senior design presentation

STATISTICAL EXPERIMENTAL DESIGN FOR As/Sb REMOVAL FROM DECOPPERIZED ANODE SLIME USING ALKALINE SULPHIDE SOLUTION

SENIOR DESIGN PROJEC IN PROCESS METALLURGY(P7007K)

SUPERVISOR:

Awe Samuel Ayowele

By

Alphonce Wikedzi

BACKGROUND • Exhausting/depleting primary copper ore reserves

• Growing interest for alternative copper sources; scraps, slag, decopperized anode slimes ,e.t.c.

• Decopperized anode slimes from copper electro-refining process contains valuables metals such as Cu, Ni, Se, Te, Ag, Au, and PGM metals.

• However, impurity elements such as As, Sb, Bi, and Hg are the challenge!.

BACKGROUND CONT.......

• Difficult to remove from the metallic copper • A selective pre-treatment process for the removal of

these impurities is necessary

• Reduced environmental problems and simplified metallurgical processes.

AIM

• To optimise the impurity(As&Sb) removal from decopperized anode slimes produced at Rönnskär copper smelter through alkaline sulphide leaching.

LITERATURE REVIEW CONT...Decopperized anode slimes: • Oxides &other compounds deposited at the bottom of

an electrolytic cell during electro-refining of copper.

• Slimes from concentrates - Au, Ag, Te and se.

• Slimes from scraps- Pb,Sn, and Ag.

• Ag:Se< 1,7 - AgCuSe formed, Ag:Se<1,7- AgSe formed

• Pb as PbSO4 and As found in electrolyte as arsenic acid

LITERATURE REVIEW CONT.....

Element % into ‘slimes’ % into electrolyte

Cu <0,2 <99,8

Au 100 0

Ag <99 <1

Se 98 2

Te 98 2

Pb 98 2

Bi 60% with 0,1% Pb in anode

40

Sb 60% with 0,1% As, Bi, Pb and Sb (each) in anode

40

Element % into ‘slimes’ % into electrolyte

As 25% with 0,1% As in anode

75

S 1 99

Ni 1 99

Co 1 99

Fe 0 100

Zn 0 100

Table 1: Impurities behavior during Electro-refining.

LITERATURE REVIEW CONT.....

• Pyrometallurgical methods-Sulphate roasting, Direct roasting in air, Alkaline roasting, Oxidation in conveters.

• Hydrometallurgical methods -Hydrogen peroxide ,Chlorine ,Nitric acid and Sulphuric acid leaching e.t.c

Treatment of decopperized anode slimes

LITERATURE REVIEW CONT....

Pd/Pt SLIME

Se RECOVERY

CRUDE SELENIUM

SILVER 99,99%

GRANULES

GOLD 99,99%

INGOTS/GRANULESES

SMELT SLAG TO COPPER

PLANT

COPPER TELLURIDE

NICKEL SULPHATE

ANODE SLIME

SOLUTION

TO THE TANKHOUSE DRYING

KALDO SMELTING& REFINING

CASTING OF ANODES

SILVER ELECTROLYSIS

GOLD REFINNING WCC

GOLD SLIME LEACHING

PRESSURE LEACHING

Figure 2: Anode slimes treatment route at Boliden Rönnskär smelter

LITERATURE REVIEW CONT...

FERRIC ION, H2SO4 AND THIOUREA

Na2CO3 AND CARBON

Pb-Sn SOLDERING

ALLOY

SILVER METALCOPPER METAL

LEACHING

S/L SEPARATION

ELECTROLYSIS

LEACHING

S/L SEPARATION

ION EXCHANGE

SMELTING

ANODE SLIMES

H2SO4 AND O2

CA

KE

CA

KE

Figure 3: Proposed route for treating anode slimes rich in Cu, Sn, Pb and Ag


BULLION

HCl LEACHING

Sb , As

Te, (Cu)

Cu, (Te )

Se

KOH LEACHING

ALKALINE ROASTING

WATER LEACHING AT ROOM TEMPERATURE

H2SO4 LEACHING

SMELTING

ANODE SLIMES

Figure 4: Treating anode slimes by selective leaching route-Proposed route


As and Sb dissolves as thio-ions: thioarsenate (AsS4

3- ), thioantimonite(SbS3

3-), thioantimonate( SbS43-) etc.

• 2CuAsS4(s) +3 Na2S(aq) = 3Cu2S(s) + 2Na3AsS4(aq)

• Cu12Sb4S13(s) + 2Na2S(aq) = 5Cu2S(s) + 2CuS(s) +4NaSbS2

• NaSbS2(aq) + Na2S(s) = Na3SbS3(aq)

Alkaline sulphide leaching theory:

MATERIAL AND METHODS Material: Decopperized anode slimes from Boliden

Rönnskär copper smelter electro-refining cell.

Table 1: Chemical analysis results

Figure 1: Particle size distribution

MATERIAL AND METHODS CONT..Methods:• Particle size analysis: CILAS-1064 liquid equipment

• Mineralogical characterisation: XRD analysis

• Experimental design: MODDE 9.0 software and Rechtschaffner experimental design technique

• Leaching experiments: Mechanically stirred glass reactor, auto-regulated heating system.

MATERIAL AND METHODS CONT..

Parameter Level 1 Level 2

Leaching tempera (oC) 60 100

Na2S

concentration(g/l)

100 200

Leaching time (hrs)4 24

Solids concent. (g/l) 50 200

NaOH

Concentration (g/l)

20 ( constant)

Table 2: Parameters and their levels Table 3: Randomized experimental order

MATERIAL AND METHODS CONT..

Figure 5 : Experimental set up

RESULTS AND DISCUSSION CONT..

Figure 7: XRD results for decopperized anode slimes after treatment with NaOHB-Bismite, -Bi2O3 , C-Copper Arsenide- Cu9.5As4 , P- Pilsenite-Bi4Te3 , R-Paramelaconite-6CuO.Cu2O , S-Copper sulfate hydroxide hydrate-Cu3(SO4)2(OH).4H2O


Figure 8: XRD results for the decopperized anode slime Residues C- Covellite-CuS, B- Bambollalte-Cu(Se,Te)2 , D- Djurlelte-Cu31S16

RESULTS AND DISCUSSION CONT..Table 6: Mass balance for other elements after leaching

RESULTS AND DISCUSSION CONT..Raw data evaluation:

Replicate plots for the responses Histogram of the responses


Regression analysis and model interpretation:

Fugure: Summary fit plot before model refinement Figure: Regression coefficients before model refinement


Regression analysis and model interpretation:

Fugure: Summary fit plot after model refinement Figure: Regression coefficients after model refinement


Evaluation of the refined model:

Figure : Normal probability plot of residuals after model refinement Figure: Predicted and Observed response relationship


Evaluation of the refined model:

CONCLUSSIONS&RECOMMENDATIONS

• The lixiviant was significantly selective for As and Sb dissolution.

• The recovery of both As and Sb was influenced by Na2S concentration, leaching time and solids concentration.

• Dissolution of As and Sb from decopperized anode slime by alkaline sulphide solution was independent of temperature.

• A statistically significant model with 95% confidence level, no lack of fit and good predictive power was obtained for both responses.

CONCLUSSIONS&RECOMMENDATIONS• Solids concentration and leaching time had the highest

effect in the model

• (Na2S*t) had positive effects, while (Sc*t) &(Na2S*Sc) had negative effects to both response.

• Optimum response values could be achieved through longer leaching time, lower solids concentrations and higher Na2S concentration for both responses.

• Optimal factor settings choice should be based on economic evaluation.

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