How do I size the equipment for unit 200 and 400 Production of Gold Background A

ID: 900044 • Letter: H

Question

How do I size the equipment for unit 200 and 400

Production of Gold

Background

A feasibility study on the production of gold at a fictitious mine (Moapa mine) in Elko County, Nevada is to be performed. The mine is capable of producing 325,800 tons of high-grade ore per year for 10 years. The deposit contains 0.12 ounces of gold per ton of high-grade ore and can be acquired at a cost of $10 per ton of ore (cost of mining ore at site). A sodium cyanide process is used to extract the gold from the ore, and various other processing techniques are used to produce 99.9% pure gold bullion from the ore.

The results of the feasibility study show that the ore can be processed by agitation leaching, which is preferred over heap leaching due to the low recovery associated with the heap leaching technology.

Process Description

Unit 100 – Size Reduction of Ore

The BFD of the overall process is shown in Figure 1. The PFD for Unit 100, shown in Figure 2, is designed to reduce 45.5 tons/hr of gold ore from a feed range of 25” to 160 microns. The mined ore is fed using a Grizzly Feeder, F-101 where over sized material consisting of rocks (6” or greater) is discarded as non-gold bearing material (not shown on the PFD) from the top of the Grizzly. The remaining gold bearing ore is sent from F-101, into a Jaw Crusher, J-101, where 80% of the ore is crushed to 1.75” or smaller. The remaining 20% (oversized material) is recycled back into F-101 (not shown on PFD).

The ore is then sent to Screen S-101 where the ore that does not pass through the first deck is sent to the Standard Cone Crusher SC-101. Ore passing through the first deck but not the second deck is sent to the Shorthead Cone Crusher SHC-101, while ore passing completely through is sent to the Ball Mill B-101.

The ore passing through the first deck is sent to a Standard Cone Crusher, SC101, which has a closed-side setting of 0.5”. Within this crusher, the ore size is further reduced to 80% passing at 0.5”. The ore leaving the SC-101 along with the second deck ore is then sent to a Shorthead Cone Crusher, SHC-101, where it leaves the equipment with 80% passing at 0.2” or less.

The ore from SHC-101 is sent back to the Screen S-101. The screen has a 0.5” sieve opening for the first deck while the second deck is 3 mesh, where all particles at or below 0.25” are sent to the grinding section for further size reduction. The screen deck oversize, consisting of particles over 0.25”, is recycled back to SC-101.

The Ball Mill, B-101, grinds the 0.25” ore until it is in the range of 160 microns. The ore leaving the ball mill is sent to six hydrocyclones that separate the larger particles from the smaller particles. The top stream leaving the cyclone is 75% of the feed into it. This top product is 160 microns or less. The bottom stream is recycled back to the ball mill. After the top stream leaves the hydrocylone processing unit (stream 15) it passes through a gravity separator (not shown in the PFD GS-101). The gravity separator is calibrated to hardness where it separates off approximately 10 % of stream 15. This is discarded because it is too hard to for additional particle size reduction by the ball mill.

Unit 200 - Leaching

The sub-millimeter particles from Unit 100, Stream 15a, are now mixed with a dilute aqueous solution of sodium cyanide, Stream 16, and a recycle stream, Stream 20a, from Unit 400. The resulting slurry, Stream 18, is fed into large mechanically stirred tanks where it is agitated with air. The compressor/blower delivers a large volume of air (to lift and mix the solid ore and maintain good surface area exposure to the cyanide extraction liquid) at 35 psi. The mechanical agitator mixes this slurry at a relatively slow speed in the baffled tank to prevent stagnant pockets within the vessel. In these vessels, leaching occurs, and the gold is transferred from the ore and forms a gold-cyanide complex. The complex is then sent to Unit 300 as Stream 19 where it is filtered.

Unit 300 – Filtering

Filters following the agitation leach are designed to separate the spent ore from the leachate. The filter section consists of 4 multi-compartment rotary drum vacuum filters in series. The spent ore is left behind on the filters and the gold remains in the leach filtrate. The leachate is pumped to unit 400 using pump P 305A/B (Note: this pump must be design and included in your project costs) where the pregnant solution containing gold is further concentrated. The concentrated solids are conveyed to the Tailings impoundment for further handling and processing. Note: While a pump (P304) is shown in the PFD this is not correct. The solids are too dry to pump and must be conveyed over 1000 ft, using a series of belt conveyers (Note: the conveyers system must be designed and included in your project costs but the waste impoundment is not part of your design) .

Unit 400 – Carbon Adsorption and Elution

The adsorption of gold from the pregnant leach solution onto the activated carbon is the key step in the recovery process. This recovery begins when the leach filtrate is sent to the carbon columns, CIC-401, via Stream 29. Gold is adsorbed onto the activated carbon. The cyanide solution passes through the carbon columns and recycled to unit 200 as concentrated solution and unit 300 the weaker wash solution containing cyanide.

While Figure 5 shows V-401 this is only presented for clarity and the vessel does not exist. The filtrate is eluted from the carbon in the carbon vessels. The gold is eluted into a water solution from the carbon by the American-Anglo Research Laboratories (AARL) method, leaving the regenerated-barren (no gold on the carbon) carbon behind using back washing setup. Figure 5 shows the carbon adsorption and AARL elution processes. A waste stream is produced which must be treated (stream 36). Note: the waste treatment system for stream 36 must be designed and included in your project. The loaded eluant, Stream 37, is then sent to the electrowinning cells and subsequently to the refining process.

Unit 500 – Electrowinning and Refining

Electrowinning Process

In the electrowinning cells the gold is deposited onto steel wool cathodes. An article about an electrowinning process at the Masbate Gold Mine gives information on how to establish a base-case design1.

Refining Process

The overall refining process is shown in Figure 6. In the acid dissolution chamber, AD-501, a 10% sulfuric acid solution is added to the loaded steel wool cathodes at 60°C in order to oxidize the excess iron present to a soluble form. Hydrogen gas must be vented to a flare throughout the batch reaction’s 12-24 hour residence time, and the acid solution with the dissolved iron must be drained and treated.

The calcination step of refining consists of spreading the loaded steel wool cathodes into thin trays and heating with 50 scfm of air at 600-700°C for 12-18 hours to oxidize the remaining base metals. Using an economizer, E-501, the inlet air can be preheated by the exhaust gas from the smelter. This minimizes energy requirements for the calcinator. The outlet air is scrubbed to remove any gaseous oxidized metals. If a mercury retort is used, it can take the place of the calcination by heating the loaded steel wool to 600-700°C at a slightly negative pressure for 2-3 hours. This will remove the mercury as well as oxidizing the base metals in the cathodes2.

The smelting step of refining consists of heating the loaded steel wool to melt the gold at 1300°C, with fluxes of silica, feldspar, and borax, to remove impurities. Exit gases leave the furnace at 1250oC and at a rate of 10 scfm. Complete separation occurs within 1.5 hours, at which point the slag is poured off and the molten gold is poured into anode casts and cooled. The anodes are approximately 99% pure and are submerged with 99.9% pure rolled gold cathodes in an electrolytic solution with 100g/L each of gold and hydrochloric acid. A current density of 800 A/m2 is applied at 60°C, and the gold collected on the cathodes is rinsed several times with a hot sodium thiosulfate solution before the 99.9% pure cathodes are melted and recast as final products.

The electrowinning process is complex but the system is small only treating 35 kg/hr containing mostly water and gold. Assume that the electrowinning process can be conducted for 10,000 dollars per gram of 99.99% gold produced less the cost associated with the economizer E-501 . Thus, it is not necessary to size the electrowinning process except for the sizing E-501 and the costs of utilities associated with this unit.

Unit 600 - Waste Treatment and Tailings Disposal

Waste Treatment

All cyanide and sodium hydroxide is recycled back into the leaching section. The hydrochloric acid leaving the elution vessel is the only solution treated. The HCl is neutralized by adding limestone to raise the pH from 3.0 to 7.0.

Tailings Impoundment

The design consists of two units, both helping to ensure that no seepage penetrates through the liners and enters the ground water. The main unit in this design is the impoundment area where 44 acres of land are used to store the hazardous filter cake. The liner system employed by this unit consists of a geotextile layer, a sand drain layer, a high-density polyethylene (HDPE) liner, and a clay layer. A monitoring well was also included in the design in order to determine the amount of seepage through these layers.

The second unit involved with this design is the leachate collection pond. This unit is considerably smaller than the impoundment area and is used to collect any seepage that collects in the drainpipes of the impoundment unit and any rainwater that runs down the embankment. The liner system associated with the leachate collection pond, however, actually provides better containment than the impoundment section because liquids increase the leakage value of liners. This liner design consists of a geotextile layer, two sand drain layers, two HDPE liners, a clay layer, and a monitoring well. Any seepage that gets collected in these drainpipes is then sent to the waste treatment unit.

For this study you must design a waste treatment system to treat the HCl wash from the carbon columns stream 36. You should provide in your design for a one day hold up for waste stream before treatment. You should also assume that the concentration of calcium chloride in the waste is small that thus can be released to the receiving stream, but this must be verified. For this study a design for the tailings impoundment is not required but you should consider the tailing as a solid hazardous waste containing CN. Assume this material can be disposed at a cost of $200/tonne.

Additional Information

Gold is leached from ore by a dilute aqueous solution of sodium cyanide. The overall reaction thought to be mostly responsible for this is

2Au + 4CN + O2 + 2H2O 2Au(CN)2 + 2OH + H2O2 (1)

Van Deventer also gives some criteria for the selection of activated carbon for use in the adsorption process, as well as values for all of the adsorption constants for each of the nine carbons that he presents3.

The reaction of HCl and limestone is

CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) (2)

The modeling of the entire process in Chem Cad is not necessary but you may chose to use Chem Cad to assist in the design of selected equipment.

Equipment Descriptions

F-101

Grizzly Feeder

J-101

Jaw Crusher

SC-101

Standard Cone Crusher

SHC-101

Shorthead Cone Crusher

S-101

Screen

B-101

Ball Mill

CY-101 A/F

Hydroclones

GS-101

C-201 A/B

Gravity separator

Compressor

P-201 A/B

Slurry Pump

AT-201

Agitation Tank

P-202 A/B

Slurry Pump

AT-202

Agitation Tank

P-203 A/B

Slurry Pump

AT-203

Agitation Tank

P-204 A/B

Slurry Pump

AT-204

Agitation Tank

P-205 A/B

Slurry Pump

AT-205

Agitation Tank

P-206 A/B

Slurry Pump

AT-206

Agitation Tank

F-301

Rotary Drum

P-301 A/B

Slurry Pump

F-302

Rotary Drum

P-302 A/B

Slurry Pump

F-303

Rotary Drum

P-303 A/B

Slurry Pump

F-304

Rotary Drum

P-304 A/B Slurry Pump

C-301 A/B Vacuum Compressor

E-401 Economizer

V-401 Elution Vessel

CIC-401 Carbon in Columns

AD-501 Acid Dissolution

C-501 Calcination

MR-501 Mercury Retort

S-501 Smelter

ST-501 Slag Treatment

E-501 Economizer

EL-501 Electrolytic Refining

F-501 Casting Furnace

N-601 Neutralization Unit

TI-601 Tailings Impoundment

References

“Gold and Silver Leaching, Recovery, and Economics,” Proceedings from the 110th AIME Annual Meeting, Chicago, Feb. 22-26, 1981, (W.J. Schlitt, W. C. Larson, and J. B. Hiskey, eds.)

Marsden, John and Iain House, The Chemistry of Gold Extraction, Ellis Horwood Ltd., Chichester, West Sussex, England, 1992.

Van Deventer, J. S. J., “Criteria for Selection of Activated Carbons Used in CIP Plants,” Reagents in the Minerals Industry, Inst. Min. and Metall., (M.J. Jones, ed.,) pp. 155-160, 1984.

Gold Production Stream Table

Unit 100 – Size Reduction

Stream

Total Flow (tons/hr)

45.5

41.5

31.4

36.4

5.0

36.4

Component Flowrates (tons/hr)

Ore

45.5

41.5

31.4

36.4

5.0

36.4

Water

Stream

Total Flow (tons/hr)

77.9

41.5

10.4

17.3

69.2

Component Flowrates (tons/hr)

Ore

77.9

41.5

13.8

55.3

41.5

Water

10.4

3.5

13.8

10.4

Unit 200 – Leaching

Stream

15a

20a

Total Flow (tons/hr)

46.66

0.0014

0.5403

93.33

46.67

Ore Flow (tons/hr)

37.33

Water Flow (tons/hr)

9.33

55.99

46.66

Component Flows (kg/hr)

Gold

0.1528

0.0019

Oxygen

113.45

0.4480

0.3733

CN-

0.5185

2.9117

2.8719

2.3932

OH-

0.1587

0.9519

0.7933

Na+

0.6733

4.0397

3.3664

Au (CN)2

0.1907

0.0016

Water

9332

55994

46662

Nitrogen

426.80

Unit 300 -- Filtration

Stream

20b

22a,b,c

Total Flow (tons/hr)

93.33

9.33

46.66

3.11

46.66

Ore Flow (tons/hr)

37.33

Water Flow (tons/hr)

55.99

9.33

3.11

9.33

Component Flows (kg/hr)

Gold

0.0019

Oxygen

0.4880

0.0747

0.0249

0.0747

CN-

2.8719

0.4786

0.1595

0.4786

OH-

0.9519

0.1587

0.0529

0.1587

Na+

4.0397

0.6733

0.2244

0.6733

Au (CN)2

0.1907

0.0002

0.0318

0.0001

0.0239

0.0180

Water

55994

9332

3111

9332

Stream

Total Flow (tons/hr)

46.67

3.11

9.33

46.66

Ore Flow (tons/hr)

37.33

Water Flow (tons/hr)

46.66

3.11

9.33

Component Flows (kg/hr)

Gold

0.0019

Oxygen

0.3733

0.0249

0.0747

CN-

2.3932

0.1595

0.4786

OH-

0.7933

0.0529

0.1587

Na+

3.3664

0.2244

0.6733

Au (CN)2

0.1589

0.0080

0.0060

0.0045

0.0184

0.0135

Water

46662

3111

9332

Unit 400 – Carbon Adsorption and Elution

Stream

20a

20b

Total Flow (kg/hr)

46669

9334

46669

9334

20.6

Ore Flow (kg/hr)

Water Flow (kg/hr)

46662

9332

46662

9332

20.0

Component Flows (kg/hr)

Gold

Oxygen

0.3733

0.0747

0.3733

0.0747

CN-

2.3932

0.4786

2.3932

0.4786

OH-

0.7933

0.1587

0.7933

0.1587

Na+

3.3664

0.6733

3.3664

0.6733

Au(CN)2

0.0016

0.0002

0.1589

0.0184

Water

46662

9332

46662

9332

20.0

HCl

0.6

Carbon

Stream

32,33

Total Flow (kg/hr)

37.02

4.00

3.66

20.6

Ore Flow (kg/hr)

Water Flow (kg/hr)

36.98

20.0

Component Flows (kg/hr)

Gold

0.1389

0.0014

Oxygen

CN-

0.036344

OH-

0.000038

Na+

0.000094

Au(CN)2

0.1738

Water

36.98

20.0

HCl

0.6

Carbon

3.655

3.66

Note: (---) Does not necessary indicate stream flow amount = 0 just that no data was available

F-101

Grizzly Feeder

J-101

Jaw Crusher

SC-101

Standard Cone Crusher

SHC-101

Shorthead Cone Crusher

Explanation / Answer

Answer:-

200 UNIT EQUIPMENT 400 UNIT EQUIPMENT

1.J-101 Jaw Crusher 1.SC-101 CONE CRUSHER

2.SC-101 SHORT HEAD CONE CRUSHER 2.F-501 CASTING FURNACE

3.The compressor/blower delivers a large 3.V-401

volume of air (to lift and mix the solid ore and 4.CIC-401

maintain good surface area exposure to the

cyanide extraction liquid) at 35 psi.

4.AT-201

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