Using of Sukary and Khlass Date Pits as a Bio-adsorbents for Adsorption of Lead and Copper Ions from Waste Water

Introduction

Lead and copper are heavy metals among the most harmful of the elemental pollutants because of their toxicities to humans. Main sources of these metals in wastewater are metal plating and industrial waste¹ (He et al. 2006). At low levels might be essential, but at high levels they become toxic in particular in the drinking water and wastewater. They cause serious health problems to human being such as liver damaging and asthma-like allergy, thyroid, heart failure, and for aquatic life, their toxicity may be harmful to wildlife² (WHO 1996).

Presently, many technologies such as membrane process³ (Rahmanian et al. 2011), chemical precipitation^4,5 (Fu et al. 2011; Mauchauffee et al. 2007), ion exchange processes⁶, and adsorption⁷ are in use to remove heavy metals such as copper and lead from different sources of waters. But most of these techniques for the adsorption of heavy metals are not cost effective. Therefore, low-cost adsorbents are adequately for adsorption process to adsorb heavy metals like copper and lead ions from drinking and wastewater.

Recently, bio-sorbents with low costs attracted many researchers to develop them with high adsorption capacities to remove heavy metals^8,9. Among these techniques, prepared activated carbon from pits of date-palm trees is considered cost effective for removing metal ions as compared to other costly methods such as ion exchange, electro-deposition, membrane filtration, electrochemical treatment, .. etc. Currently, there are lot of naturally occurring materials that may be used without treatment or by converting to activated carbon namely coconut shell is a common example¹⁰. In the Kingdom of Saudi Arabia there are more than twenty-eight million date palm trees, (Phoenix Dactylifera L.), which produce more than half a million tons of dates annually¹¹. The primary waste of date fruit is the date pits.

Few studies have investigated the adsorption of heavy metals and dyes via using activated carbon produced from date pits ^12-18. Attia¹² showed that activated carbon produced from date pits has high surface area when carbonated at 500° C in a limited supply of air followed by activation with oxidizing gases such as steam. Girgis et al.¹³ reported that activated carbon from date pits prepared by chemical activation with phosphoric acid followed by pyrolysis at high temperature (700° C) has good adsorption capacity and best porosity.  

A comparison study of investigation of efficiency of activated palm-tree date pits and non-activated one as bio-adsorbents for zinc and copper ions has been reported using batch adsorber.¹⁴ It was reported that the adsorption of ions was maximum on non-activated one. In another study, activated carbon that produced from date-palm tree pits was used for adsorption zinc.¹⁵ They observed high adsorption capacity at more than 9 milligrams per one gram. Further adsorption of phenolic compounds and methylene blue were investigated on activated carbon produced from pits of date-palm trees in Al-Ain city by Abdulkarim et al.¹⁶. They reported that the adsorption capacity of methylene blue was 590 mg g^-1. Additionally, the activated carbon was suitable for the removal of phenolic compounds from solutions. Similarly, produced activated carbon and natural pits were used for adsorption of cadmium ions¹⁷. It was found that non-activated date pits showed ions sorption capacity greater than the activated one from solution, by two to three times. In Al-ain city, activated carbon has been prepared from palm-tree date pits and was used for adsorption lead ions and methylene blue from aqueous solutions.¹⁸ Other researchers reported that the adsorption capacity was very high into prepared activated carbon from date pits for methylene blue and lead ions, 220 mg g^-1 and 23 mg g^-1 respectively, at pH=5. Adsorption of lead (II), cadmium (II), Iron (III), and Strontium (II) ions via activated carbon produced from pits of date-palm trees was studied in Egypt in aqueous solution¹⁹ . In this investigation, they observed that some anions such as NO₃-, CO₃-2, SO₄-2 in wastewater were affected the removal process of the metals.  Evaluation of the chemical composition was carried on the extraction of oil fatty acids via date-pulp seeds in Tunisia²⁰. The unsaturated fatty acid was linoleic acid which was 32.77% for the pulp and 47.66% for the pits. Types of saturated fatty acids were palmitic acid and the lauric acid, and the maximum adsorption was twenty percent for the pulp and seventeen percent for the pits.Modification of date pits using different types of acid such as tartaric acid, carboxylic acid, salicylic acid, mandelic acid, oxalic acid, and malic acid was done in Jordan for using them in the adsorption of copper, zinc, and cadmium from waste water ²¹. The study showed that adsorption of these metal ions was better via the modified than unmodified date-pits. Furthermore, the modified adsorbents namely SA-PS, CA-PS and MA-PS proved efficient adsorbents in removing these ions. For multi-components adsorbing system, the adsorbates OA-PS and TA-PS are the best adsorbents for removal of heavy metal ions.Date pits obtained from Eastern Province, Saudi Arabia were converted to activated carbon and utilized for the adsorption of methylene blue from wastewater.  It was found that the activated carbon is very suitable for adsorption of methylene blue in a high adsorption capacity.²² In another study, activated carbon obtained from date-pits from Eastern Province, Saudi Arabia was used for the adsorption of three metals ions (e.g. lead, copper, and cadmium) from wastewater.²³ This study showed that the capacity of adsorption was higher, for lead(II), than the copper and cadmium in descending order.

Some researchers used activated carbon prepared from date-pits from Eastern Province, Saudi Arabia and olive stones to adsorb methylene blue and compared it by photoactive catalysts²⁴. It was found that adsorption of methylene blue was more efficient by photocatalytic method. However, the studies regarding the adsorption of heavy metals and dyes by Saudi date pits do not seem to be comprehensive^13-15. Because, the effect of different types of date pits, their physio-chemical characteristics and performance for the removal of days and heavy metals is not investigated thoroughly. Besides, previous studies were mainly to convert date pits into activated carbon regardless of the type of the pits and no attempt was made to test the raw date pits for adsorption of heavy metals pollutants ^13-15. It is well known that date pits have different chemical composition depending on the type of the date pits and its origin^12,13,14. It is a hypothesis of this investigation that the amount of adsorption of metal ions will be affected by the type of the date pits. Since, in Saudi Arabia, date pits are easily and readily available.Therefore, study of non-biodegradable heavy metals adsorption with two famous types of natural Saudi date pits obtained from Sukary and Khlass date fruits as adsorbents may determine whether it is a desirable substitute for commercial activated carbon. Therefore, the aim of this research was to conduct a thorough investigation on two types of famous Saudi date pits namely Sukary and Khlass as adsorbents for the removal of heavy metal ions such as copper and lead from drinking and wastewater.

Materials and Methods

Materials

Two types of date-pits obtained from Sukary and Khlass of date-palm tree fruits were collected from Riyadh city, Saudi Arabia.  Lead and copper solutions were prepared from lead (II) nitrate and copper (II) sulphate supplied by VWR chemicals.

Equilibrium Experiments

Date pits were grinded to a size of 0.125 mm. Then, lead solutions prepared with concentrations from 50 to 1400 ppm. For each 50 mL solutions of lead ions one gram of grinded date pits was added. The bottles were placed in a shaker. For isotherm run, the temperature was maintained at 20^oC. The equilibrium experiments ran for 3 hrs to make sure that the process of adsorption reached astatic equilibrium. Then, the solid residue of grinded pits was removed by filtration using filter papers. The filtrate of each solution, which contains lead ions, was measured using AAS to indicate the concentrations of lead ions. The amount of lead adsorption, q_e, was calculated using the following equation:

Where, (q_e ) is the adsorption’s amount in mg g^-1, (V) is the solution’s volume of in L, (C_o ) is the initial concentration of lead in mg L^-1, (C_e ) is the lead concentration at equilibrium in mg L^-1, and (m)is the mass of grinded date pits in g.  Isotherm curves of equilibrium adsorption were graphed by plotting amount of adsorbates (Lead and Copper ions) after adsorption against the initial ions’ concentration.

Results and Discussion

Equilibrium time

Figures 1 and 2 shows the equilibrium time for the adsorption. After 50 minutes, state of equilibrium was reached.

Figure 1: Equilibrium time for copper adsorption on Sukary and Khlass date pits. Click here to View figure

Figure 2: Equilibrium time for lead adsorption on Sukary and Khlass date pits. Click here to View figure

Initial concentrations Effect

Effect of initial concentrations on adsorption process was experimentally conducted. Figures 3 and 4 show the Equilibrium isotherm for adsorption ions. I noticed that the adsorption capacity of the tow ions increases as initial concentrations of ions increase. Maximum adsorption capacity at room temperature was found to be 17.53 mg. g^-1 and 9.86 g.g^-1 for lead and copper ions, respectively, when using date pits of Sukary as adsorbents. On the other hand, adsorption capacity was reached 14.1 mg.g^-1 of lead and 7.91 mg.g^-1 of copper when using pits from Khlass dates. Presence of carboxylic acid (-COOH) functional groups in the components of date-pits electrostatically attract the cation ions (lead and copper) in the solution.¹⁷

Figure 3: Equilibrium isotherm of lead adsorption on Sukary and Khlass date pits. Click here to View figure

Figure 4: Equilibrium isotherm of  copper adsorption on Sukary and Khlass date pits. Click here to View figure

Analysis of Results from Equilibrium Experiments

Langmuir²⁸ and Freundlich²⁹ models, as equilibrium isotherm models, were used for analysis of equilibrium experimental results.

Langmuir isotherm

To estimate the maximum capacity of adsorption, Langmuir isotherm model, (equation 2) was applied. The model assumes that adsorbates form a monolayer on the adsorbents’ particles.

The linear form of Langmuir model is:

non-linear regression method (equation 3) was used to calculate equilibrium parameters (b and K).

The relationship between Ceand q_eat temperature of 20 ^oC was tested, as shown in Figures 5 and 6. Then, Kand b values (Table 1) were calculated using equation 3. In Figure 5, experimental data fit well with Langmuir model.

Figure 5: Langmuir model for lead ions adsorption on datepits of Sukary and Khlass. Click here to View figure

Figure 6: Langmuir Model of adsorption copper ions on Sukary and Khlass date-pits. Click here to View figure

Table 1: Parameters of Langmuir Equilibrium Model for the adsorption of ions using date-pits.

a.  Lead ions				b.  Copper ions
Type	K  (lit/g)	b (lit/mg)	R2	Type	K  (lit/g)	b (lit/mg)	R2
Sukary	0.2658	0.014725	0.977	Sukary	0.3702	0.036502	0.988
Klass	0.1361	0.00922	0.948	Klass	0.0547	0.0054	0.923

 

Freundlich Isotherm

The Freundlich model, (equation 4), was used to explain results from determination of equilibrium adsorption for heterogeneous surface,  

The linear form of the equation 4 is:

K_F and parameters were calculated from equation (4) with nonlinear regression.  As reported¹⁴, when n values are greater than one, that is mean cation ions favor to be adsorbed into adsorbents surface (i. e., date-pits).

Plotting LogCe verses Logq_e(Figures 7 and 8), we can see that there is relationship between ions concentration (C_e) and the adsorption amount (q_e) at temperature of 20 ^oC.The values of (K_F  and n ) are shown in Table 3, and they were calculated using nonlinear regression equation. Figures 7 and 8 show that the Freundlich isotherm well-correlates the data very well.

Figure 7: Linear form of Freundlich isotherm model for the adsorption of lead ions. Click here to View figure

Figure 8: Linear form Freundlich isotherm model for the adsorption of copper ions. Click here to View figure

Table 2: Equilibrium constants, K_F  and n, of Freundlich Isotherm Model for the adsorption lead and copper Ions.

Date Type	Lead ions			Copper ions
	KF (Lit/g)	n	R2	KF (Lit/g)	n	R2
Sukary	2.926	3.824092	0.932	5.9630	3.388	0.906
Khlass	3.916	2.286	0.891	1.899	3.586	0.951

 

Conclusions

Pits of sukary and khlass dates are by-product of dates fruits in abundance in our local environment. Advantage has been taken from this that they are low-cost adsorbents.Effect of initial concentration of copper and lead ions as adsorbates into adsorbents (two Saudi date-pits namely Sukary and Khlass) was studied. The results of this work showed that the saturation capacity was in increased with the corresponding increase in the initial concentration of adsorbates (copper and lead ions) in solution.

A maximum adsorption capacity was observed when using date-pits of Sukary type at 9.86 mg g^-1 and 17.53 mg g^-1 for copper and lead ions, respectively at room temperature. Whereas, date-pits of Khlass type gave a maximum adsorption capacity at the concentration of 7.91 mg.g^-1 and 14.1 mg.g^-1 for copper and lead ions, respectively at room temperature. Application of Langmuir and Freundlich equilibrium isotherm models described the experimental data very well.

Aknowledgment

The author extend his appreciation to the Deputyship for Research and Innovation, Ministry of Education in Saudi Arabia for funding this research work through the project number IFG-IMAMU-0701.

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