The Chemistry of Gold Extraction
1
-- The chemistry of gold extraction The chemistry of gold extraction by John Marsden and lain House. Ellis Horwood Series in Metals and Associated Materials. Chichester, Ellis Horwood. £80. The chronology has been well researched, and the book defmes all the milestones. It is a pity that there is no map of the early gold finds in South Africa, which would have offered a comparison with those shown of Australia and the USA. Nevertheless, the 'Pre-cyanidation, Cyanidation and Technical Development' eras fall logically into place, and reflect on the advances in social history and civilization, as well as in technology. ORE DEPOSITS AND PROCESS MINERALOGY This chapter is of immense value in providing all the basic information about the chemical and physical properties of native gold and gold-bearing minerals, and how these affect the performance of all the chemical processes involved in gold extraction. The important characteristics of placer ores versus free-milling ores are explained, as are the reasons for specific problems relating to gold extraction from oxidized ores, sulphides, carbonaceous ores, etc. Particularly useful are the sections dealing with the occurrence of gold in process products such as flotation and gravity concentrates, tailings, and refmery materials. State-of-the-art methods for the quantitative characterization of gold ore that can lead to increased revenues or reduced costs are described. FACTORS AFFECTING PROCESS SELECTION The all-important factors affecting the extraction process are neatly divided into six categories, which are given in- depth treatment. Specifically, the metallurgical response of an ore (or concentrate) to a process can be thoroughly determined through the application of a detailed programme of testing, which is shown diagrammatically in flowsheet form. The unit process options used in extraction are neatly displayed in a similar manner, supported by detailed text. Flowsheet options are described for the different types of ore (showing that a 'horses for courses' approach is necessary), and provide a very useful source of reference. Clearly, circuit complexity, and hence cost, vary with the degree of refractoriness of the gold-containing material. In this regard, a general guide is given for relative capital and operating cost factors for selected flow sheets, for which certain fIXedparameters are assumed. GOLD HYDROMETALLURGY In this and succeeding chapters, the book's title topic is addressed in detail. Physical-chemistry principles of reaction equilibria and reaction kinetics are generally described, but are also specifically applied to gold chemistry where appropriate. The vital role played by Reviewer:R. Graham particle characteristics in leaching reactions is stressed, both physical and mineralogical. The experimental techniques that can be employed to provide information on reaction mechanisms are briefly reviewed. Oxidatlve Pretreatment The reasons for the necessity of pretreating 'refractory' ores are given, and the various oxidative processes are detailed, i.e. hydrometallurgical sulphide, low-pressure oxygen, high-pressure oxygen (acidic and non-acidic), nitric acid, chlorine, biological, and pyrometallurgical oxidation. In all cases, the reaction chemistry and kinetics are reviewed, and attention is paid to effluent streams and gaseous emissions. The exciting concept of biological oxidation is given sound theoretical and practical treatment, identifying it as a cost-effective and environmentally acceptable process for gold-bearing sulphide ores and potentially for carbonaceous ores. The description of pyrometallurgical techniques benefits greatly from the liberal use of diagrams showing changes in structure, phase-stability diagrams, tables, and graphs. Leaching Eh;>H diagrams are used to full effect in this chapter. The chemistry of cyanidation as the classic gold-leaching technique is developed methodically, and the effects of interfering elements are discussed. A description is given of practical applications using agitated tanks, vats, heaps, etc., and alternative lixiviants and associated reaction chemistry are reviewed. However, the point is made that development and cost constraints impede the establishment of large-scale commercial processes using these reagents. Solution Purification and Concentration This chapter describes the vitally important step of concentrating and purifying gold-bearing solutions. The adsorption of the gold complex by activated carbon is dealt with in much detail, together with elution and the effects on the process parameters and the presence of other ionic species. The processes considered include carbon preparation, carbon-in-pulp, carbon-in-leach, carbon-in- column, elution, and reactivation. Ion-exchange resins are similarly dealt with, and resin-in-pulp and resin-in-solution processes are considered. Solvent extraction is reviewed briefly, its general principles being explained and specific gold-extraction systems being highlighted. The point is made that solvent extraction is not applied commercially to purify and concentrate gold-bearing solution. Recovery Details are given of the electrochemistry of the cementation (precipitation) of gold by zinc metal, effective page290; 282 OCTOBER 1992 JoumaI of tie South Amcan Institute of Mining and MelBHutgy
Transcript of The Chemistry of Gold Extraction
--The chemistry of gold extraction
The chemistry of gold extraction by John Marsden and lainHouse. Ellis Horwood Series in Metals and AssociatedMaterials. Chichester, Ellis Horwood. £80.
The chronology has been well researched, and the bookdefmes all the milestones. It is a pity that there is no map ofthe early gold finds in South Africa, which would haveoffered a comparison with those shown of Australia and theUSA. Nevertheless, the 'Pre-cyanidation, Cyanidation andTechnical Development' eras fall logically into place, andreflect on the advances in social history and civilization, aswell as in technology.
ORE DEPOSITS AND PROCESS MINERALOGY
This chapter is of immense value in providing all thebasic information about the chemical and physicalproperties of native gold and gold-bearing minerals, andhow these affect the performance of all the chemicalprocesses involved in gold extraction. The importantcharacteristics of placer ores versus free-milling ores areexplained, as are the reasons for specific problems relatingto gold extraction from oxidized ores, sulphides,carbonaceous ores, etc. Particularly useful are the sectionsdealing with the occurrence of gold in process products suchas flotation and gravity concentrates, tailings, andrefmery materials.
State-of-the-art methods for the quantitativecharacterization of gold ore that can lead to increasedrevenues or reduced costs are described.
FACTORS AFFECTING PROCESS SELECTION
The all-important factors affecting the extraction processare neatly divided into six categories, which are given in-depth treatment. Specifically, the metallurgical response ofan ore (or concentrate) to a process can be thoroughlydetermined through the application of a detailedprogramme of testing, which is shown diagrammatically inflowsheet form. The unit process options used in extractionare neatly displayed in a similar manner, supported bydetailed text.
Flowsheet options are described for the different types ofore (showing that a 'horses for courses' approach isnecessary), and provide a very useful source of reference.Clearly, circuit complexity, and hence cost, vary with thedegree of refractoriness of the gold-containing material. Inthis regard, a general guide is given for relative capital andoperating cost factors for selected flow sheets, for whichcertain fIXedparameters are assumed.
GOLD HYDROMETALLURGY
In this and succeeding chapters, the book's title topic isaddressed in detail. Physical-chemistry principles ofreaction equilibria and reaction kinetics are generallydescribed, but are also specifically applied to goldchemistry where appropriate. The vital role played by
Reviewer:R. Graham
particle characteristics in leaching reactions is stressed,both physical and mineralogical. The experimentaltechniques that can be employed to provide information onreaction mechanisms are briefly reviewed.
Oxidatlve Pretreatment
The reasons for the necessity of pretreating 'refractory'ores are given, and the various oxidative processes aredetailed, i.e. hydrometallurgical sulphide, low-pressureoxygen, high-pressure oxygen (acidic and non-acidic),nitric acid, chlorine, biological, and pyrometallurgicaloxidation. In all cases, the reaction chemistry and kineticsare reviewed, and attention is paid to effluent streams andgaseous emissions. The exciting concept of biologicaloxidation is given sound theoretical and practical treatment,identifying it as a cost-effective and environmentallyacceptable process for gold-bearing sulphide ores andpotentially for carbonaceous ores. The description ofpyrometallurgical techniques benefits greatly from theliberal use of diagrams showing changes in structure,phase-stability diagrams, tables, and graphs.
Leaching
Eh;>H diagrams are used to full effect in this chapter.The chemistry of cyanidation as the classic gold-leachingtechnique is developed methodically, and the effects ofinterfering elements are discussed. A description is given ofpractical applications using agitated tanks, vats, heaps, etc.,and alternative lixiviants and associated reaction chemistryare reviewed. However, the point is made that developmentand cost constraints impede the establishment of large-scalecommercial processes using these reagents.
Solution Purification and ConcentrationThis chapter describes the vitally important step of
concentrating and purifying gold-bearing solutions. Theadsorption of the gold complex by activated carbon is dealtwith in much detail, together with elution and the effects onthe process parameters and the presence of other ionicspecies. The processes considered include carbonpreparation, carbon-in-pulp, carbon-in-leach, carbon-in-column, elution, and reactivation. Ion-exchange resins aresimilarly dealt with, and resin-in-pulp and resin-in-solutionprocesses are considered. Solvent extraction is reviewedbriefly, its general principles being explained and specificgold-extraction systems being highlighted. The point ismade that solvent extraction is not applied commercially topurify and concentrate gold-bearing solution.
RecoveryDetails are given of the electrochemistry of the
cementation (precipitation) of gold by zinc metal, effective
page290;
282 OCTOBER 1992 JoumaI of tie South Amcan Institute of Mining and MelBHutgy
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