1. Introduction

2. Material and Method

2.1. Materials

Large pieces of kaolin clay obtained from Nagar parker region of Thar parker district of Sindh province in Pakistan. These pieces are sent to crusher and converted into powder form. Take 50gm clay powder and mixed in 500 ml deionized water. The mixture is stirred for 2 hr at 25 ⁰C. Obtained mixture product is placed for sedimentation for 2 hr and then filter the product. The obtained kaolin gel like material is dried at 100 ⁰C for 2 hr in drying oven. The obtained material is finally grinded and passed through 200 mesh size screens to obtained fine powder. This clay powder is stored in airtight bags to use further [9].

The elemental properties of kaolin are tested before and After washing kaolin. PW 2400 x-ray spectrophotometer is used to analyze the samples.

Table 4. composition of kaolin clay.

Table 4. composition of kaolin clay.

Oxides	Raw Kaolin (wt%)	Washed Kaolin (wt%)
SiO2	47.691	44.958
Al2O3	26.529	34.559
Na2O	1.302	1.241
TiO2	0.502	0.610
Fe2O3	1.052	1.057
MgO	0.596	0.573
CaO	5.833	2.356
K2O	0.591	0.590
Cl2	0.752	0
LOI	15.152	14.056

LOI (Loss on ignition) at 1000 °C.

Sigma Aldrich laboratory grade lead Nitrate (99%) is used. Take 1.6gm lead nitrate salt and mixed in deionized water to prepared stock solution. In the whole process deionized water is used because tap or other source of water contain other metal ions in it and compete with lead in adsorption process so the correct percentage of lead removal would not be determined [10].

Results and Discussions

4.2.1. Effect of Concentration 

Concentration effect is checked by preparing different concentration solutions. Adding 1g kaolin in 250 ml of different concentration solution of lead nitrate. The prepared samples are mixed using magnetic stirrer  for 2 hr at 5.5 pH of solution and room temperature to obtained equilibrium in solution.

Figure 14. Effect of kaolin on different concentration of Lead solution.

Figure 14. Effect of kaolin on different concentration of Lead solution.

The equilibrium time reported in the literature for the adsorption of kaolin is 60 min. There is only 10% increase in lead removal by varying the time from 40min to 160 min [45].

Figure 15. Effect of concentration of lead with respect to time with (A) 1g kaolin (B) 2g kaolin.

Figure 15. Effect of concentration of lead with respect to time with (A) 1g kaolin (B) 2g kaolin.

Formula:

$$\mathbf{\%} \mathit{o}\mathit{f} \mathbf{lead} \mathit{a}\mathit{d}\mathit{s}\mathit{o}\mathit{r}\mathit{b}\mathit{e}\mathit{d}\mathbf{=}\frac{\mathit{i}\mathit{n}\mathit{i}\mathit{t}\mathit{i}\mathit{a}\mathit{l}\mathit{}\mathit{c}\mathit{o}\mathit{c}\mathit{e}\mathit{n}\mathit{t}\mathit{r}\mathit{a}\mathit{t}\mathit{i}\mathit{o}\mathit{n}-\mathit{f}\mathit{i}\mathit{n}\mathit{a}\mathit{l}\mathit{}\mathit{c}\mathit{o}\mathit{n}\mathit{c}\mathit{e}\mathit{n}\mathit{t}\mathit{a}\mathit{r}\mathit{t}\mathit{i}\mathit{o}\mathit{n}}{\mathit{i}\mathit{n}\mathit{i}\mathit{t}\mathit{i}\mathit{a}\mathit{l}\mathit{}\mathit{c}\mathit{o}\mathit{n}\mathit{c}\mathit{e}\mathit{n}\mathit{t}\mathit{r}\mathit{a}\mathit{t}\mathit{i}\mathit{o}\mathit{n}}\mathbf{*}\mathbf{100}$$

(2)

Using the above formula calculate the efficiency of different solutions and draw graph and maximum lead is removed from solution using kaolin adsorbent.

It is observed from the chart that by decreasing concentration from 300ppm to 100ppm lead removal is increased from 36% to 82%. Different adsorbents are used to remove lead from water. Researches that used “bone powder, active carbon, plant powder and commercial carbon.” Bone power has removed lead capacity of 100%, active carbon has 90%, plant powder has 80% and commercial carbon has 50%.

4.2.2. Effect of Dosage 

Effect of 1g of kaolin clay is calculated. Now to study the effect of dosage the quantity of kaolin is increased. Take 250 ml solutions of lead with different concentration and add 2g kaolin in it. Same conditions are applied like 1g kaolin dosage experiment and results are calculated.

Figure 16. Effect of kaolin dosage on removal of lead at same concentration.

Figure 16. Effect of kaolin dosage on removal of lead at same concentration.

The removal efficiency of kaolin is improved by increasing dosage of kaolin. The removal efficiency of 100, 200 and 300 ppm solutions for 1g and 2g kaolin dosage are 82 to 89%, 62 to 70% and 36 to 43% respectively.

The purpose of varying the quantity of adsorbent is to be checked how much increase in lead removal form water that is 7%, 8% and 7% for 100, 200 and 300ppm solution.

4.2.3. Effect of pH 

Prepare solutions to check pH effect of solution on adsorption was determined by taking 250 ml lead solution add 1g kaolin in solution containing lead concentration of 100 ppm and adjust pH values ranging from 3.0 to 9 using 0.1M HCl and NaOH solutions. The mixture was shaken for 60 minutes at normal room temperature and then the filtered and examined the solution. The pH is an important controlling parameter in the adsorption process.

Figure 17. Effect of pH with respect to removal efficiency of lead.

Figure 17. Effect of pH with respect to removal efficiency of lead.

Figure shows the effect of pH on amount of metal ion adsorbed; removal efficiency is calculated using formula. Figure also shows that Pb+2 adsorption shows the maximum efficiency at pH of 5.5. It means that the removal of lead ions increases when the solution pH increased from 3.0 to 6.0. “The pH range was chosen as 3 to 6 in order to avoid metal hydroxides, which has been estimated to occur at pH> 6.5 [30].” when pH increases, there is a decrease in positive surface charge.

4.2.4. Effect of time 

The effect of time of Pb(II) ions onto kaolin clay was done by using 100, 200,300ppm concentration of Pb(II) at initial pH 5.5 onto(1.0 and 2.0 g/250 mL) of adsorbent dose.

Figure 18. Effect of time on removal efficiency of lead with 1g adsorbent dosage.

Figure 18. Effect of time on removal efficiency of lead with 1g adsorbent dosage.

Figure 19. Effect of time on removal efficiency of lead with 2g adsorbent dosage.

Figure 19. Effect of time on removal efficiency of lead with 2g adsorbent dosage.

The lead adsorption is maximum at the start because adsorbent places are free and lead ions easily attached with these places. A larger amount of Pb(II) was removed in first 60 mins of time content, and after that Pb(II) remove slowly till equilibrium time (2 h).

4.5. Adsorption Isotherms

The adsorption isotherms are important to study mechanism of the adsorption. Adsorption isotherm have different equations and two isotherms are selected to study, which are Langmuir and Freundlich isotherms.

4.5.1. Langmuir Isotherm

In Langmuir adsorption isotherm adsorption takes place at specific homogeneous sites within the adsorbent and has found successful applications in many adsorption processes of monolayer adsorption. The Langmuir isotherm equation is represented by the following:

Ce/qe = 1/(b.qmax) + (1/qmax) Ce

Where

qmax = Maximum adsorption capacity (mg/g)

b = Langmuir constant (L/mg)

Plot a graph between Ce/qe and Ce for the adsorption of lead(II) ions onto kaolin clay.

1/qmax = slop of the straight line and

1/(qmax b) = intercept of line.

Figure 20. Langmuir adsorption of lead ions onto different adsorbent amount at room temperature.

Figure 20. Langmuir adsorption of lead ions onto different adsorbent amount at room temperature.

Adsorbent Amount	Langmuir Isotherm Constants
Adsorbent /250ml	qmax (mg/g)	b (L/mg)	R2
1-gram adsorbent	27.70	1.71	0.9831
2-gram adsorbent	33.67	0.432	0.9874

4.5.2. Freundlich Isotherm:

The Freundlich isotherm is an empirical equation used to explain heterogeneous systems. The Freundlich isotherm equation is:

lnqe = lnKF + 1/n lnCe

where

KF and n = Freundlich constants

KF and n respectively indicating the adsorption capacity and the adsorption intensity. They were calculated from the intercept and slope of the plot between lnqe and lnCe for the adsorption of lead(II) ions onto kaolin.

Figure 21. Freundlich adsorption onto different amount of adsorbent at room temperature.

Figure 21. Freundlich adsorption onto different amount of adsorbent at room temperature.

Adsorbent Amount	Freundlich Isotherm Constants
Adsorbent/250mL	KF (L/mg)	n	R2
1-gram adsorbent	14.93	7.587	0.589
2-gram adsorbent	16.25	6.472	0.763

Results shows that the value of R² is equals to 1 in Langmuir adsorption which means the process lies in Langmuir isotherm and show physical adsorption and process is mono-layer.

4.6. Adsorption Kinetics

$$\mathit{ln}\left(qe-qt\right)=lnqe-K1t$$

(3)

$$\frac{t}{qt}=\left(\frac{1}{K2}\right)\left(\frac{1}{qe2}\right)+\frac{t}{qe}$$

(4)

Using these equations calculate the values of K1 and K2

Pseudo First Order Constants
Metal Ion	qe (mg/g)	K1	R2
Pb2+	20.575	0.0527	0.979
Pseudo second order constants
Metal ion	qe (mg/g)	K2	R2
Pb2+	20.575	0.0088	0.998

The pseudo first and second order values shows that the system lies in pseudo second order and showing higher adherence rate then pseudo first order.

Figure 22. Adsorption kinetics models of lead.

Figure 22. Adsorption kinetics models of lead.

Conclusions

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