the maximum adsorption capacity was 117 mg/g at a temperature of 60°C. Also, the adsorption process exhibited

a Langmuir and Freundlich behavior, which was shown by the coefficient (i.e. R2 > 0.99). Increased percentage of Lead

(II) removal at low solution pH is possible due to the decreased content of Lead (II) ions. On modeling, the kinetic data

fit the pseudo-first-order model well as compared to the pseudo-second-order model. The works on the adsorption of

Lead (II) by the durian shell waste in terms of isotherms, kinetics and thermodynamics have verified the process, which

has endothermic ( H°>0), spontaneous ( G°<0) and irreversible ( S°>0) characteristics.

Moreover, the peel of banana was also considered for removing Lead (II) from water (Gonzalez et al., 2006). The

works were performed as a function of: pH (i.e. with pH values in the range of 1.18 to 13.5), particle sizes (i.e. with sizes

of 600, 420, 300, 150, and 75 and <75 ìm), doses (of 0.05, 0.1, 0.2, 0.5 and 1 g), contact time (of 3hr) and temperature

(in the range of 30-70°C). The findings revealed that the optimum conditions for adsorption are achieved at a pH of

6.5, at a size of particle less than 75 ìm, a dosage of 0.5g/100ml and 1-hour contact time.

The adsorption capacities of banana peels for removing Lead (II) reduces with a rise in the solution temperature, which

shows that the adsorption process is impulsive. The type of adsorbent is an important factor. Adsorption capacity

Recently, quite a significant amount of research has been carried out for obtaining materials, which could be used as

low-cost adsorbents. These consist of natural materials, agricultural waste, and wastes produced from industries. Low-

cost adsorbents refer to those materials, which are found abundantly in the environment or are byproducts or wastes

from industries. Moreover, adsorbents are known as low-costs if they have reduced processing requirements. The

previous adsorption works concentrated on plant wastes such as the maize leaf (Babarinde et al., 2006), rice husk ash

(Feng et al., 2004), cane papyrus (Alatabe & Hussein, 2017), coconut husk (Njoku et al., 2011) and tea waste leaves (Liu

et al., 2009), which can be utilized either in their natural form or after some physical or chemical alterations. Converting

these materials into adsorbents is an effective way of reducing the costs of waste disposal and for providing alternate

treatments for replacing the commercially activated carbons (Salihi et al., 2017). Table 5 provides a summary of the

The adsorption of metal ions from wastewaters is usually dominated by the solution's pH. It is worth mentioning that

the pH of the solution influences the surface charges on the adsorbent, the extent of ionization along the class of

adsorbents. Over known pH range, mostly metal sorption is improved with pH. However, this is valid for a known

increase in pH, after which an additional rise in pH can lead to a reduction in the metal sorption. The dependency of

are competing with hydrogen ions for the binding site on the surfaces of the adsorbent. On the contrary, at increased

pH values, the Pb

Table 5. Adsorption Capacities of Lead (II) Ions Utilizing Several Different Adsorbents.