Removal Of Lead Metal Ion From Water Environmental Sciences Essay

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In this research, anew adsorbent is presented which will be considered for the recovery of heavy metals, this adsorbent is rock phosphate (low-grade).

Toxic metals including "heavy metals" are individual metals and metal compound that negatively affect people health. In very small amounts of these metals are necessary, because they become very toxic in large amount. Lead is one of heavy metals, which belong to the toxic materials that cause many harmful diseases.

The major sources of water pollution are the industrial waste containing heavy metals. Nickel, lead, cadmium and zinc are heavy metals present in ground water as a cationic form, and measured by Pb.

The type of metals present in certain wastes depends on the manufacturing processing which generated this waste. Generally, the waste problems are related to transfer of dissolved metal from plating baths or metal surface cleaning baths to rinse water by drag-out. The world health organization, 1984 made guidelines for drinking water, and it put the permissible limits before their discharge to the environment; therefore it's necessary to decrease the concentration of heavy metals to their permissible limits before their discharge to the environment.

We can reduce the concentration of heavy metals by use of adsorbent like activated carbon and by ion exchange resins, to remove traces metals from aqueous system have been widely investigated. However, because of high capital and regeneration costs of activated carbon and ion exchange resins, researchers are encouraged to look for other types of adsorbent.

The objective of this work was to examine the ability if phosphate (low- grade) to adsorb Pb from aqueous solution.

This done by studying the adsorption efficiency of heavy metals with out activation of adsorbent (phosphate (low- grade)), also by discussion of the effect of different operating parameters , such as concentration of heavy metals , adsorbent concentration , particle size of adsorbent , shaking time and initial pH of the solution on the up take of Pb by the new adsorbent were studied.

The process, which used in this work, was batch adsorption process. [1]

This research is organized into (3) chapters.



2.1 Heavy metals in waste water

Heavy metals pollution is one of the most serious environmental problems facing life on earth. Pollution of water by toxic heavy metals through the discharge of industrial waste water considers a world wide environmental problem.

Table (1) shows the type of metal released by various industries. This table shows that the type of metal present in certain waste depends on the manufacturing processing which generated this waste. Generally, the waste problems are related to transfer of dissolved metal from plating baths or metal surface cleaning baths to rinse water by drag-out.

There are several sources of water pollution by heavy metals, building paper, mining, petrochemicals, electroplating, metal Processing, textile and battery manufacturing, fertilizers, petroleum refining and steam generation power plant.

The harmful effects of heavy metals are due to the diseases resulted from them. Metals present as a soluble and particulate form in waste water, removal of metal ions from wastewater is an effective manner has become an important issue today.[2]

Precipitation followed by coagulation has been extensively employed for the removal of heavy metals from water. However, this process usually produces large volumes of sludge consisting small amounts of heavy metals. Membrane filtration is a proven way to remove metal ions but its high cost limits the use in practice.

Adsorption is an efficient method for the removal of tracer components from water. Activated carbon-produced by carbonizing organic materials-is the most widely used adsorbent. Activated carbon has shown good metal ion adsorption capacities.

However, the high cost of the activation process limits the use in wastewater treatment. Over the last few years number of investigations has been conducted to test the low cost adsorbents for heavy metal ion removal. Waste biomass, industrial waste, and mineral waste have been investigated by many workers and biomass has shown better adsorption properties.

Plant materials are mainly comprised of cellulose materials that can adsorb heavy metal cations in aqueous medium. The utilization of agricultural waste materials is increasingly becoming a vital concern because these wastes represent unused resources and in many cases present serious disposal problems. [3]

Table (2.1): Heavy metals found in major industries:




















Pulp, paper


























































Basic steel work










Basic non-ferrous









Motor veicles finishing


Flat glass, cement


Textile mill products


Leather tanning



Steam generation

2.2 Toxic and Hazardous of heavy metals.

Heavy metals such as copper, lead and zinc become major contaminants in wastewater and are main toxic industrial pollutants. In recent years, it has turned into a serious problem in which the lead pollution has been found as the most potential threat to air, water and soil. Millions of adults and children are suffering from adverse health effects and impaired intellectual developments due to exposure to excessive levels of lead around their living environment. Chemical precipitation, ion exchange, racers osmosis and electrochemical treatment and sorption are conventional technologies to remove the heavy metal ions from aqueous solution. [6]

Many alternative methods for heavy metal removal were developed in the last decades to avoid the disadvantages of the conventional ways, such as incomplete removal, high-energy consumption, and produce wastes.

Metal oxides and activated carbon are the natural and synthetic materials which have been investigated as adsorbents for heavy metals and are most extensively employed, but their high costs have limited their large-scale use for the removal of toxic heavy metals.

Phosphate minerals have been shown to possess the potential to adsorb heavy metal ions from aqueous solutions. High-grade rock phosphate has already found major

applications in phosphoric acid and fertilizer manufacturing and hydroxyapatite is too costly to be commercially used.

However, the low-grade rock phosphate and pyrophyllite are relatively inexpensive and need to be explored for application in separation of heavy metal ions.

Heavy metal toxicity can damage and reduce mental and central nervous function. Also blood composition, lungs, kidneys, liver and other vital organs can be damaged by lower levels.

2.2.1 Lead

Lead is found in various industrial activities like manufacturing of alloys, electrical goods, chemical catalysis, metal surface finishing and batteries. Similarly zinc is used in the process of galvanization, pigment formation, stabilizers, thermoplastics, alloys and batteries.

Lead pollution has been recognized as a potential threat to air, water and soil. Exposure to excessive levels of lead in the environment at home, and at work place imposes costs, with many millions of adult and children suffering adverse health effects and impaired intellectual development.

Lead is a more toxic element for human and animal lives. The presence of even low levels of lead in water is a concern primarily because it tends to bioaccumulation in the food chain.[5]

2.3 Methods of Metal Removal

A number of treatment methods have been utilized in removing heavy metal from wastewater. In practice, the choice of one type of treatment versus another depend on several factor, including the form and concentration of metal in the wastewater, other constituents present, the extent of removal desired, environmental regulations pertaining to the discharge of the treated wastewater.

Associated capital and operating cost and the amount sludge or residues generated and there disposal cost is another important factor in the treatment type selection. These days, the most commonly applied method is: precipitation, ion exchange, solvent extraction, evaporation, electrodialysis, ion flotation and reverse osmosis.

Among this method evaporation, reverse osmosis and electrodialysis exhibit no selectivity whereas precipitation, solvent extraction, membrane and ion exchange are selective for specific ions of interest. All these procedures present significant disadvantages, such as incomplete removal, high-energy requirements, and production of toxic sludge or waste products requiring disposal.[6]

They are also often very expensive. As a result, many alternative methods for heavy metal removal were developed in the last decade. The following paragraphs will briefly describe some of this method.

2.3.1 Ion exchange

Ion exchange is a particular case adsorption, this process including ion exchange resin exchanges its ions for these in solution. The process continues until the solution being treated exhausts resin exchange capacity. When this point is reached, the exhausted resin must be regenerated by anther chemical, which replace the ions given up in the ion exchange operation, the converting the resin back to its original composition and yielding concentrated regenerated brine. Ion exchange has several benefits compared to other methods because it is relatively clean and energy efficient method, which also features selectivity for certain ions even in solutions of low concentration of the target ion.

Furthermore, it has high treatment capacity, high removal efficiency, fast kinetic and can also be utilized in metal recovery and water reuse, which are of economical importance. Both organic and inorganic ion exchangers have been synthesized and exploited in heavy metal removal from waste effluents.

During the few last decades inorganic ion exchangers have become increasingly popular because of certain advantages over organic resins such as resistance towards high ionizing radiation, stability at higher temperatures and selectivity to ward certain metal ions.Within the last few years various types of inorganic ion exchangers such as titanate Molybdate, zircouia, phosphate, tangstate.[17]

2.3.2 Ion flotation

Ion flotation may be an alternative method to remove heavy metal ions from waste waters. The process of ion flotation is based on imparting the ionic metal species in waste waters hydrophobic by use of surface active agents (surfactants) and subsequent removal of these hydrophobic species by air bubbles.

A typical surfactant molecule consists of a polar ionic head and non-polar hydrocarbon chain. Attachment of the polar head group to a metal ion exposes the non-polar, hydrophobic section of the surfactant into the solution. When air bubbles are introduced into the flotation cell, the metal ion-surfactant assemblies are collected by the air bubbles due to the favored interactions between the exposed hydrocarbon chains and the air bubbles.

Therefore, this surfactant molecules are also called collectors in the flotation terminology. The air bubbles laden with the metal ions float to the surface and are removed as a froth which is rich in metal content.

The size of the air bubbles in a flotation cell should be fine (in the order of a few hundred micrometers) to present sufficient surface area for collection. The reagents which control the size of the bubbles by reducing the air/water interfacial tension is called frothers. ion flotation is about selectively concentrating the metal ions in the froth phase. However, the degree of this concentration process will be determined not only by the metal content of the froth, but also the amount of water in the froth by definition.[18]

2.3.3 Electrolysis

Electrolysis is a separation technique to separate charged molecules or ions using an electric field. This process uses a pain of electrodes ,cathode and anode ,which are capable of maintaining an electric field in which cations move to the cathodes , and ions move to the anode.

The method is widely used for metal removal from soil, this method used for the removal of cadmium from saturated kaolinite.[9]

2.3.4 Membrane

Membrane filtration is a proven way to remove metal ions but its high cost limits the use in practice [10]

2.3.5 Chemical precipitation

Chemical precipitation involves the addition of reagent which react with the dissolved metals forms insoluble or sparingly soluble compound; the more soluble the compound ,the less the metal remains in the solution

Settling , filtration or centrifugation can remove the precipitation metals in the form of the suspended solid particles.

To enhance the settling charagteristic and agglomeration of the suspended solids , coagulation agents such as alum (Al2(So4)3.14H2O), ferrous sulfate (FeSO4.7H2O),ferric chloride (FeCl3) or polymers are often added .[11]

2.3.6 Adsorption

In the following pages there is brief description for the previous work of adsorption using different types of adsorbent

2.4 Adsorption

2.4.1 Definition

Adsorption is a process in which molecules from liquid (or gas) phase land. On, interact with and attach to solid surfaces, or it's the phenomena in which mmolecules disappear from the liquid or gas phase either enter the inside of the Solid, or remain on the outside, attached to its surface.The reverse process of adsorption, i.e. the process in which adsorbed molecules escape from solid Surfaces, is called Desorption.

The solid that takes up the liquid (or gas) is called the adsorbent or sorbent, it Provides surface for adsorption high surface area with proper pore structure and Size distribution is essential good mechanical strength and thermal stability is Necessary.

The liquid (or gas) attached to the surface of the solid is called the

Adsorbate (also called substrate).

It is not always easy to tell whether the adsorbate is inside the adsorbent, or attached to its outside. Most adsorbents are highly porous bodies with tremendously large internal surfaces.

The external surface,even that visible under the best microscope, constitutes only a small fraction of the large total surface.

However, as long as the adsorbate does not penetrate into the field of force that exists between the atoms, ions, or molecules inside the solid (adsorbent), it is considered to be on the outside, even if it is adsorbed on the internal surface of the adsorbent. If the adsorbate enters the inside of a solid (adsorbent) two things may happen: either the adsorbate merely dissolves in it, forming a solid solution, or it reacts with the solid (adsorbent) and forms a compound.[12]

If the adsorbate remains attached to the surface of the adsorbent,

again two things may happen: there is either a weak interaction between solid (adsorbent) and adsorbate, similar to condensation, or a strong interaction, similar to chemical reactions.

The former is called physical adsorption, the latter chemical adsorption or chemisorption. The van der Waals forces are active in physical adsorption. The name activated adsorption implies that this type of adsorption requires activation energies, just as chemical reactions do. Other names that are occasionally used for physical adsorption is low temperature adsorption, secondary adsorption and capillary condensation. synonyms for chemisorption are high temperature adsorption and primary adsorption.

2.4.2 Comparison between Physical Adsorption and Chemical Adsorption

The differences between physical adsorption and chemisorption maybe briefly summarized in six points.

1) the most fundamental difference between the two adsorptions lies in the

forces involved; the forces between adsorbent and adsorbate in van der Waals adsorption are similar to those active in condensation phenomena, and the forces in chemisorption are similar to those active in chemical reactions.

2) The different forces of interaction between surface and adsorbate manifest themselves in a difference in the strength of binding between adsorbent and adsorbate. The heat of adsorption in van der Waals adsorption's of the same order of magnitude as the heats of condensation of gases (-40 kJ/mol), in chemisorption as the heats of chemical reactions (-400 kJ/mol).

3) A second manifestation of the difference between the forces of interactions found in the specificity of chemisorption and the non specificity of van der Waals adsorption. At sufficiently low temperatures van der Waals adsorption takes place between/any surface and any adsorbate, but chemisorption depends on chemical affinity between the particular adsorbent and adsorbate.

4) In van der Waals adsorption the rate of adsorption is rapid; the adsorbate molecules are adsorbed as rapidly as they can reach the surface. In chemisorption energy of activation must be supplied to the system before the adsorbent-adsorbate complex can form.

5) The adsorption isotherm in chemisorption always indicates monomolecular adsorption; in van der Waals adsorption it is either monomolecular or multimolecular.

6) The adsorption isobar of gases that can be adsorbed in two different forms on the same adsorbent shows two regions in which the adsorption decreases with temperature, one corresponding to physical, the other to chemical adsorption.

Some isobars show three descending regions, indicating two different activated adsorptions, besides the physical adsorption.

From the foregoing it is clear that the two adsorptions are very different from each other; as different as ordinary condensation and chemical reaction.

Essentially, van der Waals adsorption may be called surface condensation. Since the forces involved are different, the fundamental laws that deal with the mechanisms of the two adsorptions are different. On the other hand, there are laws that deal with equilibrium states only, without involving the specification of any sort of mechanism. These are valid for both adsorptions.[13]

Table (2.2) show briefly the different between the two sorption type

Physisorption Chemisorption

Force van de Waal chemical bond

Number of adsorbed layers multi only one layer

Adsorption heat low (10-40 kJ/mol) high (> 40 kJ/mol)

Selectivity low high

Temperature to occur low high

Table (2.2): Comparison between the two sorption type: physical and chemical sorption.

2.4.3 Adsorbent Characterization

The most important characteristic of an adsorbent is its high porosity. Thus physical characterization is generally more important than chemical characterization. The microporous structure of adsorbent can be characterized by standardized techniques. The most important physical characteristics include pore volume, pore size distribution, and specific surface area.

Also of practical importance are bulk density, crush strength, and attrition resistance. Adsorption properties of an adsorbent include equilibrium capacity or kinetic capacity, diffusivity and separation factor. [15]


3.1 Previous Experimental Work on adsorption

Adsorption of heavy metal ions occurs as a result of physicochemical interaction, mainly ion exchange or complex formation between metal Ions and the functional groups present on the cell surface. Various functional groups are involved such as phosphate, carboxyl, amine and amide.

3.1.1 Carbonaceous adsorbent

Activated carbon-produced by carbonizing organic materials is the most widely used adsorbent .but because of the high capital and regeneration costs of it and of ion exchange resins, many researchers Over the last few years were encouraged to look for a low cost adsorbents for heavy metal ion removal.

Waste biomass, industrial waste, and mineral waste have been investigated as sources of activated carbon. (2)

3.1.1. A Tea waste as a low cost adsorbent

Waste tea leaves carbon was found to be a good adsorbent for Cu and Pb in wastewater over a range of initial metal ion concentration (25-200 mg/l)

The maximum removal is at solution pH range (5-6) and Adsorption conformed to Langmuir and Freundlich isotherms.. Pb and Cu uptake was fast with 90% or more of the adsorption occurring within first 15-20 min of contact time. (3)

3.1.1. B Metal sludge waste as a low cost adsorbent

The electroplating waste metal sludge has been converted into a cheap carbonaceous adsorbent material; its adsorption efficiency was examined for vanadium removal from water. The adsorption capacity was found 24.8mg/g at 25â-¦C and The equilibrium adsorption was achieved within 7h.

The adsorption has been found to be endothermic and data conform to Langmuir model.(4)

3.1.1. C Different adsorbents (waste fruit residues ,rice husk ash, sugar beet pulp and grape stalk waste )

3.1.1. D Sulfuric acid-treated wheat bran (STWB)

Activated carbons prepared from (STWB) have been used for the adsorption of Pb ions from aqueous solution, (STWB) exhibits a good adsorption potential for lead with a peak value at pH=6.0. And the adsorption percentage for an initial Pb ions concentration of 100 mg/L was found to be 82.8 at 25â-¦C with 2h contact time. [5]

3.1.2 Adsorption on clinoptilolite ((Na,K,Ca)4Al6Si30O72·24H2O)

Clinoptilolite which is the most common natural zeolite and belongs

to the heulandite family has been used for the adsorption of Ni, Cu, Pb, and Cd ions. Quartz, calcite, biotite, muscovite, chlorite, and montmorillonite are the main associated minerals.

The adsorption capacity was found 4.22 mg/g for Cd ions an initial concentration of 80 mg/L and 27.7, 25.76, and 13.03 mg/g at 800 mg/L for Pb,Cu, and Ni ions and data conform to the Langmuir and the Freundlich models.[6]

Kaolinite clay as adsorbent (Al2Si2O5(OH)4)

Kaolinite clay with Specific surface area=19.43 (m2/g) was found to be a good adsorbent for lead and Zinc ions from waste water. The adsorption capacity was found as 31.75 mg/g at pH 5 and 20 â-¦C with 3 h contact time.

The equilibrium time was found to be 3 h.

If the adsorbent doses increase, the percent removal of lead and zinc increase too. [7]

3.1.4 Bentonite, Blast furnace slag and Fly ash

Bentonite was obtained from Merck and contained over 80% montmorillonite.

Blast furnace slag and fly ash were collected from the dumping .The equilibrium time was found 3 h and pH value did not effect Pb and zinc removal significantly. Adsorbent doses were varied from 5 g/L to 20 g/L for both lead and zinc solutions.[ 8]

Low grade phosphate

Adsorption capacity of rock phosphate was found to be 200 mg Pb2+/g of adsorbent for initial Pb2+ concentration of 50 mg/L at 25 °C, while the adsorbent dosage was maintained at 0.25 g/L in pH 5 and contact Time 120 min.(9)

3.2 Equilibrium Isotherms

The molecules of ion distribute themselves between the solution and the adsorbed phase when it is admitted to a thoroughly evacuated adsorbent. The molecules phase dispeares when there is great rapidity in some case and at a measurable rate and it reaches a state of stable equilibrium after the process stops for a while. Due to the function of the temperature, the pressure, the nature of the adsorbent and the adsorbate ,the amount of ions adsorbed per gram of adsorbent at equilibrium.

The most commonly used system for adsorption on a solid surface is adsorption isotherm system when the amount of adsorption is a function of pressure and the temperature is constant at set temperature.(10)

3.2.1 Isotherms Equilibrium Model

Many theories and models have been developed to interpret equilibrium isotherms which can be used to measure the amounts adsorbed on a limited number of experiments.(11) Freundlich Isotherm

This model is assuming logarithmic change of adsorption enthalpy with surface coverage from ads-des equilibrium, so if the concentration of the solute in the solution at equilibrium is Ce is raised to the power 1/n,

The amount of solute adsorbed qe, then Ce1/n/qe will be constant at a given temperature. Freundlich isotherm is represented as the follows:


Where; Kf and n are Freundlich constant that are related to the adsorption capacity and intensity, respectively.

To obtain the values of Freundlich constant:

In(qe)=ln(Kf)+1/n ln(Ce)

The intercept and the slope of the linear plot of In(qe) vs. ln(Ce) at given experimental condition provided the value of the Kf and 1/n, respectively.[12] Langmuir Isotherm

When the rate of desorption is equal to adsorption, the Langmuir model is originally a kinetic one and assuming the adsorption system is a dynamic equilibrium.

This model was based upon the following assumption:

The surface is uniform (the adsorption sites are all energetically equivalent, ∆Hads doesn't vary with coverage,).

Monolayer adsorption.

No interaction between absorbed molecules and adsorbed molecules immobile.

Following is the Langmuir isotherm:

Langmuir isotherm is represented as the follows:

qe= QobCe/(1+bCe)

Where: Ce is the equilibrium liquid-phase concentration (mg/l),

qe is the equilibrium Amount adsorbed (mg/g),

Qo is the maximum amount of sorbate per unit weight of sorbent (adsorption capacity) to form a complete mono-layer.

And b is a constant related to the affinity between sorbent and sorbate.

The equilibrium adsorption up take, qe, can be calculated by the mass balance at the adsorption process:

qe= (Co-Ce)V/w

Where Co is the initial concentration (mg/l)

Ce is the equilibrium sorbate concentration (mg/l)

V is the volume of the solution (l)

w is the mass of the adsorbent (g).(13)


Materials and Methods

4.1 Adsorbent

4.1.1 about Low Grade Phosphate

Low grade phosphate which is used in this research was found in" Jordanian phosphate company" which operates through three mines ( Hasa, White, Hedip and industrial complex) It was considered the pillars of the Jordanian economy in the recent past.

In this research, removal of Pb2+ from aqueous solution (waste water) by adsorption on rock low-grade phosphate has been occurred in batch experiments.

The laden adsorption capability of the rock phosphate depended on pH, adsorbent dosage, contact time, initial Pb2+ concentration and temperature. [20]

Constituents (% wt/wt)

SiO2 1.73

P2O5 5.53

CaO 5 1.26

MgO 1.35

Fe2O3 0.96

Al2O3 1.07

F2 0.33

Loss on ignition

Table (3.1): Chemical composition of rock phosphate.

4.1.2 Preparation of Low Grade Phosphate

Rock phosphate (low-grade) used as adsorbent after the sample was crushed, screened. The sample was ground to a very fine powder form in an agate mortar for a minimum of 10min.

After drying at 105 °C for 24 h, dilution and homogenization of 1.5 mg of rock phosphate and 300 mg KBr were carried out with additional grinding For removal of Pb2+ ions from aqueous solution the particle size was used 150-180 μm .

Purity of the samples before and after adsorption was tested by IR spectral analysis. An IR transmittance spectrum of the ground sample was obtained in the 400-4000 cm−1 range with a Perkin Elmer spectrum one FTIR spectrometer. [21]

4.2 Batch adsorption Experiment

4.2.1 Kinetic Experiment

Batch adsorption techinique was used for investigating the effect of adsorbent mass, pH of solution, initial Pb(II) concentration and temperature . Results 3.0 for Viscum album L of the optimum pH for Pb(II) adsorption were analyzed by the Langmuir, Freundilich, Temkin and Harkins-Jura,equation using linearized correlation coefficient at different temperature.

The characteristic parameters for each isotherm have been determined. The experimental data was proved very well than the other models by the Langmuir model. According to Langmuir isoterm, the monolayer saturation capacity (Qo) is 769.23 mg/g at 25 °C. Models and the isotherm constant were evaluated depending on temperature. .

Thermodynamic parameters such as ΔHo, ΔSo and ΔGo were calculated. By using the first and second-order kinetic models,the experimental data were analyzed and found that the adorption process is endothermic and spontaneous.The rate constants of adsorption for both kinetics models have been well calculated as the second-order model provides the best correlation of the data.[24]

4.2.2 Isotherm equilibrium Experiment

Equilibrium experiments were performed by using metal solutions at different initial concentration. The experiments were carried out by transferring 50ml of a metal solution into bottles.Certain amount of adsorbent was added to the above solution to make the final concentration 10mg/ml,and the system was agitated by the shaker for one hour to ensure the attainment of equilibrium.

The adsorbent was separated from the samples by filtration using filter paper, the filtration produced solution was analyzed for the metal under consideration using atomic absorption spectrophotometer.[23]

4.2.3 Effect of PH

Effect of initial solution pH on adsorption was determined by mixing 1 g of adsorbent with 100 ml of solution containing metal concentration of 100 mg/l at various pH values ranging from 2 to 7.

Solution pH was adjusted with 0.5 M, HCl and NaOH solutions. The mixture was shaken for 1 hr and the solution was filtered and analyzed.[23]

4.2.4 Effect of adsorbent dosage

The effect of the adsorbent dosage on the removal of lead ions for

various contact times was studied by varying the adsorbent dosage in

the range of 0.15-0.5 g/L with 200 rpm stirring speed and at pH 5 in

100 mL Pb2+ solutions with a concentration of 50 mg/L.

The percentage adsorption of Pb2+ increases with increasing rock phosphate dosage.

This increase can be attributed to the increase in the number of adsorption sites. For all subsequent experiments, a 0.25 g/L adsorbent dosage was chosen.

Maximum adsorption capacity of rock phosphate was found to be 200 mg Pb2+/g adsorbent.[23]