URANIUM SOLVENT EXTRACTION USING TERTIARY AMINES

URANIUM SOLVENT EXTRACTION USING

TERTIARY AMINES

by:

Dr J.M.W. Mackenzie

Manager Mining Chemicals

Henkel Australia Pty Ltd

PRESENTED AT

Uranium Ore Yellow Cake Seminar

February 1997

Melbourne, Australia

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Table of Contents

1.0 INTRODUCTION AND HISTORY .............................................................................................. 3

1.1 INTRODUCTION .................................................................................................................... 3

1.2 HISTORY ................................................................................................................................ 3

2.0 ACID LEACH CHEMISTRY FOR URANIUM ......................................................................... 4

3.0 TERTIARY AMINE EXTRACTION OF URANIUM ............................................................... 5

3.1 TYPE OF AMINE USED AND MAXIMUM LOADING CAPACITY .................................. 5

3.2 THE EFFECT OF COMPETING ANIONS ............................................................................. 6

3.3 DILUENTS AND THIRD PHASE INHIBITORS OR MODIFIERS....................................... 7

3.4 SECONDARY AMINES .......................................................................................................... 8

4.0 GENERAL CONCEPTS OF TERTIARY AMINE URANIUM ....EXTRACTION CIRCUITS

9

4.1 GENERAL CIRCUIT LAYOUT.............................................................................................. 9

4.2 LOADED ORGANIC SCRUBBING...................................................................................... 10

4.3 STRIPPING ............................................................................................................................ 10

4.4 REGENERATION OR SCRUBBING OF THE STRIPPED ORGANIC............................... 11

5.0 ASPECTS OF EQUIPMENT SELECTION AND PLANT DESIGN FOR TERTIARY

AMINE URANIUM SX CIRCUITS .................................................................................................. 11

6.0 SPECIAL PROBLEMS DUE TO ORGANIC CONTAMINANTS AND CRUD ................... 12

REFERENCES ................................................................................................................................... 13

TABLES AND FIGURES................................................................................................................... 15

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1.0 INTRODUCTION AND HISTORY

1.1 INTRODUCTION

Uranium was the first metal to be recovered in significant quantities

using solvent extraction. Much of the copper SX equipment technology

is a development from existing uranium technology. Because the

kinetics of extraction via an ion exchange mechanism are much faster

than for a chelation mechanism the mixer residence times are much

longer for copper SX than for uranium.

1.2 HISTORY

Following the development of the nuclear industry during and

immediately after World War II, attention was focussed on developing

technologies which could be used to upgrade and purify uranium from

low grade sources. Initially the nuclear industry had relied on high grade

uranium ores from the Belgium Congo and Canada. One of the main

participants in this development was the Union of South Africa and the

then Prime Minister, Jan Smuts, visited MIT in the USA in this regard.

Research in the USA lead to the first commercial use of amines in

uranium concentration at West Rand Consolidated Mines in South

Africa in 1952. The amines used in this plant were in the form of a

strong base resin and it was not until 1957 that the first commercial

solvent extraction plant using amines was opened in the USA.

Since those early days, the development of uranium hydrometallurgical

processing has developed along three main paths:

1. Ion exchange as the sole on site purification and

concentration route

This used a strong base (quaternary amine) functionality resin to

concentrate and purify the uranium.

2. Ion exchange followed by solvent extraction purification of

the IX concentration eluate

Acid leaching of uranium is a non-selective leach and ion

exchange using strong base resins is a non-selective extraction

process so it was not surprising that metallurgists looked to ways

of purifying the concentrated eluate produced by strong IX.

Attempts to improve the selectivity of the uranium IX process

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using weak base (tertiary amine) resins were not particularly

successful and a circuit based on strong base IX of the leach

solution followed by solvent extraction (SX) of the conc eluate

using tertiary amine extractants was developed. One of the first

plants of this type was installed at Buffelsfontein Gold Mine in

South Africa and this circuit is sometimes referred to as a

"Bufflex" circuit.

3. Direct solvent extraction of the leach solution

This circuit uses a single extraction process, solvent extraction

using a tertiary amine solvent and yields a product, which is as

pure as circuit (2). The direct SX circuit ("Purlex") become the

standard uranium circuit in Canada, Australia and the US. In

South Africa both direct SX and IX-SX circuits co-existed but SX

circuits predominated.

There are some hydrometallurgical circuits for uranium which use

none of the above options. These include the use of TBP to treat

nitric acid leach solutions produced in nuclear fuel reprocessing

(1) (2), and to treat nitric acid leach solutions produced at

Palaborwa, South Africa. D2EHPA/TOPO mixtures are used to

extract uranium from phosphoric acid solutions

2.0 ACID LEACH CHEMISTRY FOR URANIUM

Sulphuric acid leaching of uranium ores in the presence of an oxidising agent

(usually manganese or chlorate based) which provides a leach oxidationreduction

potential of 400 - 500 mv relative to a saturated calomel electrode,

results in virtually all the leached uranium being present in the U(6) valency.

The uranium dissolves as UO2

2+ and then forms two uranyl sulphate anion

complexes viz:

UO2

2+ + 2SO4

2- .> UO2(SO4)2

2-

UO2(SO4)2

2- + (SO4)2- .> UO2(SO4)3

4-

The uranyl sulphate anion complexes are the species, which are extracted

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