Cheat Sheet for Separation processes - chemical engineering

The onion model of process design

Water and effluent treatment

Heating and cooling utilities

Heat recovery system

Separation and recycle

system

Reactor

Environmental issues • When designing and operating process plant,

consideration must be given to:

– All emissions to land, air, water, Waste management, Smells, Noise, Visual impact, Other Environmental friendliness of product

• Continuous

• Production > 5x106 kg/h

• Single product

• No severe fouling

• Good catalyst life

• Proven process design

• Established market

• Batch

• Production < 5x106 kg/h

• Range of products

• Severe fouling

• Short catalyst life

• Uncertain design

• New product

5 Types of separation processes

Solids

Water

Thickener Design

Clarification and Thickening – Large volumes of water are used

– Environmental requirement to close the water circuit

Need to recover water from waste streams for re-use

• Most widely used method of removing fine solids from dilute slurries is by sedimentation using a THICKENER

• Two Processes Occurring...

– Thickening To increase the solids concentration of a slurry

– Clarification To produce a recycle water stream that is

free of solids (i.e. clarified)

• With the development of polymeric flocculants, the two processes occur simultaneously in one vessel

Introduction

Clarifying

Sometimes the prime objective is to get the cleanest possible overflow

In some cases the underflow density may be compromised as this is of secondary importance.

The clarifier generally looks like a thickener but may have features to enhance particle capture.

Thickening

The basic purpose of thickening is to remove as much water from a slurry as to give us a thick underflow, and a clean/clear overflow

A thickener is used to accelerate the process of settling and dewatering of solids in a slurry using flocculants

The desired end product will determine how the thickener is designed and operated.

7

Thickening – (settling) calculations

Insert your own text within this layout areas

Thickening - calculations

8

Insert your own text within this layout areas

Thickener Design

If more solids are fed to the thickener, they will not leave the thickener through the underflow!

Solids Flux and Superimposed Flow

t=0

Volume of solids passing through

the area:

due to settling

SPS = UPS = UP * CV

due to flow

SFS = UFS

= VFlow/A * CV

= UFlow * CV

UTotal

UP UP

UFlow

U: velocity in m/s Cv: concentration in g/m3 S: Flux in g/m2.s or t/m2.h

Flux below and above Feed

Settling: SPS = UP * CV

Flow: SFS = VFlow/A * CV

= UFlow * CV

TOTAL FLUX below:

STOTAL = UP * CV + UUnderFlow * CV

= UT (1-Cv)4.65 * CV + VUnderflow/A * CV

TOTAL FLUX above

STOTAL = UP * CV - UOverflow * CV

= UT (1-Cv)4.65 * CV - VOverflow/A * CV

UOFlow

UUFlow

VUFlow

VOFlow

Condition for working Thickener S

Scrit

CVcrit

Stot = SPS + SFS

SFS a CV

SPS = UP CV CVFeed

SFS a CV

Stot = SPS - SFS

Condition for working Thickener

TOTAL FLUX below Feed

has to be similar or bigger than feed solids

Scrit = F CVF / A = L CVL / A

Arequired > F CVF / Scrit

TOTAL FLUX above Feed

has to be > zero (no solids moving upwards)

STOTAL > ScritOverflow = 0 = UP * CV - UOverflow * CV UP > UOverflow = VOverflow / Arequired (for every Cv, 0<Cv<CvFeed)

Critical for the thickener is the AREA not the height. The height only improves compression.

Condition for working Thickener

Feed: suspension

Overflow: Water

Underflow: Sludge

CvUnderflow > CVFeed > CVOverFlow = 0

TOTAL FLUX below Feed

has to be similar or bigger than feed solids

TOTAL FLUX above Feed

has to be > zero (no solids moving upwards)

Thickener Design

Feeding zone Clarifying zone

Swarm settling Transient zone

Compression zone Rake

Height

Concentration

16 | |

Conventional Thickener High rate thickener

• Traditionally no flocculants and hence large diameters.

• Low unit area throughput t/m2.hr.

• Slow to react – automated (feedback) control more difficult.

• Control based on constant solids inventory difficult.

• Suitable for highly variable flow and solids loading.

• UF density can be variable

• High capital cost.

• Makes use of increased settling rate through flocculation

• Maximum unit area throughput t/m2.hr.

• Consistent high density underflow.

• Smaller footprint.

• Control based on constant solids inventory.

• Relatively fast to react – suited to automation.

• Best suited to relatively consistent process.

• Can increase density by increasing sidewall.

17 | |

Paste Thickener • Also makes use of flocculation.

• Unit area throughput t/m2.hr maximised but secondary to UF density.

• Consistent high yield stress underflow (+150 Pa)

• Small footprint but relatively tall.

• Control based on underflow properties (and torque).

• Automation important for stable operation.

• Best suited to relatively consistent process.

• High underflow solids concentration > than 50%

u High side walls

(usually in excess of 6m)

u Increased floor slope

(generally between 30º-45º)

Lamella thickeners

GL&V

u Tanks, filled with a number of closely

spaced inclined plates

u Short settling distance to the upper

surface of each plate and then slide

down the inclined plate)

Main parts:

Vessel, Feed well, drive, rake, discharge

Types:

• Conventional thickeners: 30 - 200 m diameter

• High rate thickeners

• High compression thickeners (high)

• Deep cone thickeners, Rakeless thickeners

• Lamella, Flocculation is important (feed well design)

Thickener Design

Thickener - Design Considerations (1) • FEED

– Solids flux loading

– Volumetric flux

– Feed concentration

– Particle size distribution

– Particle density

– Particle charge

• UNDERFLOW

– Rate of underflow removal

– Underflow concentration

– Viscosity of underflow material

• FLOCCULATION

– Dosage

– Temperature and pH

– Concentration of stock solution

– Number of addition points

– Mixing conditions at addition points

– Flocculant type

• OVERFLOW

– Volumetric flux

– Clarity of overflow liquid

Thickener - Design Considerations (2)

• BED

– Bed height characteristics

– Concentration profile

– Bed rise velocity

– Compression effects

– Residence time

– Feed entry position (high rate thickening)

• TANK

– Size

– Depth

– Mechanism

– Rakes

– Underflow pumping arrangement

– Lifting device

– Efficiency of raking system

Sizing Thickeners: New or Variable Applications (Coal

Tailings)

• While laboratory tests are convenient and can provide a quick solution, the estimate of underflow density is usually conservative.

• This is especially the case with Paste applications.

• Pilot testing is recommended so the effect of compression and solids flux rates can be accurately determined. (6m bed depth can not be simulated in the lab)

• Most mine tailings have solids levels that are too high for efficient flocculation and settling. This results in higher floc usage and lower underflow density.

• It has been proven that manipulation and control of the feed density is a key to better thickener performance.

• In-thickener systems such as Autodil® and Turbodil® achieve feed dilution.

Design of the Thickener – feed

dilution

Flocculation – Solid Mineral in Suspension

• All solid minerals in suspension have a charged surface

• Number of charges and sign of charge depend on...

– pH

– Other ions

• Coal tailings generally negative in charge (except at very low pH)

Surface

of

Particle

Bound

Layer

Diffuse

Layer

Bulk

Solution

Double Layer

Plane of Shear

Distance from Particle Surface

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tia

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Zeta

Potential

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-

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+

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+

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+

+

+

-

+

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+

-

+

-

+

-

+

+

-

+

-

-

+

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+

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23 | |

Flocculation • What is a flocculant?

– Long chain polymer (hydrocarbon) with charged groups attached. Very large molecules with Molecular Weights in the millions.

• How does it work? – The chains ‘uncoil’ due to charged site repulsion and hydration effects

around the charge sites. – The large molecules can ‘reach’ out a long way and can interact with

multiple particles simultaneously holding them , drawing them together.

• Flocculation

• If the amount of flocculant is increased, the underflow density will increase to a peak.

• Above this flocc dose the underflow density decreases due to over flocculation and inclusion of excess water within the floccs.

• What types of flocculants are there? – Anionic, Neutral, Cationic, Different charge species on chain

determine category. Anionic and less so neutrals most common in mining. Cationic use rare for minerals.

24 | |

Coagulants – if flocculants don’t work

• Coagulants

• Uses

• Coagulants are used when the majority of solids flocculate and settle well BUT the background liquor is murky due to the presence of colloidal particles – very fine and well dispersed.

• The cheapest option is normally to use inorganic salts but these cannot always be used. Most common are Fe3+, Al3+ and Ca2+.

• Synthetic coagulants are very effective but increase the operating costs of the thickener.

• Unlike flocculants, too much coagulant can have a dispersing effect.

• Increase polymer dilution ............

• Reduce slurry agitation ...............

• Increase dosage slightly .............

• Multi-point addition ......................

• Change pH ..................................

• Dilute feed solids .........................

Improved polymer distribution

Larger flocs

Higher effective treatment

More effective conditioning to build larger flocs

Optimised performance of polymer

Reduced hindered settling

PROBLEM Suggested Action RESULT

SETTLING RATE TOO SLOW

SETTLING RATE TOO FAST

• Decrease dosage ........................

• Increase slurry agitation ..............


Reduced effective polymer dosage

Formation of large flocs prevented (flocculant capture maintained)

More flocculant available for particle capture where shear is high

Less for floc building where flocculant is low

Problems & Remedies: Thickener (2)

• Decrease dosage ........................

• Increase slurry agitation ..............


Reduced effective polymer dosage

Formation of large flocs prevented (flocculant capture maintained)

More flocculant available for particle capture where shear is high

Less for floc building where flocculant is low


SETTLING RATE TOO FAST


• Increase slurry agitation at floc addition points .............................

• Reduce slurry agitation at floc addition points .............................

• Increase number of addition points ...........................................

Increased particle contact with polymer

to allow capture

Overshearing and floc break-up prevented

Optimised particle contact Minimised effect of shear


POOR CLARITY (1 of 2)


• Increase dosage .........................

• Vary relative amounts at floc addition points .............................

• Vary pH .......................................

• Dual chemical program ...............

• Eliminate aeration

Increased effective treatment

Optimised floc capture conditions

Optimised charge characteristics to neutralise particle charge

Optimised coagulation and bridging characteristics


POOR CLARITY (2 of 2)


• Dilute flocculant and increase dosage .........................................

• Increase slurry agitation at addition points .............................

• Dilute feed solids ........................

• Reduce pumping rate .................

Improved settling and dewatering (check

for island formation)

Provided smaller but tighter flocs

Overcome rapid hindered settling

Longer compaction time given acceptable sludge level


UNDERFLOW DENSITY TOO LOW (1 of 2)



• Lower rakes ................................

• Increase molecular weight of flocculant .....................................

• Recycle underflow to feed (least favoured option) ...........................

Produced tight flocs Optimised settling sludge dewatering

If rakes are too high to pull sludge to centre

Higher settling rate Better compaction

Increased feed solids density Increased floc density


UNDERFLOW DENSITY TOO LOW (2 of 2)

• Raise rakes .................................

• Reduce polymer dosage .............

• Increase pumping rate ................

• Add water to pump suction .........

Reduced torque

Reduced effective treatment

Reduced solids in thickener

Reduced percent solids

31 | |

Sizing Thicker on solids flux rate

m 40.5 m 1286 x 4

Area x 4

(m)Diameter

use ediameter w a toarea required econvert th To

m 1286 t0.35

hm x

h

t450

have we then,solids of tph 450say For

:h t/m0.35on based sized be should thickener theshown that hasTest work

2

AreaThickener

2

AreaThickener

solid

2

AreaThickener solid

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m 13.5 m 142.9 x 4

Area x 4

(m)Diameter

use ediameter w a toarea required econvert th To

m 142.9 m 3.5

hm x

h

m 500

have wesolids), %w/w low(at slurry'' feed of/h m 500say For

hm/m 3.5 of Loading Volumetric a toequivalent is Rate Risem/h 3.5A : Note

:m/h 3.5 of rate rise aon based sized be shouldclarifier theshown that hasTest work

2

AreaThickener

2

AreaThickener 3

slurry

2

AreaThickener

3

slurry

3

23

Sizing Thickener / Clarifier on liquid rise rate

Advantage of Fluidised Beds

• Drying in fluidised beds: Compact, simple and relative

low capital cost Absence of moving parts => low

maintenance Relatively high thermal efficiency Gentle powder handling

• Chemical reaction in fluidised beds: Good gas-solids contact Good heat transfer due to good

mixing Near isothermal conditions

possible due to good heat exchange (good control)

• Simple removing of solids from the reactor

Outcome / Expectation Fundamental understanding

(Fluid flow) Fluid flow: minimum

fluidisation & bubbling velocity

Expansion of Fluidised beds

Fluidised bed designs and shapes Mostly circular. Why?

Freeboard, wider diameter at top

Solids separation (cyclone)

Fluidised bed types such as circulating

Design examples

Fluidised bed in flowsheets:

• The gas / overflow from a fluidised bed usually has to be cleaned. This could be achieved by gas cyclones, bag house or scrubbers.

• Heat exchange could be done directly inside the fluidised bed (e.g. heat exchange pipes inside)

Fluidised Bed: Minimum Fluidisation velocity (2nd year)

Fluidised Bed: Expansion

Fluidised Bed: Expansion

A fluidised bed with powder A is working

(designed) and does not bubble. Production of

powder A changes, now the fluidised bed

bubbles, all other fluidisation properties stay the

same.

What design differences are required for the

fluidised bed?

What equal “fluidisation parameters” are necessary to have the same fluidisation?

Overview of Filtration Processes Separation: No cake formed Cake formation Deep granular beds Pressure Cartridge filter Vacuum Gravity Centrifugal batch and continuous

Solid-Liquid Separation Driving Forces

Gravity (drainage) e.g. on stockpile, bunker Vacuum

(sucking water + air through the filter cake) Mechanical pressure (squeezing) Slurry pressure (pumping through filter) Air pressure

(blowing water, air through the filter cake) Centrifugal force

(spinning packed bed in a perforated bowl) Deep Bed Filtration Applications:

Liquor clarification (polishing) after leaching Wastewater treatment Solids removal (valuable solids) Nutrient removal

(chem. precip. phosphorous) Operation: • Filtration Phase (collecting solids inside the bed) • Cleaning Phase or back-washing (removing trapped solids from the bed)

Laboratory Filter for determining filtration rate

Filtration rate (mass of filtrate versus time and filter area)

Cake formation time / drying Gas flow rate to design vacuum pump Final cake moisture (wt%) Specific filter cake resistance rc Filter media resistance Rm in (1/m)

Effect of Filtration Parameters • Operating Parameters – Pressure drop across the cake – Filter speed (interrelated with cake thickness and filtration time) – Trough slurry level for rotary filter • Material Properties – Feed size distribution, Feed solids concentration, Feed composition (ash, mineralogy, shape, hydrophobicity…) – Flocculation, Viscosity and Temperature • Design Parameters – Maximal filter speed – Filter cloth permeability

Mineral Processing

Introduction and Overview

Comminution Crushing and Grinding

Sizing Screening and Classification

Beneficiation Density Separation, Magnetic Separation Flotation, Sorting

Solid / Liquid - Separation Thickening, Clarification Filtration, Centrifugation

Tailings Handling and disposal

Storage and Transport

Schematic of mining-processing

Mining

Crushing

Grinding

Beneficiation

Solid/Liquid

Separation

Water

Tailings

Roasting Leaching

Chemicals

Solid/Liquid

Separation Purification Product

Recovery

Tailings/Waste

Solid/Liquid

Separation

Mineral Processing Flowsheet and

Equipment

COMMUNITION - Crushing

• Crushing reduces ROM ore to -10mm to -15mm • Usual • ly involves several stages - primary, secondary,

tertiary if needed, reduction ratio about 3:1 to 4:1 each stage

• Screening between stages to bypass fines and recycle oversize

• Typical crushers: jaw (primary), gyratory (secondary)

COMMINUTION - Grinding

• Reducing particles to micron size

• Grind to liberation size (P80 < 75 microns)

• Multi stages, SAG mills, rod mills, ball mills, etc

• Classification by hydrocyclones to recycle oversized materials

• Grinding also liberates unwanted impurities

Crushing Practice

Jaw crusher primary

Gyratory crushers primary

Cone crushers secondary

Roll crushers soft e. g. coal

Impact crusher

Hammer mills

High pressure grinding rolls

Shredders recycling

(d)

Crushers

Grinding Practice

Ball mill

Rod mill

Autogenous mill

Semi-autogenous mill (SAG) N>Nc

High pressure grinding roll

Critical ball mill speed:

D [m], Nc[rpm] D

42.3 Nc

Grinding Practice

Ball mill - using steel or other balls as

media

Rod mill - using steel rods as media

Autogenous mill (+ no Contamination)

using coarse product as media

(sandstone lumps used to grind sand)

Semi-autogenous mill (SAG) N>Nc

using coarse product and steel balls as medium size is not grind autogeneous

For Example

1m sample to 200μm

1. Primary Crushing (RR 5:1),

2. Secondary crushing (RR 5:1)

3. Tertiary crushing (RR 5:1),

4. Primary grinding (RR 20:1)

5. Final grinding (RR 20:1)

1m→0.2m→0.04m→0.008m→0.0004m→0.00002m

Volume occupied by the broken particles is significantly larger than the

uncrushed rock.

O/F

U/F

O/F

U/F Conventional circuit for hard rock

Comminution PSD

Q3(d)

d

100%

0%

Feed

Product A

Product B

Comminution PSD

Q3(d)

d

100%

0%

Smaller PSD with increasing time and/or mixing energy

Crushing and Grinding Practice

Wear and tear is high, spare parts

Liners used in ball mills to reduce wear

and tear

Replaceable liners or parts in mills

Ball

Crushing and Grinding Practice

Sizing

Sizing by Classification or Screening

separation depending on particle size

large (coarse) / small (fines)

Reduce loading of mill

Recycle coarse

Feed coarse and fines to different mills

Sizing and Classification

Grizzlies: Static coarse Vibrating

Screens: Vibrating screen coarse/medium

DMS sieve bend

Banana screens

Classification (Particles in a fluid)

Hydrocyclones: fines

Elutriators and others: accurate fines

VIBRATORY MOTIONS ON INCLINED SCREENS

Elliptical motion

15-20°

Straight line motion

15-20°

Circular motion

15-20°

Single Slope Screen

Feed 0.5m/s

Screen

Zone 1

Zone 2 Zone 3

Screen length

Vibrating Banana Screen

Zone 1

Zone 2

Zone 3

Screen length

3 - 4 m/s

1 - 2 m/s

0.5 - 0.8 m/s

Banana Screen

LINEAR MOTION ON A MULTISLOPE SCREEN

30°

25°

20° 15° 0°

Sizing / Classification PSD

Q3(d)

d

100%

0%

Feed

Product A

Product B

Beneficiation Recovery Definition

How much of the fed valuable do I recover in the product?

Recovery = Valuable in Product/Valuable in Feed

= 9 t/h / 10 t/h = 90% Recovery

Benefication Black Box

Feed 100t/h 10% gold =10t/h gold Tailings

Product 10t/h 90% gold =9t/h gold

Feed Product

How much of the fed valuable do I recover in the product?

Recovery

Principle:

• Float/sink method rely on differences in

specific density of minerals

Practice:

similar devices used for size classification

• Jigs (coarse size) pulsing bed on a screen

• Flowing film separators

• Drums, cones, cyclones

Gravity Separation

1) Jigging

• Oscilating jig up and down under water in the

denser and larger particles forming the low layers,

with the finer lighter particles on top.

• Two stage strokes:

1. pulsion stroke - particle bed elevated above jig plate

2. Suction stroke - particles settle back on the plate

http://www.youtube.com/watch?v=9gqzvTMnhVQ










Start

Differential

Initial

Acceleration

Hindered

settling Consolidated

trickling

Ideal Jigging Process

2) Shaking tables

Flowing film type separator - heavy minerals

The separation is controlled by

1.operating variables-wash water, feed pulp

density, deck slope, amplitude, feed rate

2. particle shape and size of ores, type of

deck

Flowing Film Separator Principal

Heavy mineral deposits such as ilmenite, rutile,

zircon, monazite

Modified semicircular cross-section

Ore introduced on top of spiral - it flows

spirally downwards - the particles stratify

due to centrifugal force - the differential

settling rates of the particles

3) Spiral

Flowing Film Separators

Humphrey’s Spiral

• Size of –3 – 0.075 mm.

• Spirals are often applied in stages such as rougher-, scavenger- and cleaner stage

• (Coal usually 1 or 2 stages, beach sand usually more stages).

-heavy mineral separations

-an inclined launder about 1m long, narrowing from

about 200 mm in width at the feed end to about

25mm at the discharge.

Pinched sluices

Gravitational force + centrifugal force

The way how it works.

1. Water is injected into rotating cone.

2. Once sample reaches the bottom of the

cone, high gravity particles are retained

in the cone as low gravity particles are

floated out.

3. high gravity particles are recovered

from the cone wall.

5) Knelson Concentrator

Dense or Heavy Media Separation

• Magnetite Fe3O4 SD = 5100 kg/m3

applied for coal SD 1450 kg/m3

• Ferrosilica FeSi SD = 6700 kg/m3

(with ca 15 % Si)

Practice:

• TESKA and Daniels Bath (gravity)

• Cyclones, LarCoDem (centrifugal)

Heavy Media Cyclones

Sorting - Principles Using different physical

properties to sort

materials:

• optical characteristics

(colour, shape)

• magnetic susceptibilities

• x-ray fluorescence

• radioactivity

• electrical and thermal

conductivity

• electrical charging

Sorter functions:

singulation - detection -

ejection

Practice:

Hand and machine sorting of

diamonds, glass, coal, radioactive

material

(PET bottles, plastics, recycling of

waste)

Magnetic Separators Principles

Paramagnetic materials:

e.g. hematite, ilmenite ... attracted by a magnetic field

Ferromagnetic materials:

iron, magnetite very strongly paramagnetic materials

Diamagnetic materials

quartz and feldspar repelled by a magnetic field

Practice

• Wet drum low intensity magnetic separator

• Wet high intensity magnetic separators (WHIMS)

Electrostatic Separation

Principles

Electrostatic charges result in separation

• Particle charging (induction, ion bombardment, contact)

• Separation at a grounded surface

• Separation by trajectory of particles

Practice

• Dynamic/High Tension: ionizing electrode

• Static/Conductive: induction

Wet Magnetic Separation

Electrostatic Separation

Typical beach sand treatment flowsheet

MAGNETIC AND ELECTRICAL SEPARATION • Dry or wet low intensity, or wet high intensity mag. sep’n,(WHIMS) - relies on

different magnetic susceptibilities

• Electric separation ( High tension separation) relies on forces acting on charged or polarised particles for separation

FLOTATION

• Relies on air bubbles to float mineral particles for collection as concentrates

• Add reagents to enhance collection (collectors) and to stabilise froth bubbles (frothers)

• Types: Conventional, column, Jamieson cells

• Produces sulphide concentrates - Cu 20% to 30% (from <2% in ores), Pb 60% to 70% (from 5%), Zn 48% to 60% (from 5%), Ni 10% to 20% (from <2%)

LEACHING • Chemical process of extracting

metal from ores using extractants (acids, bases, oxidants, reductants)

• May involve use of pressure vessels (most expensive), stirred reactors, or heaps or dumps (cheapest)

• Impurities may be leached with target metal

SOLVENT EXTRACTION (SX)

• Selectively removes target metal from pregnant leach liquor via an organic extractant

• Extensively used for copper

and nickel recovery, e.g. using oxime chemicals to extract Cu from 2g/L leach liquor and concentrate to 50g/L, or D2EHPA to upgrade Ni from 3g/L to 100g/L

• SX is also used extensively

for processing PGMs and rare earths

ADSORPTION / ION EXCHANGE • Activated carbon and ion

exchange resins are used to uptake metals from dilute solutions e.g. activated carbon is used to adsorb gold cyanide from pulp slurry in the CIP process

• The loaded materials are then stripped to recover metals in more concentrated forms

• Similar processes are used in waste water treatment

ELECTROWINNING (EW)• Recovers high purity metals by

DC electrolysis of high purity liquors (Cu, Zn, Ni, etc.)

• Products: 99.99+%Cu, 99.9% Zn

• Acid is produced during EW of Cu, Zn, etc. for recycling to leaching

• Energy consumptions: 2.5 kWh/kg Cu, 3.5 kWh/kg Zn, 12 kWh/kg Al (high temp melts)

ELECTROREFINING • Used for refining smelter products – upgrading cast

smelter anodes (95% Cu) to 99.99+%Cu cathode

• Cells dissolve copper anodes and plate copper cathodes, simultaneously

• By-products: Au, Ag and other PGM’s

• Energy consumption: 0.25 kWh/kg Cu as cells require lower voltage.

PRECIPITATION

• Achieved by adding chemicals (sulphide, hydroxide, hydrogen) to solution, precipitating the target metal as a solid (metal hydroxide, sulphide or pure metals)

• Used for liquor purification (as in water treatment) or for recovering products (production of alumina, Al2O3).

CEMENTATION • Achieved by adding a less valuable metal (A) to the solution (higher reduction

potential) • The target metal (B) electrochemically cements onto the remainder of A • Used for liquor purification (cementation of Ni, Co, etc. from zinc sulphate

liquors using zinc powder) or for product recovery (gold recovery using zinc or copper powder) PYROMETALLURGICAL PROCESSING

• Roasting - apply high temperatures (9000C) to convert sulphides to oxides,etc.

• Smelting - to melt and separate metals from slag (e.g. to produce blister copper)

• Calcining - heating to drive off water or carbon dioxide

• Sintering - heating with binder to convert fines to lumps

ACID MINE DRAINAGE produces acid and liberates base

metals back to soils

caused by bacterial/air oxidation of

sulphidic materials

minimised by encapsulation and

additives

treated by neutralisation ponds

CYANIDE MANAGEMENT • NSW-EPA sets 20-30 ppm CN (weak

acid dissociable) for tailing disposal

• Currently relies on cyanide

destruction techniques (Degussa or

Interox: H2O2, hypochlorite, INCO:

SO2/air)

• New technologies:

– Elutech (resin technology)

– Occtech (membrane technology)

RESIN TECHNOLOGY

Recovers gold and other base metals as products

-Recovers cyanide as HCN for recycling

-Discharges to tailings contain less than 5 ppm CNwad (May Day Mines)

-Yet to be accepted by industry

Documents

Cheat Sheet for Separation processes - chemical engineering