Hydrated Lime (Slaked Lime / Calcium Hydroxide) – pH Regulator Technical Data Sheet
Application Scope
Hydrated lime (calcium hydroxide) is one of the most widely used and cost-effective alkaline pH modifiers in mineral processing. Its strong alkalinity, availability, and ability to establish stable flotation conditions make it a preferred reagent for sulfide mineral beneficiation circuits.
By controlling pulp chemistry, hydrated lime influences mineral surface properties, collector adsorption, and selective depression of unwanted sulfide minerals. Its major applications include copper, gold, nickel, lead-zinc, and other critical mineral flotation systems.
Copper & Copper-Molybdenum Ores – Sulfide Flotation pH Control (Primary Application – ~55%)
Copper sulfide flotation represents the largest application area for hydrated lime. In copper beneficiation circuits, lime is commonly used to adjust pulp pH to approximately 9–11, creating favorable conditions for chalcopyrite recovery while promoting selective depression of iron sulfides.
For copper-molybdenum ores, hydrated lime functions as the primary pH regulator in bulk flotation circuits. Industrial tests have demonstrated that lime-controlled pH conditions can support copper concentrate grades of 22.48% with 92.41% recovery and molybdenum concentrate grades of 48.32% with 91.12% recovery.
The calcium ions released from hydrated lime also contribute to flotation selectivity by assisting pyrite depression in alkaline environments. Proper dosage control remains essential to maintain recovery and concentrate quality.
Gold & Silver Ores – Cyanidation and Flotation Applications
Hydrated lime plays an important role in precious metal processing, especially in cyanidation circuits where maintaining alkaline conditions around pH 10–11 helps stabilize cyanide solutions and reduce the risk of hydrogen cyanide formation.
In gold flotation operations, lime is applied for pulp pH adjustment. Simple sulfide gold ores are commonly processed under pH 7–9 conditions, while complex polymetallic gold systems may require higher alkaline conditions to selectively depress pyrite during separation flotation.
Because excessive calcium ions may influence natural gold flotation behavior, accurate lime dosage management is important for maintaining process stability.
Nickel & Nickel-Cobalt Sulfide Ores – Selective Sulfide Flotation
In nickel sulfide beneficiation, hydrated lime is used to establish alkaline flotation conditions that support selective recovery of pentlandite while depressing pyrrhotite and other iron-bearing sulfide minerals.
Stable pH control improves flotation selectivity and contributes to improved concentrate quality in nickel-bearing sulfide ore processing circuits.
Lead-Zinc Sulfide Ores – Differential Flotation Regulation
Hydrated lime is widely applied in lead-zinc flotation circuits where precise pulp alkalinity control is required for selective separation of galena and sphalerite.
The alkaline environment created by lime addition assists sequential flotation operations by depressing iron sulfides and improving separation efficiency between valuable minerals and associated gangue.
Other Applications
Hydrated lime is also used in tungsten and antimony ore processing where alkaline conditions are required for selective mineral separation. In antimony sulfide flotation, lime can assist pulp chemistry control and the depression of associated iron sulfides.
Mechanism
Hydrated lime functions as a pH regulator through dissolution in water, releasing calcium ions (Ca²⁺) and hydroxide ions (OH⁻). Hydroxide ions neutralize acidic components in the pulp and increase alkalinity, creating suitable conditions for flotation reactions.
In sulfide flotation systems using collectors such as xanthates and dithiophosphates, alkaline conditions improve collector stability and promote selective adsorption on target sulfide minerals while reducing pyrite flotation.
Calcium ions may contribute to iron sulfide depression by forming hydrophilic surface species. However, in talc- and clay-rich ores, excessive calcium ion concentration may negatively affect dispersion behavior, and alternative pH regulators may be considered.
Physicochemical Properties
| Property | Value |
|---|---|
| Chemical Name | Calcium Hydroxide / Hydrated Lime / Slaked Lime |
| CAS Number | 1305-62-0 |
| Molecular Formula | Ca(OH)₂ |
| Molecular Weight | 74.09 g/mol |
| Appearance | White powder |
| Purity (Industrial Grade) | ≥90.0% – 96.0% |
| pH (Saturated Solution) | Approximately 12.4 |
| Solubility | Slightly soluble in water (1.73 g/L at 20°C); solubility decreases with increasing temperature |
| Particle Size | Typically 200–325 mesh (74–45 μm) |
Specifications
Hydrated lime supplied for mineral processing applications is typically selected according to purity, particle size, and slaking performance requirements. Consistent physical properties help maintain stable reagent preparation and flotation operation.
Storage & Handling
Store hydrated lime in tightly sealed containers in a cool, dry, and well-ventilated warehouse. Protect the product from moisture and carbon dioxide exposure because atmospheric CO₂ can react with calcium hydroxide and reduce reagent effectiveness.
The product is hygroscopic and may absorb moisture during storage. Operators should use appropriate protective equipment, including dust masks, chemical-resistant gloves, and goggles during handling.
Avoid inhalation of dust and direct skin contact. In case of spillage, collect mechanically and dispose of according to applicable environmental regulations. Under recommended storage conditions, shelf life is typically ≥12 months.
Advantages / Limitations
Advantages
Highly cost-effective pH regulator for mineral flotation operations.
Extensive industrial application across sulfide mineral beneficiation.
Calcium ions can enhance pyrite depression in alkaline flotation circuits.
Compatible with common sulfide collectors including xanthates and dithiophosphates.
Widely available with established global supply chains.
Simpler handling compared with caustic soda in many plant operations.
Limitations
Limited solubility requires proper slaking and agitation systems.
Maximum pH control capability is lower than highly soluble alkaline regulators.
Calcium ions may negatively influence talc- and clay-rich ore systems.
Requires suitable equipment for preparation and dosing.
Excessive dosage may suppress valuable minerals and affect flotation selectivity.
Summary
Hydrated lime is an industry-standard alkaline pH regulator for sulfide mineral flotation, with copper, gold, nickel, and lead-zinc ores representing its most important applications.
Its combination of cost efficiency, reliable alkaline control, and beneficial calcium-ion effects on iron sulfide depression makes it a widely adopted reagent in mineral processing plants worldwide.
For complex ore systems where calcium interference or clay dispersion issues become significant, alternative pH modifiers may be evaluated. Our hydrated lime product meets international quality standards and is available in consistent-grade bulk supply with technical support for global mining operations.
Hydrated Lime (Calcium Hydroxide) – FAQ
Q1. What is the optimal dosage of Hydrated Lime for pH adjustment in copper-molybdenum flotation?
Hydrated Lime is widely used as an alkaline regulator in copper-molybdenum flotation circuits to control pulp pH and modify mineral surface conditions. The optimal dosage depends on ore mineralogy, pulp density, water chemistry, and the required flotation selectivity. Excessive lime addition may increase depression of certain sulfide minerals or affect molybdenum recovery, while insufficient dosage may reduce separation efficiency. In industrial operations, the dosage is normally optimized through laboratory flotation tests, monitoring pH response, reagent consumption, and concentrate quality under actual process conditions.
Q2. How is free lime content controlled when Hydrated Lime is used for pH adjustment in gold cyanidation?
In gold cyanidation processes, Hydrated Lime is commonly applied to maintain alkaline conditions and support cyanide stability. Controlling free lime content is important because excessive alkalinity may increase reagent consumption and influence downstream operations, while insufficient alkalinity may reduce cyanide protection. Mining operations typically monitor pH, calcium concentration, cyanide level, and slurry characteristics to maintain suitable conditions. Proper preparation of lime slurry, accurate dosing, and continuous pH monitoring help achieve stable operation in CIP, CIL, and heap leaching systems.
Q3. How does Hydrated Lime affect pyrite depression in high-sulfur copper flotation?
Hydrated Lime can influence sulfide mineral flotation behavior by increasing pulp alkalinity and modifying mineral surface properties. In high-sulfur copper ores, lime addition is often used to depress pyrite and improve copper selectivity. However, excessive lime concentration may also affect valuable sulfide minerals depending on ore characteristics and reagent conditions. The appropriate dosage should be determined through flotation testing by evaluating copper recovery, pyrite rejection, pulp potential, and collector performance. Process optimization requires balancing pH control with selective mineral recovery.
Q4. What are the differences between Hydrated Lime and Sodium Hydroxide for pH adjustment in mineral processing?
Hydrated Lime and Sodium Hydroxide are both alkaline regulators, but they provide different process characteristics. Hydrated Lime is commonly selected for large-scale mining operations due to its cost efficiency, availability, and ability to provide sustained alkalinity. Sodium Hydroxide offers faster dissolution and rapid pH response, which can be useful where precise adjustment is required. The choice depends on mineral type, water chemistry, reagent system, operating cost, and process requirements. Laboratory testing is recommended to determine which alkaline reagent provides the best flotation or hydrometallurgical performance.
Q5. How does Hydrated Lime slurry concentration affect pH stability in copper flotation?
The concentration of Hydrated Lime slurry directly affects dissolution rate, dosing accuracy, and pH stability in copper flotation circuits. A properly prepared lime slurry allows consistent alkaline adjustment and improves process control. If the slurry concentration is too high, incomplete dispersion or localized over-alkalinity may occur; if too low, additional pumping volume and handling requirements may increase. Mining plants usually optimize lime slurry concentration according to equipment design, ore characteristics, water quality, and automatic dosing system performance to maintain stable flotation conditions.
Q6. What should be considered when using Hydrated Lime in lithium spodumene flotation?
Hydrated Lime may be used as a pH modifier in lithium spodumene flotation to influence mineral surface properties and collector adsorption behavior. Its application should be carefully controlled because calcium ions released from lime dissolution may interact with gangue minerals or flotation reagents. The suitable pH range and dosage depend on ore mineralogy, gangue composition, water chemistry, and the selected collector system. Laboratory flotation testing is recommended to evaluate spodumene recovery, impurity removal, and reagent compatibility before industrial implementation.
Q7. How can excessive Hydrated Lime addition be controlled in high-calcium process water conditions?
High-calcium process water may influence Hydrated Lime consumption because dissolved calcium and carbonate species affect slurry buffering capacity and mineral interactions. To avoid excessive lime addition, mining operations should regularly analyze water chemistry, monitor real-time pH changes, and establish accurate reagent dosage curves through laboratory testing. Automatic pH control systems and staged lime addition can help improve process stability. Proper management reduces unnecessary reagent consumption and minimizes unwanted effects on flotation selectivity or downstream treatment processes.
Q8. What are the best practices for using Hydrated Lime in gold CIL and CIP circuits?
In gold CIL and CIP operations, Hydrated Lime is commonly used to maintain alkaline conditions during cyanide leaching and adsorption stages. Effective application requires proper lime slurry preparation, controlled dosing, and continuous monitoring of pulp pH and cyanide conditions. The target pH depends on ore mineralogy, cyanide concentration, and plant operating parameters. Maintaining stable alkalinity helps support gold dissolution while reducing operational risks associated with acidic conditions. Process engineers normally optimize lime addition through laboratory testing and plant performance evaluation.
Q9. How does Hydrated Lime influence reagent performance in flotation processes?
Hydrated Lime affects flotation performance mainly through pH adjustment, mineral surface modification, and interaction with collectors, depressants, and activators. Different minerals respond differently to alkaline conditions, meaning lime dosage must be optimized according to the specific ore system. In sulfide, oxide, and non-metallic mineral flotation, proper pH control can improve selectivity and reduce unwanted mineral recovery. The optimal conditions are usually established through mineralogical analysis, laboratory flotation tests, and industrial trial adjustments rather than using a fixed dosage for all applications.
Q10. What storage and handling factors are important for Hydrated Lime in mining applications?
Proper storage and handling of Hydrated Lime are important for maintaining product quality and ensuring reliable performance in mining operations. Hydrated Lime should be stored in dry conditions and protected from moisture absorption and contamination. During slurry preparation, controlled mixing and suitable equipment selection help achieve consistent dispersion and dosing accuracy. In flotation, leaching, and wastewater treatment applications, stable lime quality contributes to predictable pH control and process performance. Site-specific safety procedures and technical handling requirements should always be followed.