Extraction & Analysis Of Heavy Metals From Waste Water Using Response Surface Methodology

Hashim Khan (DDP-SP13-BEC-

53)

Hassan Sarfraz (DDP-SP13-BEC-

27)

Junaid(SDP-SP11-BEC-

XX)

Shahzaib Younis

(DDP-SP13-BEC-85)

Zohaib Uzair (DDP-SP13-BEC-

101)

Introduction To Heavy Metals

• Any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations.

• Heavy metals are a natural part of Earth’s crust.• Transition metals on the periodic table. They often occur

in ox anions.

• Sources• Natural Sources

– Weathering and downgradient transport by weathering– Wind erosion – Glacial erosion– Volcanism and uplift

• Industrial/Agricultural– Mining – Smelting– Automobile exhaust – Paints – Waste disposal – Pesticide and herbicide application

Cr

Al

Hg Pb

Cd

As

Ni

Why Study Heavy Metals

• They are both beneficial and detrimental.

• They degrade over extremely long periods of times and as such are destruction prone.

• Heavy metals are consumed by us daily but are fatal to our health if taken in higher than prescribed concentrations.

• Even in allowable amounts their disadvantages overshadow their advantages.

• Hence to ensure the vitality of human it is necessary they be studied so that ways to reduce their presence can be found and implemented.

• Metal processing industries consume a lot of heavy metals by the virtue of their product.

• Some of this is also drained into the public sewage. • With conc. Sometimes as high as 100 g/L. this can be

problematic.

• We have used design expert pro. 9 which is a software, licensed by the dept. to our advantage.

• Response surface methodology (RSM) is a collection of mathematical and statistical techniques for empirical model building.

Response surface models are multivariate polynomial models. They typically arise in the design of experiments (see Design of Experiments), where they are used to determine a set of design variables that optimize a response. Linear terms alone produce models with response surfaces that are hyperplanes. The addition of interaction terms allows for warping of the hyperplane. Squared terms produce the simplest models in which the response surface has a maximum or minimum, and so an optimal response.

Response surface methodology (RSM) is the process of adjusting predictor variables to move the response in a desired direction and, iteratively, to an optimum. The method generally involves a combination of both computation and visualization. The use of quadratic response surface models makes the method much simpler than standard nonlinear techniques for determining optimal designs.

• Manganese and Arsenic for example are not fully removable from the water but they can be removed till the extent that water becomes drinkable.

• You don’t have to totally eradicate the concentration of metals from the water… if you are able to bring it down to the maximum contaminant limit you can still use that water for some tasks e.g. showering…

• For example water that is 50 microgram of arsenic… you can bathe in that water… (albeit not for prolonged periods of time)…

• One of the most promising areas for recycling nonferrous metals undoubtedly lies with the metal finishing and electronics industries.

• The volume of metal containing waste water from these industries, without providing new ore sources, can yield metal concentrations high enough to favor recovery or removal.

• Following techniques have been applied to the separation and recovery of metals from aqueous solutions.– adsorption– cementation – electrolysis– ion exchange – membrane separation – precipitation– solvent extraction

In Milligrams

For 1 liter

Need For Analysis

• Because of the above mentioned risks it is necessary that techniques be developed or utilized for the analysis of these species in water and not only drinking water but also waste water.

• We know that each element can absorb a radiation of a certain wavelength and because of that the electrons in that material get excited and release radiation of a certain wavelength.

• By Inhibition Of Enzymes.

• Result is that they stop or alter metabolic processes.

• Because of their affinity for –SH groups which are a part of proteins.

• These metals are extremely dangerous for human life and are known to cause bone deformation amongst other serious problems.

Atomic Absorption Spectroscopy

• Basics• When you put a metal in a Bunsen flame it emits a certain kind of colored light.

When you pass this light through a spectroscope several lines may be seen each of which has a characteristic color, e.g. calcium given green.

• A definite wavelength can be assigned to each radiation, corresponding with its fixed position in the spectrum.

• Kinds of spectra...

• Quantum theory predicts that in each atom or ion possesses definite energy states in which the various electrons can exist; in the normal or ground state the electrons has the lowest energy. Upon application of energy one or more electrons may be removed to a higher energy state further from the nucleus.

Continuous Band Line

• These excited electrons tend to return to the ground state and hence emit the extra energy as a photon of radiation. Since there are definite energy states and since only a certain changes are possible according to the quantum theory, there are a limited number of wavelengths possible in the emission spectrum. Greater the energy of the exciting source, the higher the energy of the excited electrons, and thus more numerous lines may appear.

• Lines in a unknown spectrum may be identified by comparing them with those on a spectrum containing a number of lines of known wavelengths.

• Flame Emission Spectroscopy• If a solution containing a metal salt is aspirated into a flame, a vapor which

contains atoms of the metal may be formed. This raises some atoms to an energy level that is sufficiently high to permit the emission of radiation characteristics of the metal e.g. characteristic yellow color imparted to flames by compounds of sodium. This is the basis of flame emission spectroscopy.

• Atomic Absorption Spectroscopy• However a much larger number of gaseous metal atoms will normally

remain in an unexcited state (Ground state). These ground state atoms are capable of absorbing radiant energy of their own specific resonance wavelength which in general is the wavelength of the radiation of the radiation that the atoms would emit if exited from the ground state. Hence if the light of the resonance wavelength is passed through a flame containing the atoms in question then part of the light will be absorbed and the extent of the absorption will be proportional to the number of the ground state atoms present in the flame. This is the underlying principle of atomic absorption spectroscopy.

• Elements Detectable By AAS• Elements highlighted in pink are detectable by the AAS equipment.

GroundState

This process absorbs radiation (energy) This process

releases radiation

∆E=Et-Eo=h* =h*c/ʋ ʎ=frequencyʋ

h=Planck’s constantc=velocity of light

=wavelength of radiation absorbedʎ

In atomic absorption spectroscopy absorbance A is given by the logarithmic ratio of the intensity of incident light

signal Io to that of the transmitted light It.

1. No is the concentration of the atoms in the flame

2. L is the path length 3. K is a constant related to the

absorption co-efficient

A photometer is a device for measuring the intensity of

transmitted radiation at selected wavelengths of the

spectral range.

An optical spectrometer possesses an optical system which can produce dispersion of incident electromagnetic radiation and with which measurements can be made of quantity of

transmitted radiation at selected wavelengths of a specific range.

Flame Emission

AAS

• Operating The AAS • Turn the AAS ON. It performs some head adjustment.• There is a water tank under the burner head which is used to keep the burner

cool. • AAS is connected to a computer (PC). On the desktop there is an icon named

“spectrAA”.? We use this to access the AAS from the computer. • We start a new worksheet by providing the name of the file to the software.

Then we give the name of the element we want to detect.• Then we attach a reference known sample to the capillary that sucks the

sample into the burner. Then a window appears on the screen with the message “Present the solution”. Now we can attach the actual solution to the instrument.

• For every new sample we run the reference first.• The computer starts plotting in between the wavelength(x-axis) and

intensity(y-axis).

• Operating The AAS • You can observe at some points along the plot there are peaks. These peaks

indicate higher intensity at a specific wavelength. We note the wavelength of the peak and then match it from a paper which tells us the element who has this wavelength.

• in emission mode that can be used within the same equipment you cannot use a bulb and it is for the most part used for qualitative analysis.

• We can specify the flame type in our equipment. For most of our samples we use (acetylene + oxygen) mixture while for some metals we use (nitrous oxide + acetylene). For example we use nitrous/acetylene mixture for arsenic.

• So when the sample is sprayed into the flame the flame changes color. The catch here is that the greater the concentration of the sample the greater the color change of the flame there is.

• Operating The AAS • Other than this we set the limits for conc. a few control values such as integrate

repeat.

• Flame• When a solution containing a suitable compound of the metal to be investigated

is aspirated into a flame, the following events occur in rapid succession:– Evaporation of solvent leaving a solid residue.– Vaporization of the solid with dissociation into its constituent atoms, which initially, will be in

the ground state.– Some atoms may be excited by the thermal energy of the flame to higher energy levels, and

attain a condition in which they radiate energy.– The result is a heterogeneous mixture of gases (fuel + oxidant) and suspended aerosol (finely

dispersed sample).

Carries Air Or Nitrous Oxide To

Mix With The Fuel

Acetylene

Liquid Sample Not Flowing Into The

Flame Goes To Waste

Burns A Smooth Laminar Flame

Spectroscopy is the science of studying the interaction between matter and radiated energy while spectrophotometry is the method used to acquire a quantitative measurement of the spectrum.

Spectroscopy does not generate any results. It is the theoretical approach of science. Spectrometry is the practical application where the results are generated

Spectroscopy is the science part i.e. the study of light after its interaction with matter.

Spectrophotometry is the technique by which Spectroscopy is studied.

• Types of Pretreatment1. Dilution

• Dilute the sample with purified water, dilute acid, or organic solvents. Examples: food products (e.g., dairy products), pharmaceuticals, and biological samples (e.g., blood, urine).

2. Dry Decomposition

• Heat the sample to a high temperature (400 to 500C), Decomposition is possible in a short time (a few hours) and operation is simple. Elements with low boiling points (e.g. Hg, As, Se, and Sb) will vaporize

3. Wet Decomposition

• Heat the sample together with acid to a low temperature (approx. 300C). Suitable for volatile elements. A long time is required for the decomposition of organic substances.

• Types of Pretreatment4. Microwave Decomposition

• Decompose the sample at high pressure by heating it together with acid to a temperature in the range 100 to 200 degree C in a sealed Teflon container.

• The decomposition process is sealed; there is little vaporization of elements with low boiling points; the decomposition time is short; there is little contamination from the operating environment and the reagent; and only a small amount of acid is required.

• Examples: Sediment, soil, dust, ceramics, living organisms, food products, etc.

• Resonance Line Source (Lamp)• For both atomic absorption spectroscopy and atomic fluorescence

spectroscopy a resonance line source is required, and the most important of these is the hollow cathode lamp.

• For any given determination the hollow cathode lamp used has an emitting cathode of the same element as that being studied in the flame. The cathode is in the form of a cylinder, and the electrodes are enclosed in a borosilicate or quartz envelope which contains an inert gas (neon or argon) at a pressure of approximately 5 torr.

• The application of a high potential across the electrodes causes a discharge which creates ions of the noble gas. These ions are accelerated to the cathode and, on collision, excite the cathode element to emission.

• Resonance Line Source (Lamp)• Multi-element lamps are available in which the cathodes are made from alloys,

but in these lamps the resonance line intensities of individual elements are somewhat reduced.

• Each element can absorb a radiation of a certain wavelength and because of that the electrons in that material get excited and release radiation of a certain wavelength.

• MONOCHROMATOR• The purpose of the monochromator is to select a given emission line and to

isolate it from other lines, and occasionally, from molecular band emissions. In atomic absorption spectroscopy the function of the monochromator is to isolate the resonance line from all non-absorbed lines emitted by the radiation source. In most commercial instruments diffraction gratings (Section 17.7) are used because the dispersion provided by a grating is more uniform than that given by prisms, and consequently grating instruments can maintain a higher resolution over a longer range of wave lengths.

AAS Advantages and Disadvantages

• Advantages1. High selectivity and sensitivity2. Fast and simple working3. Doesn’t require metals

separation

• Disadvantages1. No simultaneous analysis2. Fragment have to form ready

measure solution3. Limit types of cathode lamps 4. Expensive

• Applications of AAS

Sample Preparation Guide:The following image details how we can prepare a sample solution of known concentration for purposes of analysis. It details the preparation of various concentrations of potassium permanganate samples via mathematical formulae.

Experiment Details

• Take 1000 ml distilled water in a 1000 ml beaker. Pour some 250 milligrams of this distilled water in another 1000 ml beaker. This is so that there can be an ease in the stirring of the constituents.

• In that 250 ml water we pour in 2900 milligrams of nickel chloride. Also put some 350 mg of boric acid in this beaker.

• Put the beaker on a magnetic stirrer. Keep it so till the constituents in the beaker become a single phase and are homogenized.

• Now note the pH at this point, it’d be around the magnitude of 6.5. • Now from the RSM we know that for our metal extraction we need to have a pH of around

2.5 for the first experiment. Therefore to reduce the pH to 2.5 we prepare a 3 Molar solution of sulfuric acid from pure sulfuric acid which has molarity of 18.

• After we’ve made the 3M sulfuric acid solution we now proceed towards our metal solution and pour in droplets of sulfuric acid using a dropper while we measure the pH using a digital pH meter. An important step here is to calibrate the pH meter using a buffer solution.

• After the pH has been calibrated we prepare the sonicator bath. Sonication is the act of applying sound energy to agitate particles in a sample, for various purposes. Ultrasonic frequencies (>20 kHz) are usually used, leading to the process also being known as ultra-sonication or ultra-sonication.

• We pour in 3-4 drops of liquid dishwasher (vim). It will work till you change water. For new water you will obviously have to repeat the process.

• Now turn to the 1 liter beaker that we have, we can use this as our electrochemical cell as well but certain limitations could hinder the process. Put in the carbon electrodes at a certain distance to each other (keep in mind that you must already have measured the electrodes). Measure it and note it down, for all the coming experiments you are to keep this distance similar.

• Put the metal solution in the sonicator. Keep in mind the water level in the sonicator bath should be same for all the experiments.

• Now run the sonicator for 180 minutes. Extract samples using pipette, pour them in vials and label the vials with date, run number, time in sonicator and the metal name. First sample at time 0 will be with the ultrasound off.

Boric Acid Nickel Chloride

Videos\Stirring.mp4

Sulfuric Acid

Videos\pH Maintainance.mp4

Carbon Electrodes

Videos\Electrolysis.mp4

Safety

Videos\Sulfuric Acid Dilution.mp4

• NiCl2 Properties