Biosorption of Heavy Metals by Orange Peel

By ABBAS PARVEZ KAZI APARNA VASHIST

WHAT ACTUALLY BIOSORPTION IS?Biosorption can be defined as the ability of

biological materials to accumulate heavy metals (bioaccumulation) from waste water through different types of biosorbents like fungi, yeast, bacteria and orange peel .

It can also defined as “a non directed” physio-chemical interaction between biosorbents and heavy metals ion.

BIOSORPTION AS AN ADVANCE SEPRATION TECHNIQUE

In present situation, heavy metals’ pollution has become one of the most serious environmental problems.

There are many process like electrochemical treatment, oxidation/reduction, ion exchange and membrane technology but they are ineffective and even expensive.

Whereas biosoption is a process which is effective and even easy to perform.

SELECTION OF ORANGE PEEL AS BIOSORBENT

Orange is abundantly used in soft drink industries & its peel is usually treated as wastes.

It is mostly composed of cellulose, hemi-cellulose, chlorophyll pigments and other pigments which contain many hydroxyl functional groups (-OH) thus making it a potential matrix to adsorb heavy metals.

Conventional adsorbents like activated carbon are economically non-viable & inefficient.

PREPRATION OF ORANGE PEEL BIOSORBENT.

The collected orange peels were dried in the sun for 4-5 days crushed using a crushing mill powdered materials were sieved using a 425 mµ sieve twice washed with 0.01 M HCl (10 g/1 litre) then with an extensive volume of distilled water, in order to remove soil or debris finally with distilled water again then oven-dried at 90 ◦C for one day.

OTHER SOLUTIONS USED

Before beginning the experiment, other solutions that are prepared include:

1. Sodium Thiosulphate (Burette solution; 0.001 M)

2. Potassium Dichromate (0.01 M)3. Starch solution (indicator)4. Potassium iodide (10% w/v)5. Acetic Acid6. Various Adsorbate solutions

EXPERIMENTAL PROCEDURE

I. STANDARDIZATIONII. ESTIMATION

I. STANDARDIZATIONIncludes standardization of

Sodium Thiosulphate.Conical flask 50 mL H2O

+ 10 mL of 10% KI along with 1-2 g Na2CO3 + 5 mL conc. HCl + 10 mL K2Cr2O7.

Flask dark at least 5 mins 150 mL H2O for dilution + 1 mL starch solution as indicator.

This solution of the conical flask is titrated against Na2S2O3. The titration is carried out three times.

The reaction that takes place during standardization is as follows:

2M2+ + 4KI → 2MI↓ + I2 + 4K+

II. ESTIMATIONConical flask 20 mL of M2+ solution 2-3

drops of conc. HCl + pinch of Na2CO3 10 mL CH3COOH & 10 mL of 10% KI 5 mins in dark 150 mL H2O for dilution & 1 mL starch solution.

The solution of the flask titrated against Na2S2O3.

The end point of the titration is observed to be light green from blue (in case of Cu2+).

The reaction that takes place during standardization is as follows:

I2 + 2Na2S2O3 → Na2S4O6 + 2NaI

Various parameters affecting the biosorption

Effect of ph

Effect of contact time

Effect of initial concentration

Effect of adsorbent dosage

Effect of ionic strength

•The metal ion adsorption is affected by the pH of the solution.

•Fig shows adsorption% of M2+ as the function of equilibrium pH.

•It can be seen that adsorption efficiencies of M2+ ions increases with the increase in pH.

•Almost all metal ions are absorbed to the extent of 80-100% at weakly acidic conditions.

•Order: Pb2+＞ Cu2+＞ Cd2+＞ Zn2+＞Ni2+

EFFECT OF pH

Effect of contact timeContact time is a fundamental parameter in

adsorption.

It is important to study its effect on the capacity of retention of copper, zinc, lead, cadmium and nickel by orange peel.

It can be seen that the adsorption process proceeds rapidly and the adsorption equilibrium can be attained within 20 minutes.

Effect of Initial ConcentrationThe trend of removal of the heavy metals is

irrespective of the adsorbent used.

It does not even depend upon the initial concentration of metal ions in the solution.

High percentage of removal was observed for lower concentration of heavy metals for the orange peel. The uptake of metal per unit weight of adsorbent was same.

Effect of adsorbents dosage

To study the influence of the liquid to solid ratio on the retention of the metal ions, 3 diff values taken by varying the adsorbent amount of the support while keeping the volume of the metal solution constant.

Adsorption increases with the increase in the amount of the adsorbents. This can be explained by a greater availability of the exchangeable sites or surface area at higher amount of the adsorbent.

The adsorption percentage increases from the doses of 0.25 g/100ml to1 g/100ml rapidly. But no significant adsorption was found beyond 1g/100ml.

 

Adsorption Equilibrium Isotherm

Langmuir isotherms model: in which the amount metal uptake by biomass reaches equilibrium model.

Langmuir Isotherms ModelThe influence of M2+

concentrations on adsorption was obs.

It appears that initially adsorption capacities increase with increase of ion concentration in equilibrium metal & then tend to approach constant values.

It suggests these metal ions are absorbed onto the orange peel according to the Langmuir adsorption.

Figure shows the rearranged experimental

data according to Langmuir adsorption model equation.

The values of the adsorption capacity qm, & Langmuir constant b were

obtained from linear regression and the results are presented in the table.

Metal qm/(mg·g−1) b/(L·mg−1) R2Cu2+ 77.60 0.1491 0.9999

Cd2+ 76.57 0.0586 0.9642

Pb2+ 218.34 0.0564 0.9595

Zn2+ 49.85 0.1379 0.9912

Ni2+ 15.45 0.1003 0.9982

It can be seen that the R2 values of all metal ions were close to 1, revealing the extremely good applicability of the Langmuir model to

these adsorption processes.

CONCLUSIONThus orange peel is an excellent adsorbent for the

removal of heavy metals from their aqueous solutions.

The small variation in the adsorption capacity of the adsorbent is due to the variation in affinity of the adsorbent for different metal ions.

We also saw the effect of various experimental parameters on adsorption capacity of the adsorbent. These investigations are quite useful in developing a wastewater treatment plant. The process is economically feasible and easy to carry out.

THANK YOU!

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