Lead-zinc ores are commonly processed using froth flotation, a technique that selectively separates valuable minerals (galena for lead and sphalerite for zinc) from gangue based on surface chemistry. However, achieving optimal recovery and grade requires strict adherence to operational principles and precautions. This guide outlines key flotation principles for lead-zinc ores, flotation concentration optimization, and flotation machine parameters to maximize efficiency.
General Principles of Flotation Operations
1. Clearly Define The Requirements For Product Quantity and Quality
The flotation process involves concentrating useful minerals (such as metals) in the concentrate. For the concentrate, in addition to quantity (yield) indicators, there are also quality (grade) requirements. Therefore, the requirement for flotation is to maximize recovery rates while ensuring high concentrate quality. Therefore, in flotation practice, both local operational procedures and overall process control must adhere to this principle.
2. Understand Changes in The Properties of The Ore
In flotation, ore floatability (including mineral wettability, mineral types, product varieties, grain size distribution, and the degree of oxidation and muddiness of the ore) is a key indicator that determines the difficulty of operational control. Ores with good flotability exhibit strong adaptability to various process factors and are relatively easy to achieve the desired quantity and quality indicators. However, ores with poor flotability have poor adaptability and often cause fluctuations in quantity and quality indicators. In on-site operations, it is essential to promptly identify and understand changes in the properties of the original ore, take measures, and adjust relevant factors to adapt to these changes, thereby minimizing fluctuations in quantity and quality indicators.
3. Strive to Maintain The Relative Stability of The Flotation Process
The stability of the flotation process is a prerequisite for achieving stable process indicators, and good process indicators can only be derived from a relatively stable process. Therefore, stable operation is also an important operational principle. In fact, the factors influencing the flotation process are complex, with some being adjustable and others not; thus, achieving absolute process stability is impossible. Generally, when the properties of the ore are relatively stable or undergo minimal changes, and various operational conditions are appropriate with satisfactory process indicators, stability should be maintained as much as possible. Otherwise, it is necessary to adjust various operational conditions to achieve and maintain a new equilibrium and stability under new circumstances. Therefore, this stability is conditional, relative, and represents the objective that flotation operations should strive to achieve.
When conducting flotation operations, the basic steps for assessing various factors are as follows:
- Examine the properties of the raw ore.
- Examine the quantity and quality of the product.
- Examine the grinding concentration and fineness.
- Examine the operational cycle.
- Examine the acidity.
- Examine the reagent dosage.
Among these, examining the properties of the raw ore is the foundation. Only by thoroughly understanding the situation can one have a clear understanding and develop appropriate strategies.
Checking reagent dosage is based on accurate reagent addition:
If reagent addition is inaccurate, fluctuations will be significant, making it impossible to stabilize the flotation process and difficult to control changes in other operational factors.
The flotation operation principle of “Three Diligences, Four Accuracies, Two Goods, and One Unchanged” is based on the “Three Degrees and One Accuracy” (i.e., grinding fineness, flotation concentration, acidity, and accurate reagent dosage) operation method widely adopted in Chinese flotation plants, and further summarized from production practice.
- “Three Diligences” refers to diligently measuring the concentration of each operation, diligently observing foam changes, and diligently examining samples or conducting rapid analyses of concentrate, tailings, and intermediate products.
- “Four Accuracies” refers to accurately controlling the amount of foam scraped out, accurately identifying the causes of changes, accurately controlling the dosage of oil and chemicals, and accurately controlling the number of selective flotation operations.
- “Two Goods” refers to maintaining good coordination between operations and ensuring good handover conditions.
- “One Unchanged” refers to not making unnecessary changes when the properties of the raw ore remain unchanged.
What Are the Operating Principles for Lead-Zinc Ore Flotation?
Flotation is the key process for lead-zinc ore separation. Yet many concentrators struggle with low recovery rates and inconsistent concentrate grades. Our 40 years of practice have distilled these golden rules.
Lead-zinc flotation follows the principle of "depress zinc first, float lead first". Critical control points include: pulp pH adjustment (lead 9-11, zinc 10-12), proper reagent scheme (ZnSO4+Na2SO3 as depressants), and moderate agitation intensity (lead rougher 20-25m³/min, zinc cleaner 15-18m³/min). The key lies in precisely leveraging mineral floatability differences.
These theories seem straightforward, but field operations often encounter surprises. Below, we break down three critical steps to reveal the technical essentials of each phase.
Why Should Zinc Be Depressed Before Floating Lead?
Last year, a mine suffered 30% excess mutual content in concentrates and lost over 10 million yuan due to a reversed sequence. This painful lesson proves the importance of proper flow order.
Galena (PbS) naturally floats better than sphalerite (ZnS). When floating lead first, ZnSO4 must first depress zinc mineral surfaces. Although cyanides work better, environmental restrictions favor alternatives. Test data shows proper zinc depression reduces zinc content in lead concentrate from 7.2% to 1.8%.
Reagent Mechanism Comparison
| Reagent Type | Target Mineral | Optimal Dosage (g/t) | Alternatives |
| ZnSO4 | Sphalerite | 800-1200 | Na2SO3 |
| Diethyldithiocarbamate | Galena | 40-60 | Xanthate |
| Lime | Pulp pH | 2000-4000 | NaOH |
Key findings from practice:
- pH window: Maintain 9-10 for lead flotation; exceeding 10.5 over-depresses lead
- Activation control: Copper ion activation of sphalerite is a common interference – limit water copper content
- Timing: Add depressants 5 minutes before agitation tanks for full effect
How to Optimize Pulp Density for Best Flotation?
A client increased lead recovery by 12% after reducing pulp density from 35% to 28%. This case reveals the delicate balance of density control.
Ideal densities are 25-30% for the lead rougher and 35-40% for the zinc scavenger. Too low reduces particle collisions; too high impairs bubble loading. Using Φ200mm hydrocyclones can stabilize -200 mesh content at 75-80% for optimal particle size.
Classification Operating Parameters
| Stage | Density Range | Adjustment Method | Monitoring Frequency |
| Lead rougher | 25-28% | Make-up water valve control | Every 30 minutes |
| Zinc scavenger | 32-35% | Tailings pump VFD speed | Hourly |
| Cleaning | 18-22% | Dilution water flowmeter | Real-time |
Four-step density control protocol:
- Standard sampling: Fixed point 1.5m from overflow weir
- Viscosity check: Φ100mm viscosity cup (22-25 sec drain time)
- Bubble observation: Ideal bubble diameter 1-2mm uniform distribution
- System linkage: Automatic reagent compensation triggered at ±2% density change
What Are Optimal Flotation Machine Parameters?
When a Mongolian mine reduced impeller speed from 280rpm to 245rpm, they saved ¥860k annually. This demonstrates huge optimization potential in equipment settings.
Lead rougher requires high speed (230-250rpm) and air rate (1.2-1.5m³/m²·min), while zinc cleaner needs 180-200rpm. The key metric is bubble surface area flux (25-35m²/min). CFD simulations show 45° tilted impellers save 15% energy versus traditional 60° designs.
Equipment Configuration
| Parameter | Lead Rougher | Zinc Cleaner | Technical Upgrade |
| Impeller speed | 6.8m/s | 5.2m/s | VFD motor conversion |
| Aerator hole | Φ1.2mm | Φ0.8mm | Laser-drilled ceramic diffuser |
| Cell depth | 1.8m | 2.2m | Baffle ring installation |
Field-verified golden parameters:
- Energy threshold: Check impeller clearance when power >5.5kW/m³
- Wear alert: Replace parts if the stator-rotor gap exceeds 8mm
- Bubble optimization: Gradient-pore polyethylene aerators last 3x longer
Conclusion
Lead-zinc flotation fundamentally exploits surface property differences. Through the systematic approach of "priority lead flotation – strong zinc depression – staged density – parameter linkage", we achieve over 92% lead recovery and +50% zinc concentrate grade. Remember, flotation is a precise dance of physicochemical processes where every parameter impacts profitability.