METS INSIGHTS SESSION. Solvent Extraction

Size: px

Start display at page:

Download "METS INSIGHTS SESSION. Solvent Extraction"

Adelia McDowell
5 years ago
Views:

1 METS INSIGHTS SESSION Solvent Extraction Click to edit Master subtitle style Dr Denis Yan Consulting Metallurgist > RESOURCE PROJECTS > TECHNOLOGY > INTEGRATED SERVICES

2 DISCLAIMER With respect to all the information contained herein, neither Mineral Engineering Technical Services Pty Ltd, nor any officer, servant, employee, agent or consultant thereof make any representations or give any warranties, expressed or implied, as to the accuracy, reliability or completeness of the information contained herein, including but not limited to opinions, information or advice which may be provided to users of the document. No responsibility is accepted to users of this document for any consequence of relying on the contents hereof. COPYRIGHT Passing of this document to a third party, duplication or re-use of this document, in whole or part, electronically or otherwise, is not permitted without the expressed written consent of Mineral Engineering Technical Services Pty Ltd. ACKNOWLEDGEMENTS This document is a dynamic record of the knowledge and experience of personnel at Mineral Engineering Technical Services. As such it has been built upon over the years and is a collaborative effort by all those involved. We are thankful for the material supplied by and referenced from various equipment manufacturers, vendors, industry research and project partners.

3 Who We Are Mineral Engineering Technical Services Engineering Consultants with a focus on junior and mid-tier mining companies Mineral processing since 1988 Global greenfields and brownfields project experience Guiding projects through the development path from testwork to feasibility studies through to commissioning Commodity experience across a wide range of minerals A division of Midas Engineering Group

4 Presentation Overview What is Solvent Extraction Origins of Solvent Extraction Equipment Types Types of Extractants SX operations Absorption isotherms Pilot plant

5 Solvent Extraction (SX) Solvent extraction is a Liquid-liquid extraction P-6 Extract Mass transfer operation based upon chemical differences Two inputs Feed solution containing solute (metal species) to be extracted and Feed solvent which acts as solute extractor P-4 Feed Solution P-5 Solvent Extraction Column Two resultant streams Extract (solute rich solvent-organic) and Raffinate (solute depleted residual aqueous phase) E-1 P-7 Raffinate

6 Origins of Solvent Extraction Extraction of fragrances using fats predates ancient Egypt and is widely used in Africa. However it was not until the nineteenth century that the oils absorbed from fat were extracted using ethanol in a process called enfleurage Enfleurage started in Grasse (France) with another process (maceration) used to extract the essential oils from flowers Maceration used hot oil while enfleurage was a cold process

Origins of Solvent Extraction Maceration used fat heated to 50-70 o C mixed with flowers

7 Origins of Solvent Extraction Maceration used fat heated to o C mixed with flowers for up to 48 hours The fat is then mixed with alcohol to extract the fragrant oils from the fat

Origins of Solvent Extraction Enfleurage was specifically used to extract the essential oils from flowers that were too delicate for the distillation method Flowers such as jasmine are

8 Origins of Solvent Extraction Enfleurage was specifically used to extract the essential oils from flowers that were too delicate for the distillation method Flowers such as jasmine are placed on a layer of fat smeared on a glass plate After 24 hours the flowers are replaced with fresh ones This is repeated for several months until the fat had absorbed sufficient fragrance

9 Origins of Solvent Extraction The charged fat was then mixed with alcohol to extract the fragrance from the fat

10 In 1872, Berthelot and Jungfleisch described the distribution of a metal species between two immisible phases In the 1940 s the need to separate radioactive species led to the introduction of solvent extraction on a large scale and it became entrenched as a hydrometallurgical technique for purification of metal species SX is applied to remove or extract a species from one solution to another. Can be applied by either: Remove valuable component from contaminants or Remove contaminants from the valuable components

11 Solvent Extraction (SX) (cont.) Generalised metal recovery flowsheet incorporating leach Solvent Extraction and electrowinning (EW) Source: Solvent Extraction Reagents and Application,

12 SX-EW Diluent specialised kerosene Active extractant; e.g. LIX 984 N for copper, soluble in diluent Extraction-1 st step to organic Scrubbing- optional next step cleaning impurity from organic Stripping- remove Cu from organic Electrowinning from rich copper stream SX can be used for: Copper Nickel Cobalt Uranium etc Source:

13 Equipment Types Mixer Settlers One unit approaches one equilibrium stage High liquid rates and large vessel Source:

14 Centrifuges Single Stage Source: // robatel.com/images/products/monostage-centrif- Extractorslg.png Source:

15 Columns Practical for almost all Liquid- Liquid Extraction Packing, trays or sprays increase surface area for two liquid phases to intermingle Commonly used Agitated and static Source:

16 Columns Source:

17 Counter Current Operation To increase metal loading onto organic, need to contact with aqueous solution of higher concentration To achieve low concentration of metal in raffinate need to contact with organic of low concentration

18 Counter-Current Conserves mass transfer driving force More efficient use of solvent by higher loading in contact with feed Best recovery from raffinate in contact with fresh organic Source: Cobre Las Cruces, S.A. (CLC)

19 Process Operation Several key parameters in operation of the SX process: Speciation in the feed (oxidation potential, complexation) Concentration ph Residence time Temperature Pressure is not usually considered. Mineral processes are at atmospheric pressure. The reagent driven reaction kinetics and equilibria will define the operational parameters Setting operational parameters can be used to increase the selectivity of reagents Multiple extraction and stripping stages are usual to improve concentration and recovery Regeneration step included to reactivate the organic where there is a gangue build-up on the extractant or reaction deactivating the extractant

20 Operating Limitations Temperature Selection Suitable interfacial tension and viscosity and kinetics favours higher operating temperature Flash point and vapor pressure of the organic favours lower operating temperature Solvent Selection Partially soluble with the carrier Easily recoverable Immiscible with feed components High selectivity towards solute High distribution coefficient Low viscosity Chemically stable Non toxic, non flammable and low cost

Brief Design Criteria Adequate amount of mixing is vital Amount of mixing depends on the physical properties between two phases Largest droplets controls extraction equilibrium Smallest droplets

21 Brief Design Criteria Adequate amount of mixing is vital Amount of mixing depends on the physical properties between two phases Largest droplets controls extraction equilibrium Smallest droplets controls settling time Emulsion Formed due to excessive agitation or inherent nature of chemical compounds due to contaminants Coagulants minimize emulsification Crud Layer Loose solid substances (foreign impurities) float at the interface Continuously withdrawn and filtered in continuous extraction

22 Extractable Metal Species The extractable species (which have been recovered commercially in SX) can be divided into four categories: Metal cations, such as Cu 2+, Ni 2+ and Co 2+ Complex metal anions, for example UO 2 (SO 4 ) 3 4- and Mo 8 O Complex metal cations, such as MoO 2 2+ Neutral metal species like UO 2 (NO 3 ) 2

23 Reagent Requirements For a metal extraction to be commercially successful, the extractant (reagent) must: Have very low solubility in the aqueous phase and high solubility in diluent Extract the desired metal(s) selectively from the metal-containing aqueous solution at a fast rate Be strippable at a fast rate with a solution from which eventual metal recovery can take place Be stable to the circuit conditions so it can be recycled many times Not promote stable emulsions but have good coalescing properties when mixed with diluent and modifier if necessary Have an acceptable cost It is desirable to be: nonflammable, nontoxic, noncarcinogenic

24 Diluent Selection Characteristics Mutually miscible with extractant (and modifier) High solvency of extracted metal organic species Immiscible (insoluble) with feed aqueous Low viscosity Low surface tension Low volatility and high flash point Density different from aqueous Chemically stable Desire non toxic, non flammable and low cost Aromatic content optimised for the system

25 Type of Extractants Metal extractants are classified by structure, extraction mechanism and the metal species extracted. Main extractants types include: Chelating extractants Ion Pair Extractants Neutral or Solvating Type Extractants Organic Acid Extractants Ligand Substitution

26 Chelating Extractants > Metal extraction by LIX 84-I as a function of ph > Metal extraction by LIX 84-I as a function of total NH 3 Source: Solvent Extraction Reagents and Application,

27 Ion-Pair Extractants (cont.) Source: Solvent Extraction Reagents and Application,

28 Neutral or Solvating Type Extractants Are basic in nature and will coordinate to certain neutral metal complexes by replacing waters of hydration organic-metal complex to become organic soluble and aqueous insoluble Extractions with solvating extractants are limited: The metal s ability to form neutral complexes with anions The co-extraction of acid at high acid concentrations The solubility of the organo-metal complex in the organic carrier An important extractant of this type is : trioctyl phosphine oxide (C 8 H 17 ) 3 PO, called TOPO _oxide.png/244px-trioctylphosphine_oxide.png

29 The Concept of Liquid-Liquid Extraction Liquid-liquid extraction is based on the transfer of a solute substance from one liquid phase into another liquid phase according to the solubility Extraction becomes a very useful tool if you choose a suitable extractant You can use extraction to separate a substance selectively from a mixture, or to remove unwanted impurities from a solution. One phase is a polar (aqueous) solution and the other an organic (non-polar) solvent The difference in solubility is key to success of this processing method The ratio of solubility in the two solvents is termed "distribution coefficient"

30 At a certain temperature, the ratio of concentrations of a solute in each solvent is constant (over a certain concentration range). This ratio is called the distribution coefficient, K. when solvent 1 and solvent 2 are immiscible liquids For example, suppose the compound has a distribution coefficient K = 2 between solvent 1 and solvent 2 By convention the organic solvent is (2) and water is (1)

31 (1) 30 particles of compound distributed between equal volumes of solvent 1 and solvent 2. (2) 300 particles of compound, the same distribution ratio is observed in solvents 1 and 2 (3) Double the volume of solvent 2 (i.e., 200 ml of solvent 2 and 100 ml of solvent 1 ), the 300 particles of compound distribute as shown If you use a larger amount of extraction solvent, more solute is extracted

into two portions and you extract with each.

32 What happens if you extract twice with 100 ml of solvent 2? In this case, the amount of extraction solvent is the same volume as was used in Figure 3, but the total volume is divided into two portions and you extract with each. The first extraction is as in figure You still have 100 ml of solvent 1, containing 100 particles. Now you add a second 100 ml volume of fresh solvent 2. According to the distribution coefficient K=2, you can extract 67 more particles from the remaining solution

33 An additional 67 particles are extracted with the second portion of extraction solvent (solvent 2 ).The total number of particles extracted from the first (200 particles) and second (67 particles) volumes of extraction solvent is 267.This is a greater number of particles than the single extraction (previous at 240 particles) using one 200 ml portion of solvent 2! It is more efficient to carry out two extractions with 1/2 volume of extraction solvent than one large volume!

34 Organic:Aqueous (O:A) Ratio Volumetric ratio between the organic and the aqueous phase Variation in O:A ratio will change recovery performance It is preferable where possible to have a series of countercurrent contacts (for both loading and stripping). This results in an increase in concentration for the desired species This will decrease the amount of solution required for downstream processing and improve the recovery of the final product Testwork will determine the optimal advancing O:A ratio to achieve high recovery of the desired species with reasonable number of stages and extractant flow

35 Extractant The extractant is the key organic phase component used for the metal recovery A wide range of extractants are available to suit a wide range of applications Some reagents can be more selective than others, some offer a better overall recovery Extractant properties (price, flash point, viscosity, polarity) must be considered prior to selection Testwork will determine what works for a specific process Extractant must be suitable to the system, not degraded by the leaching and stripping liquors nor detrimental to the downstream treatment Extractant is usually the most expensive component and minimising losses of this component is key to minimising cost (eg. Cyanex ~$50,000/t)

36 Diluent Diluent is used to solvate and mobilise the organic extractant, loaded and unloaded. Extractant alone can be quite viscous Immiscible in the aqueous phase High flash point, low vapour pressure Diluent should be stable in the process. Eg oxidation to carboxyl can results in non-selective extraction Effects transfer kinetics and phase disengagement

37 Modifiers Several modifier types available selected dependant on application The extraction takes place at the interface. The extractant can be assisted at this interface by a modifier component which changes interface parameters. The effect can be: Improved kinetics Improved settling Loaded extractant can have low solubility in the diluent. A modifier can improve loaded organic solubility Interaction with the extractant can improve extraction or stripping extent or rate Modifiers which increase transfer rate should be called accelerators or catalysts

38 Eh / ph Speciation in the aqueous phase depends on oxidation potential, ph and complexing reagents Eg iron could be in the species Fe 2+, Fe 3+, FeCl +, FeCl 2+ depending on conditions Selective extraction depends on this speciation Therefore control of these factors is vital to good operation Transfer can involve exchange of proton which then changes ph and equilibrium. The ph may have to be controlled to drive loading and selectivity

39 Stripping The loaded organic is stripped using an aqueous liquor. This is a stronger lixiviant than the feed liquor or more dilute in the solute In some cases several components can load during the extraction stage, not just the desired metal Manipulation of the Eh/pH/complexation can effect this, however to achieve a high level of recovery other species may be loaded Methods to deal with the impurities include selective stripping stagewise by differing ph, stripping agent or stripping agent strength This enables a higher purity product stream, can allow for multiple product recovery or a return as part of the leach reagent

40 Solvent Losses Solvent losses can be a large cost factor for a solvent extraction process Losses can occur through crud formation, phase entrainment and misting Crud formation Crud formation is driven by the contact of aqueous, organic and a solid phase / particle Crud can cause impurities to carry over into other phases resulting in poor process performance

Solvent Losses - Crud Control of crud As there is no relationship between reagent additions and crud, other prevention methods must be used Primary cause is solids or incipient solids within the feed

41 Solvent Losses - Crud Control of crud As there is no relationship between reagent additions and crud, other prevention methods must be used Primary cause is solids or incipient solids within the feed to the SX circuit Particles are sub-micron large settling tanks and or filters prior to SX feed to remove solids Flocculants / agglomerating agents can be added to increase settling speed and reducing solids in SX circuit Fast variation in ph can also increase crud formation It can be difficult to manage following a leaching step Removal of crud Pumping out of circuit at the weir Intermittent flooding of organic phase to remove and treat requires reduced production or shutdown Treatment of crud Centrifugal treatment or filtration of the crud containing organic Treated organic returned to the SX circuit

42 3 rd Phase Formation Third phase formation occurs when the organic phase splits into two distinct organic phases The organic will typically split into the diluent and the metal rich extractant phase 10% Cyanex 272, 5% TBP 20% DEHPA, 5% TBP

43 Third Phase The formation of a third phase is not always an issue, many processes will not have this issue arise Serious issues for recovery and processing can arise with third phase formation Phase inversion can result in the loaded organic flowing out with the aqueous phase Studies have shown that ensuring operation below the LOC (limiting organic concentration) can prevent the separation of the diluent and the loaded extractant Use of a modifier can maintain solubility and prevent third phase

Equilibrium compositions are determined experimentally. Source: http://firstyear.

44 Equilibrium Previously spoke of distribution coefficient K or D. This value is not constant over the entire concentration range. Equilibrium compositions are determined experimentally. Source:

McCabe Thiele Source: http://firstyear.chem.

45 McCabe Thiele Source:

46 Stripping Similar must be performed on stripping isotherm plot, operating line and stages The two ends of the operating lines are joined by the loaded organic concentration and the stripped organic concentration Usual to plot strip liquor concentration against organic concentration. In that case operating line slope is O/A

47 Pilot Plant

SX Fire Hazard Olympic Dam, 2001 - $170 million damage, effected production for 2 years Source: Factors Influencing the

48 SX Fire Hazard Olympic Dam, $170 million damage, effected production for 2 years Source: Factors Influencing the Effectiveness of Firewall Designs for Metalliferous Solvent Extraction Plants, A. MacHunter, ALTA Uranium-REE Conference, May 2014

49 SX Fire Hazard Morenci Metclaf, Phelps Dodge, 2003

50 SX Fire Hazard Source: Factors Influencing the Effectiveness of Firewall Designs for Metalliferous Solvent Extraction Plants, A. MacHunter, ALTA Uranium-REE Conference, May 2014

51 References Solvent Extraction Reagents and Application, Cobre Las Cruces, S.A. (CLC) Factors Influencing the Effectiveness of Firewall Designs for Metalliferous Solvent Extraction Plants, A. MacHunter, ALTA Uranium-REE Conference, May 2014

52 THANK YOU

Solvent extraction of cobalt and zinc from sulphate solutions using phosphoric, phosphonic and phosphinic acids

The European Journal of Mineral Processing and Environmental Protection Solvent extraction of cobalt and zinc from sulphate solutions using phosphoric, phosphonic and phosphinic acids K.C. Nathsarma* and