Gold beneficiation technology | Analysis of the entire process of gold ore from ore to beneficiation
Due to its unique physical and chemical properties and scarcity, gold has an irreplaceable position in the fields of currency reserves, industrial production and high-end manufacturing. With the development of science and technology, the application of gold has expanded from the traditional fields of currency and jewelry to modern industrial sectors such as electronics, aerospace, instrumentation, artificial fibers, chemicals and national defense. This article will systematically introduce the whole process of gold beneficiation technology from raw ore to final product, including core processes such as gravity separation, amalgamation, flotation, cyanidation, heap leaching, thiourea leaching and carbon-in-slurry method, presenting readers with a complete picture of gold beneficiation technology.
1. Overview of gold resources and pre-processing of ore dressing The global gold resources are unevenly distributed. As the world's largest gold producer, South Africa's output accounts for more than 40% of the global total. According to historical data, the world's gold production was 53.2 million ounces in 1985, increased to 55.3 million ounces in 1986, and reached 59.2 million ounces in 1987, showing a stable growth trend. The fluctuation of international gold prices directly affects the scale of gold production, and price increases often stimulate the expansion of production capacity. Ore crushing and grinding are the primary links in gold beneficiation. Different pretreatment processes are required according to the properties of the ore (such as placer gold or vein gold) and the occurrence state of gold. For vein gold ore, it is usually necessary to go through multiple stages of crushing (coarse crushing, medium crushing, fine crushing) and grinding (ball milling, rod milling) to fully dissociate the gold minerals. The grinding fineness directly affects the subsequent separation effect, and it is generally required to reach a fineness range of -250 mesh accounting for 50-60% to -325 mesh accounting for 100%. Gravity separation equipment (such as jigs, shaking tables, etc.) is often installed in the grinding circuit to carry out early gold recovery to achieve the goal of "early recovery when possible". The practice of some Shandong concentrators has proved that this measure can effectively reduce the grade of tailings and improve the overall recovery rate.
2. Conventional gold beneficiation methods and applications
2.1 Gravity separation process Gravity separation is the most economical and effective method to recover coarse-grained monomer gold. It occupies a dominant position in the selection of placer gold and is often used as an auxiliary process in vein gold beneficiation. The principle is to use the property that the density of gold (19.32g/cm³) is much greater than that of gangue minerals (usually 2.7-3.0g/cm³) for separation. Mainstream gravity separation equipment includes: Chute: simple structure, low cost, especially suitable for processing coarse-grained gold, commonly used in my country Suede chute Jig: large processing capacity, often used in grinding circuits to recover dissociated monomer gold Shaking table: high sorting accuracy, mostly used for concentrating operations Hydraulic collector: used for the recovery of fine-grained gold
In terms of technological innovation, South Africa has developed new equipment such as the Reichert cone concentrator, the Johnson drum concentrator and the lattice belt concentrator; the Soviet Union has used short-cone hydrocyclones to treat low-grade fine-grained gold ore with significant results. Application practices in Shandong and other places in my country have shown that adding a re-selection step to the grinding cycle of broken altered rock-type gold ores can significantly reduce the grade of tailings and improve the recovery rate of the entire plant.
2.2 Amalgamation method The amalgamation method is a long-standing gold recovery process that uses the property of liquid mercury to selectively wet gold particles to form amalgam for gold extraction. This method is simple and low-cost, and about 25-30% of vein gold concentrators in the United States still use this process. However, the amalgamation method faces severe environmental challenges: mercury vapor is highly toxic and endangers the health of workers. Mercury seriously pollutes the environment and is difficult to degrade. The restrictions of the International Mercury Convention are becoming increasingly stringent.
To this end, many concentrators have changed the treatment process of gold-containing re-selection concentrate from mercury amalgamation to cyanidation. The future development of mercury amalgamation depends on breakthroughs in environmental protection technology. Only under the premise of effectively controlling mercury pollution can this traditional process continue to play a role. 2.3 Flotation process Flotation is one of the most widely used methods in gold beneficiation, and is particularly suitable for treating ores in which gold and sulfide minerals (such as pyrite, arsenopyrite, etc.) coexist. Gold-containing sulfide ore concentrate can be obtained through flotation, and most of the tailings can be discarded, greatly reducing the amount of subsequent processing. Key technologies for gold flotation: Reagent system: Commonly used collectors are C2-C5 alkyl xanthate. Mixed drugs have significant effects, such as: butyl xanthate + butyl ammonium black medicine (ratio of about 2:1) can optimize the flotation of gold-containing pyrite ores. Mixing xanthate with non-polar oils such as kerosene and diesel can improve indicators. 2-sulfur basic hydrazine thiazole + ammonia water neutralizes the combination of No. 31 black medicine Synergistic effect: Improve the recovery rate through the principle of merging, co-adsorption and chelation Process design: Usually one rough, two sweep and three refine or more complex processes are adopted.
The practice of Suichang Gold Mine in Zhejiang Province shows that the gold and silver recovery rates increased by 7.11% and 10.52% respectively by changing the single butyl xanthate to a mixture of butyl ammonium black medicine and butyl xanthate, and the concentrate grade was also significantly improved. New collectors such as alkyl isothiouronium salts (dosage is only 2-15 g/ton) have good selectivity for gold-bearing pyrite.
3. Gold extraction metallurgical technology 3.1 Cyanidation method Since its industrial application in the late 19th century, cyanidation has been the mainstream process for gold extraction, with the advantages of mature technology, low cost and high recovery rate. The basic principle is that under alkaline conditions, gold and cyanide ions form a stable [Au(CN)₂]⁻ complex and dissolve. Cyanidation process classification: Cyanidation of gravity concentrate: leaching of the enriched product obtained from gravity separation Cyanidation of gold concentrate: treatment of gold-containing sulfide concentrate obtained from flotation Cyanidation of flotation tailings: recovery of fine gold not completely recovered by flotation Cyanidation of gold mud: treatment of gold-containing materials produced by electrolysis or other processes Technological progress: Multi-stage cyanidation: For example, the Teorgi Tower concentrator in Mexico uses two-stage cyanidation (gold recovery rate of 96%), and the Comink concentrator in Canada uses three-stage leaching (leaching rate of 96.3%) Bell-shaped reactor: vortex is formed by injection to enhance mass transfer, solving the problems of long leaching time and adsorption film on the surface of gold particles in traditional cyanidation Pretreatment technology: roasting, biological oxidation and other pretreatment methods are used for difficult-to-treat gold ores The limitation of cyanidation is that it has poor treatment effect on ores containing arsenic, antimony, selenium and tellurium, and cyanide is highly toxic and has great environmental pressure. Sulfides (such as pyrrhotite, chalcocite) and copper minerals, "cyanide killers" will consume a lot of cyanide and oxygen, reducing leaching efficiency.
3.2 Heap leaching technology Heap leaching is an economical and effective method for treating low-grade gold ores (usually 0.5-1.5g/t). Gold is recovered from the leachate by building a heap of ore and spraying cyanide solution. The recovery rate spans a wide range (30%-90%), depending on the nature of the ore and the level of management. Key processes of heap leaching: Site construction: Anti-seepage treatment is required, usually HDPE geomembrane is used Ore preparation: Crushed to a suitable particle size (usually -25mm), granulation technology is used to improve the permeability of fine particles Spray system: Evenly distribute the liquid, control the cyanide concentration (usually 0.05%-0.1% NaCN) and pH (10-11) Gold recovery: mostly using activated carbon adsorption (CIP) or zinc powder replacement Since the industrial application of heap leaching in the United States in the 1970s, this technology has developed rapidly around the world, enabling a large amount of low-grade resources and waste rock to be utilized. my country began research at the Hushan Gold Mine in 1979, and trials were conducted in Liaoning, Henan, Hebei and other places. However, the cost was relatively high due to the small scale and low degree of mechanization.
Heap leaching has strict application conditions: the ore should not contain too much sulfide minerals, carbonaceous materials, clay and fine particles, otherwise the permeability is poor and leaching is difficult. B.M.Clem suggested that a compostability test must be carried out before heap leaching to evaluate the suitability of the ore. 3.3 Thiourea leaching technology As a promising alternative to cyanide, thiourea (CS(NH₂)₂) has the advantages of non-toxicity, good selectivity, and fast leaching speed (10-12 times faster than cyanide). Soviet scholar ЛОЛЕЩЫКОВ pioneered the study of thiourea gold extraction in 1968. Typical thiourea leaching system: Thiourea concentration: 1% Sulfuric acid concentration: 6.5% Oxidant (Fe³⁺): 0.1% The recovery rate of thiourea leaching for Carlin-type refractory gold ore in the United States reached 90%. my country's Changchun Gold Research Institute has conducted systematic research and established a thiourea gold extraction plant that processes 10 tons of flotation concentrate per day. Thiourea is particularly suitable for treating silver-containing ores, dissolving silver 10.8 times faster than cyanide.
The challenges of the thiourea method are high reagent consumption (thiourea is easily oxidized and decomposed), severe corrosion of equipment in acidic environments, and strict process control requirements. It has not yet been applied on a large scale in industrial applications. 3.4 Carbon-in-Pulp Method (CIP/CIL) The carbon-in-pulp method is an advanced gold extraction technology developed in the 1970s. It uses activated carbon to directly adsorb gold-cyanide complexes from the slurry, eliminating the solid-liquid separation step. In 1977, the first carbon-in-pulp plant was built at the Holmesket Gold Mine in the United States, and currently there are more than 40 in use worldwide. Process core: Adsorption system: 5-8 stirring tanks in series, with countercurrent flow of slurry and activated carbon Activated carbon: 8-20 mesh coconut shell carbon is mostly used, with a concentration in the tank of about 9.5g/L Gold-loaded carbon treatment: desorption (high temperature and high pressure NaOH+NaCN solution)-electrolytic recovery of gold Carbon regeneration: acid washing-heat treatment to restore activity.
Carbon-in-Pulp Method Variant: CIL (Leaching and Absorption): Leaching and adsorption are synchronized, saving equipment investment (e.g., a scale of 100,000 tons/day can save about $200,000) Magnetic Carbon Method: Magnetic activated carbon is separated by magnetic separation to reduce screening losses. my country's Linghu Gold Mine and Chiweigou Gold Mine have successfully applied carbon-in-pulp technology. The research and development direction focuses on new adsorption materials, such as polyacrylonitrile fiber activated carbon, "carbon fabric", etc., to improve adsorption efficiency and reduce fragmentation losses. 4. Emerging Technologies and Future Prospects In addition to mainstream processes, innovative technologies continue to emerge in the field of gold beneficiation: Alternative leaching agents: Water chlorination method: using chlorine as an oxidant Polysulfide amine method: suitable for complex ores containing antimony and arsenic Thiosulfate method: low sensitivity to copper Organic nitrile method: environmentally friendly reagent Special process: Bacterial leaching: using acidophilic bacteria to oxidize and pre-treat difficult-to-treat gold ores Resin slurry method: using ion exchange resin to replace activated carbon Solvent extraction: highly selective separation of gold High-pressure cyanidation: strengthening the leaching process.
Resource expansion: Gold extraction from seawater: still in the research stage "Three slag" recovery: Comprehensive recovery of gold and silver from sulfuric acid slag, copper leaching slag, and zinc slag Electronic waste recovery: Urban mine development Equipment innovation: High-efficiency gravity separation equipment: such as centrifugal concentrator Microwave-assisted leaching: Improve reaction rate Automation control: Optimize process parameters In the future, gold beneficiation will show the following trends: Green: Develop non-toxic and low-consumption processes to reduce environmental pollution High efficiency: Improve recovery rate and reduce grade lower limit (up to 0.3g/t) Comprehensive: Collaborative recovery of associated valuable components Intelligent: Big data and AI technology optimize process control
V. Conclusion The gold beneficiation technology system has matured and continued to innovate, from traditional gravity separation, amalgamation, flotation to modern cyanidation, carbon slurry, heap leaching and other processes, forming technical solutions for different ore characteristics. Concentrators usually adopt combined processes such as "gravity separation-flotation-cyanidation" or "flotation-roasting-cyanidation" to achieve the best economic benefits. In the future, with the advancement of technology and the improvement of environmental protection requirements, green processes such as non-cyanide leaching and biometallurgy will receive more attention, and digital and intelligent transformation will further improve the technical level and economic benefits of gold beneficiation. Through continuous innovation, the gold industry will better meet the needs of industrial development and reserves and achieve efficient resource utilization.
