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Transcript of 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
LITERATURE REVIEW CONT...
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
LITERATURE REVIEW CONT...
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
RESULTS AND DISCUSSION CONT..
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
RESULTS AND DISCUSSION CONT..
Regression analysis and model interpretation:
Fugure: Summary fit plot before model refinement Figure: Regression coefficients before model refinement
RESULTS AND DISCUSSION CONT..
Regression analysis and model interpretation:
Fugure: Summary fit plot after model refinement Figure: Regression coefficients after model refinement
RESULTS AND DISCUSSION CONT..
Evaluation of the refined model:
Figure : Normal probability plot of residuals after model refinement Figure: Predicted and Observed response relationship
RESULTS AND DISCUSSION CONT..
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.