The separation of pentlandite from chalcopyrite, pyrrhotite and gangue in nickel projects throughout the world V. Lawson, G. Hill, L. Kormos, G. Marrs AusIMM Mill Operators Conference Sep 1-3 2014 Townsville
Process Control Process Mineralogy Plant Support Process Optimization, Controller & Control Solutions Quantitative Mineralogy, Mineral Processing, Sampling & Statistics On-site Support Services in Start-up & Commissioning Pyrometallurgical and Hydrometallurgical Modeling, Testing and Piloting Extractive Metallurgy Materials Selection & Equipment Failure Analysis & Prevention Materials Technology
Ni Deposits Nickel deposits represented in todays presentation 2
Taste of challenges in nickel concentrating Its not just size shape matters too Characterising deposits and the nickel entitlement Pentlandite flotation Pyrrhotite flotation and its rejection Gangue rejection Separation of chalcopyrite from pentlandite 3
Characterising Ni deposits
Variation in Ni Deposits Across the World Characterisation of nickel deposits at XPS Type 1- low to moderate Po:Pn ratios where MgO rejection is main focus (Raglan, Thompson, Norilsk) Po Type 2 moderate to high Po:Pn ratios leading to the need for Po rejection (Sudbury ores, Voisey s Bay, Norilsk) Type 3 high Po low Pn ores (generally uneconomic) Type 4 low grade, high MgO ores that may be economic (Dumont, Mt Keith, Mirabela) Pn MgO Why differentiate on this basis? Pyrrhotite content and Po/Pn ratio affects the grade of final concentrate high levels of pyrrhotite or high Po/Pn generally leads to more difficult separation MgO content in concentrate is problematic in smelting process low grade deposits contain more Mg rich gangue All these deposits may be with/without copper minerals 5
The importance of mineralogy in nickel projects Not all nickel is recoverable Nickel can be contained in solid solution in some sulphides such as pyrrhotite and pyrite as well as some gangue minerals. This is particularly an issue for low grade deposits where sometimes as little as half the nickel is in an unrecoverable form 100 90 80 70 % Ni in Ni S 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 Ni Head Grade (%) 6
Recoverable nickel Nickel entitlement" Type 4 Type 3 Ni Sulphides Type 2 Fe Sulphides Type 2 MgO minerals Type 1 Type 1 Other 0% 20% 40% 60% 80% 100% Ni deportment 7
The importance of mineralogy in nickel projects thin section 4mm x 4mm Po Pn Cp magnetite serpentine pyroxene 8
Pentlandite flotation behaviour
Pentlandite flotation Sudbury Basin ore Pentlandite is a well floating sulphide that can be floated with almost all collectors and generally in a mildly alkaline ph Pentlandite in a ultramafic environment will likely be floated in soda ash while in a pyrrhotite environment its likely to be lime Recovery down the bank Recovery (%) 100 90 80 70 60 50 40 30 20 10 0 1 1 2 1 3 1 4 1 5 Cell Cp Pn Po Gangue 10
Pentlandite flotation behaviour Size and chemistry matter The recovery by size curve indicates that both coarse and fine pentlandite float more poorly than Cp This suggests that an optimum size exists Grinding circuit preparation of pentlandite is therefore very important 100 90 80 Pentlandite Recovery (%) 70 60 50 40 30 20 10 0 Plant 1 Plant 2 Plant 3 Plant 4 Cp Plant 3 1 10 100 1000 Size (µm) 11
Pentlandite grind Grind matters To avoid losses in the finest size fraction operations commonly have unit cells in the grinding circuit Pentlandite is prone to fracturing and avoiding the production of fines is key 12
Pyrrhotite dominated ores
Pyrrhotite Flotation Complete or incomplete Pyrrhotite doesn t float as well as either pentlandite or chalcopyrite in mildly alkaline conditions. To float to completion for low sulphur tailings often acid is required Recovery down the bank Recovery (%) 100 90 80 70 60 50 40 30 20 10 0 1 1 2 1 3 1 4 1 5 RoScav Cell Cp Pn Po Gangue 14
Pentlandite / Pyrrhotite selectivity How much pyrrhotite do you need to float? Dependent on rejection strategies and pyrrhotite content in the feed the pentlandite recovery will be constrained 100 Pyrrhotite Flotation 90 80 70 60 50 40 30 20 10 Client 1 Client 2 Client 3 Client 4 Client 5 Client 6 0 0 20 40 60 80 100 Pentlandite Flotation 15
Need pyrrhotite rejection? Difference between Type 1 and Type 2 ores Rejection is dependent on the ratio of pyrrhotite to pentlandite in the feed Ratios 2.5 or less usually don t require pyrrhotite rejection unless targetting high concentrate grades Standard Approach ph of about 9.2-9.5 achieved with lime Careful control of collector Enhanced Approaches Use of high Pyrrhotite as an oxygen sink in regrind at ph >10 to promote Pentlandite flotation Amine depressants DETA in conjunction with sodium sulphite Other iron sulphide depressants have been used with limited success % Po Rejection Required 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 21% Ni Concentrate 18% Ni Concentrate 15% Ni Concentrate 12% Ni Concentrate 10% Ni Concentrate 0 1 2 3 4 5 6 7 8 Po/Pn Ratio in the Feed 16
Pyrrhotite crystallography Not all pyrrhotite is the same Pyrrhotite can exist in several forms representing magnetic and non-magnetic forms dependant on its crystal structure The use of XRD can differentiate the crystal structure, QEM can also differentiate textures but specialised measurements are required Fe 7 S 8, Fe 9 S 11, Fe 8 S 9 and FeS (troillite) (3)[1310866G.raw] 1310866 North Mine 100 OB 3710 level (2)[1310865G.raw] 1310865 Garson #1 OB 5000 level (1)[1310867G.raw] 1310867 Coleman Blended Ore 3 3 2 2 16 2.12 2.08 2.04 2.0 d Scale(Å) [SP W MLA sa_xray]<\\bruker xrd\xrd Data> Thursday, December 11, 2008 03:24p (MDI/JADE9) 17
Pyrrhotite behaviour by chrystallography Reproduced from Wercholaz (2009) 100 Pyrrhotite Flotation 90 80 70 60 50 40 30 20 10 Mixed Po Hexagonal Po Monoclinic Po 0 0 20 40 60 80 100 Pentlandite Flotation 18
Pyrrhotite flotation by crystallography Recovery by crystallography by size Monoclinic pyrrhotite in the operations reviewed is more easily rejected Hexagonal pyrrhotite is recovered well in the floatable size fractions Monoclinic pyrrhotite is recovered more readily in the finest fractions and is sufficiently floatable to not be rejected in a froth washed column. Recovery (%) 40 35 30 25 20 15 10 5 Hex Column Hex Conventional Mono Column Mono Conventional 0 CS7 CS6 CS4 5 CS3 CS1 2 +53 +106 SIze (micron) 19
Magnesium dominated ores
Magnesium dominated ores Examples Main minerals are talc, serpentine, orthopyroxene Operation examples Thompson s Birchtree mine Raglan Mount Keith (Australia) Mirabela (Brazil) Strategies for rejection Saline water CMC Combination of saline water and CMC s Prefloat Deslime 21
Pentlandite in gangue High MgO low grade deposits Deportment is important to account for textures such as the attached that will limit the recovery of pentlandite from serpentine in this case Pentlandite Shape of gangue minerals can be important. Many serpentine minerals are fibrous and this impacts the grindability and floatability of these minerals. Serpentine 22
Gangue into concentrate Sudbury ores Do we need to measure the crystal structure of the gangue minerals to determine its effect? % Mineral in Flotation Feed 60 50 40 30 20 10 0 10 9 8 7 6 5 4 3 2 1 0 % Mineral Recovery to Concentrate Amphibole Clinopyroxene Orthopyroxene Chlorite + Mica Chlorite + Mica Recovery Orthopyroxene Recovery Clinopyroxene Recovery Amphibole Recovery Other NSG (Liberated) 23
Chalcopyrite Pentlandite Separation
Chalcopyrite / pentlandite separation Difficult to demonstrate in laboratory Operation Flowsheet %Cu %Ni Cu/Ni ratio of feed Clarabelle Bulk 2.0 1.0 2 Strathcona Sequential/Bulk 1.8 1.4 1.3 Kevitsa Sequential 0.3 0.3 1 Thompson Bulk 0.1 1.7 0.1 Jinchuan Bulk 2.4 1.3 1.8 Taimyr Peninsula Bulk 2.7 1.6 1.7 Norilsk Duluth Metals Under development 0.6 0.2 3 Cosmos/Leinster/ N/A 0.2 3.5 0.06 Kambalda Voisey s Bay Bulk 2.4 3.5 0.7 Santa Rita N/A 0.1 0.5 0.2 Raglan N/A 0.8 2.0 0.4 25
Copper/Nickel Separation Key metallurgical parameters Operated at saturated lime (>12) to strip the collector from the surface Operated with high circulating load for the chalcopyrite to crowd or bully the pentlandite out In some cases cyanide or dextrin are used to help depress pentlandite and pyrrhotite The concentrate tends to be >95% chalcopyrite Ni grades of copper concentrates are targeted <0.5% Ni 26
Summary
Summary More with Less More mineralogy less guesswork Not all deposits are the same and their genesis impacts the separation of pentlandite from pyrrhotite, chalcopyrite and gangue Understanding the nickel phases present and the deportment of nickel in the gangue phases is crucial to determine the recoverable nickel content Characterising the mineralogy is key to developing successful flowsheets Size matters particularly for pentlandite and its separation from other sulphides Shape matters - Crystallography affects the flotation of pyrrhotite and gangue 28
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