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Gold Flotation

Flotation is a common method for gold concentrators to process rock gold ore, and it is often used to process sulfide mineral gold-bearing ores with high floatability. The flotation gold process can directly discard the tailings, and at the same time consider the convenience of operation, low operating cost and maximum recovery of useful minerals.

Flotation process is used to process fine gold, sulfide gold-containing quartz ore, multi metal gold-containing sulfide ore and carbon-containing ore.

Gold Flotation: Secrets to Boosting Your Gold Recovery Rate?

Last Updated: March 2025 | Estimated Reading Time: 23 minutes

Gold Ore flotation plant
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This Article Will Help You Understand:

  • What is Gold Flotation & Its Key Differences?
  • Best Gold Ore Types for Flotation? (Sulfide-Hosted, Free Gold)
  • Typical Gold Flotation Process Flow Stages?
  • Importance of Flotation Reagents in Gold Flotation?
  • Key Parameters Affecting Gold Recovery & Grade?
  • Strategies for Refractory Gold Ores? (Carbonaceous, Arsenical)
  • Post-Treatment of Gold Flotation Concentrate?
  • Main Equipment & Operating Costs for Gold Flotation?
  • How Lab Tests Assess Gold Ore Suitability?
  • Key Factors for Max ROI in Gold Flotation?

What is Gold Flotation & Its Key Differences?

Gold flotation is a mineral processing technique that separates gold-bearing particles from gangue (waste rock) by making the gold or its carrier minerals hydrophobic (water-repelling) and attaching them to air bubbles. These bubbles rise to the surface, forming a froth rich in gold, which is then collected. This differs significantly from other common gold extraction methods. Gravity concentration (like using a or Spiral Chute) relies on gold’s high density to separate it. Gold cyanidation, a hydrometallurgical process, dissolves gold into a cyanide solution.

Flotation-Machine-Working-Principle
Flotation-Machine-Working-Principle

3-fine, free (liberated) gold ore-gold-in-sulfide-minerals
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Flotation can also be used for ores containing some fine, free (liberated) gold, though it may not be as efficient for very coarse free gold, which is better recovered by gravity methods. However, the “floatability” of free gold can be a paradox. Not all “free” gold particles readily attach to air bubbles. Their surfaces can become contaminated or coated during grinding, making them less hydrophobic. This “tarnishing” can significantly hinder their recovery by flotation. Therefore, even for ores with free gold, a combination of gravity separation for coarser gold and flotation for finer gold and sulfide-associated gold is often the optimal gold processing strategy. In some cases, fine, seemingly liberated gold shows poor flotation response until pre-treatment steps like attrition scrubbing were introduced to clean the particle surfaces.

A typical gold flotation process flow involves several interconnected stages, each playing a crucial role in achieving optimal gold recovery. The process begins with comminution: crushing the run-of-mine ore using Jaw Crushers and Cone Crushers, followed by grinding, usually with Ball Mills or Rod Mills, to liberate the gold or gold-bearing sulfide particles. Proper liberation size is critical and is determined by ore mineralogy. After grinding, the ore slurry is conditioned in Mixer tanks with specific flotation reagents.

4-gold-flotation-plant-circuit-flowsheet

The conditioned slurry then enters a series of Flotation Machines. These are typically arranged in banks: rougher, scavenger, and cleaner stages. Rougher flotation aims to recover as much gold as possible, even at a lower grade. The tailings from the rougher stage may go to scavenger flotation to recover any remaining gold. The rougher concentrate is then usually sent to cleaner flotation stages (often multiple stages) to upgrade the gold flotation concentrate by removing entrained gangue and unwanted minerals. The final concentrate is dewatered using thickeners (like a High Efficiency Concentrator) and filters. The choice and configuration of gold ore beneficiation equipment are tailored to the specific ore characteristics and project scale. One often overlooked aspect is the strategic placement of “flash flotation” cells within the grinding circuit. These can recover liberated gold as soon as it’s freed, preventing overgrinding and surface contamination, significantly boosting overall gold recovery.

Importance of Flotation Reagents in Gold Flotation?

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Modifiers-Soda-ash
5-Flotation-Reagents-Collectors-Xanthates
Collectors-Xanthates
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Frothers-MIBC

Frothers (e.g., MIBC, pine oil, glycols) are added to create stable, yet suitably brittle, air bubbles that can carry the hydrophobic mineral particles to the surface. The froth structure is vital for effective collection of the gold flotation concentrate. Modifiers are used to control the pulp chemistry and enhance selectivity. These include pH regulators (like lime or soda ash to adjust alkalinity), activators (to enhance the floatability of certain minerals, e.g., copper sulfate for some gold-associated sulfides), and depressants (to prevent unwanted minerals like certain gangue or non-gold-bearing sulfides from floating). The interplay between these reagents is complex. For example, the pH significantly affects collector adsorption and the behavior of many minerals. You should notice that “more is not always better” with reagents. Overdosing can lead to non-selective flotation, poor froth characteristics, and increased costs. Careful laboratory testing and plant optimization are essential to find the optimal reagent suite and dosages for your specific ore.

6-Key Factors affecting Gold Flotation (1)
6-Key Factors affecting Gold Flotation (2)
grinding size affect gold flotation

Reagent dosage and conditioning time are also key. Insufficient collector means poor hydrophobicity, while too much can lead to non-selective flotation. Adequate conditioning time allows reagents to properly interact with mineral surfaces. Aeration rate and froth depth in the Flotation Machines control the bubble generation and the selectivity of the froth collection. A less commonly discussed but highly influential factor is the electrochemical potential (Eh or ORP) of the pulp. For sulfide gold ore flotation, the Eh can significantly impact the surface chemistry of sulfide minerals and the effectiveness of certain collectors. Managing the “carrier minerals” for gold is another layer. If gold is hosted in pyrite, you need to float pyrite efficiently. But if there are multiple sulfide species, some barren of gold, you need to selectively float only the gold-bearing ones, which requires precise control of depressants and activators.

Refractory gold ores, such as those containing carbonaceous material (“preg-robbing” ores) or finely disseminated gold in arsenical sulfides, present significant challenges for gold flotation and require special processing strategies. Carbonaceous material can adsorb dissolved gold if any pre-cyanidation occurs, or it can float non-selectively, diluting the gold flotation concentrate and consuming reagents. For these ores, strategies include: pre-flotation of carbon (carbon scalping), using blinding agents (like kerosene or specialized polymers) to passivate the carbon surface before gold flotation, or employing a flotation-roast-leach sequence.

7-Complex Ore Bodies
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Arsenical gold ores, where gold is often locked within arsenopyrite or other arsenic-bearing sulfides, require effective flotation of these carrier minerals. However, arsenical concentrates can incur penalties from smelters or require specialized downstream processing like pressure oxidation (POX) or bio-oxidation before gold cyanidation. Fine-grained gold, whether free or encapsulated, demands very fine grinding for liberation, which can lead to slime issues. In such cases, techniques like ultra-fine grinding followed by flotation, or specialized flotation cells designed for fine particles, might be necessary. The management of “carrier minerals” is critical. It’s not just about floating any sulfide; it’s about selectively floating the gold-bearing sulfides while depressing barren ones. This requires detailed mineralogical knowledge and tailored flotation reagent schemes, possibly involving multiple stages of differential flotation.

Post-Treatment of Gold Flotation Concentrate?

Gold flotation concentrate typically requires further processing to extract the elemental gold, as the gold is still often encapsulated or not in a pure, saleable form. The choice of post-treatment depends on the nature of the concentrate (e.g., free gold content, sulfide association, presence of refractory components) and economic considerations. A common route for sulfide-rich gold flotation concentrate is gold cyanidation. The concentrate is reground (if necessary) and then leached with a dilute cyanide solution to dissolve the gold. The gold is then recovered from the pregnant leach solution by methods like Carbon-In-Pulp (CIP), Carbon-In-Leach (CIL), or Merrill-Crowe precipitation.

8-Gold Flotation Concentrate
8-gold bars

If the concentrate is highly refractory (e.g., gold locked in arsenopyrite or significant preg-robbing carbon), pre-treatment before cyanidation is often essential. This can include roasting (to oxidize sulfides and carbon), pressure oxidation (POX), or bio-oxidation. Roasting converts sulfides to oxides and burns off carbon, liberating the gold for subsequent leaching, but it generates SO2 gas that must be managed. POX and bio-oxidation are hydrometallurgical methods that break down the sulfide matrix under specific conditions. In some cases, particularly for very high-grade concentrates with coarse free gold, direct smelting might be an option, though this is less common. The overall goal is to select a post-treatment method that maximizes gold recovery economically and environmentally.

Main Equipment & Operating Costs for Gold Flotation?

Investing in a gold flotation circuit involves specific gold ore beneficiation equipment and ongoing operating costs that you need to carefully consider. The main equipment includes crushing units (Jaw CrushersCone Crushers), grinding mills (Ball Mills), conditioning tanks (Mixers), banks of Flotation Machines (roughers, scavengers, cleaners), thickeners, filters, and reagent preparation/dosing systems. The scale of operation (tonnes per day) will largely dictate the size and number of these units, directly impacting capital expenditure (CAPEX).

Operating costs (OPEX) for gold flotation primarily consist of:

  1. Reagents: Flotation reagents (collectors, frothers, modifiers) can be a significant cost, especially for complex ores requiring specialized or high dosages.
  2. Power: Grinding is very energy-intensive, and flotation cells, pumps, and other equipment also consume considerable power.
  3. Labor: Skilled operators and maintenance personnel are required.
  4. Maintenance & Spares: Wear parts for crushers, mill liners, flotation cell impellers/diffusers, and pump parts need regular replacement.
  5. Water: While much is recycled, some makeup water is usually needed.

The “hidden cost” of poor carrier mineral management can also inflate OPEX. If you’re floating large quantities of barren sulfides along with the gold-bearing ones, you’re wasting reagents, power, and downstream capacity on material that doesn’t contribute to your gold recovery rate. Optimizing selectivity is key to managing these costs effectively.

Gold ore flotation test
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Flotation tests are then conducted on representative ore samples. These batch tests explore various parameters:

  • Grind size: Determining the optimal liberation.
  • Flotation reagent schemes: Testing different types and dosages of collectors, frothers, and modifiers.
  • pH levels: Finding the best pH for selectivity.
  • Conditioning and flotation times.

Locked cycle tests (LCTs) simulate a continuous circuit by recycling intermediate streams, providing a more realistic estimate of plant performance. The results will indicate the achievable gold recovery rate and gold flotation concentrate quality. These tests also help identify issues like preg-robbing or the presence of difficult-to-float gold. For instance, the behavior of “free gold” in flotation is often counterintuitive. Lab tests can reveal if fine, liberated gold is being lost due to surface contamination, requiring specific pre-treatment or specialized collectors.

Maximizing your return on investment (ROI) in a gold flotation project hinges on several key factors, extending beyond just purchasing gold ore beneficiation equipment. 

  • Firstly, thorough ore body knowledge and detailed metallurgical test work are paramount. Understanding your ore’s variability and how gold occurs (deportment) allows for a robust flowsheet design that can handle ore changes.
  • Secondly, selecting the right gold processing technology and equipment for your specific ore type is crucial. Don’t over-engineer, but also don’t cut corners on critical components. Energy efficiency, particularly in grinding, and optimized flotation reagent consumption significantly impact operating costs and thus ROI.

Effective process control and automation can lead to more stable operation and higher gold recovery. Investing in good instrumentation and skilled operators pays dividends. A critical factor, often underestimated, is the management of “carrier minerals.” If your gold is hosted in specific sulfides, ensure your flotation circuit is optimized to recover those sulfides selectively, not just bulk sulfides. This avoids diluting your gold flotation concentrate and reduces downstream processing costs. Finally, consider the entire value chain, including concentrate transportation, smelting/refining terms, and environmental compliance. A holistic approach that balances CAPEX, OPEX, gold recovery rate, and risk management will ultimately ensure the best ROI for your gold flotation venture.

Gold Flotation FAQs

Question 1: Can gold flotation recover 100% of the gold from an ore?
No, 100% gold recovery is practically impossible. The achievable gold recovery rate depends on ore mineralogy, liberation, particle size, and process efficiency. Typical recoveries can range from 70% to over 95% for suitable ores.
Question 2: What is the main difference between a gold collector and a frother?
collector makes gold or gold-bearing mineral particles hydrophobic (water-repelling) so they attach to air bubbles. A frother helps create stable air bubbles that carry these mineral-laden bubbles to the surface to form a collectable froth.
Question 3: Why is pH important in gold flotation?
pH affects the surface charge of minerals and the ionization/effectiveness of many flotation reagents, especially collectors. Optimizing pH is crucial for selective flotation and maximizing gold recovery.
Question 4: How is preg-robbing carbon handled in gold flotation?
Strategies include pre-floating the carbon before gold flotation, using blinding agents (like kerosene) to deactivate the carbon, or employing specialized leaching circuits (like CIL/CIP) if flotation is followed by cyanidation.

ZONEDING is your expert partner for a full range of mineral processing equipment and complete gold processing solutions. ZONEDING specializes in gold flotation technology, providing everything from Jaw Crushers and Ball Mills to state-of-the-art Flotation Machines and concentrate handling systems. Our experience spans global projects, offering flowsheet design, equipment supply, installation, commissioning, and ongoing support to help you achieve the highest possible gold recovery and operational efficiency.

Contact ZONEDING’s specialists today to discuss your gold project and let us help you turn your ore into gold!

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Last Updated: March 2025

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