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Processing Gold Ores Good Morning, ladies and gentlemen.

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Presentation on theme: "Processing Gold Ores Good Morning, ladies and gentlemen."— Presentation transcript:

1 Processing Gold Ores Good Morning, ladies and gentlemen.
I'm here to present the paper "Process design for gold ores: a diagnostic approach" The authors are: myself; Professor Arthur Chaves, from University of São Paulo, Brazil, and Professor John Meech, from University of British Columbia, Canada

2 Agenda Evolution of the gold industry
Gold ore types and characteristics Processing gold ores processing stages unit operations Process development for gold ores An expert system for gold process design A gold mine in Amazon Summary

3 Evolution of the gold industry

4 Evolution of gold industry
Pre-cyanidation Ancient Egypt (3050 a.c) Turkey - gold coins (700 a.c.) Gold refining (560 a.c.) Roman Empire Gold rushes Spanish and Portuguese Colonies South America California, New Zealand, Canada, Australia

5 Evolution of gold industry
“100 years of cyanidation” Crown Mine - New Zealand Exploitation of Witswatersrand deposits South Africa as main gold producer Processing route evolution application of basic mineral processing technology Low incentive from low gold prices

6 Gold price over the last 50 years

7 Gold price since 1344

8 Evolution of the gold industry
“Accelerated development years ( ) Driving force: gold price Development of gold processing CIP process Heap Leaching SAG Milling Refractory ore treatment

9 Evolution of the gold industry
Evolution of gold industry Gold industry in the 1990’s declining gold prices need for cost reduction low cash cost properties Trends for next decade new “rump-up” of gold prices development of projects now “on hold” increasing control and automation

10 Gold ore types and characteristics

11 Gold ores Gold: Process and Mineralogy
Most noble metal, native occurrence Also associated with silver, tellurium, bismuth and PGM’s typical ore grades: 0.5 to 20 g/t Primary gold source: ores Secondary gold sources gravity concentrates flotation concentrates plant tailings refinery tailings recycled gold * PGM means platinum group metals

12 Types of gold deposits Placer ores Oxidized ores Primary ores

13 Types of gold mining methods
Placer ores => Placer mining Oxidized ores => Open pit Primary ores => Underground mining

14 Gold Ore Types Main ore types (after Marsden) placers oxidized
free milling silver rich iron sulphide bearing arsenic sulphide bearing carbonaceous copper bearing antimony bearing gold telluride bearing easy processing refractory

15 Gold ore characterization and testing
Mineralogical characterization Technological tests exploratory testwork diagnostic leaching optimization testwork pilot plant

16 Gold Liberation “Free gold” definition and discussion
Classic definition: Gaudin Physical liberation of the valuable mineral from gangue Limitation: Hydrometallurgical and Pyrometallurgical processes: access of gas or solution to mineral is the issue Definition adopted: free gold = accessible gold direct correlation with processes used by hydrometallurgists

17 Refractory gold Refractory gold: cannot be made accessible using only comminution Ore needs chemical pretreatment prior to gold extraction Main causes of gold refractoriness gold encapsulated in quartz/silicates gold encapsulated in sulphides ore containing active carbonaceous matter

18 Industrial gold ore processing

19 Gold ore processing Gold Ore Gold Gold Purification Production
Preparation Gold liberation Particle size adjustment to next processes Physical concentration and oxidation pretreatment Gold Extraction Extraction of gold from ore into solution and/or concentrate Gold Purification Purification of gold bearing solution Gold Production Recovery of gold from solution or concentrate to produce a bulliion bar

20 Unit operations for each step
Intelli Gold Ore Preparation Gold Extraction Gold Purification Gold Production

21 Process development for gold ores

22 Process development

23 Process design Process routes Geology Project context Mineralogy
Industrial processes Process routes Project context Mineralogy Technological tests

24 Choice of oxidation processes
Gold ore Free gold Refractory gold Gravity concentration and conventional Cyanidation Oxidation followed by leaching Direct Roasting Biooxidation Chemical oxidation CIL Alternative reagents under pressure Acid Pressure Alkaline Flotation concentration

25 Feed Primary Crushing Secondary SAG Milling Crushing Rod Milling
Ball Milling (or pebble mill) Gravity Agglomeration Thickening To smelting Concentration Heap Flotation t Oxidation c Heap Pressure Roasting Bio-oxidation Neutralization Oxidation Heap Pre-aeration Pre-aeration Cyanidation Carbon-in- Carbon-in- Cyanidation Cyanidation leach leach Carbon-in- Carbon-in- Carbon-in- CCD CCD column pulp pulp Elution Elution Elution Zinc Zinc Electrowinning Electrowinning Electrowinning Precipitation Precipitation Smelting GOLD

26 Primary Crushing Secondary SAG Milling Rod Milling Ball Milling
(or pebble mill) Thickening Gravity Concentration Agglomeration Flotation Heap Oxidation Pressure Bio-oxidation Roasting Neutralization Pre-aeration Cyanidation Carbon-in- leach pulp CCD column Elution Electrowinning Zinc Precipitation Smelting Feed To smelting t c GOLD Primary Crushing Secondary SAG Milling Ball Milling Pre-aeration Carbon-in- leach Elution Electrowinning Smelting Feed GOLD

27 Fazenda Brasileiro ore
Main ore characteristics deposit type: “greenstone belt” mineralogy: fine gold (d95=37 microns), free or in borders/fractures, associations with sulphides and quartz laboratory tests: high recoveries for both direct cyanidation and flotation, good recovery in gravity concentration

28 Fazenda Brasileiro ore
Conventional process route

29 Refractory sulphide ore
Main ore characteristics deposit type: “greenstone belt” mineralogy: very fine gold(d95=3 microns), encapsulated and in borders/fractures, association with sulphides laboratory tests: low recoveries in direct cyanidation and gravity concentration tests, high recoveries in flotation tests, high recoveries by cyanidation after bio-oxidation or pressure oxidation

30 Refractory sulphide ore
Processing route with pretreatment

31 Placer ore Main ore characteristics deposit type: “placer”
mineralogy: medium size gold(d95=100 microns), some physically liberated, some associated with sulphides

32 Placer ore Physical only processing route Feed Primary Crushing
Secondary Crushing Ball Milling Gravity Thickening To smelting Concentration Physical only processing route Flotation Smelting GOLD

33 Expert system for gold process design

34 Intelligold - expert system for process design
Objective: Integration of gold process design knowledge into artificial intelligence software Principles Use of logical variables and fuzzy sets to represent information Organization of information into a “knowledge building” stepladder

35 Intelli Gold Project start DECISION MAKING Decision rules, fuzzy sets
Ore/deposit information Intelli Gold Process routes indication Continue investigation . Do research . Gather more data Flowsheet alternatives Hypertext with literature review and case studies DECISION MAKING Abandon or hold Cost and revenues calculation Mining method user input INTELLIGOLD aims to be an expert system for gold project design. It works in this way: the user inputs ore and deposit information in the system, the application of decision rules and fuzzy sets leads to possible process routes indication, which are presented in a hypertext using flowsheet alternatives together with information on these alternatives; after that, costs, revenues, return and risk are evaluated for each alternative and presented to the user, that has to make the decision of either implement, abandon or study it more; if the decision is to study more, new information can be now added to the system, and refined answers are produced; this cycle continues until sufficient basis for the “go-no go” decision exists. Implement project Ranking of alternatives Alternative NPV/IRR Risk factors

36 Knowledge building Process routes Process options Behavior
combined W2= f ( sampling, demonstration testwork) W1=1 inferred measured knowledge Process options combined W1=1 W2= f ( sampling, preliminary testwork) inferred measured knowledge Contradictions management and feedback Behavior This slide illustrates how the system "builds knowledge", to accomplish the task intended. The system is designed like a step ladder. Its inferencing goes, step by step, verificating, in each step, the compatibility about the inferred and measured variables. Or, in other words, knowledge and data. Each combined variable is therefore the weighted combination of measured and inferred sub-variables, that, in theory, have to be compatible, or have an approximate meaning. Usually, the weight of measured attributes are higher than the inferred. The system goes therefore inferencing and combining values until the suggestion and automatic drawing of feasible process routes are possible. Sometimes, when the system finds an incompatibility, like if mineralogy suggests gold is cyanidable and testwork finds it is not. The system then feedbacks the information, asking the user to verify the data in each level. If still the contradiction persists, it goes to the lower level, in a verification of causes and consequences. Ultimately, if the ore behavior is particular, the user has the ability of changing weights, telling the system which information it has to trust more. To have one idea of the size of the step ladder, it can be said that the process design module itself has around 600 rules and manipulates among 1300 variables and sub-variables. combined W1=1 W2= f ( sampling, equipment, precision) 1300 variables 600 rules inferred measured knowledge Mineralogy Geology

37 models and adjustment parameters
Economic evaluation Flowsheets and process information Project site Mining method Economic parameters Environmental issues Unit operation models Generic models Infrastructure models and adjustment parameters Costs Revenues Cash flow Economic indicators Key operations Key variables Risk factors After the metallurgical evaluation is finished, the next step is the economic evaluation. . it uses generated flowsheets as input . estimate costs for each unit operation, using actual costs and adjustment factors and applying inflation indexes . calculate revenues based on gold recoveries and prices, and finally, . calculates the economic parameters . of course, the system assigns a degree of certainty to the economic parameters and indicates the main risk factors

38 A gold mine in the Amazon

39 A gold mine in the Amazon
Igarapé Bahia Mine Largest Brazilian gold mine 10-12 tons of gold/year Very low cash cost Located in the Carajas Reserve Forest reserve area owned by a mining company - CVRD Only 0.4% of area occupied by mine activities Preservation of area and native cultures

40 Aerial view of mine site
Mill Infrastructure facilities

41 Mine

42 Processing installations

43 Grinding mills

44 Gold smelting furnace

45 Waste disposal

46 Summary Gold is an important resource to economy
Gold ores are found in different types Processing is highly dependent on mineralogical characteristics Process design is a challenging activity Intelligent systems can be used to design and operate gold plants Advanced use of information technology in mineral industry is a key issue in the 21st century

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