EBS 315 L2- Intro Hydrometallurgy ( 13 Sept 2012)

SCHOOL OF MATERIALS & MINERAL

RESOURCES ENGINEERING

EBS 315/3:

HYDROMETALLURGY

SMMRE

Academic Session 2012/13

Lecturer: Dr. Norlia Baharun

1.0Introduction to Hydrometallurgy

Material Sources for Hydrometallurgical Processing

INTRODUCTION

13 Sept 2012EBS 315 Chapt 1

Slides 1-553

Terms MeaningMineral A naturally occurring compound

Ore deposits A naturally occurring aggregate of minerals from which one or more metals or minerals may be extracted economically

Ore minerals Useful minerals obtained when the ore deposits are exploited

Gangue Minerals Waste products

SECTION TOPIC CONTENTS

1.1 Mineral Reserves and Resources

1.2 Principle and uses of Hydrometallurgy and Electrometallurgy

1.3 Hydrometallurgy vs Pyrometallurgy

1.4 Reclamation and Recycling, Advantages and Importance of Hydrometallurgical Processing

1.5 Advancement in Hydrometallurgy / Electrometallurgy


Slides 1-554

INTRODUCTION

• Extractive Metallurgy deals the extraction and refining of metals

• It is also discipline in Engineering • Some of the principles of extractive metallurgy that

governs the extraction and refining processes were based on the scientific basis of the subject – using principles of physical chemistry

• The outcome from this is the development of the subject known as Chemical Metallurgy

- which deals with the chemical fundamentals of metallurgy


Slides 1-555

INTRODUCTION

• In Extractive Metallurgy, heat and mass transfer, momentum as well as mathematical techniques constitute the engineering fundamentals & the application of these has led to the development of the subject termed as Process Engineering Metallurgy

• Physical chemists, chemical and other Engineers have played significant roles besides the Metallurgist

• Extractive Metallurgy is multi-disciplinary in nature


Slides 1-556

1.1 Mineral Reserves and Resources

1.1.1 Natural Occurrence of Metals• Naturally occurring Minerals – oxides, sulphides and

halides in simple chemical composition [eg: hematite: Fe2O3 , chalcopyrite: CuFeS2, dolomite:

CaMg(CO3)2 ]

• Most abundant minerals: silicates• The exact nature of association of a metallic element

with other elements depends on the reactivity of the metal, distribution of other elements in the neighbourhood as well as the geological conditions to which the mineral deposites are subjected through the ages


Slides 1-558

1.1.2 Sources of Metals• Metals and their compounds are available from three

sources: (i) Ore deposits in the Earth’s crust (ii) Ocean waters (iii) Scrap metals – A man-made source which is getting more important and freely available with the industrial growth of societies


Slides 1-559

1.1.1 Sources of Metals• Increasing amounts of scrap are being recycled in

technologically developed countries. • Reclaimed and recycled lead and Aluminum

constitute about 50% of feedstock for production of respective metals in UK and USA.

• Table 1.1 and 1.2: show the average chemical analysis of the Earth’s crust and the sea water respectively.

• There are several hundred billion tons of nodules in the ocean floor and they continue to form at the rate of about 10m tons/yr

• Table 1.3 – gives some figures to indicate the reseves, the composition and the relative abundance of nodules as compared to deposits in land


Slides 1-5510

Table 1.1: Average analysis of the Earth’s Crust

Element Percent Element Percent

O 46.7 Cr 0.01

Si 27.7 Cu 0.01

Al 8.1 Ni 0.008

Fe 5.0 Zn 0.004

Ca 3.6 Pb 0.002

Na 2.8 Co 0.001

K 2.6 Be 0.001

Mg 2.1 Mo 0.0001

Ti 0.44 Sn 0.0001

Mn 0.10 Hg 0.00001

Zr 0.017 Ag 0.000001

V 0.014 Pt 0.0000001

Au 0.0000001


Slides 1-5511

Table1.2: Average concentration of some elements present in solution in sea water

Element Concentration(g/tonne)

Element Concentration(g/tonne)

Na 10,500 Zn 0.005-0.014

Mg 1,270 Cu 0.001-0.09

Ca 400 Mn 0.001-0.01

K 380 Pb 0.004-0.005

Al 0.16-1.9 Sn 0.003

Li 0.1 Ni 0.0001

Si 0.02-0.04 Au 0.000005

Fe 0.002-0.02


Slides 1-5512

Table 1.3: Reserves of Metals in Pacific ocean nodules

Element Wt % in nodule Estimated reserve (109 tonnes)

Ratio of Nodule reserve

Land reserve

Mg 1.66 25 -

Al 2.86 43 200

Ti 0.66 9.9 -

V 0.05 0.8 -

Mn 23.86 358 4000

Fe 13.80 207 4

Co 0.35 5.2 5000

Ni 0.98 14.7 1500

Cu 0.52 7.9 150

Zn 0.46 0.7 10

Zr 0.06 0.93 1000

Mo 0.05 0.77 60

Ag 0.0001 0.001 1

Pb 0.09 1.3 5013 Sept 2012EBS 315 Chapt 1

Slides 1-5513

1.1.2 Commercial Production of Metals

• The availability of metals for use is not only governed by its abundance alone

• As shown in Table 1.4, although Cu is the third tonnage metal after Fe and Al, its concentration in the Earth’s crust is quite low (only about 0.01%)

• Tonnage of metal depends on: - Accessibility of ore deposits - Richness of the Ore deposits - Nature of extraction and refining processes for the metal - physical and chemical properties of the metal and - demand for the metal which is governed by many factors including its physical and chemical properties of the metal


Slides 1-5514

• A fundamental consideration in all the above mentioned factors, is of course, economics.

• A metal becomes a common one, if it is readily available and easily produced with low processing cost and if it allows development of attractive properties

• Table 1.4 presents approximate world production figures for some metals

• It is seen that, iron as steel is by far the most widely produced metal.

• This is so because, iron ores are available in plenty in easily accessible deposits.

• Also, the processing of iron ores, is relatively easy and economical.

• Finally, alloy of iron has a wide range of useful properties


Slides 1-5515

Table 1.4: World Production of some metals (1985)

Metal/Alloy Production (Thousands metric tonnes /year)

Raw steel 12,230

Pig iron 11,590

Al 240

Cu (blister) 39

Cu (electrolytic) 22

Zn 61

Pb 30

Sn 0


Slides 1-5516

• Because of the importance of iron and steel, Ferrous Extractive Metallurgy, is a subject on its own right

• The non-ferrous metals which are produced in large quantities include metals such as, Al, Cu, Pb and Zn

• The non-ferrous metals strictly means all metals other (common metals) than iron

• But mMetals such as thorium, Vanadium, which are not commonly used, which are far more expensive, are commonly referred to as rare metals or less common metals


Slides 1-5517

1.2 EXTRACTIVE METALLURGY – A process of separation

• Any extraction and refining process consists of some individual sequential steps: unit steps.

• Each unit steps can be found in more than one process

• For eg: (i) electrolysis is practised for Al, Zn, Cu and a variety of other metals (ii) smelting is carried out for the extraction of Fe, Pb, Cu etc.• The various extraction and refining routes are formulated essentially by the

selective combination of these units• The unit steps are classified into: Unit Operations and Unit processes


Slides 1-5518

1.2.1 Unit Operations & Unit Process

• It refers to physical operations such as comminution, filtration, casting, distillation etc.

• In all subsequent discussions, the term ‘process’ will be used to mean both unit operation and unit process


Slides 1-5519

1.2.2 Separation process

• Production of metals of desired purity from natural ores is principally a separation process

• The separation process may be classified into two stages:

(1) Separation of the compound containing the desired

metals from other constituents. It is the separation of ore mineral from other gangue minerals. This is known as Concentration and it comes under the discipline of Minerals Engineering


Slides 1-5520

1.2.2 Separation process

(2) Separation of the desired metal from other constituents of the metallic compound and

further purification of the metal. This is known as Extraction and Refining

and constitutes the subject matter of

Extractive Metallurgy


Slides 1-5521

1.2.2 Separation process• For some metals such as Al, the two stages are

distinct• Pure alumina (Al2O3) is produced by the Bayer’s

process from the ore. The Al metal is extracted by electrolysis.

• However, for Fe, there is no separate concentration step for the production of iron from high grade ores.

• The gangue materials are by and large separated during extraction in the blast furnace.

• Lean ores may, however, require beneficiation13 Sept 2012

EBS 315 Chapt 1 Slides 1-55

22

1.2.3 Classification of Processes

• Processes can be classified in various ways depending

on the aim• Traditionally, methods of extraction and refining

have been classified into the following categories: Pyrometallurgy

Hydrometallurgy Electrometallurgy


Slides 1-5523

• Pyrometallurgical processes (in Greek, ‘pyr’ means ‘more at fire’) are carried at high temperatures.

• Hydrometallurgy (in Greek, ‘hydro’ means ‘ more at water’) is carried out in aqueous media at or around room temperature

• Electrometallurgy employs electrolysis for separation at room temperature as well as at high temperature


Slides 1-5524

Another way of classification:

In terms of unit operations or unit processes, pyrometallurgy can be classified as follows:

1. Solid-state processing : This does not involve any melting. It is typically carried out in the temperature range of 500-1200 ºC, as exemplified by roasting of sulphides, calcination, solid state reduction of metal oxides by H2 and CO. Solids are mostly immiscible and hence the product of solid state processing is either pure or is a mechanical mixture. In the later case, it requires further separation.


Slides 1-5525

2. Liquid-state processing: This involves melting of at least the metal-containing phase and is carried out at a higher temperature.

Examples are blast furnace smelting, steelmaking, distillation refining of zinc from impure

lead etc. Liquid state processing separates out the metal either

in pure or in impure form. Appreciable compositional changes in the liquid are possible due to miscibility, rapid diffusion and mixing.


Slides 1-5526

• This system of classification can be extended to hydro and electrometallurgy as well.

• Processes can be also classified according to type of chemical reaction, mode of energy input etc.

• Based on all the above discussions, an attempt has been made to characterise some important unit processes and unit operations in Extractive Metallurgy as shown in Table 1.5


Slides 1-5527

Table 1.5: Characteristics of some unit processes and unit operations

Name of Process Broad Classification

~ Temp Range (ºC)

Type of Chemical Rxn

Purpose Mode of Energy Input

Contacting Phases

Typical Reactors employed

1 2 3 4 5 6 7 8

Roasting of sulphide

Pyromet, unit process, solid-state

processing

500-1200 Oxidation Pretreatment Fuel, exothermic heat of rxn

Solid, gas Shaft furnace, fluidized bed reactor, flash roaster, rotary kiln

Calcining -do- -do- Decomposition -do- Fuel -do- -do-

Carbothermic smelting

Pyromet, unit process, liquid-state processing

1200-1600 Reduction Extraction Fuel, electrical energy

Solid, liquid, gas

Blast furnace, retort, electric arc furnace

Metallothermic reduction of metal oxides,

chlorides

-do- 900-2400 -do- -do- -do- -do- Bomb, retort

Leaching Hydromet, unit proces, solid-state

Room temp.-200

Dissolution Pretreatment Fuel, electrical energy

Solid, liquid Vats, autoclaves

Distillation, refining

Pyromet, unit process, liquid-state processing

1000-2000 -do- Refining Fuel, sensible heat of input

materials

Liquid, gas Retort

Solvent Extraction

Hydromet, unit proces, liquid-state

processing

Room temp. Exchange Pretreatment Nil Liquid Packed bed, plate column

Electrolysis Electromet, unit proces, solid or

liquid-state processing

Room temp.-900

Electrochemical Extraction. Refining

Electrical Solid, liquid Electrolysis tank


Slides 1-5528

1.2 Principles & Uses of Hydrometallurgy &

Electrometallurgy

HYDROMETALLURGY

• The development of extractive metallurgical processes for reactive metals and nuclear metals after 1940s gave a great filip to the more sophisticated hydrometallurgical methods

• The early applications were mainly for oxide ores or native metals


Slides 1-5530

HYDROMETALLURGY

• Later applications: - Leaching of sulphide ores by oxidizing leachants

like ferric salts

- Ammoniacal pressure leaching (Sherritt Gordon processes) for nickel-cobalt sulphides and arsenides during 1946-55 - Pressure leaching of sulphide ores and concentrates also was actively pursued around 1950 onwards


Slides 1-5531

HYDROMETALLURGY

• The extraction of metals by using aqueous methods, as against pyrometallurgy where reactions at much higher temperatures are involved

• In hydrometallurgy, the ore is ‘leached’ i.e. dissolved slowly using suitable economical leaching agents, which could be acids, alkalis, salts or complex chemicals.


Slides 1-5532

HYDROMETALLURGY

• After leaching, the solutions are purified, concentrated as necessary and may also undergo solid-liquid separation. The metal is recovered from the purified, concentrated solution by precipitation and reduction methods


Slides 1-5533

1.3 Hydrometallurgy Vs Pyrometallurgy

Advantages of Hydrometallurgy

• Metals can be obtained directly in the pure form from the leach solutions, without any lengthy refining process.

• The interest in hydrometallurgical approach grew as the pressure of environmental regulations against the SO2 pollution in sulphide ore pyrometallurgy became a major issue.

• But with developments such as double contact acid plants, modern pyrometallurgical plants are able to meet SO2 requirements.


Slides 1-5536

Advantages of Hydrometallurgical Approach

Hydrometallurgical processing is characterized by several distinct advantages:

1. Hydrometallurgical methods are suitable for lean and complex ores. With gradual depletion of rich ore deposits, it is becoming increasingly difficult in many situation to apply conventional pyrometallurgical methods for metal extraction


Slides 1-5537

Advantages of Hydrometallurgical Approach

If there are too much gangue, then processing of ores at high temperatures causes wastage of energy as well as problems of slag disposal.

The siliceous gangue in ore is unaffected by most leaching reagents; whereas in pyrometallurgical smelting processes, the gangue must be slagged.


Slides 1-5538

2. Hydrometallurgy allows greater control over every step in processing of ores, resulting in recovery of valuable by-products. Metals may be obtained directly in a pure form from the leach liquor using one of several methods. Handling of materials is also easier.

3. Hydrometallurgical operations are often preferable from the point of view of reducing environmental pollution. Thus, while pyrometallurgical processing of sulphide ores eg: copper ores produces SO2 , the leaching of ores keep sulphur in solution.


Slides 1-5539

SO2, liberated during roasting of sulphides as well as during the other steps in pyrometallurgical processing, is not always suited for use in H2SO4 production. Even if it is used in acid production, there is still also SO2, escaping into the air, unless stringent anti-pollution measures are effected.

4. A hydrometallurgical process may start on a small scale and expand as required. However, a pyrometallurgical process usually must be designed as a large scale operation for reasons of process economy


Slides 1-5540

There are advantages as well:5. For example, in some hydrometallurgical recovery,

the metal can be produced in a variety of physical forms eg: powder, nodule, coherent surface deposits etc.

6. Again, very reactive metals are difficult to refine by pyrometallurgical methods. Therefore, pure compounds can be first obtained by hydrometallurgy and then reduced to pure metal.


Slides 1-5541

7. Also, corrosion problems are relatively mild in hydrometallurgy as compared with deterioration of refractory linings which requires periodic shut down in pyrometallurgy.


Slides 1-5542

Disadvantages of Hydrometallurgy

1. Aqueous solutions employed are generally dilute (1 Molar). Thus, large volumes of solutions are to be handled for relatively, smaller metal outputs. This requires considerable amount of handling as well as space.

2. Some reagents are expensive and must recycled or regenerated for economy.

3. Reactions rates are lower at room temperatures as compared to processing at high temperatures. Hence, tonnage capacity of a plant is lower as compared to that obtainable in pyrometallurgy


Slides 1-5544

3. Reactions rates are lower at room temperatures as compared to processing at high temperatures. Hence, tonnage capacity of a plant is lower as compared to that obtainable in pyrometallurgy .


Slides 1-5545

• With reference to the environmental aspects, though hydrometallurgical approach avoids sulphur emissions, the effluents carry heavy metals and must be carefully treated or impounded.

• The gangue rejected by hydrometallurgy in the form of active iron oxides and jarosites can create a considerable cost burden.

• One may even argue that the slags in pyrometallurgy can be relatively non-reactive and can be easily stored.


Slides 1-5546

From the energy point of view:

• Many have the misconception that since pyrometallurgy involves high temperatures, it requires much more energy per metric tonne of metal as compared to hydrometallurgy

• It is true that, since most hydrometallurgical processes are carried out at room temperatures, there is no direct consumption of large amounts of fuel.


Slides 1-5547


However, correct comparison may be state asfollows: 1. For direct treatment of low-grade ores,

pyrometallurgy is inapplicable and therefore, there can be no comparison.

On the other hand, for recovery of metals from high-grade ores and concentrates, both methods are feasible.


Slides 1-5548

From the energy point of view:But, with one or two possible exceptions, pyrometallurgy requires less energy than hydrometallurgy to produce one metric tonne of metal. The lower energy requirements of many pyrometallurgical processes as compared to hydrometallurgy are ascribed to the following beneficial factors in the former:

1. concentrated process streams2. accelerated reaction rates and reduced residence

times which increase throughput and3. exothermic nature of many reactions13 Sept 2012

EBS 315 Chapt 1 Slides 1-55

49


• Also, heating, evaporation and steam stripping of aqueous solutions in hydrometallurgy are energy-intensive despite the low temperature involved.

• Finally, electrowinning, the most used means of metal recovery, is also energy-intensive. Table 1.5 and Table 1.6, present some data on comparative intensity and energy requirements of the two routes, respectively.


Slides 1-5550

Table 1.5: Intensity of Pyrometallurgical and

Hydrometallurgical ProcessesProcess Concentration g.mole/m3

X 10-3

Productivity, metric tonne/day/m3

(a) Pyrometallurgy: Iron blast furnace, less

auxiliaries. Iron blast furnace, with

stoves, dust system. Flash smelting of Cu

with O2, less auxiliaries Flash smelting of Cu

with O2, including dust collection system

1500 -

1100

-

1.6

0.4

1.0

0.4


Slides 1-5551

Table 1.5: Intensity of Pyrometallurgical and

Hydrometallurgical ProcessesProcess Concentration g.mole/m3

X 10-3

Productivity, metric tonne/day/m3

(a) Hydrometallurgy: Leaching zinc calcine,

purifying solution. Electrowinning of zinc Electrowinning of

Copper

150 75

35

0.10

0.08

0.04


Slides 1-5552

Table 1.6: Energy requirements for metal production from concentrates per metric tonne of metal

Process Product Energy requirements (J) 109 per metric tonne metal

(a) Pyrometallurgy: Fe: Blast furnace-

oxygen steel making Cu: Flash smelting (O 2)

– converting electrorefining

Pb: Blast fiurnace dross –fire refining

Zn: ISP blast furnace-reflux

Steel Ingot

Cathode Cu

Refined Pb

Special high grade Zn

22

23

21

51


Slides 1-5553

Table 1.6: Energy requirements for metal production from concentrates per metric tonne of metal

Process Product Energy requirements (J) 109 per metric tonne metal

(a) Hydrometallurgy: Cu: Leaching of

sulphide concentrate

Zn: Roasting – Leaching - Electrowinning

Al: Bayer leaching-Hall

electrolysis

Cathode Cu

Special high grade Zn

Al ingot

~ 100

55

280


Slides 1-5554

On the whole, however, the advantage often outweigh the disadvantages and hydrometallurgy is becoming increasingly important for many non-ferrous metals.

The choice therefore is made on the basis of specific details of a particular process and its technical and

economic viability for a plant at a given location


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Documents

EBS 315 L2- Intro Hydrometallurgy ( 13 Sept 2012)