Multivariable Modelling for the Cathodic Quality

Multivariable Multivariable ModellingModelling for the for the CathodicCathodic QualityQuality

CompaCompañíñía Minera Doa Minera Doñña Ina Inéés de Collahuasi SCMs de Collahuasi SCMGerencia LixiviaciGerencia Lixiviacióónn

““Multivariable Multivariable ModellingModelling

for the for the CathodicCathodic QualityQuality””

G. G. ÁÁvila; F. Romero; R. vila; F. Romero; R. FesterFester (CMDIC) & L. (CMDIC) & L. YacherYacher (CONTAC Ing. Ltda.)(CONTAC Ing. Ltda.)


Collahuasi LocationCollahuasi LocationChilean Altiplane (First Region).Mean height of operations: 4,400 m.a.s.l.230 Km SE of Iquique.Patache Port 60 Km S of Iquique.


Oxide Oxide PlantPlant DataData

Process design for 50,000 [Ton/y] of Cathodes High Grade, leaching Oxides ores.Cathodes production started on July 1998. LME “Grade A” Certification.

Process: Primary Crusher (1) – Secondary Crusher (1) & Tertiary Crushers (4) – Agglomeration Drums (2) – Static Heaps (main pad: 550[m]x1,950[m]) with Coveyor Belts Train and Radial Stacker – Two Leaching Cycles (ILS & Raffinate) – SX (1 train for 1,000 [m3/h]) : 2E+1W+2S –EW : 188 cells (60 SS cathodes+61 Pb anodes per cell), Kidd Process, 36 [KA].

Actual production data (average):

•Ore to Heaps : 6,500,000 [Ton/year], 18,000 [Ton/d].•Ore : oxide & mixed ores; grade CuT 1.28 [%].•Leaching recovery : 75 [%]•PLS : Cu = 8.0 [gpl], Mn = 12.0 [gpl]•SX : extraction efficiency 94 [%]•EW : current efficiency 95 [%], current density 290 [A/m2]•Cathodes production : 62,000 [Ton/y]


1,0%9,0%90,0%2005

2,8%2,4%94,8%2004

2,3%0,2%97,5%2003

Refinery RejectionOut of Specification(S>15, Pb>5)Grade “A” LME

Historically Collahuasi have had excellent quality records: ~ 96% Grade “A” LME.

Grade “A” LME : S ≤ 15 [ppm] & Pb ≤ 5 [ppm].

Since 2004 an increase of Sulphur (S) in cathodes has affected quality. Pb O.K.

Production/Quality trade-off since 2004 because high copper price.

On 2005 it was decided to develop an study using an multivariable analysisapproach to give clarity on cathodic quality. The SCAN (Contac Ing. Ltda.) software was used.

IntroductionIntroduction..


SCAN software (off-line version) was used with the following methods:VFA (Variability Factors Analysis)

PLS (Partial Least Squares).

Operational data since Jan-2003 to Dec-2005.Year 2003 was identified as the desired “pattern” (best quality, production and stability).

VFA analysis defined the “pattern model” (2003) allowing to compare 2004 and 2005 operation against this model. Variables that most explain the “operational drift”those years were identified.

Sulphuric acid in electrolyte has remain almost constant (~200 [gpl]) during the period, so does not implies the increase of S in cathodes.

Using PLS method it was developed a predictive model of Sulphur (S) content in cathodes as function of Cu in outcoming (poor) electrolyte, flow and temperatureof incoming electrolyte to cells and current.

MethodologyMethodology..


VFA VFA analysisanalysis..Process variables (21) for the analysis.

CLAVE VARIABLE

Fe+2 EEC (gpl) Fe+2 en el electrolito entrante a celda (gpl)

Mn+2 EEC (ppm) Mn+2 electrolito entrante a celda (ppm)

T EEC (°C) Temperatura electrolito entrante a celda (°C)

Q SN (m3/hr) Caudal electrolito por sector de nave EW (m3/hr)

Co ER (ppm) Co+2 electrolito rico (ppm)

Mg ER (ppm) Mg+2 electrolito rico (ppm)

Al ER (gpl) Al electrolito rico (gpl)

SiO2 ER (ppm) SiO2 electrolito rico (ppm)

SÓL. SUS ER (ppm) Sólidos en suspensión electrolito rico (ppm)

Cu EP (gpl) Cu+2 electrolito pobre (gpl)

AC EP (gpl) Ácido electrolito pobre (gpl)

Corriente promedio por celda (A) Corriente promedio por celda (A)

Adición de Goma Guar (Kg) Adición de Goma Guar diaria (Kg)

Adición Sulfato de Cobalto (Kg) Adición Sulfato de Cobalto diaria (Kg)

Adición Sulf_ Ferroso (Kg) Adición Sulfato Ferroso diario (Kg)

Descarte Electrolito (m3/hr) Caudal de Descarte electrolito (m3/hr)

Peso Promedio Cátodos Día (Kg) Peso Promedio Cátodos Día (Kg)

Cu en Cámara de Lavado (gpl) Cu en Cámara de Lavado (gpl)

Temp. cámara lavado (°C) Temperatura cámara lavado (°C)

PESO BORRA DIARIO (Kg) Peso de borra diario (Kg)

Guar (gr/ton) Adición Goma Guar por tonelada diaria de cátodos cosechados (gr/ton)


Objective: to reduce the number of variables that “explain” the process, generating a few variability factors (VF) that explain a high percentage (>70%) of whole process variability.

VARIABILIDAD EXPLICADA

0

10

20

30

40

50

60

70

80

1 2 3 4 5 6 7 8 9 10 11

N° VF's

%VA

RIA

BIL

IDA

D E

XPLI

CA

DA

The VFA analysis of 21 variables concludes with 11 VF that explain more than 70% of whole process variability of 2003.

VFA VFA analysisanalysis..


PATTERN MODEL 2003 AND OPERATION MAP 2003

SCORE PLOT 2003 GLOBAL HOTELLING INDEX 2003

The Global Hotelling Index measures thedegree of belonging for the operational data set to the pattern model defined, establishing a maximum statistical limit “1”.

Score plots diagrams allow to supervise the 21 process variables jointly.

The two first VF (VF1 and VF2) explain33% of whole process variability.



SCORE PLOT 2004 GLOBAL HOTELLING INDEX 2003-2004

Effect of gradual increase in electrolyte temperature

Effect of decreasing currentin cells

227%Incoming electrolyte temp.

275%Cu+2 poor electrolyte

328%Current in cells

Difference % (*)Variable



(*): (<Hotelling of variable in 2004> - <Hotelling of variable in 2003>)/<Hotelling of variable in 2003>


SCORE PLOT 2005 GLOBAL HOTELLING INDEX 2003-2005

227%Cu+2 poor electrolyte

252%Current in cells

438%Incoming electrolyte temp.

Difference % (*)VariableEffect of gradual increasein electrolyte temperature



(*): (<Hotelling of variable in 2005> - <Hotelling of variable in 2003>)/<Hotelling of variable in 2003>


VFA VFA analysisanalysis..Effect of gradual increase in incoming electrolyte temperature (TEEC)


Objective: to generate a predictive model of output variable as a function of manyinput variables. By definition the model explains a short-term relationship between thevariables.

CLAVE VARIABLE

T EEC (°C) Temperatura electrolito entrante a celda (°C)

Q EEC (m3/hr) Caudal electrolito entrante a celdas por sector de nave EW (m3/hr)

Cu EP (gpl) Cu+2 electrolito pobre (gpl)

I (A) Corriente promedio por celda (A)

For comparison purposes two PLS models of S in cathodes were generated:

S2003(ppm) = f ﴾ TEEC, QEEC, Cu+2EP, I ﴿, normal operation

S2005(ppm) = f ﴾ TEEC, QEEC, Cu+2EP, I ﴿, high sulphur in cathodes operation

PLS PLS analysisanalysis..

To predict the sulphur (S) content in cathodes the following input variables werechosen:


2003 PLS model for cathodic quality (sulphur content in cathodes):253I4107,2

EP2Cu2,0

EECQ2,0

EECT1,0)ppm(S +×−×+⎥⎦

⎤⎢⎣⎡ +×−×−×−=


Scaled regression coefficient for eachinput variable in 2003 PLS model of S


365I4104.5EP

2Cu1,0EEC

Q2.0EEC

T)ppm(S +×−×+⎥⎦⎤

⎢⎣⎡ +×−×−−=


2005 PLS model for cathodic quality (sulphur content in cathodes):

Scaled regression coefficient for eachinput variable in 2005 PLS model of S

More stable operation in January-May period, formodelling purposes.


The VFA pattern model for 2003 operation was a good pattern model to representa normal operation of EW tankhouse.

It can be clearly seen the “operational drift” of 2004 and 2005 in the score plots compared with the operation in 2003. The evolution of Global Hotelling Index in 2003-2005 period also reflects this behavior.

According to VFA analysis the variables that mainly explain the 2004 operationaldrift were current in cells (I) and Cu+2 poor electrolyte (Cu+2

EP) because its highvariability. The third variable was the incoming electrolyte temperature (TEEC). TheSX-EW process was disturbed because of major changes in Heaps Leachingprocess.

Also with the VFA analysis extended to 2005, the variable that becomes more relevant to explain the 2005 operational drift was the incoming electrolytetemperature (TEEC). This variable increased gradually since 2004.

ConclusionsConclusions..


The PLS analysis for 2005 (January-May) also demonstrates the great influence ofTEEC over sulphur content in cathodes. It is known that in the short-termtemperature favors the transport phenomena, so it was necessary to study theexternal agents that difficult them.

Considering a long-term analysis, the gradual increase in TEEC also increased thesulphur content in cathodes S (decreasing the quality). This apparent contradictionin the effect of TEEC over S can be solved by the following hypothesis:

The external agent that difficult transport phenomena is the reagent (Guar Gum) that isused to improve the Cu crystal deposit over the cathode, but in presence of highertemperatures than specification for the reagent.

Guar Gum in presence of higher temperatures rapidly decreases its mean life, generatingdegraded by-products in the electrolyte. It is not possible to measure the amount ofdegraded Guar Gum in the electrolyte.

Those degraded by-products generates an irregular Cu deposit over the cathodes body, promoting the occlusion of electrolyte (and hence sulphur) inside cathodes structure.

Electrolyte bleeding in tankhouse can be used to decrease the amount of degraded GuarGum and hence to improve cathodic quality in terms of sulphur.

ConclusionsConclusions..

Multivariable Modelling for the Cathodic Quality

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