report on cyanide removal from industrial waste water

Project report on

Cyanide removal from industrial waste water

Prepared by

Utkarsh Sethia

Undergraduate student, SRM University, Kattankulathur

Reg no – 1071310038

Under the guidance of

Prof. (Dr.) Sirshendu De

H.O.D., Chemical engineering, IIT Kharagpur

&

Mrs. Raka Mukherjee

Research Scholar at IIT, Kharagpur

Self Declaration I Utkarsh Sethia a student of SRM University Kattankulathur, Chennai (Reg no – 1071310038) states that I have completed my Internship in IIT Kharagpur from 2/06/2016 to 22/06/2016.

I affirm that this Project report is the record of authentic work carried out by me and no part or whole of this report has been submitted to any where for any purpose.

Signature

Acknowledgment I take this opportunity to thank Department of Chemical engineering, IIT Kharagpur for giving me the opportunity to do internship here. It gives me immense pleasure to acknowledge all those who have given me data, time and energy to supply all the valuable facts and opinions that has helped me in gaining some technical knowledge in waste water treatment technologies during this internship.

I express my profound sense of gratitude to Prof. (Dr.) Sirshendu De (H.O.D., Chemical engineering, IIT Kharagpur) & Mrs. Raka mukherjee (Research scholar at IIT Kharagpur) who have rendered constant guidance, advice and help me when needed to complete this Internship successfully. I also express my gratitude to all the research scholars in Membrane separation lab, IIT Kharagpur who have helped me during this time.

Introduction to cyanide treatment 1) Cyanide treatment is classified as either a destruction-based

process or a recovery-based process. 2) In a destruction process, either chemical or biological reactions

are utilized to convert cyanide into another less toxic compound, usually cyanate.

3) Recovery processes are a recycling approach in which cyanide is removed from the solution or slurry and then re-used.

4) Three classes of cyanide are:

• total cyanide

• weak acid dissociable (WAD) cyanide

• free cyanide

Cyanide destruction processes Most cyanide destruction processes operate on the principle of converting cyanide into a less toxic compound through an oxidation reaction.

Types:-

1) INCO Sulfur Dioxide and Air Process 2) Copper Catalyzed Hydrogen Peroxide Process 3) Caro's Acid Process 4) Alkaline Chlorination Process 5) Iron-Cyanide Precipitation 6) Effluent Polishing with Activated Carbon

INCO Sulfur Dioxide and Air Process Sulfur dioxide (SO2

) and air process was developed by INCO Limited in 1980's and is currently in operation at over thirty mine sites worldwide.

Key points are as follows:-

1) The process utilizes SO2

and air at a slightly alkaline pH in the presence of a soluble copper catalyst to oxidize cyanide to the less toxic compound cyanate (OCN‾).

2) Theoretical usage of SO2 in the process is 2.46 grams of SO2 per gram of CN‾ oxidized, but in practice the actual usage ranges from about 3.5 to 5.0 grams SO2 per gram of CN‾ oxidized.

3) Reaction is typically carried out at a pH of about 9.0 in one or more agitated tanks, and lime is added to neutralize the acid (H+

4) Copper (Cu

) formed in the reaction to maintain the pH in this range. Lime usage is generally on the order of about 3.0 to 5.0 grams per gram of CN‾ oxidized.

+2) is required as a catalyst, which is usually added as a solution of copper sulfate (CuSO4-5H2

0) to provide a copper concentration in the range of about 10 to 50 mg/L, depending upon the corresponding cyanide concentration.

5) Upon completion of the cyanide oxidation reaction, metals previously complexed with cyanide, such as copper, nickel and zinc, are precipitated as metal-hydroxide compounds.

6) Iron cyanide removal is affected through precipitation according to the following generalized reaction where 'M' represents copper, nickel or zinc:

7) Treatment Results Using the INCO Sulfur Dioxide and Air Process

Parameter Solution Tailings Slurry

Untreated (mg/L)

Treated (mg/L)

Untreated (mg/L)

Treated (mg/L)

Total Cyanide 450 0.1 to 2.0 115 0.1 to 1.0

Copper 35 1 to 10 17 0.2 to 2.0

Iron 1.5 < 0.5 0.7 0.02 to 0.3

Zinc 66 0.5 to 2.0 18 < 0.01

Copper Catalyzed Hydrogen Peroxide Process

Hydrogen peroxide reacts with cyanide to form cyanate and water.

Key points:-

1) Theoretical usage of H2O2 in the process is 1.31 grams of H2O2 per gram of CN‾ oxidized, but in practice the actual usage ranges from about 2.0 to 8.0 grams of H2O2

2) H

per gram of CN‾ oxidized.

2O2

3) Copper (Cu

used in the process is typically provided as a concentrated liquid in 50% or 70% strength.

+2) is required as a soluble catalyst. It is usually added as a solution of copper sulfate (CuSO4-5H2

4) Reaction is usually conducted at a pH of about 9.0 to 9.5 for optimal removal of residual metals such as copper, nickel and zinc initially complexed to cyanide.

0) to provide a copper concentration in the range of about 10 to 50 mg/L, depending upon the initial cyanide and copper concentrations.

5) If iron cyanide must also be removed to low levels, then a lower pH is needed to maximize the precipitation of copper-iron-cyanides at the expense of lowering the removal efficiencies of copper, nickel and zinc. It is common in these instances to use a two-stage system with intermediate removal of the precipitated iron cyanide.

6) Upon completion of the indicated reaction, metals previously complexed with cyanide, such as copper, nickel and zinc, are precipitated as metal-hydroxide compounds.

7) Treatment Results Using hydrogen peroxide Process

8) Primary application of hydrogen peroxide process is with solutions rather than slurries, due to the high consumption of hydrogen peroxide that occurs in slurry applications.

Parameter Solution

Untreated (mg/L)

Treated (mg/L)

Total Cyanide 19 0.7

WAD Cyanide 19 0.7

Copper 20 0.4

Iron < 0.1 < 0.1

Caro's Acid Process Peroxymonosulfuric acid (H2SO5

), also known as Caro's acid is produced from concentrated hydrogen peroxide and sulfuric acid in an exothermic reaction

Due to its instability, Caro's acid is produced on-site and used immediately for cyanide detoxification with only minimal intermediate storage.

Key points:-

1) Overall oxidation reaction of Caro's acid with cyanide

2) Theoretical usage of H2SO5 in the process is 4.39 grams H2SO5 per

gram of cyanide oxidized, but in practice 5.0 to 15.0 grams H2SO5 per gram of cyanide oxidized is required.

3) Acid produced in the reaction (H+

) is typically neutralized with lime, if necessary, and the reaction is normally carried out at a pH in the range of about 7.0 to 10.0.

4) Treatment Results Using Caro's Acid

Test Number

Slurry WAD Cyanide Concentration

Untreated (mg/L)

Treated (mg/L)

1 44.5 8.5

2 37.5 4.2

3 46.0 14.0

4 39.8 4.0

5 115.0 27.1

6 113.1 16.3

7 101.5 18.7

5) Caro's acid is used in slurry treatment applications where the addition of a copper catalyst is not desirable

6) In solution applications, other destruction processes, such as the hydrogen peroxide process, are preferred to the Caro's acid process.

Alkaline Chlorination Process Cyanide destruction reaction has two steps. In the first step cyanide is converted to cyanogen chloride (CNCl) and in the second step cyanogen chloride hydrolyzes to yield cyanate.

Key points:-

1) In the presence of a slight excess of chlorine, cyanate is further hydrolyzed to yield ammonia in a catalytic reaction.

2) If sufficient excess chlorine is available, the reaction continues through "breakpoint chlorination" in which ammonia is fully oxidized to nitrogen gas (N2

).

3) In addition to reacting with cyanide, cyanate and ammonia, the alkaline chlorination process will preferentially oxidize thiocyanate, which in some cases can lead to excessively high consumptions of chlorine. It is the removal of thiocyanate that makes this cyanide treatment process unique when compared to other chemical oxidation processes.

4) Theoretical usage of Cl2 to oxidize cyanide to cyanate is 2.73 grams Cl2 per gram of CN‾ oxidized, but in practice the actual

usage ranges from about 3.0 to 8.0 grams Cl2

5) Reaction is carried out at a pH of greater than 10.5 to ensure potentially irritating cyanogen chloride is rapidly hydrolyzed to cyanate.

per gram of CN‾ oxidized.

6) Treatment Results Using Alkaline Chlorination Process

Parameter Solution

Untreated (mg/L)

Treated (mg/L)

Total Cyanide 2,000 8.3

WAD Cyanide 1,900 0.7

Copper 290 5.0

Iron 2.4 2.8

Zinc 740 3.9

7) The reactions generate varying amounts of acid (H+

8) An advantage of the process is that copper is not required as a catalyst as with the sulfur dioxide/air and hydrogen peroxide processes.

) which is typically neutralized by adding lime or sodium hydroxide to the reaction vessels.

9) Upon completion of the cyanide oxidation reaction, metals previously complexed with cyanide, such as copper, nickel and zinc, are precipitated as metal-hydroxide compounds.

10)

Primary application of this process is with solutions rather than slurries due to the high consumption of chlorine that occurs in slurry applications.

Iron-Cyanide Precipitation Free, WAD and total cyanides all react with ferrous iron to yield a variety of soluble and insoluble compounds

These reactions act to lower free and WAD cyanide concentrations by converting them to stable iron cyanide compounds (soluble and insoluble), while the iron-cyanide concentration is lowered as a result of precipitation reactions.

Key points:-

1) The process is optimally carried out at a pH of about 5.0 to 6.0 and iron is added as ferrous sulfate (FeSO4-7H2

2) Ferrous sulfate usage ranges from about 0.5 to 5.0 moles Fe per mole of CN‾ depending on the desired level of treatment

O).

3) Treatment Results Using Iron-Cyanide Precipitation Process

Parameter Solution

Untreated (mg/L)

Treated (mg/L)

Total Cyanide 8.8 0.89

4) Drawbacks:- • Generation of cyanide precipitates • Formation of stable and soluble iron-cyanide compounds

that will persist for many years and may require further treatment.

Effluent Polishing with Activated Carbon Activated carbon has a high affinity for many metal-cyanide compounds, including the soluble cyanide compounds of copper, iron, nickel and zinc.

Key points:-

1) Activated carbon is suitable for use as a polishing treatment process to remove cyanide to low levels, when the initial cyanide concentrations are already below about 2.0 mg/L.

2) This is a simple and effective process, convenient for installation at sites where activated carbon is used in metallurgical processes for precious metals recovery.

3) At these sites, newly purchased carbon can be used for water treatment. Then when the carbon breaks through and is no longer suitable for water treatment, it can be transferred to the metallurgical circuit for continued use.

4) Treatment Results Using Activated Carbon Adsorption Process

Parameter Solution

Untreated (mg/L)

Treated (mg/L)

Total Cyanide 0.98 0.20

Copper 0.02 < 0.02

Iron 0.22 0.02

Nickel 0.15 0.15

Zinc 0.02 < 0.02

Introduction to Biological processes have been proven effective in the treatment of elevated concentrations of cyanide. Biological treatment facilities may include chemical and/or physical processes, but the primary treatment takes place through one or more biologically mediated reactions.

Biological Treatment Processes

Key points:-

1) Biological reactions occur as the result of enhanced biological activity in the water.

2) Biological treatment occurs under carefully controlled conditions. 3) Important Definitions:-

• Aerobic biological reactions occur in the presence of dissolved oxygen and result in the oxidation of chemical compounds. Examples include the oxidation of cyanide (CN‾) to yield cyanate (OCN‾) and the oxidation of ammonia (NH4+) to yield nitrate (NO3

• Anaerobic biological reactions occur in the absence of dissolved oxygen and result in the reduction of chemical compounds. An example is the reduction of sulphate (SO

-).

4-2) to yield sulphide (S-2

• Anoxic biological reactions occur through an aerobic pathway but do not include the use of dissolved oxygen. These reactions take place at low dissolved oxygen levels or in the absence of dissolved oxygen. An example is denitrification in which microorganisms utilize nitrate (NO

).

3-) for growth, thereby reducing nitrate to nitrogen gas (N2

).

4) Systems for promoting the growth of microorganisms:- • Suspended growth activated sludge systems, in which

microorganisms are maintained in slurry form in suspension within the solution.

• Attached growth system in which microorganisms are attached to some inert medium such as rocks or plastic media.

5) Critical reaction environment conditions:-

• Temperature • PH • Oxygen level • Nutrient availability

6) Optimal temperature range for aerobic and anaerobic treatment is about 10 to 30°C and 25 to 45°C, respectively.

7) Optimal pH range for aerobic and anaerobic treatment is 6.0 to 9.0 and 6.5 to 7.5, respectively.

8) Oxygen must be absent in anaerobic systems, while in aerobic systems the dissolved oxygen level should be maintained above 1 to 2 mg/L.

9) Depending upon the bacteria utilized, nitrogen can be added as ammonia or nitrate, while phosphorous can be supplied through addition of phosphoric acid regardless of the bacterial process employed.

10) Note:- In certain cases the compounds targeted for treatment, although known to be degradable, are present in sufficient concentration to

induce bacterial inhibition or toxicity. Lowering influent concentrations through dilution may be required to initiate treatment.

Biological treatment process chemistry There are several biological reactions which are of interest in water treatment applications

1) Cyanide is oxidized in aerobic biological treatment processes to form cyanate.

:-

2) WAD cyanide can be removed by metal complex absorption onto biomass and subsequent internal decomposition of the cyanide to form cyanate.

3) Strongly complexed cyanides such as iron cyanide are not readily treatable biologically, but can be removed to a limited extent in the process through precipitation and adsorption.

4) Cyanate is biologically converted to ammonia and bicarbonate

5) Thiocyanate is aerobically converted to ammonia, sulphate and bicarbonate

6) Nitrification:-

• Ammonia is oxidized by nitrifying organisms in two steps first to nitrite and then to nitrate

• Overall reaction for the nitrification process is:

• The combined nitrification reaction consumes alkalinity and

releases acidity, therefore it is necessary to control pH and maintain alkalinity to optimize the process. During the process, 7.2 kg of alkalinity (as CaCO3

• Operating temperatures above 15°C are desirable to achieve complete nitrification

) is destroyed per kg of ammonia nitrogen oxidized.

• Nitrifying bacteria are sensitive to low dissolved oxygen; dissolved oxygen concentrations at or above 2.0 mg/L are desirable.

• pH in the range of 7.8 to 8.5 is theoretically optimal with significant losses of efficiency below 7.0

7) Denitrification:- • The biological process of denitrification involves the

conversion of nitrate and nitrite to gaseous nitrogen. • The conversion of nitrate to nitrogen gas is a two step

process. The reactions as written for the use of methanol (CH3

OH) as the organic carbon source are:

• Overall reaction for denitrification can be described by:

• Denitrification process produces alkalinity so it requires the addition of sulphuric acid to control pH in the optimum range of 6.5 to 7.5.

• Denitrification rate is very sensitive to temperature with the rate doubling with each 4°C increase. The process will operate at temperatures as low as 5°C but generally requires temperatures greater than 10°C.

Case study 1

Homestake Mine Biological Treatment Process

A full-scale biological treatment facility was designed and put into operation at the Homestake Mine in Lead, South Dakota in late 1984

1) All forms of metal complexed cyanides are removed in this plant, including WAD cyanides and the stable iron complexed cyanides, which are removed through a combination of oxidation and sorption into the biofilm.

. Key points are as follows:-

2) Metals present in the wastewater are removed through a combination of coagulant addition and adsorption onto the biofilm.

3) Ammonia is converted to nitrate via a two-stage biological nitrification process.

4) Solids from sloughed biofilm and precipitated metals, which are suspended in the water, are removed by clarification.

5) An inorganic carbon source (soda ash) is periodically added to the untreated water to aid nitrification and phosphorus is added as a trace nutrient (H3PO4

6) The biological species located in rotating biological contactors (RBC's) stages are responsible for oxidation of cyanide and thiocyanate and for the adsorption of trace metals.

).

7) Biological species present in RBC’s stages are also responsible for nitrification process.

8) Homestake Mine Water Treatment Plant Performance

Constituent Untreated Water Treated Water

Copper maximum minimum average

0.73 0.17 0.49

0.13 0.01 0.05

Total Cyanide maximum minimum average

6.4 0.8 3.4

0.67 0.06 0.31

WAD Cyanide maximum minimum average

5.2

0.31 2.3

0.14 0.01 0.03

Total Suspended Solids maximum minimum average

-- -- --

16.0 1.0 3.0

Ammonia maximum minimum average

10.4 1.0 5.3

0.35 0.10 0.12

pH maximum minimum

9.0 7.5

8.35 7.13

9) Note:- All concentrations are in mg/L

Case study 2

Nickel Plate Mine Biological Treatment Process

1) The full-scale combined biological and chemical treatment facility now in operation at the site uses the following three steps:

• A two-stage aerobic activated sludge treatment step to convert cyanide, thiocyanate and cyanate to ammonia; and to oxidize the ammonia formed to nitrate.

• An anaerobic denitrification step to reduce nitrate to nitrogen gas.

• A high density sludge (HDS) step utilizing lime and ferric sulphate to precipitate arsenic and other residual metals.

2) Reagent usages in the nickel plate mine Biological water treatment plant in 1999

Reagent Usage (kg/million gallons)

Methanol 3,274

Ferric Sulphate 2,227

Sulphuric Acid 441

Phosphoric Acid 68

Soda Ash 139

Lime 3,893

Flocculant 45

3) Block diagram of nickel plate mine Biological water treatment plant:-

4) Performance of the Nickel Plate Mine Biological Water Treatment Plant

Constituent (1) Influent

Aerobic Circuit Effluent

Anaerobic Circuit Effluent

HDS Circuit Effluent

Permit Limitation

pH 7.70 8.26 7 to 10

Total Dissolved Solids 2,853 3,176 7,500

Total Suspended Solids 11.5 8.2

Total Cyanide 1.04 0.50 0.51 0.44 3.0 (2)

WAD Cyanide 0.33 0.12 0.10 0.04 0.20

Thiocyanate 379 0.06 0.07 0.08 3.0 (2)

Ammonia 25.4 0.01 0.01 0.15 1.0

Nitrate 2.83 98.3 0.04 0.13 10.0

Sulphate 1,316 1,908 1,948 2,000 3,500

Arsenic 0.21 (3) 0.001 0.07 (4)

Cobalt 0.97 (3) 0.82 0.76 0.72

Copper 0.02 (3) 0.006 0.004 0.005 0.04 (4)

Iron 0.06 (3) 0.02 0.03 0.02 0.50

Notes: (1) All concentrations in mg/L., (2) Total cyanide plus thiocyanate limitation, (3) Dissolved concentrations, (4) Limitation for total concentration

Other Cyanide Treatment Processes

1) Ion exchange and reverse osmosis:-

• In both of these processes waste brine is generated as a by-

product. • Disposal or further treatment of this brine is difficult and

expensive, and in some cases the brine may be hazardous and require special handling.

• The amount of waste brine generated by ion exchange and reverse osmosis typically ranges from about 10% to 30% of the volume of water treated.

• Ion exchange and reverse osmosis processes are also relatively expensive and complex to construct, operate and maintain.

• Ion exchange and reverse osmosis are limited to situations where waste brine can be easily disposed of or treated, or where very high quality effluent is required.

• An advantage of reverse osmosis is that in some cases simultaneous removal of cyanide, cyanate, thiocyanate, ammonia, and nitrate can be affected.

• Ion exchange is occasionally used to target ammonia or nitrate removal from the effluent.

2) Ozone treatment

• Ozone is a strong oxidant and capable of oxidizing free and WAD cyanides to cyanate, ammonia and nitrate.

• Ozone is relatively expensive to produce and this has limited its use for cyanide destruction, particularly for large water flows, but it may be useful in small-volume polishing applications.

• At an elevated temperature and in the presence of ultraviolet radiation, iron cyanides are converted to cyanate by ozone.

BUREAU OF INDIAN STANDARDS

Guide for treatment and disposal of Steel plant effluents

Key points:-

1) Production of coke by high temperature carbonization is an integral part of steel plants in India.

2) The gas produced during the coking of coal contains valuable substances which are recovered in the by-product plant.

3) Water is used in different processes such as quenching of coke, cooling, washing and scrubbing of coke oven.

4) Bulk of water used in a coke plant is for cooling purposes, but the aqueous wastes from process operations contain tar, ammonia, benzole, phenols, hydrogen sulphide, cyanides, pyridine, oils, etc.

5) The effluent from the quench tower, where the hot coke is deluged with water, contains coke dust called ‘breeze’ which is commonly recovered from the quench water.

6) Source of contaminants in steel plant:-

S.no. Unit operation Contaminants

1) Coke quenching Coke breeze, sulphurous acid , tar , ammonia , phenol , cyanides , and hydrogen sulphide

7) Composite effluent in a steel plant:-

pH value 8.5 to 9.5

Thiocyanate 50 ,, 100 Thiosulphate 110 ,, 220 Total ammonia 800 ,, 1400 Sulphide 10 ,, 20

Cyanide 10 ,, 50

Phenol 500 ,, 1000 Chloride 4000 ,, 4200

Note:-

• All concentrations are in mg/l • Volume of the composite effluent is usually 100 to 150 liters

per tonne of coal carbonized but in some plants the volume is reported to be as high as 300 to 400 liters.

8) Major pollution effects due to the waste waters from an

integrated steel plant are as following: • Toxicity to aquatic life • Lowering of dissolved oxygen in the receiving water course • Taste and odour problem in the receiving water

• Rise in the temperature of the receiving water

9) Relative toxicities and oxygen demand of substances found in steel plant effluents

10) Ammonia, phenols (monohydric, polyhydric and derivatives of phenol), cyanides and sulphides are well known for their toxicity to aquatic life. Among the toxicants mentioned above, free ammonia and cyanide are the most toxic substances. The concentration of free ammonia increases with increase in the pH value of the medium. Hence ammonia toxicity is particularly severe at high pH values only.

S.No. Constituent Relative Toxicity Oxygen Absorption

Rate

Rate of Biochemical Oxidation

1 Free ammonia High (10 mg/l)

Nil Very slow

2 Fixed ammonia Nil Nil Very slow

3 Sulphide High High Fast

4 Cyanide High (10 mg/l)

Slow Very slow

5 Thiocyanate (as CNS)

Low (200 mg/l)

Slow Slow

6 Thiosulphate Low High Fast

7 Phenol (as C6H5OH)

Medium

(10 mg/l)

High Fast

8 Higher tar acids Low (10 mg/l)

High Very slow

Coke breeze 1) Definition

A fine coke separated by screening from the larger sizes before or after crushing

Ref: http://www.merriam-webster.com/dictionary/coke%20breeze

2) Description Coke breeze, also called as coke fines, is low ash metallurgical coke of very small grain size (0 - 10 mm). During metallurgical coke production in coke oven batteries, the screening operation is carried out where pieces and dust too small for steel making are removed. These fines are called coke breeze. It is used in refractories, sintering operations and cement industries.

3) Specifications:-

• Moisture (arb): 15% • Ash : 20% Max dry basis • Volatile Matter (arb): 3.0% max • Fixed carbon: 77% min • Size: -3mm (80% min.); +3mm (17% max.); +6mm (5% max.)

Ref: http://www.futurecarbonsolutions.com/Coke-Breeze

4) Key points from 104th

• Three main criteria for development of good adsorbents are: annual report (2010 – 2011) of Tata steel:-

Ability of removal of more than 99% colour from effluent. Cost of adsorbent. Regeneration or reuse of the adsorbent.

• Coke breeze was identified as such an adsorbent which fulfils all of the above requirements.

• Coke breeze removes more than 99% colour and also substantially reduce the chemical load by removing toxic organic refractory material like cyanide, thiocyanate and phenolic compounds.

• The spent adsorbent can be well consumed by the sinter plant in Tata steel itself.

• By the use of coke breeze the final aim to develop a low cost adsorber from steel industry by-product which can be reused by processes in steel industry and to obtain colour free eco-friendly discharge water can be achieved.

Ref: http://www.tatasteel.com/investors/annual-report-2010-11/annual-report-2010-11.pdf

Experiment - 1

Aim:-

To find the optimum ratio of coke breeze to activated carbon in a mixture which can best be used in cyanide treatment process.

Chemicals required:-

Feed (effluent from Tata steel), 0.1 N HCl solution, Distilled water, Activated carbon, Coke breeze, 10 N NaOH solution

Apparatus required:-

Beaker, Pipette, Stirrer, pH meter, Conical flask, Measuring cylinder, Parafilm, incubator shaker, small plastic bottles, filter paper, vials, Cyanide ion selective electrode

Procedure:-

1) 400 ml of feed (effluent from Tata steel) was taken into a beaker. 2) pH of the solution in the beaker was adjusted to 3 by adding

suitable amount of 0.1 N HCl solution (using pipette) into the beaker. Note: - Solution was thoroughly mixed using stirrer after the addition of each drop of 0.1 N HCl into the solution and the pH of the solution was recorded by pH meter.

3) The solution in a beaker was mixed well and made homogeneous.

4) Four conical flasks were taken and labeled as A, B, C, and D. To each of these flasks activated carbon and coke breeze was added as follows:-

Conical flask Activated carbon (g) Coke breeze (g) A 0.5 2 B 0.5 5 C 1 2 D 1 5

5) Using measuring cylinder 100 ml of solution from the beaker was added to each of these flasks.

6) The flasks were closed and sealed by using parafilm to avoid any harmful vapour leakages.

7) Flasks were kept in incubator shaker for 24 hours and temperature was set to 25 degree Celsius. Note: - The content in the flasks was shook so as to minimize the time required for attaining equilibrium.

8) Four small plastic bottles were taken and labeled as a, b, c, and d. 9) Filtrate from the flasks A, B, C, and D was collected (using filter

paper) into the small plastic bottles a, b, c, and d respectively. 10) 10 ml of solution from the small plastic bottle “a” was transferred

to vial using pipette. 11) 0.1 ml of 10 N NaOH solution was added to the vial and the

contents in the vial were mixed well. 12) The concentration of cyanide in the vial was measured using

Cyanide ion selective electrode. 13) Similar procedure was adopted for the filtrate collected from B, C

and D.

Reason for using 10 N NaOH solution is as follows:- • Total concentration, Ct, consists of free ions, Cf, and complexed

or bound ions, Cc. In solutions: Ct = Cf + Cc

• Since the electrode only responds to free ions, any complexing agent in the solution reduces the measured concentration of ions.

• Hydrogen ions and many metal ions form complexes with cyanide ions. The presence of any complexing agent lowers the measured concentration.

• Since the electrode measures only free cyanide ions, use of 10 N NaOH is essential, since it eliminates complexation by hydrogen.

Observation:-

Conical flask

Initial concentration

(mg/l)

Activated carbon

(g/l)

Coke breeze

(g/l)

Final concentration

(mg/l)

A 10 5 20 3.61 B 10 5 50 5.88 C 10 10 20 5.55 D 10 10 50 5.84

Note:-

Initial pH of the feed was 7.8

Conclusion:-

A ratio of 1:4 for activated carbon to coke breeze in a mixture is best for cyanide treatment process.

Experiment – 2

• An adsorption column was prepared with coke breeze as adsorbent.

• Height of coke breeze taken in the column – 9 cm • An experimental setup was prepared. The Key

components of experimental setup being:- Feed tank Pump Bypass line Rotameter Manometer Adsorption column Outlet

• A 5 liter feed sample was taken and its pH was adjusted to 3 by using 1 N HCl solution.

• The feed was put to the feed tank of the experimental setup and the experimental setup was started.

• The outlet was adjusted to 10 ml/min and the setup was run for 7 hours.

• 7 samples were collected with one hour gap in their collection time

Preliminary Guide to Selecting Cyanide Treatment Processes

Treatment Process

Iron Cyanide Removal

WAD Cyanide Removal

Slurry Application

Solution Application

INCO SO2 Partial /Air

Hydrogen Peroxide Partial

Caro's Acid

Alkaline Chlorination

At High Temperature

Iron Precipitation

Cyanide Recovery

Activated Carbon

Limited to Low Levels

Biological Processes Partial

Natural Attenuation

Bibliography

• Website - http://www.edumine.com/ • Website - http://technology.infomine.com/cyanidemine/ • Online course - Cyanide Management in Mining - 6: Treatment

Technologies for Cyanide and Related Compounds • Review paper – “Overview of cyanide treatment methods” by

Michael Botz. • Report – 104th

• Guide – Guide for treatment and disposal of steel plant effluents from Bureau of Indian standards.

(2010-2011) annual report of Tata steel

• Information and knowledge gained from research scholars in membrane separation laboratory, IIT Kharagpur.