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REMOVAL OF LEAD FROM WASTEWATER BY ADSORPTION ON SAPONIFIED MELON PEEL GEL.

Byline: Hina Chaudhry and Maryam Ijaz

ABSTRACT

A cost effective bioadsorbent was prepared by the saponification of melon peel with calcium hydroxide Ca(OH)2. The adsorption behavior of lead ions for this gel was investigated and results showed excellent property of adsorption. The result showed that pH above 4 is the best for enhanced adsorption".

80.13% removal was achieved at pH 3.92 in 10 min. The maximum absorbance of lead ions was found to be 12.29 mg/L. presence of pectic acid in the melon peel is the main factor for the uptake of ions onto the gel and the chemical modification process in this study is assumed to be effective method for the preparation of other biomaterials. The high adsorption capacity and the adsorption rate indicated that saponified melon peel gel in present study has potential to be used as a cheap and cost effective bioadsorbent for the removal of lead from water.

Key words: Melon peel Pectic acid Adsorption Lead ions Saponification.

1.INTRODUCTION

With the fast industrialization of modern society the event of uncontrollable release of various toxic effluents into the environment occurs frequently causing serious disasters to the mankind. Heavy metals have been used in a variety of

ways for many centuries. For the past three centuries the production of heavy metals such as lead copper and zinc has increased exponentially. Plumbing and insect control (as lead arsenate in apple orchards) are a couple of common examples of lead application. Exposure to heavy metals leads to developmental retardation various cancers kidney

damage and even death in some instances. Exposure to high levels of lead has also been associated with the development of autoimmunity. The primary heavy metals of concern are arsenic lead cadmium chromium and mercury. Various forms of these metals may enter the environment from sources including abandoned dumping sites wastes from

metal plating and metal smelting by-products from refining operations and from manufacturing of computer components. Lead as one of the typical heavy metals even at its very low concentration may bring substantial threat to human health through the food chains [1-3]. The following industrial fields may produce the lead bearing wastes such

as lead acid storage battery [4-5] solders [6] painting [7] pigments [8] pesticides [9] lead smelting slag and mine tailings [10]. Lead can cause severe damage to the kidney liver brain nervous system and reproductive system even at ppm levels [11]. Many treatment methods have been developed to remove the toxic impurities from the drinking

water such as precipitation [12] ion exchange [13] electrochemical treatment [14] membrane separation [15] and adsorption [16]. Adsorption is an attractive technique for water purification and activated carbon is one of the most extensively utilized materials although its adsorption effectiveness and selectivity for heavy metal ions as well as

its cost usually is not so satisfactory [17-18]. Thus there is an urgent need to develop more effective and more efficient low-cost adsorbents for water treatment. Many agro-wastes like orange and apple juicing residue [19] peanut husk [20] garlic peel [21] waste tea [22] deoiled soya [23] and sugar bagasse fly ash [24] have been developed for this purpose. In

the present study the muskmelon peel one of the common kitchen biowastes produced in large amount each year is considered for the adsorbent preparation because it contains pectic acid which has been verified to have good affinity to the heavy metal ions [25]. A satisfactory agro-based adsorbent should have the following advantages: simple synthesis operation effectiveness with high selectivity and large capacity abundantly available biomaterials as the raw materials; another largely ignored requirement is that no or less toxic or poisonous reagents are introduced in the preparation and/or synthesis of these bioadsorbent. For this purpose a cheap eco-friendly and effective modification process is proposed in this study to prepare the bioadsorbent for lead ions removal by using muskmelon peel as the raw materials. Its reutilization as an adsorbent for the removal of heavy metal ions can relieve the problem of disposal of toxic effluents and increase economic gain to such industries.

2.MATERIALS AND METHOD

2.1.Pretreatment of water samples

10-15ml of water sample was transferred into a beaker and stirred for certain period of time with the magnetic stirrer to make the sample uniform. After filtration of the sample 10-

15ml of deionized water and 1M HCL solution upto 5 ml was added and heated on hotplate till dryness with the addition of 5ml 1M HCl which was again heat on hotplate

till dryness. After its dryness 50ml of deionized water was

added along with few drops of 1M HCl and filtered through filter paper to get a clear solution which is ready to run on Atomic Absorption Spectrophotometer AAS.

2.2.Preparation of a bioadsorbent

Melon peel pieces were cut up to 2mm of size and weighed on weighing machine to get 100g wet peel particles. These wet peel particles were than mixed with 10g of Calcium hydroxide Ca(OH)2 with 500ml deionized water in a beaker and stirred at room temperature for 24hrs. After 24hrs of stirring the solution was filtered through filtration assembly and washed to neutral pH up to 7 with distilled water and

filtered again by filtration assembly. The remaining filtrate was dried in convection oven at 60oC for 12hrs. Dried particles than crushed through pestle and dried particles than crushed through pestle and mortar and then with grinder as mashed below 300 micrometer. These dried particles are named as saponified melon peel gel (SMP).

2.3.Adsorption test

Adsorption experiment was conducted by stirring 80mg gel with 50ml pretreated clear solution in a conical flask at a speed of 150rpm with magnetic stirring for 1hr. During whole process 5ml of aliquot was withdrawn from the solution after 10 minutes in a centrifuge tube along with the account of change in its pH with the help of pH meter and centrifuged for 10 minutes in a centrifuge at 4000rpm. Concentration of lead before and after adsorption was checked with the help of Atomic Absorption Spectrophotometer (AAS).

2.4.Adsorption analysis

After the completion of analysis for lead concentration in water samples results were scrutinized and tabulated. The adsorption Q(mg/L) of lead ions before and after adsorption were calculated using: Equation

Where Ci and Ce were the lead concentrations before and after adsorption respectively the weight of dried gel W and the volume of the aqueous solution V.

The %age of removal (R%) defined as the ratio of different lead concentrations before and after adsorption (Ci - Ce) to its initial concentration Ci was calculated as: Equation

3.RESULTS

The study revealed that the concentration of lead in a clear solution before and after treatment with SMP gel showed a drastic difference which shows a percentage removal of above 80% and in this process pH range plays an important role as it is concluded that pH range of 1~4 is best to reach the maximum adsorption capacity (Fig. 3). The calculation of absorbance level for the sample reveals that when absorbance will be high lower will be the concentration of lead ions in a solution (Fig. 4). The %age removal of lead ions is also dependant on its absorbance level like higher will be the absorbance higher would be the %age removal (Fig. 5). The treatment of sample with SMP gel is its contact time which is 60 minutes and to attain equilibrium centrifuge of sample for 10 min at 4000 rpm makes the removal of lead from the solution possible and with the increase of time removal of lead in a solution increases in terms of its absorbance and %age removal (Fig. 67). Comparison of solution in terms of before and after treatment proves the working of melon peel gel in removal of lead ions from water (Fig. 8).

4.DISCUSSION

The result of present study reveals that the adsorption of lead ions on SMP gel is a very fast process. This adsorption behavior means that in the remote places the use of expensive purification processes are scarce and drinking water has been polluted by heavy metal ions such as lead ions than this adsorbent play an important role for the purification of toxic metals from drinking water in a short time. pH values absorbance levels and percentage removal indicates the best ways to check the concentrations of lead ions after treatment with the gel.

The use of alkaline reagent like calcium hydroxide played an important role in the removal of lead ions in such a way that it helps in the removal of chlorophyll pigment and other lower weight molecular components that are useless in the bioadsorbent preparation as it acts as a phase out component for the useless material and boost up the presence of pectic acid in the melon or other bioadsorbent. Due to extensive presence of pectic acid in many biological materials the proposed method would be helpful in preparation of other bioadsorbent as well. It is a cost effective bioadsorbent in a way that adsorbent that cost less than a rupee is required to treat the water and is comparatively cheaper than other treatment processes.

5.CONCLUSION

Melon peel was converted into bioadsorbent for lead ions by a simple process of saponification with calcium hydroxide. The prepared adsorbent was effective to remove lead ions from water. Adsorption of lead ions is a very fast process like 10 min is required to attain equilibrium which is quite effective for the purification process. Pectic acid is the main component and calcium hydroxide plays an important role as well and the proposed process is effective for other bioadsorbent preparation and makes contaminated water useful for different purposes.

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