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Liquid Analysis for Metals Extraction and Processing Visualize > Analyze > Optimize

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Liquid Analysis for Metals Extraction and Processing

Visualize > Analyze > Optimize

2

TRUSTED AROUND THE WORLD: THE MOST ADVANCED LIQUID ANALYSIS SOLUTIONS

LIQUID ANALYTICAL SOLUTIONS FOR METALS

Visualize the benefits of optimizing yields and minimizing

expenses for metal extraction processing.

Analyze with Emerson’s exclusive PlantWeb® concept using

a scalable control system with independent devices and

final control elements that link these various steps together

to optimize production parameters for a complete mining

operation.

Optimize production parameters with Rosemount Analytical

instruments and PlantWeb by monitoring conditions in liquid

solutions containing metals and other chemicals, enabling

feedback control of important liquid parameters such as pH,

electrical conductivity and ORP. These products can also be

used in standalone mode to control individual processes as

needed. Processes will vary depending on the metal

involved, the grade of ore, and the technology employed.

This brochure shows examples of how Rosemount Analytical

liquid analytical products are used throughout extraction

and processing.

EMERSON PROCESS MANAGEMENT

COMPREHENSIVE SOLUTIONS

LEACHING AND ORE EXTRACTION PAGE 3

CONCENTRATION AND SEPARATION 4-6

FINISHED PRODUCT PURIFICATION 7

WASTE DISPOSAL 8-9

ROSEMOUNT ANALYTICAL INSTRUMENTATION 10

PLANTWEB® 11

3

Leaching Process

Rich ores are ground down to about80% -200 mesh and mixed with a0.1% cyanide solution and enoughlime to keep the pH between 11 and12. An agitated leach is faster andmore efficient than a heap becausethe smaller particles have more sur-face area. The leaching process isconducted in leach tanks that have atotal residence time of about 24hours. The gold cyanide in the preg-nant solution is typically adsorbedon granular activated carbon insidethe carbon in pulp (CIP) tanks. Thecoarse laden carbon particles arescreened out of the last tank,

Cyanide-based extraction

Precious metals such as gold and silver are

commonly processed using cyanide compounds.

Cyanide dissolves the precious metal by forming a

chemical complex with it, thus separating the

precious metal from the other constituents of the

ore, which do not dissolve. The leaching process

can be accomplished inexpensively by placing the

ore on a simple liner (heap leaching) or more

efficiently in a stirred tank (agitated leaching).

More concentrated ores justify the expense of

more complex extraction methods.

LEACHING AND ORE EXTRACTION

washed with caustic to remove thegold cyanide, and the gold metal isproduced using electrowinning.Due to the rapid reactions takingplace in an agitated leach process,automatic pH control is stronglyrecommended. See ApplicationData Sheet #3300-08 for moreinformation on cyanide leaching.When the pregnant liquor containslarge amounts of silver, zinc metalis added to liberate the gold metalinstead of carbon adsorption.

pH for Safety and Efficiency

pH values below 11 favor theformation of hydrogen cyanide thatinterferes with the leaching processand is a colorless, poisonous gasthat can quickly become deadly.Gas leaks into the environment area risk to the mine personnel and afuture liability to the mining corpo-ration that can be avoided withcontinuous pH control.

Continuously measuring pH with aninline sensor is complicated by thenature of the leaching solution. Thesolution has finely ground abrasiveore, which can abrade glassmeasurement electrodes andgenerally coat the sensor. Lime(CaO) is frequently used for pH con-trol, however it has low solubilityand can form a hard coating on thepH sensor, effectively taking thesensor out of service. In addition,the high concentration of cyanidecan, over time, penetrate the pHsensor and contaminate the

reference, also causing large errors.The recommended pH sensor forthis application must be ruggedenough to withstand abrasion,resistant to attack by cyanide, andalso resistant to coating. ThePERpH-X® design is an excellentchoice for this environment.

The PERpH-X sensor includes a hightemperature glass electrode forresisting temperature shock, arefillable reference electrolyte, anda replaceable reference junction forlong life. The model 3500 sensorhas forward and reverse facingthreads for mounting versatility. Forextra resistance to coating, a jetspray cleaner accessory is availableas PN 12707-00.

The Model 1056 analyzer can moni-tor up to two pH sensors and is idealfor monitoring and controlling thepH of the leaching area. Standardfeatures include two 4-20 mAoutputs, three (3) process alarmrelays, and pH sensor diagnostics. Atimer relay is included for periodicactivation of a cleaning cycle.

Jet Spray Cleaning Attachment

Model 1056 Dual Measurement Analyzer

PERpH-X High Performance pH Sensor

CONCENTRATION AND SEPARATION

4

In the flotation process, crushed sul-fide ore (containing 1 to 2% copper),along with water and lime slurry forpH control, is fed into a ball mill. Arotating drum with steel balls crush-es the ore to a fine powder. Whenthe ore/lime slurry emerges fromthe mill, it is fed to a rake classifier.Particles that are too large to pass

Flotation

Metals are typically recovered from a raw ore in a

combined form with other metals. Processing

these metals requires concentrating the desired

metals using physical and chemical processes that

select the product metal over the impurities. One

proven technology employed in copper sulfide

ore processing is flotation, in which copper sulfide

particles are lifted on a froth while iron and other

common impurities are left behind.

from the classifier are returned tothe mill, while the overflow isdischarged to flotation cells. Theground ore is mixed with a collectorchemical such as potassium amylxanthate which reacts with the cop-per sulfide to make it hydrophobic.Air is injected into the flotationcells, and foaming agents areadded, creating a froth. Thehydrophobic copper sulfideparticles latch onto the air bubblesand ride them to the surface, form-ing a froth that is skimmed off.When the pH is high enough, thecollector chemical bonds to the

copper ore chalcopyrite (CuFeS2)and not the iron ore pyrite (FeS2),enabling the concentrating step.The copper-rich froth, containing20 to 40% copper, is separated fromthe solution and dried to form cop-per concentrate, which can be soldas a commodity product or furtherprocessed. Copper concentrate maybe treated by either hydrometallur-gical methods or sintered beforepyrometallurgical methods areused to produce copper metal.

The efficiency of this concentratingstep is directly dependent on pH.The flow rate of lime slurry is there-fore regulated to keep the pH with-in the acceptable range. If pH is toolow, iron will be entrapped with thecopper, decreasing the value of thecopper concentrate. If too muchlime is added, the result is a dilutefroth that requires additionalconcentration in later stages,increasing operating costs andwasting lime.

Reliable pH measurement in thislocation can be difficult because ofthe fine powder particles coating thepH sensor. High area referencedesigns like the TUpH sensor model396P have performed well in thisenvironment. The Model 5081pHtransmitter can be field mountednear the flotation cells and performscontinuous diagnostics to determineif the pH sensor requires cleaning oris not immersed in liquid.

Model 396P Insertionand Submersion pH Sensor

Model 5081 Transmitter

PH MEASUREMENT IN FLOTATION CELLS

PREC

IPIT

ATO

R

BAUXITE

DIG

ESTE

RS

SLURRYMIXER

RED MUDWASHER

REDMUD

GREENLIQUOR

RECYCLECAUSTIC

ALUMINAPRODUCT

FLASH TANKS

SEPARATOR

FILTERS

5

ity into a coffee colored liquid andthe red mud. The level of red mud isdetermined using Emerson’s Model226 large bore toroidal conductivitysensor that can be lowered into theseparator until the conductivity set-point is reached. The red mud iswashed free of caustic and then dis-posed as tailings. The product liquoris filtered and turned into aluminaproduct through precipitation anddrying.

Electrical conductivity is an additiveand non-specific property. All acids,bases, and salts will contribute tothe total value. In applicationswhere mixtures are present, such asthis one, detailed information onthe process is needed to providequantitative information.

Conductivity can be used to controldigestion because the processconsumes caustic and produceshydrated alumina that has muchlower conductivity. Establishing acertain minimum operating conduc-tivity (typically in the 300-500mS/cm range) insures that enoughcaustic has been added to dissolvethe bulk of the alumina. Conductivitymeasurement of wash water is usedto prevent loss of caustic andminimize waste volume.

CONCENTRATION AND SEPARATION

Alumina Refining

Raw bauxite (mostly Al2O3·H2O) orecontains iron oxide and silica thatare removed by treatment withcaustic in a digester. This dissolvesthe alumina and allows separationand purification in later steps.

The caustic feed rate is controlled tooptimize extraction of the alumina.Feedback control is achieved using

electrical conductivity which tendsto drop as caustic reacts with thebauxite ore. If insufficient caustic ispresent, the conductivitytransmitter will read low and thecaustic feed can be increased.Impurities remain solid in the formof "red mud" that tend to scale theprocess equipment, requiringfrequent cleaning. Emerson’s model242 flow through toroidalconductivity sensor has been specif-ically designed for this rugged appli-cation by locating the sensor’sdetection circuit outside of theprocess where it is not subject tothe abrasive scouring of the aluminaslurry. The Model 242 conductivitysensor uses externally-mountedtoroids to measure conductivity in alined pipe. The lining is available inteflon, PEEK, or alumina – which isespecially recommended for thisabrasive application. Sensors for linesizes from 1" (25mm) to 4"(100mm) are available.

Following the digester, the productslurry is cooled in heat exchangersand then separated, usually by grav-

Phase difference

A powerful technique for increasing the

concentration of a product metal is to use a

phase difference (such as solid to liquid) to

separate the product from the base metals.

Alumina is refined from raw bauxite in precise-

ly this way. In this process, Emerson’s flow-

through toroidal conductivity sensor is used to

monitor the digestion step, while the large

bore submersion sensor is used to optimize

chemical recovery from the tailings.

Model 242 Flow-Through Sensor

ALUMINA/CAUSTICRATIO CONTROL

6

CONCENTRATION AND SEPARATION

Sulfate Process

In the sulfate process, ilmenite(FeTiO3) is soaked in sulfuric acid todissolve the titanium as titaniumsulfate and bind the iron as solid fer-rous sulfate for removal by settling.The titanium sulfate reacts withcaustic and water in a hydrolysistank at high temperature toproduce a hydrated form oftitanium dioxide. This precipitate isfiltered and washed to removetraces of iron impurities. Othermetal ions such as potassium, phos-phorus, or aluminum may be addedto control particle size anddurability. The hydrate paste thenundergoes a high temperature calci-nation stage that yields the solidwhite product.

The properties of the producttitanium dioxide pigment arestrongly affected by the conditionspresent during the hydrolysis andcalcination stages.

Temperature, pH, deposition rate,ore quality, and additives all play afactor in determining the crystalstructure. Specifically, the pH in thehydrolysis step influences thereactivity of the TiO2 and the ease ofremoving the impurities. However,the finely dispersed ore particlestend to badly coat standard pHsensors, first causing sluggishnessand eventual total failure. This prob-lem is compounded if the process isallowed to dry on the pH sensor. ThePERpH-X model 3300HT is rated foroperations up to 145°C anddesigned for a long lifetime indifficult applications like this one.The replaceable reference junctionallows rapid troubleshooting and

maintenance when the sensor isresponding slowly due to coating.

In addition, the PASVE Mountingand Service valve can be used toenable automatic flushing andcleaning of the sensor as need be.The PASVE removes the sensorfrom the process line by rotatingthe sensor into a cleaning positionand has many mounting options.For additional information on thePASVE valve see the PDS-71-PASVE.

TITANIUMORE

PURE WHITETITANIUM DIOXIDE

IRONIMPURITIES

CONTACTTANK

SETTLING TANK

HYDROLYSISTANK

FILTERWASHER

CALCINATION DRYER

WATER

WATERNaOHH SO2 4

PERpH-X High Performance pH Sensor

PASVE Valve in measurement position

TITANIUM OXIDE MANUFACTURING PROCESS

7

Steel Treatment

Stainless steel is an alloy of various different

formulations that is widely used in industry. Each

different formulation has different specifications

for the final product but despite the best

production methods some off-spec product may

result. Frequently, impurities can be removed

with a short soak in acid, a common finishing

technique for steel rolls. Control of the acid

concentration is crucial in removing just the

right amount of surface contamination. The

process is frequently called steel pickling, and is

one of the largest bulk consumers of

hydrochloric acid worldwide.

Steel is produced in long thin rolls forconvenient transportation to endusers. Contaminants fromproduction processes and storageoxidation are heavily concentrated

on the surface of the rolls and cantherefore be removed by surfaceactive chemical processes. A shortdip in hydrochloric or sulfuric acid isbeneficial in removing contami-nation, but a long dip or a highlyconcentrated acid can remove toomuch product, lowering yield. Thetemperature of the bath is around180°F (82°C) to increase the speed ofthe pickling process. Theconcentration of HCL acid can bemonitored using Emerson’s ruggedModel 228 toroidal conductivitysensor and any of Emerson’sanalyzers listed on page 10. Toroidalconductivity sensors are virtuallyimmune to surface coating effects

FINISHED PRODUCT PURIFICATION

Model 228 Submersion/Insertion Sensor

1 2 3 4

RINSEWATERHCl

RAWSTEEL

TREATEDSTEEL

STEEL TREATING PROCESS

and are the sensors of choice forliquids with suspended solids. Themodel 228 sensor is injectionmolded of polyetheretherketone(PEEK), an extremely robustengineering thermoplastic.

The process typically will haveseveral acid baths of varyingpercent concentration and at leasttwo rinse baths. Care must betaken to remove all traces of acidfrom the steel or long termexposure will cause extensivedamage to the metal roll.Conductivity measurement is aversatile tool for monitoringconcentrated acids since manysolutions have been measured anddocumented for conductivity levelsat various temperatures. Over time,buildup of iron and other metals inthe acid baths will change theconductivity behavior of thesolution somewhat, so it issometimes advisable to monitorthe conductivity directly and notrely on published data.

MINEWASTE

ALKALI

Cl 2

REACTION TANK NO. 1pH 10 ORP 400mV5 TO 15 MINUTES

ACID

REACTION TANK NO. 2pH 8.52 TO 5 MINUTES

DISCHARGE

ALKALI

Cl 2

REACTION TANK NO. 3pH 8 ORP 600mV10 TO 15 MINUTES

600 mVpH 8.5

400 mVpH 10

0 mV

CONCENTRATIONCN 0 Cl 2

MIXER

MIXER

MIXER

8

Oxidation

Cyanide, commonly used inprecious metals extraction, is atoxic chemical with dischargelimits typically around 0.5 ppm,depending on the governing regu-

Model 3500 Rechargeable pH Sensor

Keeping it clean

Waste products from mining and refining opera-tions can be in the form of liquid, gas, and solids.Liquid analytical products are involved in all ofthese operations. They help minimize disposalcosts involved with chemicals adhering totailings, toxic cyanide, noxious gases, and acidmine runoff. Emerson’s analytical sensorsrespond quickly to changes in pH and ORP,protecting both the environment and the minefrom the dangerous effects of these chemicals.

WASTE DISPOSAL

latory body. Since mining solutionscan contain thousands of timesthat concentration, the best policyis to totally destroy the cyanidebefore discharging any liquidwaste. A common method fordestruction is to add an oxidant,typically chlorine, to the wastestream until the cyanide is gone.pH and ORP measurements areused to control the destructionprocess and verify completion.ORP stands for OxidationReduction Potential and indicateswhether the solution is underoxidizing (high ORP) or reducing(low ORP) conditions. Sincecyanide can only be present under

reducing conditions, adding anoxidant both destroys the cyanideand raises the ORP. The cyanidecompound is converted to cyanateand then to harmless nitrogen andcarbon dioxide. pH measurementprotects against discharge ofcyanide gas during the multi-stageprocess and improves the accuracyof the ORP reading by removinginterference from other chemicals.

Emerson’s PERpH-X model 3500 pHand ORP sensors are ideal for moni-toring this chemical reactionbecause they respond quickly tochanges in ORP and can berecharged with reference gel whenneeded. Diagnostics notify theoperator immediately when thereference junction is becomingcoated or if the process is attackingthe reference electrolyte.

Tailings, depleted ore remains, aretypically a major discharge hazardand large piles can usually be found

CYANIDE OXIDATION

9

Rechargeable sensor can be customizedwith different solutions

WASTE DISPOSAL

near any operating mine. Thesesolids typically contain various sortsof heavy metal compounds in oreform and will have traces of acid orcaustic used in the mining process.Rinsing the tailings to reclaim thesechemicals and regenerating orreusing them renders the tailingsless hazardous. Monitoring the rinsewater for electrical conductivity is alow-cost method of reclaiming thechemicals without wasting water.The recommended sensor is themodel 228 toroidal conductivitysensor which monitors waterconductivity levels down to below250 µS/cm.

Scrubbers

Scrubbers are used to remove harm-ful and odorous gases that arecollected from various locationsthroughout the facility. These gasesare typically acidic and are thereforeremoved by contact with a causticliquid stream. Monitoring thereused scrubber solution for pH

ensures that the gases are trappedin the liquid phase for subsequenttreatment. Conductivitymeasurement monitors the buildupof dissolved solids in the scrubbingliquid so that some of the liquid canbe removed before the nozzles arescaled up. Emerson’s PERpH-X pH

sensors and 228 toroidal conductiv-ity sensors are designed to conductthese measurements with aminimum of maintenance. All theEmerson instruments on page 10are compatible with these sensors,but the field-mounted 5081 modelis most popular in this application.

UPPER CHEVRONS

LOWER CHEVRONS

MAKEUP15%

NaOH

WASTE GAS

SCRUBBERSOLUTION

CLEAN

INTERNAL OXIDATIONAIR SPARGER

NORMAL LIQUID LEVEL

Model 228 Submersion/Insertion Sensor

MEASUREMENT CONTROLS MAKE-UP OF SCRUBBER SOLUTION

10

ROSEMOUNT ANALYTICAL INSTRUMENTATION

Features

6081 Series

1056 Series

1057 Series

56 Series

5081 Series

SoluComp Xmt Series

Power

Lithium pow

er11

5 - 2

30 VAC

or

115 - 2

30 VAC

or

115 - 2

30 VAC

24

VDC

24 VDC

Requirem

ent

mod

ule

24 VDC

24 VDC

or 24 VD

C

Num

ber of 4-20

Wire

less

Two

Four

four

One

One

mA Outputs

Num

ber of

One

Two

Three

Two

One

One

Sensor Inputs

Available

pH and

pH

/ORP

/ISE, Con

ductivity

, pH

/ORP

/ISE,

pH/O

RP, resistiv

ity/con

duc-

Select one

: pH,

Select one

: pH,

Measurements

contac

ting

Resistivity

, % Con

centratio

n,Co

ntac

ting

tivity

/TDS, % con

centratio

n, ORP

, Con

ductivity

, ORP

, Con

ductivity

, co

nduc

tivity

Dissolved

Oxyge

n, Ozo

ne,

Cond

uctiv

ityratio

con

ductivity

, total and

Resistivity

, Dissolved

Re

sistivity

, Dissolved

Flow

,* Tu

rbidity

,* Ch

lorin

e free

chlorine, dissolved

O2

Oxyge

n, Ozo

ne,

Oxyge

n, Ozo

ne,

(Total, Free, M

onoc

hloram

ine,

dissolve

d ozon

e, tu

rbidity

, Ch

lorin

e, Gaseo

us

Chlorin

epH

Inde

pend

ent F

ree Ch

lorin

e)pu

lse flo

w, tem

perature

Oxyge

nan

d raw 4-20m

A inpu

t

SMART pH

Yes

Yes

Yes

Yes

No

No

HART

Yes

Yes

No

Yes

Yes

Yes

Compatible

F OUNDATIONfieldbus

No

No

No

No

Yes

Yes

Compatible

Wireless THUM

NA

Yes

No

Yes

Yes

Yes

Adaptor com

patible

Multi-lingual Menus

Yes

Yes

Yes

Yes

No

Yes

Relays

NA

44

4NA

NA

PID Control

No

Timer con

trol only

Timer con

trol only

Yes

Yes/Ff

Yes/Ff

Advanced Diagnostics

Yes

Complete

Complete

Yes

Complete

Complete

Capability

Area

Class 1

, Div. 1

Class I, D

iv 2

Class I, D

iv 2

TBD

Class I, D

iv. 1

& Div. 2

,Class I, D

iv. 1

& Div. 2

Classifications

(future op

tion)

Explosion proo

f

Available Approvals

CE, C

SAFM

, CSA

, CE, UL

CE, U

L, CSA

TBD

CE, FM, C

SA, A

TEX

CE, FM, C

SA, A

TEX

11

PLANTWEB® BRINGS IT ALL TOGETHER

Emerson is the world’s largest provider of gaschromatography, process gas, combustion andenvironmental analysis solutions.

GAS CHROMATOGRAPHY SOLUTIONS

Rosemount Analytical gas chromatographs arethe world leaders in process gas measurement,separating process gas into identifiablecomponents. Our family of chromatographshas a worldwide reputation for accuracy,repeatability, and dependability.

Call 866.422.3683, or see us on the web atwww.raihome.com

PROCESS GAS AND COMBUSTION SOLUTIONS

Emerson is the world’s premier supplier ofcombustion analysis, process analysis andenvironmental monitoring solutions. Withmore than 80 years of experience, we go waybeyond simple data collection and offer provable analytical solutions, advancedRosemount Analytical® instrumentation andthe professionals who really know how to keepyou up and running efficiently, safely andeconomically.

Call 800.433.6076, or see us on the web atwww.raihome.com

MORE ANALYTICALSOLUTIONS FROMEMERSON PROCESS MANAGEMENT

Rosemount Analytical field devices are corecomponents of the PlantWeb digital plantarchitecture, and capture rich diagnosticdata about the health of the device, as wellas the process itself. Device functionality ispresented at the user interface in ways thatare consistent, intuitive, and easy to use.

PlantWeb architecture consists of intelligent field devices,scalable platforms and integrated modular software, allworking together. The result is optimal plant performanceby getting the right information to the right user, in time tomake a difference. The advanced diagnostics in RosemountAnalytical sensors alert users to device or processproblems, before they happen. Control in the field canprovide more reliable process control.

Increase Accuracy and Throughput, Reduce Costs – PlantWeb Makes the Difference

WORLDWIDE STRENGTH

Emerson Process Management is part of Emerson, a global

company that brings together technology and engineering to

provide innovative solutions for our customers in a wide range

of industrial, commercial and consumer markets. Our priority

is to design, produce and deliver products, systems and

solutions that make people's lives better.

SMART pH measurement loops which include SMART pHsensors and SMART-enabled instruments have the advantageof not requiring calibration of pH sensors in the field. AllSMART sensors automatically download critical calibrationdata and performance parameters to the instrument uponcalibration in the lab. Simply reconnect the pre-calibratedsensor to a SMART-enabled fieldinstrument and the pH loop isautomatically calibrated.

Rosemount Analytical SMART Technology – The smart solution for pH measurement

Sensor data transferred to analyzer

91-6036 10.10

LIQUID ANALYTICALEmerson Process ManagementRosemount Analytical 2400 Barranca ParkwayIrvine, CA 92606 USAT +1.949.757.8500T 800.854.8257F [email protected]

Emerson Process Management, Rosemount Analytical, ENDURANCE and PUR-Sense are marks of Emerson Process Management group of companies. All other marks are theproperty of their respective owners.

The contents of this publication are presented for informational purposes only, and while every effort has been made to ensure its accuracy, they are not to be construed aswarranties or guarantees, expressed or implied, regarding the products or services described herein or their use or applicability. All sales are governed by our terms and conditions,which are available on request. We reserve the right to modify or improve the designs or specifications of such products at any time without notice.

© Rosemount Analytical Inc. 2012. All rights reserved. Printed in the U.S.A.

Online ordering available.

RosemountAnalytical.com

GAS CHROMATOGRAPHSEmerson Process ManagementRosemount Analytical10241 West Little YorkSuite 200Houston TX 77040 USAT +1.713.396.8700T 866.422.3683F [email protected]

PROCESS & COMBUSTIONEmerson Process ManagementRosemount Analytical 6565 P Davis Industrial ParkwaySolon, OH 44139 USAT +1.440.914.1261T 800.433.6076F +1.440.914.1262gas.csc@emerson. com

> COMPLETE PROCESS ANALYTICAL SOLUTIONS

GAS CHROMATOGRAPHY GAS LIQUID SAFETY

INDUSTRIAL HAZARD SAFETYEmerson Process ManagementNet Safety Monitoring2721 Hopewell Place N.E.Calgary, AB T1Y 7J7 Canada T +1.403.219.0688T 866.347.3427F [email protected]