HIGH PRESSURE LEACH PLANT PRESENTATION

 

HIGH PRESSURE LEACH PLANT PROCESS DESCRIPTION.

 Dated:  April 2015

TABLE OF CONTENTS

• 1PROCESS DESCRIPTION3• 1.1INTRODUCTION3• 1.2PROCESS FLOW DIAGRAM5• 1.3AUTOCLAVE FEED SYSTEMS6• 1.3.1CONCENTRATE SURGE TANK6• 1.3.2AUTOCLAVE DILUTION SURGE TANK6• 1.4AUTOCLAVE LEACH CIRCUIT7• 1.5AREA 220 – BFS LEACH CIRCUIT8• 1.6AREA 230 – RESIDUE FILTRATION8• 1.7SERVICES9• 2Design Basis10

PROCESS DESCRIPTION.

– INTRODUCTION.

• Sulphide flotation concentrate produced at Kansanshi will contain a nominal 29% copper, 18-32% sulphur and 8g/t gold. The concentrate is oxidised utilising the two Autoclaves and the dissolved copper in the Autoclave discharge is recovered in the existing and new SX/EW circuits in the Kansanshi Process Plant. The Autoclave residue will be pumped to the new Gold Pant for further treatment

• • It should be noted that the HPL Plant will have the following benefits to Kansanshi;• Reduce the amount of Kansanshi sulphide concentrate that will need to be transported to be toll treated elsewhere.• Produce extra acid that will be used in the rest of the Kansanshi Copper Circuit.• Produce waste heat to elevate the Atmospheric Leach temperature.• Produce Ferric Sulphate which increases leach recovery in the Atmospheric Leach.• Increase the leach recovery of some of the secondary copper sulphides due to elevated temperature and ferric.• Kansanshi will produce more cathode copper.• The gold contained in the sulphides that are treated in the Autoclave, as well as the Gravity Gold Concentrate, will be treated on site to form bullion bars.• • In general terms the circuits that comprise the pressure oxidation plant are:• • The Slurry feed systems to the Autoclaves.• The High Grade Raffinate feed systems for temperature control to the Autoclaves.• The Autoclave leach circuits comprising two Autoclaves, Flash Tower and Splash Heaters.• The BFS Leach Circuit currently comprising of three tanks.• Solid/liquid separation comprising a thickener and a belt filter.• Process plant services comprising of; a boiler, raw water, gland water, treated water and Autoclave seal water systems.• The 270 tpd Gaseous Oxygen Plant• A new Gold Plant which will treat both Gravity Concentrate and BFS Residue.•

AG 14002

Raffinate and strongacid dilution tank

PP14004A -CAG 14001

PP14001 B

PP14001 A Felluwa pumps

14003A - C

Oxygen 98%

Autoclave Vent 156 Am3/h

Cons Surge TankTK14001

Operating 220 C, 3100 kPag Design 265 C, 3300 kPag

Raffinate 250m3/h

Operating103 C

11 kPagDesign148 C

350 kPag

SplashHeater

PV21005

Steam 466 Am3/h

Steam1700 Am3/h

|| P.D. ||

5.62 tph

Low Pressure

FlashPV21004

Operating102C

1 kPagDesign150 C

50kPag

Acid 1.96 m3/hRaffinate Surge TankTK14002

6.66 tph

83.6 m3/h

57.9 m3/h

Cons

ScrubberSR21001

Basic Ferric Sulphate (BFS) Leach Tanks

TK22012 TK22013 TK22014

BFS Thickener TH22001

BFS ResidueFilter Surge

Tank TK22016

Hot Raffinate164 m3/h

Hot Slurry107 m3/h

41 m3/h 142 m3/h

BFS Thickener Underflow 12 m3/h

Hot Raffinate to Kansansi Atmospheric Leach 562 m3/h

BFSThickener O/F

Tank TK22020

Second Autoclave 164 m3/h

Flocculant

Gold Plant Feed 7.6 m3/h

BFS ResidueFilter FL23001 BFS Residue

Filter Repulp Tank TK22020

Filtrate return to Thickener 11.6 m3/h

12 m3/h Wash3m3/h

107 m3/h

Autoclave VA21001

AUTOCLAVE FEED SYSTEMS

• CONCENTRATE SURGE TANK• The Autoclave Slurry Surge Tank TK14001 receives thickened flotation concentrate from the existing Kansanshi Concentrate Storage Tank and provides surge capacity

between the Autoclave circuit and the flotation circuit. A small Vibrating Screen SC14001 on top of the tank screens the concentrate to remove any trash from the concentrate. The trash oversize is collected for disposal in a bin next to the tank, whilst the screen undersize falls into the tank.

• • An agitator AG14001 is provided to keep the solids in suspension in the tank.• • The duty Concentrate Header Feed Pumps PP14001A or B circulates the flotation concentrate around a ringmain that feeds each of the three Feluwa Autoclave Feed

Pumps. Excess flotation concentrate returns back to the surge tank. A density meter on the ringmain measures the flotation concentrate slurry density feeding the Autoclave.

• • There are three Feluwa Autoclave Feed Pumps PP14003A, B, C; one duty pump for each Autoclave and a common standby pump. These pumps feed the flotation

concentrate into the northern end of the Autoclave.• • •

• AUTOCLAVE DILUTION SURGE TANK• The Autoclave Dilution Surge Tank TK14002 receives High Grade Raffinate from the HG Copper Solvent Extraction pumps and may be combined with additional

sulphuric acid before discharging liquor to the Autoclave. A small Vibrating Screen SC14002 on top of the tank screens the Raffinate to remove any trash in the liquor as the Autoclave dilution pumps are easily damaged by oversize materials and solids. There are three Autoclave Dilution Pumps PP14004A, B, C; one duty pump for each Autoclave and a common standby pump.

• • The Sulphuric Acid, if high ferric values are needed, is added to the trash screen underflow through a small in line mixer to thoroughly mix the Raffinate and the acid. • • This HG Raffinate is used to control the slurry temperature within the Autoclave to approximately 220oC and hence prevent over-pressure and thermal damage.• •

AUTOCLAVE FEED SYSTEMS

– AUTOCLAVE LEACH CIRCUIT

• • Each Autoclave VA21001, VA21002 is a brick-lined pressure vessel divided into five strongly agitated compartments by internal walls across the vessel. The slurry overflows from

compartment to the next compartment along the length of the Autoclave and is eventually discharged at the southern end via the discharge dip-tube to the Flash Tower vessel.• • To start the Autoclave it is necessary to slowly heat the Autoclave up to operating temperature by direct sparging of externally generated steam. Once the Autoclave reaches the

operating temperature of 220oC, flotation concentrates and gaseous oxygen are injected into the Autoclave whilst ambient Raffinate is injected to control the temperature at the required setpoint. The exothermic oxidation reaction of the sulphides generates heat whilst ambient Raffinate prevents the Autoclave temperature going too high.

• • Each Autoclave can treat between 6-9 tph of flotation concentrate depending on the sulphur grade at approximately 29% Cu when all of the oxygen from the Oxygen Pant is used.

(Refer to Addendum 1) Each compartment in the Autoclave is agitated to ensure that the flotation concentrate, Raffinate and oxygen are thoroughly mixed so that the minerals oxidize uniformly.

• • The Autoclaves leach the primary sulphide flotation concentrates under a pressure of approximately 32Bar, at a temperature of 220 C and have an approximate residence time of

98mins. Oxygen gas, (or GOX Plant) supplied by a 272 tpd Cryogenic Oxygen Plant is injected into each compartment in the Autoclaves. • • Acid is both consumed and generated by the leaching reactions, with the net effect being the generation of between 80 and 150 tons of new acid. This is dependant on both the

sulphur feed grade and the amount of ferric required. The leaching reactions also generate heat that acts to sustain the Autoclave at its desired operating temperature. The cooling Raffinate solution flowrate to each compartment is controlled by instrumentation to maintain the target operating temperature and the flotation concentrate slurry flowrate to each Autoclave is maintained at, as constant a flowrate as possible.

• • The iron leached in the Autoclave is precipitated as basic ferric sulphate (BFS), or hematite. By manipulating the acid addition to the Autoclave one controls the proportions of each

type of precipitate, with precipitation of Basic Ferric Sulphate favored by a high acid level in the Autoclave feed.• • FLASH VESSELS• • Leached slurry exiting each Autoclave is brought to atmospheric pressure and a temperature of 100oC in a single Flash Vessel PV21004, PV21008, for each Autoclave respectively.

The Flash Vessel allows the removal of the heat generated in the Autoclave by the controlled release of steam and other hot gases, and allows a drop in the pressure of the Autoclave discharge slurry in the Flash Vessel. The slurry discharge from the Flash Vessel flows to the BFS Leach Tanks and the steam is piped to the Splash Heater Vessels PV21005 and PV21009.

• •

AUTOCLAVE FEED SYSTEMS

• SPLASH HEATERS• • The steam recovered from the Flash Vessel is then used to heat Raffinate for the Kansanshi Atmospheric Leach Circuit by direct contact in the Splash Heaters

PV21005, PV21009. The heat transfer into the Raffinate enables the Atmospheric Leach Circuit temperature to be raised to approximately 55 oC. Raffinate is added to the top of the splash heater and hot Raffinate flows from the bottom of the splash heater to the BFS Thickener Feed Tank. The uncondensed steam flows from the top of the Splash Heater to the Venturi Scrubber SR21001, SR21002 where the acid mist is washed from the gas by a water wash. The scrubbed residual steam and other gas are then vented to atmosphere.

• • AREA 220 – BFS LEACH CIRCUIT• • Iron precipitated in the Autoclave as Basic Ferric Sulphate (BFS – FeOHSO4) is dissolved in the three BFS Leach Tanks TK22012, TK22013, and TK22014 at

atmospheric pressure and 98oC providing a source of ferric for leaching the previously insoluble secondary copper sulphides in the Atmospheric Oxide Leach. The additional recovery varies between 6 – 20% depending on the blend of the ore being treated.

• • The residence time of the BFS circuit is 4 hours. The temperature in the leach vessels is maintained at about boiling to maximize the rate at which the BFS re-

leaches to Ferric Sulphate (Fe2(SO4)3). Each tank is agitated AG22016, AG22017 AND AG22018 to keep the Autoclave residue solids suspended. The last BFS leach tank discharges, under gravity, to the BFS Thickener Feed Tank TK22020. The heated Raffinate from the two splash heaters is also added to the BFS thickener feed tank to reduce the temperature of the thickener feed to approximately 70oC.

• • The remaining unleached solids in the BFS residue are then settled with the aid of flocculant in the BFS Thickener TH22001. The thickener produces an underflow

containing approximately 30 -35%w/w solids. This underflow is then pumped to the BFS Residue Filter Surge Tank TK23016, which provides 8 hours of surge capacity between the Thickener and the Leach Residue Filter.

• • The thickener’s clear solution overflow gravitates to the BFS Thickener Overflow Tank TK22019. This leachate overflow contains all of the leached copper, all of the

“produced” acid and the ferric produced in the Autoclave. Two pumps, the BFS Thickener Overflow pumps PP22039A, B pump the solution to the Kansanshi Atmospheric Oxide Leach Circuit where it promotes additional copper leaching before it is treated to recover the copper. The stripped HG Raffinate is then returned to the HPL Plant to be used again as coolant in the Autoclaves.

•

AUTOCLAVE FEED SYSTEMS

–  – AREA 230 – RESIDUE FILTRATION

• • The BFS Leach Residue Filter separates the copper barren Autoclave residue solids from the process liquor containing the copper, iron and acid filtrate. The solids on the belt

filter are washed with water three times to recover the copper, iron and acid. This is also to reduce the amount of copper and acid reporting to the Gold Plant Cyanide Leach Process.

• • Thickened Autoclave residue is pumped from the Leach Residue Surge Tank by the duty BFS Residue Filter Feed Pump PP23029A, B to the BFS Residue Filter FL23001. Wash

water is added in three places along the Belt Filter to wash the dissolved copper and acid from the solids cake. Wash liquor and primary filtrate from the Leach Residue Filter are combined in the filtrate tank TK23021 and is pumped back to the BFS thickener feed tank by the duty BFS Residue Filter Filtrate Transfer Pump PP23034A, B.

• • Leach residue filter cake at 20% moisture is discharged from the end of the belt filter and is re-slurried with water in the Neutralisation Tank TK23024 before being pumped to

either the Gold Plant or the BFS Residue Pond. Two agitators AG23036A, B are provided in the neutralisation tank to ensure that the filter cake is re-slurried with water to make up a density of 30-35% solids.

• • The re-slurried filter cake is pumped away by the duty BFS Residue Transfer Pump PP23036A, B.• • •

– SERVICES• • The plant services area is located adjacent to the boiler shed. • Raw water is supplied to the Fresh Water tank TK28046. Water is pumped from this tank for a number of duties in the plant.• The HP Flush Pumps PP28075A, B supply water to the wash slurry from the underside of the Autoclave agitator seals within the Autoclave. These pumps are high pressure

pumps.• The Gland Water Pumps PP28076A, B supply water from the Fresh Water Tank to the glands on all of the slurry pumps.• The Boiler Water Treatment Feed Pumps PP28077A, B supply raw water from the Fresh Water Tank to the Boiler Water Treatment plant, XM28003. Chemical addition pumps

provide reagents to the demineralised water plant from two small Boiler Chemical Tanks TK28049 and TK28050.• Demineralised water from the boiler water treatment plant is discharged to the DeminWater Tank TK28054. The steam boiler is fed with demineralised water by the duty

Boiler Makeup Water Pump PP28081A, B and by the Boiler Feed Pumps PP28060A, B

AUTOCLAVE FEED SYSTEMS• The High Pressure Boiler BO28001 provides steam as required to heat up the Autoclaves at start-up. The

boiler burns diesel to generate steam and the diesel is fed to the boiler by the Burner Diesel Feed Pump PP28080.

• An agitated tank is provided to make up Autoclave seal solution. A factory mixture of 50% water and 50% glycol is used as a lubricant in the agitator seals. This solution has to be mixed prior to its use.A Glycol Supply Pump PP21085 is used to pump glycol into the Agitator Seal Solution Storage Tank TK21055. The duty Water Makeup Pump PP28087A, B is used to pump demineralised water into this tank. The Seal Solution Storage Tank Agitator is used to mix the water and glycol. The mixed solution is transferred automatically to the agitator seal solution system by the duty Agitator Seal Solution Pump PP21088A, B.

• Agitator seal solution is pumped to each of the eight agitator seals on each Autoclave by the duty Agitator Seal Solution Pump. For Autoclave VA21001 these pumps are PP21070A, B and for Autoclave VA21002 these pumps are PP21070 C, D.

• The seal solution is stored in the Agitator Seal Demin Vessel PV21013, which is topped up as required from the Agitator Seal Solution Storage Tank. The seal solution is pumped through each seal at approximately 36 Bar and back to the Agitator Seal Demin Vessel in a closed circuit with a heat exchanger used on the agitator seal return line used to keep the solution cooled